Intercalation of silsesquioxane surfactant in layered double hydroxide for silicone rubber composites: Enhancing interfacial interactions toward improvement of mechanical, thermal, and gas barrier properties

The incorporation of two-dimensional layered metal hydroxides (LDHs) into nonpolar silicone rubber (SR) is not yet universal, mainly because of their originally hydrophilic surface and limited interlamellar galleries that make nanoparticle dispersion and intercalation of polymer segments more difficult. In this work, we develop a modified Ca-Mg-Al LDH form by conjugating the ternary Ca-Mg-Al LDH with silsesquioxane (SQ) surfactants containing benzoic acid moieties and polyethylene glycol chains via an in-situ intercalation process. The bulky anions conjugation to the hydroxide layers dictated both the surface hydrophobicity and interlayer spacing of the modified Ca-Mg-Al LDH, enabling strong inter-constituent interactions within the nanocomposites as well as extensive polymer penetration after incorporation into the SR matrix. The SR/modified LDH nanocomposites show excellent thermal stability and satisfactory mechanical properties due to the homogeneous dispersion and good compatibility of modified Ca-Mg-Al LDH. Moreover, we have observed that the shear-induced orientation of the nano-layered particles upon application of stress imparts a more notably decreased SR/LDH-SQ-40 gas transmission rate (reduced by 55% with respect to that in the unstretched composite films). This result also corroborates the better interfacial bonding and highly efficient load transfer between silsesquioxane-modified LDH and polymer in melt extrusion mixing of such composites.