Network formation and elasticity evolution in dibenzylidene sorbitol/poly(propylene oxide) physical gels

We have investigated dibenzylidene sorbitol (DBS) physical gels with different gelator concentrations in a poly(propylene oxide) (PPO) matrix by frequency dependent rheological measurements. Defining the gel point according to the Winter and Chambon criterion, we have obtained the critical gel concentration c(g) = 0.153 wt%. Analyzing the experimental data in the delta-\G *\ plot for samples very close to the gel point, we found that a critical gelation concentration range would be more appropriate for describing the gelation process in DBS/PPO system rather than a single concentration value. By extrapolation from the delta-\G *\ plot we obtained a characteristic modulus G(ex) for the samples above the gel point. The analysis of elasticity evolution with increasing gelator concentration revealed the existence of two distinct regimes. A critical domain is identified between c(g) and a turn-over DBS concentration of about 0.5 wt % in which G(ex) exhibits power-law dependence on the relative distance from the gel point. Above 0.5 wt % DBS the characteristic modulus is found to scale with the DBS concentration. The results are discussed within the framework of different models describing physically gelling systems. (C) 2004 The Society of Rheology.