Network Analysis of Triblock Copolymer Gels via Quasi-Static Tensile Experiments

Physically-crosslinked triblock copolymer gels are highly elastic and persist down to low copolymer concentrations (~1 wt%) due to the copolymer’s propensity to form nanoscale networks consisting of endblock domains connected by copolymer midblocks. Such materials’ have been extensively studied rheologically, and their resultant plateau modulus, G₀, is found to be dominated by either the crosslinked network (low concentrations in which midblocks are not entangled) or midblock entanglements (higher concentrations). For styrenic triblock copolymers (e.g., poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) in aliphatic solvents, the former case leads to moduli that scale linearly with the concentration of elastically effective midblocks, c_eff, whereas the latter case yields supralinear behavior (i.e., G₀ ∝ c_eff^2.0-2.4). Quasi-static tensile stress-strain data modeled using slip-tube network (STN) theory, on the other hand, enable modulus contributions from both the crosslinked network, G_c, and midblock entanglements, G_e, to be deciphered. This presentation will examine the relationship between these moduli and triblock copolymer concentration in a variety of gel systems. We anticipate that this data will provide new insights of the network structure in semi-dilute gels.