Anisotropic expansion

This intermolecular potential for ADN ionic crystal has further been developed to describe the lowest phase of ammonium nitrate (phase V) [150]. The intermolecular potential contains similar potential terms as for the ADN crystal. This potential was extended to include intramolecular potential terms for bond stretches, bond bending and torsional motions. The corresponding set of force constants used in the intramolecular part of the potential was parameterized based on the ab initio calculated vibrational frequencies of the isolated ammonium and nitrate ions. The temperature dependence of the structural parameters indicate that experimental unit cell dimensions can be well reproduced, with little translational and rotational disorder of the ions in the crystal over the temperature range 4.2-250 K. Moreover, the anisotropic expansion of the lattice dimensions, predominantly along a and b axes were also found in agreement with experimental data. These were interpreted as being due to the out-of-plane motions of the nitrate ions which are positions perpendicular on both these axes. 

The heat of solution of hydrogen in the delta-hydrided phase decreases with increasing solute concentration" from — 195 J/mol in 5 of composition ZrHi,4 to — 158J/mol in 6 of composition ZrHi.g. No discontinuity in the function occurs throughout the d-to-e range, involving H/Zr compositions of 1.4-1.9. This is compatible with the transition from fcc-<5 to fct-s, involving a continuous anisotropic expansion... 

The findings above support the idea of an anisotropic expansion of holes with the temperature in PPGs, at least for molecular weights of dimer and above. Only in the absence of constraints (an ideal case) or with constraints acting with the same intensity in all directions, does one expect to find an isotropic expansion. Such a situation could explain the result for the monomer, whose molecules are arranged more symmetrically with respect to the other PPG samples. Indeed, in this case the value of k deduced from the fit to experiment is the highest and quite near 3. 

Figure 8.9 The anisotropic expansion of uniaxially stretched film...

Figure 8.83 shows the schematic construction of a chemomechanical rotor, where anisotropic expansion causes rapid bending of the film due to the sorption of water vapor from one side of the film [140]. The rotation continued until the adsorbates were completely vaporized. This moving device may become a clean and silent power source for use as a molecular engine where the chemical free adsorption energy is transduced into the mechanical work. 

Berdichevsky, Y., and Y.-H. Lo. 2003. Polymer microvalve based on anisotropic expansion of polypyrrole. Presented at the Material Research Society Symposium. Fall 2003 Meeting, Boston. 

If the anisotropic expansions of the unit cells are considered, CZP behaves in an opposite way to Sro 5Zr2(P04)3 (SZP). Increasing the temperature of CZP leads to c axis expansion and a axis contraction, while in the case of SZP the c axis contracts and the a axis expands. The use of a suitable CZP/SZP solid solution with composition (Ca,Sr)o 5Zr2(P04)3 leads to almost constant a and c axis lengths as the temperature is increased with a resultant thermal expansion coefficient of almost zero (Table 12.28). 

Roudier E, Fernandez A., Fujita M., Himmelspach R., Bomer G., Schindelman G., Song S., Baskin T., Dupree P., Wasteneys G, and Benfey P. (2005). COBRA, an Arabidopsis extracellular GPl-anchored protein, specifically controls highly anisotropic expansion through its involvement in cellulose microfibril orientation. The Plant Cell 17 1749-1763. 

Berdichevsky Y, Lo Y-H (2003) Polymer mierovalve based on anisotropic expansion of polypyrrole. In Proceedings - Materials Research Society Symposium. Boston, United States, 782 pp 101-107... 

Alici G, Huynh NN (2007) Performance quantification of conducting polymer actuatois for real applications a microgripping system. lEEE/ASME Trans Mechatron 12 73-84 Bay L, Jacobsen T, Skaarup S, West K (2001) Mechanism of actuation in conducting polymers osmotic expansion. J Phys Chem B 105 8492-8497 Berdichevsky Y, Lo YH (2003) Polymer microvalve based on anisotropic expansion of polypyrrole. MRS Online Proc Libr 782 101-107... 

The thermal properties of fibre-reinforced composites are anisotropic. Expansion in the direction of the fibre is usually very small or negative, but the thermal conductivity of some carbon fibre composites in the fibre direction can be high. Most polymers and several types of fibre are good electrical insulators. Carbon and some ceramic fibres have a much lower resistivity. It is thus possible to use composites for manufacturing radomes as well as for electromagnetic screening materials and systems which absorb radar signals. 

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