SVIBOR - Project code: 1-07-133

MINISTRY OF SCIENCE AND TECHNOLOGY

Strossmayerov trg 4, HR - 10000 ZAGREB
tel.: +385 1 459 44 44, fax: +385 1 459 44 69
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Project code: 1-07-133


EQUILIBRIA AND SOLID/LIQUID PHASE TRANSITIONS


Main researcher: TEŽAK, ĐURĐICA (49440)


Assistants
Type of research: basic
Duration from: 01/01/91. to 12/31/96.
Papers on project (total): 55
Papers on project quoted in Current Contents: 12
Institution name: Prirodoslovno-matematički fakultet, Prirodoslovni odjeli, Zagreb (119)
Department/Institute: Laboratory of Physical Chemistry
Address: Marulićev trg 19/II,p.p.163
City: 10000 - Zagreb, Croatia
Communication
Phone: 385 (0)1 446 528
Fax: 385 (0)1 446 528
Summary: The unusual kinetics of aggregation of dodecylbenzenesulfonate amphiphilic micelles in aqueous solution was demonstrated using light scattering, microscopic and X-ray diffraction data. Dynamics of the formation of lamellar mesophasis is explained as a consecutive process of growth, fluctuation of micellar shapes and aggregations. These long-range driving forces cause the maximum aggregation rate to occur during the periods of non-equilibrium states, as well as the zero aggregation rate in the periods of steady states. Applying fractal approach, some aggregates can be considered as multifractals and some as fractals; according to the related slopes of straight lines in a "lg I(Q) vs. lgQ" plot in the case of multifractals the values are higher then 3. The lyotropic mesophases binary systems of surfactants in water: n-alkylbenzenesulfonates (C8-C12), two chain C12-surfactants, and dodecylbenzenesulfonic acid, were investigated. The phase diagrams were determined using crossed polarizers, 2H-NMR spectroscopy and polarization microscopy. Besides lamellar and inverse cubic phases, new nematic lyotropic phases have been found, presenting precursors for the lamellar phases, and exhibiting were fast aligment in a magnetic field. The formation of colloidal and liquid crystalline aggregates of aluminium dodecylbenzenesulphonates is interpreted by fractal approach. A model of multiscalling for the calculation of fractal dimension in the formation of the liquid crystalline phases is proposed. The molecular organization in lamellar mesophases was proposed on the basis of dynamic and static light scattering, polarizing and transmission electron microscopy, and X-ray diffraction measurements. The basic symmetries of the dynamics of formation and structures of the lamellar bilayers and multylayers of the surfactants were found to be consistent from the beginning of the precipitation process from the homogeneous solution until the aggregation to the macroscopic aggrefates due to the self-similarity. The formation of colloid and liquid crystalline aggregates in aqueous solutions including electrolytes and alkylbenzenesulfonates at 20 C, was indicated by related solubility products of the order of magnitude of 10 E-12 for bi-valent ions, and of 1E-17 for tri-valent ions. The investigation of precipitation effects performed in natural sea-water of different salinities including surfactants and heavy metal ions (mercury(II)-, lead(II)-, calcium(II)-, ferric(III)-, aluminium(III)-ions), showed noticable synergism, expressed mostly in the case of mercury. The formation and structural characteristics of alkaline earth fatty acid salts was indicated by solubility temperature dependence, and by enthalpy-entropy changes. Scientific activities of the staff of the Chemistry Department at the Faculty of Science of the University of Zagreb was analysed throughout the seventeen-year period of 1976-1992, and it was confirmed that the publicity yield can be related to the world average.

Keywords: alkylbenzenesulfonates, lyotropic mesophases, nematic phases, liquid crystals, micelles, phase diagrams, precipitation, solubility product, sea-water, surfactant, fatty acids, heavy metal ions, aggregation, lamellar bilayer and multilayer, self-similarity

Research goals: Colloid chemical, particulary physico-chemical measurements, are involved in almost all spheres of science, technology, pharmacy, medicine and investigations of development, growth, and patology mechanisms of living organisms. The goals of the proposed project have been planed to be the investigations of physico-chemical processes of the dynamics and structure of surfactant aggregation. Surfactant applied in the investigations, is a product of the chemical industry "Chromos", Zagreb (dodecylbenzenesulfonic acid, HDBS), which is used in the production of household detergents, as well as in the industrial processing, and because of that it is a subject of ecological toxicology. The precipitation equilibria in the aqueous solutions involving HDBS and heavy metal ions in natural sea-water, were investigated, presenting the simulation of the related processes in the Kaštela bay, as well as in the other natural aquatic systems. A synergistic effect of the enviroment (aquatic systems and sediments) have been shown. It is a positive result of investigation of solubility/precipitability equilibria, the defining of the critical parameters of the extraction of heavy metals from the aquatic systems by the precipitation with the detergent. The objectives of the investigation of the self-association of amphiphiles in water (alkylbenzenesulfonates in our case) have been the formation and transformations of phases: micelles, liquid crystals, emphasizing lyotropic nematics, which present the precursors of flat and bended lamellar phases. Self-association of amphiphiles plays very important role in the investigation of biological systems due to their capability of forming membranes with hydrophilic polar groups at a water interface. In addition, surfactants in water, or in oil-water media, self-associate to form micelles, vesicles, liposomes, continous phases, liquid crystals; it is the reason that such investigation play very important role in the drug production and other pharmaceutical products. Recent work on this project improved the knowledge on the kinetics of the formation, sizes, shapes, transformations, and the structure of micelles and lyotropic liquid crystals alkylbenzenesulfonates. The cooperation with the domestic pharmaceutical industry will be welcome.

COOPERATION - PROJECTS


  1. Name of project: > "DEFINED CLUSTERS OF ASSOCIATION COLLOIDS IN AQUEOUS SOLUTION'
    Name of institution: Universitaet Bayreuth, Lehrstuhl fuer Physikalische Chemie
    City: Bayreuth, Njemačka

COOPERATION - INSTITUTIONS


  1. Name of institution: Institut Rugjer Bošković
    Type of institution: State institute
    Type of cooperation: Joint publishing of scientific papers
    City: 10000 - Zagreb, Croatia
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