Thermorheological behavior of coexisting physical networks: combining SAFIN and SAMIN organogels

Abstract

Organogels, like their hydrogel analogs in aqueous media, consist of chemically or physically cross-linked networks that endow simple (or even viscoelastic) organic liquids with solid-like characteristics. Of particular interest here are physical networks composed of either low-molar-mass organic gelators, which tend to form self-assembled fibrillar networks (SAFINs) by site-specific interactions such as hydrogen bonding and/or π–π stacking, or microphase-separated triblock copolymers, which form self-assembled micellar networks (SAMINs) due primarily to bridged midblocks that connect neighboring micelles. In this study, we combine these two physical networks by mixing the gelator 1,3:2,4-dibenzylidene-D-sorbitol with a series of midblock-swollen triblock copolymers differing in molecular weight to produce coexisting SAFIN/SAMIN networks in two midblock-selective solvents differing in polarity. The thermorheological properties of the resultant mixed network systems are investigated for three cases: (i) the order–disorder transition temperature (TODT) of the SAMIN is much lower than the dissolution temperature (Td) of the SAFIN, (ii) TODT < Td and (iii) TODT ≈ Td. Employing dynamic rheology, we show how these transitions are affected by the order in which self-organization occurs.