Study On The Preparation And Performance Of PVDF/ZnS:Mn²⁺Flexible Mechanoluminescence Films

Flexible mechanoluminescence film has the characteristics of high luminous efficiency,a certain linear relationship between luminous intensity and stress,low stress threshold required for luminescence,and repeatable luminescence.There are more and more applications in fields such as robotics,electronic skin,non-destructive testing,stress imaging and information anti-counterfeiting,but there is still a lack of research on the preparation technology and luminescence mechanism of flexible mechanoluminescence films.In this paper,ZnS:Mn2+luminescent matrix was prepared by high-temperature solid-phase sintering method,high β phase content PVDF film substrate was prepared by electric-assisted 3D printing method.On the basis of 3D printing process,the PVDF/ZnS:Mn2+ flexible composite film was prepared by combining ZnS:Mn2+luminescent matrix and PVDF film substrate.In this paper,the effect of Mn2+doped on the luminescence performance of ZnS was studied,the effect of 3D printing process on the content of β phase in PVDF film and the mechanism of the dual piezoelectric effect on the mechanoluminescence performance were discussed.And the conclusions are as follows:(1)ZnS:Mn2+luminescent matrix was prepared by high-temperature solid-phase method.After sintering at 1050℃,the structure of ZnS changes from cubic structure to non-centrosymmetric hexagonal structure.The ultraviolet absorption edge of ZnS is blue-shifted,and there is no obvious absorption peak in the visible light region.The doping of Mn2+makes the ultraviolet absorption edge of ZnS continue to blue-shift and an absorption peak appears in the visible light region.When the luminescent particles are excited with a light source of 320 nm,the cubic ZnS does not emit light,the hexagonal ZnS emits green light,and the hexagonal ZnS doped with Mn2+emits orange light;With the increase of Mn2+,the maximum luminescence intensity of ZnS:Mn2+gradually increases,but when the doping concentration of Mn2+exceeds 4 mol%,the luminescence intensity decreases.(2)PVDF flexible substrate was prepared by electric-assisted 3D printing method.When the mass fraction of PVDF is 16%,the relative β-phase content(F(β))in the film is up to about 74%;CaCl2 can reduce the non-uniform nucleation barrier as nucleation interface,and CaCl2 exists in the solution with ions form,which can improve the conductivity of the solution,making it easier for transformation ofα-phase to β-phase,at the same time it promotes the crystallization of the PVDF flexible film and improves the content of β-phase.When the content of CaCl2 is 0.2 wt%，the F(β)of PVDF/CaCl2 composite films is up to 83.83%.(3)In the electric-assisted 3D printing PVDF/ZnS:Mn2+composite luminescent films process,the addition of ZnS:Mn2+particles can not only provide nucleation sites,reduce nucleation barriers,and promote non-uniform nucleation,but also the formation of S-H hydrogen bonds causes the molecular chain of PVDF to twist,promotes the formation of β phase in the film,and increases the content of piezoelectric phase.The PVDF film with high β-phase provides an external piezoelectric field as a substrate,under the action of internal and external double piezoelectric fields,the bending degree of the ZnS band increases and the trap depth decreases.Under the same stress,the mechanoluminescence intensity of PVDF/ZnS:Mn2+composite film is higher.