Birefringence Relaxation Research Articles

Electric birefringence of kilobase-sized DNA molecules

Transient electric birefringence has been used to characterize the rotational diffusion of linear, circularly permuted pBR322 and SV40 DNA molecules. The birefringence relaxation times vary with the site of linearization, suggesting that the circularly permuted DNAs have different conformations in solution. The longest relaxation times are observed for DNA sequence isomers linearized at the major bend centers identified by gel electrophoresis 1 1 N.C. Stellwagen, Electrophoresis, 15 (1995) 691. . SV40 sequence isomers linearized at other locations have faster, but approximately equal, terminal relaxation times, suggesting that their free solution conformations are relatively independent of the location of the bend center within the sequence. By contrast, the terminal relaxation times of the various pBR322 sequence isomers vary approximately in accord with their electrophoretic mobilities in large-pore polyacrylamide gels, suggesting that the different mobilities may reflect real conformational differences between the sequence isomers.

Azo Polymers for Reversible Optical Storage. 5. Orientation and Dipolar Interactions of Azobenzene Side Groups in Copolymers and Blends Containing Methyl Methacrylate Structural Units

Abstract : Two amorphous copolymer series and one blend series based on Disperse Red I and methyl methacrylate are compared using absorption spectra and optically induced birefringence on spin-coated films. Observed blue shifts in the absorption spectra with increasing azo concentration suggest that, locally, azo dipoles are paired antiparallel both intramolecularly and intermolecularly. Induced birefringence studies indicate that the intramolecular dipolar interaction affects the orientability of the azo dipoles. The intermolecular dipolar interaction does not appear to have a large effect on orientability. The dependence of induced birefringence on azo content in the sample is different in the blend series (linear) and in the two copolymer series (nonlinear). A triad sequence distribution model is used to explain this difference. Observed writing efficiencies as a function of composition are also analyzed using a sequence distribution model. Dynamics of the inducing and birefringence relaxation processes are compared using biexponential fitting equations. jg p.2

Structure and properties of a photosensitive polyimide: Effect of photosensitive group

AbstractThe photosensitive poly(p‐phenylene biphenylteracarboximide) (BPDA‐PDA) precursor was synthesized by attaching photocross‐linkable 2‐(dimethylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) through acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the photosensitive precursors with various concentrations of DMAEM. The structure and properties of the polyimide films were investigated by small‐angle and wide‐angle x‐ray scattering, refractive indices and birefringence analysis, residual stress and relaxation analysis, stress‐strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were imidized from the photosensitive precursors, exhibited a better molecular order and microstructure; however, they exhibited less molecular orientation in the film plane. Despite the enhancement in both the molecular order and microstructure, the film properties (i.e., mechanical properties, thermal expansion, residual stress, optical properties, dielectric constant, and water sorption) degraded overall due to both the decrease in molecular in‐plane orientation and the formation of microvoids caused by the bulky photosensitive group during thermal imidization. That is, on one hand, the PSPI precursor formation provides an advantageous, direct patternability to the BPDA‐PDA precursor, and on the other hand, it results in degraded properties to the resulting polyimide film. © 1995 John Wiley & Sons, Inc.

Injection molding of semicrystalline polymers. I. Material characterization

AbstractVarious material data for an isotactic polypropylene were acquired for the simulation of the injection molding of this material. Viscosity as a function of shear rate and temperature was measured using a capillary rheometer at high shear rates and a cone‐and‐plate rheometer at low shear rates. Heat‐flow properties, characterizing kinetics and induction time of quiescent crystallization, were obtained from DSC measurements. Material data characterizing shear‐induced crystallization were obtained from extrusion experiments through a slit die with subsequent quenching of the material in the die after various rest times. The thickness of the shear‐induced crystallization layer was measured along with the birefringence in this layer. A model of shear‐induced crystallization developed by Janeschitz‐Kriegl and co‐workers was used to fit the kinetic data. Thus, kinetic parameters such as the limiting shear rate below which no shear‐induced crystallization can occur and the characteristic time for the relaxation of birefringence were obtained. © 1995 John Wiley & Sons, Inc.

Modeling the Electric Birefringence Relaxations of AOT/Isooctane/H2O Water-in-Oil Microemulsions

Modeling the Electric Birefringence Relaxations of AOT/Isooctane/H2O Water-in-Oil Microemulsions

Kerr effect from fractal aggregates of polystyrene microspheres

We study the slow aggregation of aqueous suspensions of optically isotropic microspheres by means of transient electric birefringence. Aggregating clusters exhibit large Kerr constants, and consequently we provide direct experimental evidence that the clusters do posses form anisotropy. From the birefringence relaxation time we derive information on the average cluster size and on the size distribution, and determine their evolution during the aggregation process. Static and dynamic light scattering data confirm the validity of the transient electric birefringence results.

Relaxation of electric birefringence near a critical consolute point.

Relaxation of electric birefringence near a critical consolute point.

Monomer-Level Description of Stress and Birefringence Relaxation in Polymer Melts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMonomer-Level Description of Stress and Birefringence Relaxation in Polymer MeltsJ. Gao and J. H. WeinerCite this: Macromolecules 1994, 27, 5, 1201–1209Publication Date (Print):February 1, 1994Publication History Published online1 May 2002Published inissue 1 February 1994https://doi.org/10.1021/ma00083a019RIGHTS & PERMISSIONSArticle Views202Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Stress and birefringence relaxations of noncrystalline linear polymer

Internal stressses in noncrystalline, linear polymer materials arise from two different sources: deviation of polymer conformation from is equilibrium state and change of intersegment distances. The separation of the two components in stress relaxation by simultaneous measurements of tensile stress and birefringence was carried out over the temperature range from the glassy state to the terminal zone, using three samples of polystyrene with different molecular weights. The master curves and relaxation spectra of the two stress components were constructed from the data. Discussion was given to the relaxation spectra for comformational deformation

Transient flow birefringence of calf skin collagen solutions.

The objective of this study is to confirm Doi’s molecular theory of the solution of rigid rodlike polymers by analyzing experimentally the transient flow birefringence of collagen solutions. Phase-modulated flow birefringence measurements were performed in the transient flow condition to obtain birefringence and orientation angle of sample simultaneously in a single experimental run.Following the cessation of simple shear flow, relaxation of birefringences was recorded to show two distinct relaxation times due to the molecular weight distribution of calf skin collagen, which turns out to be bimodal. Initial rapid drop corresponds to the relaxation of a short chain (monomer) as well as a long chains (dimer), but slow decay follows due to relaxation of long chains only.For a bimodal system consisting of monomer and dimer, such as calf skin collagen, not only the mole fraction but also the rotational diffusivity can be determined experimentally from the relaxation of birefringence. Rotational diffusivity decreases rapidly with concentration increase around C = 0.94mg/ml, as expected. But the semidilute regime starts at a rather large value of cL3 owing to the flexibility of polymers chains, which can be resolved by using the effective length proposed by Doi.

Flow birefringence of disordered block copolymer melts

The birefringence relaxation after a step strain S(t), and the oscillatory flow birefringence S* are calculated for disordered block copolymer melts, on the basis of four models for the chain dynamics: the Rouse model, the Doi-Edwards reptation model, the reptation model with constraint release, and the reptation model with orientational coupling. All the calculations are performed in the mechanically-uniform limit, i.e., the average subchain length and friction coefficient are independent of block. The net birefringence is assumed to contain no form contribution, and the approach of Kuhn and Gruen is employed in the computation of the intrinsic birefringence. The most important feature of the results is that the stress-optic relation does not apply in general for block copolymers; therefore, unique information about chain relaxation mechanisms can be obtained from measurements of flow birefringence. It is shown that the phase angle of S* can be particularly sensitive to the lengths and chain locations of the various blocks, with the most striking effects occurring when two (or more) blocks have optical anisotropies of opposite sign. In contrast, in the mechanically-uniform limit the viscoelastic properties are independent of block length and location.

Study of stress and birefringence relaxation of new amorphous polyarylates

New types of polyarylates with very low molecular anisotropy have been invented using a molecular design technique (MNDO computer calculation [M.J.S. Dewar and W. Thiel, J. Am. Ceram. Soc. 99 (1977) 4899]). The computer-designed polyarylates were then chemically synthesized. As predicted by computer calculations, these new polyarylates indicate very low birefringence in drawn films. Constant strain stress and birefringence relaxation measurements were made on these new polyarylates and the conventional polyarylate. These four polymers behave as a typical amorphous material in the mechanical sense, since the stress relaxes at the glass transition temperature. However, the conventional polyarylate and polycarbonate behave like crystalline polymers in respect of the birefringence relaxation. It is suggested that there is some local order in the structures of the conventional polyarylate and polycarbonate. The stress optical coefficients were derived from the relaxation birefringence divided by stress. The stress optical coefficients of all four polymers in the glassy state are almost two decades smaller than those in the rubber state. The shift factors for stress and birefringence are almost identical.

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.

Stretched-exponential relaxation of electric birefringence in complex liquids

The relaxation of electric birefringence is experimentally investigated in three distinct systems: critical binary mixtures, polydisperse micellar solutions and dilute polyelectrolyte solutions. The asymptotic behaviour is shown to be consistent with a stretched-exponential form exp(-(t/ tau )alpha ). Most of the data are quantitatively explained by a simple model of parallel relaxation of many independent processes characterized by a wide distribution of sizes.

Accessibility and Structural Role of Histone Domains in Chromatin. Biophysical and Immunochemical Studies of Progressive Digestion with Immobilized Proteases

The accessibility and role of histone regions in chromatin fibres were investigated using limited proteolysis with enzymes covalently bound to collagen membranes. The changes in chromatin conformation and condensation monitored by various biophysical methods, were correlated to the degradation of the histone proteins revealed by antibodies specific for histones and histone peptides. Upon digestion with trypsin and subtilisin, chromatin undergoes successive structural transitions. The cleavage of the C-terminal domains of H1, H2A and H2B, and of the N-terminal tail of H3 led to a decondensation of chromatin fibres, indicated by increases in electric birefringence and orientational relaxation times. It corresponds to a 15% increase in linear dimensions. The degradation of the other terminal regions of histones H3, H2A and H2B resulted in the appearance of hinge points between nucleosomes without alteration of the overall orientation of polynucleosome chains. Despite the loss of all the basic domains of H1, H3, H2A and H2B, no significant change in DNA-protein interactions occurred, suggesting that most of these protease-accessible regions interact weakly, if at all, with DNA in chromatin. Further proteolysis led to H4 degradation and other additional cleavages of H1, H2B and H3. This caused the relaxation of no more than 8% of the total DNA but resulted in changes in the ability of chromatin to condense at high ionic strength. More extensive digestion resulted in a total unravelling of nucleosomal chains which acquired properties similar to those of H1-depleted chromatin, although the globular part of H1 was still present. The data suggest that histone-histone interactions between H1 and core histone domains play a central role in stabilizing the chromatin fibres, and cuts in H3, H2A and H2B as well as H1, seem necessary for chromatin expansion. On the contrary, H4 might be involved in the stabilization of nucleosomes only.

Conformational changes of linear polymers in the glassy state

Internal stresses in glassy polymer materials arise from two different sources; deviation of polymer conformation from its equilibrium state and change of intersegment distances. These stress components may be separately observed by carrying out simultaneous measurements of tensile stress and birefringence relaxations of polymer films, assuming that they are additive. It is pointed out that the change of intersegment distances occurs first, and conformational deformation is gradually induced if a glassy polymer film is elongated

Strain, birefringence, and volume relaxation and recovery in polymer glasses

Stress and volume relaxation, creep, strain recovery and thermally activated strain recovery measurements have been made on bisphenol-A polycarbonate, a polyetherimide, and poly(2,6-dimethyl-1,4-phenylene oxide) as functions of thermal history, room temperature aging, strain, hold time and temperature. It was observed that as the temperature was increased, the amount of persistent strain not only increased, but also affected the stress relaxation behavior, and was observed to be partially recoverable at the test temperature. These data are interpreted in terms of a network model wherein it is proposed that the motion of defects between and past entanglements, their loss at chain ends, and the disentanglement of chain ends from other segments serve as the primary mechanisms of relaxation in the glassy state.

Rotational Viscosities of Nematic Sodium Decylsulfate, 1-Decanol, D2 O Mixtures

The studied mixtures of sodium decylsulfate, 1-decanol and D 2 O show a sequence of three nematic phases, a low temperature uniaxial phase N L , a biaxial phase N bx , and a higher temperature uniaxial phase N C . We report rotation experiments in magnetic fields to determine the anisotropy of the diamagnetic susceptibility and the rotational viscosity, electrical conductivity measurements to study micellar order and realignment in magnetic fields, and birefringence measurements and relaxation studies on thin surface aligned films. The measured rotational viscosities in N C range from a few poise to nearly 100 poise. There is a strong pretransitional decrease of the viscosity with decreasing temperature at the N C -N bx transition. The data in the N L range indicate also a pretransitional decrease as the N L -N bx transition is approached. Near the transition the viscosity is considerably smaller in the lower temperature N L -phase than in N C . The conduction anisotropy and birefringence in N C show some differences in the temperature dependence. Both decrease slightly as the uniaxial-biaxial transition is approached but the decrease of conduction anisotropy is more pronounced

Stretched-exponential relaxation of electric birefringence in polymer solutions.

The relaxation of electric birefringence in dilute solutions of a polyelectrolyte is shown to be consistent with a stretched-exponential form, exp[-(t/\ensuremath{\tau}${)}^{\ensuremath{\alpha}}$]. The exponent \ensuremath{\alpha} depends on polymer length L and solvent ionic strength only through the ratio x==L/${L}_{p}$, where ${L}_{p}$ is the persistence length, and crosses over from \ensuremath{\alpha}\ensuremath{\simeq}1 for stiff chains (x\ensuremath{\simeq}1) to \ensuremath{\alpha}\ensuremath{\simeq}0.44\ifmmode\pm\else\textpm\fi{}0.02 in the self-avoiding-walk regime x\ensuremath{\gg}1, the latter in accord with a simple scaling theory of polymer statistics and dynamics.

Anisotropic counterion polarizations and their dynamics in aqueous polyelectrolytes as studied by frequency-domain electric birefringence relaxation spectroscopy

Etude avec les sels de sodium du polystyrenesulfonate, de la carboxymethylcellulose et de l'ADN