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CAMP Professor Sokolov Investigates continued from page3

Liquid Crystal Growth on the Surface: Beyond the First Monolayer

Self organization of liquid crystals, that are controlled at the nanometer level and induced by the substrate, are of great importance to nanotechnology. This is because of its simplicity, speed, and low cost. Professor Sokolov performed the first in situ solution phase imaging study of the surface of a lyotropic liquid crystal film. This imaging was achieved at heights that are far beyond those documented in the literature , 25 thick hemicylindrical micellar monolayer on graphite. The ability to directly visualize the mesostructure and morphology of a lyotropic liquid crystal film is an important breakthrough in an emerging new area of materials chemistry (i.e., mesochemistry, mesostructures, morphology control). It is certainly one of the necessary experimental prerequisites to enable the intentional design of surfactant-templated inorganic mesostructured films with tunable orientation pores. His results show that the self-organization spreads beyond the first monolayer, and can be detected as far as ~10 molecular layers from the substrate.

Future studies will include the investigation of self-organization in different conditions, substrates, and reactants.

Cell Surface Electrochemical Heterogeneity

Interaction of biological cells with bacteria in the environment is of great interest to modern science and technology. The interaction takes place on the cell surface. Any chemical interaction can be interpreted as redistribution of charge from the physical point of view. So it is very important to study the distribution of charges on these surfaces. Professor Sokolov studied such a distribution by means of Electrostatic Force Microscopy (EFM) ( a modification of the AFM) on the surface of the Fe(III)-reducing bacteria, Shewanella putrefaciens. He found that the charge distribution strongly depends on the acidity and concentration of metals (Ni, Cr, Ur, Fe) in the solution environment. Future research efforts will attempt to extend this technique to other materials to distinguish between different 3D surface charge distributions. (See figure 4.)


 

 

 

 

 



Figure 4: AFM image of a Shewanella putrefaciens bacterium (right). A zoomed in area is shown by a black square on the right image and presented on the left image in electrical charge contrast. The darker shade means a higher charge density. Spatial resolution in the charge image is ~5-10nm.


Modeling the Long-range Force Interactions between Nano/Micro/Particles and Surfaces

To understand possible surface modifications, one needs to study surface forces. While the short-range interaction is more or less universal, the long-range component can be strongly non-additive, and consequently, cannot be obtained by simple pair-wise summation over the volumes of the interacting bodies. From an industrial point of view, long-range force interaction is important in such devices as MEMs, colloids, and aerosols. Calculation of such forces by rigorous quantum mechanical methods is rather difficult. Therefore, the development of an approximation method with known accuracy of calculation is needed. Existing Deriaguin-type methods do not give any information about accuracy of those methods. It is not clear if those methods give correct force dependencies. Moreover, as derived, the Deriaguin-type methods work only for configurations that are close to two parallel plates, which are far from a typical application problem that can occur for MEMs, colloids, and aerosols. Professor Sokolov is developing a method that is applicable to any convex-shaped bodies. It simplifies the problem of pair-wise summation over the volumes of the interacting bodies. It takes into account non-additivity of such long-range forces as van der Waals forces to renormalization of the force constant. The accuracy, of force dependencies obtained in this method, is being studied.

Conclusion

Professor Sokolov's research focuses on the modification and characterization of surfaces at the nanometer level. He combines basic experimental scanning probe techniques, used in modern nanotechnology, with theoretical simulations to obtain insights into various surface phenomena.

For more information about
Professor Sokolov and his research,
you may refer to his web site
(http://www.clarkson.edu/~isokolov/).
You may also contact him by telephone
(315-268-2375) or by email
(isokolov@clarkson.edu).

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