科研之友
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摘要
In this work, extremely high molecular weight (M-w) poly(allylamine hydrochloride) (PAH, 900K g/mol) and poly(acrylic acid) (PAA, 225 K g/mol) were selected to amplify the difference in the growth of multilayers in comparison with low M-w PAA (15K g/mol) and PAH (15K g/mol). By varying the pH conditions, the PAH/PAA multilayers were fabricated via the layer-by-layer (LbL) assembly in both linear and exponential growth regimes. In the linear growth regime with interlayer diffusion suppressed, high M-w polyelectrolytes with low charge density could slow down the adsorption step, leading to the decrease of thickness compared to low M-w polyelectrolytes when the deposition time was limited. However, the effect of M-w could be reversed by increasing the deposition time, for the adsorption of low M-w polyelectrolyte reached equilibrium, while the adsorption of high M-w polyelectrolyte continued. The larger coil size of high M-w polyelectrolyte could enable the surpassing of multilayer thickness compared with low M-w polyelectrolyte. In the exponential growth regime, besides the slow adsorption, the application of high M-w polyelectrolytes further suppressed the interlayer diffusion, leading to the decrease of multilayer thickness regardless of deposition time. We further studied the effects of deposition time, M-w of polyelectrolytes, and the number of bilayers on the surface morphology in the exponential growth regime. Surface roughness significantly increased with the application of high M-w PAA and the increase in deposition time. For the first time, the unique LbL film growth patterns of islet, ring and cantaloupe skin-like structures that consecutively formed on the surface of polyelectrolyte multilayers were reported by tuning the above parameters.
- 出版日期2017-1-27
