Surface Science of a Filled Polydimethylsiloxane-Based Alkoxysilane-Cured Elastomer: RTV11.

Characterization of a filled polydimethylsiloxane (PDMS)-based elastomer, RTV11, is reported. Included in this work is resin characterization, kinetics of cure as a function of catalyst concentration, and surface properties of pristine and water-aged films. X-ray spectroscopy for chemical analysis (ESCA), dynamic contact angle (DCA) analysis, and ATR-IR were used to characterize cured films. ESCA reveals C and Si peaks in ratios expected for PDMS, but CaCO3 which comprises 32% of the bulk is not detected. The surface of cured RTV11 films is thus predominantly a PDMS network crosslinked by a siliceous domain, the latter comprising about 1.3% by weight. The presence of Ca was confirmed by energy dispersive X-ray analysis (EDX) which probes at micron depth. Stability of films in water was evaluated by tapping mode atomic force microscopy (TM-AFM), mass loss, changes in contact angles, ESCA, and optical microscopy. TM-AFM images of films aged in water for three months show an increase in surface roughness due to the formation of micro-pits which occupy about 4% of the surface. Gravimetric analysis showed fully cured films lose mass at a rate of about 0.09%/wk over a three month period in water. The mass loss associated with pitting/surface roughening comprises only 0.85% of that measured gravimetrically and by analysis of immersion water. Analysis of Si and Ca in the storage water was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) in order to quantify the products of surface erosion. An unexpected finding was the surface depletion-limited loss of CaCO3 during the first two months of immersion. The results of surface analytical studies are discussed in the context of the use of alkoxysilane cured PDMS resins for nontoxic fouling release applications. Copyright 1999 Academic Press.