Solid-like state

The mechanisms of static friction and stick-slip motion, as discussed in the last section, are supposed to be a good description of dry friction. Another case, perhaps more general in engineering practices, to be addressed in this section is lubricated sliding where liquid lubricant, consisting of a few molecule layers, is confined between two solid walls. Both experimental and theoretical studies indicate, as we have discussed in Chapter 5, that there are substantial changes in rheology of the confined lubricant, and the liquid may transit practically to a solid-like state when film thickness becomes molecularly thin [32,33]. 

Domain formation in binary mixtures of a polymerizable lipid and non-polymerizable lipid is well established for diacetylenic lipids. The rigid diacetylenic unit facilitates the formation of enriched domains in the condensed phase of monolayers or the solid-analogous phase of bilayers. Since diacetylenes polymerize most readily in solid-like states, most studies have focused on conditions that favor domain formation. Only in the case of a mixture of a charged diacetylenic lipid and a zwitterionic PC was phase separation not observed. Ringsdorf and coworkers first reported the polymerization of a phase-separated two-dimensional assembly in 1981 [33], Monolayer films were prepared from mixtures consisting of a diacetylenicPC (6) (Fig. 5) and a nonpolymerizable distearoyl PE (DSPE). 

Trappe, V., and Sandkuhler, P. (2004). Colloidal gels low-density disordered solid-like states. Curr. Opinion Colloid Interface Sci. 8,494-500. 

Sheiko, S.S. Eckert, G. Ignat eva, G. Muzafarov, A.M. Spickermann, J. Raedar, H.J. Moeller, M. Solid-like states of a dendrimer hquid displayed by scanning force microscopy. Macromol. Rapid Commun. 1996, 17, 283-297. 

Starting from a solid-like state obtained in the above test under the condition of p=p state of the phase in pore under the condition of p//ij[Pg.37]

Typical results are shown in Fig. 6 for U-methane in graphite pores of H =7.5 at T=114 K. At p/ps=l the system is solid-like at this temperature, but a discrete change in density occurs around p ps ca.0.5. The self diffiisivity along axial direction also shows drastic change at this point. Further examination of various characteristics of molecular state such as snapshots, in-plane pair correlations and static structure factors confirmed that this change in density is the result of a phase transition from solid-like state to liquid-like one, or melting. Since the critical condensation condition for this pore is far lower than this transition point to stay around p ps= ca.0.2, the liquid-like state is not on metastable branch but thermodynamically stable. Thus a solid-liquid coexistence point is found for this temperature. 

Figure 7. The Allan variances for time series of a geometrical parameter of Ao for the cases of (a) the liquid-like state and (b) coexistence region where the frequent transitions between solid-like and liquid-like states are observed. The Allan variance for the solid-like state is qualitatively the same aside from the magnitude. [Reprinted with permission from C. Seko and K. Takatsuka, J. Chem. Phys. 104, 8613 (1996). Copyright 1996, American Institute of Physics.]...

We analyzed the distribution of solid-like H2O molecules (SI-H2O molecules) near the interface to investigate the interface structure. The SI-H2O molecules were defined as the molecules that have four nearest neighbors and are connected by a hydrogen bond (HB) with each of the nearest neighbors. In this study, in order to search for the H2O molecules that were in a stable solid-like state for a long time, the SI-H2O molecules were analyzed using the time-averaged coordinates of H2O molecules over a period of 0.1 ns. 

Simatos et al. (1981) measured the mobility of a spin-label probe, TEMPO, a stable free radical commonly used for electron paramagnetic resonance (EPR) spectroscopy. She found that the probe showed no mobility below a critical that correlated to Wq. A critical a also existed at which the probe demonstrated a partitioning into a dissolved and a solid-like state. This critical a could represent the moisture content correlating to Tg, though this concept had not been introduced in foods at that time. The partitioning of a... 

If the four particles had 16 possible positions, there would be 1820 possible combinations. Nine of these would be in solid-like states, and the other 1811 would be in gas-like states. Thus over 99.5% of the possible arrangements would represent gaslike states, as opposed to 96% for the system with 9 possible positions. This shows that an increase in the number of possible positions leads to an increase in the probability that the system will be in a more dispersed, gas-like state. In real systems, which provide a huge number of possible positions for particles, there is an extremely high probability that substances will shift from the less dispersed, solid form, which has fewer ways of arranging the particles, to the more dispersed, gas form, which has more ways of arranging particles. 

In Fig. 22, three typical types of DSC curves are shown for the DMPE-water system at the same water content. A distinct difference in the thermal behavior is observed not only for the phase transition of the Upid but also for the melting of the ice. Figure 23 shows a schematic diagram of relative enthalpy (AH) versus temperature (t) curves that was constructed on the basis of the transition enthalpies and temperatures associated with the lipid phase transitions shown in Fig. 22. By reference to the diagram, it becomes apparent that the DMPE-water system can be present in two phases, designated the L- and //-subgel phases, other than the gel phase at temperatures where the hydrocarbon chains of the lipids are in a solid-like state and the thermodynamic stability of these phases increases... 

For purpose of this book distinctions will be made between physical adsorption for the liquid-like state and in the solid-like state. Figs. 1 and 2 illustrate... 

The state of the oil film in the dimple zone would behave as liquid state according to the high temperature rise in the dimple zone. At the beginning when Kaneta s dimple was discovered, it was thought that the state of Ae dimple behaved as solid-like state. Ehret et al [15] developed a model based upon the oil solidification to explain the dimple phenomena. However, the solidification of oil is bard to be considered in the conditions of above 200 K. Therefore, we can conclude that the dimple would be formed by the viscosity wedge action due to the temperature variations across the oil film. 

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