Layered nanocomposites

Wang, S.J., Cheng, G., Jiang, X.H., Li, Y.C., Huang, Y.B., and Du, Z.L. (2006) Direct observation of photoinduced charge redistribution of WCfi—Ti02 double layer nanocomposite films by photoassisted Kelvin force microscopy. Applied Physics Letters, 88 (21), 212108. 

In the next section, we demonstrate how exfoliation and ordered restacking of aminopropyl-derivatized magnesium phyllosilicates in the presence of proteins, enzymes or DNA can be used to prepare new types of bio-inorganic layered nanocomposites. 

The enzymatic activities of intercalated GOx-AM P layered nanocomposites at various pH values and temperatures were compared with the native enzyme in aqueous solution. In both cases, characteristic linear plots consistent with Michalis-Menton kinetics were obtained. The Lineweaver-Burk plots indicated that the reaction rates (Vmax) for free and intercalated GOx (3.3 and 4.0 pM min 1 respectively), were comparable, suggesting that the turnover rate at substrate saturation was only marginally influenced by entrapment between the re-assembled organoclay sheets. However, the dissociation constant (Km) associated with the activity of the enzyme was higher for intercalated GOx (6.63 mM) compared to native GOx (2.94 mM), suggesting... 

In conclusion, we have highlighted in this and the preceding section two versatile synthetic strategies to bio-inorganic layered nanocomposites based on the self-assembly of organically functionalized magnesium phyllosilicates (Figure 8.18). 

Fig. 8.18 Schematic diagram showing the potential scope of organically functionalized magnesium phyllosilicate (shown in top centre of figure) for the preparation of functional bioinorganic nanomaterials. (A) biomolecule-induced co-assembly of exfoliated aminopro-pyl-functionalized organoclay sheets to produce layered nanocomposites containing functional protein molecules (top left) or DNA (bottom left). (B) molecular wrapping...

Nanohybrids can be prepared in the form of intercalated layered nanocomposites produced by co-assembly of guest biomolecules in the presence of exfoliated organoclay sheets (Section 8.4), or by wrapping single biomolecules in ultrathin layers of condensed organoclay oligomers (Section 8.5). Such approaches should provide new general routes towards the development of functional biomaterials with numerous applications. 

J. Wu, and M. M. Lerner, Structural, thermal, and electrical characterization of layered nanocomposites derived from Na+-montmorillonite and polyethers, Chem. Mat. 5, 835-838 (1993). 

Figure 38 shows the XRD pattern (a) and hysteresis loop (b) of FePt C double-layered nanocomposite thin-film medium. The soft underlayer FeCoNi (111) peak and the Zl0 FePt (001) and (002) peaks are shown only in the XRD pattern. This means that the preferred crystal orientation of Tl0 FePt C nanocomposite film is successfully obtained on this SUL by nonepitaxial growth. The polar-Kerr measurement shows a square loop that is only sensitive to the top layer the Kerr effect data shown in this loop give the coercivity Hc = 8.5 kOe, nucleation field Hn = 5.65 kOe, remanence ratio S = 1, and loop slope ( at Hc) a = 3.3, respectively. 

The nanostructure of the double-layered nanocomposite FePt C thin film medium was characterized by TEM. Electron diffraction shows that the crystallites are FePt with the Ll0 structure. Figure 39 shows the bright-field and cross-section TEM image, which verifies that FePt crystallites are imbedded in C matrix and well isolated from each other. 

Intercalated compounds offer a unique avenue for studying the static and dynamic properties of small molecules and macromolecules in a confined environment. More specifically, layered nanocomposites are ideal model systems to study small molecule and polymer dynamics in restrictive environments with conventional analytical techniques, such as thermal analysis, NMR, dielectric spectroscopy and inelastic neutron scattering. Understanding the changes in the dynamics due to this extreme confinement (layer spacing < Rg and comparable to the statistical segment length of the polymer) would provide complementary information to those obtained from traditional Surface-Force Apparatus (SFA) measurements on confined polymers (confinement distances comparable to Rp [36]. 

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

FIGURE 13.6 Schematic illustration of pillaring process in bidimensional clay (a) ion exchange with precursor cations and (b) conversion to oxide by calcination. (From Yamanaka, S., Design and synthesis of functional layered nanocomposites. Am. Ceram. Soc. Bull., 70, 1056, 1991. With permission.). 

The layered nanocomposites can be obtained as shown in Figure 16.20. Intercalation ofe-caprolactone into the silicate galleries was done simply by suspending... 

Figure 16.21. Schematic representation of layered nanocomposite with ion mobility. [Adapted, by pennission. from Ruiz-Hitzky E, Aranda P, Casal B. Galvan J C. Adv. Mat., 7, No.2, 1995, 180-4.]...

Wu, J. Lerner, M. (1993) Structural, Thermal, and Electrical Characterization of Layered Nanocomposites Derived from Sodium-Montmorillonite and Polyethers. Chem. Mater. Vol.5, No.6, pp.835-838... 

OOZha Zhang, Q., Fu, Q., Jiang, L., Lei, Y. Preparation and properties of polypropylene/ mont-morillo-nite layered nanocomposites. Polymer International. Vol. 49 (2000) 12, 1561-1564. 

C. Oriakhi, Synthesis and Luminescence Properties of a Poly(p-Phenylenevinylenej/Montmorillonite Layered Nanocomposite. Appl. Clay Sci. 1999,15,109-118. 

Thermogravimetric analysis of polyvinylidene-co-trifluoroethylene layered nanocomposites have indicated that their thermal stability is improved when the anionically modified layered silicate content was increased [30]. Differential scanning calorimetry showed that thermal transitions in the nanocomposites depended on the layered silicate content. 

The chemical s mthesis and analysis of properties of layered nanocomposites devoted tens publications. In the last decade for the synthesis of metal, oxide, hydroxide nanostructures used method of laser ablation of metals in a liquid medium [10-12]. However, the researches aimed at producing layered organic-inorganic composites by this flexible, simple method are not enough [13]. Practically important is also the question of the structural stability of these composites in the colloidal state under the influence, in particular, laser radiation optical range (colloidal stability of drugs, film, optical data carriers, etc.). 

Usui, H. Sasaki, T. Koshizaki, N. Ultraviolet emission from layered nanocomposites of ZnfOH) and sodium dodecyl sulfate prepared by laser ablation in liquid . Applied Physics Letters, 2005,87(6), 63105-63108. 

Layered silicates, single-wall nanotubes (SWNTs), and other extreme aspect ratio, very thin (0.5-2 nm) nanoparticles, exhibit translational symmetry within the powder." Polymer/layered nanocomposites in general can be classified into three diflferent types, namely intercalated nanocomposites, flocculated nanocomposites and exfoliated nanocomposites (see Figure 6.4). ... 

The exfoliated state takes place when the dispersion of the sheets of the clay is fully achieved and, therefore, no interaction between sheets occurs (Figure 8.2, right). The ideal exfoliated state is that in which the clay platelets are homogeneously distributed throughout the polymer matrix. Generally speaking, layered nanocomposites never exhibit a pure structure on the contrary, their morphology is a combination of all three possibilities with one of them dominant. 

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