Controlling Surface Wettability of Nanoporous Block Copolymer Membranes by Plasma Treatment

Muhammed Oruc, Department of Chemical Engineering, Yildiz Technical University, Esenler, Turkey
Paul Nealey, The Institute For Molecular Engineering, University Of Chicago, Chicago, United States Of America



Thin film block copolymer (BCP) membranes are a promising candidate for the applications from molecular sieving to water filtration due to their desired features: well-ordered nanopores with narrow size distribution, high porosity, and tunable chemical and physical properties. The separation of small molecules based on size and electrostatic interactions are well studied. Besides, it is necessary that membranes can perform separations based on hydrophobicity in order to expand the use of this technology to a wider range of applications. Modifying the chemistry during membrane preparation or self-assembly monolayer formation on metal/oxide deposited membrane surfaces allows to provide hydrophobic or hydrophilic membranes. It is, however, highly desirable to control the wettability of membranes through a wider range. To this end, we have showed that the hydrophobicity of BCP membrane can be controlled by plasma treatment with O2 and CF4 gases. In this work, we prepared nanoporous membrane with polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) BCP via thermal annealing. After etching the PMMA domain, we performed O2 and CF4 plasma treatment on PS nanoporous membrane with the pore size ~30nm. We studied the effect of the parameters of plasma power, gas flow rate and treatment time on wettability. We observed that the hydrophobic recovery leads to change in contact angle upon aging in air at room temperature. This approach enables us to control the contact angle of PS membrane between 30 and 120 by adjusting the plasma treatment parameters.