Stabilizing grafted colloids in a polymer melt: favorable enthalpic interactions

The interactions between spherical colloids covered with end-grafted polymers (brushes) immersed in a polymer melt are studied theoretically. We show that attractive enthalpic interactions between the two polymer species, characterized by a negative Flory parameter (chi<0), can stabilize the colloidal dispersion. The stabilizing mechanism is a result of a structural change from a dry brush, where the melt chains do not penetrate deeply into the brush, to a wet brush, where the free chains penetrate the brush and force the grafted chains to extend into the melt.

Rheological aging and rejuvenation in microgel pastes

We have studied experimentally the rheological behavior of concentrated suspensions of soft deformable microgels below the yield point. We have found history-dependent effects which are interpreted in terms of aging and rejuvenation phenomena, analogous to those existing in glassy systems. The stress amplitude controls the long-time memory and determines the slow evolution of the suspensions.

Switchable tackiness and wettability of a liquid crystalline polymer

The spreading velocity of liquids on the surface of a liquid crystalline polymer can be tremendously affected by a slight temperature change. Indeed, a bulk transition between a highly ordered smectic and an isotropic phase induces a sharp change from a rigid to a soft behavior, with consequent effects on the tack properties of the liquid crystalline polymer and on the dewetting dynamics of a liquid on its surface.

Enhancement of drug-induced motor activity by an inhibitor of phenylethanolamine-N-methyltransferase.

The behavioral effects of DCMB (2,3-dichloro-alpha-methylbenzylamine, Lilly), an inhibitor of brain phenylethanolamine-N-methyltransferase (PNMT; EC 2.1.1.28), were studied in rats and mice. The drug decreased spontaneous motor activity and induced stereotypic gnawing in both species. The motor activity response of rats to d-amphetamine was enhanced after DCMB, and unusual stereotypic head bobbing developed. The stereotypic motor responses of mice to morphine were increased after DCMB. These findings suggest that adrenaline neurons (which project to the extrapyramidal system) are involved in normal motor activity and in the suppression of some forms of stereotypy.