Phase transitions, of surfaces

Hellium-Scattering Studies of the Dynamics and Phase Transitions of Surfaces 211... 

He then spent three years as a postdoctoral member of the technical staff at AT T Bell Laboratories, Murray Hill NJ, where he conducted research of the structure, kinetics, and phase transitions of surfaces and interfaces, using X-ray diffraction. He is currently as Senior Research Scientist in the James Franck Institute and Consortium for Advanced Radiation Sources (CARS) at the University of Chicago. He has been involved in synchrotron radiation research since 1986 and during the past seven years has been involved in the design, construction and operation of the GeoSoilEnviroCARS (GSE)CARS laboratory at the Advanced Photon Source. Here he has applied lower dimensional X-ray diffraction, X-ray absorption fine structure, X-ray fluorescence microprobe, microtomography and microcrystallography to study problems in earth and environmental science. 

E. V. Albano. Finite-size effects in kinetic phase transitions of a model reaction on a fractal surface Scahng approach and Monte Carlo investigation. Phys Rev B 42 R10818-R10821, 1990. 

At higher temperatures, other degrees of freedom than the radius R must also be considered in the fluctuation. However, this becomes critical only near the critical point where the system goes through a phase transition of second order. The nucleation arrangement described here is for heterogeneous or two-dimensional nucleation on a flat surface. In the bulk, there is also the formation of a three-dimensional nucleation, but its rate is smaller ... 

The terminology of L-B films originates from the names of two scientists who invented the technique of film preparation, which transfers the monolayer or multilayers from the water-air interface onto a solid substrate. The key of the L-B technique is to use the amphiphih molecule insoluble in water, with one end hydrophilic and the other hydrophobic. When a drop of a dilute solution containing the amphiphilic molecules is spread on the water-air interface, the hydrophilic end of the amphiphile is preferentially immersed in the water and the hydrophobic end remains in the air. After the evaporation of solvent, the solution leaves a monolayer of amphiphilic molecules in the form of two-dimensional gas due to relatively large spacing between the molecules (see Fig. 15 (a)). At this stage, a barrier moves and compresses the molecules on the water-air interface, and as a result the intermolecular distance decreases and the surface pressure increases. As the compression from the barrier proceeds, two successive phase transitions of the monolayer can be observed. First a transition from the gas" to the liquid state. 

Wu S, Lipkowski J, Magnussen OM, Ocko BM, Wandlowski T. 1998. The driving force for (p X - 3) <->(1x1) phase transition of Au(lll) in the presence of organic adsorption A combined chronocoulometric and surface X-ray scattering study. J Electroanal Chem 446 67-77. 

Cevc, G. Watts, A. Marsh, D., Titration of the phase transition of phosphatidylserine bilayer membranes. Effects of pH, surface electrostatics, ion binding, and head group hydration. Biochemistry 20, 4955 -965 (1981). 

Recently, in the theoretical studies on the simulation for N2 adsorption in micropore, some researchers102-104 reported that the monolayer adsorption occurs even in the micropore whose pore width is greater than the bilayer thickness of N2 (about 0.7 nm). In addition, Kaneko et al. showed the presence of the orientational phase transition of N2 on the graphitic micropore wall, which is the same as the phase transition of the monolayer on the flat graphite surface,105 and gave an effective method for the surface area determination in the microporous system.106 Therefore, even for micropores whose width is greater than 0.7 nm, dV MS can be... 

Using an automated film balance the behavior of mixed monomolecular films exhibiting deviations from ideality was studied. Particular attention was paid to condensation effects obtained when cholesterol is mixed with a more expanded component. The deviations at various film pressures are discussed in terms of the partial molecular areas of the film components. Slope changes in these plots are caused by phase transitions of the expanded monolayer component and do not indicate the formation of surface complexes. In addition, the excess free energies, entropies, and enthalpies of mixing were evaluated, but these parameters could be interpreted only for systems involving pure expanded components, for which it is clear that the observed condensation effects must involve molecular interactions. 

Figure 15.2. Types of adsorption isotherms (I) monomolecular layer (II and HI) multimolecular layers (IV and V) multimolecular layers and condensation in pores (VI) phase transition of a monomolecular layer on the surface (after Brunauer, Physical Adsorption, Princeton Univ. Press, 1945).

In contrast, the phase transition of polymeric liposomes is retained if the polymer chain is more flexible or located on the surface of the vesicles instead within the hydrophobic core. Polymerized vesicles of methacrylamide (29) show a phase transition temperature which is slightly lower than the one for the corresponding monomeric vesicles (Fig. 26). This can be explained by a disordering influence of the polymer chain on the head group packing 15). 

First of all, we want to study the case in which all surface sites are activated (5 = 1). This means that a N2 molecule can adsorb at every pair of free surface sites. Figure 9.11 represents the behaviour of the surface coverages 0i of the various chemical species i as a function of the mole fraction of N2 in the gas phase, yn, for the case 5=1 and D = 1. The most prominent feature in this figure is the kinetic phase transition of the second order at yN = yl fa 0.21. For j/n < Vi the surface is nearly completely covered by... 

Different SPM systems were developed to study the thermal properties. Thus a tiny thermocouple can be used to measure the heat flow from the surface and to test the local thermo conductivity of polymer surfaces [161]. Recently, a bimetallic cantilever has been used as temperature sensor to investigate phase transitions of n-alkanes with a heat sensitivity of 500 pj for a sample mass as low as to... 

Phase transitions of the system such as chain ordering transitions of lipids, appear in the isotherm as regions of constant pressure in the case of first order phase transitions involving the coexistence of two phases, or as a kink in the isotherm corresponding to a second order phase transition. These kinds of surface measurements are highly sensitive to impurities and must be carried out using very pure water and sample materials. 

Dietrich, S., (1991), Fluid interfaces - wetting, critical adsorption, van der Waals tails, and the concept of the effective interface potential , in Taub, H., Torzo, G., Lauter, HJ. and Fain, S.C., (eds), Phase. Transitions in Surface Films 2, NATO Advanced Science Series, Physics, Vol. 267, 391-423. 

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