Influence of backbone rigidity on the surface rheology of acrylic Langmuir polymer films

Abstract

We present an experimental study on the surface rheology of ultrathin films of poly(tert-butylacrylate) (PTBA) and poly(tert-butylmethacrylate) (PTBMA) for which steric hindrance imposed by the methyl group leads to a large intrinsic rigidity of the polymer chain. Whilst PTBA films show weak temperature dependence, PTBMA films undergo a solid–liquid transition at a temperature well below T_g, the glass transition temperature of the bulk polymer. The peculiar behaviour observed for the shear moduli beyond the fluid–solid transition is similar to that observed recently with dispersions of soft colloidal spheres [D. A. Sessoms, et al., Phil. Trans. R. Soc. A, 2009, 367, 5013–5032], where, upon cooling, the system undergoes first a glass transition, followed by a jamming transition. The transition that we observe in PTBMA films could be similar or, alternatively, could be analogous to the glass transition of the bulk polymer.