The dielectric properties of undiluted liquid atactic polypropyleneoxide have been studied as functions of temperature and molecular weight. The principal dispersion occurs at essentially the same frequency for all molecular weights at a given temperature, but at ower frequencies there is a small secondary loss peak that depends strongly on molecular weight. This secondary dispersion is shown to result from relaxation of a ``cumulative'' dipole, about 0.18 D per monomer unit, whose resultant magnitude depends on the long-range conformation of the chain molecule. Experimental relaxation times for the secondary dispersion agree well with predictions based on Rouse—Bueche—Zimm theory. The main dispersion shifts with temperature according to the WLF equation.

No abstract

Dielectric dispersion, relaxation of the Kerr effect, and relaxation of the Benoit-Wippler effect are discussed for flexible chain molecules in terms of the model used by Zimm to treat viscoelastic behavior of dilute polyrner solutions. Low-frequency dispersion is related to the long-wave Fourier components of the electrical charge distribution along the chain backbone.

A total of 1098 students, from second graders to university chemistry students, drew representations of highly magnified views of air at 1.0 atmosphere of pressure and at 0.5 atmosphere of pressure. The drawings were classified and the authors inferred from them a relatively limited number of preconceptions of the nature of gases. Several major trends occurred in the frequencies of these inferred preconceptions held at different grade levels. The majority of the drawings that were not in fairly close agreement with atomic theory seemed to reflect one or more of the following misconceptions: (a) air is a continuous (nonparticulate) substance, (b) gas behavior is similar to liquid behavior, and (c) there is relatively little space between gas particles. The number of drawings that gave evidence of particulate views ranged from 8% for Grades 2–4 to 85% for university chemistry students. However, 33% of the university students' drawings showed highly packed particles, and only 37% showed particles in an approximately correct geometrical distribution. The authors suggest a technique for promoting conceptual change among students who possess alternative views of the nature of gases.

A theoretical treatment of migration of electrons, holes, and singlet and triplet electronic excitations in ideal DNA helical chains is presented. A localized model is adopted, in which charge and excitation migration is considered to take place through discrete site to neighbor site transfer neglecting long-range quantum mechanical coherence effects. Accordingly a probability function to describe the location of a charge or excitation is introduced. A stochastic equation is developed to describe the time evolution of this function and hence the average behavior of the migrating species. The formalism permits the introduction of base sequencing information through the use of probabilities for occurrence of each of the 16 distinct kinds of nearest-neighbor pairs of bases in a single strand. Migration in a nonuniform but nonrandom DNA chain can then be treated to within a perturbation approximation. The fundamental base-to-base charge and excitation transfer parameters which enter the stochastic equation are calculated for each migrating species and possible pair of neighbor bases using SCF LCAO molecular orbital methods without configuration interaction. A noteworthy feature is the much larger magnitude of the triplet excitation exchange term in this work compared to previous work, leading to relatively large triplet transfer coefficients. Implications of the calculated transfer coefficients for excitation trapping are examined and found to be consistent with experiment. Numerical results for the time dependence of the probability function and for diffusion coefficients for migrating species in DNA's of biophysical interest are presented. The general aspect of these results is similar to that for a uniform DNA chain, but some important differences of detail are present. The mobility of electrons and holes moving along the DNA chain and the resultant electrical conductivity along the chain axis are estimated and found to be considerably larger than in organic crystals.