The role of organic modification of layered nanosilicates on mechanical and surface properties of organic-inorganic coatings

The effect of alcohol- and amino-functional compatibilizers in nanocomposites of organic-inorganic (O-I) matrices with layered nanofillers (LN) was studied. The alcohol-functional compatibilizers are shown to have a marked influence on morphology, surface- and mechanical properties of the coatings prepared, in spite of the very small amount of both filler and compatibilizer (together 0.5 wt%). The studied O-I matrices were polyepoxy-functional polysiloxanes cured with organic diamines. Two commercial clays were used as LN in the concentration of 0.5 wt%: natural montmorillonite (Cloisite Na, abbreviated MNa) and Bentonite for water systems (BW). These clays were compatibilized by three hydroxyl-containing substances: Polyethylene glycol 4000, TWEEN 80, and tris(hydroxymethyl)aminomethane (TRIS). All compatibilizers improve the dispersion of the clay fillers, while TRIS always supports full exfoliation. They also cause an increase in the microroughness of the coatings and strongly modify their large-scale surface patterns. Mechanical properties are also strongly affected by the compatibilizers: toughness is increased, sometimes markedly, as well as stress at break. Tensile and shear moduli are reduced by the compatibilizers, while the glass transition temperature is specifically shifted to higher or lower values, sometimes markedly.