Abstract

Thin polymer films based on polymer blends can be used as coatings with tunable properties. Such films can be created with the Langmuir film method: polymers are deposited on water controlling their density by compression, potentially cross-linked to obtain networks, and subsequently transferred onto a solid substrate resulting in stable thin films. As a first step to design such films, the miscibility properties of non-cross-linked polymer blends must be understood. In this work, we focus on understanding the miscibility properties of amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer and predominantly hydrophobic poly(dimethylsiloxane) (PDMS). We analyzed surface pressure-area isotherms to determine the phase transitions of the blends and used Brewster angle microscopy (BAM) to understand the mixing behavior at the interface. We combined these results to build a surface pressure-composition phase diagram and identified a miscibility region independent of composition at low surface pressure. To connect the phase diagram with molecular level information, sum frequency generation (SFG) spectroscopy has been performed. With this method basically the vibrational spectrum of the interface can be obtained. From peak amplitudes in the CH-OH and CO spectral region, we conclude that polymers change their orientation after the phase transition. To make a stable network, as a second step towards coatings, light induced cross linking of the end groups of the PDMS in the miscibility region on the water surface has successfully been conducted.