Fundamental Study on Morphology Control of Polymer Alloys in an Electric Field.

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A droplet suspended in a dielectric medium deforms into an ellipsoid under a relatively low electric field but bursts under a high electric field. This phenomenon suggests a possibility that morphology of polymer alloys especially that of polymer blends could be controlled with an electric field. In this study deformation of viscoelastic droplets in an electric field of was studied for droplets of aqueous solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) and those of aqueous poly(acrylamide) (PAA) suspended in media of poly(dimethyl siloxane) (PDMS). Under an AC field of calpha. 10^5 Vm^<-1>, the droplet deformed into an ellipsoid with a degree of deformation D defined by (X-Y)/(X+Y) where X and Y are the major and minor semiaxes of the ellipsoid, respectively. The D versus logarithm of time curve was double-step sigmoidal and was characterized with two retardation times. The deformation in the short time region was attributed to an elastic deformation due … More to a balance between the electric stress and the elasticity of the droplet. With increasing elapsed time, stress relaxation occurs in the droplet and hence the drop deforms further until it reaches an equilibrium deformation given by a balance between the electric stress and the interfacial tension. Theoretically, the magnitude of deformation D_F and the retardation time tau_F for the fast process are calculated theoretically as follows:D_FF = (9epsilon_oK_2E^2/16)(gamma/b + 5G/4)^<-1> (1) tau_F tau_F = eta_2/(G + b/gamma) (2) where epsilon_O is absolute dielectric constant of vacuum; K_2, the relative dielectric constant of the medium; E, the electric field; G, the quasi- -equilibrium shear modulus; gamma, the interfacial free energy; b, the radius b of the droplet; and eta_2, the viscosity of the medium. The observed D_F and tau_F agreed approximately with equations (1) and (2). The behavior of the slow process were also explained approximately by the theory of a viscous droplet reported previously. However, the equilibrium deformation was 1.4 times larger than the theoretical value. The time dependence of D was modeled by a mechanical model composed of parallel combination of a Maxwell element and a Voigt element. Less