Sol—Gel Processing of Silica—Poly(vinyl acetate) Nanocomposites

Abstract

Sol-gel processing of organic/inorganic composite materials has attracted much study in recent years. The low temperature sol-gel process and its inherent versatility allow microstructural control on the nanoscale, leading to many interesting materials. In this preliminary study, we have synthesized silica/poly(vinyl acetate) (SiO 2 /PVAc) composite materials and investigated the effect of formamide substitutions for ethanol as the solvent. The interaction between SiO 2 and PVAc is primarily hydrogen bonding between silanols on the silica surface and the carbonyl groups of the PVAc. The time to gel, skeletal density, and the linear shrinkage were significantly dependent on the presence and quantity of formamide. Nitrogen sorption was used to evaluate the xerogels structures. The thermal behavior was studied with thermogravimetry/Fourier transform infrared spectroscopy (TG/FTIR).Sol-gel processing has been used to prepare inorganic oxides by hydrolyzing alkoxides. In addition, sol-gel processing lends itself quite well to the synthesis of inorganic-organic hybrid materials. First, the low temperature aspect of sol-gel processing can be exploited to create many inorganic-organic composite materials unattainable with typical high temperature ceramic processing (7). Second, sol-gel processing can provide intimate mixing of chemically dissimilar materials at room temperature.There are several ways in which organic materials may be incorporated into inorganic matrices. The strength of the interactions between the phases can divide these types of hybrid materials into two classes (7). Class I hybrid materials correspond to weak phase interactions such as van der Waals interactions, hydrogen bonding (2), or simple mechanical blending of the inorganic and organic phases (3). Class Π hybrid materials possess strong covalent or iono-covalent bonds, usually via -Si-C-linkages (1,4), between the inorganic and organic phases. Class II hybrids are discussed first because they represent the larger group. Both of these groups contain some subdivisions, usually differing by way of preparation or specific function (5).

Silica-Based Sol-Gel Organic-Inorganic Nanocomposite Materials: A Review of Different Material Technologies

“…Some polymers do exist (see Figure 11) which possess moieties capable of hydrogen bonding with an inorganic sol-gel network [47][48][49]. Hydrogen bonding of the sol-gel component with these polymers retards severe phase separation during network densification.…”