Effect Of Interfacial Interaction On Phase Structure And Piezoelectric Properties Of Polyvinylidene Fluoride

Poly（vinylidene fluoride）（PVDF）is a flexible piezoelectric polymer,which can be used for sensors,transducers,electronic skin and non-volatile memory,etc.PVDF is a semi-crystalline polymer,whose crystalline region has a variety of phase states.Only the PVDF with polar phase own piezoelectric properties.In order to produce PVDF containing polar phase,complex processes such as stretching and polarization are used.Although these methods can produce PVDF films with polar phase,there are many disadvantages such as high cost and cumbersome operation.Therefore,how to prepare PVDF piezoelectric membrane with high polar phase content through a simple process and how to improve piezoelectric properties are still the problems that need to be solved.In this thesis,the intermolecular interactions between chitosan and cellulose nanocrystals（CNC）and PVDF induced the latter to produce polar phase.At the same time,the interface coupling effect between PVDF and CNC was investigated in order to further improve the piezoelectric performance.The experiment is divided into the following two aspects:（1）The free-standing chitosan and CNC films and PVDF films are tightly pressed together by hot pressing method.The intermolecular force at the interface is used to produce polar phase（polar phase content>93%）from PVDF without polar phase.The piezoelectric charge coefficient(d₃₃)is-30 p C/N.（2）The solution method was used to disperse CNC in PVDF and intermolecular force was used to induce PVDF to produce polar phase.When CNC accounted for 10wt%in the composite film,the content of polar phase reached 99%.The interface coupling between CNC and PVDF further improved the piezoelectric properties of the composite material.The d₃₃≈-26.4 C/N when the content of CNC is 10 wt%.The effects of interface coupling are proved by PFM test.The effects of interface coupling on piezoelectric properties were further revealed from this paper.These findings will provide new ideas for the preparation of polymer flexible sensors.