Submitted for the MAR06 Meeting of The American Physical Society Fabrication and Characterization of Polyamide Nanocomposites Using Functionalized Nanotubes. KAREN I. WINEY, M. MONIRUZZAMAN, University of Pennsylvania, J. CHATTOPADHYAY, W.E. BILLUPS, Rice University — We have prepared nylon 6,10 nanocomposites with functionalized single wall nanotubes (fSWNT) using an interfacial polycondensation method previously developed in our lab. The specific functional groups (CH2)nCOCl on the sidewall of the nanotubes were designed to permit covalent bonding to the nylon matrix while fabricating the nanocomposite. Using a binary mixture of dichlorobenzene/water solvent system, we have been able to prepare nylon 6,10 and nylon 6,10 / fSWNT nanocomposites with a yield of 80%. The composites were characterized using FTIR and Raman spectroscopies, optical and scanning electron microscopies, differential scanning calorimetry, and thermogravimetric analysis. The composites show good dispersion of nanotubes at the micron and submicron levels. Improved protocols have been developed to reduce the degradation of the composites at elevated temperatures. The nylon 6,10 / fSWNT nanocomposites were spun into fibers using melt fiber spinning at 240C and the mechanical properties of the fibers were studied as a function of nanotube loading. Karen I. Winey University of Pennsylvania Date submitted: 11 Jan 2006 Electronic form version 1.4

We have fabricated the first organogel/carbon nanotube composites using 12-hydroxystearic acid (HSA) as the gelator molecule, multi-wall carbon nanotubes as the nanofillers, and 1,2-dichlorobenzene as the organic solvent. We have achieved significant improvements in the mechanical and electrical properties of the organogels by incorporating pristine or carboxylated carbon nanotubes. For example, the linear viscoelastic regime of the HSA organogel, an indicator of the strength of the gel, extends by a factor of four with the incorporation of 0.2wt% of the carboxylated nanotubes. Also, the carbon nanotubes (specially the pristine tubes) improve the electrical conductivity of the organogels, e.g. six orders of magnitude enhancement in electrical conductivity with 0.2wt% of pristine tubes. Differential scanning calorimetry experiments indicate that the nanotubes do not affect the thermoreversibility of the organogels.

Studies on self-assembly of molecules, mediated by, e.g., hydrogen bonding interactions, are a major theme currently. The consequence of such self-assembly of hydrogen-bonding molecules, when dispersed in a polymer matrix, has not been studied so far. We describe such a polymer dispersed self-assembling small molecule system, in which a homologous series of small molecules, with a hydrogen-bonding moiety and alkyl side chains, is dispersed in polycarbonate. These are not liquid crystalline. The self-assembling molecules form colloidal size domains in the polymer, and this involves a hierarchy of three levels of assembly. The molecules self-assemble into small crystallites, which then organize into spherulitic structures. These spherulites then aggregate to form large, uniform near-spherical domains. The size and uniformity of the domains depend on the length of the alkyl side chain. The domain formation is reversible; that is, these domains can be melted and reformed.

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.

We review the present state of polymer nanocomposites research in which the fillers are single-wall 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 0.05wt% 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.