Surface evaluation of reactive plasma-modified microporous polypropylene membrane by static contact angle analysis

The surface modification of micro-porous polypropylene membrane is achieved by low-pressure reactive plasma treatments using Ar and He gases. The reactive plasma modified microporous polypropylene membranes which are used as the battery separators were evaluated by the electrochemical performance and static contact angle analysis. It is found that the plasma modified polypropylene separators obtain the superior property for Lithium-ion battery and the variations in surface wettability and surface free energy were examined by static contact angle measurement. The static water contact angle of the plasma-modified polypropylene membrane separator significantly decreased with rising plasma power input at both glow region and remote region in the reactive plasmas. An obvious increase in the surface energy of microporous polypropylenes because of low molecular weight oxidized materials from Ar and He plasma treatment was observed in the rinsing process by static contact angle analysis. The experimental results show the vital part of low molecular weight oxidized materials in the interaction between reactive plasma and polypropylene membrane, which can be controlled by the surface modification to tailor the hydrophilicity of micro-porous polypropylene membrane.