Organoclay Nanoplatelets at the Air/water Interface
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Organoclay Nanoplatelets at the Air/water Interface Kwanwoo Shin*, Yimin Zhang, Henry White, Miriam H. Rafailovich, Jonathan Sokolov and Dennis Peiffer1 Materials Research Science and Engineering Center, Department of Materials Science and Engineering, State University of New York at Stony Brook, New York 11794-2275 1 Exxon-Mobil Research and Engineering Co., Annandale, NJ 08801 *Current Address: NIST Center for Neutron Research, NIST, Gaithersburg, MD 20899-8562 ABSTRACT We have demonstrated that films of single clay platelets can be produced by the Langmuir technique where a solution of organoclay particles dissolved in xylene was spread at the air water interface. The total thickness of the layer was found to be 21 ± 3Å which is in good agreement with previous X-ray diffraction data. Scanning probe microscopy showed the individual platelets to be rectangular in shape with an aspect ratio in excess of 100 to 1 and of uniform organic surfactant coverage. INTRODUCTION Inorganic clay nanoparticles consisting of layered silicates, have been of scientific and technological interest, since clay-modified materials exhibits dramatic physical improvements and unique functionalities.1-8 It is well established that small organic molecules can diffuse into interlayer cations, and rendering the otherwise hydrophilic silicate packets organophilic.1,4 These organoclays are then easily exfoliated when they are mixed with organic solvents. On the other hand, exfoliation with polymers is much more difficult to achieve due to the entropic barrier encountered by large molecules trying to penetrate into the interstices of the galleries. Hence a large experimental effort exists in trying to develop new ways of producing layered polymer clay nanostructureswith molecular level control of the layer ordering and spacing. 1,4,5,6,9 One promising approach for producing ordered layered polymer/clay structures is the Langmuir-Blodgett method. With this method films are prepared by spreading the clay from solution at the air water interface.7,8 The films are then transferred to solid substrates. This procedure can be repeated several times to prepare materials specifically tailored for different applications. The structural properties of these films such as molecular orientation, degree of exfoliation and ordering depend on the interaction between the materials and substrates or subphases. Hence, in order to understand these factors, in-situ X-ray reflectivity was performed at the air/water interface and scanning probe microscopy was used to characterize the films lifted onto solid substrates. Here we report the correlation of the phase diagram and the structure of the films as determined by these two techniques. EXPERIMENTAL DETAILS Materials Commercially available organoclay (Bentone-34), consisting of SiO2 (~50%) and various oxides (Al2O3, MgO, CaO, Na2O, K2O and Fe2O3) was used. The intercalation organic KK8.4.1
molecules were dimethyl, dehydrogenatedtallow ammonium (2M2HT). The ratio of inorganic part to organic modifier is 62:38 and the
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