Confinement effects on liquid-liquid transitions: pore size dependence of sulfur's living polymerization

Modifications in the living polymerization or lambda-transition of liquid sulfur, caused by confinement in nanonoporous sol-gel-derived glasses, are investigated by Raman scattering. Raman spectra are analyzed to provide the extent of polymerization, through which the temperature-dependence of the respective heat capacity is calculated. The data reveal that the sharp, second-order-type transition which takes place in bulk sulfur experiences severe rounding (loss of sharpness of the lambda-transition) and systematic shift (increase) of the characteristic transition temperature upon restricting the liquid to smaller pore sizes. The observed confinement-induced changes in the transition temperature are discussed in the framework of theoretical predictions of finite-size scaling phenomena revealing a dependence on the inverse first power of the mean pore size in accordance with theoretical and experimental data.