Volume 110, Issue 21, 01 June 1999
Index of content:
- POLYMERS, BIOPOLYMERS, AND COMPLEX SYSTEMS
Reversal in the dielectric relaxation time during polymerization: Thermal energy compensation on macromolecular growth110(1999); http://dx.doi.org/10.1063/1.478991View Description Hide Description
The increase in the dielectric relaxation time and in the number of covalent bondsn formed during polymerization of an equimolar mixture of cyclohexylamine and a diepoxide have been studies in real time, in two experiments: (i) under isothermal conditions when the dielectricspectrum monotonically shifts to the low-frequency side and the configuration entropy decreases and (ii) on heating the polymerizing liquid at a fixed rate when the spectrum initially shifts to the low-frequency side, reverses direction at a certain temperature, and shifts towards the high-frequency side. This reversal in occurs when an increase in thermal energy begins to dominate the effects of increase in n. Consequences of the two competitive effects on the measureddielectric behavior have been discussed and relations between the change in configurational entropy, and of the ultimately formed linear chain polymer, are discussed. It is shown mathematically that for a fixed and a configurational entropy, there are an infinite number of combinations of temperature and n, some of which may be explored by altering the temperature–time profile during the macromolecular growth.
110(1999); http://dx.doi.org/10.1063/1.478992View Description Hide Description
A well-studied 46-bead protein model is the vehicle for examining principal coordinate analysis as a tool for interpreting topographies of complex potential surfaces. This study compares the effectiveness of several definitions of the comparison variable for revealing information about topographies. The extent of the information is ascertained by comparing the results of the various forms of principal coordinate analysis with results obtained from construction of interconnected monotonic sequences of linked stationary points (IMSLiSP) on the same surface. The conclusion is that the most powerful formulation of principal coordinate analyses for understanding protein folding and, in general, topographies of complex potentials, uses the changes in the set of interparticle distances as the definition of the comparison vector. However, even with this choice, the more efficient principal coordinate analysis is not able to reveal the extent of information contained in a more cumbersome IMSLiSP analysis.
110(1999); http://dx.doi.org/10.1063/1.478993View Description Hide Description
Binary and ternary mixtures of -octane, and were examined by neutron scattering experiments. The scattering data are evaluated using the generalized indirect Fourier transformation, GIFT, to determine the particle shape and structure in real space. This recently developed technique allows for the simultaneous determination of the form factor and the structure factor with a minimum of a priori information. All microemulsion data, both on the water-rich side and on the oil-rich side, can be evaluated using the whole range of scattering data to determine the form factor and the structure factor in one procedure. By example of the binary water-surfactant mixture known to contain elongated particles, we were able to show the great advantage in using the GIFT instead of other techniques. Suppression of the interaction effects during the evaluation procedure by eliminating data at low angles leads to incorrect results because elongated particles appear to be globular. The GIFT, however, allows us to distinguish between intra- and interparticle scattering contributions so that the correct elongated shape of the particles is recovered from the scattering data. Therefore, the GIFT can be regarded as the method of choice to determine size, shape, and internal structure of colloidal particles with high accuracy in the size range of 1 to 100 nanometers up to volume fractions of about 0.3.