Polymers thermal diffusivity data

Here the subscript i refers to the solvent, whereas the superscript (A or B) refers to the component homopolymer. For example, ai is the thermal diffusion coefficient of a homopolymer consisting of component B in solvent 1. Parameters [rj]i and Xi are the intrinsic viscosity and retention parameter measured on the copolymer in solvent i T g in equation 9c is the temperature at the center of gravity of the retained polymer zone in solvent i, while rjo is the viscosity of solvent i at Teg- Equations 7 through 9 are applicable to copolymers with only two components similar equations could be derived for n-component copolymers, in which case My and Xa are determined from retention and viscosity data in n separate solvents. 

Any attempts to obtain the parameters of the chromatograms and the physicochemical constants which are measurable in theory, by FFF, will be affected by the sample mass injected into the FFF channel. All of the concentration effects on the chromatograms discussed in the previous sections will be transferred, in turn, to those measured parameters and the physicochemical constants, such as the mass selectivity (S ), the common diffusion coefficient (D), the thermal diffusion coefficient (Dj-), and so forth. The increased retention of large polymers will result in enhanced mass selectivity in ThFFF. For a long time, this enhanced selectivity, in turn, the enhanced ThFFF universal calibration constant n, has led to confusion concerning the accuracy and repeatability of FFF, because different research groups have reported different data for selectivity and physicochemical constants measured by FFF for a given polymer-solvent combination [2,11]. Recent studies show that the enhanced selectivity and the different values of the physicochemical constants reported by different laboratories, measured by ThFFF, may be caused by different concentrations (sample mass) used by different laboratories. 

In the previous chapters experimental data on ablation of the designed polymers have been shown. Polyimide was applied as reference polymer to compare the ablation behavior of the designed polymers versus a commercial polymer which exhibits similar absorption properties. Polyimide is most probably also the most studied polymer in ablation, and numerous reference data about ablation, but also about the chemical properties, exist (e.g., thermal diffusivity, heat capacity, reflectivity, lifetime of exited states etc.). This is also the reason why many models are benchmarked against ablation data of polyimide. 

Figures. Thermal-diffusion coefficient Dfh=DST of the polystyrene-toluene solutions as a function of the polymer concentration. The symbols indicate the values deduced from the experimental data obtained for D and ST with an optical beam-bending technique [22]. The curve represents the values calculated from Eqs. (7) and (10) for D and S. ...

It is difficult to calculate thermal conductivity of oriented filled polymers, all the more to ascertain the temperature dependence of thermal conductivity ( ), thermal diffusivity (a), and specific heat (c). The calculation formulae cannot allow for such phenomena as the glass-transition of polymers, the possible lamination of polymer films due to the great discrepancy between the coefficients of linear expansion of the binder and filler, the effect of multiple thermal loading, etc. Therefore, most valuable are the experimental data on thermophysical properties of composite polymers in a wide temperature range (between 10 and 400 K). 

Thermal conductivity (K) and thermal diffusivity (/c) measurements versus temperature or blend composition can be employed to reveal structural information. However, it is not as sensitive as other methods and relatively few studies have been reported on blends. Thermal diffusitivies of polymers are generally in the range of 10 cm /s. A relevant review of thermal conductivity of polymer blends has been reported by Tsutsumi [197], where PVME/PS, PVC/PCL, PMMA/PC and PVF2/PMMA blend data were reviewed. The thermal conductivity, K, and thermal diffusivity, K, have analogies with permeability, P, and diffusion coefficient, D, respectively. This analogy is the result of the similarities between Fourier s law and Fick s law ... 

H. G. Kilian, M. Pietralla (Polymer 7P, 664-672, 1978) derive from the anisotropy A of the thermal diffusivity a = X/cpp of oriented polyethylenes that the intrinsic anisotropy Ai of the orienting, partly crystalline lamellar clusters increases with the degree of crystallinity (Aj = 7 to 26, linear extrapolation yields Aj = 2 for the fully amorphous and Aj = 50 for a completely crystalline cluster) the average degree of orientation of the lamellae, , as determined from thermal measurements agrees very well with X-ray data the observed increase of orientation with draw ratio is more rapid than it would be in affine deformation. 

The thermophysical properties, such as glass transition, specific heat, melting point, and the crystallization temperature of virgin polymers are by-and-large available in the literature. However, the thermal conductivity or diffusivity, especially in the molten state, is not readily available, and values reported may differ due to experimental difficulties. The density of the polymer, or more generally, the pressure-volume-temperature (PVT) diagram, is also not readily available and the data are not easily convertible to simple analytical form. Thus, simplification or approximations have to be made to obtain a solution to the problem at hand. 

The diffusion coefhcients of dilute solutions of polystyrene in toluene are plotted in Fig. 8.20. Data on dilute solutions of flexible polymers obey Eq. (8.23). The data in Fig. 8.21 exhibit the expected crossover from -solvent scaling (z/ = 1 /2) at low molar masses where the coils are smaller than the thermal blob to athermal solvent scaling (i/ = 0.588) at high molar masses where there are many thermal blobs per chain. 

Durill, P.L. Griskey, R.G. Diffusion and solution of gases in thermally softened or moten polymers Part I. Development of technique and determination of data. AIChE J. 1966, 12, 1147-1151. 

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