SSP's thin film products can be broken down into two areas, true membranes and thin films. Membranes are used to separate, enrich, or deplete gas mixtures and are typically under .005" thick. Thin films are considered anything under .025" in thickness and are used for gasketing, sealing, flapper valves and many other applications.
Membrane Separation
Dimethyl silicone possesses the unique ability to allow various gases to permeate rapidly through it. This phenomenon is due primarily to the flexible silicone-oxygen-silicone linking sites of the silicone chain and an abscence of crystallinity in silicone rubber. Technically speaking, the process of permeation through a non-porous membrane is actually a three stage activity. Whereas a porous material uses size exclusion as its method of separation, the process by which a non-porous membrane allows a separation to occur is a much more complex means to an end. These steps are: sorption in, diffusion through, and desorption from the membrane by the permeating gas. The rate of permeation is the product of diffusivity and solubility coefficients of the permeating gas. The solubility coefficients for gases into dimethyl silicone are comparable to those of most polymers but the diffusion rates through the silicone are nearly an order of magnitude greater than any other membrane polymers. Therefore dimethyl silicone owes its rapid transport of gases to the high rate of diffusion and not solubility. Another key to a successful separation is the selectivity of the membrane. Selectivity is the ratio at which one gas permeates versus the rate at which another gas permeates through the membrane. This factor is what ultimately determines the efficiency of a particular separation. Obviously a membrane that permeates oxygen and nitrogen at the same rate would be worthless for the generation of oxygen rich or oxygen depleted air. Therefore a high selectivity ratio of the component gases in the feed stream would result in an efficient separation.
More variables: Although the driving force behind gas transfer through a membrane is pressure, it does not actually effect permeability. Furthermore membrane thickness and temperature variables have very little effect on permeability. Flux, on the other hand, is effected by pressure differentials and membrane thickness. A high pressure differential and a very thin membrane will result in significant increases in flow rate of the permeate gas component.
Thin Films
SSP's calendaring capabilities allow for a multitude of thin film silicone products. We can produce custom formulations for your specific applications. Whether your needs are high temperature, low temperature, fuel & oil resistant, thermally or electrically conductive, SSP can produce thin films to your exacting requirements. SSP manufactures composite laminations such as silicone/PTFE, silicone/aluminum, silicone/stainless and many others. SSP's capabilties extend to complex die cutting of gaskets, valves and many other parts.
