Mass-induced Phase Transition

Figure 3.4.22 EtOH vapor adsorption istotherm curves at 5, 10, 15, 20 °C for [Cu2(bza)4(pyz)](a), Clausius-Clapeyron plot from ad- and desorption jumps (b), temperature difference between the curves at 10 and 20 °C (c), and the deduced mass-induced phase transition profile during a- 3 host crystal phase transition induced by the gas adsorption (d).

Figure 3.4.25 Generation and diffusion of crystal phase boundary in mass-induced phase transition in the single crystal. The cases of smooth guest diffusion (a) and not smooth (b) are shown. This can explain the pressure selective on-off adsorption shown in Fig. 3.4.24.

It is now well established that proteins can induce phase transitions in lipid membranes, resulting in new structures not found in pure lipid-water systems (c/. section 5.1). However, this property is not peculiar to proteins the same effect can be induced by virtually any amphiphilic molecule. Depending on the structure and nature of proteins, their interactions with lipid bilayers can be manifested in very different ways. We may further assume that the role of proteins in the biogenesis of cubic membranes is analogous to that in condensed systems, and lipids are necessary for the formation of a cubic membrane. This assumption is supported by studies of membrane oxidation, which induce a structure-less proteinaceous mass [113]. However, the existence of a lipid bilayer by itself does not guarantee the formation of a cubic membrane, as proteins may also play an essential role in setting the membrane curvature. In this context, note that the presence of chiral components e.g. proteins) may induce saddle-shaped structures characteristic of cubic membranes. (This feature of chiral packings has been discussed briefly in section 4.14)... 

Small molecular mass liquid crystals do not respond to extension and shear stress. Liquid crystalline polymers may exhibit a high elastic state at some temperature due to the entanglements. However, the liquid crystalline network itself is an elastomer, showing rubber elasticity. In the presence of external stress, liquid crystalline networks deform remarkably and then relax back after the release of stress. The elasticity of liquid crystalline networks is more complicated than the conventional network, such as the stress induced phase transition, the discontinuous stress-strain relationship and the non-linear stress optical effect, etc. 

Phase transition occurs at a state of thermodynamic equilibrium, inducing a change in the microstructure of atoms. However, corrosion is a typical nonequilibrium phenomenon accompanied by diffusion and reaction processes. We can also observe that this phenomenon is characterized by much larger scales of length than an atomic order (i.e., masses of a lot of atoms), which is obvious if we can see the morphological change in the pitted surface. 

In pharmaceutical systems, both heat and mass transfer are involved whenever a phase change occurs. Lyophilization (freeze-drying) depends on the solid-vapor phase transition of water induced by the addition of thermal energy to a frozen sample in a controlled manner. Lyophilization is described in detail in Chapter 16. Similarly, the adsorption of water vapor by pharmaceutical solids liberates the heat of condensation, as discussed in Chapter 17. 

The existence of a curved conformation associated with the action potential is supported by the fact that the ion influx at the spike will induce an increased average wedge-shape of the molecules, due to electrostatic screening of the lateral repulsion of phosphatidylserine molecules. Furthermore a conformation associated with the spike would directly relate action potential propagation to the mass-cooperative vesicular fusion, involved in the chemical signal transfer by transmitter molecules at the pre-synaptic membrane. Experimental support for this concept has been recently reported [39]. This well-controlled fusion process of numerous "vesicles" with the presynaptic membrane must take place as a phase transition. The... 

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