Self-assembly of a patterned hydrophobic-hydrophilic surface by soft segment microphase separation in a segmented polyurethane: Combined experimental study and molecular dynamics simulation

Abstract

Designing surfaces with patterns of varying wettability is of significant importance for many applications. This fascinating feature is inspired from nature where it is absolutely vital for survival of some living creatures. This research shows that an inherent incompatibility between different soft segments of segmented polyurethanes can play a pivotal role in designing such surfaces. We employed coarse-grained molecular dynamics (CG MD) simulations as well as experimental techniques to illustrate the microphase separation between soft segments with significantly different wettability. We started with poly(hexamethylene carbonate) polyurethane and partially replaced the polycarbonate diol (PC), the hydrophobic soft segment, with poly (ethylene glycol) (PEG), the superhydrophilic soft segment. Our simulation shows that a clear microphase separation between PC and PEG exists. This led to a core-shell structure in which the hard segments are squeezed between two incompatible soft segments. Experimental analyses, e.g., Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) merely confirmed the soft segment phase separation. Our combined simulation and experimental analyses showed that there is a concurrent phase mixing of hard/soft segments with phase separation between soft segments. Moreover, the CG MD simulations elucidated the evolution of microphase organization as the polymerization proceeds and our further analysis shed light on the microarchitecture of the individual PU chains.