Study On Self-Nucleation Crystallization Behavior Of Poly(3-Hexylthiophene) Ultrathin Film

The chain rigidity and strong π-π interaction determine that conjugated polymers can form crystalline structures of different scales.It has become a consensus that the photoelectric properties of devices can be controlled by changing the aggregation structure of conjugated polymers.Polymer crystallization follows a typical nucleationgrowth process.The size of primary nuclei is close to the thickness of the film and the molecular chain is difficult to diffuse,resulting in difficulty of homogeneous nucleation in the polymer ultrathin film.Due to the high lattice matching degree,the selfnucleation has high nucleation efficiency.The density and distribution of selfnucleation in polymer films mainly to depend on the competition between lamellar melting and recrystallization under the influence of initial crystalline structure and space limitation and interface effect.In this paper,the crystallization morphology of poly(3-hexylthiophene)(P3HT)thin films was characterized by atomic force microscopy(AFM).The effects of partial melting temperature,partial melting time,film thickness and initial crystal structure on self-nucleation were studied.This study not only provides a new method of studying the melting and crystallization behavior of conjugated polymers,but also provides a new idea about the aggregation state and performance regulation of conjugated polymers.The main conclusions are as follows:1.The morphology and structure of P3 HT crystal were characterized by AFM and grazing incidence wide-angle X-ray(GIWAXS).The effects of film thickness,crystallization temperature and crystallization time on the crystal morphology of P3 HT were studied.The results showed that nanocrystals existed in the P3 HT initial film obtained by spin-coating,and the number and size of nanocrystals increased with the increase of film thickness.The amorphous molecule and fine crystals on the crystal surface can be removed by selective dissolution to study the crystal morphology of isothermal crystallization;the height of P3 HT fiber crystals increases with the increase of film thickness;for P3 HT films with the same thickness,the height of fiber crystals increases;at the same crystallization temperature,with the extension of crystallization time,the fiber crystal branching density increases.2.The effects of different partial melting temperature,partial melting time,melting heating rate,film thickness and initial crystal structure on the self-nucleation and crystallization of P3 HT in ultrathin films were studied by AFM.The results show that during the heating process,the initial and crystalline films of P3 HT undergo melting and recrystallization,and both the initial crystalline structure and the recrystallization process have significant effects on the self-nucleation density.With the increase of partial melting temperature,the nucleation density of P3 HT decreases exponentially;under different holding time(20 s～60 min),the nucleation density of P3 HT crystals is basically unchanged;with the increase of heating rate,the melting recrystallization becomes difficult,and the nucleation density decreases.The more imperfect the initial crystalline structure of P3 HT,the lower the onset temperature of melt recrystallization and the higher the self-nucleation density.