I tried to prepare aligned PLLA nanofibers by gap electrospinning method. But after the deposition, when I tried to measure its piezoelectric sensitivity, it actually did not exhibit any piezoelectricity. In comparison, when I prepared random PLLA nanofiber by electrospinning, it can exhibit piezoelectricity. And also, in some papers using PVDF, they can get piezoelectric PVDF nanofiber by gap electrospinning. One relevant paper is DOI 10.1088/1361-6528/aa7f6b.

Does anyone know why? How can I improve the piezoresponse of aligned PLLA nanofibers?