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

Designing surfaces with patterns of varying wettability is of significant importance for many applications. This fascinating feature is inspired by nature where it is vital for the 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 experimental techniques as well as coarse-grained molecular dynamics (CG MD) simulations 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. Experimental analyses indicated a phase separation between PEG and PC, as soft segments, and our simulations merely confirmed it. This led to a core-shell morphology in which the hard segments are squeezed between two incompatible soft segments. Our combined simulation and experimental analyses proved 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.