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

悬浮在介质中的液滴在相对较低的电场下会变形为椭球体，但在较高电场下会发生爆炸。这一现象表明，聚合物合金的形态，特别是聚合物共混物的形态可以通过电场来控制。本文研究了十六烷基三甲基溴化铵(CTAB)和水杨酸钠水溶液以及悬浮在聚二甲基硅氧烷(PDMS)介质中的聚丙烯酰胺(PAA)水溶液在电场作用下粘弹性液滴的变形。在交流电磁场的作用下。10^5Vm；-1；gt；，液滴变形成椭球体，变形程度D由(X-Y)/(X+Y)定义，其中X和Y分别是椭球体的长半轴和次半轴。时间曲线的D-对数呈双阶梯S型曲线，表现为两次延迟。短时区域的变形归因于…引起的弹性变形更多的是在电应力和液滴弹性之间取得平衡。随着时间的延长，液滴中会发生应力松弛，因此液滴会进一步变形，直到达到由电应力和界面张力之间的平衡所给出的平衡变形。从理论上计算了快过程的变形量D_F和延迟时间T_u_F：D_ff=(9epsilon_OK_2e^2/16)(Gamma/b+5G/4)^&lt；-1&gt；(1)T_F T_f=Eta_2/(G+b/Gamma)(2)式中，epsilon_O是真空的绝对介电常数，K_2是介质的相对介电常数，E是电场，G是准平衡剪切模数，伽马是界面自由能；B是液滴的半径b，而eta_2是介质的粘度。观测到的D_F和T_F与方程式(1)和(2)基本一致。慢过程的行为也可以用以前报道的粘性液滴理论来近似解释。但平衡变形量是理论值的1.4倍。D的时间依赖性由Maxwell单元和Voigt单元的平行组合组成的力学模型来模拟。较少

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