物理化学学报 >> 2015, Vol. 31 >> Issue (6): 1162-1168.doi: 10.3866/PKU.WHXB201504013

催化和表面科学 上一篇    下一篇

在气液界面上压缩诱导聚(L-乳酸)膜的结构变化

王丽, 季姗, 陈启斌, 刘洪来   

  1. 华东理工大学化学系, 化学工程国家重点实验室, 上海200237
  • 收稿日期:2015-01-29 修回日期:2015-04-01 发布日期:2015-06-05
  • 通讯作者: 陈启斌 E-mail:qibinchen@ecust.edu.cn
  • 基金资助:

    国家自然科学基金(21273074)及中央高校基本科研业务费专项资金资助项目

Structural Transition of Poly(L-lactic acid) Film Induced by Compression at Air/Water Interface

WANG Li, JI Shan, CHEN Qi-Bin, LIU Hong-Lai   

  1. State Key Laboratory of Chemical Engineering, Department of Chemistry, East China University of Science and Technology, Shanghai 200237, P. R. China
  • Received:2015-01-29 Revised:2015-04-01 Published:2015-06-05
  • Contact: CHEN Qi-Bin E-mail:qibinchen@ecust.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21273074) and Fundamental Research Funds for the Central Universities of China.

摘要:

聚乳酸(PLA)是一种环境友好及生物可降解的聚合物, 其界面性质受到了广泛关注. 本文以Langmuir-Blodgett (LB)膜天平、原子力显微镜(AFM)研究了聚(L-乳酸) (PLLA)在气液界面上的性质. 表面压-面积(π-A)等温曲线的结果表明, 在膜压缩的初始阶段, 表面压逐渐增大; 当膜压为9.0 mN·m-1时, 曲线出现了一个平台,其重复单元的面积大约在0.11-0.17 nm2之间. 原子力显微镜的结果发现, 在压缩过程中, 膜结构发生了明显的变化: 平台刚出现时, 膜内出现了大量的纤维结构; 在平台区内, 界面上出现了多层膜结构. 特别地, 当表面压为20.0 mN·m-1时, PLLA在界面上可形成约6.0 nm厚的薄膜. 由此可见, PLLA等温线中的平台与其膜结构的变化紧密相关. 这有别于普通双亲分子的性质, 即这类双亲分子π-A等温线中的平台通常表示它们在二维空间上发生了单分子膜的相转变.

关键词: 聚(L-乳酸), 界面, 单分子膜, 相转变, 结构特征

Abstract:

Poly(lactic acid) (PLA) has attracted considerable interest as an environmentally friendly and biodegradable polymer. The properties of poly(L-lactic acid) (PLLA) at an air/water interface were studied based on the Langmuir-Blodgett (LB) film balance and atomic force microscopy (AFM). The surface pressure-area (π-A) isotherm indicated that the surface pressure of PLLA initially increased as the interfacial film was compressed; at π=9.0 mN·m-1, a plateau was observed in the π-A isotherm, in which the area of the repeat unit was in the approximate range 0.11-0.17 nm2. The AFM results showed that there is a clear structural transition in the PLLA film during the compression: (i) at the beginning of the plateau, a number of fibrils are present at the air/water interface and (ii) multilayer structures (at least bilayer, i.e., the underlying layer and top layer consisting of fibrils) is formed in the plateau region. In particular, when π=20.0 mN·m-1, a thin film of PLLA of thickness about 6.0 nm was fabricated. Our findings suggest that the plateau in the PLLA π-A isotherm is closely related to a change in the film structure from monolayer to multilayer at the air/water interface. This is significantly different from the behavior of conventional amphiphiles, because the plateau in amphiphiles π-A isotherm is equivalent to a phase transition of monolayers derived from amphiphiles in a two-dimensional plane.

Key words: Poly(L-lactic acid), Interface, Monomolecular film, Phase transition, Structure characteristic

MSC2000: 

  • O647