Quasi-solid materials

Combined systems of charge transfer in groimd and excited states have been mentioned in Section 14.2. This provides a fundamental idea for designing future electronic and photonic devices to solve global problems such as environment and energy resources. New quasi-solid materials composed of polysaccharide containing a large excess water have been described in which electrochemical and photochemical reactions can be carried out in the same way as in pure water without any outer cell or flask. These new materials could open the way to a new chemistry and devices in the future. 

In building mathematical models of product formation in a mold it is possible to treat a polymeric material as motionless (or quasi-solid), because the viscosity grows very rapidly with the formation of a linear or network polymer thus, hydrodynamic phenomena can be neglected. In this situation, the polymerization process itself becomes the most important factor, and it is worth noting that the process occurs in nonisothermal conditions. 

However, the presence of liquid electrolyte has the problems of leakage, robust sealing, and device stability, thus results in limited commercialization. Quasi-solid-state and solid-state DSSCs based on nonvolatile ionic liquid or organic hole-conducting material/polymer as the electrolyte are, therefore, developed to circumvent the sealing problem. 

Quasi-solid state dye-sensitized solar cells (DSCs) have been constructed using a new polymeric ionic fluid as the electrolyte.119 The electrolyte was synthesized by the sol-gel route using MTMSPI+I as the precursor that was made by derivatizing methylimidazolium with triethyoxysilane. Condensation of this material in the presence of formic acid and in the absence of water led to Si-O-Si-O-type polymerization and formation of a polysilsesquioxane-type structure. When this material was mixed with iodine, it served as a redox electrolyte for DSCs. The DSCs made this way are robust and easy to assemble but their efficiency of 3.1% is relatively low. However, possible improvement lies in modification of the organic groups attached to the polysilsesquioxane backbone. 

Wang, P., S.M. Zakeeruddin, J.E. Moser, M.K. Nazeeruddin, T. Sekiguchi and M. Gratzel (2003b). A stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizer and polymer gel electrolyte. Nature Materials, 2(6), 402-407. 

In a surprising recent development, Kratschmer et al. have shown that certain all-carbon molecules are produced in large quantities in the evaporation of graphite and can be isolated as soluble, well-defined solids. The major species was identiHed as molecular C ) through mass spectrometry and by comparison of the infrared spectrum with theoretical predictions for the celebrated truncated-icosahedron structure, which had earlier been proposed to account for cluster beam observations. The solid material, described as a new form of elemental carbon in a nearly pure state, has a disordered hep lattice of packed quasi-spherical molecules, but determination of the precise molecular structure awaits diffraction from well-ordered crystals. 

In practice, a solid catalyst is most conveniently modeled as a quasi-homo-geneous phase. Even if the catalyst particle is porous, visualize it as a homogeneous, but permeable solid. Mass transfer in its interior is retarded by two effects obstruction of part of the cross-sectional area by the solid material, and diffusion paths that are longer because molecules have to wind their way around the obstructions (tortuosity effect). In the quasi-homogeneous model, the retardation is accounted for by the use of appropriately smaller "effective mass-transfer or diffusion coefficients. 

Our tribological experiments with the liquid crystals can be summarized as follows. LCl, which is in the nematic phase at the room temperature was subjected to a traction test. The traction of this sample is almost half of a normal liquid lubricant under the same conditions. Note that the traction did not change with die increasing speed after the initial sharp drop. These results are consistent with a quasi-solid lubricant shearing between the bounding surfaces. It should be mentioned here that a surface active material was put on the surface of the steel ball before the LCl was inserted. It was used to prevent the liquid crystal from slipping on the smooth steel surface. In any case, the traction data were unusual and would put liquid crystals of this type into a special class of lubricants. 

There are two kinds of polymer material that used in quasi-solid/solid state DSSCs. For quasi-solid electrolytes, polyionic liquids have been proposed as solvent and redox couple as solute. They appear in molten salts and present many promising properties, such as, high chemical and thermal stability and high ionic conductivity Their main drawback is related to its high viscosity, which makes the ions diffusion rather slow. As the transport of ions to the counter electrode in an ionic liquid matrix represents a rate-limiting step in DSSC (Bella, 2015), the performance of quasi-solid electrolytes based solar cell is imsatisfled. 

Fan, L. Q., J. Zhong, J. H. Wu, J. M. Lin, and Y. F. Huang. 2014. Improving the energy density of quasi-solid-state electric double-layer capacitors by introducing redox additives into gel polymer electrolytes. Journal of Materials Chemistry A 2 9011-9014. 

The reversing heat capacity and the total heat-flow rate of an initially amorphous poly(3-hydroxybutyrate), PHB, are illustrated in Fig. 6.18 [21]. The quasi-isothermal study of the development of the crystallinity was made at 296 K, within the cold-crystallization range. The reversing specific heat capacity gives a measure of the crystallization kinetics by showing the drop of the heat capacity from the supercooled melt to the value of the solid as a function of time, while the total heat-Uow rate is a direct measure of the evolution of the latent heat of crystallization. From the heat of fusion, one expects a crystallinity of 64%, the total amount of solid material, however, when estimated from the specific heat capacity of PHB using the ATHAS Data Bank of Appendix 1, is 88%, an indication of a rigid-amorphous fraction of 24%. 

Finally, with Fig. 2.11 taken as an example, the method called dynamic capacity is discussed [49] When employing the methods of investigation of the HASP, some researchers use the CVA at extremely low scan rates, down to few microvolts per second. It is suggested that at such rate, no concentration gradient forms in the solid material, and the insertion proceeds at quasi-equilibrium conditions. The value Hv is called the dynamic capacity (v is the potential scan rate), and is equivalent to the derivative dx/d eq- It is believed that the analysis of the dx/d eq versus eq allows determining the points of phase transitions. 

Capillary columns have a very small internal diameter, on the order of a few tenths of millimeters, and lengths between 25-60 meters are common. The inner column walls are coated with the active materials (WCOT columns), some columns are quasi solid filled with many parallel micropores (PLOT columns). Most capillary columns are made of fused-silica (FSOT columns) with a polyimide outer coating. These columns are flexible, so a very long column can be wound into a small coil. 

Up to now, many types of polymer gel electrolytes have been used in quasi-solid-state DSSCs, including polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polymethylmethacrylate (PMMA), and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). PVDF-HFP exhibits high ionic conductivity and stability at room temperature however, the complex preparation technology and the poor mechanical strength of these gel polymer-based DSSCs represent a bottleneck to their introduction to the market. To overcome this problem, the electrospinning of such polymers has been performed with the aim of integrating the resulting fibrous, easy-to-obtain, and low-cost materials as electrolytes [23]. 

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