Study On Phase-Separation Behavior Of Poly(n-methyl Methacrylimide)/Poly(Vinylidene Fluoride) Blends

In this dissertation,a novel amorphous/crystalline polymer blend,poly(n-methyl methacrylimide)/poly(vinylidene fluoride)(PMMI/PVDF)blend was selected as model system.The liquid-liquid phase-separation(LLPS)behavior of PMMI/PVDF blend was studied by using small angle laser light scattering(SALLS).Meanwhile,the viscoelastic behavior of PMMI/PVDF(50/50 wt)blend was investigated based on dynamic rheological measurements.The LLPS behavior of PMMI/PVDF blend was studied by using SALLS during heating process.Dependence of cloud points on heating rate for PMMI/PVDF blends was detected. The cloud point(T_c)curve of PMMI/PVDF blend was obtained at the heating rate of 1^oC·min^-1and it was found that PMMI/PVDF exhibits a typical low critical solution temperature(LCST)behavior.Furthermore,T_c of different composition samples is far above their T_m.In that case,the phase separation and the crystallization behaviors may occur in different temperature regimes so that a separate control of these two processes can be expected.It offers a favorable model to study this kind of polymer blends.Based on the nonlinear phase-separation behavior during heating process,the phase behaviors for the above mentioned blends were studied during isothermal annealing by using SALLS method.It is found that their thermal-induced phase-separation behavior follow spinodal decomposition(SD)mechanism within the temperature region investigated.The temperature dependence of phase-separation kinetics for PMMI/PVDF blend follows the principle of time-temperature superposition(TTS)at the early phase-separation stage and may be described with a WLF-like equation.The apparent diffusion coefficient(D_app)and the product(2Mk)of the molecules mobility coefficient(M)and the energy gradient coefficient(k) arising from contributions of composition gradient to the energy for PMMI/PVDF blend were calculated on the basis of Cahn-Hilliard theory.Both D_appand 2Mk increase with the increase of temperature nonlinearly,indicating that it is impossible to gain the equilibrium SD temperature of this blend through extrapolating plot of D_appand 2Mk against temperature.It is proposed that the morphology evolution of PMMI/PVDF blend follows the characteristic of SD during isothermal annealing using phase contrast microscopy(PCM)measurement.Small amplitude oscillatory shear rheology was employed to investigate the viscoelastic behavior of PMMI/PVDF(50/50 wt)blend.The range of linear viscoelastic behavior is relatively wide.The binodal temperatures(T_b)of this blend detected by advanced rheometric expansion system(ARES)decrease with the decrease of heating rate nonlinearly.Times for approaching the terminal of phase-separation decrease with the increase of the temperature during isothermal annealing.Complex behavior of PMMI/PVDF(50/50 wt)blend was detected through the investigation on the relationship between G',G",tanδandω,as well as "Cole-Cole" curve.Further works need to be done to describe these properties during this kind of process.A two-phase structure with the bio-continuous characteristic was observed by scanning electron microscope(SEM)when phase-separation occurs.