Organization of mixed dimethyldioctadecylammonium and choline modifiers on the surface of synthetic hectorite

• Published in: Journal of colloid and interface science 2013-11, Vol.409, p.72-79
• Main Authors: Andriani, Yosephine, Jack, Kevin S., Gilbert, Elliot P., Edwards, Grant A., Schiller, Tara L., Strounina, Ekaterina, Osman, Azlin F., Martin, Darren J.
• Format: Article
• Language: English
• Subjects: ammonium compounds; Chemistry; Choline; Choline - chemistry; Conformation; Dual-modified organoclay; Exact sciences and technology; Fourier transform infrared spectroscopy; General and physical chemistry; hydrophobicity; Mixed surfactants; Nanocomposites; Nanomaterials; Nanostructure; Nuclear magnetic resonance; nuclear magnetic resonance spectroscopy; Organizations; physical chemistry; polymer nanocomposites; Polyurethane nanocomposites; polyurethanes; Quaternary Ammonium Compounds - chemistry; reflectance; Self assembly; separation; silicates; Silicates - chemical synthesis; Silicates - chemistry; Solid-liquid interface; stable isotopes; surface interactions; Surface physical chemistry; Surface Properties; Surfactants; thermogravimetry; thermoplastics; X-ray diffraction
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2013.07.055

•Dual-modified organoclays have demonstrated advantages in nanocomposites.•The characterization of dual-modified organoclays is thus crucial yet challenging.•Synthetic hectorite was modified with mixed polar (P) and nonpolar (NP) surfactants.•NP domains with some degree of P/NP mixing were observed at the clay surface.•The effects of P/NP molar ratios on the morphology of organoclays were elucidated. Understanding the nature of mixed surfactant self-assembly on the surface of organoclays is an important step toward optimizing their performance in polymer nanocomposites and for other potential applications, where selective surface interactions are crucial. In segmented thermoplastic polyurethane nanocomposite systems, dual-modified organoclays have shown significantly better performance compared to their single-modified counterparts. Until now, we had not fully characterized the physical chemistry of these dual-modified layered silicates, but had hypothesized that the enhanced composite performance arises due to some degree of nanoscale phase separation on the nanofiller surface, which enables enhanced compatibilization and more specific and inclusive interactions with the nanoscale hard and soft domains in these thermoplastic elastomers. This work examines the organization of quaternary alkyl ammonium compounds on the surface of Lucentite SWN using X-ray diffraction (XRD), thermogravimetric analysis (TGA), attenuated total reflectance Fourier-transfer infrared (ATR FT-IR), 13C cross-polarization (CP)/magic angle spinning (MAS) nuclear magnetic resonance (NMR), and small-angle neutron scattering (SANS). When used in combination with choline, dimethyldioctadecylammonium (DMDO) was observed to self-assemble into discontinuous hydrophobic domains. The inner part of these hydrophobic domains was essentially unaffected by the choline (CC); however, surfactant intermixing was observed either at the periphery or throughout the choline-rich phase surrounding those domains.