Facile physical modification of ultrathin polyethylene by trace poly(vinyl alcohol)

Poly (vinyl alcohol) (PVA) modification to nonpolar polymers has been intensively investigated due to the performance improvement in membrane separation, tissue engineering, and other applications. Slightly deviated from the conventional route, no covalent bonding by crosslinking or hydrogen bonding is needed to anchor PVA onto the target matrix. This work harnessed van der Waals interaction only to achieve the modification. Owing to the high surface energy and aspect ratio of ultra-high molecular weight polyethylene (UHMWPE) ultrathin membranes, the physical binding between PVA and PE was found stable and easy to establish. This interaction is initiated by the entropy-driven hydrophobic effect at the liquid-solid interface to reduce surface energy. By encapsulation of PVA on the fibrils, the PE hydrophilicity could be overturned (from 134.6° to 48.4°) with micro-structures remaining almost intact at the low loading of modification (0.001% conc. solution dip-coating). The resultant hydrophilic ultrathin PVA-PE membranes showed high transparency, high mechanical strength (380 MPa in tensile max. stress), and high porosity with only 200 nm thickness in a freestanding state. This work provides a facile approach to switch the hydrophilicity of nonpolar polymer ultrathin membranes by establishing vdW physical bonding only. By trace-adsorption, this method could also be helpful in fine-tuning nanostructures of the target polymer matrix by a resolution of nanometer level.