Layer-by-layer (LbL) assembled polyelectrolyte multilayers (PEMs), followed by simple post treatment at acidic pHs provide one of the most promising methods to generate porous polymeric thin films. The primary aim of this work is to obtain a precise control on the porous structures, design the porous multilayers according to the specific applications, and meanwhile shorten the processing time that goes into the LbL assembly. Firstly, we studied the preliminary step to fabricate the porous multilayers, that is, the LbL assembly of the poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayers. More specifically, we investigated the growth behavior and surface topography of the multilayers. It was found that the effect of molecular weights of both PAA and PAH on the film growth is highly dependent on the charge density and deposition time in both linear and exponential growth regimes. Unique surface patterns were obtained by tuning the molecular weight of polyelectrolytes, deposition time, and the number of bilayers.Secondly, we developed the porous multilayers for the application of functional compound delivery. We first studied the formation of porous multilayers. Both the LbL assembly and the post treatment would affect the porous structures in a synergetic manner. The application of polyelectrolytes with distinct molecular weights and different deposition time enabled a wider and more precise control on the porous structures in both nano- and micro-scales. Having gained a precise control over the pore size, layered multi-scale porous thin films were further built up with either micro-sized porous zone on top of nano-sized porous zone or vice versa. Then, we loaded novel hydrophobic anti-biofilm compounds (ABCs) into the porous multilayers. The release of ABCs, which is highly dependent on the porous structure, led to a good anti-biofilm performance on the substrate surface. We further applied the porous PEMs onto the atomic force microscopy (AFM) cantilever for the local delivery of hydrophilic proteins. We successfully demonstrated that the porous PEMs enabled much higher protein loadings than the conventional silanization with (3-aminopropyl) triethoxysilane (APTES). More importantly, the protein molecules could be locally delivered in a contact manner. Lastly, we considered the development of the nano- and micro-scaled hierarchical surface structures from porous multilayers to achieve superwettability. We systematically investigated the effects of molecular weight of polyelectrolytes, deposition time during LbL assembly and pH for post treatment on the porous surface topography and wetting behavior. With the optimization of the processing conditions, we achieved a switch from superhydrophilicity to superhydrophobicity via a simple chemical vapor deposition (CVD) of fluorinated silane molecules onto the porous multilayers.
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