Dr. Alex Nikolov joined the IIT community (the Department of Chemical and Biological Engineering) in the summer of 1990. His research interest is focused on the colloidal (nano-sized) particle self-assembly phenomenon in confined geometry (e.g. liquid films, foam and meniscuses). He observed that the liquid films formed from colloidal dispersions thin in a step-wise manner (stratifies). It has been discovered that the film step-wise thinning phenomenon is a manifestation of the colloidal particle self-layering (structuring) inside the thinning film. As a result of the of particle layering/structuring, the mean potential of interactions between the constrained film surfaces is the oscillatory decay. He elucidated that the oscillatory decay potential (the potential generated by the particle layering (structuring) determines the stability of dispersions (e.g. foam, emulsion and suspensions).

His goal is to reveal the origin of the structural transitions in confined geometry, and to explore fabricated 2D materials with novel mechanical, optical, and electro-optical properties. Currently his research focuses on the following areas:

Colloidal (Nano-sized) Particle Structural Transitions Inside Films: A Method for Developing Structured Materials

The foam and emulsion films thinning in the presence of colloidal particles have been studied by the capillary force balance and by light diffraction techniques. The particles constrained by the film surfaces form different structures. A layered structure is formed at the film thickness of several particle diameters. The particles' structure is transformed into an in-layered structure as the film thickness decreases to a few particle diameters. Moreover, the particles' in-layered structure (with a decreasing film thickness) changes from 2D cubic to 2D hexagonal.

The experimental results and computer simulations reveal that the particles' in-layer structure also depends on the position of the layer (e.g. the layer at the film surfaces are more structured than the layers in the middle).

A Novel Approach to Control Foam, Emulsion and Suspension Stability

The knowledge gained for the role of the structural forces on the film thinning, and stability is being applied to develop new industrial products: an advanced fuel was developed based on a water-in-diesel emulsion (tested by Caterpillar Co. and in the process of implementation), and a new effective anti-foamer, which eliminates the foaminess during the immobilization of high level nuclear materials (successfully tested, and implemented at Westinghouse Savannah River Co.) The antifoamer is commercially available.

Spontaneous Spreading on Hydrophobic Surfaces

The spontaneous spreading of aqueous trisiloxane ethoxylate surfactant solutions on waxy hydrophobic solid surfaces (1 cm/sec, with the overall spread area 50 times greater than the aqueous phase alone) is a fascinating phenomenon with substantial practical applications, such as spray deposits on leaf surfaces, textile fiber wetting, painting, and cooling. The super-spreading ability of the trisiloxane ethoxylate surfactant has been known from decades, but its mechanism was puzzling. A quantitative model was proposed to explain the spontaneous spreading. The model depicts the specific properties of the superspreaders to efficiently reduce the surface tension at the water/air surface, and to induce a surface tension gradient at the front of the spreading droplet.

Tata, B. V., Ramajani, P. V., Chakrabarti, J., Nikolov, A. and Wasan, D. T., "Gas-Liquid Transition in a Two-Dimensional System of Millimeter-Sized Like-Charged Metal Balls," J. Physical Review Letters, Vol. 84, No 16, 3626 - 3629, 2000.

Trokhymchuk, A., Henderson, D., Nikolov, A. and Wasan, D. T., "A simple Calculation of Structural and Depletion Forces for Fluids / Suspensions Confined in a Film," J. Langmuir, Vol. 17, No 16, 4940 - 4947, 2001.

Trokhymchuk, A., Henderson, D., Nikolov, A. and Wasan, D. T., "Entropically driven ordering in a Binary Colloidal Suspension Near a Planar Wall," J. Physical Review E, Vol. 64, 12401(1) - 12401(4), 2001.

Kumar, K., Nikolov, A. D. and Wasan, D. T., "Mechanisms of Stabilization of Water-in-Crude Oil Emulsions," J. Industrial and Engineering Chemistry Research, Vol. 40, No 14, 3009 - 3014, 2001.

Sunil, K. B., Nikolov, A. D. and Wasan, D. T., "Foaming in Simulated Radioactive Waste," J. Environmental Science and Technology, Vol. 35, No 19, 3941 - 3947, 2001.

Trokhymchuk, A., Henderson, D., Nikolov, A. D. and Wasan, D. T., "Depletion and Structural Forces between Two Macrosurfaces Immersed in a Bidisperse Colloidal Suspension," Journal of Colloid and Interface Science, Vol. 243, 116 - 127, 2001.

Wasan, D. T., Nikolov, A. D. and Brenner, H., "Droplets Speeding on Surfaces," J. Science, Vol. 291, No 5504, 605 - 606, 2001.

Dutta, A., Chengara, A., Nikolov, A. D. and Wasan, D. T., "Texture and Stability of Aerated Food Emulsions. 1. Effects of Buoyancy and Ostwald Ripening," Journal Food Engineering, (in press 2001).

Nikolov, A. D., Wasan, D. T., Chengara, A., Koszo, K., Policello, G. and Kolossvary, I., "Superspreading Driven by Marangoni Flow," J. Advances in Colloid and Interface Science, Vol. 96, 325 - 338, 2002.