PS nanocomposites

FIGURE 11.27 Decomposition temperature as a function of MMT loading of PS nanocomposites. The MMT is modified with (filled square) dimethyl(hydrogenated tallow alkyl)benzyl ammonium ion, (filled circle) dimethyl di(hydrogenated tallow alkyl) ammonium ion, (filled triangle) dimethyl(hydrogenated tallow alkyl) 2-ethylhexyl ammonium ion, and (open square) NaMMT. (From Doh, J.G. and Cho, I., Polym. Bull., 41, 511, 1998. With permission.)... 

In the work of Wilkie et al.,55,56 oligomers of styrene, vinylbenzyl chloride, and diphenyl vinyl-benzylphosphate and diphenyl vinylphenylphosphate (DPVPP) have been prepared and reacted with an amine and then ion-exchanged onto clay. The resulting modified DPVPP clays have been melted blended with polystyrene and the flammability was evaluated. XRD and TEM observations proved the existence of intercalated nanocomposite structures. Cone calorimeter tests have shown a substantial reduction in the PHRR of about 70% in comparison with pure PS. According to the authors, this reduction was higher than the maximum reduction usually obtained with PS nanocomposites. Other vinylphosphate modified clay nanocomposites were also elaborated. The reduction in PHRR was greater with higher phosphorus content than for DPVPP. Consequently, the reduction in PHRR seemed attributed to both the presence of the clay and to the presence of phosphorus. 

A characterization of copper/porous silicon (Cu/PS) nanocomposites fomied by an immersion displacement method is presented. Morphology and structural properties of Cu-PS samples were analyzed using SEM and XRD techniques. The SEM study demonstrates the complicated structure of the Cu/PS samples. The XRD study confirms that deposited Cu is polycrystalline. Copper deposition time has a strong influence on Cu crystal size and the Cu/PS composition. 

The morphology of fresh PS and Cu/PS nanocomposites was studied by a Hitachi-S4800 SEM. The crystallographic structure of Cu/PS samples was investigated with a X-ray diffractometer with the Cu Ka radiation. 

Figure 2, XRD patterns of Cu/PS nanocomposites formed after 4 s (a) and 180 s (b) immersion of PS layer into the CUSO4 + HF + H2O solution.

SEM and XRD data show that Cu/PS nanocomposites are polycrystalline. Large Cu grains deposited at the surface of PS are crystals while small Cu nanograins are mostly oriented randomly with small texturing. 

PS layers have been impregnated in chloride solution of europium for more than 2 hours to ensure total infiltration of Eu. Just after the infiltration, the sample was dried by nitrogen gas. In a second step, the PS layer was impregnated in a mixture of EuCl3 ethanol and TbChrethanol solutions to form (Eu +Tb /PS nanocomposites. Three parts of the same PS sample impregnated in the same conditions. We have used three different concentrations of (EuCla+TbCls) ethanol solution (C, 2C and 4C). 

Figure . PL spectra of PS layer (a), Eu /PS nanocomposite (b) and after annealing at 1000°C (c).

Figure 3. Cross section TEM image of the Eu /PS nanocomposites after annealing at 1000°Cfor60s.

The PL spectra for A,exc= 488 nm of (Eu +Tb )/PS nanocomposite are shown in Fig. 5a. By increasing the concentration of Eu -Tb solution, we show an increase of the PL intensity for Eu and Tb " emission. Moreover, we confirm the RBS results in Fig. 4. It was found also, that the PL intensity of PS emission increases when the concentration of the solution increases. Nevertheless, the Eu ions in PS are directly excited by absorption of laser energy. The same result has been shovm with Tb ions in PS [6,8]. Each behavior suggests that energy transfer can occur from rare earth (Eu and Tb ) ions to Si nanocrystallites. 

The dispersion of 120 nm MPS-modified silica particles in styrene with a subsequent miniemulsion polymerization, initiated by AIBA (azodiisobutyramidine dihydrochloride) and stabilized by CTAB, led to cationic core-shell particles. Adding titanium tetraisobutoxide to the system generated a thin titania shell around the silica/PS nanocomposites [127]. 

Park and co-workers presented a surface TLIRP to synthesize PS-functionalized MWCNTs in toluene at 100 °C for 24 h. FTIR spectroscopy, XPS, SEM and TEM measurements were employed to investigate the as-prepared core-shell nanostructure hybrid nanocomposites. The MWCNT-PS nanocomposites possess good dispersibility in common organic solvents. 

Desorption kinetics of oxidized igfrom FesOVT PS nanocomposite surface. 

Figure 9.19 Frequency dependence of (a) dielectric constant (cO and real permeability ip. ), (b) dielectric loss (e")> and magnetic loss (p") of PANI-MWCNT/PS nanocomposites with increasing loading (10, 20, and 30 wt.%) of PANl-MWCNT filler. Reprinted from Ref [11] with permission from Elsevier.

Advances in nano-material research have opened the door for transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. Transparent electrodes are necessary components in many modem devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, such as indium tin oxide. A review exploring these innovations in transparent conductors and the emerging trends is presented recently (Hecht et al. 2011). Electrical conductivity in PS nanocomposites with ultralow graphene level was found to enhance significantly (Qi et al. 2011). 

Recently, Tiwari and Paul (2011 a) carried out detailed studies on the effect of PP viscosity on the dispersed phase particle size, stability of dispersed phase morphology upon annealing, phase inversion behavior, and changes in the mechanical properties of PP/PP-g-MA/MMT/PS nanocomposites prepared with different molecular weight grades of PP. PP-g-MA was added to PP to facilitate dispersion of organoclay in the nonpolar PP moreover, it also provides better reinforcement effect when PP forms the continuous phase. 

The preparation of ZnO/ PS nanocomposites preceded as follows [112] First, 110 mg bare ZnO or 110 mg PMMA-grafted ZnO were added into a three-necked bottle. Then, 10 mL styrene was added into the reactor. The mixture was stirred with the aid of ultrasonic oscillation until a uniform dispersion of the ZnO particles in styrene was attained. Afterwards, 36 mg azobisisobutyronitrile (AIBN) was added into the reactor as initiator. The subsequent polymerization was conducted at 85°C for 2.5 h. Then, the obtained composites were dried under vacuum for 24 h. The differential scanning calorimetry (DSC) heating curves of neat PS, PS/ZnO (bare), and PS/ZnO (PMMA grafted) are shown in Fig. 10. DSC traces in Fig. 10a show that neat PS has a lower glass transition temperature (Tg = 87.7°C) than PS/ZnO (bare, 7 g = 97.9°C) and PS/ZnO (PMMA grafted, Tg = 95.3°C). This behavior can be explained by the restricting effect of the nanoparticles in polymer. ZnO... 

Fig. 4 (a) Image of low density polyethylene (LDPE) and polystyrene (PS) nanocomposite films incorporating sepiolite modified with Ag and Au nanoparticles, (b, c) Representative TEM images of those nanocomposites. Reproduced from [61] with permission of The Royal Society of... 

Figure 1.20 Schematic of the nitroxyl-based organic cation modification of montmorillonite surface and generation of PS nanocomposite. Reproduced from Ref [44] with permission from American Chemical Society.

The choice of the organic modification is probably the most important factor in order to achieve good dispersion in PS nanocomposites prepared through in-situ polymerization [8]. 

Taking a different tact, a zwitterionic surfactant (4) was used to modify MMT for PS nanocomposites [7]. Zwitterionic surfactants contain both a cation and an anion. The claimed advantage of using this surfactant was that in certain solvents... 

The commonality between the surfactants described in this section is that they do not contain a reactive group which is capable of reacting with styrene. It has been found that for these types of nonreactive surfactants, although styrene monomer can intercalate between the clay layers, exfoliated morphologies have not been achieved for in-situ polymerized PS nanocomposites. 

Using a sHghtly different tact, Akat et al. investigated exchanging a chain transfer agent (diethyl octyl ammonium ethylmercaptan bromide, 42) [50] onto MMT prior to the free radical polymerization of PS. They found that while PMMA nanocomposites formed with this modified clay led to exfoHated structures, PS nanocomposites led to intercalated morphologies. 

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