Phase Evolution and Morphology

Generally speaking, one of the most important roles that determine the conductivity of conductor/insulator composite is morphology, which was directly described in percolation models. No doubt that the conductivity of SP/IP composite strongly depends on the spatial distribution of SP component within the SP matrix, which is sensitive to the phase evolution during sample preparation. Therefore, here we would like to exclusively discuss the influence of phase evolution and thus formed morphology on material conductivity. 

C total /sP-rich SP rich +/ip.rich lP-rich (fSP-rich +/lP-rich )- 

Actually, for a realistic SP/IP composite, these two connections between SP-rich and IP-rich domains should both contribute to the macroscopic conductivity. The above discussion implies that in cases of Osp-rich S Uip.nch ot tsp-rich tip-rich. the spatial distribution of SP-rich domains within IP-rich domains is very crucial for 

Although some groups have achieved enhanced FET mobility of the SP/IP composite, they somehow proposed different morphological requirements for this enhancement, according to their respective sample preparation conditions. In Table 9.1, the phase evolution routes (tentatively drawn by the author of this chapter, 

Enhanced Conductivity of Conjugated Polymer/lnsulating Polymer Composites at Low Doping Level Interpenetrated Three-Dimensional Interfaces 

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Liu, Q., Mao, D., Chang, C. and Huang, F. (2007) Phase conversion and morphology evolution during hydrothermal preparation of orthorhombic I iMiiO, nanorods for lithium ion battery application, journui of Power Sources, 173, 538-544. 

An experimental paper by Akki et al [75], which provides a qualitative phenomenological framework for phase transitions and morphological evolution in polymer solutions (and especially for polymer crystallization from solution) based on the consideration of experimental data, is very informative from a practical standpoint. 

A. S. Barnard and P. Zapol. Predicting the energetics, phase stability, and morphology evolution of faceted and spherical anatase nanocrystals. J. Phys. Chem. B, 108 18435-18440, 2004... 

Jovic VD, Lacnjevac U, Jovic BM, Karanovic LJ, Krstajic NV (2012) Ni-Sn coatings as cathodes for hydrogen evolution in alkaline solution. Chemical composition, phase composition and morphology effects, hit J Hydrogen Energy 37 17882-17891... 

Phase Field Modeling on Phase Separation and Morphology Evolution... 

The various topics are generally introduced in order of increasing complexity. The text starts with diffusion, a description of the elementary manner in which atoms and molecules move around in solids and liquids. Next, the progressively more complex problems of describing the motion of dislocations and interfaces are addressed. Finally, treatments of still more complex kinetic phenomena—such as morphological evolution and phase transformations—are given, based to a large extent on topics treated in the earlier parts of the text. 

The pressure gap is also a considerable challenge in model catalysis. It has been only recently addressed thanks to new techniques that can work under high-pressure conditions (relative to UHV). As we have seen in the introduction, several techniques are now available but they have up to now rarely been applied on supported model catalyst. Indeed we can expect that the effect of the pressure can be more dramatic than on extended surfaces because small particles are easier subject to structural and morphological evolution during reaction. Thus, it will be necessary to probe the reactivity and to characterize structurally the model catalyst in realistic reaction conditions. Microscopy techniques like STM, AFM, and TEM, coupled with activity measurements are suitable. The ultimate goal would be to measure the reactivity at the level of one supported cluster and to study the coupling between neighbouring clusters via the gas phase and the diffusion of reactants on the support. 

Several research approaches are pursued in the quest for more efficient and active photocatalysts for water splitting (i) to find new single-phase materials, (ii) to tune the band-gap energy of TJV-active photocatalysts (band-gap engineering), and (iii) to modify the surface of photocatalysts by deposition of cocatalysts to reduce the activation energy for gas evolution. Obviously, the previous strategies must be combined with the control of the s)mthesis of materials to customize the crystallinity, electronic structure, and morphology of materials at nanometric scale, as these properties have a major impact on photoactivity. 

The temperature of the binodal and onset of phase separation is dependent on the composition. In a quench experiment, the time evolution of the phase separation is dependent on the end temperature and the composition. This means that the depth into the incompatibility region at a given position has an impact on the time evolution. Phase separation will then be trapped by gel formation, and it is the relative kinetics between phase separation and gel formation that determines the final morphology. Figure 13.12 gives an example of how the morphology of a discontinuous system depends on the composition and the relative kinetics of phase separation and gel formation (Loren and Hermansson 2000). 

Anatase, brookite and rutile are three polymorphs of titanium dioxide. Anatase is a kind of thermodynamically metastable form while rutile is a kind of stable one. Anatase can transform irreversibly to rutile at elevated temperatures ranged from 400 to 1200 °C according to particle size, morphology and additives. The solid-state phase transformation behavior has been widely investigated while the phase evolution between anatase and rutile under hydrothermal condition has been little paid attention to so far [5]. In this work, the structural evolution from anatase to rutile under milder hydrothermal conditions is proposed as well [7, 10]. 

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