Nano-Sized Phase Diagrams

Calculation of Nano-Sized Phase Diagrams of Binary Alloys... 

The synthesis of nano-sized particles from CaCC>3 and BaCC>3 was carried out in a recurrent reactor equipped with stirrer and was close to reactor with ideal mixing. Chemical interaction between CO2 and the corresponding alkali suspension (dispersed in organic phase) takes place in the reactor. The process is endothermic so the device was equipped with cooling jacket. A diagram of the device is shown in Fig. 1. 

The authors have described some fundamental procedures to evaluate the solid-liquid phase relations of nano-sized particles in binary alloys from the calculation of the surface properties as well as the phase equilibira on the basis of thermodynamic databases, which are usually used for the calculation of phase diagrams of the bulk materials. In order to obtain quantitatively precise values of the melting points and liquidus temperatures in alloys, we should carry out further investigation as follows ... 

We can, however, evaluate the phase equilibria of small particles qualitatively from the macroscopic thermodynamic point of view as described in the present paper. Thus, the authors wish that enormous attention be paid to the application of thermodynamic databases to the calculation of the phase diagrams of the nano-sized particles, whose information will be in demand increasingly in the near future. 

The case of block copolymers is peculiar and deserves a specific development. In such a structure, the A and B blocks are connected to one another by a covalent bond, and their respective molar mass and composition can be varied independently. Being incompatible, A and B blocks tend to minimize their surface of contact but, contrary to the mere blends of two polymers they cannot phase separate to a macroscopic scale due to the bond which links them. Classical composition-temperature phase diagrams cannot be constructed for block copolymers as for the corresponding blends. Indeed the A and B blocks are forced to self-organize in domains of more reduced nano- or mesoscopic size. The transition from a homogeneous blend to a system composed of ordered phases as well as the size and the morphology of these ordered phases depend on two elements the product Xab " (X = total degree of polymerization) and the dissymmetry in size of the two blocks. 

Morales et al. [50] systematically studied the relation between the emulsion droplet sizes and the phase behavior at the HLB temperatures for different compositions in the water/CigEg/mineral oil system. Figure 21.2 shows the fish-shaped phase diagram obtained as a function of temperature and surfactant concentration for a fixed oil/(water -f oil) weight ratio, = 0.2. Several nano-emulsions were prepared at different concentrations of the CigEg surfactant, from 1 to 9 wt%, observing a sharp decrease in emulsion droplet sizes when the CigEg concentration was around 3-4 wt%... 

All the authors report a decrease in the nano-emulsion droplet size when the surfactant concentration increases, since there is more surfactant available to stabilize more interfaces, and therefore smaller droplets can be obtained. In general, it is observed in the phase diagrams that the region with phases with planar structure, that precedes the region where nano-emulsions are formed, extends to higher water concentrations when the surfactant/oil ratio increases, because when more surfactant is present, it can dissolve more water inside the bicontinuous or liquid crystal structure (as an example, see Eigure 21.6). 

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