In this work, the structure of poly(acrylic acid) (PAA) molecules in electrolyte solutions obtained from molecular dynamic simulations was compared with experimental data derived from dynamic light scattering (PCS), dynamic viscosity, and electrophoretic measurements. Simulations and measurements were carried out for polymer having a molecular weight of 12 kD for various ionic strengths of the supporting electrolyte (NaCl). The effect of the ionization degree of the polymer, regulated by the change in the pH of the solution in the range 4-9 units, was also studied systematically. It was predicted from theoretical simulations that, for low electrolyte concentration (10(-3) M) and pH = 9 (full nominal ionization of PAA), the molecule assumed the shape of a flexible rod having the effective length L(ef) = 21 nm, compared to the contour length L(ext) = 41 nm predicted for a fully extended polymer chain. For an electrolyte concentration of 0.15 M, it was predicted that L(ef) = 10.5 nm. For a lower ionization degree, a significant folding of the molecule was predicted, which assumed the shape of a sphere having the radius of 2 nm. These theoretical predictions were compared with PCS experimental measurements of the diffusion coefficient of the molecule, which allowed one to calculate its hydrodynamic radius R(H). It was found that R(H) varied between 6.6 nm for low ionic strength (pH = 9) and 5.8 nm for higher ionic strength (pH = 4). The R(H) values for pH = 9 were in a good agreement with theoretical predictions of particle shape, approximated by prolate spheroids, bent to various forms. On the other hand, a significant deviation from the theoretical shape predictions occurring at pH = 4 was interpreted in terms of the chain hydration effect neglected in simulations. To obtain additional shape information, the dynamic viscosity of polyelectrolyte solutions was measured using a capillary viscometer. It was found that, after considering the correction for hydration, the experimental results were in a good agreement with the Brenner's viscosity theory for prolate spheroid suspensions. The effective lengths derived from viscosity measurements using this theory were in good agreement with values predicted from the molecular dynamic simulations.

No abstract

No abstract

No abstract

Dissociation constants of 25 phenols and homoconjugation constants of 14 phenol-phenolate systems in acetonitrile have been determined from emf measurements. From these results a linear relationship log K t N = 1.9 pKt20 + 8.3 has been derived. Stronger homoconjugation of weaker proton donors has been found to be a result of various (steric, inductive, mesomeric, charge delocalization) effects; however, the increase of homoconjugation constants with electron density at the phenolic oxygen seems to be unquestionable. Ten hydrogen bis-phenolates were prepared to complete this study, some of which crystallized well from water.

An optical method which allows quantitative determination of L-alanine contents in L-alanine doped TGS crystals is described. L-alanine content was determined in (001) and (110) growth pyramids of LATGS crystals grown above and below T c. Relation between E b and alanine content in crystals established from Devonshire's theory is in reasonable agreement with the experimerttal results.

No abstract

No abstract