engleski

Liquid crystalline phases determined by electron microscopy: adsorption of counterions on the liquid crystal/water interface

The investigation in this work represents an approach to the application of precipitation processes in a treating the natural eco-systems containing chemical pollutants including surface-active agents and heavy metal ions. Already a small concentration of the toxic cadmium in the sea water can cause the precipitation synergistic effect [1,2]. The precipitation reactions include the anionic and cationic macro constituents of the sea water and dodecylbenzenesulphonate ions (DBS). The structures of heterogeneous phases are both the crystalline and liquid crystalline. The determination of the phases can be performed by the polarized light microscopy (PLM), by the light microscopy with differential interference contrast (DIC), as well as by the scanning electron microscopy (SEM) and cryo transmission electron microscopy (Cryo-TEM). In this work the liquid crystalline structures were determined using SEM, and in addition, the quantitative analysis were performed of the elements within. The textures of the lyotropic liquid crystals from cadmium dodecylbenzenesulphonate in water and sea water solutions have been investigated by the polarized light microscope. In addition, the chemical composition and the structure of liquid crystalline phases have been determined using the qualitative and quantitative analysis with the energy detectors for the chemical elements on the SEM Jeol JSM-5800 at room temperature. The solubility product of the crystal form, kso = (3.6ą0.6)x10-12, was determined using light scattering method; the stoichiometric relation [Cd++] : [DBS-] = 1 : 2 was fully satisfied. This concentration relation was different in the case of the liquid crystal formation, [Cd++] : [DBS-] = 9 : 1, i.e., it is shifted towards higher cadmium concentration due to the sorption of cadmium into the viscous liquid crystal matrix. A good agreement of the results achieved by the complexometric analysis, atomic absorption, X-ray diffraction, as well as, thermogravimetric analysis, was found. These methods showed that the cadmium partly was included into the lamellar bilayers, and besides, it was partly crystallized within the liquid crystal matrix in the form of Ca-dodecylbenzenesulphonate and CdCl2. Due to the non-stoichiometric relation of the constituents in the liquid crystalline phase it can be assumed that some amount of cadmium has been adsorbed at negatively charged surface of the surfactant micelles. In the SEM picture the crystal of cadmium dodecylbenzenesulphonate taken from the liquid crystalline matrix in the sea water medium is represented. In this mapping picture the small monoclinic crystals can be seen that are loosely associated into the six-angled crystal’ habitus.. Using SEM the quantitative elementary analysis of cadmium and chlorine in the crystal showed that there the stoichiometric relationship does not exist, since the relation Cd : Cl = 70.07 : 29.93 (in percentage) with the standard correction factor of 0.98 and 0.94, respectively, was found. The related spectra showed the contents of elements within the liquid crystalline sample. LITERATURE: 1 M. Tudja, M. Galešić and Đ. Težak, Journal of Computer-Assisted Microscopy 9 (1997) 65-66. 2 Đ. Težak, O. Babačić, V. Đerek, M. Galešić, S. Heimer, V. Hrust, Z. Ivezić, D. Jurković, S. Rupčić and V. Zelović, Colloids Surfaces A: Physicochem. Eng. Aspects 90 (1994) 261-270.

Adsorption; Counterion; Liquid crystal/water interface

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