Swelling behaviour of poly(butadiene) gels in liquid crystal solvents

Abstract

The swelling behaviour of poly(butadiene) gels in four different nematogenic liquid crystalline (LC) solvents has been investigated as a function of temperature (T). Microscopy with crossed polarizers reveals that the nematic to isotropic phase transition temperature of the LC solvents inside the gels (TNI g) is slightly lower than that of the surrounding pure LC solvents (TNI o), but the degrees of depression in TNI g in each system are comparable regardless of the considerable differences in the degrees of equilibrium swelling (Q) at TNI g between the various systems. In general, Q in the isotropic phase is larger than that in the nematic phase, but a unique swelling behaviour of the gel is found in the vicinity of TNI due to the phase transition of the LC solvents. Q remains constant in the temperature range of TNI g ≤ T ≤ TNI o in which the phases of the LCs outside or inside the domain of the gels are different, namely, nematic and isotropic phase, respectively. In addition, a finite abrupt (discontinuous-like) change in Q is observed at around TNI. The gels swollen in the LCs, having an ability to interact with the crosslinking points via hydrogen bonding, show a significant thermal hysteresis for the temperature dependence of Q in the vicinity of TNI, while no discernible thermal hysteresis is observed for the gels in the LCs incapable of forming hydrogen bonds.