Nano-clays ultrasonics

Over the past decade extensive work has been done to develop a novel extrusion process with the aid of high power ultrasound [18-22], A number of studies on the effect of ultrasound on polymers have been published and reported in various review articles and books. It was shown that ultrasonic oscillations can breakdown the 3-D network in vulcanized rubber within seconds. Ultrasound was found to improve the compatibilization of immiscible plastic blends, plastics/rubber and rubber/rubber blends during extrusion process [23]. In recent years, use of ultrasound to disperse nanofdler in a polymer matrix is gaining attention. Ultrasound helps in rapid exfoliation and intercalation of nano-clay in a polymer matrix [24]. 

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

The intercalation of nano-gold into clay layers comprised two steps. The first step was the intercalation of the polymer (surfactant) into clay matrix for increasing the interlamellar space between the clay layers. The second step was the replacement of the intercalated polymer (surfactant) by Au nanoparticles by adding different amounts of nanoparticles to the polymer (surfactant)/clay composite. Both steps were performed by applying ultrasonic irradiation. The solution was sonicated at 20 kHz, 500 W. The intercalation progress was monitored as a function of time. The precipitated nano-Au/intercalated product was separated by centrifugation, washed with water and dried under vacuum overnight. After that samples were calcined in air at 800 °C for 4 h. 

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