水滴模板法制备聚乳酸微纳米纤维薄膜

Preparation of Poly(Lactic Acid) Nanofiber Film by Breath Figures Method

目的采用水滴模板法制备聚左旋乳酸(PLLA)微纳米纤维薄膜,研究聚合物溶液浓度和环境湿度(相对湿度)对微纳米纤维形貌和直径的影响。方法在不同质量浓度(10、25、50mg/mL)的PLLA/四氢呋喃(THF)溶液和不同环境湿度(40%、50%、60%、70%)条件下,通过水滴模板法制备PLLA微纳米纤维薄膜。采用扫描电子显微镜(SEM)对薄膜的表面形貌进行观察,用Image J软件对电镜照片中的微纳米纤维进行直径测量,计算平均直径,并统计直径分布。由纤维的平均直径计算薄膜表面积与体积之比。用密度法计算薄膜的孔隙率。结果水滴模板法制备的PLLA微纳米纤维薄膜具有光滑连续的三维网络状结构,其直径范围可控制在200～1000 nm之间,孔隙率>90%,表面积与体积比在6～8μm^(-1)左右。直径随着聚合物溶液浓度的增加而变大,随环境湿度的增高先减小后增大,孔隙率和表面积与体积比的变化规律与直径相反。结论 PLLA三维微纳米纤维结构形成的主要机理是,水滴模板过程中溶剂的快速挥发引起孔壁温度急剧降低,导致热致相分离。在环境温度为25℃,THF为溶剂,溶液用量为50μL及气体流量为300m L/min的动态气氛条件下,采用水滴模板法制备PLLA微纳米纤维膜的适宜条件为:溶液浓度25mg/mL,环境湿度50%。该条件下获得的微纳米纤维直径分布范围为200～900 nm,平均直径为476 nm,薄膜孔隙率以及表面积与体积之比分别为96.7%和8.4μm^(-1)。

The work aims to prepare the micro/nano fibers film via breath figures method, and study the effect of polymer concentration and ambient humidity(relative humidity) on the morphology and diameter of micro/nano fibers. The PLLA micro/nano fiber membrane was prepared under different mass concentrations(10, 25, 50 mg/mL) of PLLA/tetrahydrofuran(THF)solution and different ambient humidity(40%, 50%, 60%, 70%). The morphology of the micro/nano fibers was observed by scanning electron microscopy(SEM), the diameter of micro/nano fibers was counted by image analysis software and the average diameter and diameter distribution were calculated. The surface-to-volume ratio of the film was calculated by the average diameter of the fibers. The porosity of the film was calculated by the density method. PLLA nanofiber film prepared by breath figures method had a diameter range of 200~1000 nm, porosity >90% and surface-to-volume ratio range of 6~8 μm-1 with a smooth and continuous three-dimensional network-like structure. The diameter rose as the concentration of the polymer solution increased,and decreased first and then increased with the increase of ambient humidity. The change law of porosity and surface-to-volume ratio was opposite to that of the diameter. The characteristic 3 D nanofibrous architecture of PLLA film is mainly formed by the combination thermal induced phase separation(TIPS) with water assisted breath figure mechanism, because of the sharp temperature drop caused by the quick solvent evaporation in the process. The optimal parameters to prepare microlnano fibers film are50 μL(the dosage of PLLA solution), 300 mL/min(gas flow rate), 25 mg/mL(polymer concentration), 50%(environmental humidity) under 25 ℃ dynamic atmosphere with THF as solvent. The microlnano fibers have a diameter ranging from 200 to 900 nm and an average diameter of 476 nm. The porosity and surface-to-volume ratio of the film are up to 96.7% and 8.4 μm-1, respectively.