Exploring structure-property relationship on a nanoscale for tailoring films of amphiphilic polymer co-networks

Abstract

Amphiphilic polymer co-networks (APCNs) provide a large toolbox for tuning coatings important for applications such as bio-interfaces. Therefore, we investigate the influence of network composition and environmental conditions on the structure and mechanical and adhesive properties of thin films composed of hydrophobic tetra-PCL and hydrophilic tetra-PEG stars of varying sizes. State-of-the-art atomic force microscopy (AFM) techniques, including phase imaging, fast quantitative static indentation and dynamic indentation, provide insights into the structure-property-relationship on various length scales. PEG-rich networks exhibit amorphous morphologies with spherical nanodomains and elastic moduli of a few MPa, while PCL-rich networks form semicrystalline cylindrical arrangements with moduli up to several hundred MPa in water. Temperature-dependent measurements in water revealed a strong hysteresis of elastic moduli while shifting the melting/crystallization transitions or preventing crystallization in PEG-rich networks. All networks displayed predominantly elastic behavior. Co-networks in non-selective solvent conditions are overall softer, less adhesive and structurally more homogeneous. These results establish a predictable correlation of network composition, physical and chemical environment, structure and properties, which makes them suitable for a rational design of amphiphilic systems for various applications.