Influence of polymer concentration and midblock length on the mechanical behavior of [ABA] triblock copolymer gels in a B-selective solvent

We present the effect of polymer concentration and midblock length on the large deformation behavior of [ABA] triblock copolymer gels in a midblock selective solvent. In our case, “A” represents poly(styrene) [PS], “B” represents poly(isoprene) [PI], and the solvent is mineral oil. The micellar microstructure of these gels consists of collapsed PS endblock aggregates acting as crosslinks, which are bridged by PI midblocks. The polymer concentration and polymer midblock lengths were varied to introduce midblock entanglement in the gels. Small-angle x-ray experiments capture the micellar microstructure of these gels. Tensile testing reveals a rate dependent moduli for the samples with entangled midblocks. The sample stretchability is governed by stretch rate, midblock length, and polymer concentration. Fracture experiments with a predefined crack reveal a linear dependence of energy release rate with the crack-tip velocity. Fracture in these gels occurs due to endblock pullout from the aggregates and we have estimated the theoretical energy release rate by considering all entropic and enthalpic processes.