Controlled structure and hydrophilic property of polymethylhydrosiloxane thin films attached on silicon support and modified with phosphorylcholine group

Abstract

Thin films of crosslinked polymethylhydrosiloxane (PMHS) are grafted on silica using sol-gel process allowing subsequent coupling of molecules by hydrosilylation grafting to Si–H groups. The aim was to fabricate stable polysiloxane film on solid supports with well-characterized functionalities and surface properties for various applications. The pristine PMHS surface was modified with phosphorylcholine group by reaction at room temperature or 40 °C catalyzed by Karstedt's catalyst with a phospholipid molecule containing linoleoyl chains to form hydrophilic surfaces as a model. The purpose was to characterize precisely the structure and composition of virgin and treated PMHS films in relation with the wetting properties by using IR and X-ray photoelectron spectroscopies (XPS). The surface properties were studied by pure water contact angle measurements in air by using sessile drops and captive bubbles, atomic force microscopy, and scanning electron microscopy. The modified surfaces are highly hydrophilic with a contact angle varying from 40 to 0°. Analysis of the composition of the surface showed that the reaction of linoleoyl chains gives the 2:1 (Si:phospholipid) hydrosilylation adducts resultant from one fold addition of methylhydrosilane on each linoleoyl chain. The graft yield in terms of molecular percentage determined by XPS in various conditions was correlated in good agreement with wetting properties and previous protein adsorption measurements for comparison purpose.