Physikalische Chemie intuitiv verstehen - und dann nachschlagen. Einführung in die Physikalische Chemie. Von P. W. Atkins. VCH Verlagsgesellschaft, Weinheim, 1993. 472 S., Broschur 78.00 DM. – ISBN 3-527-28027-8
Hydrophilic/Hydrophobic Nanostripes in Lipopolymer Monolayers
Poly(styrene sulfonate) self-organization: electrostatic and secondary interactions
We investigate the self-organization of PSS in brushes and polyelectrolyte multilayers with X-ray, neutron and optical reflectivity. The electrostatic force dominates brush phases and adsorption behavior, additionally we find evidence of a strong hydrophobic force: (i) within amphiphilic diblock copolymer monolayers, a PSS monolayer adsorbs flatly to the hydrophobic block, (ii) on temperature increase (and with screened electrostatic forces), more PSS is adsorbed onto oppositely charged surfaces, and (iii) a polyelectrolyte multilayers shrinks when heated at 100% r.h. The latter two effects are consistent with the well-known increase of the hydrophobic force on heating: The increased PSS su…
Supersaturation and Crystal Nucleation in Confined Geometries
Surface aggregation as a necessary condition for interfacially induced crystal nucleation is studied with a surface forces apparatus (SFA).1-3 As a model system, we use the chloride salt of the rod...
The Phases of Phosphatidyl Ethanolamine Monolayers
For the first time phospholipid monolayers at the air/water interface have been studied by X-ray diffraction and reflection along the whole isotherm from the isotropic fluid to the ordered phases [1]. The model used to analyze the data — and the accuracy of the parameters deduced — were tested by comparing the results obtained with two lipids having the same head group but different chain lengths.
Computer-Controlled Experiments in the Surface Forces Apparatus with a CCD-Spectrograph
We present a computer-controlled technique to measure the distance-dependent forces in the surface forces apparatus. The power of our setup is shown by a measurement of the repulsive forces between mica surfaces immersed in a 0.01 M NaCl solution. At close distances we find an oscillatory force with a periodicity of 0.30 nm, which roughly corresponds to the diameter of a water molecule. For the distance determination we use the standard interferometric technique: the interferometer consists of a medium sandwiched between two mica sheets of equal thickness silvered on the backside. The surface separation is measured by comparing the resonance wavelength to the one obtained from contacting m…
Polyelectrolyte Brushes Grafted at the Air/Water Interface
A new approach for the study of grafted polyelectrolytes is investigated: monolayers at the air/water interface of block copolymers consisting of a liquid hydrophobic and a polyelectrolyte block. ...
Immobilization of functionalized lipids in a random poly(methacrylate) copolymer monolayer
It is shown that a monolayer of random poly(methacrylate) copolymer with a hydrophobic and a hydrophilic substituent exhibits a transition from the fluid to amorphous state. Above this transition any amphiphilic molecules mixed with the monolayer are immobile. Furthermore, such functionalized lipids are immobilized in the monolayer during the Langmuir-Blodgett transfer. The hydrophilic head-groups of the biotin-lipids remain on the formerly water-adjacent side of the monolayer, even if this side is exposed to air
Properties of Hydrophobic Polymer Melts Tethered to the Water Surface As Determined with in Situ X-ray Reflectivity
Insoluble monolayers of hydrophobic polymers with low glass transition temperature (perfluoropolyethers, polyisoprenes) and a single ionic head group (carboxylic acid, sulfonate) have been characterized at the air/water interface via X-ray reflectivity measurements. The films are considerably thicker (30−420 A) than conventional Langmuir monolayers of low molecular weight substances or polymers with surface active repeat units. The thickness is inversely proportional to the area per head group and is in accordance with a model assuming a solvent-free hydrophobic layer of the same density as the bulk material.
Nonlinear hairy layer theory of electrophoretic fingerprinting applied to consecutive layer by layer polyelectrolyte adsorption onto charged polystyrene latex particles
The consecutive layer-by-layer adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) on colloidal charged latex particles is investigated by measuring the electrophoretic mobility as a function of pH and ionic strength over a broad range (electrophoretic fingerprinting). Meaningful interpretation of the data required the development of a nonlinear approach to hairy particle electrophoresis including dissociation, adsorption, and association. Steric and electrostatic exclusion of mobile ions from the hairy layer has been considered. Also, the surface conductivity correction is extended to the case of charged hairy layer particles. We deposited up to three polyel…
Synchrotron X-ray Diffraction and Reflection Studies of a Polymacromonomer Monolayer at the Air−Water Interface: Transition from Aligned Single Molecules to Homogeneous Layer
Monolayers of polymacromonomers with poly(vinyl)pyridine side chains of different lengths, polyPVP20.8 and polyPVP46.7, are studied at the air/water interface. Combination of reflection data and diffraction peaks allows the establishment of a structural model. In the expanded phase at pressures below approximately 15 mN/m, the side chains are adsorbed to the air/water interface, causing polymer backbone stretching and alignment of the single molecules. The in-plane peaks are due to the lateral electron density variation above and below the adsorption layer. The diameter of the flattened cylindrical molecules corresponds to twice the contour length of the side chains (25 and 12.5 nm, respect…
Characterizing the Glassy Phase of a Statistical Copolymer Monolayer
Monolayers of a statistical copolymer with a poly(methacrylate) chain and hydrophilic and hydrophobic side groups are investigated at the air/water interface. The isotherms suggest a fluid and a frozen phase. With in-situ X-ray reflectivity the monolayer thickness is determined to be 2.5 nm or less. The shear viscosity in the fluid phase is extremely high yet can be described in the framework of the free area model. However, the parameter which characterizes the overlap of holes available for a diffusing monomer unit is a factor of 2 higher than expected, suggesting local diffusion barriers formed by nanosized clusters. In the glassy phase single-molecule fluorescence shows anomalous diffus…
Ligand-receptor interactions directly measured with the surface forces apparatus
Ligand-receptor interactions give rise to very strong bonds due to perfect geometrical fit. Using the Surface Forces Apparatus we have studied the interactions between membrane-bound biotin ligands and streptavidin receptors. We find an unusually strong short-range binding force associated with equally specific molecular rearrangements-both qualitatively and quantitatively unlike anything previously measured.
Role of hydrophobic forces in bilayer adhesion and fusion.
With the aim of gaining more insight into the forces and molecular mechanisms associated with bilayer adhesion and fusion, the surface forces apparatus (SFA) was used for measuring the forces and deformations of interacting supported lipid bilayers. Concerning adhesion, we find that the adhesion between two bilayers can be progressively increased by up to two orders of magnitude if they are stressed to expose more hydrophobic groups. Concerning fusion, we find that the most important force leading to direct fusion is the hydrophobic attraction acting between the (exposed) hydrophobic interiors of bilayers; however, the occurrence of fusion is not simply related to the strength of the attrac…
X-ray scattering studies of fatty acid films on water and on Cdcl2 solutions
X-ray diffraction methods for Langmuir films on the surface of water are briefly presented, together with recent results for docosanoic acid monolayers on pure water and for eicosanoic acid monolayers on an ionic subphase.
Role of calcium in the adhesion and fusion of bilayers.
The interaction forces and fusion mechanisms of mixed zwitterionic-anionic phospholipid bilayers were measured with the surface forces apparatus. The bilayers were 3:1 mixtures of either dimyristoylphosphatidylcholine and dimyristoylphosphatidylglycerol (DMPC/DMPG) or dilauroylphosphatidylcholine and dilauroylphosphatidylglycerol (DLPC/DLPG), and experiments were carried out in NaCl solutions with and without CaCl2. In NaCl solutions, the forces between either mixed bilayer system were consistent with the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory of repulsive electrostatic and attractive van der Waals forces, and fusion did not occur. At high pH (> 6) and in high (20 mM) NaCl concentra…
Molecular Mechanisms Controlling the Self-Assembly Process of Polyelectrolyte Multilayers
The distance dependent interaction between polyelectrolyte-covered mica surfaces in aqueous solution was investigated with the surface forces apparatus. We find the following: (i) The surface charge changes sign, when an oppositely charged polyelectrolyte from a concentrated polyelectrolyte solution is adsorbed. (ii) Tails and loops of the adsorbed polyions dangle into the bulk phase, inducing a small steric force. If polycations and poyanions are adsorbed on top of each other, a strong short range attractive force is seen due to ion-pair formation after crossing a large repulsive electrostatic/steric barrier. (iii) Obviously, after polyelectrolyte adsorption, there are still nonoccupied b…
The role of the hydrophobic force in bilayer adhesion and fusion
The Surface Forces Apparatus technique was used for measuring the adhesion, deformation, and fusion of bilayers supported on mica. The technique allows the molecular rearrangements to be followed in real time during the fusion process, and the most important forces involved to be identified. The adhesion between two bilayers can be increased by two orders of magnitude if they are thinned so as to expose more hydrophobic groups. For all the bilayer systems studied a single basic fusion mechanism was found in which the bilayers do not “overcome” the short-range repulsive steric-hydration forces; instead, local bilayer deformations allow these repulsive forces to be “bypassed”. The results fur…
The solid-state architecture of a metallosupramolecular polyelectrolyte
Self-assembly of Fe(II) and the ditopic ligand 1,4-bis(2,2′:6′,2″-terpyridine-4′-yl)benzene results in equilibrium structures in solutions, so-called metallosupramolecular coordination polyelectrolytes (MEPEs). It is exceedingly difficult to characterize such macromolecular assemblies, because of the dynamic nature. Therefore, hardly any structural information is available for this type of material. Here, we show that from dilute solutions, where small aggregates predominate, it is possible to grow nanoscopic crystals at an interface. A near atomic resolution structure of MEPE is obtained by investigating the nanoscopic crystals with electron diffraction in combination with molecular model…
X-Ray Scattering Studies of Organic Monolayers on Electrolytic Solutions: Arachidic Acid on CdCl2
The interaction between a charged monolayer of fatty acid molecules on the surface of a CdCl2 aqueous solution and the ions below has been investigated by means of X-ray Reflection and Grazing-Incidence Diffraction. A stoichiometric, localised layer of Cd++ ions forms an epitaxial 2×3 superstructure below the 2D-crystalline fatty acid monolayer.
Tail and Head Group Interactions in Phospholipid Monolayers
Abstract The order/disorder transition of the phospholipid 1,2-dihexadecyl-sn-glycero-3-phosphocholine and its derivatives was studied by X-ray reflection and thermodynamic measurements. We find that increasing the length of an ethylene oxide spacer (zero to three EO groups) between the phosphate group and the hydrophobic chains (i) induces a slight shift of the main transition, (ii) reduces the influence of the head groups on the chain lattice, and (iii) increases the head group length and promotes its hydration. For DH(EO)3PC in the ordered phase we find that the small phosphate groups (which are the main source of contrast in X-ray reflectivity) are homogeneously distributed within the h…
Wetting of mesoscopic soft cylinders: structure and layering transitions.
The wetting of soft mesoscopic long-chain particles is studied. As a model system, a cylindrical brush with poly(vinyl)pyridine side chains on the water surface is characterized by isotherms and x-ray reflectivity. The forces from the two planar interfaces and the intra- and interparticle interactions are all of comparable magnitude. Two layering transitions occur, one from the monolayer to the double layer, the next to a homogeneous multilayer. The hard wall from which layering starts is the smooth polymer/air interface. Indeed, they particles in the top layer of both the double- and the multilayer have their cylinder axis parallel to the surface and are laterally compressed. In contrast, …