@article { ISI:000231426000052, title = {Layered inorganic-organic clay-like nanocomposites rearrange to form silsesquioxanes on acid treatment}, journal = {Journal Physical Chemistry B}, volume = {109}, number = {33}, year = {2005}, month = {AUG}, pages = {16034-16039}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The formation of talc-like compounds by the condensation of organotrialkoxy silanes with magnesium hydroxide has been recently reported. These represent layered hybrid nanomaterials that have a layer thickness of around 1 nm, have organic moieties covalently linked to the layer surfaces, and are called {\textquoteleft}{\textquoteleft}organoclays.{\textquoteright}{\textquoteright} We show that such compounds are sensitive to acid treatment. When a phenylclay is treated with hydrochloric acid, magnesium leaches out, destroying the layered structure. The extent to which magnesium is leached out is a function of the time of the acid treatment and the concentration of the acid used. Magnesium leaches out rapidly when the concentration of acid used to treat the phenyl-clay is higher, and the extent of structural magnesium that is leached out is also higher for higher acid concentrations. Removal of the magnesium rearranges the structure of the phenyl-clay to form oligomeric phenylsilsesquioxanes. FTIR and NMR suggest that the silsesquioxanes formed by acid treatment of the phenyl-clay comprise a mixture of ladderlike and cagelike structures.

}, issn = {1520-6106}, doi = {10.1021/jp0526400}, author = {Kumaraswamy, Guruswamy and Deshmukh, Yogesh S. and Agrawal, Vikrant V. and Rajmohanan, P.} } @article { ISI:000231573100016, title = {Polycondensation in liquid crystalline phases of nonionic surfactants. Kinetics and morphology}, journal = {Polymer}, volume = {46}, number = {19}, year = {2005}, month = {SEP}, pages = {7961-7968}, publisher = {ELSEVIER SCI LTD}, type = {Article}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND}, abstract = {

We have investigated acid-catalyzed polycondensation of alkoxysilane monomers in liquid crystalline phases of nonionic CnEm surfactants. The liquid crystalline phase is retained when the monomers polymerize. The high molecular weight molecules formed phase separate from the mesophase and are subsequently organized by it to form micron-sized particles. A variety of particle morphologies are formed by organization of the polymer particles in the mesophase. For condensation of dimethyldimethoxysilane (DMS, with trimethoxysilane, TMS as crosslinker) in hexagonal and lamellar phases, specific reaction conditions, viz. slow condensation kinetics and low crosslink density, give rod-like particles in hexagonal phases and sheet-like structures in lamellar phases. However, when higher acid concentrations are used, the reaction kinetics accelerates and irregular particles form. Irregular particles also form when the fraction of trifunctional crosslinker is increased, and finally complex flower-like structures form for condensation of trimethoxysilane in the hexagonal phase. The particle morphology formed is crucially dependent on the details of the polycondensation rate, crosslinker density and surfactant-monomer/oligomer interactions. (c) 2005 Elsevier Ltd. All rights reserved.

}, keywords = {nonionic, surfactant, templated synthesis}, issn = {0032-3861}, doi = {10.1016/j.polymer.2005.07.001}, author = {Kumaraswamy, Guruswamy and Wadekar, M. N. and Agrawal, Vikrant V. and Pasricha, R.} } @article { ISI:000256290100015, title = {Composites of polypropylene with layered Mg-silsesquioxanes show an unusual combination of properties}, journal = {Industrial \& Engineering Chemistry Research}, volume = {47}, number = {11}, year = {2008}, month = {JUN}, pages = {3891-3899}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We report the synthesis of vinyl modified magnesium silsesqiuoxanes ({\textquoteright}{\textquoteright}vinyl clay{\textquoteright}{\textquoteright}), and the formation of their composites with isotactic polypropylene (iPP) by melt compounding. Vinyl clay is a layered compound with a layer thickness of approximately 1 nm. Vinyl clay does not exfoliate in iPP; rather, it disperses to form a network that exhibits a characteristic low frequency solid-like plateau in the elastic modulus in dynamic melt theological measurements. Strangely, vinyl clay also plasticizes iPP-there is a decrease in the high frequency complex viscosity. The decrease in the complex viscosity is higher at higher frequencies, suggesting the influence of slip at the iPP-vinyl clay interface. The combination of the low frequency elastic plateau and plasticization makes the vinyl clay composite significantly more shear thinning than the matrix iPP. In the solid state, vinyl clay-iPP composites exhibit increased tensile modulus (showing approximate to 50\% increase for a 5\% loading), but surprisingly, no corresponding decrease in the elongation at break. Thus, while microstructural characterization indicates that only a small fraction, if any, of the vinyl clay is exfoliafed, the enhancement in mechanical properties is similar to that observed for iPP-exfoliated montmonillonite nanocomposites. Our compounding protocol is unable to effectively disperse the clay in the iPP at clay loadings greater than about 7.5\%. Therefore, the low frequency plateau in the melt elastic modulus and the solid tensile modulus increase with clay loading until 7.5\% but exhibit a nonmonotonic decrease at higher clay loadings.

}, issn = {0888-5885}, doi = {10.1021/ie071658p}, author = {Kumaraswamy, Guruswamy and Deshmukh, Yogesh S. and Agrawal, Vikrant V. and Nisal, Anuya} }