Biomedical subjects

V Trappe

Publications and source records attributed to V Trappe.

6 recordsLinked to original sources

PubMed2005

Glasslike arrest in spinodal decomposition as a route to colloidal gelation.

Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected colloid-rich regions solidify. We show that this occurs when these regions undergo a glass transition, leading to dynamic arrest of the spinodal decomposition. The characteristic length scale of the gel decreases with increasing quench depth, and the nonergodicity parameter exhibits a pronounced dependence on scattering vector. Mode coupling theory gives a good description of the dynamics, provided we use the full static structure as input.

Colloids↗

PubMed2004

Heterogeneous dynamics of coarsening systems.

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 time-resolved correlation, a recently introduced light scattering method. Theoretically we study the Ising model, and present exact results in one dimension, and numerical results in two dimensions. For all systems the same dynamic scaling of fluctuations with domain size is observed.

Journal Article↗

PubMed2004

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.

Colloids↗

PubMed2003

Rideal lecture. Universal features of the fluid to solid transition for attractive colloidal particles.

Attractive colloidal particles can exhibit a fluid to solid phase transition if the magnitude of the attractive interaction is sufficiently large, if the volume fraction is sufficiently high, and if the applied stress is sufficiently small. The nature of this fluid to solid transition is similar for many different colloid systems, and for many different forms of interaction. The jamming phase transition captures the common features of these fluid to solid translations, by unifying the behavior as a function of the particle volume fraction, the energy of interparticle attractions, and the applied stress. This paper describes the applicability of the jamming state diagram, and highlights those regions where the fluid to solid transition is still poorly understood. It also presents new data for gelation of colloidal particles with an attractive depletion interaction, providing more insight into the origin of the fluid to solid transition.

Journal Article↗

PubMed2001

Jamming phase diagram for attractive particles.

A wide variety of systems, including granular media, colloidal suspensions and molecular systems, exhibit non-equilibrium transitions from a fluid-like to a solid-like state, characterized solely by the sudden arrest of their dynamics. Crowding or jamming of the constituent particles traps them kinetically, precluding further exploration of the phase space. The disordered fluid-like structure remains essentially unchanged at the transition. The jammed solid can be refluidized by thermalization, through temperature or vibration, or by an applied stress. The generality of the jamming transition led to the proposal of a unifying description, based on a jamming phase diagram. It was further postulated that attractive interactions might have the same effect in jamming the system as a confining pressure, and thus could be incorporated into the generalized description. Here we study experimentally the fluid-to-solid transition of weakly attractive colloidal particles, which undergo markedly similar gelation behaviour with increasing concentration and decreasing thermalization or stress. Our results support the concept of a jamming phase diagram for attractive colloidal particles, providing a unifying link between the glass transition, gelation and aggregation.

Journal Article↗

PubMed2000

Scaling of the viscoelasticity of weakly attractive particles

The rheological data of weakly attractive colloidal particles are shown to exhibit a surprising scaling behavior as the particle volume fraction, straight phi, or the strength of the attractive interparticle interaction, U, are varied. There is a critical onset of a solid network as either straight phi or U increase above critical values. For all solidlike samples, both the frequency-dependent linear viscoelastic moduli, and the strain-rate dependent stress can be scaled onto universal master curves. A model of a solid network interspersed in a background fluid qualitatively accounts for this behavior.

Journal Article↗