On pinning and snapping of elastic strands

The transient network literature up to now has considered that the connection probability of a free strand does not depend on the strand extension, in contrast with the disconnection probability. We argue that, on thermodynamic grounds, both probabilities must have the same dependence on the strand extension. We propose a model for the pinning/snapping of elastic strands reversibly binding to sticky sites, giving explicit expressions for the connection and disconnection rates.Comment: 4 pages, RevTe

Rheothermodynamics of transient networks

The transient network model of Green-Tobolsky [1946], Yamamoto [1956] and Tanaka-Edwards [1992] is formulated within the frame of thermodynamics of irreversible processes, using as a fundamental quantity the chemical potential associated to the connection of strands to the network and treating these connections as chemical-like reactions. All thermodynamic quantities are thus naturally defined in and out of equilibrium. Constitutive equations are derived, giving the stress and the heat production as functions of the thermomechanical history. The Clausius-Duhem inequality, stating that the source of entropy is non-negative, is shown to hold for any thermomechanical history, ensuring the thermodynamic consistency of our model. The presented model includes the Green-Tobolsky model, whereas those of Yamamoto and Tanaka-Edwards fit within ours on the condition that their free parameters obey a detailed balance condition stemming form Boltzmann equilibrium statistics.Comment: PostScript, 26 pages, submitted to Journal of Rheolog

Optical Nonlinearities at the Interface between Glass and Liquid Crystal

In this paper, the optical behavior of a nonlinear interface is studied. The nonlinear medium has been a nematic liquid crystal, namely MBBA, and the nonlinear one, glasses of different types (F-10 and F-2) depending on the experimental needs. The anchoring forces at the boundary have been found to inhibit the action of the evanescent field in the case of total internal reflection. Most of observed nonlinearities are due to thermal effects. As a consequence, liquid crystals do not seem to be good candidates for total internal reflection optical bistability