Temperature, closed display cases

Temperature. An interesting interplay between temperature and RH has been seen in closed display cases housing moisture-containing material (22). Normally, as the temperature in the display case rises, the local RH would correspondingly decrease. With moisture-containing material, however, the RH actually increases with increasing case temperature. At elevated temperatures, water evaporates from the wood structure. This liberated water vapor enters warmed air, which has a greater potential to retain moisture. Thus, RH within the case increases. 

In all of these applications the particles are soft and must be capable of forming a film at temperatures close to room temperature. In addition, they must display favorable interactions with the surface of the substrate on which they are applied. In this respect, a review of recent publications and patents showed that structured latex particles still represent an active area of research, the principal objective being to improve the performances of the coating formulation. Indeed, as will be illustrated below in the case of organic/inorganic colloids, structured latexes represent a possible means to overcome the usual compromises between a good film quality and optimal properties. 

A question arises about the reason for the failure of the additivity law in the above-mentioned systems, both the polyolefins blends [10] and the multiblock copolymer. Obviously, one has to assume that, for multicomponent and/or multiphase systems, when one of the components (phases) is characterized by a viscosity at room temperature close to those of the low-molecular-weight liquids, the mechanism of the response to the applied external mechanical field is different from that when all the components (phases) have Tg and higher than room temperatme. In the latter case all the components (phases) plastically deform as a result of the applied external force. In the former case, in addition to the plastic deformation of the harder components (phases), they are also displaced within the soft (liquid) matrix in which they are floating . The extent of this displacement depends on the viscosity of the matrix (the softer component and/or phase). This is the reason why the harder components cannot display their inherent microhardness. The microhardness is reduced by the ability of the harder components to move. This situation is illustrated in Figure 13.3. 

Figure 6.39(a) shows the vs. T curve, normalized to the RT value, for a 100 nm thick a-/ -NPNN/glass film obtained from electron paramagnetic resonance (EPR) measurements with the static magnetic field applied perpendicular to the substrate plane. As previously shown in Fig. 3.19, the molecular a -planes are parallel to the substrate s surface. The data points closely follow the Curie-Weiss law = (T — w)/C, where C stands for the Curie constant. In this case w — —0.3 K, indicating that the net intermolecular interactions are weakly anfiferromagnetic. No hint of a transition at low temperature is observed. These results coincide with those derived from SQUID measurements on a single a-p-NPNN crystal (Tamura etal, 2003), where 0.5 < w < 0, which are displayed in Fig. 6.40. 

Numerical calculations of (Sz) at 300 K obtained with eq. (22) for all /((III) free ions are collected in table 3 (Golding and Halton, 1972). Pinkerton et al. (1985) have demonstrated that (Sz) are relatively insensitive to the choice of various sets of reported spin-orbit coupling constants. Moreover, except for R = Sm and Eu, (Sz) displays a minor dependence on the temperature and the data calculated at 300 K (table 3) are amenable for a reliable treatment of contact shifts in solution around room temperature. The close proximity of excited states possessing different J manifolds for Sm(III) requires a precise calculation of (Sz) at each temperature as is the case for R = Eu. However, the latter metal brings some specific complications associated with the absence of a well-defined gj value for its 7 = 0 ground state. Golding... 

Figure 29.2 displays three situations at constant temperature, T and pressure, P. In diagram (a) we have a single closed phase (labelled a) which contains two components labelled 1 and 2 whose chemical potentials are and but the thermodynamic system is such that no matter can be transferred across the boundaries of the system. Hence adapting equation (29.6) to apply to this case, the change in free energy, dG a) for the system is given by ... 

The commonest polymorphic changes of this type are those associated with the onset of free rotation in a crystal structure. Many simple molecular compounds (HC1, HBr and CH4 are examples) show a transition with rising temperature from a complex structure to a simple close-packed arrangement in which the molecules effectively acquire spherical symmetry by free rotation. Similar effects are displayed by a number of ionic crystals containing complex ions of un-symmetrical shape. Thus NaCN, KCN and RbCN have complex structures at low temperatures but transform at higher temperatures to the sodium chloride structure in which the CN ions behave as spherical entities. In some cases rotation may take place only about one axis, so that the molecule or group acquires cylindrical rather than spherical symmetry, and in other cases rotations about different axes may be excited successively at different temperatures. An extreme example of this is ammonium nitrate, in which both cation and anion are capable of... 

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