A5058542508- Material Dynamics and Properties
- Pickering emulsions and particle stabilization
- Rheology and Fluid Dynamics Studies
- Surfactants and Colloidal Systems
- Surface Roughness and Optical Measurements
- Electromagnetic Scattering and Analysis
- Liquid Crystal Research Advancements
- Theoretical and Computational Physics
- Phase Equilibria and Thermodynamics
- Electrostatics and Colloid Interactions
- Advanced Thermodynamics and Statistical Mechanics
- Polymer Nanocomposites and Properties
- Polysaccharides Composition and Applications
- Hydrogels: synthesis, properties, applications
- Random lasers and scattering media
- Proteins in Food Systems
- Spectroscopy and Quantum Chemical Studies
- Sports Dynamics and Biomechanics
- Thermoregulation and physiological responses
- Advanced Polymer Synthesis and Characterization
- Advanced X-ray Imaging Techniques
- Polymer Surface Interaction Studies
- Botanical Research and Applications
- Advanced Physical and Chemical Molecular Interactions
- Enhanced Oil Recovery Techniques
University of Fribourg
2015-2025
UNSW Sydney
2020
Procter & Gamble (United States)
2020
Federal Institute For Materials Research and Testing
2020
University of Freiburg
1991-2005
Argonne National Laboratory
2001
Harvard University Press
2001
University of Pennsylvania
1999-2000
Harvard University
2000
Technische Universität Braunschweig
1994
We demonstrate the use of an ordinary white-light microscope for study q-dependent dynamics colloidal dispersions. Time series digital video images are acquired in bright field with a fast camera and image differences Fourier-analyzed as function time delay between them. This allows characterization particle independent on whether they can be resolved individually or not. The characteristic times measured wide range wavevectors results found to good agreement theoretically expected values...
The rheological data of weakly attractive colloidal particles are shown to exhibit a surprising scaling behavior as the particle volume fraction, $\ensuremath{\varphi}$, or strength interparticle interaction, $U$, varied. There is critical onset solid network either $\ensuremath{\varphi}$ $U$ increase above values. For all solidlike samples, both frequency-dependent linear viscoelastic moduli, and strain-rate dependent stress can be scaled onto universal master curves. A model interspersed...
Attractive colloidal particles can exhibit a fluid to solid phase transition if the magnitude of attractive interaction is sufficiently large, volume fraction high, and applied stress small. The nature this similar for many different colloid systems, forms interaction. jamming captures common features these translations, by unifying behavior as function particle fraction, energy interparticle attractions, stress. This paper describes applicability state diagram, highlights those regions...
Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected regions solidify. We show that this occurs these a glass transition, leading to dynamic arrest of the decomposition. The characteristic length scale gel decreases with increasing quench depth, nonergodicity parameter exhibits pronounced dependence on scattering vector. Mode coupling theory gives good description dynamics, provided we use full static...
The enthalpically favoured hydration of hydrophobic entities, termed hydration, impacts the phase behaviour numerous amphiphiles in water. Here, we show experimental evidence that is strongly determined by mean energetics aqueous medium. We investigate aggregation and collapse an amphiphilic polymer, poly-N-isopropyl acrylamide (PNiPAM), solutions containing small amounts alcohol find thermodynamic characteristics defining transitions PNiPAM evolve relative to solvent composition at which...
We describe the use of a bright-field microscope for dynamic light scattering experiments on weakly samples. The method is based collecting time sequence images and analyzing them in Fourier space to extract characteristic constants as function wave vector. derive theoretical model imaging that accounts (a) three-dimensional nature sample, (b) arbitrary coherence properties source, (c) effect finite numerical aperture objective. tested successfully against performed colloidal dispersion...
Abstract We investigate the phase behaviour of aqueous dispersions poly-N-isopropyl acrylamide (PNiPAM) microgels above their lower critical solution temperature (LCST) and find that beyond a well-defined concentration systems exhibit peculiar behaviour: assemble into space-spanning gels shrink in time while maintaining shape container which they have been formed. Over wide range concentrations this shrinking is independent PNiPAM concentration, but systematically depends on significantly...
We introduce a new scheme for investigating temporally heterogeneous dynamics, which is termed time-resolved correlation (TRC). TRC applied to data obtained by diffusing wave spectroscopy probing the slow dynamics of strongly aggregated colloidal gel. Other examples data, collected different jammed materials in single and multiple scattering, are provided demonstrate wide range applicability this method. In all cases we find evidence that results from series discrete steps rather than...
Time resolved correlation (TRC) is a recently introduced light scattering technique that allows one to detect and quantify dynamic heterogeneities. The based on the analysis of temporal evolution speckle pattern generated by scattered sample, which quantified cI(t, tau), degree between images recorded at time t + tau. Heterogeneous dynamics results in significant fluctuations cI(t,tau) with t. We describe how optimize TRC measurements avoid possible artifacts. statistical properties cI are...
We introduce a new dynamic light scattering method, termed photon correlation imaging, which enables us to resolve the dynamics of soft matter in space and time. demonstrate imaging by investigating slow quasi-two-dimensional coarsening foam made highly packed, deformable bubbles rigid gel network formed dilute, attractive colloidal particles. find both systems be determined intermittent rearrangement events. For foam, rearrangements extend over few bubbles, but small dynamical is observed...
For PNiPAM in water–alcohol mixtures addition of alcohol to water suppresses hydrophobic hydration and alcohols decreases the solvent quality, which leads phenomenon co-nonsolvency.
We explore the glassy dynamics of soft colloids using microgels and charged particles interacting by steric screened Coulomb interactions, respectively. In supercooled regime, structural relaxation time $\tau_\alpha$ both systems grows steeply with volume fraction, reminiscent behavior colloidal hard spheres. Computer simulations confirm that growth on approaching glass transition is independent particle softness. By contrast, softness becomes relevant at very large packing fractions when...
We use time-resolved x-ray photon correlation spectroscopy to investigate the slow dynamics of colloidal gels made moderately attractive carbon black particles. show that is temporally heterogeneous and quantify its fluctuations by measuring variance chi instantaneous intensity function. The amplitude dynamical has a nonmonotonic dependence on scattering vector q, in stark contrast with recent experiments strongly [Duri Cipelletti, Europhys. Lett. 76, 972 (2006)]. propose simple scaling...
We explore the flow behavior of concentrated emulsions for which viscosity continuous phase can be significantly varied by changing temperature. The exponents obtained fitting shear rate-dependent stress with popular Herschel–Bulkley (HB) model display a systematic dependence on phase, revealing that viscous dissipation via suspending fluid cannot neglected in description soft glassy systems. thus propose simple constitutive equation accounts three distinct mechanisms: elastic, plastic, and...
We show that the dynamics of large fractal colloid aggregates are well described by a combination translational and rotational diffusion internal elastic fluctuations, allowing both aggregate size elasticity to be determined dynamic light scattering. The comparison results obtained in microgravity on Earth demonstrates cluster growth is limited gravity-induced restructuring. In absence gravity, thermal fluctuations ultimately inhibit set fundamental limitation lowest volume fraction which will gel.
Suspensions of carbon black in oil, stabilized with adsorbed polyisobutylene succinimide (PIBSI) dispersant, are commonly used as model systems for investigating the soot-handling characteristics motor oils. The structure carbon-black agglomerates changes dramatically temperature; this results a concomitant change suspension rheology. Linear and nonlinear rheological experiments indicate large increase interparticle attractions temperature is raised. To elucidate origin behavior, we...
We show by means of experiments, theory, and simulations that the slow dynamics coarsening systems displays dynamic heterogeneity similar to observed in glass-forming systems. measure via novel multipoint functions which quantify emergence dynamic, as opposed static, correlations fluctuations. Experiments are performed on a foam using time-resolved correlation, recently introduced light scattering method. Theoretically we study Ising model, present exact results one dimension, numerical two...
We investigate dynamical heterogeneities in the collective relaxation of a concentrated microgel system, for which packing fraction can be conveniently varied by changing temperature. The fraction-dependent mechanical properties are characterized fluid-solid transition, where system switch from viscous to an elastic low-frequency behaviour. Approaching this transition below, we find that range xi spatial correlations dynamics increases. Beyond reaches maximum, extending over entire...
Views Icon Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Twitter Facebook Reddit LinkedIn Tools Reprints and Permissions Cite Search Site Citation J. C. Conrad, H. M. Wyss, V. Trappe, S. Manley, K. Miyazaki, L. Kaufman, A. B. Schofield, D. R. Reichman, Weitz; Arrested fluid-fluid phase separation in depletion systems: Implications of the characteristic length on gel formation rheology. Journal Rheology 1 March 2010; 54 (2): 421–438....
A new microscopy method is demonstrated for the characterisation of viscoelasticity nematic liquid crystals. Both aligned and spatially disordered samples are studied successfully. Several other heterogeneous soft materials could be with this approach.
Particle-tracking microrheology probes the rheology of soft materials by accurately tracking an ensemble embedded colloidal tracer particles. One-particle analysis, which focuses on trajectory individual tracers is ideal for homogeneous that do not interact with By contrast, characterization heterogeneous, micro-structured or those where particles directly medium requires a two-particle analysis characterizes correlations between trajectories distinct particle pairs. Here, we propose...