Dynamic rheological behavior of DBS-induced poly(propylene glycol) physical gels

Physical gelation can be induced in various organic and silicone-based liquids, as well as in polymeric melts, upon addition of 1,3:2,4-dibenzylidene sorbitol (DBS). Such gels are stabilized by the formation of a percolated DBS network composed of highly interconnected nanofibrils. In this study, we explore several factors affecting the rheological properties of poly(propylene glycol) (PPG) gelled by DBS. To ascertain the effect of PPG molecular weight (M-PPG) on gel formation and rheology, we have investigated three series of DBS-induced PPG gels in which M-PPG varies from 425 g/mol to 4000 g/ mel. Dynamic stress measurements reveal that the DBS concentration identifying the onset of PPG gelation decreases with increasing M-PPG. Since the solubility parameter (delta (s)) of PPG decreases sharply as M-PPG increases over this M-PPG range, this observation suggests that DBS gelation is sensitive to delta (s) of the matrix liquid, in agreement with previously reported data collected from DBS-gelled solvents. Moreover, the elastic modulus and yield stress are found to increase with increasing (i) DBS concentration for the three series of PPG/DBS gels examined here and (ii) recovery time after cessation of an introductory shear.