Responsive Polymer/Clay Aerogel Composites
- PDF / 1,038,253 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 95 Downloads / 237 Views
EE9.36.1
Responsive Polymer/Clay Aerogel Composites Suneel Bandi1 and David A. Schiraldi1* 1. Case Western Reserve University, Department of Macromolecular Science and Engineering, Cleveland, OH
Abstract: Clay aerogels are a relatively unexplored form of matter that are only now being investigated for use in the reinforcement of organic polymers. We have recently demonstrated an efficient process for producing these aerogels; we now report our preliminary work describing the preparation and properties of polymer/clay aerogel composites, including temperature-responsive materials. Introduction: Clay Aerogels Aerogels are considered to be among the least dense materials known, being largely composed of air containing a relatively low level of (generally) inorganic matter. The term aerogel, now often used to describe inorganic materials with apparent bulk densities in the 0.1 – 0.01 g/cm3 range, is generally attributed to Kistler, who was the first to describe their preparation from silica.1 While the majority of inorganic 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 production of low density structures from clays was reviewed by Mackenzie2, with structural properties then reported by Call,3 and Weiss.4 Materials with improved mechanical stability were reported by Norrish,5 with the identification of a “house of cards” structure, and stabilization by incorporation of polyelectrolytes made by Van Olphen.6 The importance of processing conditions to the final stability of clay aerogels was demonstrated by Nakazawa.7 The structure of typical layered clay is shown in Figure 1. Figure 2 shows an SEM micrograph of starting montorillonite clay, which undergoes structural changes and results in a layered structure as shown in Figure 3. Polymer/clay nanocomposites have been an area of intensive investigation over the past decade, due in large part to the reported enhancement of nylon 6 thermal and mechanical properties which occur when in situ polymerization of caprolactam in the presence of ca. 4 wt% of smectic clay produced an exfoliated structure. An alternative route to incorporation of clays into organic polymers could be to pre-form clay matrices that do not require exfoliation, then fill or impregnate these clay structures with polymer (melt or solution) or monomers (which then could be polymerized in situ). In this manner, an interpenetrating system of clay and polymer could be obtained. The approach of pre-converting clay into an aerogel is appealing from its simplicity, its ability to be adapted to a wide range of polymeric matrixes, and from the absence of thermodynamic and kinetic barriers present when polymerization reactions are conducted within swelled clays. Using a clay aerogel as starting material, no separation of clay sheets is required, and polymerization reactions can proceed in the normal fashion.
EE9.36.2
Figure1: Structure of MMT clay “house of cards”8
Fig
Data Loading...
