무정형 고분자 재료의 비선형 유전특성

초록

Linear and nonlinear complex permittivities have been measured for amorphous copolymers of vinylidene cyanide (VDCN) with ninyl acetate (VAc), vinyl propionate (VPr), vinyl benzoate (VBz), styrene (St) and methyl methacrylate (MMA). It is found that the third order permittivity ε3 depends upon frequency according to a function Δε3/(1+iωτ3)3 while the linear permittivity obeys a Debye function Δε1/(1+iωτ1). Experimental results are well fitted by the above predicted functions except at low frequencies where dc conduction dominates. The τ1 and τ3 are nearlu equal, and depend upon temperature according to a WLF form. The relaxation strength Δε1 depends upon comonomers ranging from 130ε0(VAc) to 20ε0(MMA). the Δε3 is negative and depends more strongly upon comonomers. combined knowledge about linear and nonlinear permittivities predicts very large correlation factors which indicates strongly cooperative dipolar motions in those amorphous copolymers.