Phase transitions, laboratory experiments

With more beam time available in the laboratory, we were able to go through the phase transition in much smaller temperature steps. Before the measurements were taken, the system was kept at each temperature for at least half an hour to ensure that thermal equilibrium had been achieved. The diffraction patterns obtained from a sample with r = 0.1, c = 0.1 M (the same conditions as for the LAD experiment) are shown in Figure 10.3a at live temperatures between -2 and 2°C, in 1°C steps. 

Determination of crystal structure or unit cell volume in isolation of other physical property measurements is the routine practice in much of solid state research under both ambient and non-ambient conditions. This is often necessitated because the cell assemblies required for property measurements are not compatible with X-ray beams typically available in the laboratory. Centralized facilities, such as are available at the synchrotron, provide a cost-effective environment and opportunity to do more definitive experiments. One recent example from the Stony Brook laboratories will suffice to demonstrate what will become, I believe, the normal mode of operation for the study of important phase transitions in the future. For the study of mantle mineralogy, simultaneous measurements of elastic properties, structure and pressure is now established in large volume devices, (Chen et al. 1999) and being established in DACs as well... 

At the National Institute of Chemistry (NIC), in the frame of CMD subproject of EUROTRAC-2, experimental studies of the role of soluble constituents of atmospheric aerosols in the aqueous-phase autoxidation mechanisms of S(IV) was studied. The research focused on atmospheric water droplets (clouds, fog), where soluble constituents of atmospheric particles may be important in aqueous SO2 oxidation under non-photochemical conditions. In the frame of CMD project laboratory experiments in a semi-batch continuous stirred tank reactor under controlled conditions (T, air flow rate, stirring), were made in order to study the autoxidation of S(IV)-oxides catalyzed by transition metal ions (Fe(III), Fe(II), Co(II), Cu(II), Ni(II), Mn(II)). These studies were carried out at the National Institute of Chemistry. 

The foremost thermodynamic property associated with any phase boundary is the location of its surface in the p-V-T phase diagram. Most laboratory experiments of glass formation are carried out in a particular V-T plane, usually for atmospheric pressure, and the temperature dependence of volume through the transition is determined. If the glass transition is indeed dictated by the repulsive part of the potential, we expect, at least for simple steeply repulsive systems, that it will occur at the same molecular-reduced volume for many real and model systems and that this will be largely insensitive to the strength of the attractive component of the pair potential relative to kT. 

To summarize, the results that have been described demonstrate that in laboratory experiments anisotropic dimensional changes, or complementary tension development, can be produced in the fibrous proteins as a consequence of a phase transition between the oriented crystalline and amorphous states. This transition can be induced either thermally or isothermally by interaction with a diversity of chemical reagents. The same physical-chemical principles are followed that govern the structurally simpler fibrous synthetic polymers. 

Gravity is such a pervasive force that its ramifications on erq)eriments are often not considered since the influence of gravity is perceived to be unavoidable. As a result, laboratory platforms that achieve an effective reduction of acceleration on e q)eriments are often under appreciated. Based on the above arguments it is apparent that the reduction in the effects of acceleration on e q)eriments can be used fi>r studies of diffusive processes, sur ce-tension driven convection, containerless processing of materials, research on the scaling properti of phase transitions, etc. Space Shuttle experiments have been conducted involving each of the above topics. 

Nowadays, the phase transitions are probably the most intensively studied aspects of adsorption on heterogeneous surfaces. The recent developments presented in the previous section are focused on the role of surface heterogeneity in these phenomena. Although many interesting conclusions have been formulated, much room remains to explore, even for simple surface models, either in the fi amework of theoretical treatments or by computer simulation. In this case, computer simulations can be viewed as a promising tool for investigation because analytical approaches are limited to crude approximations and laboratory experiments are really difficult. 

For the study of the thermotropic mesomorphism of membranes the sample preparation is very important. Lipid dispersions are generally prepared by mixing the desired amounts of solid lipid and solvent (H2O, D2O or buffer solution). When using D2O as solvent a closed vessel should be used in order to minimize exchange with atmospheric water. In order to ensure proper hydration the lipid water mixture should be first heated above the temperature of the gel to liquid crystal phase transition of the corresponding lipid, then cooled before commencing the measurements. The study of natural membranes involves re-hydration only if the membranes are isolated from the other cell components and lyophilized (6-8). The experiments on bacterial membranes currently under way in our laboratory utilize live bacteria or isolated membranes which have not been lyophilized, therefore no hydration procedure is involved (9). 

Abstract Water ice consists about a half of mass and therefore about 0.75 of volume of most of the icy satellites. Differentiated, with water ice forming outer shells, and undifferentiated models of internal structure of the icy satellites of the giant planets are mentioned. It is stressed that the modelling of the evolution of satellites structure should be supported by laboratory experiments (i) concerning rheology of compaction of icy/mineral granular porous media, and (ii) concerning kinetics of phase transitions of water ice in these media. 

Comparison ot Tables V and VI demonstrates that the thermal behavior of MelOCOO-PPO and MelOCOO-PECH are very similar, with the glass transition temperatures converging with substitution. Therefore, it appears that when very long spacers are used with the same mesogen, the polymer backbone has little effect on the thermotropic phases formed. This conclusion is supported by additional unpublished experiments performed in our laboratory. 

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