Polymer-Attached Functional Inorganic-Organic Hybrid Nano-composite Aerogels

Abstract

ABSTACTNovel materials in which modified inorganic-organic hybrid silica aerogels are attached to polymer chains have been synthesized. The aerogels are based on chitosan, a bioderived polymer from chitin, and they contain silica. The first stage of the modifications includes attachment of isocyanate, amine onto the chitosan chains embedded within the aerogel. These groups are employed in the second stage to develop the reactions required to "string" aerogel particles along functionalized linear polymers or to employ these polymers to crosslink the composite aerogels. The initial chitosan-silica aerogel particles have an ultimate size of about 2nm, and their functionally modified forms were reacted at sizes up to 1 jum. These aerogels can take up and hold dyes and water-soluble drugs. The chemistry to synthesize polyamino-siloxane based aerogel composite was discussed. In addition, two approaches to synthesize PHEMA aerogel hybrid were studied. INTRODUCTIONChitosan silica aerogels in transparent or translucent monolithic solid form have been synthesized by an initial sol-gel process, followed by extraction with supereritical CO 2 [1-6]. The chitosan silica aerogels have high porosity, up to 95%(v/v), and densities ranging from 0.2 to 0.3g/cm 3 . The chitosan silica aerogels have average pore size of 3-5nm[2-3]. They have a three dimensional network which can be thought of as a Si-O-Si bonded framework with the chitosan polymer winding through the network like a snake that interacts with silica by both hydrogen bonds and Si-O-C bonds.In recent work, we have demonstrated that the amine groups on the chitosan in the silica network are able to react with externally provided compounds. Thus, it is possible to carry out reactions on the chitosan molecule that is essentially suspended in the dry aerogel space. That makes it feasible to do chemical reactions where water must be excluded on a molecule (chitosan) that otherwise would only be available in solvents with active hydrogen [7]. Small molecules such as bis (4-isocynatocyclohexyl) methane (HMDI), succinic anhydride (SA), isocyanatoethyl methacrylate (LEMA), and dansyl chloride (DC) have been used in this work to modify the chitosan in aerogel through chemical reactions with amines present in chitosan [7].Of particular interest are the reaction of HMDI with chitosan silica aerogel, which results in a new -NCO terminated material, and, the reaction of IEMA with chitosan silica aerogel to produce a methacrylate terminated new aerogel material. They are valuable not only because they have new physical properties, but also because they bring new functional groups into these aerogels, making it possible to carry out new chemistries. This should lead to novel materials with varied properties.One possibility is to attach these -NCO terminated aerogel particles in the 100nm to Igm size range to linear polymers such as poly (allyamine), aminopropylmethylsiloxane-dimethylsiloxane copolymer, or poly (2-hydroxyethyl methacrylate) (PHEMA).The aminopropylmethylsiloxane-co-dimet...

Facile One-Pot Synthesis of Mechanically Robust Biopolymer–Silica Nanocomposite Aerogel by Cogelation of Silicic Acid with Chitosan in Aqueous Media

“…In terms of chemical functionality, it is a polysaccharide as well as a polyamine. Previous studies have shown the versatile nature of chitosan and the good chemical compatibility with sol–gel based silica materials. ,− The abundant amino and hydroxyl functional groups on the backbone of chitosan promote the widespread application of the material as effective biosorbents for the removal of dyes, , heavy metals, , and inorganic ions . The presence of polar functional groups (amine and hydroxyl) on the polymer backbone introduce strong dipole moments which favor the interaction with polar molecules (solvent, silica but also other chitosan units) through hydrogen bonding or dipole–dipole interactions.…”

Temperature-Responsive Clay Aerogel−Polymer Composites

“…[7][8][9][10] A growing body of literature exists in which silica aerogels are combined with organic polymers to produce nanocomposite materials. [11][12][13][14][15][16] While the majority of aerogels described in the literature are silica-based, there are a limited number of references to clay-based aerogels (though in many cases, the authors did not use this nomenclature). The conversion of clay to clay aerogel through freeze-drying results in a rearrangement of clay sheets, creating a lightweight, fabric-like material.…”

Photo-formed Metal Nanoparticle Arrays in Monolithic Silica-Biopolymer Aerogels

“…In the case of the Au-chitosan-silcia aerogels, there are some special chemical possibilities, because the matrix is porous, the chitosan can be functionalized [14,15], and the Au(0) nanoparticles are present. As described briefly in the introduction, this can form the basis for assay, separation and identification methods.…”

“…The synthesis of chitosan-silica aerogels was described in our former work [14,15]. These used in this work are based on a matrix composition, before metal salt addition, that is 10% chitosan and 90% silica by mass.…”