Glass transformations, glass transition temperatures, various glassy states under elevated pressures, and polyamorphism are reviewed. There are two types of polyamorphism in the glassy states: the first is that produced from the history of glass-forming conditions, and the second is that produced from changes in the structure of liquids. A critical point of structural polyamorphism is deduced from the recent experiments on the first-order like glass-glass transition of tetrahedral glasses. The critical point locates on the equilibrium liquid surface in the P-V-T space under an elevated pressure below the glass transition temperature, but above the Kauzmann temperature. The low-temperature limit of the liquid under the critical pressure is the critical point; and the liquid, except the critical pressure, vitrifies gradually without any transition. The equations of the glassy states are briefly discussed.
Our recent calorimetric studies on glass transition, especially for high pressure experiments, are reviewed in this article. The materials examined are molecular liquids with relatively simple molecular structure. The content of the article is as follows. (1) Introduction (2) Adiabatic Calorimeter under High Pressure (3) Configurational Entropy and Short-Range Ordering (4) Configurational Entropy and α Relaxation Time (5) Pressure Dependence of Glass Transition and Adam-Gibbs Theory. (6) Prigogine-Defay Ratio and Internal Parameter Theory (7) Structural Relaxation in (Volume) - (Internal Energy) - (Gibbs Energy) Space (8) Concluding Remarks
We review some recent developments in glassy dynamics research using neutron scattering. We focus on the following three topics: (i) low-energy excitation, (ii) fast process, (iii) dynamic heterogeneity in glassy state. In the fast and second topics, we show that recent research on glassy materials with various degrees of disorder provide useful information about the microscopic origin of low-energy excitation and fast β process. In the third topic, a non-Gaussian parameter is introduced to evaluate dynamic heterogeneity of glassy materials through mean square displacement, and a correlation between the non-Gaussian parameter and fragility index is pointed out. Distribution functions of the mean square displacement are evaluated on the basis of Gaussian, log-Gaussian and bimodal distributions.
Highly supercooled liquids with soft-core potentials are studied via molecular dynamics simulations in two and three dimensions in quiescent and sheared conditions. We may define bonds between neighboring particle pairs unambiguously owing to the sharpness of the first peak of the pair correlation functions. Upon structural rearrangements, they break collectively in the form of clusters whose sizes grow with lowering the temperature T. The bond life time Tb, which depends on T and the shear rate γ, is on the order of the usual structural or α relaxation time Tα in weak shear γTα <<1, while it decreases as 1/γ, in strong shear γTα >> 1 due to shear-induced cage breakage. Accumulated broken bonds in a time interval (∼0. 05Tb) closely resemble the critical fluctuations of Ising spin systems. For example, their structure factor is well fitted to the Ornstein-Zernike form, which yields the correlation length ζ representing the maximum size of the clusters composed of broken bonds. We also find a dynamic scaling relation, Tb∼ζz, valid for any T and γ with z=4 in two dimensions and z=2 in three dimensions. The viscosity is of order Tb for any T and γ, so marked shear-thinning behavior emerges. The shear stress is close to a limiting stress in a wide shear region. We also examine the motion of tagged particles in shear in three dimensions. The diffusion constant is found to be of order Tb-v with v=0. 75∼0. 8 for any T and γ, so it is much enhanced in strong shear compared with its value at zero shear. This indicates breakdown of the Stokes-Einstein relation in accord with experiments. The origin of the breakdown is discussed in detail.
The effects of pressure on the aggregation of swine erythrocytes were investigated by monitoring the erythrocyte sedimentation rate under high pressure, up to 40 MPa. The aggregation of erythrocytes in plasma was propor-tionally enhanced by pressure, whereas aggregation of erythrocytes was not observed in saline solution up to 40 MPa. These results suggest that the adhesion energy between erythrocytes is not directly affected by pressure, but through a change in the interaction energy between plasma components and erythrocytes.
Procedures for in-laboratory construction of an autofrettaged cylinder is described, including design, choice of the materials, machining as well as heat treatment of the cylinder. Details of high pressure-high temperature experiments up to 1 GPa and 400°C are given with special emphasis on encapsulation and sealing techniques.
The Research Institute for Solvothermal Technology (RIST), opened in September 1997 to carry out research related to high-temperature and high-pressure fluid technology. RIST has recently developed new technologies using supercritical fluids, especially carbon dioxide and water, in areas related to the environment, such as the treatment of organic waste, the production of new materials, such as new-carbon substances, materials for batteries and electromagnetic wave absorption; and in the area of energy and resources, such as the conversion or the recycling of industrial plastic waste. This paper also describes the general concept of solvothermal technology, critical phenomena, the philosophy on high pressure research development and the problems of joint research projects with the cooperation of enterprises, universities and government.