One-component room temperature vulcanizing-type silicone rubber-based sodium-selective membrane electrodes

Two different types of one-component room temperature vulcanizing (RTV) silicone rubber (Dow Corning 3140 and 730 RTV) are examined as alternatives to PVC for formulating ion-selective membranes. Ion-selective membranes are made by incorporating five different sodium ionophores along with either a plasticizer or an ionic additive (without plasticizer). In most cases, these silicone rubber based membranes exhibit better potentiometric ion response and selectivities when formulated with plasticizer rather than with ionic additive. Incorporating high levels of plasticizer does not appreciably affect the adhesion of 3140 RTV-based membranes, but it significantly deteriorates the adhesion of 730 RTV-based membranes. Membranes based upon 730 RTV have lower impedances than those based upon 3140 RTV, and in fact compare favorably to similarly formulated PVC-based membranes in this regard; as a result, they are better suited for plasticizer-free membrane systems. The use of membranes based upon either of the RTV materials rather than their PVC-based counterparts greatly enhances the lifetime of solid-state sensors.