Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (6): 1162-1168.doi: 10.3866/PKU.WHXB201504013

• CATALYSIS AND SURFACE SCIENCE • Previous Articles     Next Articles

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
  • 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.


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