In: Soft Matter, 2010, vol. 6, no. 21, p. 5514-5522
We use photon correlation imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude...
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In: Soft Matter, 2010, vol. 6, no. 13, p. 3030-3037
Foams are ideal model systems to study stress-driven dynamics, as stress-imbalances within the system are continuously generated by the coarsening process, which, unlike thermal fluctuations, can be conveniently quantified by optical means. However, the high turbidity of foams generally hinders the detailed study of the temporal and spatial distribution of topological bubble rearrangement events,...
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In: Journal of Rheology, 2010, vol. 54, no. 2, p. 421-438
We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of Φ=0.15–0.35. Our systems are density-matched, residual charges are screened, and the polymer-colloid size ratio is ~0.37. For these systems, the transition to kinetically arrested states, including disconnected clusters and gels, coincides with the fluid-fluid phase...
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In: Philosophical Transactions of the Royal Society A, 2009, vol. 367, no. 1909, p. 5013-5032
We investigate dynamical heterogeneities in the collective relaxation of a concentrated microgel system, for which the packing fraction can be conveniently varied by changing the temperature. The packing fraction-dependent mechanical properties are characterized by a fluid–solid transition, where the system properties switch from a viscous to an elastic low-frequency behaviour. Approaching this...
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In: Physical Review E, 2009, vol. 80, no. 3, p. 031403
We describe the use of a bright-field microscope for dynamic light scattering experiments on weakly scattering samples. The method is based on collecting a time sequence of microscope images and analyzing them in the Fourier space to extract the characteristic time constants as a function of the scattering wave vector. We derive a theoretical model for microscope imaging that accounts for (a) the...
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In: Physical Review Letters, 2009, vol. 102, no. 1, p. 018301
Suspensions of charged liposomes are found to exhibit typical features of strongly repulsive fluid systems at short length scales, while exhibiting structural heterogeneities at larger length scales that are characteristic of attractive systems. We model the static structure factor of these systems using effective pair interaction potentials composed of a long-range attraction and a shorter range...
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In: Physical Review Letters, 2009, vol. 102, no. 08, p. 085702
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. We demonstrate photon correlation imaging by investigating the slow dynamics of a quasi-two-dimensional coarsening foam made of highly packed, deformable bubbles and a rigid gel network formed by dilute, attractive colloidal particles....
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In: Physical Review E, 2007, vol. 76, p. 051404
We use time-resolved x-ray photon correlation spectroscopy to investigate the slow dynamics of colloidal gels made of moderately attractive carbon black particles. We show that the slow dynamics is temporally heterogeneous and quantify its fluctuations by measuring the variance ϰ of the instantaneous intensity correlation function. The amplitude of dynamical fluctuations has a nonmonotonic...
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In: Physical Review Letters, 2008, vol. 100, no. 18, p. 188102
We demonstrate the use of an ordinary white-light microscope for the study of the q-dependent dynamics of colloidal dispersions. Time series of digital video images are acquired in bright field with a fast camera, and image differences are Fourier analyzed as a function of the time delay between them. This allows for the characterization of the particle dynamics independent of whether or not they...
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In: Physical Review Letters, 2004, vol. 93, p. 11570-11573
We show by means of experiments, theory, and simulations that the slow dynamics of coarsening systems displays dynamic heterogeneity similar to that observed in glass-forming systems. We measure dynamic heterogeneity via novel multipoint functions which quantify the emergence of dynamic, as opposed to static, correlations of fluctuations. Experiments are performed on a coarsening foam using...
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