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This study describes the preparation of polycarbonate (PC)/multiwalled carbon nanotube (MWCNT) composites by melt processing the PC and PC/MWCNT master batch at 260°C. The PC/MWCNT master batch was prepared using ultrasonic mixing the carboxylic acid containing MWCNT and PC in a tetrahydrofuran (THF) solution. The HRTEM images of PC/MWCNT master batch and PC/MWCNT nanocomposites show that the MWCNT is well separated and uniformly distributed in the PC matrices. Mechanical properties of the fabricated nanocomposites measured by dynamic mechanical analysis indicate significant improvements in the storage modulus when compared with that of pure PC matrix. The conductivities of 2 and 5 wt% PC/MWCNT nanocomposites are more than four and seven orders in magnitude higher than that of PC without MWCNT, respectively. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

The detail of nanoscaled dispersive behavior for layered clay in polyimide was first illustrated using temporal analyses. The layered structure of pristine clay remained in the poly(amic acid) and polyimide matrixes almost throughout curing process. However, the clay was mutilated by polymer chain motion during the process (cluster size reduced from ∼700 to ∼298 nm). On the other hand, organo-clay modified with octadecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride initially exfoliated in the poly(amic acid) solution (d-spacing >42 nm). At room temperature ∼200 °C, the layered structure of the clay recovered due to loss of solvent and poly(amic acid) chains intercalating into the organo-clay interlayer (d ∼ 3.49 nm). After polyimide fully formed at 350 °C, organo-clay d-spacing decreased to ∼2.27 nm. The reduction of d-spacing was ascribed to some of the polyimide molecular chains being squeezed out of the organo-clay interlayer since hydrogen bonds between the organo-clay and poly(amic acid) molecules diminished. The change in organo-clay cluster size behaved like pristine clay, finally decreasing to ∼367 nm after polyimide formed completely. The relatively large size of the organo-clay clusters in polyimide was ascribed to the confinement effect of polymer chain motion by organo-clay since the chains were frozen in the organo-clay interlayer.

X-ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)-modified maleic-anhydride-grafted polypropylene/clay (PP-g-MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP-g-MA (designated as PP-g-HMA) and then mixing the PP-g-HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X-ray diffraction data and transmission electron microscopy images of PP-g-HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP-g-HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP-g-HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three-dimensional crystal growth to a two-dimensional spherulitic growth. Mechanical properties of PP-g-HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP-g-HMA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3242–3254, 2005

Colloidal ZnSe quantum dots were successfully synthesized from ZnO in a lauric acid/hexadecylamine mixture. X-ray diffraction patterns indicated that the ZnSe quantum dots possess a wurtzite structure. Transmission electron microscope images of the quantum dots showed that the average diameter are in the range of 25∼60 A. The size-dependent photoluminescence was controlled from 400 to 440 nm with the quantum yields of 6∼10% at room temperature. After passivation with 1.8 monolayer of ZnS overcoat by a traditional two-step method, the quantum yields of ZnSe/ZnS QDs are increased ∼4.5-fold (quantum yield ∼32%). An in-situ method of overcoating was done by directly injecting TOPS into the flask containing ZnSe, ZnO/lauric acid/hexadecylamine, and TOPSe. The photoluminescence quantum yields were improved ∼3.8-fold after introduction of 1.6 monolayer ZnSeS overcoat to the ZnSe QDs.

The copolymerization of styrene and maleic anhydride in ethyl methyl ketone as solvent and with benzoyl peroxide as initiator at 60–80°C in the entire feed composition range was studied. The resulting copolymers appear to have negative and positive deviations from alternation as determined by use of elemental analysis. The experimental data were found to fit a three-reactivity-ratio copolymer composition equation from the penultimate model. The inclusion of the reactivity ratio, kSM (=kSMM/kSMS), in addition to rSS (=kSSS/kSSM) and rMS (=kMSS/kMSM), allows prediction of a positive deviation from the alternation, i.e. the mole fraction of maleic anhydride in the copolymer being higher than 0,5.