Search results for "Light scattering"
showing 10 items of 464 documents
The effect of the internal architecture of polymer micronetwork colloids on the dynamics in highly concentrated dispersions
2007
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…
Suzuki polycondensation with a hairpin monomer.
2009
Two straight monomers were subjected to an AA/BB-type Suzuki polycondensation with a hairpin-shaped 1,8-anthrylene monomer as the counterpart leading to a novel polyarylene which should have the preferred conformation of a folded chain. The molar masses were determined by gel permeation chromatography and dynamic light scattering and found to be M(w) = 14,000 and M(n) = 7,000. MALDI-TOF MS analysis of a fraction provides a fingerprint of the step-growth nature of this polymerization.
Nanofiber-based optical trapping of cold neutral atoms
2012
We present experimental techniques and results related to the optimization and characterization of our nanofiber-based atom trap [Vetsch et al., Phys. Rev. Lett. 104, 203603 (2010)]. The atoms are confined in an optical lattice which is created using a two-color evanescent field surrounding the optical nanofiber. For this purpose, the polarization state of the trapping light fields has to be properly adjusted. We demonstrate that this can be accomplished by analyzing the light scattered by the nanofiber. Furthermore, we show that loading the nanofiber trap from a magneto-optical trap leads to sub-Doppler temperatures of the trapped atomic ensemble and yields a sub-Poissonian distribution of…
Resonant Rayleigh scattering by confined two-dimensional excitonic states
1997
A systematic study of resonant Rayleigh scattering in semiconductor single quantum wells has been carried out. The dependence of the scattering efficiency on the well width and the temperature has been investigated. The behaviour observed in the resonant Rayleigh spectra can be explained in terms of the confinement of the excitonic states in the plane of the well due to fluctuations in the well width. A microscopic theoretical model for the elastic scattering of light by weakly confined two-dimensional excitonic states has been developed. The Rayleigh scattering efficiency has been calculated to the lowest-order of perturbation theory and the results found to be in good agreement with the e…
Revealing Magnetite Nanoparticles Aggregation Dynamics – A SLS and DLS Study
2010
\(\mathrm{Fe}_{3}\mathrm{O}_{4}\) nanoparticles in aqueous suspensions are not stable but aggregate, tremendously changing the rheological properties of the nanofluid. Modified version of both the Static Light Scattering (SLS) setup and of Dynamic Light Scattering (DLS) setup experiment were used to monitor \(\mathrm{Fe}_{3}\mathrm{O}_{4}\) nanoparticle aggregation in aqueous diluted suspension. The experiments are described in detail and the variation of the average aggregate diameter in time is presented in this work.
Approaching the limits of multiple scattering decorrelation: 3D light-scattering apparatus utilising semiconductor lasers
2007
Light scattering as a function of scattering angle can be regarded as a standard method to investigate the dynamics of dilute colloidal suspensions. Concentrated suspensions, which are of interest if interactions between the particles are to be investigated, usually show strong multiple scattering. Decorrelation of multiple scattered light, which isolates single scattering events at the expense of a reduced signal-to-noise ratio, has been proven to work using the two-colour crosscorrelation scheme.
Frustration of structural fluctuations upon equilibration of shear melts
2002
Abstract We report on the formation of amorphous solids from aquaeous suspensions of charged colloidal spheres. Comprehensive light scattering and microscopic studies show that in these systems the nucleation rate density continuously increases to very high values. At the highest particle densities of 47.5 μm −3 (packing fraction Φ =0.146) an amorphous state is observed of only short range order, finite static shear modulus and frozen long time dynamics. This state is composed of a piling of––as we propose pre-critical––nuclei. Differences from the Hard Sphere case are discussed in some detail. There the arrest of density fluctuations is observed and described by Mode Coupling scenarios. In…
Fourfold tetraurea calix[4]arenes--potential cores for the formation of self-assembled dendrimers.
2005
Wide rim tetraurea calix[4]arenes monofunctionalized at the narrow rim by COOH or NH2 have been synthesized in five steps from t-butylcalix[4]arene tripropylether. Their covalent linkage via the narrow rim to a central calix[4]arene fixed in the 1,3-alternate conformation led to pentacalix[4]arenes 9 bearing four tetraurea derivatives in the cone conformation in a flexible tetrahedral arrangement. Their self-assembly via the formation of hydrogen bonded dimeric capsules has been studied under different conditions. A fourfold heterodimerisation of tetrakis-tetraurea derivatives of type 9 with tetratosylurea 10 has been confirmed by 1H NMR-spectroscopy and dynamic light scattering.
Thermoreversible gelation of kappa-carrageenan: relation between conformational transition and aggregation.
2003
Abstract We have studied, by optical rotation dispersion, light scattering and rheology, the κ-Carrageenan system to elucidate the processes involved in gel formation (on decreasing the temperature) and gel melting (on increasing the temperature). Our results show that, on decreasing the temperature, a conformational transition from coils to double helices first occurs, followed by aggregation of the double helices into domains and gel formation at appropriate polymer concentration. Structural details of this sequence are better revealed by re-heating the system. Melting appears as a two-step process characterized by first a conformational change of helices involved in junction zones betwee…
Protofibril formation of amyloid beta-protein at low pH via a non-cooperative elongation mechanism.
2005
Deposition of the amyloid beta-protein (Abeta) in senile or diffuse plaques is a distinctive feature of Alzheimer's disease. The role of Abeta aggregates in the etiology of the disease is still controversial. The formation of linear aggregates, known as amyloid fibrils, has been proposed as the onset and the cause of pathological deposition. Yet, recent findings suggest that a more crucial role is played by prefibrillar oligomeric assemblies of Abeta that are highly toxic in the extracellular environment. In the present work, the mechanism of protofibril formation is studied at pH 3.1, starting from a solution of oligomeric precursors. By combining static light scattering and photon correla…