Series of liquid separation system made of homogeneous copolymer films with controlled surface wettability

Exquisite surface wettability control of separation system surface is required to achieve separation of liquids with low surface tension difference. Here, we demonstrate a series of surface-energy-controlled homogeneous copolymer films to control the surface wettability of polyester fabric, utilizing a vapor-phase process, termed as initiated chemical vapor deposition (iCVD). The homogeneous copolymer films consist of a hydrophobic polymer, poly(2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane), pV4D4, and a hydrophilic polymer, poly(4-vinylpyridine), p4VP. Because the mixing of two or more components is always favorable in vapor phase, the iCVD process allows the formation of homogeneous copolymers from two immiscible, hydrophilic/hydrophobic monomer pairs, which is highly challenging to achieve in liquid phase. Simply by tuning the flow rate ratio of monomer pairs, a series of homogeneous copolymers with systematically controlled surface energy were formed successfully. The fabricated separation system could separate water (surface energy = 72.8 mJ/m²), glycerol (64 mJ/m²), ethylene glycol (48 mJ/m²), and olive oil (35.1 mJ/m²) sequentially with excellent selectivity, just by choosing a copolymer-coated polyester fabric with proper surface energy. Considering the small differences in the surface tension of the liquids used in this work, the surface-energy-controlled separation system can be a powerful tool to separate various kinds of liquid mixtures.