Water-enhanced Adhesion at Interface in Immiscible Bilayer Film of Polystyrene and Poly(methyl methacrylate)

Abstract

Abstract. From nano-scratch tests, strong interfacial adhesion has been found for polystyrene (PS) and poly(methyl methacrylate) (PMMA) bilayer films prepared by a water floating (WF) method, while a PS layer on a PMMA film produced by a spin coating (SC) method peels off easily at the interface. Neutron reflectivity measurements demonstrated a clear difference in the interfacial width (σ) between the two bilayers; σ = 9 nm for the film obtained by the WF method, whereas σ = 5 nm for that by the SC method. Plasticization of the films by water would be responsible for broadening of the interface to enhance adhesion strength. IntroductionControl of interfacial toughness between two kinds of polymers is one of the most important targets in research and development of coatings and blends. To understand the mechanical properties of the interfaces between polymers, the interfacial structure was investigated and the correlation between the width of the interfaces and the energy of adhesion was clarified for polymer bilayers [1,2]. The origin of the interfacial strength was interpreted with an entanglement model of polymer chains that the interface energy is governed by the number density of the entanglement points per the interface area [3]. Therefore, the adhesion strength between polymer films increases by thickening of the mixed layer at the interface, and above a critical thickness cohesive failure could occur in the films.The interfacial thickness of immiscible polymers for annealed bilayers are dominated by the Flory-Huggins interaction parameter and the Kuhn segment length. However, most of interfaces between polymers in practice are far from equilibrium. Here, we focus on the effect of coating process, where some small molecules mediate the formation of the interface. Bilayer films consisting of polystyrene (PS) and poly(methyl methacrylate) (PMMA) are employed, since the interface between PS and PMMA is well understood system in equilibrium [4].For investigation of the interfacial width between immisible polymers, neutron reflectivity (NR) measurements have been a powerful tool. However, the samples must be thin films on very flat substrates. Although the energy of adhesion has been studied macroscopically by various experimental techniques, the mechanical properties for thin films can be analyzed by nano-scratch (NS) tests. By combining the NR measurements and the NS tests, structure and strength of interfaces are evaluated for the same bilayer films.

Nanomechanical and nanoscratch performance of polystyrene/poly(methyl methacrylate)/multi‐walled carbon nanotubes nanocomposite coating

“…Among them are Lorenzoni et al who studied the nanomechanical properties of solvent cast polymer thin polystyrene (PS) and poly(methyl methacrylate) (PMMA) blends and PS‐ b ‐PMMA block copolymers. Using the nanoscratching procedure Harada et al found a strong interfacial adhesion for PS and PMMA bilayer films prepared using water floating technique, while a PS layer on a PMMA film was produced via spin coating method which peels of easily at the interface . The nanomechanical properties of PS‐ b ‐PMMA copolymers combined with reduced graphene oxide sheets (RGO) were analyzed using Berkovich nanoindentation .…”