Structure and Properties of Clay

Montmorillonite (MMT), hectorite, and saponite (SAP) are the most commonly used clay minerals for the preparation of nanocomposites. Clay minerals generally have two 

For the preparation of clay containing polymer nanocomposites, two particular characteristics of clay minerals are generally considered. First is the ability of the silicate particles to disperse into individual layers. The second characteristic is the ability to modify their surface chemistry through ion-exchange reactions with organic and inorganic cations. These two characteristics are, of course, interrelated since the degree of dispersion of sihcate layers in a particular polymer matrix depends on the interlayer cations. 

FIGURE 19.1 X-ray diffraction patterns and bright field transmission electron microscopy images of PLA nanocomposites prepared with organically modified synthetic fluorine mica. The number indicates amount of organoclay loading [27]. Reproduced from Ref. 27 with permission of American Chemical Society, USA. 

In subsequent research, Sinha Ray et al. [26,27] prepared PLA nanocomposites with organically modified synthetic fluorine mica (OMSFM). For the characterization of structure and morphology of prepared nanocomposites, they first 

Maiti et al. [32] prepared a series of PLA-based nanostructured materials with three different types of pristine clays, saponite, MMT, and synthetic mica (SM), and each was modified with alkylphosphonium salts having different chain lengths. In their work, they first tried to determine the effect of varying the chain length of the alkylphosphonium modifier on the properties of the organoclay, and how the various clays behaved differently with the same organic modifier. They also studied the effects of dispersion, intercalation, and the aspect ratio of the clay on the properties of PLA. 

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Clay Minerals and Clay Colloids. The literature on clays and clay colloids is expansive, but there remains a degree of uncertainty in many areas of their study due to their inherent heterogeneity. Descriptions of the structures and properties of clay minerals can be found in Grim (1968), Brindley and Brown (1980), Newman and Brown (1987), Sposito et al. (1999), and Giese and van Oss (2002). 

STRUCTURE AND PROPERTIES OF NANOADDITIVES 11.2.1 Structure and Properties of Clays... 

The third group of clay minerals of minor technological significance comprises the illite minerals. The structure and properties of clay minerals and clays are dealt with in detail, for instance, in the treatise by Grim (1962), by van Olphen (1977), in the textbook by Worall (1964, 1969), and elsewhere. 

Abstract Clays are ubiquitous constituents of the Earth s crust that serve as raw materials for traditional ceramics. Mineralogically, clays are phyllosilicates or layered aluminosilicates. Bonding is strong within layers, but weak between layers, allowing clays to break into micrometer-sized particles. When mixed with water, clays develop plasticity and can be shaped easily and reproducibly. When heated, clays undergo a series of reactions that ultimately produce crystalline mullite and a silica-rich amorphous phase. Beyond the structure and properties of clays, the science that developed to understand traditional ceramics continues to serve as the framework for the study of advanced ceramics. 

So far, most polymer nanocomposites contain only one type of nanofiller. Recent studies revealed that combination of clay and Si02 has a more enhanced effect on the polymer matrix. In this chapter, we discuss the structure and properties of clay- and silica-based polymer nanocomposites prepared by in situ emulsion polymerization, especially polyacrylonitrile (PAN)-clay-silica ternary nanocomposites. The chapter consists of three parts (1) synthesis and structure of polymer-clay-silica nanocomposites (2) thermal properties of polymer-clay-silica nanocomposites and (3) mechanical properties of polymer-clay-silica nanocomposites. 

Morphological structures and properties of a series of poly(ethyl acrylate)/clay nanocomposites prepared by the two distinctively different techniques of in situ ATRP and solution blending were studied by Datta et al. [79]. Tailor-made PNCs with predictable molecular weights and narrow polydispersity indices were prepared at different clay loadings. WAXD and studies revealed that the in situ approach is the better option because it provided an exfoliated morphology. By contrast, conventional solution blending led only to interlayer expansion of the clay gallery. 

Structures of Clay Minerals. The term "clay minerals" generally refers to fine-grained (< lpm) sheet silicates. Many detailed discussions of the structures and compositions of clay minerals exist (e.g., 14-16). and their interesting chemical properties have been reviewed previously (H). However, a short introduction to their structures is necessary to understand their HRTEM images. 

Rovere M, Ricci MA, Vellati D, Bruni F. (1998) A molecular dynamics simulation of water confined in a cylindrical Si02 pore. / Chem Phys 108 9859-9867. Delville A. (1993) Structure and properties of confined liquids A molecular model of the clay-water interface. J Phys Chem 97 9703-9712. 

Conceptually, the next simplest clay mineral is pyrophyllite, which is produced by attaching tetrahedral sheets above and below an octahedral layer (Fig. 6), compared with just one octahedral sheet for kaolin [15]. The resulting chemical composition of pyrophyllite is AI2Si4Ol0(OH)2, which is equivalent to the mineral formula Al20 4Si02-II20. The structure and properties of pyrophyllite are summarized in Table 2. 

Delville, A. 1993. Structure and properties of confined liquids A molecular model of the clay-water interface. J. Phys. Chem. 97 9703-9712. 

In order to gain a clear idea of the clays from which ceramics are manufactured, it is necessary to study the structures and properties of their clay minerals, but it must be remembered that the properties of any clay in the bulk will also depend on the nature and proportion of the impurities. 

Nam P. H. Okamoto M. Kotaka T. Hasegawa N. Usuki, A. A hierarchical structure and properties of intercalated polypropylene/ clay nanocomposites. Polymer, vol.42, (2001), 9633-9640... 

Figure 9.3 Structure and properties of organically modified clay (a) monolayers,...

Nasegawa, H., Okamoto, H., Kawasiuni, M., Hasegawa, N., and Usuki, A. 2001. A hierarchical structure and properties of intercalated polypropylene/clay nanocomposites, h/mer 42 9633-9640. 

Computations have been carried out to better understand the structures and properties of these types of nanocomposites. One subject of particular interest is the observed enhanced gas transport performance of PDMS nanocomposite membranes containing layered silicates, which is not expected based on studies of magnetically alligned particles disuc-ssed in the next section. Clays have also been used to improve the properties of silsesquioxane polymers. ... 

However, this task becomes more challenging with polyolefins, and it is generally necessary to have some polar functionality present, most commonly by inclusion of MA grafted polymer in the composition (typically at a 5% polymer addition level) [114], Aco-rotating twin-screw extruder is frequently recommended for this purpose, however the form of screw profile used and feed location of the components, can influence the structure and properties of compounds produced [115]. For example, it was reported that combined dosing of polymer and filler at the feed end of the extruder gave better intercalation than downstream addition of the clay. 

As a consequence, the goal of our study was to prepare layered silicate nanocomposites from montmo-rillonites organophilized not only with an co-amino acid, but also with alkylammonium salts and protonated amines [27, 28, 29, 30, 31]. The use of the two dissimilar modifiers was expected to lead to significant differences in the interaction of the clay and the polymer matrix. The effect of interfacial adhesion on exfoliation and on the structure and properties of the nanocomposites prepared were determined and are discussed in this paper. Less attention is paid to changes in the crystalline morphology of the PA matrix. 

Bordes P, Pollet E, Bourbigot S, Averous L (2008) Structure and properties of PHA/clay nano-biocomposites prepared by melt interealatiotL Macromol Chem Phys 209(14) 1473—1484... 

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