Research Description - Project Summary

Interfaces (the region separating two phases) play essential role in numerous processes in nature, ecology (accumulation and removal of pollutants, green chemistry), technology (colloids, paints, adhesion, adsorption, catalysis, energy production and storage, nanotechnology, electronics, biosensors), medicine (physiology, membranes), pharmacy (formulation of drugs and drug delivery) etc. Interfacial area, with respect to amount of the material, is extremely large in the case of colloidal dispersions and especially in nano-dispersions. Therefore, interfacial properties are directly related to surface reactivity, adsorption of biomolecules, but also to the permeability of membranes. At present time, key physico-chemical properties of solid/electrolyte interfaces remain insufficiently understood at a fundamental level.

In order to contribute to the understanding of basic interactions between the mineral phases and water molecules, ions and complex macromolecules we propose the investigations of processes at solid/liquid interfaces. Particular attention will be paid on a role of water, simple counterions, as well as surface structure in surface charging and formation of electrical interfacial layer.

Recently developed experimental techniques enable characterization of individual crystal planes. The unexpected difference between inner surface potential and electrokinetic potential of a particular crystal plane leads to conclusion of pH dependent charge of interfacial water layer. This phenomenon will be examined in details. The single crystal electrodes, device constructed recently in our laboratory, will be used for determination of inner surface potential of specific crystal planes. Inner surface potential affects directly the state of ionic species bound to defined surface plane and is thus essential parameter governing interfacial equilibrium. Electrokinetic experiments provide information on the net charge of surface and stagnant interfacial water layer, so that the mentioned data will be analyzed in order to elucidate equilibrium processes taking place at the interface. Since adsorption processes depend on the speciation of surface species, both in adsorbed and desorbed states, the properties of both states will be analyzed. The role of interfacial water in interfacial equilibrium will be analyzed by considering its behavior at inert surfaces (gas/water, diamond/water) but also at metal oxide surfaces.

A special case of interfaces are polyelectrolytes at the metal oxide surface. Therefore, such interfaces and their correlation with the behaviour of polyelectrolytes in solution will be also extensively studied in the frame of the proposed project. The reason lies in fundamental interest to understand their properties in relation with the role of natural polyelectrolytes and proteins in biological processes, as well as in industrial applications. The latter are not limited to polyelectrolytes in solution, but include also the polyelectrolyte (or interpolyelectrolyte) complexes and multilayers. The formation of multilayers of polyelectrolytes at solid surfaces, as well as interpolyelectrolyte interactions in solution, will be examined. Special emphasis will be given on specific ionic effects.

The proposed project can be classified as a project in the field of physical chemistry of colloids and interfaces and it is oriented to dynamic and equilibrium aspects of accumulation and distribution of ions and molecules within the interfacial layer. Predominantly the experimental methods will be applied, while the results will be analyzed quantitatively. In addition, theoretical tools will be developed in order to better understand behavior, reactivity and equilibrium at interfaces.