Effect of molecular weight and substrate on silicone segregation from UV Resin at plasma polymerized mold interface

Pristine-, poly(octafluorotoluene)- (POFT), and poly-acetylene (PAc)-coated Si wafers were used as substrates for the study of segregation of silicone diacrylate (SA) from a formulation containing other oligomeric and monomeric acrylates. POFT and PAc were microwave plasma polymerized on the Si wafers. Three SAs with molecular weights ranging from 700 to 6000 Da were synthesized and characterized. Formulations with 2 wt % SA were ultraviolet cured on the silicon wafers. The surface composition of formulation-substrate side of the cured film was analyzed with X-ray photoelectron spectroscopy, and the depth profile was analyzed with time of flight-secondary ion mass spectrometry. The analysis results indicated that SA aggregated on all three types of Si surfaces. However, SA segregation is highest on the low surface energy POFT-coated Si substrate, and low-molecular-weight SA is favorable to the segregation. For high-molecular-weight SA, the different Si substrates do not affect the degree of aggregation at the formulation-substrate interface. The observed SA aggregation trend can be predicted by the Gibbs-adsorption equation correlated to the resin surface tension and contact angle on substrates.