Forms molecularly aligned

Nucleation can occur either homogeneously or heterogeneously. Homogeneous nucleation occurs when random molecular motion in the molten state results in the alignment of a sufficient number of chain segments to form a stable ordered phase, known as a nucleus. The minimum number of unit cells required to form a stable nucleus decreases as the temperature falls. Thus, the rate of nucleation increases as the temperature of the polymer decreases. The rate of homogeneous nucleation also increases as molecular orientation in the molten polymer increases. This is because the entropy difference between the molten and crystalline states diminishes as molecular alignment in the molten state increases. 

Methacrylic acid also polymerizes in bulk under precipitating conditions. It forms molecular associations very similar to those of acrylic acid. However, the conversion curves were found to be linear under a variety of experimental conditions temperatures of 16.5 to 60°C and broad ranges of initiation rates and monomer concentration in numerous solvents (7). It was assumed that structures of type III do arise but owing to steric hindrance and to the rigidity of the poly(methacrylic acid) molecule the monomer cannot align to form a "pre-oriented" complex as in the case of acrylic acid and propagation is not favored. 

Equation 2.74 is a general form that is used in a number of field-based approaches to 3-D molecular alignment and similarity. For example, in the program Seal (64) the coefficients given either in Eq. 2.73 or Eq. 2.74 are subsumed into a single property coefficient, a /> => wtJ, which may account for the effect of multiple types of properties,... 

Other forms for the pseudo-energy penalty term have also been investigated (61,62). In any case, pseudo-energy penalty term acts as a constraint on the overall energy of the system, which is a balance between favorable conformational energies and overall molecular alignment as measured by field-based similarity (dissimilarity). 

As pointed out above with relation to the data at 87 °C, the Tic of the crystalline-amorphous interphase is appreciably longer than that of the amorphous phase, suggesting the retention of the helical molecular chain conformation in the interphase. We also note that a Tic of 65-70 s for the crystalline phase is significantly shorter than that for other crystalline polymers such as polyethylene and poly-(tetramethylene oxide), whose crystalline structure is comprised of planar zig-zag molecular-chain sequences. In the crystalline region composed of helical molecular chains, there may be a minor molecular motion in the TiC frame, with no influence on the crystalline molecular alignment that is detected by X-ray diffraction analyses. Such a relatively short TiC of the crystalline phase may be a character of the crystalline structure that is formed by helical molecular chain sequences. 

Figure 11. Time-resolved PADs from ionization of DABCO for linearly polarized pump and probe pulses. Here, the optically bright S E state internally converts to the dark 5i state on picosecond time scales, (a) PADs at 200 fs time delay for pump and probe polarization vector both parallel to the spectrometer axis. The difference in electronic symmetry between S2 and Si leads to significant changes in the form of the PAD. (b) The PADs at 200 fs time delay for pump polarization parallel and probe polarization perpendicular to the spectrometer axis, showing the effects of lab frame molecular alignment, (c) and (d) The PADs evolve as a function of time due to molecular axis rotational wavepacket dynamics. Taken with permission from C. C. Hayden, unpublished.

Since ocs was shown to reflect the molecular alignment of the sorbed liquid relative to the monomer unit in true solution (see Sect. 3.4) then a or a must also reflect how well the molecular structure of the adsorbed liquid is accommodated by that of the monomer unit of polymer at its respective level of polymer swelling, i.e. after a sizable fraction (y) of that solvated polymer has undergone some form of self-association and all of the non-adsorbed molecules have been eliminated. 

Yamamoto, T., Hasegawa, M. Kanazawa, A., Shiono, X, and Ikeda, T. Phase-type gratings formed by photochemical phase transition of polymer azobenzene liquid crystals Enhancement of diffraction efficiency by spatial modulation of molecular alignment. ]. Phys. Chem. B 1999, 103, pp. 9873-9878. 

The analytical solutions above confirm that the cis (trans) population decreases (increases) with as a time constant, while the molecular alignment is governed by together with the diffusion times in the trans and the cis forms that are given by rf = l/n(n + 1)D and rf = l/n(n + 1)D. It is worth noting that relations 21 do not couple tensorial components of... 

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