The research group of Professors Mikhail A. Anisimov and Jan V. Sengers at IPST is concerned with theoretical and experimental studies of mesoscopic fluctuations in soft matter, both in molecular fluids and in complex fluids. Some of the ongoing projects within the research group are listed here. For more information on these projects, please contact Professor Anisimov and/or Professor Sengers.

Supercooled Water - Dr. Vincent Holten, Post-Doctoral Researcher

The peculiar thermodynamic behavior of supercooled water continues to receive considerable attention, despite several decades of work in this field. Upon supercooling, water exhibits an anomalous increase of its isobaric heat capacity and its isothermal compressibility, and an anomalous decrease of its expansivity coefficient. One explanation of these anomalies is based on the presumed existence of a liquid–liquid critical point (LLCP) in water in the deeply supercooled region. We have demonstrated that a theoretical model based on the presumed existence of this second critical point is capable of representing, accurately and consistently, all available experimental thermodynamic property data for supercooled ordinary and heavy water.

Self-Assembly of Small Molecules in Aqueous Solutions

Our research group is currently trying to understand the mesoscopic properties of certain aqueous solutions. Aqueous solutions of certain low molecular weight organic compounds, such as tertiary butyl alcohol, 3-methyl pyridine, tetrahydrofuran, although form a homogeneous solution with water, show the presence of certain heterogeneities on the mesoscale. These heterogeneities are not seen by the naked eye, but show a strong scattering when seen through a laser beam. By using experimental techniques such as static and dynamic light scattering and optical confocal microscopy, we are investigating the nature of these mesoscopic heterogeneities. Understanding the properties of these mesoscopic heterogeneities will help us understand self-assembly of small molecules in aqueous solutions and will help us create stable colloidal nanoparticles.

Supercooled Water - John Biddle, Graduate Student

In addition to its unusual thermodynamics, supercooled water displays anomalous transport properties. Our research group aims toward a better understanding of these anomalies. In particular, we study the relationship between dynamics and thermodynamics in water, including the possible effect of the hypothesized second critical point on the dynamics.

Study of "smooth" interfaces

Another interesting topic is an effect of fluctuations on the behavior of smooth (or "fuzzy") interfaces. Smooth interfaces are ubiquitous in soft matter. The examples include near-critical vapor-liquid and liquid-liquid interfaces in simple and complex fluids, interfaces in polymer solutions and polymer blends, liquid membranes and vesicles. A smooth interface is characterized by the interfacial density/concentration profile with a characteristic length scale, or "thickness" of the interface. Such interfaces are mesoscopic, extending from nanometers to microns. One cannot define a droplet size smaller than the thickness of its interface. The surface tension of a smooth interface is usually very low; hence the interface undergoes strong fluctuations. Fluctuations fundamentally change thermodynamics of smooth interfaces. In particular, the curvature correction to the surface tension, known as Tolman's length, may become as large as the thickness of the smooth interface itself. This effect crucially depends on the degree of asymmetry in the fluid phase coexistence, which is properly described by "complete scaling". A broader impact of this research includes filtration through microporous media in oil recovery, microfluidics, nanoscale liquid bridges, and nucleation phenomena: wherever science and technology deal with fluid droplets at submicron and nano scales.

Our research work is funded by the National Science Foundation, ACS Petroleum Research Fund and the International Association for the Properties of Water and Steam