Multiwalled carbon nanotubes (MWNTs) and ultrahigh molecular weight polyethylene (UHMWPE) composites were prepared by gelation/crystallization from solution. The dried composites of MWNTs−UHMWPE with 15 wt % of MWNTs would be elongated up to more than 100-fold (λ = 100). The electric conductivity was 10-3 S/cm termed as conductive materials, and the Young's modulus reached 58 GPa at room temperature. The composites possess extraordinary stability in electric conductivity during many repeated heating cycles from room temperature to 150 °C. Scanning electron microscopy revealed that MWNTs with continuous networks are oriented predominantly parallel to the stretching direction. Such characteristic alignment of MWNTs was found to play an important role in forming effective conductive paths in the highly oriented composites.

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Thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) spherical microgels with different charge distribution were prepared by different monomer and comonomer feeding methods. The frequency ( f, 10 −2 −10 7 Hz) and temperature (T, 5−50 °C) dependent complex dielectric/electric properties of these microgels were analyzed by dielectric relaxation spectroscopy. Each microgel can be treated as a large multicharged macroion surrounded by many small counterions, and the relative displacement and the diffusion of counterions contribute to the permittivity and conductivity of the microgel dispersion. Both the dielectric permittivity at f > 10 3 Hz and the conductivity at f > 10 6 Hz decrease when the microgels shrink at temperatures higher than the lower critical solution temperature (LCST) of PNIPAM due to the shrink-induced counterion dissociation. The variation of either permittivity or conductivity with temperature reveals a sharper transition for the microgels or the microgel shell with a more uniform charge distribution than those with an inhomogeneous dense core−loose shell structure, indicating a more gradual chain shrinkage for the latter. By detecting the counterions' behaviors, we can use dielectric relaxation spectroscopy to probe the microscopic structural and dynamic heterogeneities of PNIPAM microgel dispersions.

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Semiconductor and metal nanoparticles are of scientific interest because of their unique physical properties, which are in stark contrast to their bulk counterparts. They can be utilized in a wide variety of applications, including electronic and optical devices and optical and magnetic storage systems, sensors, magnetic fluids, medical diagnostics, membranes, and catalysts. [1][2][3][4] The most critical factor towards the realization of nanoparticle-based technology is the ability to synthesize a nanoparticle assembly with defined size and spatial organization in three [5] and two dimensions, [6][7][8] and to some extent one dimension.[9] The size and interparticle spacing of the nanoparticles can have a dramatic effect on their properties. [10][11][12] For example, the chemical sensitivities and optical properties of nanoparticle-based materials can be tuned by varying the particle size, leading to a shift in the energy levels or band gap. In addition, the properties of nanoparticle-based nanostructures may also be seriously altered by particle-particle interactions. [13,14] One great challenge that remains is to develop effective ways to fabricate high density nanoparticle films with controllable size, density, and functional structures. While most strategies have been conceived and developed to fabricate homogeneous nanostructures, recently there has been increased interest in generating and utilizing heterogeneous patterning of nanoparticles, such as the so-called gradient assemblies, [15] in which the number density or size of the immobilized particles varies continuously along the substrate. This family of nanostructures offers a combinational surface that can be used to test and optimize particle-dependent properties. For example, varying the properties and sensitivities of the nanoparticle-based sensors can be achieved by the controlled variation in distribution and/or size of the nanoparticles, which will enable detection of a wide range of analytes by the same sensor arrangement. Furthermore, the gradient assemblies of nanoparticles may also have large practical applications in nano-optoelectronic devices, micro-sensors, and catalysts. However, until recently, very little effort has been expended to fabricate and explore the properties of this interesting heterogeneous patterning of nanoparticles. Assemblies of gold nanoparticles with continuous number density gradients were prepared by Genzer et al [16] on flat silica-covered substrates.They first generated a 1D molecular gradient of amino groups (-NH 2 ) on the substrate by vapor deposition of amine-terminated silane molecules, and then attached gold nanoparticles to the -NH 2 functional groups by immersing the substrate in a colloidal gold solution. The number density of the nanoparticles on the substrate shows a 1D continuous gradient on a millimeter length scale. Vossmeyer and Tomita proposed a method to prepare metal and semiconductor nanoparticles with a size gradient by means of thin-layer-chromatography or electrophoresis.[17] Size gradients ...

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Several kinds of polymer composites with carbonaceous fillers such as carbon black (CB), vapor-grown carbon fiber (CF), and carbon nanotube (CNT) are prepared by a gelation/crystallization process or a melt mixing method. The electrical phenomena, changes of electrical conductivities with different filler's type, filler's concentration and temperatures, and the mechanism of electron transport in these carbon-filled polymer composites are directly influenced by the geometric grain shape and aggregating morphology of the fillers dispersed in the polymer matrix. For the composites of CB and CF, long-range macroscopic conduction are governed by the percolation phenomenon, the conduction is behaved through the conductive path formed by the conductors' contacting, and the thermal expansion changes the physical dimensions of the entire electrical network and leads to the changes in the electrical phenomenon. Microscopic conduction between conductive elements is influenced by the tunneling barrier or tunneling voltage, which varies with the temperature change, explaining the apparent observation of the temperature dependence of the composites. In comparison with fillers of CB and CF, the CNT performs unique electric properties for their nonspherical geometry and morphology as a three-dimensional network (high structures), which has been visually proved by SEM photos in our former research, leading to the percolation threshold lower than 1% in the volume fraction and much less temperature dependence in its composites.