Pressure Dependence of Polymer Surface Tension under Vacuum for Block Copolymer Nanopatterning.*

Herein, this work aims to examine the pressure dependence on the surface tension for various polymer melts under high vacuum. With the increase of vacuum degree, the surface tension of polymer melts decreases; in contrast to the effect of temperature, the pressure effect on surface tension is much more significant under low pressure. Most interestingly, a linear log relationship between surface tension and pressure can be found for various polymer systems, in line with theoretical prediction. Note that the surface tension of polymer melt is one of the crucial parameters in the orientation control of block copolymers (BCP) thin films for nanopatterning. Usually, an additional effect to create a neutral surface for BCP with a large discrepancy between constituent blocks, such as polystyrene-b-polydimethylsiloxane (PS-b-PDMS), is required to achieve the formation of perpendicular orientation of nanostructured monolith. By taking advantage of the large dependence of surface tension on pressure under vacuum, it is possible to give the aimed perpendicular orientation by simply reducing the pressure for thermal annealing due to the equivalent surface tension for the constituent blocks at specific low-pressure conditions.