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    Characterization of Langmuir–Blodgett organoclay films using X-ray reflectivity and atomic force microscopy

    Year: 2008

    Journal: Journal of Colloid and Interface Science, Volume 318, Issue 1, 1 February 2008, Pages 103-109, 20111221

    Authors: Jaseung Koo, Seongchan Park, Sushil Satija, Aleksey Tikhonov, Jonathan C. Sokolov, Miriam H. Rafailovich, and Tadanori Koga

    Organizations: Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2275, USA, bCenter for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA, Consortium of Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA, Brookhaven National Laboratory, National Synchrotron Light Source, Beamline X19C, Upton, NY 11973, USA, Chemical and Molecular Engineering Program, State University of New York at Stony Brook, Stony Brook, NY 11794-2275, USA

    Monolayers of organoclay platelets were formed at the air/water interface using the Langmuir technique and were then investigated either by in situ or lifted onto Si wafers and studied ex situ, using X-ray reflectivity (XR) methods. The XR data showed that the surfactant molecules on the clay platelets formed a dense, self-assembled monolayer where the molecules were tilted at an angle of 35°±6° from the normal to the dry clay surface. The surfactant layers only covered a fraction of the clay platelet surface area, where the fractional surface coverage for the three clays studied (C6A, C15A, and C20A) was found to be 0.90, 0.86, and 0.73, respectively. These values were significantly higher than those estimated from the cation exchange capacity (CEC) values. Rather than being uniformly distributed, the surfactant was clustered in patchy regions, indicating that the surface of the clay platelets had both polar and non-polar segments. This heterogeneity confirmed the hypothesis which was previously invoked to explain the distribution of the clay platelets in melt mixed homopolymer and polymer blend nanocomposites.