Aqueous solutions of random poly(methyl methacrylate-co-acrylic acid): effect of the acrylic acid content

Abstract

Aqueous solutions from two types of PMMA–AA polymers (PMMA–25AA and PMMA–50AA) are investigated. The aim is to outline the effect of AA content on the bulk solution and air/solution interface properties. The experiments include dynamic light scattering, surface tension and interfacial rheology measurements. The drainage kinetics and stability of microscopic foam films are also investigated. It is established that at similar conditions (pH = 10, temperature 20 °C) the polymer molecules have almost the same mean molecular weight and size distribution of the bulk globules. Dynamic and equilibrium surface tension measurements reveal systematically higher values for PMMA–50AA as compared to PMMA–25AA. These outcomes are related to higher bulk electrophoretic mobility in the PMMA–50AA case and the overall more stretched configuration of the polymer at the air/solution interface. Surface dilational rheology characteristics are particularly sensitive to the polymer structural peculiarities: while no significant changes are registered in the case of PMMA–25AA, the solutions of PMMA–50AA exhibit a pronounced maximum in surface dilational elasticity for the concentration ∼1 × 10⁻⁴ mol L⁻¹. This observation is a clear sign of specific bulk and/or interfacial (structure) transition which has to be investigated in further studies. Microscopic foam films provide additional evidence for the effect of fine-tuning the AA content of the copolymer. All microscopic films are stable which is due predominantly to the overwhelming electrostatic repulsion effects. The obtained results add new knowledge to the structure–property relationships of the PMMA–AA based aqueous formulations. They give valuable hints for further fine-tuning opportunities of these systems, that have high innovative potential for various applications.