Preparation And Functionalization Of Polymer/Laponite Layer-by-layer Self Assembled Nanocomposite Films With High Mechanical Strength

Layer-by-layer(LBL) assembly technique is an attractive method to fabricate ultrathin films with precisely designed structure and thickness at nanoscale. It is a simple way to combine materials with different functions together. However, slow thickness growth, low mechanical strength and insufficiency application research hampers the future development of LBL materials. Laponite is an artificial montmorillonite-like silicate with 2:1 layered structure. It has been demonstrated that the introduction of Laponite can improve the mechanical and thermal properties of the materials apparently. In this paper, isocyanate, aminosilane modification and functional component were introduced to deal with these problems. The main work is listed below:(1) Nanocomposite multilayer film was prepared by employing hydrophilic aliphatic polyisocyanate(HAPI), Laponite and polyvinyl alcohol(PVA). The reaction between isocyanate groups on HAPI and hydroxyl groups on Laponite or PVA crosslinked the components together to form covalently bonded LBL films. The loading amount of Laponite was increased, the breaking strength of the films was improved from 4.9 MPa to 11.9 MPa, and the transparency of the films were improved from 85.5% to 93.6%.(2) Nanocomposite multilayer film with exponential growth thickness was fabricated with silane modified Laponite and polyacrylic acid(PAA) by LBL technique. The nanosheets of Laponite were functionalized with aminosilane, so that the electrostatic interaction between amino and carboxyl groups can be employed as the driving force in the LBL process. In addition, the silanol with strong activity formed by the hydrolysis reaction can react with the carboxyl groups on PAA. The thickness of the films increased exponentially, and a freestanding film with thickness of 10 μm can be prepared by 10 monolayers. The films were found to be humidity sensitive. The breaking strength of the film was 79.6 MPa in relative humidity of 55%, while this value decreased to 27.1 MPa in relative humidity of 55%.(3) Thermal sensitive nanocomposite multilayer film was fabricated with PVA-poly(N-isopropylacrylamide-co-acrylic acid) and Laponite. Anionic polyelectrolyte was synthesized by copolymerization of acrylic acid(AA) and thermal sensitive N-isopropylacrylamide(NIPAM). There were hydrogen bonding interactions between Poly(NIPAM-co-AA) and PVA. The influence of Laponite and thermal sensitive polymer on the properties of the film was investigated. The lower critical solution temperature(LCST) of the film was 30~40oC. The breaking strength of the film was 101 MPa, and its transparency was above 82%.