Crystallite Evolution Behavior Of Vinylidene Fluoride-chlorotrifluoroethylene Random Copolymer Under The Action Of Temperature

The coating and bonding effect of polymer binders on explosives is one of the main factors affecting the performance of polymer viscous explosives.Under the action of temperature,the microstructure will change and the macroscopic aggregation state will change.Vinylidene fluoride-chlorotrifluoroethylene random copolymer is a commonly used polymer explosive binder,and its microscopic crystalline evolution behavior has not been systematically studied.In this paper,a manual scraping method and a solution casting method were used to prepare poly(vinylidene fluoride-chlorotrifluoroethylene)(P(VDF-CTFE))(VDF:CTFE=1:4)random copolymer ultra-thin film and micron level Thick film,with temperature change as the main variable,the ultra-thin film thickness and isothermal crystallization time are controlled to process the ultra-thin film,and the use of atomic force microscope(AFM),atomic force microscope infrared on-line(AFM-IR),Fourier infrared spectroscopy(FTIR)),X-ray diffraction(XRD),grazing incidence X-ray diffraction(GIXRD),differential scanning calorimeter(DSC)and other characterization methods explored the crystallite evolution behavior of P(VDF-CTFE)ultra-thin film after isothermal crystallization treatment.The crystalline state and nanostructure distribution of P(VDF-CTFE)ultra-thin films are analyzed,as well as the crystallite evolution of different nucleation processes at different isothermal crystallization temperatures and at the same temperature.And the reasons for the evolutionary behavior are discussed.The experimental results show that 135?is higher than the equilibrium melting point Tm0 of P(VDF-CTFE)ultra-thin film,and this temperature can be used to prepare amorphous samples.The GIXRD experiment of the 30 nm thickness crystalline sample found that obvious crystal diffraction peaks appeared at?=16.1°,16.5°and 17.1°,corresponding to the(101),(102),(103)crystal planes of the PCTFE crystal,respectively.AFM-IR single-point experimental results show that the infrared absorption signal of the characteristic peak of VDF(methylene combined frequency)on the P(VDF-CTFE)ultra-thin film crystalline crystal is weaker,while the infrared absorption signal of the amorphous region is stronger.It shows that the crystalline component is the CTFE component,and chemical imaging at the peak position of the C-F bond at 962 cm^-1 further confirms this result.Under the induction of temperature,the crystalline composition of P(VDF-CTFE)ultra-thin film is CTFE segment.As the temperature increases,the crystal density decreases,but its single crystal grows faster.At room temperature,the thin film formed by volatilization from the solution can generate numerous crystal nuclei and fine worm-like crystals.The surface is dominated by homogeneous nucleation at 50,65,and 80?,forming edge-on oriented crystals and flat-on oriented crystals.The lower the temperature,the greater the probability of edge-on distortion,and the greater the probability of flat-on wafers.The crystal density increases with the increase in thickness,and flat-on orientation lamellae appear when the thickness of the ultra-thin film increases to 60 nm at 80?.Under the condition of 120?,numerous crystal nuclei,worm-like crystals and flaky crystals are formed on the surface.The lamella crystals are formed by preferential heterogeneous nucleation,and the nuclei and worm-like crystals are formed by subsequent homogeneous nucleation.In the multiple isothermal crystallization,the first crystal growth is more perfect.With the increase of the number of isothermal crystallization,the crystal density increases,but the crystal growth state becomes slower.At the same time,the increase in density increases the probability of the appearance of twisted edge-on lamellae.The self-seeding experiment of P(VDF-CTFE)ultra-thin film shows that the surface morphology of heterogeneous nucleation is obviously different from that of homogeneous nucleation,and the thickness of 30 nm is close to the size of the gyration radius of crystallizable P(VDF-CTFE)molecular chain,The crystallization is dominated by diffusion limited agglomeration(DLA).