Preparation And Performance Of Silica Based Free-standing Film By Layer-by-Layer Self Assembly Technique

The layer-by-layer (LbL) assembly technique is widely used in the preparation ofuniform micro-nano structures of organic/inorganic composite films. In this article,we prepared core-shell poly[3-(trimethoxysilyl)propyl methacrylate]-methacrylic acid(poly(MPS-MAA)) anionic composite emulsion by graft condensation polymerizationof [3-(Trimethoxysilyl)propyl methacrylate] and methacrylic acid. Here, poly(MPS-MAA) and N-[3-(trimethoxysilyl)propyl]diethylenetriamine (TPDT) werechosen as silica source and one of assembly materials, while polyurethane (PU) andpoly(acrylic acid)(PAA) were used as the other assembly materials respectively.Silica-based thin films were prepared by the LbL technology driving by electrostaticforce. Mechanical properties, hydrophilicity and adsorption performance of heavymetal ions and methylene blue (MB) of the films were investigated. The main resultswere listed below.(1) Poly(MPS-MAA) core-shell composite emulsion was prepared as filmcomponent. Then, PU/PAA/PU/poly(MPS-MAA) free-standing films were preparedby the LbL technique. The films were hydrophilic, and introduction ofpoly(MPS-MAA) emulsion could improve the mechanical properties of the films. Themaximum tensile strength of free-standing film reached21MPa.(2) TPDT/PAA free-standing films were fabricated by LbL technique. Themechanism of film formation and mechanical properties were researched. PEG400,PEG800, PEG6000and sodium alginate were use to improve the stretchability of thefilm. The results showed that the hydrophilic films grew exponentially withtransparency of98%and could be used as antifogging materials. The introduction ofTPDT could increase the strength and rigidity of the films, and the increase of thePAA concentration could improve the elongation at break. The maximum tensilestrength of free-standing film reached32.8MPa.(3) The dynamic adsorption behaviors of single and mixed heavy metal ions byTPDT/PAA and PU/PAA/PU/poly(MPS-MAA) LbL films were studied. The effects of operational conditions such as initial concentration, flow rates, and kinds of heavymetal ions on the adsorption capacties were examined. And the adsorptionperformance of PU/PAA/PU/poly(MPS-MAA) films toward Cu2+and MB wascompared. The results showed that the adsorption capacity of TPDT/PAA films forheavy metal ions were higher than the PU/PAA/PU/poly(MPS-MAA) films, becausethe complexing effect of amino in TPDT increased the adsorption sites for heavymetal ions. In a mixed metal ions solution, the silica-based films showed the higheradsorption selectivity for Cu2+and Pb2+. PU/PAA/PU/poly(MPS-MAA) films withcore-shell structure increased the adsorption capacity for MB. All findings presentedin this study suggested that silica-based films could be described by the pseudofirst-order model and intraparticle diffusion model. The adsorption isotherm ofTPDT/PAA films could be described by Freundlich isotherm equations, but theLangmuir adsorption isotherm yielded a better fit to PU/poly(MPS-MAA)/PAA films.