Preparation of poly(acrylic acid) nanofilms by in-situ polymerization of acrylic acid macroclusters oil silicon oxide surfaces

A new method for preparing poly(acrylic acid) (PAA) films on silicon oxide surfaces with smooth morphology has been developed. Acrylic acid (AA)was preferably adsorbed on silicon oxide surfaces in AA/ chloroform binary liquids and formed a hydrogen-bonded organized structure, which was called molecular macrocluster. AA macroclusters on silicon oxide surfaces were in-situ polymerized to obtain molecularly flat polymer films with thickness up to 10 nm. In-situ polymerizations were conducted by photo-irradiation in the presence of a photo initiator, 2,2-dimethoxy-2-phenyl-acetophenone (DPA). As a reference, the adsorption of PAA polymerized in the bulk solution was examined on silicon oxide surfaces. A series of techniques such as attenuated total reflection-FTIR (ATR-FTIR) spectroscopy, ellipsometry and atomic force microscopy (AFM) was utilized for characterizing two types of films. it was found that flat PAA films with linear hydrogen-bonded COOH could only be obtained by in-situ polymerization, which demonstrated this method was an effective way for preparing molecularly uniform polymer films. The surface morphology and thickness of obtained PAA films were found to be dependent on the monomer concentration, initiator amount and photoirradiation time. Molecularly uniform and flat PAA films were obtained after 5 min irradiation at 0.8 mol% AA in the presence of 5 wt% DPA.