Dynamic properties of microemulsions modified with homopolymers and diblock copolymers: the determination of bending moduli and renormalization effects

The properties of bicontinuous microemulsions, consisting of water, oil, and a surfactant, can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. Here, the influence of the addition of homopolymers (PEP(X) and PEO(X), X=5k or 10k molecular weight) on the dynamics of the surfactant layer is studied with neutron spin echo spectroscopy (NSE). Combining the results with the previous findings for diblock copolymers allows for a better separation of viscosity and bending modulus effects. With the addition of homopolymers, a significant increase of the relaxation rate compared to the pure microemulsion has been observed. The influence on the bending rigidity kappa is measured with NSE experiments. Homopolymer addition reduces kappa by up to Deltakappa approximately -0.5k(B)T, whereas the diblock copolymer yields an increase of kappa by approximately 0.3k(B)T. Comparison of the bending moduli that are obtained by analysis of the dynamics to those obtained from small angle neutron scattering (SANS) sheds light on the different renormalization length scales for NSE and SANS. Variation of the surfactant concentration at otherwise constant conditions of homopolymer or diblock-copolymer concentration shows that NSE results are leading to the pure bending rigidity, while the renormalized one is measured with SANS.     

Organometallic aluminum compounds derived from 2-(1,3,5-dithiazinan-5-yl)ethanol ligands

The reactions of AlMe(2)Y (Y = Me or Cl) with new ligands 2-(1,3,5-dithiazinan-5-yl)ethanol (1), 2-(1,3,5-dithiazinan-5-yl)-1-methylethanol (2), and 2-(1,3,5-dithiazinan-5-yl)-1-phenylethanol (3) are described. The ligands are coordinated to aluminum atoms by nitrogen and oxygen atoms, with a nitrogen based spiranic structure. Equimolar reactions gave dimeric structures bearing pentacoordinated aluminum atoms O-(AlMeY)-2-(1,3,5-dithiazinan-5-yl)ethanolates (4-7) as well as monometallic compounds with tetracoordinated aluminum atoms O-(AlMeY)-2-(1,3,5-dithiazinan-5-yl)ethanolates (8-9). Reactions with 2 equiv of the aluminum reagents afforded tetracoordinated dialuminum complexes O-(AlMeY)-O-(AlMe(2)Y)-2-(1,3,5-dithiazinan-5-yl)ethanolate (10-18). The structures of the new compounds were determined by NMR ((1)H,(13)C, and (27)Al) and complemented by X-ray diffraction of compounds 4, 10, and 16-18. Relevant intermolecular interactions C-H...S, C-H...Cl, and C-H...pi found in the crystalline network are reported.     

Polymer drying. VIII. Molecular interpretations of desorption from polystyrene–liquid systems

The results obtained in time studies that monitored evaporation from liquid-saturated poly(styrene-co-divinylbenzene) to virtual dryness at temperatures ranging from 20 to 80°C confirm those reported earlier for multireplicated time studies at 23 ± 1°C; i.e., when the residual composition (α_t, in sorbed molecules per phenyl group) attains the glassy state composition, the value of α_t thereafter is given by a linear combination of no more than six exponential decay functions. The logarithms of the rate constants (k_i) for decay of these populations at a given temperature decreased linearly with i, the population identification number in the order of decreasing decay rate. The Arrhenius activation energy (ΔE_i) for increase in k_i with temperature was characteristic of the sorbed species, but it was independent of i. The logarithms of the frequency factors (A_i) decreased linearly with i, the slope of which was numerically equal to that observed for the corresponding k_i relationships, signifying that the stepwise decrease of the latter at a given temperature is attributable primarily to a corresponding incremental decrease in entropy. It is suggested that this reflects discrete changes in the molecular structure of polymeric inclusion complexes formed during the transition from the rubbery to the glassy state, as discussed in the text. © 1993 John Wiley & Sons, Inc.     

On the numerical evaluation of a sum involving binomial coefficients

An efficient way to evaluate \(\sum\limits_{j = k}^n {( - 1)^{j - k - 1} \left( {\begin{array}{*{20}c} n \\ j \\ \end{array} } \right)\left( {\begin{array}{*{20}c} {j - 1} \\ {k - 1} \\ \end{array} } \right)} \ln j\) is described. This sum, connected with the logarithmic Weibull distribution, is hard to evaluate directly, because the binomial coefficients become quite large, and then the alternating signs cause severe loss of significant figures. By converting the sum to an integral, we avoid this difficulty.     

On the use of the derivative of electroglottographic signals for characterization of nonpathological phonation

Electroglottography is a common method for providing noninvasive measurements of glottal activity. The derivative of the electroglottographic signal, however, has not attracted much attention, although it yields reliable indicators of glottal closing instants. The purpose of this paper is to provide a guide to the usefulness of this signal. The main features that are to be found in this signal are presented on the basis of an extensive analysis of a database of items sung by 18 trained singers. Glottal opening and closing instants are related to peaks in the signal; the latter can be used to measure glottal parameters such as fundamental frequency and open quotient. In some cases, peaks are doubled or imprecise, which points to special (but by no means uncommon) glottal configurations. A correlation-based algorithm for the automatic measurement of fundamental frequency and open quotient using the derivative of electroglottographic signals is proposed. It is compared to three other electroglottographic-based methods with regard to the measurement of open quotient in inverse-filtered derived glottal flow. It is shown that agreement with the glottal-flow measurements is much better than most threshold-based measurements in the case of sustained sounds.     

Experimental and theoretical charge density of aluminum

Several recent experimental determinations of the aluminum charge density form factors are compared to one another and found to agree within the accuracy claimed. Comparison of experimental form factors to theoretical values of Walter, Fong and Cohen (WFC) and Ascarelli and Raccah (AR) indicates good agreement at all reflections except for the (220) reflection, where only the AR theory agrees with experiment.     

Studies on structures of lipid A-monophosphate clusters

Single crystalline clusters of lipid A-monophosphate were grown from organic dispersions containing 5-15% (v/v) water at various volume fractions, φ, and temperatures. The morphology of the single lipid A-monophosphate crystals was either rhombohedral or hexagonal. The hexagonal crystals were needlelike or cylindrical in shape, with the long dimension parallel to the c axis of the unit cell. The crystalline clusters were studied using electron microscopy and x-ray powder diffraction. Employing molecular location methods following a Rietveld refinement and whole-pattern refinement revealed two monoclinic crystal structures in the space groups P2(1) and C2, both converged with R(F) = 0.179. The two monoclinic crystal structures were packing (hydrocarbon chains) and conformational (sugar) polymorphs. Neither of these two structures had been encountered previously. Only intramolecular hydrogen bonding was observed for the polymorphs, which were located between the amide and the carboxyl groups. Another crystalline structure was found in the volume-fraction range 2.00 × 10(-3) ≤ φ ≤ 2.50 × 10(-3), which displayed hexagonal symmetry. The hexagonal symmetry of the self-assembled lipid A-monophosphate crystalline phase might be reconciled with the monoclinic symmetry found at low-volume-fractions. Therefore, lowering the symmetry from cubic, i.e., Ia 3d, to rhombohedral R 3 m, and finally to the monoclinic space group C2 was acceptable if the lipid A-monophosphate anion was completely orientationally ordered.     

Structure of blue phase III of cholesteric liquid crystals

We report large scale simulations of the blue phases of cholesteric liquid crystals. Our results suggest a structure for blue phase III, the blue fog, which has been the subject of a long debate in liquid crystal physics. We propose that blue phase III is an amorphous network of disclination lines, which is thermodynamically and kinetically stabilized over crystalline blue phases at intermediate chiralities. This amorphous network becomes ordered under an applied electric field, as seen in experiments.     

Synthesis and characterization of polystyrene chains on the surface of silica nanoparticles: comparison of SANS, SAXS, and DLS results

An extensive characterization of well-defined polystyrene (PS)-grafted silica nanoparticles is reported. Bare SiO₂ particles (diameter 50 nm) were functionalized with a suitable initiator for the surface-initiated anionic polymerization of styrene. Both grafted and free PS chains were characterized and compared by size-exclusion chromatography (SEC). PS-grafted particles were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), small-angle x-ray scattering (SAXS), small-angle neutron scattering (SANS), and dynamic light scattering (DLS). The thickness of the grafted PS chains was obtained by SANS and DLS and scaled with $M_{\mathrm {w}}^{0.6}$ displaying similar behavior with free PS chains in the same solvent used, tetrahydrofuran (THF). Grafting densities obtained from SANS data and TGA were found to be small, and the thickness of the grafted PS chains determined by SANS was found to be similar to $2R_{\mathrm {g}}$ of free PS chains in THF. Both results are consistent with a “coil-like” conformation of the grafted PS chains.