Thermal force experimental results

In this review, we show our own results of thermal molecular motion of PS at the free surface by mainly scanning force microscopy and at the substrate interface by space-resolved fluorescence spectroscopy. To do so, we also adopt coarse-grained molecular dynamics simulation to strengthen experimental results. Finally, we... 

In this section experimental results are discussed, concerned with analyses of melting and crystallization kinetics, as well as reversibility of the phase transition. The frame of the discussion is set by Fig. 3.76, which will be supported by experimental data on poly(oxyethylene). The thermal analysis tools involved are TMDSC, optical and atomic-force microscopy, DSC, adiabatic calorimetry, and dilatometry. Most of these techniques are described in more detail in Chap. 4. Results from isothermal crystallization, and reorganization are attempted to be fitted to the Avrami equation. This is followed by a short remark on crystallization regimes and finally some data are presented on the polymerization and crystallization of trioxane crystals. 

The thermal force is sufficiently complex that experimental investigations have often obtained widely different results. Recent advances in experiment and theory may resolve some of these differences. However, the theory of the thermal force still lacks a general rigorous development. 

The temperature effect on the gel friction is shown in fig. 11.11 [20]. An increase in temperature from S C to 45°C leads to both a decrease in the frictional force and an increase in the velocity where the friction force shows the maximum. This temperature dependence agrees well with the surface adhesion mechanism. An increase in temperature should result in a decreased friction force due to an increase in the thermal agitation that favors desorption. At the same time, the v, of the polymer chain increases with an increase in temperature, originating partly from the increased thermal energy and partly from the decreased viscosity of the solvent, as shown by eq. (11.2). As shown in fig. 11.11, when the temperature is raised from 5°C to 45°C, the velocity at which the friction shows a maximum, v iuCTeases five times. The theory expressed in eq. (11.2) predicts about a three-times increase in Vj, which roughly agrees with the experimental results. 

Peles et al. [22] investigated heat transfer and pressure drop phenomena over a bank of micro-pin fins in a micro-heat sink. The dimensionless total thermal resistance was expressed as a function of Re)molds number, Prandtl number and the geometrical configuration of the pin-fin microheat sink. They compared their theoretical model with their experimental results and concluded that very high heat fluxes can be dissipated at a low wall terr5>erature rise using a microscale pin-fin heat sink. Thus, forced convection over shrouded pin-fin arrays is a very effective cooling device. In many cases, the primary cause for the rise in wall temperature is the increase of the fluid tempera-... 

Reasonable ab initio results have also been obtained for the thermal expansion coefficient and isothermal compressibility [S(/c = 0)] of Polyethylene melts. The latter was computed using the experimental T-dependent density and the assumed dominance of soft repulsive forces. The resulting S(0) was found to be roughly 20% larger than the experimental values, although excellent agreement was obtained for the relative temperature dependence over the entire experimental range of 7 = 380-525 K. 

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