Inhomogeneous Field Method for the Study of Large Polarizable Particles

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Abstract
An inhomogeneous electric field applied to a solution of polarizable particles causes a movement of the particles toward the region of lowest potential energy. The resulting creation of concentration gradient can be observed, for large particles, by a method involving measurement of capacitance change of a cylinder containing a solution of the polymer. This effect has been measured in terms of weight average molecular weight; the system investigated is polystyrene in cyclohexane. The basic Debye theory relating capacitance change at equilibrium to weight average molecular weight has been extended to make it applicable to experimental conditions found to be necessary in work with random coil polymers. The theory is substantiated by the agreement obtained between molecular weight calculated by this method and by the method of light scattering. The polarizability of the particles present determines not only their equilibrium position, but also the rate at which they move. This idea is the basis of a theory presented here relating the time dependence of capacitance change to molecular weight distribution of a given sample. Another theory presented here shows how the shape of the curve for capacitance change as a function of applied field strength is related to the moments of the weight distribution function of the polarizable substance.