Phase transitions characteristics

Figures 46 and 47 show the effect of successive incorporation of meso-diastereomer on the phase transition characteristic of the ( )-isomer as the concentration of meso-isomer increases, the phase transition surface pressure IT occurs at higher n. The same result was found (Arnett et al., 1988b) for mixtures of ( )- and meso-C-15 6,6 and C-15 9,9, which are not shown here. According to the surface phase rule, this is indicative of...

KIM Kim, C., Lee, S.C., Kang, S.W., Kwon, I.C., and Jeong, S.Y., Phase-transition characteristics of amphiphilic poly(2-ethyl-2-oxazoline)/poly(s-caprolactone) block copolymers in aqneons solntions J. Polym. Sci., Part B Polym. Phys., 38, 2400, 2000. 

The g-values (Table 1) are close to the free electron value of 2.0023, indicating ver> small spin-orbit coupling ( ) [7]. Although small, the contribution of from each band at the Fermi surface will add to the width of the EPR signal. In all cases, only a single Lorentzian line is observed. The g-value is temperature-independent, within the accuracy of the experiment. For p -(BEDT-TTF)2AuCl2 an increase in g-value is observed at the phase transition, characteristic of a transition to a SDW ground state. 

The surface pressure (7i )-area (A) isotherms for pure CiiCONH-j6-CD and its mixed monolayers with DPPC are illustrated in Fig. 4, and those for pure PEO-lipid (12,13) and its monolayers with DMPC are shown in Fig. 5. From Fig. 4 it is apparent that while at all studied surface concentrations of CnCONH-j8-CD the two components behave independently of each other, as indicated by the location of all isotherms of mixed films falling between those corresponding to pure components, their collapse pressures gradually increased with the increase in the DPPC surface concentration. From Fig. 4 it is also apparent that the presence of CuCONH-j9-CD led to the disappearance of the liquid-expanded (LE) to the liquid-condensed (LC) phase transition characteristic of pure DPPC. 

DSC measurements showed an endothermic peak (Tc) at 40°C and at 51 °C in Me-Im-C2OC1 and in Me-Im-CiOCi respectively. This indicates that the phase transition characteristics of the glycobilayers are affected by the chemical structure of the IL. In addition, a similar behavior was observed for dialkyldimethylammonium bromides in the same ILs (Nakashima and Kimizuka, 2002). In both studies, bilayer vesicles were observed by dark-field optical micrographs only above the transition temperature. Moreover, no aggregate was formed with these surfactants in a conventional IL BmimPF6. 

For the analysis heat and mass transfer in concrete samples at high temperatures, the numerical model has been developed. It describes concrete, as a porous multiphase system which at local level is in thermodynamic balance with body interstice, filled by liquid water and gas phase. The model allows researching the dynamic characteristics of diffusion in view of concrete matrix phase transitions, which was usually described by means of experiments. 

The indicated transition pressure of 15 GPa is in agreement with the published data with shock-wave structure measurements on a 3% silicon-iron alloy, the nominal composition of Silectron. A mixed phase region from 15 to 22.5 GPa appears quite reasonable based on shock pressure-volume data. Thus, the direct measure of magnetization appears to offer a sensitive measure of characteristics of shock-induced, first-order phase transitions involving a change in magnetization. 

Typical runs consist of 100 000 up to 300 000 MC moves per lattice site. Far from the phase transition in the lamellar phase, the typical equilibration run takes 10 000 Monte Carlo steps per site (MCS). In the vicinity of the phase transitions the equilibration takes up to 200 000 MCS. For the rough estimate of the equihbration time one can monitor internal energy as well as the Euler characteristic. The equilibration time for the energy and Euler characteristic are roughly the same. For go = /o = 0 it takes 10 000 MCS to obtain the equilibrium configuration in which one finds the lamellar phase without passages and consequently the Euler characteristic is zero. For go = —3.15 and/o = 0 (close to the phase transition) it takes more than 50 000 MCS for the equihbration and here the Euler characteristic fluctuates around its mean value of —48. 

The behavior of the internal energy, heat capacity, Euler characteristic, and its variance ( x ) x) ) the microemulsion-lamellar transition is shown in Fig. 12. Both U and (x) jump at the transition, and the heat capacity, and (x ) - (x) have a peak at the transition. The relative jump in the Euler characteristic is larger than the one in the internal energy. Also, the relative height of the peak in x ) - x) is bigger than in the heat capacity. Conclude both quantities x) and x ) - can be used to locate the phase transition in systems with internal surfaces. 

Phase transitions have been characterized in a number of different pure and mixed lipid systems. Table 9.1 shows a comparison of the transition temperatures observed for several different phosphatidylcholines with different fatty acyl chain compositions. General characteristics of bilayer phase transitions include the following ... 

Particular phospholipids display characteristic transition temperatures (Tm). As shown in Table 9.1, increases with chain length, decreases with unsaturation, and depends on the nature of the polar head group. For pure phospholipid bilayers, the transition occurs over a narrow temperature range. The phase transition for dimyristoyl lecithin has a peak width of about 0.2°C. 

Native biological membranes also display characteristic phase transitions, but these are broad and strongly dependent on the lipid and protein composition of the membrane. 

The boundary layers, or interphases as they are also called, form the mesophase with properties different from those of the bulk matrix and result from the long-range effects of the solid phase on the ambient matrix regions. Even for low-molecular liquids the effects of this kind spread to liquid layers as thick as tens or hundreds or Angstrom [57, 58], As a result the liquid layers at interphases acquire properties different from properties in the bulk, e.g., higher shear strength, modified thermophysical characteristics, etc. [58, 59], The transition from the properties prevalent in the boundary layers to those in the bulk may be sharp enough and very similar in a way to the first-order phase transition [59]. 

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