Improved dielectric and mechanical properties of polystyrene-hybrid silica sphere composite induced through bifunctionalization at the interface.

Hybrid silica spheres (HS) of size 270-350 nm with vinyl and aminopropyl surface groups were incorporated in polystyrene (PS), and its effect on dielectric properties, coefficient of thermal expansion (CTE), and strength of PS-HS composite was studied. Incorporation of HS in PS followed a decrease in the dielectric constant from 3.2 for PS to 2.6 for composite with 7.5 vol % HS. The decrease in the dielectric constant was attributed to (i) increased interfacial porosity, (ii) formation of anhydrous HS having low dielectric constant, during hot processing of the composites, and (iii) dispersion and preservation of the anhydrous HS in the hydrophobic matrix. The dielectric constant of the composites with HS content up to 7.5 vol % does not vary much with temperature in the range from -20 to 65 °C. These composites also exhibited reduced CTE and improved flexural strength/stiffness due to good interfacial bonding through HS vinyl groups and dispersion of the filler in the matrix. The dielectric loss increased with HS content, and the loss measured for 7.5 vol % PS-HS composite was 6 × 10(-3), as compared to 10(-4) for PS. At HS loading above 7.5 vol %, the tendency of HS to agglomerate and form percolated structure lead to an increase in the dielectric constant and decrease in the mechanical properties of the composites.

Micropatterned surfaces through moisture-induced phase-separation of polystyrene-clay nanocomposite particles.

We report micropatterned polystyrene-clay nanocomposite (PCN) surfaces with concavities by moisture-induced phase separation of PCN particles. Micropatterned film with concavity size of 800 nm to 1.3 microm and a high number density of 2 x 10(8) features/cm(2) was obtained by drop-casting PCN solution (20 mg/mL PCN/THF) under ambient relative humidity of 70-80%. It is proposed that water droplets were channeled through the hydrophilic interfaces between the PCN particles, and the two-dimensional array of concavities was formed by spontaneous phase separation due to the presence of rigid clay platelets. The concavity size and number density can be tuned by varying the solvent for PCN. Micropatterned film with concavity size in the range of 650 nm to 1.1 microm with a number density of 5 x 10(7) features/cm(2) was obtained using chloroform as solvent, whereas a concavity size of 150-740 nm and number density of 10(8) features/cm(2) were obtained using carbon disulfide.

Nanostructured multifunctional electromagnetic materials from the guest-host inorganic-organic hybrid ternary system of a polyaniline-clay-polyhydroxy iron composite: preparation and properties.

A nanostructured electromagnetic polyaniline-polyhydroxy iron-clay composite (PPIC) was prepared by oxidative radical emulsion polymerization of aniline in the presence of polyhydroxy iron cation (PIC) intercalated clays. Morphological observation through SEM, TEM, and AFM suggested the formation of self-assembled nanospheres of PIC with self-assembled PANI engulfed over PIC, and the presence of iron in PPIC was confirmed by the EDS analysis. XRD studies revealed that PPIC are comprised of exfoliated clay layers with PIC in the distorted spinel structure. Magnetic property measurements showed that saturation magnetization increased from 7.3 x 10(-3) to 2.5 emu/g upon varying the amount of PHIC content from 0 to 10%. Electrical conductivity measurements with the same composition were observed to be in the range of 3.0 x 10(-2) to 1.1 S/cm. Thermal stability studies using TGA in combination with DTG suggested that PPICs were thermally stable up to 350 degrees C. The interaction among clay layers, PIC, and PANI chains in PPIC were manifested from the studies made by FTIR and DSC analysis. The prospects for the direct application of this material are developing low-cost chemical sensors and also processable electromagnetic interference shielding materials for high technological applications.

Microvesicles through self-assembly of polystyrene-clay nanocomposite.

Polystyrene-clay nanocomposite (PCN) particles, which exhibited concentration dependent self-assembling property in THF were synthesized by in situ intercalative polymerization of styrene with vinyl POSS amine-modified organoclay. While the particles from dilute solution of 0.001 mg mL(-1) showed a lateral dimension of 190-800 nm and thickness of 120 nm, microvesicles of diameter of 2.5-3.5 microm and average membrane thickness of 85 nm were produced from solution concentration of 2.5 mg mL(-1) by consuming the particles. The particle possessed a sandwich structure consisting of polystyrene(PS)-POSS-intercalated clay tactoid of thickness of 12.6 nm at the core and PS chains growing from the tactoid surfaces on either side, exposing the hydroxylated edges of the silicate layers. Vesicle was formed by edge-edge association of the silicate layers so that the layers lie flat along the vesicle membrane. Guest-encapsulated vesicles were obtained when prepared from solutions containing guest molecules.

Bifunctionalized hybrid silica spheres by hydrolytic cocondensation of 3-aminopropyltriethoxysilane and vinyltriethoxysilane.

Facile, surfactant free synthetic strategy for bifunctionalized hybrid silica spheres (HS) with structural ordering is presented. HS was prepared by casting and drying of stable siloxane solution from hydrolytic co-condensation of 3-aminopropyltriethoxysilane (AS) and vinyltriethoxysilane (VS) with AS:VS mole ratio of 1:3 in ethanol/water mixture. Spheres of size in the range of 250 nm to 2.5 microm were produced by adjusting the concentration of reacted siloxane solution using ethanol. Characterization by FTIR, XRD, TGA, and DSC revealed that the HS was formed from coprecipitation of fully condensed polyhedral oligomeric silsesquioxane (POSS) bilayer and incompletely condensed siloxanes (SIL) produced during drying. Formation of POSS bilayer was confirmed by intercalating and stabilizing POSS within a smectite clay and characterizing the modified clay. XRD, FTIR, SEM, and HRTEM of HS heated to 170 degrees C revealed transformation from disordered into ordered lamellar structure of POSS bilayer assembly and siloxane network due to rearrangement and densification of low melting SIL.