COLL 412 |
| Dotchi Exerowa, Institute of Physical Chemistry, Institute of Physical Chemistry, Bulgarian Academy of Sciences, Acad. g., Bonchev str. bl 11, 1113 Sofia, Bulgaria |
| The colloidal stability is considered from the point of view of realization of a bilayer contact between interacting surfaces (phases) on the basis of model experimental studies and the Kashchiev-Exerowa theory of nanoscopically holes nucleation rupture of bilayers in contact with surfactant solution or insoluble monolayer. The main experiments are monitored by foam and emulsion films using our Microinterferometric Method in its contemporary version, which allow the direct (long-range surface forces) and indirect (short-range surface forces) measurement of molecular interactions. The short-range molecular interactions are presented by the parameter binding energy Q of an amphiphile molecule in the bilayer. The amphiphile bilayers (Newton black films) are formed from different surfactants: synthetic surfactants, biosurfactants, phospholipids, natural mixtures, etc. The equilibrium concentration Ce at which there is no driving force for bilayer rupture according to the theory and the amphiphile bilayer is infinite stable is determined as well. Occurrence of two-dimensional chain-melting phase transition in foam bilayers is established for the first time. The binding energy Q of two neighbouring phospholipid molecules is calculated for the gel (30-60 kT) and liquid crystalline state (16-18 kT) of the bilayers from dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), egg phosphatidylcholine (Egg PC) and amniotic fluid (AF). The formation and stability of amphiphile bilayers from polymer surfactants is considered too. Their stability is considered on the basis of de Gennes theory for steric repulsion between two polymer adsorption layers, where brush-to-brush contact is realized. This state of the films from ABA triblock copolymers is established by direct measurement of disjoining pressure thickness isotherms through the Thin Liquid Film-Pressure Balance Technique and molecular optic model of foam film. A comparison is done between model studies of amphiphile bilayers (formed from surfactants and polymers) and real disperse systems (for example foams, concentrated O/W emulsions, lung surfactants, etc.). This comparison clearly shows the reasons for the colloid stability at bilayer contact and the possibility to predict it through model studies. It is worth to be mentioned that the model studies of amphiphile bilayers allow the study of the bilayer contact in biological systems and biological structures, the interaction between biomembranes, etc. |
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ACS Award in Colloid and Surface Chemistry Symposium Honoring Clay Radke
Division of Colloid and Surface Chemistry |