Crystallization path dependence

Seguela and Prud homme (1989) investigated a PE-PEP-PE triblock copolymer containing 27wt% poly(ethylene) cast from a neutral solvent close to the Tm of PE and well below it. The samples cast above Tm crystallized within the assumed hexagonal-packed cylinder microphase-separated structure. However, SAXS experiments performed on the samples cast at room temperature suggested that crystallization occurred without prior microphase separation in the melt. This path dependence is a general feature of crystallization in block copolymers. 

The crystallization path of mixtures, the figurative points of which lie in the region of the primary crystallization of the component A, pc(A), depend on the part of this crystallization field, in which the figurative point of the system lies. Three cases may occur. 

The velocity relevant for transport is the Fermi velocity of electrons. This is typically on the order of 106 m/s for most metals and is independent of temperature [2], The mean free path can be calculated from i = iyx where x is the mean free time between collisions. At low temperature, the electron mean free path is determined mainly by scattering due to crystal imperfections such as defects, dislocations, grain boundaries, and surfaces. Electron-phonon scattering is frozen out at low temperatures. Since the defect concentration is largely temperature independent, the mean free path is a constant in this range. Therefore, the only temperature dependence in the thermal conductivity at low temperature arises from the heat capacity which varies as C T. Under these conditions, the thermal conductivity varies linearly with temperature as shown in Fig. 8.2. The value of k, though, is sample-specific since the mean free path depends on the defect density. Figure 8.2 plots the thermal conductivities of two metals. The data are the best recommended values based on a combination of experimental and theoretical studies [3],... 

The qualitative voltammetric behavior of methanol oxidation on Pt is very similar to that of formic acid. The voltammetry for the oxidation of methanol on Pt single crystals shows a clear hysteresis between the positive- and negative-going scans due to the accumulation of the poisoning intermediate at low potentials and its oxidation above 0.7 V (vs. RHE) [Lamy et al., 1982]. Additionally, the reaction is also very sensitive to the surface stmcture. The order in the activity of the different low index planes of Pt follows the same order than that observed for formic acid. Thus, the Pt(l 11) electrode has the lowest catalytic activity and the smallest hysteresis, indicating that both paths of the reaction are slow, whereas the Pt( 100) electrode displays a much higher catalytic activity and a fast poisoning reaction. As before, the activity of the Pt(l 10) electrode depends on the pretreatment of the surface (Fig. 6.17). 

Compton profile. Furthermore the contribution of the multiple scattered photons to the measured spectra has to be taken into account (for example by a Monte Carlo simulation [6]). Additionally one has to take heed of the fact that the efficiency of the spectrometer is energy dependent, so the data must be corrected for energy dependent effects which are the absorption in the sample and in the air along the beam path, the vertical acceptance of the spectrometer and the reflectivity of the analyzing crystal. 

Simply visualised, the infrared beam penetrates (of the order 0.3-3 pm, dependent on its wavelength) just beyond the ATR crystal-specimen boundary before it is reflected back and makes its way through the crystal to the detector. On this short path (of the evanescent wave) into the sample surface layer, light is absorbed, and the reflected beam carries characteristic spectral information of the sample. The decaying amplitude of the evanescent wave and the depth of penetration dp at which it has decreased to a proportion of 1 /e is defined by the Harrick equation (Equation (2)), where X is the wavelength of the incoming... 

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