Effect of graphene on the self-assembly and rheological behavior of a triblock copolymer gel

Abstract

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

Temperature-dependent self-assembly and rheological behavior of a thermoreversible pmma-PnBA-PMMA triblock copolymer gel

“…All these differences can be explained in terms of a slight difference in the PMMA solubility parameter in two solvents chosen here. The difference in total solubility parameters (Hilderbrand) between PMMA and 2‐ethyl‐1‐hexanol is 2.59, which is larger than 0.41, the difference between PMMA and n ‐butanol (see Table S1 in SI) …”

“…For example, in the case of a strong association, during deformation the chains can be stretched to their full length before being pulled out of the aggregates. In those instances, distinct strain‐stiffening responses have been observed …”

“…Thermoreversible gels consisting of PMMA–P n BA–PMMA in mid‐block selective solvents display interesting mechanical properties, such as strain‐stiffening behavior . However, the evolution of structure at different length scales over a wide range of temperature and the effect of these structural changes on the mechanical properties have not been thoroughly investigated.…”

Activation Energy for Dissociation of Hydrogen‐Bonding Crosslinkers in Phase‐Change Salogels: Dynamic Light Scattering versus Rheological Studies

“…For physical gels, stress relaxes through breaking and reforming of physical bonds . The data on the stress relaxation at different temperatures were fitted using the Kohlrausch's stretched exponential relaxation model (Equation ) where τ is the characteristic relaxation time, G 0 is the plateau modulus, and β is the relaxation exponent. The results show that the stress relaxation time followed the Arrhenius behavior (Figure d) with E a of ≈144 ± 4 kJ mol −1 as calculated using the following equation.…”

A New Class of Renewable Thermoplastics with Extraordinary Performance from Nanostructured Lignin‐Elastomers

“…When the value of χ is less than that of the upper critical limit, miscibility is favored. [ 33,34 ] In this study, we exploited this high-temperature induced-phase miscibility of lignin and NBR-41 by shearing the mixture at 160 °C long enough to cause some degree of chemical reactivity. Coleman and co-workers [ 32 ] have shown that for components having weak and moderate hydrogen bonding, the critical χ values are about 0.02-0.2 and 0.2-1.0 [corresponding Δ δ 's are 1.0-2.0 and 2.0-5.1 (MPa) 0.5 ], respectively.…”