Development of core-shell colloids to study self-diffusion in highly concentrated dispersions

To study single particle motion in highly concentrated colloidal dispersions, a host-tracer colloid system was developed, consisting of crosslinked polymer micronetwork spheres placed in a good solvent. The host colloid is made invisible to the experimental probe by matching its refractive index to that of the solvent. For the tracer particles a core-shell structure was chosen to ensure the interaction potential to be identical to that of the host particles. Therefore the shell was made of the same polymer as the host. The core differs in refractive index from the solvent and is therefore visible due to scattered light.

Localized Motion in Supercooled Glycerol as Measured by 2 H-NMR Spin-Lattice Relaxation and Incoherent Neutron Scattering

Selectively deuterated glycerol has been subjected to 2H-NMR spin-lattice relaxation and quasi-elastic neutron scattering experiments. The measurements yield relaxation rates and a non-Gaussian Q-dependence of the Debye-Waller factor which are different for the two hydrogen sites. The data analysis shows that below the onset of the glass transition α-process the hydrogens perform a local motion (≈ 10-12 s) in addition to what is expected from harmonic phonons. The resulting mean-square displacements are highly temperature dependent but are significantly smaller than those found in van der Waals glasses. Amplitudes and activation energies of the carbon-bonded and oxygen-bonded hydrogens are …

Gibt es Selbste in der Welt? – Die Selbstmodell-Theorie von Thomas Metzinger

„Es gibt keine Selbste in der Welt“, behauptet Thomas Metzinger, der an der Universitat Mainz die Philosophie des Geistes vertritt. Was wir als unser Selbstbewusstsein erleben, ist ein „phanomenales Selbst“, das uns nur so real erscheint, weil die Natur dies im Verlauf der Evolution so eingerichtet hat. Selbstbewusste Wesen, die noch dazu wissen, dass auch ihre Artgenossen selbstbewusst sind, haben einen offensichtlichen Uberlebensvorteil. Sie konnen ihre Umgebung und alles, was dort geschieht, aus ihrer eigenen subjektiven Perspektive ordnen und bewerten, und sie konnen dabei einkalkulieren, dass auch ihre Freunde oder Gegner diese Fahigkeit besitzen: „Ich weis, dass du weist, dass ich wei…

Selbstbezüglichkeit und Selbsttäuschungen – Ach arme Welt du trügest mich

Die eigentliche Sprache der Mathematik ist die Logik, deren Entwicklungsgeschichte parallel und eng verbunden mit der Geschichte der Mathematik verlaufen ist. Schon im Altertum wurden logische Paradoxa, Aporien und Antinomien entdeckt, die auch die scheinbar heile Welt der Mathematik bedroht haben. Die letzte Bastion der Mathematiker, in der Aussagen, die zu logischen Widerspruchen fuhren konnten, einfach verboten wurden, war das System der Principia Mathematica von Whitehead und Russell. Kurt Godel konnte jedoch 1931 nachweisen, dass selbst dieses Bollwerk nicht sicher ist gegenuber dem Circulus vitiosus der Selbstbezuglichkeit. Dem „ignorabimus“ von Emil Dubois-Reymond (1818–1896) hatte D…

Inelastic Neutron Scattering Experiments on Van der Waals Glasses - A Test of Recent Microscopic Theories of the Glass Transition

Etude realisee sur un verre d'o-terphenyle afin de montrer l'existence d'une relaxation secondaire presentant des caracteristiques inhabituelles et le comportement Kohbrausch de la fonction de correlation de densite decrivant la relaxation structurale

Single Particle Motion of Hard-Sphere-Like Polymer Micronetwork Colloids Up to the Colloid Glass Transition

Polymer micronetwork spheres swollen in a good solvent can be regarded as colloids which require no special stabilisation to avoid aggregation. Their interactions can be timed by changing the degree of internal crosslinking. The phase behaviour and the static structure factor demonstrate that crosslink density of 1:10 (inverse number of monomer units between crosslinks) is sufficient to achieve hard sphere behaviour. We designed a host-tracer system consisting of core-shell micronetwork spheres (core: polystyrene; shell: poly-t-butylacrylate) in a host of refractive-indexmatched poly-t-butylacrylate micronetwork colloids. Employing a crosslink density of 1:10 and tuning the polydispersity s…

Deuteron relaxation times T1 of polystyrenes deuterated at the backbone (PS-d3) and the phenyl ring (PS-d5), respectively, have been measured in solutions of benzene and diethyl malonate as a function of concentration and temperature. We conclude that the motion of the phenyl ring is faster than that of the backbone, the difference being smallest at high temperatures around 180°C. The temperatures dependence is discussed in relation to the activation energies in polystyrene.

Stochastic models for heterogeneous relaxation: Application to inhomogeneous optical lineshapes

Dynamic heterogeneity has often been modeled by assuming that a single-particle observable, fluctuating at a molecular scale, is influenced by its coupling to environmental variables fluctuating on a second, perhaps slower, time scale. Starting from the most simple Gaussian Markov process we model the exchange between 'slow' and 'fast' environments by treating the fluctuating single-particle variable as a projection from a higher-dimensional Markov process. The moments of the resulting stochastic process are calculated from the corresponding Master equations or Langevin equations, depending on the model. The calculations show the importance of the way to treat exchange processes. The result…

Dissolution de polystyrene marque par de la fluorescence dans une matrice de masse moleculaire moyenne en poids de 110000

Anomalous tracer diffusion in film forming colloidal dispersions

Film forming colloidal dispersions can be conceived as a material composed of interpenetrating hydrophobic (polymer) and hydrophilic (partially broken interfaces) phases where the transport properties of one phase are influenced by the geometric confinement effect imposed by the other. We studied the transport properties of film forming colloidal dispersions by introducing hydrophobic dye molecules into the colloidal particles and determining their motion with forced Rayleigh Scattering as a function of length scale (grating distance A) and water content. At water contents between 18 and 3 weight percent we find signatures of anomalous tracer diffusion, namely stretched exponential decay cu…

The effect of the internal architecture of polymer micronetwork colloids on the dynamics in highly concentrated dispersions

Motivated by the finding that colloidal dispersions of polymer micronetwork spheres with a cross-link density of 1:50 (inverse number of monomer units between crosslinks) show significant deviations from the dynamics of hard spheres in the colloid glass as seen by dynamic light scattering (DLS) (E. Bartsch, V. Frenz, H. Sillescu J. Non — Cryst. Solids 172–174 (1994), 88–97), we have undertaken a systematic study of the effect of the crosslink density on the dynamics at high concentrations. Long-time self-diffusion coefficients D S L and collective diffusion coefficients D c were measured for colloids with crosslink densities of 1:10, 1:20 and 1:50 by forced Rayleigh scattering (FRS) and the…

Forced Rayleigh scattering from non-harmonic gratings applied to complex diffusion processes in glass-forming liquids

Abstract Tracer diffusion of 9,10-phenanthrenequinone (PQ) and its photoproduct in super-cooled phenolphthalein-dimethyl-ether (PDE) was studied by forced Rayleigh scattering. In order to investigate the spatial frequency dependence of the grating dynamics, several spatial harmonics of the grating with non-sinusoidal phase profile produced by non-linear recording were monitored. An optical scheme with a diverging reading beam is proposed for simultaneous reconstruction of the harmonic components.

Der alte Hans im Glück

Das Marchen vom „Hans im Gluck“ kennt viele Deutungen – wie das Gluck selber, von dem ja auch niemand so genau sagen kann, was es bedeutet. Wer nach einem Leben voll redlicher Arbeit in Rente geht, mag auf die Idee kommen, dieses Marchen konne auch als Bild eines glucklichen Alters gedeutet werden, in dem einer mit einem Goldklumpen auf der Schulter in den Ruhestand eintritt und am Ende mit leeren Handen bei seiner Mutter (naturlich der Mutter Erde) ankommt. Wahrend Hans in den Augen seiner Mitmenschen ein Bild unuberbietbarer Dummheit darbot, als er seinen Goldklumpen gegen ein Pferd, sein Pferd gegen eine Kuh, seine Kuh gegen ein Schwein, sein Schwein gegen eine Gans und am Ende diese geg…

Spin lattice relaxation rates of tunnelling CD3 groups

The spin lattice relaxation rates of deuterated methyl groups are calculated for threefold and sixfold potentials. It is shown that it should be possible to determine the symmetry of the potential hindering the methyl groups from deuteron spin lattice relaxation experiments. The temperature dependence of the spin lattice relaxation rates is discussed using a simple model. The similarities and the differences between proton NMR and deuteron NMR are pointed out. The main difference is thatEa↔Eb transitions are forbidden by spin selection rules in case of CH3, but not for CD3. Therefore, and due to the fact that the quadrupolar interaction is a single particle interaction, deuteron NMR allows …

Credo – warum ich es trotzdem mitspreche

Das Glaubensbekenntnis ist eine durchaus offentliche Angelegenheit. In jedem Gottesdienst sagt jeder laut und deutlich, was er glaubt, und zwar ganz personlich. Denn es heist nicht „wir glauben…“, sondern „ich glaube…“ und was dann kommt, sind in der Regel faustdicke Lugen. Als erwachsener Mensch von 31 Jahren wollte ich diese Heuchelei nicht langer mitmachen. Daher habe ich damals fur mich selber beschlossen, bei meinen selten gewordenen Gottesdienstbesuchen zu schweigen, wenn die anderen ihren Glauben bekannten. 30 Jahre spater habe ich zum ersten Mal das Glaubensbekenntnis wieder mitgesprochen – warum, das steht im letzten Absatz dieser Betrachtung.

Reorientational dynamics in simple supercooled liquids

Abstract The geometry of the reorientational dynamics in the van der Waals liquid, toluene, and the hydrogen bond network, glycerol, are compared. Both systems have contributions from small angle fluctuations. In glycerol the fraction of these small angle fluctuations is much larger than in toluene, due to the stronger anisotropic interactions in the former substance. The average reorientational angle in both systems is similar and on the order of 10 ∘ . In addition we analyze the stretching of the rotational correlation functions of rank one and two. In both cases we find that the second rank correlation function has a more pronounced stretching than the corresponding first rank correlatio…

Self-Diffusion in Concentrated Colloid Suspensions Studied by Digital Video Microscopy of Core−Shell Tracer Particles

Optical video microscopy and digital image processing have been used to study the self-diffusion of colloidal particles with a hard-sphere potential. The colloid particles consist of cross-linked polymers and are dispersed in a good solvent to avoid aggregation. To investigate single particle motion in highly concentrated dispersions, a host−tracer system, consisting of two different kinds of polymer particles, has been designed:  the host particles are made of poly-t-butylacrylate (with ethanedioldiacrylate as cross-linker) and have the same refractive index as the employed solvent, 4-fluorotoluene. The tracer particles have a core−shell structure with a polystyrene core (cross-linked with…

Mögliche Welten in Philosophie und Physik

Gottfried Wilhelm Leibniz (1646 – 1716) ist uns heute hauptsachlich als Philosoph und Mathematiker bekannt. Aber in seiner Zeit war er auch ein bedeutender Theologe, dessen Abhandlung uber die Theodizee (Leibniz 1710) eine Antwort auf die Frage nach dem Ursprung des Bosen in der Welt geben sollte. Seine Behandlung dieses Problems ist die eines Mathematikers. Voraussetzungen sind die Allmacht und Allwissenheit sowie die unendliche Gute und Gerechtigkeit Gottes, die in der kirchlichen Dogmatik festgelegt sind. Aufgrund seiner Allwissenheit waren Gott schon vor aller Zeit alle moglichen Welten bekannt. Unter diesen hat er die beste Welt ausgesucht, die mit den Bedingungen seiner unendlichen Gu…

Translational and rotational molecular motion in supercooled liquids studied by NMR and forced Rayleigh scattering

It has been shown that translational diffusion coefficients, Dt, in the supercooled van der Waals liquids, orthoterphenyl, phenolphthaleindimethylether, and salol, have a weaker temperature dependence than the shear viscosity, η, at T ≲ 1.2Tg and can be described by Dt ∼ η−χ with χ < 1 whereas Dr ∼ η−1 applies for the mean rotational diffusion coefficients, Dr, down to the glass transition temperature, Tg. This apparent decoupling of translational and rotational motion has been discussed in relation with possible anomalous short time diffusion, spatial heterogeneity, and cooperative molecular motions close to Tg.

Toluene self-diffusion in solutions of linear and crosslinked polystyrene

Toluene self-diffusion coefficients in solutions of linear and crosslinked polystyrene (PS) at concentrations up to 30 wt% polymer have been determined over the temperature range 143–230 K using the1H n.m.r. static gradient stimulated echo method. At similar polymer concentrations, the diffusion coefficient values of toluene were higher for mixtures with crosslinked PS than for solutions containing linear PS. On cooling and approaching the solution glass transition, the amplitude decays in diffusion and spin-relaxation measurements become non-exponential and are interpreted in terms of a two-component decomposition. The estimated fraction of the toluene motionally bound to polymer increases…

Tracer diffusion coefficients D* of both components were measured in mixtures of polystyrene (PS) and polymethylstyrene (PMS), a random copolymer from 60 wt.-% of m-methylstyrene and 40 wt.-% of p-methylstyrene. The results are interpreted in terms of the free-volume theory which yields master curves even for “asymmetric” mixtures of oligomer and polymer chains, if D* is drawn versus the distance from the glass transition temperature, T–Tg. Whereas D* was measured by the forced Rayleigh scattering technique, we also studied photon correlation spectroscopy in these mixtures and observed “slow modes” with decay constants that correspond to diffusion coefficients 2–3 decades smaller than the i…

Experimental Determination of Four-Time Stimulated Echoes in Liquids, Colloidal Suspensions, and Crystals

Four-time stimulated echo experiments have been used to monitor the temporal evolution of the reorientation rates of deuterated molecules or colloidal suspensions. We present extended phase cycles for this seven-pulse experiment. In order to test its performance three vastly different materials are chosen. These include a crystal in which the molecules carry out well-defined 180 degrees flips and a supercooled liquid characterized by a distribution of jump angles centered around 10 degrees. As an example for rotational diffusion, data on a concentrated suspension of polystyrene spheres in a viscous medium are presented. Copyright 1998 Academic Press.

Gottes Wort – nicht nur in der Bibel

Hermann Hartmann, mein akademischer Lehrer an der Universitat Frankfurt, war ein echter Humanist, der die grose Literatur der Antike liebte und seine Schuler immer wieder mit langen, auf Griechisch oder Lateinisch rezitierten Texten uberraschte, wobei er noch unterstellte, dass naturlich jeder alles verstunde. Als gleichsam langjahrigster Schuler von Hartmann wurde ich ausersehen zum Festkolloquium an seinem 65. Geburtstag die Laudatio zu halten. Nach der ausfuhrlichen Wurdigung seiner wissenschaftlichen Verdienste kam ich auch auf seine Liebe zur klassischen Literatur zu sprechen, konnte mir aber nicht verkneifen zu erwahnen, dass ich von ihm nie ein Bibelzitat vernommen hatte. Nach meinem…

Size Dependence of Tracer Diffusion in Supercooled Liquids

We have determined by forced Rayleigh scattering the diffusion coefficients D of several photochromic tracers with van der Waals radii between 0.38 and 8 nm (the largest ones being photolabeled polystyrene micronetworks) in 10 glass-forming liquids at temperatures between the glass temperature Tg and ∼1.2Tg. The results were analyzed in terms of power law plots, D(T) ∝ T/η(T)ξ, where η is the solvent shear viscosity, and temperature shifts, D(T) ∝ T/η(T + ΔT). The shift ΔT was related with the width of the rotational correlation time distribution via the time−temperature superposition principle.

Synthesis and properties of model - micronetworks

Microgels are small network particles with overall dimensions in the 100nm-region. Some experiments concerning the behaviour of cross-linked matter can be more easily performed using the molecular nature of μ-gels. In this publication, the synthesis and characterization by light and neutron scattering and dynamic-mechanical shear experiments of two different types of μ-gels are presented.

Dynamic anomaly in the glass transition region of orthoterphenyl

We report on incoherent and coherent neutron scattering results in the supercooled liquid and the glassy regime of the van der Waals fluido-terphenyl using the backscattering and spin echo technique, respectively. A critical comparison of both techniques is presented. The data are analysed in the time domain assuming that microscopic correlation times (τ) scale with the viscosity η according to τ(T)∼η(T)/T. With this assumption we obtain an agreement with several predictions of mode coupling theory: the existence of a critical temperatureT c is shown, independently for both incoherent and coherent data, by a cusp in the temperature dependence of the Debye-Waller factorf Q (T). BelowT c fQ(T…

Four-time rotational correlation functions

A scheme to analyze four-time rotational correlation functions of any rank is developed and details for rank L = 1 and 2 are given. The scheme provides a transparent way for identifying deviations from simple Markovian dynamics as observed, e.g., in complex liquids close to the glass transition. The method should be applicable to NMR and optical multiple-pulse techniques as well as to photon correlation spectroscopy. Results are given for 2H-NMR multiple-pulse data in supercooled glycerol. We identify and analyze the dynamical heterogeneity of molecular reorientation in a range of 205 − 215 K close to the glass temperature Tg = 190 K.

Probing Poly(n-butyl-methacrylate) Latex Film via Diffusion of Hydrophilic and Hydrophobic Dye Molecules

In the study of holographic grating relaxation (forced Rayleigh scattering, FRS) in nascent latex films we examined poly(n-butyl methacrylate) films using two complementary diffusing probes:  a hyd...

Diffusion of labeled macromolecules in molten polystyrenes studied by a holographic grating technique

Diffusion de polystyrene, de differentes masses moleculaires marque a la fluoresceine. Influence de la temperature

Rotational diffusion of colloid spheres in concentrated suspensions studied by deuteron NMR

We present a study of the application of deuteron-nuclear magnetic resonance spectroscopy (NMR) to the investigation of the rotational diffusion of spherical colloidal particles. We performed NMR pulse experiments on colloidal suspensions of polystyrene latex spheres in water-glycerol mixtures in a wide range of particle volume fractions \ensuremath{\varphi} from the dilute suspension up to \ensuremath{\varphi}=0.504. We have analyzed the stimulated echo NMR signal in the time domain. The full shape of the orientational correlation function deviates from an exponential behavior in the whole \ensuremath{\varphi} range examined. We evaluate the rotational diffusion coefficient and calculate i…

Atomangst – Die Bombe und der Müll

Im November 1991 war ich im Anschluss an eine Tagung in Fukuoka zu einem Vortrag an der Universitat von Osaka eingeladen. Zum Abendessen hatte mich der Gastgeber in ein gutes Restaurant eingeladen, wo wir zu zweit an einem kleinen Tisch in einem abgetrennten Raum sasen und ein vorzugliches japanisches Essen serviert bekamen. Im Verlauf des Abends stellte sich heraus, dass wir etwa gleich alt waren und fast zur gleichen Zeit als siebenjahrige Kinder Bekanntschaft mit amerikanischen Bombenangriffen gemacht hatten. Ich hatte in Frankfurt (am 4. Oktober 1943) keine Angst, weil meine Mutter mir versicherte, dass uns im Bunker nichts passieren konne, was auch stimmte. Denn tatsachlich hielt unser…

The effect of free polymer on the glass transition dynamics of microgel colloids

Abstract From the phase behavior we establish that 1:10 crosslinked polystyrene microgel colloids in a good solvent can be considered as hard spheres whereas 1:50 crosslinked particles are slightly softer. Nevertheless, the glass transition dynamics of 1:10 microgels and a binary mixtures of 1:50 microgels can be described in both cases within the mode coupling theory for hard spheres. The only difference is that the increase of the polydispersity from about 7% to about 13% when going from the one-component system to the mixture is accompanied by a shift of the glass transition from ϕ g ≈0.56 to ϕ g ≈0.595. On addition of linear polystyrene to the 1:50 binary mixture we find a tremendous ac…

Molecular dynamics near the glass transition

Solid state 13C NMR spectroscopy has been applied to investigate the time scale and the geometry of rotational motions near the glass transition of the low-molar-mass van der Waals glass former 1,3,5-tri-α-naphthylbenzene (T g = 342 K). Two-dimensional 13C exchange spectra were taken between 347 and 372 K. With the principal values of the 13C chemical shift tensors determined from 13C CP/MAS spectra and static one-dimensional 13C spectra, the two-dimensional spectra are interpreted according to the isotropic rotational diffusional model to yield mean correlation times τ0 in the range 10 ms ˇ- τ0 ˇ- 50 s, and a log-Gaussian distribution of correlation times with a width of 1·5 decades. The m…

2D NMR spectra have been measured at variable temperatures between −100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component…

Anisotropic motion of toluene above and below the glass transition studied by 2H NMR

Abstract 2 H nuclear magnetic resonance spin-lattice relaxation experiments on two selectively deuterated toluene molecules have been performed over a wide temperature range, spanning liquid and glassy states, to examine anisotropic molecular dynamics. In the liquid regime, the relaxation data are analyzed by the model of anisotropic rotational diffusion. A more phenomenological ansatz is used for the whole temperature regime to obtain information about anisotropic reorientation and its temperature dependence. We find that the anisotropy is reduced in the supercooled state and the motion becomes approximately isotropic below 140 K which is interpreted as the onset of cooperative reorientati…

Heterogeneity at the glass transition: a review

Theoretical concepts and experimental evidence of heterogeneity in glass-forming liquids and polymers are reviewed. The main purpose is to provide an introduction to theoretical developments and recent experiments which have led to rapidly increasing knowledge. Realizing that there is no consensus in regard to the various scenarios of the glass transition starting from rather different assumptions we try to give a balanced overview although we also compare and interrelate some of the approaches. The experimental part describes recent nuclear magnetic resonance, dielectric, and optical experiments from which dynamically distinguishable subensembles can be selected thus proving the existence …

Eine der seltenen Heiligen? Erinnerungen an Helga Masch

Es kommt immer wieder vor, dass ich erzahle, wie ich zu meinem schonen Cello gekommen bin. Ich verdanke es einer Cellistin, bei der meine Frau Beate 1973 Gamben-Unterricht hatte. Helga Masch erlebte in dieser Zeit eine schwere Lebenskrise, in der sie schlieslich ihren ganzen Haushalt aufloste, um in der Schweiz ein neues Leben anzufangen. Als sie auch noch ihr Cello verkaufen wollte, habe ich es ihr abgekauft, fur den Preis, den ein Geigenbauer ihr geboten hatte. Ich wollte es nur retten, weil ich dachte, dass sie nach dem Ende ihrer Krise ja wieder als Cellistin arbeiten musse. Als ich allerdings zum ersten Mal auf dem Cello spielte, wunschte ich mir insgeheim, dass ich es nie wieder herge…

Eine zweite Jugend – Der chemische Jungbrunnen und die Folgen

Von Zeit zu Zeit kann man in der Zeitung lesen, die neuesten Methoden der Genforschung hatten uns der Erfullung des uralten Menschheitstraums vom Jungbrunnen wieder einen Schritt naher gebracht. Zum Beispiel sei es gelungen, die Lebensspanne von Plattwurmern durch Genmanipulationen zu verdoppeln, und wer weis, vielleicht gelinge in Zukunft Ahnliches beim Menschen. Selbst renommierte Genforscher wollen derartige Moglichkeiten nicht mehr ausschliesen. (Welsch 2015) Dies sollte uns veranlassen, etwas grundlicher uber die Folgen nachzudenken.

From strong to fragile glass formers: secondary relaxation in polyalcohols.

We have studied details of the molecular origin of slow secondary relaxation near T(g) in a series of neat polyalcohols by means of dielectric spectroscopy and (2)H NMR. From glycerol to threitol, xylitol, and sorbitol the appearance of the secondary relaxation changes gradually from a wing-type scenario to a pronounced beta peak. It is found that in sorbitol the dynamics of the whole molecule contributes equally to the beta process, while in glycerol the hydrogen bond forming OH groups remain rather rigid compared to the hydrogens bonded to the carbon skeleton.

Die Entstehung kindlicher Welten – Das Werden der einen Welt

In jedem Menschen entwickelt sich schon im Sauglingsalter eine ganz personliche eigene Welt, die bestimmt und gepragt wird durch die Eigenheiten seiner Anlagen sowie seiner personellen und materiellen Umwelt. Es entsteht dabei wohl zuerst ein gewisses Selbstgefuhl und besonders in der Konfrontation mit den Forderungen der Eltern ein eigener Wille, der zumindest in unserer westlichen Kultur zu einem selbstbewussten Ich fuhrt, das sich gegen Ende des zweiten Lebensjahrs zum ersten Mal sprachlich artikuliert. Von den Psychologen und Padagogen, die sich mit der fruhkindlichen Entwicklung beschaftigen, konnen wir lernen, dass hier faszinierende Parallelen zur Phylogenese des Homo sapiens bestehe…

Relation of Interdiffusion and Self-Diffusion in Polymer Mixtures

From different assumptions one obtains linear relationships either between the interdiffusion coefficient and the self-diffusion coefficients or between the inverse interdiffusion coefficient and the inverse self-diffusion coefficients. The nature of these assumptions and possible experiments for discriminating between them are discussed.

Heterogeneity at the glass transition: what do we know?

We critically discuss the information that can be obtained from experiments with respect to the existence, the life time, and the length scale of dynamical heterogeneity in glass-forming liquids. The ability to select a dynamically distinguishable subensemble and observe its return to the full equilibrium ensemble is illustrated by examples from multi-dimensional NMR. We also discuss non-resonant hole burning spectroscopy as an example for which two separate time scales are involved.

Anselm – seltsam, aber liebenswert

Vor vielen Jahren, als man noch Liebesbriefe mit der Post verschickte, hatte ich eine witzige Idee. Ein nicht mehr ganz junger Mann, mit etwas verknittertem Gesicht, aber grosen, sprechenden, etwas vertraumten Augen, verschickt einen Liebesbrief. Er ist klein, von, sagen wir, schmachtiger Statur und der unsportlichen Haltung des typischen Buromenschen. Seine sorgfaltig gescheitelten, etwas schrag zur Seite gekammten Haare passen zu einer fast zu korrekten Kleidung, wie sie im unteren Mittel der Angestelltenhierarchie einer Grosbank selbstverstandliche Pflicht ist. Vielleicht ist er aber auch Buchhalter, einer der alten Schule, in der es selbstverstandlich war, dass ein Buchhalter sich nicht…

Heterogeneity at the Glass Transition:  Translational and Rotational Self-Diffusion

Self-diffusion coefficients, D, have been measured in the glass forming liquids salol, glycerol, phenolphthaleine dimethyl ether (PDE), cresolphthaleine dimethyl ether (CDE), and ααβ-trinaphthylbenzene (TNB) in the supercooled regime. The NMR static magnetic field gradient technique was applied where D >10-14 m2 s-1 can be attained. The results are similar to previous diffusion experiments where an enhancement of translational diffusion was found in comparison with rotational diffusion and shear viscosity. Various models of spatial heterogeneity are related to a phenomenological environmental fluctuation model in view of recent diffusion and relaxation data close to the glass transition.

Isotope effects on the dynamics of a supercooled van der Waals liquid

Deuteron magnetic resonance was used to study three differently isotope-labeled species of the fragile glass-forming liquid ortho-terphenyl. The calorimetric glass transition of the isotope deuterated only at the central phenyl ring is significantly lower than that of the perdeuterated one. It is shown that while the ortho-terphenyl molecule is not as rigid as previously often assumed, its overall reorientation geometry is independent of deuteration. The characteristic jump angles are found to increase with temperature, thus resolving an apparent discrepancy previously noted when comparing typical jump sizes from NMR with other data.

Organic Glasses and Polymers

Scale dependent diffusion in latex films studied by photoinduced grating relaxation technique

The transition from an aqueous dispersion of polyacrylate latices into a homogeneous polymer film on drying has been studied by monitoring the diffusion of hydrophobic and hydrophilic photochromic molecular probes with the help of a holographic grating relaxation (forced Rayleigh scattering) technique. Experiments with the hydrophobic probe in wet films result in an unusual spatial scale-dependence of the apparent diffusion coefficient that degenerates into a normal scale-independent diffusion coefficient as the film dries. Employment of a two-state diffusion model allows extracting the diffusion coefficients and mean displacements of the tracer in the polymer cores of the latex particles a…

Ein ewiges Paradies ohne Leben nach dem Tod?

Wenn Kinder fragen, wie lange die Ewigkeit dauert, erzahlt man ihnen manchmal die Geschichte vom Diamantberg. Alle tausend Jahre kommt ein kleines Vogelein und wetzt an ihm seinen Schnabel. Und wenn es den Diamantberg vollstandig abgewetzt hat, ist eine Sekunde der Ewigkeit vergangen. Diese nicht enden wollende Zeit passt besonders gut zu den menschlichen Vorstellungen der Holle, „das ewige Feuer, da ihr Wurm nicht stirbt und ihr Feuer nicht verloscht“ (Markus-Evangelium, Kap. 9, 43–44).

Hans Wolfgang Spiess 60

Entanglement in polystyrene detected by translational diffusion of photo-labeled molecules

Mesure des coefficients de diffusion de polystyrenes marques et comparaison avec une equation phenomenologique reliant la masse moleculaire critique entre les enchevetrements Mc a ces masses moleculaires respectives de la chaine diffusant et de la matrice. Comparaison avec les theories recentes

Ich und die große Welt

Hier geht es auch um die Wahrheit uber den sogenannten „bescheidenen Wissenschaftler.“ Zu diesen habe ich mich selber solange gezahlt, bis mir meine ganz personliche Eitelkeit und der dazugehorige Ehrgeiz im Jahre 1991 schmerzlich bewusst wurden. Ich hatte zum ersten Mal ein Manuskript an die prestigetrachtigen Physical Review Letters geschickt, weil ich dachte, unsere neuen Ergebnisse seien so bedeutend, dass sie unbedingt dort erscheinen mussten. Doch das Manuskript wurde abgelehnt; es war dies uberhaupt das erste meiner Manuskripte, das je abgelehnt wurde. Meine nachfolgenden Gefuhle haben sich tief in mein Gedachtnis eingepragt, es waren schlicht und einfach Gemutszustande einer zutiefs…

Temperature dependence of the static structure factor of ortho-terphenyl in the supercooled liquid regime close to the glass transition

Abstract Studying the temperature dependence of the static structure factor of ortho-terphenyl from the liquid state down to the glass we find that the main peak of S ( Q ) is split into two maxima which behave quite differently. While the maximum at Q =1.4 A −1 is not much affected by the temperature variation the one at 1.9 A −1 is significantly enhanced. This effect is connected with a change of the short range order, i.e. of the intermolecular distances, but evolves continuously. Thus the dynamic anomalies that have been observed in this system around a characteristic temperature T c ≈290 K are not simply due to a discontinuous change in S ( Q ) but can be attributed to the existence of…

Self-diffusion coefficients in plastic crystals by multiple-pulse NMR in large static field gradients.

Measurements of self-diffusion coefficients in solids with the gradient spin echo technique have until now been limited due to short spin-spin relaxation times. Here we make use of multiple-pulse sequences, which average out the nuclear dipole interaction, to expand the measurable range for macroscopic self-diffusion coefficients by 2 orders of magnitude. By combining multiple-pulse NMR, in our case using the MREV-8 sequence, with a high static gradient we measured the self-diffusion coefficient in a molecular crystal of camphene down to a value of $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{m}}^{2}{\mathrm{s}}^{\en…

Die Welt des Pythagoras – Objektive oder hypothetische Realität

Der Urvater dessen, was wir heute in den exakten Naturwissenschaften unter „objektiver Realitat“ verstehen, ist die legendare Gestalt des Pythagoras von Samos. Der nach ihm benannte Satz, nach dem im rechtwinkligen Dreieck das Hypotenusenquadrat gleich der Summe der beiden Kathetenquadrate ist, war schon tausend Jahre vor ihm bekannt, und Pythagoras hat ihn zweifelsohne auf seinen ausgedehnten Reisen durch die antike Welt kennengelernt. Denn uberall interessierte er sich fur die in vielen Generationen von Priestern, Sterndeutern und Landvermessern gewonnenen Kenntnisse der Mathematik. Was wir ihm verdanken, ist also nicht der Satz des Pythagoras, sondern sein Beweis.

Diffusion coefficients D of singly and doubly end-labeled polystyrenes (PS) with molecular weights in the range 6500 ≤ M ≤ 75400 were measured in a PS matrix of molecular weight M′ = 111000, and in matrices with M′ = M. At 212°C, we find no influence of the label. In a power-law description D = D0 · M−α · M′−β we find α = 2,0 for M′ = 111000 and α + β = 2,4 for M = M′. The crossover to Rouse-like behavior for short-M chains is at Me ≈ 18000 for the former (high M′), and at Mc ≈ 33000 in the latter (M′ = M) case. At 185°C, we find a more complex scaling behavior and different D values for singly and doubly labeled PS.

Far-off-resonance averaging of dipolar interactions in solids

Abstract The far-off-resonance performance of several line-narrowing sequences is investigated. Both theoretically and experimentally, it is found that transverse relaxation times, dominated by dipole–dipole interactions, are most effectively prolonged not only on-resonance but also for certain, generally large, resonance offsets. These correspond to a situation when, during the basic pulse separation, the frequency offset rotates the toggling-frame Hamiltonian by multiples of 180°. The implications of these results for the study of macroscopic translational diffusion using static-field-gradient NMR are discussed.

Die Endlichkeit des Lebens

In seinem Buch „Der EGO Tunnel“ (Metzinger 2009, S. 294) hat der Mainzer Philosophieprofessor Thomas Metzinger das Problem der Endlichkeit des Lebens sehr klar ausgesprochen: „Fur Wesen wie uns ist Sterblichkeit nicht einfach nur eine objektive Tatsache, sondern ein subjektiver Abgrund, eine offene Wunde in unserem phanomenalen Selbstmodell. Wir haben einen tiefen, in uns selbst eingebauten existentiellen Konflikt, und wir scheinen die ersten Lebewesen auf diesem Planeten zu sein, die diese Tatsache bewusst erleben.“

Vom Haus auf dem Felsen zum Floß der Hoffnung

Individuelles Leben, Bewusstsein, Sinn, die Grundfragen des Menschen sind zu allen Zeiten in Bilder und Vorstellungen gefasst worden, die zwar nur eine Seite der Wahrheit darstellen, aber dieser Wahrheit oft naher kommen als Worte. Das biblische Bild vom Menschen, der sein Haus auf einen Felsen baute, weckt heute Assoziationen zum Fundamentalismus. Doch das Bild kann viel allgemeiner verstanden werden. Es beschreibt den Menschen, der in seiner Jugend eine Existenz aufbaut und darin seine Identitat findet, ein Fundament, das ein Leben lang halten wird. Dieses Grundvertrauen ist Glaubigkeit, auch wenn kein fundamentalistischer Dogmenglaube damit verbunden ist. Der Verlust dieses Glaubens ist …

Nonexponential 2H spin-lattice relaxation as a signature of the glassy state

Abstract High-precision measurements of 2H spin-lattice relaxation on several molecular glass-forming liquids have been performed. As a general feature the following can be stated: At temperatures more than ten to twenty degrees above the calorimetric glass transition temperature Tg the 2H spin-lattice relaxation is exponential; below that temperature regime the relaxation is nonexponential. This crossover from exponential to nonexponential magnetization recovery implies that no common spin temperature caused by spin diffusion exists in a 2H glass. This contrasts 1H spin-lattice relaxation which is found to be strictly monoexponential throughout. The occurrence of nonexponential 2H relaxati…

Solid state NMR - A tool for studying molecular motion in polymers

After an introduction describing the development of 1H, 2H, and 13C solid state NMR two sections on 13C and 2H NMR, respectively, outline the physical background as related with molecular motion. Some representative examples demonstrate the potential of recent NMR techniques in polymer dynamics studies.

Spatial heterogeneity in glassy polystyrene detected by deuteron NMR relaxation

Using deuteron NMR, the dynamics of supercooled polystyrene-d 3 was investigated near the calorimetric glass transition. At these temperatures non-exponential spin lattice relaxation is found, indicating the presence of spatial heterogeneity. With increasing temperature, structural relaxation becomes fast enough to average efficiently over different spatial environments, leading to exponential magnetization decays. A qualitative comparison with toluene as a representative of a low molecular weight glass former is carried out. Indications are found that in polystyrene the observed averaging process is more effective at T g than it is in toluene.

Nachruf auf Gerald Fleischer

We have determined by forced Rayleigh scattering the diffusion coefficients of photo-labeled polystyrene micronetwork spheres (radii ≤ 10 nm) in melts of linear polyvinylmethylether (M W ≤ 40000 g/mol) at temperatures of 20-80°C. An expected slippage of the spheres through the meshes of the entanglement network appears possible but is still within the experimental uncertainty of our results.

Applications of “Forced Rayleigh Scattering” and “Photon Correlation Spectroscopy” for the examination of transport properties in polymer melts

The importance of optical techniques for the characterization of the dynamics in polymers has increased in the last 10 years. This was caused by the rapid development in optics and microelectronics which has made these techniques easily available and extremely precise. However, in case of the examination of transport properties in bulk polymers, new difficulties arise due to the comparably slow dynamics underlying these phenomena. The topic of this paper is a small survey of two optical techniques which can be applied to solve the arising problems and a presentation of some results of our working group concerning slow translational transport processes in polymers. In a first part, the techn…

Wissen, Glauben, Wunder

„Alle wissen, dass sie sterben mussen, aber keiner glaubt daran.“ Dieser altbekannte Aphorismus scheint die Rangordnung von Wissen und Glauben auf den Kopf zu stellen. „Ich glaube, dass ich gestern Herrn Meier gesehen habe, aber ich weis es nicht genau.“ So bewerten wir normalerweise Glauben und Wissen, oder aber: „Ich glaube, dass ich in den Himmel komme, wenigstens hoffe ich darauf, naturlich kann ich es nicht wissen.“ Wenn ein glaubiger Islamist sich auf ein Selbstmordattentat vorbereitet, glaubt er, dass er ganz gewiss in den Himmel kommen wird. Doch dies ist eine Glaubensgewissheit, mit beweisbarem Wissen hat das nichts zu tun.

Relaxation and phonons in viscous and glassy orthoterphenyl by neutron scattering

We present an extended set of incoherent neutron scattering measurements on the van der Waals liquido-terphenyl, obtained by time-of-flight and backscattering spectroscopy. In the supercooled liquid regime, data from three instruments are combined and analysed in terms of the selfcorrelationS(Q, t). In the time range 1...100 ps, the crossover from α-to β-relaxation is well described by the masterfunction of mode coupling theory, and fitted parameters are consistent with the previously established critical temperatureT c [Z. Phys. B83, 175 (1991)]. In the glassy regime, vibrations are harmonic and can be described by a density of states. Deviations at lowQ are quantitatively explained by a m…

Telechelic α,ω-macrozwitterions — narrowly distributed polystyrene chains oppositely charged at each end — were synthesized via anionic polymerization using direct functionalization with the initiator and the termination agent. The resulting products were purified (zwitterion content ≥ 0,95) and characterized with gel permeation chromatography, viscometry, static and dynamic light scattering and small-angle neutron scattering. In unpolar solvents as toluene, the polymeric zwitterions form clusters with molecular weights depending on concentration. In the dilute case, the clusters are relatively small and consist of approximately 8 zwitterions. The structure of these clusters is discussed by…

Dynamic heterogeneity in supercooled ortho-terphenyl studied by multidimensional deuteron NMR

Using deuteron NMR, we have studied molecular reorientation rates and rate exchange processes in supercooled ortho-terphenyl. We monitor the re-equilibration of differently selected subensembles through four-time stimulated echo experiments. A comparison of the two-time with the four-time echoes suggests that the characteristic time scales for reorientation and dynamical exchange are relatively similar. The four-time correlation functions were described using various multi-state rate exchange models.

Persönliches über die Existenz eines persönlichen Gottes

Dietrich Bonhoeffer hat in meinem Leben eine eigentumliche Rolle gespielt. Als ich mit Widerstand und Ergebung (Bonhoeffer 1951) seine Briefe aus dem Gefangnis zum ersten Mal las, war ich tief betroffen von seinem Schicksal wie viele andere, die das Buch gelesen hatten. Ganz anders ging es mir mit seinen Gedanken zu einer neuen Theologie, die er in einigen dieser Briefe ansatzweise entwickelte. Mit seinem Entwurf eines „religionslosen Christentums“ hat er wesentlich dazu beigetragen, dass ich den pietistisch gepragten Glauben meiner Jugend verlor. In einem Brief, den ich am Jahresende 1966 an meinen Freund Wilfried geschrieben habe, kann ich heute noch nachlesen, was damals in mir vorgegang…

Seltsame Welten in veränderten Gehirnen – In welcher Wirklichkeit leben Geisteskranke?

Es ist bemerkenswert, dass Philosophen wie John Locke, David Hume und Immanuel Kant, die sich im 17. und 18. Jahrhundert mit der Natur des menschlichen Verstandes auseinandersetzten, praktisch nur normale erwachsene Menschen im Blick hatten. Erst im 19. Jahrhundert wurde einer breiteren Offentlichkeit bewusst, dass abseits des Normalen keineswegs nur Irre dahinvegetieren, bis sie sterben. Mit der Entdeckung des Genies kam die Einsicht, dass Genie und Wahnsinn haufig nahe beieinander liegen. Seit in Napoleons Armeen gut ausgebildete Mediziner die Verwundeten versorgten, erkannte man anhand der Symptomatik nach Kopfschussen, dass mit der Zerstorung bestimmter Hirnregionen bestimmte geistige B…

Solutions of chain- (PS-d3) and phenyl ring (PS-d5) deuterated polystyrenes in perdeuterated PS-d8 have been investigated with 1H and 2D NMR relaxation and wide line methods. The intra- and intermolecular parts of the 1H second moments at −100°C are 3,7 G2 and 2,0 G2, respectively, for PS-d3, and 14,7 G2 and ca. 0 G2, respectively, for PS-d5. The intermolecular contribution to the 1H spin lattice relaxation rate, determined at 55 MHz between 150°C and 250°C, is about one third of the total rate in PS-d3, and negligible in PS-d5. We suggest that this contribution is caused by rotational fluctuations of the intermolecular H H vectors. The intramolecular 1H- and 2D-relaxation rates indicate th…

Secondary relaxation in the glass-transition regime of ortho-terphenyl observed by incoherent neutron scattering.

We report on incoherent-neutron-scattering measurements in the supercooled regime of the van der Waals liquid ortho-terphenyl. A secondary localized relaxational process on the picosecond time scale is found. In accordance with mode-coupling theories of the glass transition, the relaxational dynamics around a critical temperature ${\mathit{T}}_{\mathit{c}}$ decomposes into two time regimes.

2H spin relaxation times, T1 and T2 and solid echo line shapes were investigated in 2-propanol (2-POH) solutions of poly(butyl methacrylate) (PBMA) in a wide concentration and temperature range, covering the solution, gel and glass states. From the results in deuterated 2-POH-d6 we found that the polymer influence upon solvent mobility is largely suppressed in the gel and glass states in contrast to normal polymer solutions where below the glass transition an increasing amount of solvent slows down with decreasing temperature. From 2H NMR of deuterated butyl side groups in the PBMA-d9/2-POH system we found that the side group motion is anisotropic and largely independent of solvent concentr…

1,3,5-triisopropylbenzene diffusion in polystyrene solutions

Self-diffusion coefficients of 1,3,5-triisopropylbenzene (TIB) in binary solutions with polystyrene and ternary mixtures comprised of TIB, toluene, and polystyrene have been measured by static gradient nuclear magnetic resonance (SG-NMR) techniques. These data, as well as mutual-diffusion coefficient data measured by capillary column inverse gas chromatography (CCIGC), have been analyzed here with the Vrentas-Duda free-volume diffusion model. Although both binary and ternary diffusion coefficient data can be accurately correlated with the model, the results contradict those of an earlier investigation, which suggested that TIB diffuses as a single unit in polystyrene solutions. The new data…

Dynamic Anomalies and their Relation to the Glass Transition: A Neutron Scattering Study of the Glass Forming Van der Waals Liquid Ortho-terphenyl

Neutron scattering experiments on the molecular glass former ortho-terphenyl reveal a dynamic anomaly at a temperature Tc ≈ 290 K well above the calorimetric glass temperature Tg = 243 K. Close above Tc the density autocorrelation function ΦQ(t) shows a two step decay over 4–5 decades in time. The slower component obeys the time-temperature superposition principle. Its line shape can be well parametrized by a Kohlrausch law and is strongly temperature dependent as its relaxation time scales with the shear viscosity. Thus this component is identified with the structural relaxation (α-process). The faster component (β-process) is much less temperature dependent. Its line shape factorizes in a…

Capacitive scanning dilatometry and frequency-dependent thermal expansion of polymer films

The dilatometric properties of polymer films near and above their glass-transition temperatures were explored using capacitive high-frequency detection in temperature ramping as well as in harmonic temperature cycling experiments. The broad applicability of capacitive scanning dilatometry is demonstrated by the investigation of macromolecular systems of vastly different polarity such as polystyrene, polybutadiene, and polyvinylacetate. From temperature cycling experiments the real and imaginary parts of the frequency-dependent thermal-expansion coefficient are determined in the sub-Hz regime.

Nature of the non-exponential primary relaxation in structural glass-formers probed by dynamically selective experiments

Several experimental methods feature the potential to distinguish between slow and fast contributions to the non-exponential, ensemble averaged primary response in glass-forming materials. Some of these techniques are based on the selection of subensembles using multi-dimensional nuclear magnetic resonance, optical bleaching, and non-resonant spectral hole burning. Others, such as the time-dependent solvation spectroscopy, measure microscopic responses induced by local perturbations. Using several of these methods it could be demonstrated for various glass-forming materials that the non-exponential relaxation results from a superposition of dynamically distinguishable entities. The experime…

The proton spin-lattice relaxation time T1 was determined at 13,8, 55,2, and 90 MHz in polystyrene (PS-d0) and polystyrene deuterated at the chain (PS-d3) and the phenyl groups (PS-d5), respectively, at temperatures between −130 and +230°C. Furthermore, T1 was measured in isotopic mixtures of PS-d3 and fully deuterated PS-d8 where a separation into intramolecular and intermolecular contributions was possible through the deuteron dilution technique. Above 130°C, various distributions of correlation times provide a semiquantitative understanding of the different motins seen by the protons of the partially deuterated systems. Rotating frame relaxation times in PS-d3 and PS-d5 reveal librationa…

2H NMR Time Domain Analysis of Ultraslow Reorientations in Supercooled Liquids

A method for evaluating 2H NMR stimulated echo experiments in the time domain is presented. It exhibits a high sensitivity to molecular reorientation mechanisms for small angles. Reorientations with jump angles below 25degrees can be resolved with a precision of approximately 1degrees so that, e.g., rotational diffusion and finite jump angle mechanisms become distinguishable. The method, applicable to isotropic reorientation models, is thought to extend the domain of 2D exchange spectroscopy where the best resolution is obtained in the large angle range of anisotropic reorientational mechanisms. Application to reorientation in the supercooled melt of ortho-terphenyl is presented. These data…

Sterben, damit andere leben?

Alte Menschen mussen sterben, damit die jungen leben konnen. Das ist eine uralte Einsicht, die man schon in Grimms Marchen „Die Boten den Todes“ findet. Als der Tod, von einem Riesen niedergeschlagen, kraftlos am Boden liegt, sagt er: „Was soll daraus werden, wenn ich da in der Ecke liegen bleibe? Es stirbt niemand mehr auf der Welt, und sie wird so mit Menschen angefullt werden, dass sie nicht mehr Platz haben, nebeneinander zu stehen.“ Tatsachlich kommt er wieder zu Kraften, und alles ist wieder in Ordnung.

Denn bei Gott ist kein Ding unmöglich? – Eine Betrachtung über biblische Wunder

Anlass fur die nachfolgende Betrachtung uber biblische Wunder sind Auserungen von Papst Benedikt XVI . in seinem Buch Jesus von Nazareth, dessen dritter Band 2012 erschienen ist. In diesem Buch bezeichnet er Jungfrauengeburt und Auferstehung als „Prufsteine des Glaubens“. Er schreibt dazu: „…Aber gerade darum geht es, dass Gott Gott ist und sich nicht nur in den Ideen bewegt.“ Weiterhin schreibt er: Wenn „Gott nicht auch Macht uber die Materie hat, dann ist er eben nicht Gott.“ Zitiert aus einer Rezension des Buchs von Jorg Bremer in der Frankfurter Allgemeinen Zeitung vom 24. 11. 2012. Offenbar ist die Zeugung Jesu durch den Heiligen Geist fur den Papst ein unverzichtbarer Teil seines Glau…

Slow and fast methyl group rotations in fragile glass-formers studied by NMR

Abstract The spin-lattice relaxation times of the selectively ring deuterated, fragile glass-formers propylene carbonate and toluene were compared with those measured for species which were specifically labeled at the methyl groups. It was found that the dynamics of the CD 3 group is strongly decoupled from that associated with the primary response of toluene, while for propylene carbonate the degree of decoupling is relatively weak. The experimental results could be described successfully using a model which takes into account the ring dynamics as well as those of the methyl group.

Diffusion of spherical micronetworks in polymer diluent systems and melts studied by dynamic light scattering techniques

Spherical polystyrene (PS) micronetworks can be prepared in microemulsion with bulk radii of 5–60 nm and different cross-linking densities. The diffusion of these PS spheres has been studied in polymer diluent systems ranging from dilute solutions to plasticized melts by using forced Rayleigh scattering and photon correlation spectroscopy. On increasing the PS concentration, a colloid glass transition is observed at a volume fraction ΦC ≈ 0.64 of the swollen spheres. At higher concentration inside the “colloid glass” state the sphere diffusion is slowed down and becomes very complex but can be observed up to the limit of a melt of collapsed spheres.

Loblied auf Roby

Es ist einfach wunderbar beruhigend, einen Roby zu haben, der immer Zeit hat, der sich von selber auf meine Wunsche einstellen kann und vieles diskret erledigt, was ich doch nur vergessen wurde. Vor allem kennt er meinen Gesundheitszustand. Wenn er Abweichungen von meinem Wohlbefinden registriert und diese nicht selbst beheben kann, ruft er sofort professionelle Hilfe. Dadurch wird mir ein einigermasen schmerzfreies Leben ermoglicht, obwohl ich nach fruheren Masstaben gewissermasen auf dem letzten Loch pfeife. Besonders genial ist die heutige Schmerzbehandlung, die sich aus Beobachtungen von Vilayanur Ramachandran in den Neunzigerjahren des vergangenen Jahrhunderts ergeben hat. In seinem da…

Introduction into the study of translational diffusion by laser techniques

Breve description de la technique du reseau holographique pour mesurer les coefficients de diffusion de traceurs dans des polymeres et de la technique de spectrometrie de correlation de photon pour la mesure des coefficients de diffusions mutuelle dans des melanges de polymeres

Was ist ist?

Im alten Rom gab es zur Zeit von Kaiser Nero eine verbotene Sekte, deren Anhanger an geheimen Orten zusammenkamen und dort Menschenfleisch asen und Blut tranken. Aufrichtige Romer fanden es vollig in Ordnung, dass diese Kannibalen im Kolosseum den Lowen zum Frase vorgeworfen wurden. Wenn man jedoch ein Sektenmitglied privat befragte, was es denn mit dieser Menschenfresserei auf sich habe, erfuhr man, eigentlich werde ja nur Brot gegessen und Wein getrunken. Aber diese werden in dem Mysterium der heiligen Wandlung, der Transsubstantion , in das Fleisch und Blut Jesu Christi verwandelt, sodass im Heiligen Abendmahl in der Tat Fleisch und Blut des Menschensohnes Jesus verzehrt werden.

2 H-NMR-Stimulated Echo Study of Ultraslow Reorientational Motion in Viscous Glycerol near Its Glass Transition Temperature

2H-NMR stimulated echo experiments have been performed in order to study the molecular basis of the ?-process in viscous glycerol near its glass transition temperature. Decay functions following modified Jeener-Broekaert pulse sequences were compared with predictions from different models for molecular reorientation. Rotational diffusion, rotational random jumps, rotational fixed-angle jumps and combinations of diffusive and jump motions have been tested. All data are fitted with a log-Gaussian distribution of correlation times. Thereby, small-but finite-angle reorientation processes turn out to dominate in the 10-3 s.. 100 s regime. Pure large-angle rotational jumps can be ruled out with h…

Deuteron n.m.r. in relation to the glass transition in polymers

Abstract 2H n.m.r. is introduced as a tool for investigating slow molecular motion in the glass transition region of amorphous polymers. In particular, we compare 2H spin alignment echo spectra of chain deuterated polystyrene with models for restricted rotational Brownian motion. Molecular motion in the polystyrene-toluene system has been investigated by analysing 2H n.m.r. of partially deuterated polystyrene and toluene, respectively. The diluent mobility in the mixed glass has been decomposed into ‘solid’ and ‘liquid’ components where the respective average correlation times differ by more than 5 decades.

Simultaneous measurement of rotational and translational diffusion by forced Rayleigh scattering. Colloid spheres in suspension

Abstract It is shown that the technique of forced Rayleigh scattering, traditionallyemployed to probe translational diffusion, can be employed to probe rotational diffusion as well. Thus with a single experiment both quantities are measured. The system under investigation is colloid spheres suspended in a glass-forming liquid. Furthermore, it is shown that the Stokes-Einstein and Debye-Stokes-Einstein relations for translational and rotational diffusion, respectively, are valid for spherical colloid particles in a supercooled liquid matrix in the vicinity of the glassy state.

Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition

Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down toD t =3·10−14 m2s−1 using a1H-NMR technique applying static field gradients up to 53T m−1 In a range of more than two decades theD t values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperatureT g . A change of mechanism is found for translational diffusion atT c ≈1.2T g whereD t is proportional to the inverse shear viscosityη −1 atT>T c butD t ∼η ξ with ξ=0.75 atT<T c . Rotational correlation times determined by2H-NMR stimulated echo techniques in deuterated OTP remain proportinal toη −1 down toT g . Our re…

Coefficients de diffusion de traceurs dans les melanges de PS avec poly(o-methylstyrene), poly(p-methylstyrene et un copolymere statistique p-m-methylstyrene

Interdiffusion in blends of polystyrene and polymethylstyrene studied by light scattering after temperature jumps across the phase boundary

Abstract We describe a simple light scattering set-up for measuring interdiffusion coefficients D in polymer blends by generating spinodal decomposition and subsequent dissolution after temperature jumps across the phase boundary. In blends of polystyrene and polymethylstyrene (random copolymer of 60% m-methylstyrene and 40% p-methylstyrene) D values were obtained between 10−11 and 10−15 cm2s−1 at temperatures up to 50 K above the upper critical solution temperature. The results are discussed in relation to tracer diffusion in the same system.

Multi-speckle autocorrelation spectroscopy — a new strategy to monitor ultraslow dynamics in dense and nonergodic media

We present a modification of the conventional dynamic light scattering set-up which allows to monitor the intensity fluctuations of many independent spatial Fourier components of the density fluctuations, i.e. “speckles”, simultaneously by using a charge-coupled device (CCD) camera as area detector. By averaging over the intensity autocorrelation function the final 10–20% decay of the intermediate scattering function in very dense colloidal dispersions is obtained with much higher accuracy. At the same time this multi-speckle autocorrelation spectroscopy provides an alternative route for constructing ensemble-averaged intermediate scattering functions in nonergodic media by replacing the av…

Brief an einen Enkel

Lieber Jakob, ich habe ein Buch mit Briefen prominenter Christen an ihre Enkel gelesen, geschrieben im Jahr 1999, Briefe als gutgemeinte Wegweiser ins neue Jahrtausend. – Bei uns ist das ja gerade umgekehrt. Du hast mir, dem Opa, einen Wegweiser gegeben, den ich nie vergessen werde: „Ich glaub’, wenn die Leute sterben, kommen sie in den Himmel und fangen ein neues Leben an. Das glaub’ ich.“ – Dein Vater hat es nicht geglaubt. Aber er hat Deinen Satz auf ein Zettelchen geschrieben und an die Pin-Wand in der Kuche gehangt, damit er jeden Tag daran erinnert wird. Ich glaub’s auch nicht. Aber ich habe bei der Trauerfeier zu Euer beider Beerdigung eine Ansprache gehalten, bei der es ganz wesentl…

Die Welt der Astronomie – Das kosmologische Standardmodell

Am Anfang war der Urknall, jeder kennt ihn, und die meisten wissen auch, dass danach, innerhalb eines winzigen Bruchteils einer Sekunde, unser Universum so gros wurde wie ein Tennisball. In rasendem Tempo hat es sich dann weiter ausgedehnt, bis es die gewaltigen Dimensionen erreicht hat, an die wir heute gewohnt sind. Was vor dem Urknall war, daruber kann man bei einem Glas Wein lange diskutieren. Doch meist wird falsch verstanden, was mit dem Wort „Urknall“ eigentlich gemeint ist. Nun, es gab keinen Knall, und es ist auch nichts explodiert. Wo sollte auch der „grose schwarze Raum“ herkommen, in den hinein das Universum explodiert ist? Tatsachlich wurde und wird bei der Expansion des Univer…

Polymer and Dye Probe Diffusion in Poly(methyl methacrylate) below the Glass Transition Studied by Forced Rayleigh Scattering

By dissolving tracer quantities of 9,10-phenanthrenequinone (PQ) in poly(methyl methacrylate) (PMMA) it was possible to study by forced Rayleigh scattering (FRS) the tracer diffusion of the unbleached PQ as well as the photoproduct which is covalently bound to the PMMA molecules. The PMMA samples with molecular weights, Mw, of 103−105 were intermittently annealed at 80 °C for diffusion times of up to one year. From the results we conclude that polymer chain diffusion may be possible at temperatures more than 20 K below the glass transition temperature Tg, but further experiments are necessary, in particular, since we cannot exclude that our results are due to yet unexplained long time aging…