In this project, the REU student will use optical techniques to explore liquids as they transform to a glassy solid in the little explored regime of very high pressure. To emphasize the significance of both the problem and the proposed approach, one need only refer to two statements made by leading scientists in the field. The Princeton Nobel Laureate, Phil W. Anderson, expressing a viewpoint in the journal Science states, "The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition." A leading scientists working on glassy solids, C. Austen Angell, states in the concluding remarks of a colloquium paper presented in 1995 at the National Academy of Sciences that, "The key problems are those of ... determining the general behavior of liquids near their T_g (glass transition temperature) at high pressure, where attractive forces will be less important ..." These two statements attest to the fact that the nature of the glass transition is interesting and not well understood and that applying high-pressure techniques to this problem is key to furthering our understanding.

In this project, the REU student will study the pressure dependence of the glass transition temperature, T_g(P), in prototypic liquid glass-forming system up to pressures as high as 120 kbar. Diamond anvil cells (DACs) will be used to achieve high pressures and custom fabricated heaters and closed-cycle helium refrigerators will be used to vary the temperature of the DAC. The pressure will be measured by focusing blue or green light from a Coherent Inova 306 Ar-ion laser on to tiny chips of ruby within the high-pressure cell and measuring the spectrum of the fluorescent light emitted by the ruby chip. This will be done using a customized microscope, which allows for precise positioning of the sample in a laser beam passed through the microscope system. Fluorescence from the ruby chip is coupled into a fiber optic which passes the light into a spectrometer where it is detected by a photodiode array detector. Furthermore, by measuring the pressure at more than one point within the cell, we can determine the temperature at which pressure differences appear across the sample. These pressure gradients indicate the formation of a solid glass since, unlike a liquid, a solid can support shear stresses. Prototypic glassformers, such as glycerol and liquid mixtures of pentane and isopentane, will be studied since they are good glass formers and the results can be used to improve the analysis of already existing light scattering data in these systems.

Basic techniques used in these experiments can be mastered within the first week or so of the project, making the probability of success high. In addition, the REU student will gain valuable experience in the use of many types of experimental apparatus and computer-aided data analysis techniques.