Flow birefringence and optical anisotropy of poly(N-vinylpyrrolidone) molecules

Concentration dependences of flow birefringence and viscosity of poly(N-vinylpyrrolidone) solutions in water and benzyl alcohol are investigated. The intrinsic anisotropy for a poly(N-vinylpyrrolidone) macromolecular segment, (α₁ ? α₂) = ?(82 ± 8) × 10^?25 cm³, is determined from the results of birefringence measurements in benzyl alcohol. For aqueous solutions, a strong concentration dependence of the specific anisotropy of solution is obtained, a result that may be explained by the heterogeneity of coils. A model allowing for this heterogeneity is suggested. It makes it possible to fit the concentration dependence to a hyperbolic function, to separate contributions of heterogeneity anisotropy and form anisotropy to the birefringence of a solution, and to estimate the segment asymmetry parameter as p = 3.0 ± 0.5.     

Hydrodynamic,optical, and electrooptical properties of macromolecules of third-generation cylindrical dendrimers in chloroform and dichloroacetic acid

Acrylic polymers containing side dendrons of the third generation based on L-aspartic acid have been studied via the methods of molecular hydrodynamics, dynamic and static light-scattering, optics, and electrooptics. There are marked differences in hydrodynamic and optical properties of the macromolecules under study and previously examined polymers with side dendrons of first and second generations. In the range of degrees of polymerization from 10 to 40, these macromolecules possess an extremely low shape asymmetry. Experiments demonstrate the predominant orientation of end side dendrons along the main molecular chain. In chloroform solutions, the orientation of macromolecules in hydrodynamic and electric fields occurs according to the large-scale mechanism. In dichloroacetic acid, the hydrodynamic dimensions of macromolecules decrease, an effect that is accompanied by an increase in the kinetic flexibility of polymer chains.     

Hydrodynamic, conformational, and optical properties of cellulose tridecanoate molecules in solutions

Cellulose tridecanoates of various molecular weights were synthesized, and their characteristics in chloroform and tetrachloroethane solutions were studied by methods of translational diffusion, velocity sedimentation, flow birefringence (Maxwell’s method), and viscometry. The effects of solvent and temperature on the conformational characteristics of the macromolecules under consideration were examined. The anisotropy of the monomeric unit of cellulose tridecanoates was studied, and the contribution of pendant chains to the optical anisotropy of macromolecules of cellulose esters with aliphatic substituents was analyzed.     

Optical anisotropy of absorbing particles: Light scattering depolarization,electric- and flow birefringence and dichroism of suspensions of carbon blacks

Summary The use of a rather: elongated spheroid, the compacity of which decreases with its weight, equivalent to the aggregates allows to explain the effects of depolarized light scattering and of birefringence. In particular, a very unusual negative macroform birefringence has been found. Moreover the theoretical expressions concerning the absorbing particles which simultaneously exhibit an electric dichroism and birefringence have been written. They were tested by means of suspensions of carbon blacks.

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Zusammenfassung Die Effekte der Depolarisation von Streulicht und der Str?mungsdoppelbrechung k?nnen mit Hilfe des Modells von relativ gestreckten Rotationsellipsoiden erkl?rt werden. Insbesondere wurde die Existenz eines ganz ungew?hnlichen Ph?nomens wahrscheinlich gemacht, n?mlich eine negative Formdoppelbrechung. Weiter wurden theoretische Beziehungen entwickelt, die Suspensionen von absorbierenden Teilchen betreffen, die zugleich Doppelbrechung und Dichroismus zeigen. Diese Gleichungen werden anhand von Ru?-Suspensionen verifiziert.

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Résumé Les effets de dépolarisation de la lumiére diffusée et de la biréfringence d'écoulement peuvent être expliqués á l'aide de modéles d'ellipsoídes de révolution équivalents relativement allongés. En particulier, on a mis en évidence l'existence d'un phénoméne tout-á-fait inhabituel: celui d'une biréfringence de macroforme négative. De plus, on a développé des relations théoriques concernant des suspensions de particules absorbantes, présentant à la fois de la biréfringence et du dichroisme. Ces expressions ont été vérifiées á l'aide de suspensions de noirs de carbone.

     

Optical properties and orientational order of deoxyribonucleic acid molecules at interfaces

A high degree of planar orientational order of DNA molecules in thin films has been discovered by the oblique-polarized-beam method. The coefficients of surface birefringence of films with different thicknesses are measured. The thickness of optically anisotropic surface layers, which are characterized by macroscopic values higher than the diameter of DNA molecules by three orders of magnitude in terms of thickness, is determined. A difference in the main polarizabilities of the monomer unit of DNA, which is estimated for the films, is compared with the corresponding value for the solution measured by flow birefringence. The effect of temperature on the coefficient of birefringence of the films is examined. A comparison of the data on the native and denatured DNA shows that the degree of orientational order for the single-helix structure is smaller than that for the double helix.     

Composition,structure, and anisotropy of magnetic properties of d- and dℝ-tartrates of Dy3+ from proton magnetic relaxation and magnetic birefringence data

We have determined the composition and stability of d- and d-tartrates of Dy³⁺. In the pH region 4.0–7.0, we have shown that binuclear particles are formed. The relative stability of isomeric d- and d-tartrates of Dy³⁺ is determined only by the statistical factor. From data on the paramagnetic birefringence effect, binuclear d- and d-tartrates of dysprosium(III) have a polycyclic structure including six five-membered metallocycles, two of which are condensed with the central twelve-membered ring. The paramagnetic anisotropy of Dy³⁺ in the studied dimers has twice the absolute value of the anisotropy of the aqua ion of Dy³⁺ (k=–2860·10^–29 cm³). Using the magnetic susceptibility measurements, we have demonstrated the virtually complete absence of Dy³⁺–Dy³⁺ magnetic interactions in binuclear d- and d-tartrates.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 47–52, January, 1990.We thank A. E. Nepryakhin for taking the NMR spectra, and O. Yu. Tarasov for calculating the values of the molar magnetic susceptibility.     

Hydrodynamic properties and equilibrium rigidity of polyamidobenzimidazole molecules in dimethylacetamide and sulphuric acid

Translational diffusion, velocity sedimentation and viscometry of polyamidobenzimidazole (PABI) solutions in the range of M = (1–61) · 10³ have been investigated in N,N-dimethylacetamide (DMA) and 98% H₂SO₄. The dependences of D₀, S₀ and [η] on M were obtained. Tsvetkov-Klenin's hydrodynamic invariant was found to be $\text{A}{}_0\text{= 3.55 · 10}{}^{\mathrm{?10}}\text{erg deg}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$. The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment $\text{A = 250 ± 100}\text{A}\text{?}$. The chain diameter was $\text{7 ± 4}\text{A}\text{?}$. The values of A in 98% H₂SO₄ and in an aprotic solvent, DMA, were virtually identical, implying that the rigid-chain conformation of PABI molecules in 98% H₂SO₄ is due to their geometrical structure rather than to the protonization of amide bonds. The significance of the latter evidently increases in PABI solutions in 100% H₂SO₄ in which A is 1.5 times as high. The decrease in rigidity of PABI as compared to that of poly-p-phenylene terephthalamide ($\text{A = 400 ± 100}\text{A}\text{?}$) is in reasonable agreement with the presence of imidazole rings in PABI molecules. The presence of these rings results in kinks in the PABI chain with angles of about 30° and hence, in the depature from parallelism of rotating bonds.     

Synthesis and optical properties of triangular gold nanoplates with controllable edge length

Gold triangular nanoplates with a uniform size were synthesized by a simple seeds-growth method in a lamellar lyotropic liquid crystal (LLC) medium consisting of F127, n-C₄H₉OH and H₂O. The edge length of gold nanoplates can be adjusted from tens to several hundreds nanometers (and even a few micrometers) by varying the concentration of Au³⁺ and the seeds solution volume. The optical properties of the synthesized gold nanoplates were studied. The vis-NIR spectra of the synthesized gold nanoplates exhibited a good linear correlation between the in-plane plasmon resonance λ_max and the average edge length of the corresponding nanoplates.

     

The effect of side-chain length of cellulose fatty acid esters on their thermal,barrier and mechanical properties

Currently, long-chain cellulose esters are not produced commercially because of high price, and since their preparation typically requires a large quantity of chemicals. To reduce the chemical consumption, cellulose reactivity needs to be increased without losing its quality. One way to increase the reactivity of cellulose is to decrease its molar mass in a controlled manner. In this study, we have synthesized cellulose esters with different side-chain length (C6–C18) in a homogeneous system using ozone molar mass-controlled cellulose. The target was to keep the degree of substitution as low as possible while still ensuring the suitability of cellulose esters for solvent casting. Thermal, barrier and mechanical properties were studied depending on cellulose fatty acid ester side-chain length. All our molar mass-controlled cellulose esters form optically transparent, flexible and heat-sealable films with good water barrier properties and are processable without the addition of an external plasticizer. Furthermore, the films have mechanical properties comparable to some generally used plastics. These good properties suggest that our molar mass-controlled cellulose esters could be potential candidates for various applications such as films and composites.     

Syntheses,structures, and optical properties of two cadmium complexes with chelidamic acid

[Cd₂(C₇H₃NO₅)₂ · 4(H₂O)] _n · 3nH₂O · 0.5n(CH₃OH) (1) and [Cd₃(C₇H₂NO₅)₂ · 10(H₂O)] · 2H₂O ·0.5CH₃OH (2) were synthesized and characterized by X-ray single-crystal diffraction. The crystal structure of 1 reveals that both Cds are seven-coordinate with pentagonal bipyramid geometries. Coordination polyhedra are interlinked into a 1-D chain, further linked by hydrogen bonds into a 3-D network. Complex 2 is a discrete structure, then independent [Cd₃(C₇H₂NO₅)₂ · 10(H₂O)] are linked by hydrogen bonds into a 3-D network. The optical properties of 1 and 2 were investigated with fluorescent spectra; both exhibit strong green luminescence probably originating from π–π* transition of the ligand.     

The structure, vibrational spectra and nonlinear optical properties of the L-lysine x tartaric acid complex--theoretical studies

The room temperature X-ray studies of L-lysine x tartaric acid complex are not unambiguous. The disorder of three atoms of carbon in L-lysine molecule is observed. These X-ray studies are ambiguous. The theoretical geometry study performed by DFT methods explain the most doubts which are connected with crystallographic measurements. The theoretical vibrational frequencies and potential energy distribution (PED) of L-lysine x tartaric acid were calculated by B3LYP method. The calculated frequencies were compared with experimental measured IR spectra. The complete assignment of the bands has been made on the basis of the calculated PED. The restricted Hartee-Fock (RHF) methods were used for calculation of the hyperpolarizability for investigated compound. The theoretical results are compared with experimental value of beta.     

Facile route to Zn-based II-VI semiconductor spheres, hollow spheres, and core/shell nanocrystals and their optical properties

A convenient chemical conversion method that allows the direct preparation of nanocrystalline ZnE (E = O, S, Se) semiconductor spheres and hollow spheres as well as their core/shell structures is reported. By using monodisperse ZnO nanospheres as a starting reactant and in situ template, ZnS, ZnSe solid and hollow nanospheres, and ZnO/ZnS and ZnO/ZnSe core/shell nanostructures have been obtained through an ultrasound-assisted solution-phase conversion process. The formation mechanism of these nanocrystals is connected with the sonochemical effect of ultrasound irradiation. The photoluminescence and electrogenerated chemiluminescence properties of the as-prepared nanocrystals were investigated.     

Effect of temperature, pressure, and cosolvents on structural and dynamic properties of the hydration shell of SNase: a molecular dynamics computer simulation study

It is now generally agreed that the hydration water and solvational properties play a crucial role in determining the dynamics and hence the functionality of proteins. We present molecular dynamics computer simulation studies on staphylococcal nuclease (SNase) at various temperatures and pressures as well as in different cosolvent solutions containing various concentrations of urea and glycerol. The aim is to provide a molecular level understanding of how different types of cosolvents (chaotropic and kosmotropic) as well as temperature and high hydrostatic pressure modify the structure and dynamics of the hydration water. Taken together, these three intrinsic thermodynamic variables, temperature, pressure, and chemical potential (or activity) of the solvent, are able to influence the stability and function of the protein by protein-solvent dynamic coupling in different ways. A detailed analysis of the structural and dynamical properties of the water and cosolvents at the protein surface (density profile, coordination numbers, hydrogen-bond distribution, average H-bond lifetimes (water-protein and water-water), and average residence time of water in the hydration shell) was carried out, and differences in the structural and dynamical properties of the hydration water in the presence of the different cosolvents and at temperatures between 300 and 400 K and pressures up to 5000 bar are discussed. Furthermore, the results obtained help understand various thermodynamic properties measured for the protein.     

Influence of the length of side substituents on optical and electro-optical properties of polydialkoxyphosphazenes

The electro-optical and dynamo-optical properties of dilute solutions of polydialkoxyphosphazenes with different lengths of side substituents are studied. Sign inversion of the specific Kerr constant and of the reduced flow birefringence for the number of carbon atoms in side aliphatic chains, m, varying from 3 to 7 is ascertained. The anisotropy of optical polarizability of a monomer unit changes in the studied series of polydialkoxyphosphazenes. It attains the minimum values and changes its sign from positive to negative at m = 5?C6. The resulting data provide an explanation for the mesomorphism of these polydialkoxyphosphazenes, which is connected with the possibility of alternative orientation of monomer units.     

The synthesis and high optical birefringence of nematogens incorporating 2,6-disubstituted naphthalenes and terminal cyano-substituent

A range of nematogenic materials which incorporate a 2,6-disubstituted naphthyl moiety and a terminal cyano-substituent have been synthesized by using palladium-catalysed cross-coupling procedures involving arylboronic acids and alkynylzinc reagents with aryl iodides, bromides and trifluoromethanesulphonates (triflates). The compounds have very high nematic phase stability, but their melting points are also quite high. The birefringences were measured using an extrapolation technique and the values were found to be between 0·26 and 0·42.