We have developed an infinite dilution extrapolation procedure for determining the molecular second order optical susceptibility β using dc induced second harmonic generation. We show how the effects of solute–solute and solvent–solvent interactions are minimized by this procedure, and how several local field models used in the procedure affect the calculation of β. Using hexane as a solvent for nitrobenzene, we have determined the best experimental value in solution for the intrinsic β of nitrobenzene of (1.11±0.17)×10−30 esu.

Measurements of molecular second order optical susceptibilities using dc induced second harmonic generation

Computation of dielectric constants of solvent mixtures and electrolyte solutions

Sublimation pressures of crystalline α-glycine were measured between 138 and 153°C by the effusion method. The pressure equationlogP(mmHg)=13.666-(6816.8/T) fits well the experimental data. The heat, entropy and free energy (at 25°C) of sublimation were 31.18±0.49 kcal./mole, 49.33±1.17 cal./deg. mole and 16.47±0.60 kcal./mole, respectively. An energy cycle was constructed which correlates zwitterion and molecule in crystal and vapor states, and hydrated zwitterion and molecule in solutions. The observed heat of sublimation corresponds to the change in heat content in going from the zwitterioncrystal to gaseous molecules. The molecular configuration is more stable in vapor state. By using the experimental values of the heat of sublimation, the heat of solution of crystals into water and the temperature dependence of pKa in solution, with the help of the theoretical values of the lattice energy of the crystal, the following heat values were determined; the heat of proton jump in vapor, NH3+CH2COO− → NH2CH2...

Vapor Pressure of Molecular Crystals. XIII. Vapor Pressure of α-Glycine Crystal. The Energy of Proton Transfer

The hierarchical self-assembly at the submicrometer, nanometer and α-helical length scales has been studied in a miktoarm star rod−coil chimera composed of poly(γ-benzyl-l-glutamate) (PBLG), polystyrene, and polyisoprene blocks by X-ray scattering, solid state NMR, and transmission electron microscopy. The propensity of the rod block toward α-helices that are further hexagonally packed gives rise to pure PBLG domains and induces the partial mixing of the two amorphous blocks. These structural results were confirmed by independent dynamic probes at the segmental and α-helical level by NMR and dielectric spectroscopy, respectively.

Hierarchical Self-Assembly and Dynamics of a Miktoarm Star chimera Composed of Poly(gamma-benzyl-L-glutamate), Polystyrene, and Polyisoprene

Dielectric spectroscopy (DS) is a powerful method for studying molecular dynamics. Compared with scattering techniques (such as neutron scattering and light scattering) though, it lacks spatial resolution, but due to its extraordinary broad frequency range it is by far the most suitable technique for studying the dynamics of soft matter (glass-forming liquids, polymers, ionic systems, etc.). In addition, DS can be coupled with methods that provide independent structural information (such as X-rays and NMR), and hence provide the dynamics appropriate for each phase. The intention of this chapter is to provide a short description of the relevant theoretical background and analysis of dielectric spectra and to highlight some of the most important advances in dielectric research over the past decade. These include (1) the better understanding of the liquid-to-glass ‘transition’ through the application of pressure (we review the two main approaches based on the thermodynamic scaling and the role of monomer volume and local packing), (2) the dynamics of polymers under confinement and the possibility of probing the local dielectric properties of homogeneous and heterogeneous materials via electric force microscopy, and (3) the dynamics of a class of biopolymers (polypeptides).

2.32 – Dielectric Spectroscopy

The theory presented in an earlier paper is here developed as a method for the evaluation of' true dipole moments from data obtained from solutions in polar solvents. As illustrations, the new method is applied to values relating to solutions of several substances in chloroform, chlorobenzene, and nitrobenzene. The results, considering the nature of the problem, are satisfactory. The accuracy is greatest when the solute is highly polar and the dielectric constant of the solvent small. Aqueous solutions of pyridine and of two amino acids are also considered. In the latter cases especially, the predicted dipole moments agree most favourably with anticipated values obtained for the zwitterions by multiplying the electronic charge by the expected charge separation.

AD Buckingham

Papers

The calculation of true dipole moments form solutions in Polar Solvents