Anomaly In Stretching-Induced Swelling of Slide-Ring Gels with Movable Cross-Links

Stretching-induced swelling is investigated for polyrotaxane (PR)-based slide-ring gels with movable cross-links. The osmotic Poisson's ratio (mu(os)), which is a measure of strain-induced swelling, examined as a function of imposed stretching (alpha(1)) for three types of PR gels with various degrees of the mobility of slide- rings. Classical gels with topologically fixed cross-links and PR gels with constrained slide-rings exhibit alpha(1)-independent mu(os). In contrast, PR gels with highly mobile slide-rings exhibit alpha(1)-dependent mu(os). The mu(os) increases with alpha(1) in the case of moderate stretching (alpha(1) < 1.5), whereas it levels off in the case of high stretching (alpha(1) > 1.5). An increase in mu(os) with elongation results from the molecular pulley effect of slide-rings that homogenizes the structure of deformed networks. The pulley effect suppresses the stretching-induced swelling that orginates from an entropic force to reduce the configurational anisotropy of the deformed networks.