Poly(methyl methacrylate) (PMMA) and polystyrene (PS)/clay nanocomposites were prepared via in-situ bulk polymerization. The compatibility of the initiator and monomer with the clay surface was found to profoundly affect the clay dispersion. By using a surfactant containing a polymerizable group to modify the clay surface, exfoliated PMMA and PS/clay nanocomposites were synthesized. The clay dispersion was quantified by both X-ray diffraction (XRD) and transmission electron microscopy (TEM). The dimension stability of nanocomposites was studied and related to both nanoscale (layer separation) and mesoscale (long-range distribution) clay dispersion.

drop of the suspension on a TEM grid, and letting the solvent evaporate slowly in a fume hood. XRD patterns were recorded on powder samples using a Philips PW1710 diffractometer (Cu Ka radiation, k = 1.54056 ) at a scanning rate of 0.02 s ±1 for 2h in the range of 10 to 70. UV-vis spectra were measured using a diode array spectrophotometer (Hewlett Packard 8452 A, Palo Alto, CA) with a resolution of 2 nm. Photoluminescence spectra were recorded using a luminescence spectrophotometer (Perkin Elmer LS-50B, Norwalk, CT) with pulsed high pressure xenon source. Polymer±Clay Nanocomposite Foams Prepared Using Carbon Dioxide** By Changchun Zeng, Xiangmin Han, L. James Lee,* Kurt W. Koelling, and David L. TomaskoPolymeric foams (or porous polymeric materials) are used in many applications because of their excellent strength-toweight ratio, good thermal and sound insulation properties, flexibility of generating desired morphologies to meet specific applications, materials savings, etc.[1] Foams with nanometersized voids are under investigation for potential applications as the next generation materials of low dielectric constants.[2]However, compared to bulk polymers, foams have reduced mechanical strength and lower dimensional and thermal stability. Recently developed microcellular foams provide improved mechanical properties over conventional foams,

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin-screw extruder. The effect of molecular weight of PP-MA (maleic anhydride-modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP-MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X-ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP-MA330k/clay, a well-dispersed two-component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP-MA330k/clay, an intercalated three-component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content.

Intercalated and exfoliated polystyrene/nano-clay composites were prepared by mechanical blending and in sihr polymerization respectively. The composites were then foamed by using CO, as the foaming agent in an extrusion foaming process.The resulting foam structure is compared with that of pure polystyrene and polystyrene/talc composite. At a screw rotation speed of 10 rpm and a die temperature of ZOO' C, the addition of a small amount (i.e., 5 wt%) of intercalated nano-clay greatly reduces cell size from 25.3 to 1 1.1 pm and increases cell density from 2.7 x lo7 to 2.8 x 108 cells/cm3. Once exfoliated, the nanocomposite exhibits the highest cell density (1.5 X lo9 cells/cm3) and smallest cell size (4.9 pm) at the same particle concentration. Compared with polystyrene foams, the nanocomposite foams exhibit higher tensile modulus, improved fire retardance, and better barrier property. Combining nanocomposites and the extrusion foaming process provides a new technique for the design and control of cell structure in microcellular foams.

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Polymeric nano-composites are prepared by melt intercalation in this study.Nano-clay is mixed with either a polymer or a polymer blend by twin-screw extrusion. The clay-spacing in the composites is measured by X-ray diffraction (XRD). The morphology of the composites and its development during the extrusion process are observed by scanning electron microscopy (SEW. Melt viscosity and mechanical properties of the composites and the blends are also measured. It is found that the clay spacing in the composites is influenced greatly by the type of polymer used. The addition of the nano-clay can greatly increase the viscosity of the polymer when there is a strong interaction between the polymer and the nano-clay. It can also change the morphology and morphology development of nylon 6/PP blends. The mechanical test shows that the presence of 5-10 wt.% nano-clay largely increases the elastic modulus of the composites and blends, while sign& cant& decreases the impact strength. The water absorption of nylon 6 is decreased with the presence of nano-clay. The effect of nano-clay on polymers and polymer blends is also compared with Kaolin clay under the same experimental conditions.

wileyonlinelibrary.comsuch as transistor, [ 5 ] triboelectric, [ 6 ] capacitive, [ 7,8 ] piezoelectric, [9][10][11] and piezoresistive properties.Piezoresistive pressure sensors, which transform an input force into an electrical signal caused by the change in the resistance, have attracted considerable attentions by virtue of its simplicity and low cost in design and implementation. Most fl exible piezoresistive sensors are prepared by loading conductive nanomaterials (e.g., carbon nanotubes (CNTs), [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] graphene, [29][30][31][32] nanowires, [33][34][35] nanoparticles) onto fl exible substrates (e.g., fi bers, [ 12,13 ] fi lms, [14][15][16][17] opencell foams [ 29 ] ) via a number of processing methods, such as blending, [ 19,20 ] coating, [ 21,29 ] and printing. [ 17 ] Among the different conductive nanomaterials, carbon nanotubes have attracted a considerable amount of attention due to their remarkably high piezoresistive sensitivity. [ 36,37 ] In addition to the nanomaterials, which are the active sensing elements, the properties of the substrates also play a key role in determining the overall sensor performance. [ 27,28 ] Most studies on the effects of the substrates focus on the modulus, and it has been suggested that porous substrates with reduced elastic modulus result in increased sensing properties. [ 19 ] Yet from the classical mechanics point of view, the other most fundamental property that dictates the elastic properties is the Poisson ratio, which is defi ned as the ratio of the lateral contractile strain to the longitudinal tensile strain for a material undergoing tension in the longitudinal direction. Collectively, they defi ne the elastic properties and deformation characteristics of the materials in a 3D space. Conceivably, the Poisson ratio would impact the sensing performance of piezoresistive sensors; however, this effect has not been studied.Classical mechanics predicts that for isotropic materials, the Poisson ratio lies between -1 and 0.5, a fairly small range. [ 38 ] With a few exceptions such as α-cristobalite, [ 39 ] certain cubic metal, [ 40 ] and few biological tissues, [ 41 ] the range of Poisson ratio of almost all natural or synthetic materials is even smaller, typically 0.3-0.5. [ 42 ] Research on fabrication of auxetic materials or materials with negative Poisson ratios has progressed steadily since the initial report by Lakes [ 43 ] on the possibility of such materials. [ 44,45 ] The performance of fl exible and stretchable sensors relies on the optimization of both the fl exible substrate and the sensing element, and their synergistic interactions. Herein, a novel strategy is reported for cost-effective and scalable manufacturing of a new class of porous materials as 3D fl exible and stretchable piezoresistive sensors, by assembling carbon nanotubes onto porous substrates of tunable Poisson ratios. It is shown that the piezoresistive sensitivity of the sensors increases as the substrate's Poisson's ratio decrease...

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