We review the present state of polymer nanocomposites research in which the fillers are singlewall or multiwall carbon nanotubes. By way of background we provide a brief synopsis about carbon nanotube materials and their suspensions. We summarize and critique various nanotube/polymer composite fabrication methods including solution mixing, melt mixing, and in situ polymerization with a particular emphasis on evaluating the dispersion state of the nanotubes. We discuss mechanical, electrical, rheological, thermal, and flammability properties separately and how these physical properties depend on the size, aspect ratio, loading, dispersion state, and alignment of nanotubes within polymer nanocomposites. Finally, we summarize the current challenges to and opportunities for efficiently translating the extraordinary properties of carbon nanotubes to polymer matrices in hopes of facilitating progress in this emerging area.

A new method for preparing SWNT/epoxy nanocomposites has been developed which involves high shear mixing of the epoxy resin and SWNT and heat treating the mixture prior to introducing the hardener. The glass transition temperature of the epoxy resin is unaffected by the presence of nanotubes. An improvement of 17% in flexural modulus and 10% in flexural strength has been achieved at 0.05 wt% of nanotubes. These improvements in flexural modulus and strength are attributed to good dispersion of the nanotubes and grafting of epoxy resin to SWNT by an esterification reaction. AbstractA new method for preparing SWNT/epoxy nanocomposites has been developed which involves high shear mixing of the epoxy resin and SWNT and heat treating the mixture prior to introducing the hardener. The glass transition temperature of the epoxy resin is unaffected by the presence of nanotubes. An improvement of 17% in flexural modulus and 10% in flexural strength has been achieved at 0.05 wt% of nanotubes. These improvements in flexural modulus and strength are attributed to good dispersion of the nanotubes and grafting of epoxy resin to SWNT by an esterification reaction.

Thermoreversible organogels were prepared from carbamates with alkyl side chains of different lengths. Gelation was possible only up to an alkyl side chain length of 12 carbons, beyond which crystallization occurs, due to the dominant van der Waals interaction between the alkyl chains. This is in contrast to other alkane-based organogels, in which gelating efficiency increased with the length of the alkane chain (see Abdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237). The critical concentration for gelation decreases drastically with an increase in the side chain length. Xerogels of these show birefringent fibers with uniform cross section and unlimited growth in one direction. The extent of this unlimited growth is affected by the length of the alkyl side chain in the carbamate, which finally ceases the gel formation ability of the carbamate. Cryogenic scanning electron microscopy images of the gels are similar to those of xerogels. From X-ray diffraction of the fibers, we propose that the growth direction is along the plane of hydrogen bonds between the carbamate molecules. The thickness of the fibers depends on the length of the alkyl side chain. Morphological differences are seen between gels prepared by slow cooling and quenching of the solution. Thus, the morphology of the fibrous xerogels of the carbamates can be tailored for specific applications, by the choice of the alkyl side chain length and the rate of cooling the solution.

We have prepared nylon 6,10 nanocomposites using functionalized single wall carbon nanotubes and our interfacial in situ polycondensation method. The specific functional groups -(CH2)nCOCl [n = 4 and 9] on the sidewalls of SWNT were designed to covalently link nanotubes to the nylon matrix via alkyl segments. The composites with functionalized SWNT show significant improvements in tensile modulus, strength, and toughness relative to nylon and nylon modified with non-functionalized SWNT. The alkyl linkages at the SWNT/nylon 6,10 interface contribute significantly to improving the toughness of the composites.

The difference in the morphology and crystallization aspects of hydrogen-bond-mediated self-assembling systems with single and double hydrogen-bonding motifs is studied here with carbamates as an example. These carbamates have alkyl side chains of various lengths, from C(4) to C(18). The biscarbamates with double hydrogen-bonding sites and symmetric substitution of alkyl segments show a significantly different morphological behavior as compared to the N-octadecyl carbamate alkyl esters (ref 5, referred to as simple carbamates henceforth) with a single hydrogen-bond motif and asymmetric substitution of alkyl side chains. In contrast to the simple carbamates in which no significant difference was found in the spherulite size from C(4) to C(12), with the biscarbamates we find that the spherulitic size, rate of growth of spherulites, and rate of crystallization show a maximum with an alkyl chain length of C(8). This is rationalized in terms of the relative contributions of the hydrogen-bond and van der Waals interaction energies. Oriented X-ray diffraction patterns from the fibrils of the spherulites lead to a model for the growth patterns of the hydrogen-bond planes and the molecular orientation in the spherulites.

Hydrogen bond mediated self-assembling carbamates with alkyl side chains of different lengths were investigated with respect to thermal behavior and morphology. The length of the side chain has an influence on the heat of fusion, crystallinity, and crystallite size. Morphologies of samples slowly cooled from the melt and those quenched were different. While plasticizers or clarifiers are usually used to modify the crystalline morphology of materials, we examined the possibility of effecting similar changes by blending any two types of carbamates. Although both the heat of fusion and crystallinity decrease initially with the addition of the second component, they recover beyond a certain composition. The spherulite size also decreases significantly, enhancing the transparency of the sample. Thermal analysis shows that the components of the blend exercise a mutual plasticizer effect, reducing the melting temperatures. The changes in morphology upon blending are not due to a decrease in the extent of hydrogen bonding but can be attributed to the disorder in the packing of the alkyl side chains.

Fruits ofSonneratia apetala (Buch.-Ham.) are widely used as food and in treatingvarious diseases in the tropical coastal areas. This study evaluated nutrient compositions in pericarp and seed of this fruit. Each of pericarp and seed was successively fractionated into n-hexane, diethyl ether, chloroform, ethyl acetate and methanol. Polyphenols contents and antioxidant activities of different pericarp and seed fractions were measured in different in vitro methods and phenolic compounds were determined by HPLC. Carbohydrates, proteins, lipids and ash contents were 29.6, 8.8, 2.8 and 25.5% of dry weight (d.w.) in pericarp whereas 28.3, 11.5, 4.2 and 22.7% in seed, respectively. Among the mineral macro-elements, K content was the highest (pericarp: 1.81%, seed: 0.88% of d.w.) followed by Na, Ca, Mg, P and S while in micro-elements, Fe was at the largest (pericarp: 132.5 ppm, seed: 107.3 ppm of d.w.) followed by Mn, Zn and Cu.A c c e p t e d M a n u s c r i p t 2 Methanol fraction of seed (MS) showed the highest polyphenols content (221.9 mg GAE (gallic acid equivalent)/g fraction), DPPH (IC 50 = 2.1 μg/mL) and NO (IC 50 = 490.8 μg/mL) free radical scavenging. Similarly, MS also attained very strong reducing power (OD = 1.67 at 100 µg/mL), Fe 2+ chelating and total antioxidant capacity. When subjected to HPLC analysis of MS, six polyphenols namely caffeic acid, (+)-catechin, (-)-epicatechin, ellagic acid, gallic acid and quercetin were detected and quantified as 88.1, 1459.3, 310.1, 616.9, 416.7 and 71.8 mg/100g of MS, respectively. Therefore, the fruit of S. apetala, especially its seeds could be of great use in preparation of functional foods and dietary supplements.

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