Birefringence Of Solutions Research Articles

Birefringence in solutions and films of poly[4,4'-bis(4''-N-phenoxy)diphenylsulfon]imide of 1,3 bis(3',4-dicarboxyphenoxy)benzene

Birefringence in solutions and films of poly[4,4'-bis(4''-N-phenoxy)diphenylsulfon]imide of 1,3-bis(3',4-dicarboxyphenoxy)benzene macromolecules is studied. The method of birefringence in the flow of polymer solutions in DMF allows one to determine the proper specific optical anisotropy of the repeating unit of chain βM = +15 × 10–27 cm3 mol/g. Spontaneous birefringence in polymer films of different thickness is studied under various incidence angles of a polarized beam. The total data analysis allows one to estimate the orientation order parameter of polymer chain fragments in the vicinity of surface S 0 =–0.01, which is typical of flexible-chain polymers.

Birefringence in solutions and films of poly(N-methyl-N-vinylacetamide) macromolecules

The flow birefringence of aqueous solutions of poly(N-methyl-N-vinylacetamide) macromolecules for samples of various molecular masses is studied. It is found that the sign of birefringence changes from positive to negative with a decrease in molecular mass in accordance with the manifestation of the macroform effect on condition that the value of the inherent optical anisotropy of macromolecules is negative. With the use of the macroform-effect theory in the Maxwell phenomenon of polymer solutions, the inherent optical anisotropy of the repeating polymer unit is estimated as (a ‖−a ⊥) = −(5 ± 1) × 10−25 cm3. In turn, the value of (a ‖−a ⊥) makes it possible to separate structural and orientational contributions to the effect of spontaneous birefringence for films of various thicknesses that are cast from aqueous solutions of poly(N-methyl-N-vinylacetamide). The parameter of orientational order of chain fragments for this polymer in the near-surface layers of the films is −(0.05 ± 0.01).

Electro-optics of solutions of biopolymers and their complexes

The review summarizes the results of electric-birefringence studies of the molecular properties of biopolymers and their complexes. The application of alternating electric fields makes it possible to study the kinetics of orientation of DNA, RNA, and polypeptide molecules in diluted solutions. An analysis of molecular-mass dependences of relaxation times of biopolymer molecules in terms of the rotational friction theory is used to determine the equilibrium rigidity of macromolecules characterized by Kuhn segment length A. For DNA molecules in buffer solutions with a low ionic strength, the value of A derived from electro-optical measurements is 114 nm. The high sensitivity of electric birefringence to changes in the secondary and tertiary structures of biopolymers ensures its use for the analysis of sequence curvature in short fragments of DNA and for investigation of transitions between different tertiary structures of RNA. The study of electro-optical birefringence in solutions of complexes of DNA and polypeptides with oppositely charged ions of surfactants makes it possible to gain insight into their conformational properties in organic solvents. The stoichiometric complexes of DNA in chloroform occur in the compact globular state, whereas the conformation of complexes formed by various polypeptides depends on their composition and may vary from rodlike to coiled. Electric birefringence in solutions of biopolymer complexes is associated with the orientation of molecules that is due to the external-field-induced dipole moment that appears as a result of a small displacement of ions along the contour of polyion chains. The time of reaching the induced dipole moment is equal to or greater than the time of orientational relaxation of the complex as a whole.

Anisotropy of the magnetic susceptibility of mesogeneous lanthanide complexes

Liquid crystalline adducts of lanthanide tris(β-diketonates) with 5,5′-diheptadecyl-2,2′-bipiridine forming a nematic mesophase were obtained. Molar constants of magnetic birefringence and the magnetic susceptibility anisotropy of synthesized complexes were determined according to the magnetic birefringence in solution. The values of magnetic susceptibility anisotropy are two orders of magnitude higher than those of organic liquid crystals.

Electrooptical properties of mesogenic chain molecules in solution and in nematic state

AbstractElectrooptical characteristics of mesogenic chain molecules in solution and in mesophase can be described in terms of intra‐ and intermolecular orientational orders. The value and sign of electric birefringence δn in a solution of kinetically rigid chain molecules are determined by the combination of two factors: intramolecular orientational order which depends on the dipolar and anisotropic architecture of the molecule and intermolecular orientational order caused by the action of the external electric field E. The value and sign of the dielectric anisotropy δε of the polymer nematic phase are also determined by the combination of intra‐ and intermolecular orders. However, in this case the latter is not maintained by the external field but by the nematic potential of the mesophase. Therefore, comparative investigations of electrooptical properties of polymers in solutions and in nematic melts make it possible to obtain information about the intra‐ and intermolecular orientational orders of the molecules under investigation in these two states. These investigations were carried out using the method of electric birefringence in solutions and the method of orientational deformations of nematic textures in an electric field. The objects being investigated were nematogenic dimers and trimers. Experimental data obtained for these compounds showed the presence of intramolecular order in their molecules, which is manifested in the odd‐even oscillations of the value and sign of Kerr constant K≈δn/E2 in solution and δε in the nematic phase when the number of C‐C bonds in the methylene spacers of these molecules is varied. This effect is particularly dramatic in the mesophase where it is enhanced by intermolecular nematic potential.

Supermolecular structures and flow birefringence in polymer solutions

Experimental studies of supermolecular structures and localized flow birefringence in solutions of high-molecular weight polymer are described. Advantage is taken of poly(ethylene oxide) and polyisobutylene. Supermolecular structures are examined with the aid of optical microscopy using freeze-dried samples of the polymer solutions. Birefringence is investigated that arises in planar elongational flow in a cross-slot cell. Flow velocities at which the onset of the localized birefringence occurs are determined. Then these velocities are correlated with viscoelastic characteristics of the solutions. The presence of a liquid-crystalline fibrillar network in the polymer solutions exhibiting flow birefringence is ascertained. The fibrils are birefringent objects. The fibrils are birefringent objects. The localized birefringence phenomenon is explained in term of the orientation of the fibrils in elongational flow. It has been shown that the onset of localized birefringence occurs at a critical Weissenberg number, the value of which is close to unity.

Analysis of the Conformation of a Stiff-Chain Polyester by Measurements of the Magnetic Birefringence in Solution

The analysis of the conformation of a stiff-chain polyester by magnetic birefringence is presented. The specific Cotton−Mouton constant, C2b, has been measured for five different molecular weights of the polyester. A general analysis of the data is presented, including the effect of polydispersity. A weak dependence of C2b on molecular weight is found, which shows that the persistence length of the polyester is approximately 11 nm. Estimates of the specific Cotton−Mouton constant per unit length by using group increments compare favorably with the measured value.

Electric Birefringence in Solutions of Bis-4-Cyano-Biphenyloxyalkanes

Abstract The electrooptical properties of 4,4′-bis- cyanobiphenyloxyalkanes in dioxane and benzene were investigated by the method of equilibrium electric birefringence. A non-monotonic dependence of the Kerr molar constant of these compounds on the length of the oxyalkane spacer was found. This dependence is due to the influence of the odd-even effect on the intramolecular orientational polar and anisotropic order. The problems are discussed of the effect of equilibrium and kinetic spacer flexibility on the value and sign of the observed birefringence and on the degree of correlation in orientations of mesogenic chain fragments in an electric field.

Dynamic birefringence in solutions of poly (naphthoyleneimide benzimidazole) in different stages of hydrolytic thermal degradation

Flow birefringence (FB) has been investigated in solutions of products of hydrolytic degradation of poly(naphthoyleneimide benzimidazole) (PNIB) in 96% sulphuric acid PNIB solutions have previously been subjected to heating at various temperatures from 65 to 120°C and then investigated at 22°C by FB and viscometry. A monotonic decrease in intrinsic viscosity and the molecular weightM of thermal degradation products with increasing degradation temperature was detected. At the same time, the shear optical coefficients in series of products with decreasingM first increases and then, at treatment temperatures exceeding 90°C, decreases with decreasing [ν] in accordance with decreasingM of the product. Possible reasons for the detected anomaly have been discussed.

Transient electric birefringence in solutions of self-assembled rods

We study, theoretically, the transient electric birefringence of semidilute and concentrated solutions of self-assembling rodlike aggregates in the fast reaction regime. The aggregates interact via a hard core excluded volume potential. We find that although the rods are very polydisperse, the zero-field relaxation is characterized by at most three exponentials depending on whether or not the assemblies have a permanent dipole moment. The static response, and one of the relaxation times, diverges at the nematic spinodal.

Orientational–deformational nature of flow birefringence in solutions of rigid‐chain polymers

AbstractThe orientational–deformational nature of flow birefringence (FB) in solutions of rigid‐chain polymers is confirmed experimentally. The possibility of a direct determination of the internal viscosity parameter by the dependence of the FB relaxation time on the solvent viscosity is demonstrated. Indirect manifestation of internal viscosity in the FB relaxation time is confirmed by the dependence of the form factor on the degree of coiling. © 1993 John Wiley & Sons, Inc.

Electric and dynamic birefringence in solutions of poly-bis-trifluoroethoxyphosphazene

Electro-optical properties in solutions of poly-bis-trifluoroethoxyphosphazene (PBFP) have been investigated by means of flow and electric birefringence. The postive experimental value of the shear optical coefficient [ n]/[ η] of 12 · 10 −10 determines the segmental optical anisotropy of molecules ( α 1 – α 2) of 160 · 10 −25 cm 3. The values of [ n]/[ η] and ( α 1 – α 2) for PBFP molecules correspond to the optical characteristics of most flexible-chain polymers and indicate that the main chain exhibits considerable coiling. The experimental Kerr constant in PBFP solutions exceeds by three or four orders of magnitude those for flexible-chain macromolecules. The equilibrium values of the Kerr constant and the kinetics of the rise and decay of the Kerr effect show that the orientation of PBFP molecules is determined by large scale motions of the macromolecules. PBFP molecules are characterized by high chain polarity determined by the component of dipole moment of the monomer unit, which is longitudinal with respect to the chain.

Orientational-deformational nature of flow birefringence in solutions of worm-like chains

It has been confirmed experimentally that dynamic birefringence in solution worm-like chains is orientation-deformational in nature. It is shown that it is possible to determine the coefficient of internal viscosity of a worm-like chain directly from the way in which the relaxation time depends on the solvent's viscosity and that it is displayed indirectly in the relaxation time in the way in which the model coefficient depends on the degree of chain convolution.

Orientation of flow birefringence in solutions of rigid chain polynaphthoylene imidoquinazoline

The orientation of dynamic birefringence in solutions of molecules of rod-like polynaphthoylene imidoquinazoline of high equilibrium chain rigidity (length of Kuhn segment 1500 Å) is studied. It is shown that the experimental birefringence relaxation times of very short chains, which are much shorter than a segment, cannot be adequately described in terms of rotational relaxation of a rigid rod but require allowance for intramolecular chain dynamics.

Dynamo-optical and electro-optical properties of solutions of diphenyl-substituted poly- para-phenylene terephthalate in polar and non-polar solvents

The flow and electrical birefringence in solution of a number of fractions of para-aromatic polyester are studied, using dioxane and dichloracetic acid as solvents. In passing from a non-polar (dioxane) solvent to a polar solvent the optical and hydrodynamic properties of the molecular chain remain unchanged, whereas the electro-optical characteristics undergo sharp changes. The hydrodynamic and dynamo-optical characteristics of the polymer under study in dioxane correspond to the properties of a typical rigid chain polymer, whereas the electro-optical properties are typical of a flexible chain. This unique combination of properties can be explained by the specific dipole structure of the monomer unit and the significant difference in the longitudinal and lateral dipole rigidity of the polymer chain of the polyester under study.

Flow birefringence in solutions of rigid chain polynaphthoylene imidoquinazoline

The optical and conformational properties of polynaphthoylene imidoquinazoline molecules, consisting of rigid arimide fragments joined by simple bonds are studied by flow birefringence and viscosity methods. Modern theories of the dynamooptical properties of worm-like chains are used to show that in sulphuric and sulphonic acids they have a worm-like chain conformation with a low degree of coiling: persistence length a = (800 ± 200) Å, optical anisotropy of a unit of length β = 26 × 10 −17 cm 2. The value of a obtained is almost double the corresponding assessment a = 300 A ̊ for the para-aromatic analogue, poly- n-benzamide, which is associated with the presence in the chain of the latter of an amide group, which permits deformation.

Electric birefringence in solutions of rigid-chain aromatic polyamides

Electric birefringence (EB) in solutions of a number of fractions and samples of polyamide benzimidazole (PABI) in dimethylacetamide (DMAA) and polyamide hydrazide (PAH) in dimethylsulphoxide (DMSO) has been investigated by using rectangular pulsed and sinusoidal pulsed fields. Study of EB dispersion in sinusoidal fields and the kinetics of rise and decay of EB in rectangular pulse fields indicates that the main mechanism responsible for the measured EB for both polymers is the large-scale motion of their polar molecules caused by the orienting effect of the field on rigid permanent dipoles of their chains. Relaxation times τ are determined from the dispersion of EB. The Kuhn segment lengths are estimated from the dependence of τ on molecular weight. The values of these length for PABI and PAH chains virtually coincide at (25 ± 10) nm. Study of the value of the Kerr constant and its dependence on molecular weight shows that strongly polar and electroconducting solvents, DMAA and DMSO, used in this work play an important part in the formation of macromolecular dipoles.

Electrical birefringence in solutions of p-aromatic polyamides

The electrical birefringence in solutions of some fractions and samples of polyamidobenzimidazole in DMMA and polyamidohydrazide in DMSO are studied with the aid of rectangular and sinusoidal pulse fields. A study of the dispersion of the electrical birefringence in sinusoidal fields and the kinetics of the rise and fall of the electrical birefringence in rectangular pulse fields leads to the conclusion that the main mechanism responsible for the measured electrical birefringence for both polymers is the large scale motion of their polar molecules, produced by the orienting action of the field on the rigid permanent dipoles of the molecular chains. The relaxation times τ are determined from the dispersion of the electrical birefringence, and the lengths of the Kuhn segments are determined from the relation between τ and MM; these lengths are almost the same for polyamidobenzimidazole and polyamidohydrazide respectively: A = (25 ± 10) nm. A study of the value of the Kerr constant K and its dependence on the MM shows that the strongly polar and strongly conducting solvents used in this work play a significant part in the formation of the macromolecular dipoles.

Transition Phenomena in Poly(diacetylene) Solutions Studied by Electric Birefringence Measurements

AbstractAn external electric field induces strong birefringence in solutions of poly(diacetylenes) when they are in the red (low temperature) form. The transient behaviour and the field‐strength dependence of the steady‐state birefringence reveal that the orientation of particles is predominantly due to a permanent dipole moment rather than to the anisotropy of polarizability. The estimated permanent dipole moments are in the order of tenthousand Debye units, this order of magnitude being incompatible with single macromolecules. Thus the view that aggregated particles are formed at low temperatures is supported by our experiments.

Phenomenon of magnetic birefringence in solutions of paramagnetic substances. 3. Structure and paramagnetic anisotropy of the 3-trifluoroacetylcamphorates of praseodymium and dysprosium

1. The 3-trifluoroacetylcamphorates of Pr and Dy are dimeric in C6H6 and CCl4. 2. According to the data on the paramagnetic birefringence effect, the conformation of the ligands surrounding the central ion in Pr2(facam)6 and in Dy2(facam)6 can be described by an octahedron. The same form is also characteristic of the monomer of Dy(facam)3. In the case of the monomer of Pr(facam)3, a structure which is intermediate between a prism and an octahedron is realized.