Biomedical subjects

A Knaebel

Publications and source records attributed to A Knaebel.

3 recordsLinked to original sources

PubMed2005

Flocculation, deflocculation, and ions migration in latex suspensions.

We have studied the dynamics of the flocculation of poly(styrene-butadiene-acrylic acid) latex suspensions. These suspensions were flocculated by the addition of Ca2+ ions at high concentrations of latex particles. Using diffusing wave spectroscopy and dynamic single light scattering after dilution, we have observed--depending on the pH and on the Ca2+ concentration--several scenarios for flocculation including successive flocculation and deflocculation. This complex behavior reveals that the Ca2+ migration within the shell of the latex is slow in acidic solvent but fast in basic solvent.

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PubMed2003

Partial rejuvenation of a colloidal glass.

We study the effect of shear on the aging dynamics of a colloidal suspension of synthetic clay particles. We find that a shear of amplitude gamma reduces the relaxation time measured just after the cessation of shear by a factor exp(-gamma/gamma(c)), with gamma(c) approximately 5%, and is independent of the duration and the frequency of the shear. This simple law for the rejuvenation effect shows that the energy involved in colloidal rearrangements is proportional to the shear amplitude gamma rather than gamma(2), leading to an Eyring-like description of the dynamics of our system.

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PubMed2003

Aging processes and scale dependence in soft glassy colloidal suspensions.

The aging behavior of colloidal suspensions of laponite, a model synthetic clay, is investigated using light scattering techniques. In order to measure the complete dynamic structure factor as a function of time and of wave vector, we have developed an original optical setup using a multispeckle technique for simple light scattering. We have thus measured the correlation of the scattered light intensity as a function of the age of the sample t(w) for various concentrations. For sufficiently concentrated samples, we observe a two-stage relaxation process. The fast relaxation is diffusive, stationary, and reminiscent of the liquidlike behavior observed in less concentrated samples. The slow relaxation behavior, however, is more complex. It exhibits two successive regimes as the sample ages. In the first regime, the decay time tau(a) increases exponentially with t(w) as long as tau(a)<t(w). In the second one, "full aging" is observed in which tau(a) is proportional to t(w). In this second regime, the relaxation of concentration fluctuations are hyperdiffusive, scaling as exp[-(t/tau(a))(beta)] with beta=1.35+/-0.15. In addition, the spatial dependence of this relaxation time scales as tau(a)(q) approximately q(-x) with x approximately 1.3.

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