Paper Title
Effect of Surfactant Concentration on Surface Modification of Layered Double Hydroxides

Abstract
Silylationis an effective method to modify the surface of layered double hydroxides (LDH) used for formulation of clay-based nanocomposites and polymer-based adhesives.In this work, a series of magnesium and aluminum (MgAl)LDH intercalated withanionic surfactant, sodium dodecyl sulfate (SDS),were synthesized via co-precipitation method, followed by chemical grafting withaminopropyl(triethoxy)silane (APS) via silylation. The effect of SDSconcentration on the surface modification of MgAl LDH was investigated by varying a SDS/Al molar ratio of 0.6–1.2.The resulting modified LDH samples were characterized using various techniques. Fourier transform infrared spectroscopy revealedthat the interlayercarbonate (CO32−) and nitrate (NO3−)anions were replaced by the SDS molecules.The presence of aminopropyl groupschemically grafted onto the LDH surfacewere confirmed by the Si-O stretching vibrationbands. Accordingly, X-ray diffraction indicated an expanded interplanar spacing of (003) plane of LDH phase. 29Siliconnuclear magnetic resonance spectroscopy suggested thatAPS was mainlydispersed as monodentate speciesat the SDS/Al molar ratio of 1.2. As a result, this SDS concentration enhanced the surface hydrophobicity of modified LDH as evidenced by water contact angle measurement. It can be concluded that the structural properties, bonding modes of functional group, and surface hydrophobicity of LDH can be readily tunedby changing the concentration of anionic surfactant. Keywords - Layered double hydroxides, Modification, Intercalation, Silylation