Preparation and properties of silicon- and titanium-containing hybrid nanocomposite films based on ethyl cellulose

Abstract

Abstract-Nanocomposite hybrid films containing silicon and titanium compounds in the polymer matrix are prepared through the sol gel method via the hydrolytic polycondensation of Si and Ti alkoxides (tetra ethoxysilane and titanium tetrabutoxide) in the THF solution of a hydrophobic polymer, ethyl cellulose. Their structure and properties are studied with the use of a complex of physicochemical methods. During the hydrolysis of tetraethoxysilane and the subsequent polycondensation of the reaction products, silicon atoms are incorporated into the polymer and form -O-Si-O-bonds involving hydroxyl groups of ethyl cellulose. In the sol gel method, titanium alkoxide yields nanosized particles of titanium dioxide that play the role of fillers in the polymer matrix. Titanium containing films show solubility in THF and, after prolonged contact with the solvent, precipitate titanium dioxide from the solution. Hybrid films containing silicon are insoluble owing to the formation of a chemical network between polymer molecules and Si-OH groups of the products of hydrolysis of silicon alkoxide, as confirmed by the IR data. It is shown that the amounts and types of alkox ides and the diameters of the structures formed in the polymer matrix via the sol gel procedure affect the hydrophilicity levels of ethyl cellulose hybrid films and their abilities to swell in water and aqueous solutions of organic dyes (brilliant blue and methylene blue). Ethyl cellulose hybrid films are hydrophilic, and they facilitate the removal of dye molecules from aqueous solutions. The best properties are featured by the films containing nanosized particles of titanium dioxide in the polymer matrix.

Chemical networks of poly(vinyl alcohol)-Si hybrid films and the thermodynamics of their interaction with water

“…As is known [32], frequencies of the stretching vibrations of C-O and Si-O groups are seen at 1060-1100 cm -1 ; therefore, the presence of the band at 1080 cm -1 and its enhancement with an increasing content of Si in a film may be explained by the appearance of new inter chain bonds O-Si-O through the interaction of the hydroxyl groups of the polymer with siloxane groups Si-OH in the products of hydrolysis of TEOS during the sol-gel process. Similar behavior was observed for the films of partially substituted cellulose derivatives [23,26] that were prepared via the sol-gel process. For PVA, for which the content of OH active groups in a unit was 38.6%, this process was even more probable.…”

“…On the surfaces of the hybrid films, as in [23][24][25][26], nanosized asperities (~5-7 nm) were observed via AFM. The hydrophilicity levels of the films were estimated from the values of cosθ found for contact angles θ [29,30] formed by water droplets on the film/air interface.…”

“…The films were obtained via the sol-gel method through the interaction of PVA with tetraethoxysilane (TEOS) in a 4% aqueous polymer solution at a TEOS-PVA molar ratio of 1 : 4-1 : 1. The reactions of hydrolytic conden sation of TEOS were performed at a temperature of 50°C, as described in [23][24][25][26], but at an excess of the hydrolyzing agent, water, which served as a solvent for the polymer. The thixotropic gel that formed during the synthesis transformed under intense stirring into a viscous homogeneous transparent liquid, from which films with thicknesses of 100 ± 5 µm were cast on a flu oroplastic substrate.…”

“…This scheme includes not only the formation of hydrogen bonds between the products of hydrolysis of alkoxides and active groups (OH, OR) of the polymer in whose solution the sol-gel process is performed but also the feasibility of covalent interaction between them. As was shows for cellulose esters containing such groups [23][24][25][26], silanol Si-OH groups that result from the hydrolysis of silicon alkoxide are involved in hydro lytic condensation reactions with cellulose esters via hydroxyl groups of the polymer accompanied by the formation of siloxane bonds O-Si-O between chains. The appearance of interchain bonds in hybrid polymer films leads to the formation of a three dimensional chemical network and, hence, to a decrease in the ability of the material to swell in liquid media.…”

“…The appearance of interchain bonds in hybrid polymer films leads to the formation of a three dimensional chemical network and, hence, to a decrease in the ability of the material to swell in liquid media. How ever, no quantitative characteristics of their network structures are available in papers [7][8][9][10][11][12][13][14][15][16][17][18][19][20][23][24][25][26] devoted to organic-inorganic film materials.…”