Template-Assitant Fabrication Of Piezoelectric Nylon 1111 Nanofibers

Piezoelectric materials have received a lot of attention due to their ability to convert mechanical energy into electrical energy.Piezoelectric polymer materials have special flexibility and lightness,and show stronger electrical properties in the nano dimension.Therefore,the study and application of piezoelectric polymer nanomaterials can help solve the energy supply problem of electronic devices,which is of great importance in fields such as artificial intelligence and wearable devices.Nylon 1111（PA1111）,as a representative product of long carbon chain odd-odd numbered nylon,has the potential to prepare piezoelectric nanodevices due to its high dipole density,hydrogen bonding of amide groups and good biocompatibility,which makes it excellent in piezoelectric ferroelectricity,high temperature stability and excellent mechanical properties.In this thesis,PA1111 piezoelectric nanofibers were prepared by porous anodic aluminum oxide templates,as well as characterized the crystalline state,crystallization behavior within the nanopore channel and piezoelectric properties of the nanofibers.Finally,we assembled them into nanodevices and analyzed the factors affecting the output performance.The main conclusions were obtained as follows:（1）Using the template solution method,PA1111 nanofibers with high aspect ratios of 40 nm and 200 nm in diameter were successfully prepared.Only when the concentration of the solution exceeds 10 wt%,homogeneous and complete nanofibers are obtained in morphology.After investigating the effects of solution concentration and template pore size on the crystallinity of nanofibers,it was found that both solvent quenching and template limiting effects favored the generation of theγ-phase of nanofibers with a percentage around 37%,which was doubled compared to the solution cast film.The percentage of sub-stableγ-phase of 40 nm fibers increased from 37%to 39%,though the crystallinity decreased.The polymer molecular chain axis within the template is perpendicular to the growth direction of the nanofibers,creating preferred chain orientation and crystal orientation in the template.There exists the piezoelectric response of PA1111 nanofibers prepared by the template method.The higher the crystallinity andγ-phase ratio of PA1111 piezoelectric nanofibers,the larger the value of the piezoelectric constant d₃₃,with a maximum value of 1.16 p C/N.The phase diagram of the piezoelectric microscope demonstrates that the polarization direction of PA1111 piezoelectric nanofibers is parallel to the nanopore axis and has a"self-polarization"property.Nanofiber-based piezoelectric nanogenerator（PENG）output performance is proportional to the magnitude of d₃₃value,with the highest open-circuit voltage(V_oc)value of 3.4 V for the PENG assembled from the most crystalline nanofibers.In addition,the“self-polarized”PA1111 piezoelectric nanofibers,which maintain a macroscopic orientation within the template,prepared tribological devices with a V_ocvalue four times higher than that of the randomly arranged nanofibers.（2）Nanofibers prepared using the melt-press template-wetting method also tend to generate sub-stableγ-crystalline forms,the slow annealing by melt cooling increases the crystallinity of nanofibers from 16%to 21%and the microcrystalline size increases.However,the lack of solvent quenching effect reduced the percentage ofγ-phase by about 10%,and the combined effect of the piezoelectric constants d₃₃of the nanofibers did not differ much from the solution method.The non-isothermal crystallization process of PA1111 melt proper and inside the nanopore channel was fitted experimentally,and the parameters showed that the melt had a stronger crystallization nucleation ability and higher crystallization growth rate inside the nanopore channel,with heterogeneous nucleation and rapid crystallization.However,the crystals collide within the nano-space right after the rapid growth and it is difficult to continue to refine the growth.This leads to the easy generation of sub-stable crystalline forms but reduced crystallinity of the crystals within the nanopore channel compared to the native,which in turn clarifies the effect of the template limiting effect on the crystallization of nanofibers.This thesis explores the application of PA1111 in the field of nano self-generation,which not only greatly expands the application space of piezoelectric odd-odd numbered nylon materials,but also accumulates experience for the research and application of piezoelectricity of other kinds of nylon materials.