Profile: Claudiu Stan

Assistant Professor

Department of Physics

Claudiu Stan received his Ph.D. from Massachusetts Institute of Technology. He was a postdoctoral fellow at Harvard, and a scientist at the SLAC National Accelerator Laboratory. His research focuses on phase transitions and ultrafast dynamics in liquids and soft matter.

(1) Generation and investigation of ultrafast phenomena with X-ray free-electron lasers

X-rays, due to their very short wavelength, allow us to “see” how matter is assembled from atoms. We have now the chance of observing the dynamics of atoms in matter: atoms moving inside a molecule during a chemical reaction, or atoms self-organizing into a crystal when a liquid freezes. This possibility was opened by X-ray free-electron laser facilities (XFELs), which produce extremely intense and extremely short X-ray pulses. Experiments at XFELs are an exciting new area of research, with new facilities being opened, and new applications or phenomena being discovered.

A major part of our research uses XFELs to study hydrodynamics, metastable systems, and phase transitions. We observed and studied the microexplosions induced by X-ray lasers in liquids, and then used these microexplosions to generate large negative pressures in liquid water. We are also using XFELs to study protein dynamics, and the non-equilibrium crystallization of ice in deeply supercooled water.

(2) The nucleation of ice in supercooled water

Pure water in micron-sized drops can be supercooled to temperatures close to -40 °C, where it spontaneously freezes due to homogeneous nucleation. Such supercooled drops have been observed in the atmosphere, and their freezing is an important process in atmospheric science; for example, precipitation is often initiated by the freezing of water droplets in clouds.

We previously developed a microfluidic instrument for studying ice nucleation in ensembles of tens of thousands of supercooled water microdrops. This instrument can take tens of measurements each second, more than any other previous tools for the study of ice nucleation. We used it to make one of the highest accuracy measurements of ice nucleation in pure water. A promising future application is to investigate the heterogeneous nucleation of ice due to foreign particles, because high-rate measurements allow us to characterize heterogeneous nucleation over a wide range of samples and temperatures. Such data that is important for understanding nucleation and for predicting how impurities in the atmosphere affect precipitation.

(3) Microscale hydrodynamics

Our research involves flowing liquids at micron length scales, and as we develop new instruments or methods, we often encounter new hydrodynamic phenomena and find ways to use them. For example, we used the temperature dependence of viscosity to control the generation of microfluidic droplets, and we investigated the strength and nature of hydrodynamic lift forces on droplets in microchannels.

Currently, we are investigating the dynamics of shock waves generated by X-ray laser microexplosions in jets and drops. Using these shock waves, we aim to trigger ultrafast processes such as non-equilibrium phase transitions, crystal failure, and structural changes in proteins.

  • Education

    B.Sc. University of Bucharest
    Ph.D. Massachusetts Institute of Technology
  • Publications

    Selected Recent Publications:

    How Cubic Can Ice Be?, A. J. Amaya, H. Pathak, V. P. Modak, H. Laksmono, N. D. Loh, J. A. Sellberg, R. G. Sierra, T. A. McQueen, M. J. Hayes, G. J. Williams, M. Messerschmidt, S. Boutet, M. J. Bogan, A. Nilsson, C. A. Stan, B. E. Wyslouzil., J. Phys. Chem. Lett. 8, 3216 (2017)

    Liquid explosions induced by X-ray laser pulses, C. A. Stan, D. Milathianaki, H. Laksmono, R. G. Sierra, T. A. McQueen, M. Messerschmidt, G. J. Williams, J. E. Koglin, T. J. Lane, M. J. Hayes, S. A. H. Guillet, M. Liang, A. L. Aquila, P. R. Willmott, J. S. Robinson, K. L. Gumerlock, S. Botha, K. Nass, I. Schlichting, R. L. Shoeman, H. A. Stone, and S. Boutet., Nat. Phys. 10, 966 (2016)

    Negative Pressures and Spallation in Water Drops Subjected to Nanosecond Shock Waves, C. A. Stan, P. R. Willmott, H. A. Stone, J. E. Koglin, M. Liang, A. L. Aquila, J. S. Robinson, K. L. Gumerlock, G. Blaj, R. G. Sierra, S. Boutet, S. A. H. Guillet, R. H. Curtis, S. L. Vetter, H. Loos, J. L. Turner, and F.-J. Decker., J. Phys. Chem. Lett. 7, 2055 (2016)

    The magnitude of lift forces acting on drops and bubbles in liquids flowing inside microchannels, C. A. Stan, A. K. Ellerbee, L. Guglielmini, H. A. Stone, and G. M. Whitesides., Lab Chip 13, 365 (2013)

    A microfluidic apparatus for the study of ice nucleation in supercooled water drops, C. A. Stan, G. F. Schneider, S. S. Shevkoplyas, M. Hashimoto, M. Ibanescu, B. J. Wiley, and G. M. Whitesides., Lab Chip 9, 2293 (2009)

  • Research Initiatives

    Ultrafast molecular and nanoscale dynamics, X-ray lasers, microfluidics, phase transitions, metastable liquids, biophysics.