No abstract

Self‐assembly and mechanical properties of triblock copolymers in a mid‐block selective solvent are of interest in many applications. Herein, we report physical assembly of an ABA triblock copolymer, [PMMA–PnBA–PMMA] in two different mid‐block selective solvents, n‐butanol and 2‐ethyl‐1‐hexanol. Gel formation resulting from end‐block associations and the corresponding changes in mechanical properties have been investigated over a temperature range of −80 °C to 60 °C, from near the solvent melting points to above the gelation temperature. Shear‐rheometry, thermal analysis, and small‐angle neutron scattering data reveal formation and transition of structure in these systems from a liquid state to a gel state to a percolated cluster network with decrease in temperature. The aggregated PMMA end‐blocks display a glass transition temperature. Our results provide new understanding into the structural changes of a self‐assembled triblock copolymer gel over a large length scale and wide temperature range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 877–887

The self-assembly behavior of physical gels and the effect of such an assembly on the mechanical properties are of significant interest. Here, graphene nanoplatelets have been incorporated in a triblock copolymer gel consisting of poly(methyl methacrylate)-poly(n-butyl acrylate)-poly(methyl methacrylate)[PMMA-PnBA-PMMA] in a midblock selective solvent, 2-ethyl-1-hexanol. The thermoreversible nature of the gel allowed us to incorporate the graphene nanoplatelets in a liquid stage and these nanoplatelets then become part of the network structure as the solution is cooled. Shear rheology is used to investigate the change of mechanical properties as a function of graphene concentration. Graphene nanoplatelets affect the self-assembly behavior as demonstrated by the decrease of gelation temperature. Interestingly, no significant increase of modulus was observed with the incorporation of graphene, as typically observed in polymer nanocomposites. This indicates that the graphene nanoplatelets are not actively participating in load-bearing, i.e. the platelets are not elastically active. A small change of relaxation time in graphene containing triblock copolymer gels has been observed, as captured by stress relaxation experiments. Our results provide a method to incorporate nanomaterials in physically crosslinked polymer gels without affecting the mechanical properties significantly. † Electronic supplementary information (ESI) available: Transmission electron micrographs and electron diffraction patterns of graphene nanoplatelets for different graphene concentrations in 2-ethyl-1-hexanol ( Fig. S1 and S2); edge view of graphene nanoplatelets (Fig. S3); steady-shear viscosity data at 50 C (Fig. S4); creep data tted with Maxwell-Jefferys model (Fig. S5) and stretched exponential function (Fig. S6); schematic of the viscoelastic Maxwell-Jeffreys model (Fig. S7). See