Multiwalled carbon nanotubes (MWNTS)/nylon-6 (PA6) nanocomposites with different MWNTS loadings have been prepared by the simple melt-compounding approach.A fine and homogeneous dispersion of MWNTS throughout PA6 matrix is observed by transmission electron microscopy.Scanning electron microscopy observation on the fracture surfaces of the composites shows not only a uniform dispersion of MWNTS but also a strong interfacial adhesion with the matrix,as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTS) in the matrix and by the absence of debonding of CNTS from the matrix.Beadlike morphology is also observed along the stretched CNTS and their bundles,probably indicating the anchoring locations of the CNTS defects (within the beads) along the tubes where the PA6 matrix has strong interfacial interactions with the CNTS,thus being favorable to stress transfer from polymer to CNTS.Mechanical testing (by tensile and nanoindentation tests as well as dynamic mechanical analysis) shows that,compared with neat PA6, the elastic modulus and the yield strength of the composite are greatly improved by about 214% and 162%,respectively,with incorporating only 2 wt % MWNTS.In addition,a unique crystallization and melting behavior of MWNTS/PA6 composites are observed and discussed by combining differential scanning calorimetry and X-ray diffraction;that is,only the R-form crystals are observed in MWNTS/PA6 composites,which is quite different from the case observed in PA6/clay nanocomposites.

The structural evolution and properties of poly(9,9-dihexylfluorene-alt-2,5-dialkoxybenzene) with different lengths of alkoxy side chains on phenylene have been systematically investigated by means of thermogravimetric analysis (TGA),X-ray diffraction (XRD),differential scanning calorimetry (DSC),polarizing light microscopy (PLM),atomic force microscopy (AFM),and cyclic voltammetry (CV) techniques.The polymer self-organizes into a lamellar structure consisting of both two- and one-layer packing,and the two-layer packing style is the dominant structure.In addition,the two-layer and one-layer packing structures also accompany the presence of planar stacking and/or crystalline and noncrystalline structures,thus maintaining the stability of the packing. PF6OC6 shows three ordered phases (two crystalline phases and one nematic phase) during the heating process.With further increase of the length of alkoxy side chains, only two ordered phases (one crystalline phase and one nematic phase) are observed and the polymers show a melting-recrystallization phenomenon,which is steadily inhibited as the length of the alkoxy side chains increases.The optical and electrochemical properties of the polymers do not exhibit noticeable dependence on the length of the alkoxy side chains.However,the thermal stability,the vibronic structures, and the full width at half-maximum (fwhm) in photoluminescence spectra of the films gradually decrease,and the oxidation onset potentials and the corresponding HOMO energy levels slightly increase with increasing length of alkoxy side chains on phenylene.These results indicate that the length variation of alkoxy side chains does not change the electronic structure of the polymer backbones,but remarkably affects the microphase separation between the flexible side chains and the conjugated backbones.

Multi-walled carbon nanotube (MWCNT)/polyetherimide (PEI) nanocomposite films have been prepared by casting and imidization.A homogeneous dispersion of MWCNTs throughout the PEI matrix is observed by scanning electron microscopy of fracture surfaces,which shows not only a fine dispersion of MWCNTS but also strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTS) in the matrix and by the absence of debonding of CNTS from the matrix.Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperature of PEI increases by about 10℃ by the addition of 1 wt% MWCNTS.Mechanical testing shows that for the addition of 1 wt% MWCNTS,the elastic moduli of the nanocomposites are significantly improved by about 250% while the tensile strength is comparable to that of the matrix.This improvement is due to the strong interfacial interaction between the MWCNTs and the PEI matrix which favors stress transfer from the polymer to the CNTS.

Analysis of the nonisothermal melt and cold crystallization kinetics of poly (aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC).The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK.And,the Ozawa analysis,when applied to this polymer system,failed to describe its nonisothermal crystallization behavior.A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation.By evaluating the kinetic parameters in this approach,the crystallization behavior of PEEKK was analyzed. According to the Kissinger method,the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization,respectively.

Nanoindentation technique has been used to investigate the mechanical properties of exfoliated nylon 66 (PA66)/clay nanocomposites in present study.The hardness, elastic modulus and creep behavior of the nanocomposites have been evaluated as a function of clay concentration.It indicates that incorporation of clay nanofiller enhances the hardness and elastic modulus of the matrix.The elastic modulus data calculated from indentation load-displacement experiments are comparable with those obtained from dynamic mechanical analysis and the tensile tests.However,the creep behavior of the nanocomposites shows an unexpected increasing trend as the clay loading increases (up to 5 wt%).The lowered creep resistance with increasing clay content is mainly due to the decrease of crystal size and degree of crystallinity as a result of clay addition into PA66 matrix,as evidenced by optical microscopy and X-ray diffraction. At lower clay concentration (here ≤5 wt%),morphological changes due to addition of clay plays the dominant role in creep behavior compared with the reinforcement effect from nanoclay.