MESOSCOPIC FLUCTUATIONS IN SOFT CONDENSED MATTER

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.

Fluctuations fundamentally change thermodynamics at nano and meso scales, making all properties locally inhomogeneous and revealing the true statistical meaning of the second law of thermodynamics. Anisimov teaches a cross-disciplinary elective course: "Mesoscopic and Nanoscale Thermodynamics". This field of science can be defined as a semi-phenomenological approach to systems and phenomena in which a length scale, intermediate between the atomistic scale and the macroscopic scale, emerges and where this intermediate length scale does affect the physical properties profoundly. This is still thermodynamics, as the phenomena are still governed by statistical physics, but, in contrast to "macro-thermodynamics" it explicitly contains a mesoscopic length scale associated with the structure of soft matter.

In molecular fluids thermal fluctuations are known to become mesoscopic near critical points. Light-scattering experiments in their laboratory have contributed to the experimental verification of the concept of universality of critical behavior in fluids and fluid mixtures, including electrolyte solutions. With the concept of isomorphism of critical behavior, a large variety of apparent different experimental observations can be transformed into a single universal representation in terms of appropriate scaling fields. IPST Professor Michael E. Fisher and coworkers have recently extended the concept of scaling fields in terms of so-called "complete scaling", that is, that the relevant scaling fields should be combinations of all physical fields. Incorporating the concept of "complete scaling" into the principle of isomorphic critical behavior of fluids, Anisimov and Sengers have been able to elucidate the nature of the order parameter in fluid mixtures and its relation to the asymmetry of critical phase-separation phenomena in liquid mixtures.

Complex fluids differ from molecular fluids by possessing a mesoscopic structure even far away from critical points. Such a mesoscopic structure will induce coupling between different hydrodynamic fluctuations. Light-scattering experiments in polymer solutions in their laboratory at IPST have shown that the intensity of the fluctuations is affected by a competition between the spatial extent of the critical fluctuations and the radius of gyration. Moreover, the dynamics of critical fluctuation is strongly affected by a coupling with viscoelastic relaxation of the polymer chains. Hence, dynamic light-scattering experiments can provide microrheological information about the hydrodynamic environment of macromolecules in solution.

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.

It turns out that fluctuations in fluids in nonequilibrium states are always spatially long ranged. This phenomenon was first predicted by IPST Professors Theodore R. Kirkpatrick and J. Robert Dorfman in collaboration with E.G.D. Cohen at Rockefeller University. The long-ranged nature of hydrodynamic fluctuations in nonequilibrium is caused by a coupling between hydrodynamic modes through any thermodynamic or velocity gradient. It is known that thermal fluctuations in fluids in thermodynamic equilibrium can be described by fluctuating hydrodynamics originally developed by Landau. Light-scattering experiments in fluids with a temperature gradient and in polymer solutions with a concentration gradient at IPST have for the first time convincingly demonstrated the validity of fluctuating hydrodynamics for describing fluctuations in nonequilibrium states as well. Studies of fluctuations in liquid under shear are currently in progress. It is hoped that such studies could yield a bridge between the methods of nonequilibrium statistical mechanics pursued at IPST, in collaboration with J.M. Ortiz de Zárate at the Complutense University of Madrid, and the approach commonly found in the fluid-mechanics literature.

	2008 Back row:  Chris Bertrand, Jan V. Sengers, Mikhail Anisimov, Hassan Behnejad, Kirt Linegar Front row:  Daphne Fuentevilla, Adedayo Adeniran, Heather St. Pierre, Deepa Subramanian
	2007 Daphne Fuentevilla, Heather St. Pierre, Chris Bertrand, Mikhail Anisimov, Kirt Linegar, Adedayo Adeniran Not shown:  Jan V. Sengers (Article!)
	2006 Back row:  Andrei Kostko, Mikhail Anisimov, Jan V. Sengers, Adedayo Adeniran, Huan Zhang Front row:  Kirt Linegar, Daphne Fuentevilla, Amanda Woodward, Heather St. Pierre
	2004 J. V. Sengers, S. Hsieh, M. A. Anisimov, J. Sun, E. E. José Ortiz de Zárate
	2001 Back row:  J. Wang, J. S. Hager Front row:  A. F. Kostko, J. V. Sengers, M. A. Anisimov, E. E. Gorodetskii
	1999 V. A. Agayan, A. Singh, A. Wyczalkowska, J. V. Sengers, M. A. Anisimov, A. Povodyrev, T. Edison

Research group

Our research group is as dynamic as the critical phenomena we study. This is why we include our current and recent members on this web page, because of those who worked with us want to come back! The below will be updated periodically. Visit the members' homepages!

• Mikhail A. Anisimov, Professor
• Jan V. Sengers, Distinguished University Professor Emeritus and Research Professor
• Hassan Behnejad, Visiting Professor (University Tehran, Iran)
• Heather St. Pierre, Graduate Student
• Daphne Fuentevilla, Graduate Student
• Chris Bertrand, Graduate Student
• Kirt Linegar, Graduate Student
• Deepa Subramanian, Graduate Student
• Adedayo Adeniran, Graduate Student

• Professor Claudio Cerdeiriña, University of Vigo, Ourense, Spain
• Professor José M. Ortiz de Zárate, Complutense University, Madrid, Spain
• Professor Jan Thoen, Catholic University, Leuven, Belgium

• Juixun Sun, Visiting Scientist (University of Electronic Science and Technology, China)
• Suzanne Hsieh, Research Associate
• Andrei F. Kostko, Assistant Research Scientist (2000-2004)
• Iosif Shinder, Research Associate (2001-2003)
• Jingtao Wang, Graduate Student (2001-2003)
• Johannes Hager, Research Associate (2001-2002)
• Igor K. Yudin, Visiting Scientist (1998,2000-2001)
• Evgenii E. Gorodetskii, Visiting Scientist (1998, 2001)
• Anna J. Wyczalkowska, Postdoc (1998-2001)
• Jaby Jacob, Research Associate (1999-2000)
• Vakhtang A. Agayan, Graduate Student (1996-2000)
• Khapissat S. Abdoulkadirova, Postdoc (1998-1999)
• Yevgenyi Burya, Research Assistant (1999-2000)
• Anup Singh, Graduate Student (1996-1999)
• Andrei Povodyrev, Research Associate (1995-1999)
• Thomas Edison, Graduate Student (1994-1999)

Laboratories

Thermodynamic and Transport Properties of Fluids and Fluid Mixtures

Experimental Lab on Fluctuation Phenomena in Complex Fluids

Light-Scattering Tools

Photocor-Complex Setup:  Overview

Photocor-Complex Setup:  Corporate site

Selected publications

1. A.F. Kostko, M.A. Anisimov, and J.V. Sengers, Dynamics of critical fluctuations in polymer solutions, Phys. Rev. E 76, 021804 (2007).

2. M. A. Anisimov and J. T. Wang, Nature of asymmetry in fluid criticality, Phys. Rev. Lett. 97, 25703 (2006); Nature of vapor-liquid asymmetry in fluid criticality, Phys. Rev. E 75, 051107 (2007).

3. D. A. Fuentevilla and M. A. Anisimov, Scaled equation of state for supercooled water near the liquid-liquid critical point, Phys. Rev. Lett. 97, 195702 (2006).

4. M. A. Anisimov, Divergence of Tolman's length for a droplet near the critical point, Phys. Rev. Lett. 98, 035702 (2007).

5. S.K. Das, J.V. Sengers, and M.E. Fisher, Simulating critical dynamics in liquid mixtures: short-range and long-range contributions, J. Chem. Phys. 127, 144506 (2007).

6. J.M. Ortiz de Zárate and J.V. Sengers, Hydrodynamic Fluctuations in Fluids and Fluid Mixtures (Elsevier, Amsterdam, 2006).

7. J.M. Ortiz de Zárate, J.V. Sengers, D. Bedeaux, and S. Kjelstrup, Concentration fluctuations in non-isothermal reaction-diffusion systems, J. Chem. Phys. 127, 034501 (2007).

8. J.V. Sengers and J.M. Ortiz de Zárate, Thermal fluctuations in non-equilibrium thermodynamics, J. Non-Equilibrium Thermodynamics 32, 319-329 (2007).

9. C.A. Cerdeiriña, J.T. Wang , M.A. Anisimov, and J.V. Sengers, Principle of isomorphism and complete scaling for binary-fluid criticality, Phys. Rev. E 77, 031127 (2008).

10. J.M. Ortiz de Zárate and J.V. Sengers, Transverse-velocity fluctuations in a liquid under steady shear, Phys. Rev. E 77, 026306 (2008).

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