![]() Consequently, ion viscosity often differs from mechanical viscosity by only a scaling factor and is a useful probe of the cure state of epoxies, polyurethanes, polystyrenes, bulk molding compounds (BMC), sheet molding compounds (SMC) and other thermosets.įigure 1 presents data from the non-isothermal cure of an epoxy. Why? Because r DC is determined by ionic mobility, and the state of a material’s polymer chains or networks affects both ionic mobility and mechanical resistance to flow. Ion viscosity has units of ohm-cm and is defined below: The term ion viscosity ( IV) was coined in the early 1980’s by David Day, also of Micromet Instruments, as a synonym for frequency independent resistivity. Resistivity itself has a frequency independent ( r DC ) component due to the flow of mobile ions and a frequency dependent ( r AC ) component due to the rotation of stationary dipoles. In general resistivity provides the most useful information about cure state, so let’s focus there. Dielectric cure monitoring measures a polymer’s resistivity ( r ) and permittivity ( e ’ ), which are the material’s dielectric properties. Since then I’ve almost exclusively been designing dielectric cure monitors and working with DEA, and the most common question I hear is: “What is ion viscosity?”īefore defining ion viscosity, I have to explain how DEA works. At that time Steve, with myself and several others in his research group at MIT, had recently founded Micromet Instruments to commercialize cure monitoring technology we had developed. ![]() ![]() Stephen Senturia speak about dielectric sensors. In the first post of his series about dielectric cure monitoring (DEA), Jeff Gotro mentioned the “ AHA” moment at a Gordon Conference when he heard Prof. ![]() Guest Post by Huan Lee, Lambient Technologies ![]()
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