Steady-state Birefringence Research Articles

Effects of glow-discharge nitrogen-plasma on the linear birefringence of polyester sheets

A simple white light interferometric method is used to study the effects of plasma on the steady-state linear birefringence of polyester sheet films. Glow-discharge nitrogen-plasma of power 13 W with nine different exposure times from 0 to 25 min is applied to films of 0.22 mm thickness. The relationship between the linear birefringence and some atomic parameters is derived theoretically and tested experimentally. Effects on the linear birefringence, the linear retardance and Herman's orientation parameter are investigated. The increase of plasma exposure time produces an increase in the linear birefringence and Herman's orientation parameter. Characterization of plasma-treated and plasma-untreated polyester samples have been thoroughly examined using Fourier transform infrared (FTIR) spectroscopy. It is noted that no new bands have appeared after treatment for all the tested samples at different time intervals. There is an increase in intensity and band definition, and a shift of some bands that were already present in the spectrum of the untreated sample, assigned to the trans conformer.

Anomalous electric birefringence behavior of sonicated DNA fragments as observed in reversing-pulse transients and steady-state sign reversal: A multicomponent approach

Anomalous electric birefringence signals of a sonicated and column-fractionated medium-size calf thymus DNA sample (bp = 570) in Na + solutions were measured at 7 °C. The reversing-pulse electric birefringence (RPEB) signal pattern was theoretically calculated in the low electric field region for two axially symmetric models coexisting in equilibrium in solution. The RPEB theory is based on the electric dipole moment due to ion-fluctuation along the longitudinal direction and the electric polarizability anisotropy (Δ α′), together with various electric and optical parameters assigned to the models. An analytical method was developed for the steady-state birefringence of the two-component system in a wide range of electric fields. The NaDNA samples exhibit complex RPEB patterns mixed with negative- and positive-going profiles. An experimental RPEB signal of NaDNA at an absorbance ( A 260) of 8 was fitted to theoretical curve at weak electric fields. The anomalous RPEB signal was attributed to the component 2, which shows a dip in the buildup and another in the reverse processes with a positive sign and a larger relaxation time. For the component 1, a normal DNA profile with negative sign is associated with a narrow dip in the reverse and a faster relaxation time in the decay signal. The field-strength dependence of observed steady-state birefringence δ(∞) could be fitted for NaDNA at A 260 = 8 by the SUSID orientation function with saturated ionic and electronic moments. An apparent positive maximum and the sign reversal in δ(∞) at weak electric fields is an interplay between the positive component 2 with positive optical factor Δ g and negative Δ α′ and the negative component 1 with negative Δ g and positive Δ α′. Possible conformation of two DNA components involved in solution was estimated.

Electrooptics of β-FeOOH particle in aqueous media : 2. Field-strength dependence of decay and steady-state birefringence, and the hydrodynamic and electrooptic properties

Steady-state and decay birefringence, expressed in terms of the optical phase retardation per cell length δ / d , was measured on β-FeOOH in aqueous ionic media at 633 nm and at 25 °C by an electric square-pulse technique over a wide range of field strength E to ca. 6 kV/cm. The field-strength dependence of both δ / d and field-free rotational relaxation time τ was determined at the sample concentrations between 0.0011 and 0.055 g/L and in the 0.02–2.0 mM NaCl concentration range. Extrapolation of both δ / d and τ values to infinitely high fields ( E 2 → ∞ ) could yield birefringence- and weight-average quantities, respectively. Observed τ values were decreased at weak fields but leveled off to ca. 0.3 ms at very high fields due to a slight polydispersity regarding the length and volume of particles. The weight-average relaxation time 〈 τ 〉 w was calculated with Perrin's expressions theoretically from the length, width, and volume of β-FeOOH particles estimated in the dried state from electron micrograph. These quantities were variously averaged. The size distribution was discussed in terms of observed discrete histogram and theoretical (Weibull and Lansing–Kraemer) distribution functions. The sign of observed δ / d value was always positive. The infinitely high-field ( δ / d ) ∞ values and the reduced optical anisotropy factor Δ g / n were evaluated by fitting to theoretical orientation functions. The intrinsic birefringence ( n 3 − n 1 ) could be estimated with the mean refractive index n p reported in the literature. For the spindle-shaped particle with an axial ratio of ca. 4, the sign of Δ g / n is always positive, whereas the quantity ( n 3 − n 1 ) was either negative ( n p > 2.35 ) or positive ( n p < 2.05 ) in sign or nearly zero (ca. n p = 2.26 ), depending critically on the n p values.

Birefringence, Deformation, and Scattering of Wormlike Macromolecules under an External Agent. Steady-State Properties in an Electric Field

In this paper, we study the steady-state birefringence, deformation, and scattering of wormlike macromolecules under the influence of an electric field. We use a model of N + 1 pointlike elements whose connectors define N axially symmetric subunits. The model is able to describe some properties of segmentally flexible and wormlike macromolecules depending on the choice of N. We use the Monte Carlo computer simulation technique to characterize the effect of the electric field on the orientation and deformation of molecules with permanent and induced dipoles. Using this technique, we study the effect of the field in different models with the same flexibility (defined as 〈s 2 〉0/〈s 2 〉0,str). Orientation is studied through changes in birefringence and deformation through changes in the gyration tensor of the molecule. When the behavior of a broken rod (typical case of segmental flexibility) and a wormlike chain is compared, the differences are generally quantitative although significant enough to be used to obtain information about the internal structure of a macromolecule.

Birefringence due to free electrophoresis

We calculate the steady-state birefringence and dichroism for the case of a rigid bent rod molecule due to the free electrophoresis. In order to find the orientational distribution function, we use the Fokker–Planck equation and solve it by the perturbation method (for the steady state) at low electric field. We find that, using convenient parameters to characterize the DNA solution, both, the calculated electric birefringence and the dichroism, for low electric fields, have positive values in concordance with the experimental results.

Dependence of DNA steady-state electric birefringence on field strength

Abstract A major task in our work has been to calculate the dependence of DNA steady-state electric birefringence on field strength for a ‘hinged bent rod’ (HBR) composed of two rod-like arms of length L with a restoring force proportional to the angle of bending at the hinge. The system is considered to have a permanent dipole moment due to asymmetric charge distribution with respect to its centre of diffusion. The electric and optical polarizability tensors of HBR macroions are also calculated. To calculate the electric birefringence, the statistical averages of the differential optical polarizability per molecule in the directions parallel and perpendicular to the applied electric field are made over all conformations as well as over all spatial orientations and all the velocities in the presence of the electric field. Using this approach, numerical calculations are carried out to achieve a fitting of electric birefringence experimental curves versus the square of the electric field for the sonicated and fractioned DNA and restriction enzyme fragments of DNA. It is shown that the HBR macroion presents a reversal of the birefringence sign at low electric fields for certain chain lengths, electric polarizability and stiffness constant values, in agreement with the experimental results obtained for DNA. It is observed that the HBR model adequately represents DNA elastic properties.

On the Kinetics of Polymer Crystallization in Opposite-Nozzle Flow

The present work was encouraged by the successes obtained previously in this laboratory with short-term shearing experiments on slightly undercooled melts of i-PP: post-shearing lamellar growth on (inconspicuous) thread-like precursors. For the present purpose (evaluation of the influence of extensional flow) the pioneering work by Mackley and Keller is taken as the point of departure. Our own machine of the same type has been adapted for creep experiments (adjustment to steady flow in fractions of the time needed in the original machine). The range of extension rates, where a transition takes place from a mere multiplication of the number of nuclei to the induction of highly oriented structures, appears to be quite narrow in undercooled i-PP melts. In the range of high extension rates (≅50 s−1 ) the critical time for the formation of an oriented structure could not be measured because of its shortness (less than 0.2 s). It turns out that the flow pattern in the opposite-nozzle machine is far from ideal. A proposal had to be made for a redesign. In spite of the preliminary nature of some of our results, several interesting insights should not be “bottled up”. First of all, there is the usefulness of creep flow (because of its fast transition into steady state, after an almost instantaneous compliance). Secondly, there is the quite unexpected ineffectiveness of lower stretching rates for the formation of oriented structures. Thirdly, there is the overwhelming influence of a change of the geometry: the provisional introduction of trumpet-shaped (nearly hyperbolic) entrance regions to the nozzles caused a remarkable broadening of the birefringent zone, which was previously observed as a very thin “string” connecting the nozzles. Finally, the almost certain usefulness of the revised machine for other (sometimes purely rheological) purposes, e.g., for steady-state flow birefringence measurements in extensional flow should be mentioned.

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (〈m2〉1/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of 〈m2〉1/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).

Transient electric birefringence of colloidal particles immersed in shear flow: Part III: A preliminary report on determination of anisotropy of electric polarizability

We have constructed an electric birefringence apparatus having a flow cell with parallel platinum electrodes to measure the initial values and initial slopes of the transmitted light intensity in two cases. One is the case that the polarizer is at 0° to the electric field and 90° to the direction of flow; the other is the case that the polarizer is at 45° to the electric field and the direction of flow. By using theoretical relationships derived previously, we tried to estimate the anisotropy of electric polarizability, the axial ratio, the optical anisotropy factor and the velocity gradient for a fractionated bentonite solution. The signs of the optical anisotropy factor and parameter R related to the axial ratio as ( P 2−1)/( P 2+1) were easily determined. However, we could not obtain reliable values of the axial ratio and the optical anisotropy factor because it was difficult to maintain the same conditions in two different observations. On the other hand, it is easy to estimate the anisotropy of electric polarizability at various electric fields because it can be evaluated from one signal. The anisotropy of electric polarizability of bentonite particles had the same negative sign as Shah's conclusion. However, it was unexpected that its magnitude at low fields (<200 V/cm) increased rapidly with a decrease of electric field. The dependence of the steady-state birefringence on electric field also supports this result.

Comparison of dumbell-based theory and experiment for a dilute polymer solution in a corotating two-roll mill

The Chilcott–Rallison FENE dumbbell model is used to solve for the polymer and flowfield response in transient startup flow of a dilute solution in a corotating two-roll mill. These predictions are then compared to experimental results obtained in an identical geometry using a high molecular weight dilute (c/c*∼0.1) polystyrene solution. As predicted by the dumbbell model, the experiments indicate a substantial coupling between the polymer deformation and changes to the Newtonian flowfield. As the polymer stretches, the experimentally measured shear rate decreases, as does the flow-type parameter. However, dumbbell model parameters based upon an isolated chain do not result in FENE model predictions quantitatively similar to the experimental results. Based upon steady-state birefringence values for the same dilute solution in an extension dominated flow at large strain rates, it appears that chain–chain interactions restrict the maximum attainable polymer deformation. Further calculations incorporating th...

Reversing-Pulse Electric Birefringence of Montmorillonite K10 in Aqueous Media: Electric Moments, Field Orientation, and Changes in Sign and Profile of Signals Observed in the Low-Field Region

The reversing-pulse electric birefringence (RPEB) of a montmorillonite K10 (MK-10) sample was measured at 25°C and 633 nm in aqueous suspensions in the concentration range 0.005–0.145 g/L in the 0–200 V/cm region. The sign of the RPEB signals was negative and the profile was associated with a deep dip in the reverse process in all cases at weak fields lower than the sign-inversion point,Esi. AboveEsi, the sign became positive, whereas the signal profile usually showed a hump in the buildup process and a larger hump in the reverse process. A complex signal pattern appeared at the highest MK-10 concentration (0.145 g/L). For the multicomponent equilibrium system, theoretical RPEB expressions were derived in terms of three electric dipole moments: the permanent moment, the fluctuating counterion polarizability (ς3) with ionic relaxation time (τI) along the symmetry axis, and the covalent polarizability anisotropy (Δα′). Analysis of profiles of the observed RPEB signals showed that the MK-10 particle possesses no permanent dipole moment. The ratio ς3/Δα′ was less than −1, and τ1was comparable with the overall rotational relaxation time τ of the disklike MK-10 particle. RPEB signals at 0.145 g/L were analyzed with the two-state equilibrium theory and the MK-10 particle was found to form thin platelike aggregates with partially overlapping surfaces. The field-strength dependence of the steady-state birefringence was fitted with SUSID orientation functions. The field orientation mechanism of MK-10 particles in aqueous media was discussed.

Optical Rheometry of Silk in Aqueous LiBr Solution

The rheo-optical response of solutions of silk in aqueous 9 M LiBr of concentrations ranging from 7.5 to 15 wt % was investigated. These samples were found to be birefringent under flow, with the steady state birefringence having a concentration scaling of c3.9. This scaling behavior suggests a wormlike conformation of the silk molecules in solution. The relaxation was fast, and Maxwellian behavior was observed at low shear rates. No dichroism was detected suggesting that electrostatic screening suppresses structure formation under shear.

The conformation of semi-rigid polymers during flow through a fixed fiber bed

Linear conservative birefringence measurements of dilute and semi-dilute solutions of the semi-rigid polymer xanthan gum in a glycerine and water solvent are conducted during flow through a disordered fiber bed. Even though the plug flow through the bed contains no average velocity gradient our results show that the xanthan gum molecules stretch, on average, in the direction of flow. The polymer stretch or birefringence increases with the number of fiber interactions within the bed until a steady-state conformation is attained. The degree of stretch increases monotonically with increasing De pore (the ratio of a characteristic polymer relaxation time and the characteristic flow time in a bed pore). The results show a number of qualitative differences when compared to those for the flow of flexible polyisobutylene (PIB) (Evans et al., J. Fluid Mech., 28 (1994) 319) through the same fiber bed. In particular, xanthan gum attains a steady-state conformation after convecting 12 pore-lengths in the bed (compared to approximately 25 for the PIB solution) and this value is independent of De pore whereas it increased with increasing De pore for the flexible polymer. Additionally the steady-state birefringence of the xanthan gum solutions displays no critical De pore at which the birefringence increases dramatically (as does the flexible polymer system) and instead exhibits a slow growth with increasing De pore. These unique results are interpreted and understood using novel Brownian dynamics simulations of a semi-rigid bead-rod polymer model flowing through a simulated stochastic porous bed flow field created via a spectral expansion. Our results show that the simulations can predict most of the experimental results, at least qualitatively, and in some instances quantitatively, and therefore provide an important tool for understanding these complicated phenomena.

Magnetic birefringence particle size distribution

A novel use for magnetic birefringence experiments is in the measurement of the birefringence of commercially important colloidal vermiculite particles. When aligned in a magnetic field, results at low field strengths show a steady state birefringence proportional to the applied field. The effects on the relaxation time of the birefringence on removal of the field are found to decrease with increasing field strength. This has been attributed to polydisperity of particle size. A theory analogous to that of electric field relaxation and used for magnetic field relaxation data has been further developed and modified to incorporate the more general case of diamagnetism. The modified theory is then used to obtain a two-parameter log-normal size distribution function for the suspended particles. The experimental results obtained are in accord with data acquired from electron micrographs. It is therefore concluded that use of the modified theory is justified and forms the basis of a valid measurement technique applicable to rigid particulate systems of any uniform, regular spheroidal morphology.

Electro-Optical and Hydrodynamic Properties of Synthetic Polyribonucleotides in Solutions as Studied by Electric Birefringence

Abstract The electro-optical and hydrodynamic properties of four synthetic polyribonucleic acids were clarified by electric birefringence methods which take the molecular-weight distribution into consideration. Parallel double-stranded helices, poly(adenylic acid)·poly(protonated adenylic acid), I, and poly(cytidylic acid)·poly(protonated cytidylic acid), II, are known to possess an electric permanent dipole moment, because the reversing-pulse electric birefringence (RPEB) signals of these duplexes exhibit dips upon pulse reversal. The RPEB signals of antiparallel double-stranded poly(adenylic acid)·poly(uridylic acid), III, and poly(guanylic acid)·poly(cytidylic acid), IV, show no dip; therefore, these polynucleotides have no permanent dipole moment. By analyzing the relaxation time of the birefringence decay signals, the axial translations of the polynucleotides per base-pair were determined to be 4.0 Å for I, 2.7 Å for III, and 2.4 Å for IV, respectively. By analyzing the dependence of the steady-state birefringence values on the electric-field strength, the magnitudes of the permanent dipole moments per unit length of I and II projected onto the helix axes were found to be ca. 0.4 debye Å−1. The electric properties unraveled by electric birefringence experiments were compared with calculations based on a recent Manning theory. An unsaturable induced dipole moment may result from the polarization of the Debye–Hückel ion-atmosphere, while a saturable induced dipole moment is probably caused by the polarization of counter ions that are condensed on the charged sites of a polyion. The experimental values deviate from calculated values at ionic strengths lower than 0.0001; hence, the Manning theory is not applicable in this region.

Stretching and overstretching of DNA in pulsed field gel electrophoresis. I. A quantitative study from the steady state birefringence decay

AbstractUsing a sensitive birefringence instrument, the birefringence arising from the orientation of the DNA chain during electrophoretic transport has been recorded. This birefringence is shown to proceed both from the alignment (stretching) of the molecule in the direction of the electric field and from the extension of the length of its primitive path (overstretching). The contribution of these two processes can be separated in the decay of the birefringence after the end of the application of the electric field. The fast relaxation of the overstretching occurs first and is demonstrated to be the main contribution to the birefringence. The orientation factor of the remaining stretched state and its decay can be quantitatively understood using the biased reptation model. It provides, in addition, a high value for the tube diameter or gel pore size a (4500 ± 450 Å for a 0.7% agarose gel with a c−0.6g dependence in the agarose concentration cg) and a low value for the effective charge per base pair (0.2e as compared to 0.5e using the condensation hypothesis). The contribution of overstretching to the birefringence is also quantitatively interpreted in term of the change in the mean length l of DNA inside a pore size a. The dynamics of decay of this overstretching is well represented by a stretched exponential with a stretching exponent α = 0.44. The mean decay time decreases slightly with increasing fields and scales with the overall DNA length close to N20. © 1993 John Wiley &amp; Sons, Inc.

Structural analysis of Trypanosoma brucei brucei chromatin by limited proteolysis

The sensitive electric-birefringence method was used to reveal structural differences between the soluble chromatin of procyclic Trypanosoma brucei brucei and the chromatin of the higher eukaryotes. The orientation of the nucleosomal chains and the presence of extended DNA were analysed from the sign and amplitude of the steady-state birefringence, and the conformational properties (overall dimensions and flexibility) were studied in relation to the orientational relaxation times. In contrast to the higher eukaryotes, the birefringence of T. brucei brucei is negative and of low amplitude, corresponding to that of H1-depleted rat liver nucleosomes. Furthermore, the relaxation times are very small, about 10 microseconds. If salt is added, the birefringence as well as the relaxation time decreases dramatically, indicating that condensation affects T. brucei brucei chromatin although it behaves like nucleosome filaments, with less stable DNA-protein interaction than for the higher eukaryotes. However, this condensation does not induce the formation of regular higher-order structure. This complies with the hypothesis that typical histone H1 is absent from T. brucei brucei chromatin and that a protein or protein domain fulfils the role of histone H1. The accessibility and structural role of histone-like proteins in T. brucei brucei chromatin were also investigated using limited proteolysis with enzymes covalently bound to nylon spheres. The analysis of protein products obtained after digestion with immobilized trypsin and subtilisin shows that proteins a and d, which are classified as H3 and H4 histones, respectively, are the first to be attacked. The changes in chromatin conformation indicate that chromatin undergoes a structural transition, leading to decondensation, as indicated by increases in negative birefringence and relaxation time, and to a change in its orientation mechanism, indicated by the appearance of a permanent moment. This result is very interesting since, in rat liver, H4 was very resistant and was the last histone to be attacked, suggesting internal location and its involvement in nucleosome stabilization rather than higher-order condensation. Therefore, in T. brucei brucei chromatin, the characteristic properties of proteins a and d (their composition and interaction with DNA), as well as their external location on the nucleosome surface, suggest that if these proteins play a role similar to that played by H3 and H4 in higher eukaryotes, probably through their N-terminal regions and interaction either with DNA or protein domains, the mechanisms involved in chromatin compaction are quite different.(ABSTRACT TRUNCATED AT 400 WORDS)

Low field theory of polymer transient electric birefringence

Using the Rouse/Zimm model for polymers, we have derived the low field dynamics for a flexible polymer in transient electric birefringence (TEB). Three orientation mechanisms were included; a permanent dipole from fixed charges, a local induced dipole dependent on the local conformation, and a global induced dipole dependent on the global conformation. The rise, decay, and reverse pulse behavior have been determined for all three, independently and combined. The condensed ion theory of Manning has been used to describe the global orientation mechanism of DNA. We find good agreement for the steady state birefringence and the predictions from theory with no adjustable parameters.

Electric birefringence imaging of electrokinetic agarose orientation.

Time-resolved and steady-state electric birefringence imaging with a slow-scan video camera is used to study orientation during DNA agarose gel electrophoresis. The hydrodynamically induced gel distortion is shown to be the major source of birefringence under electrophoresis running conditions and to generate a birefringence image that approximates the image of the DNA concentration gradient in the electric field direction. A fluid kinematic model is presented to describe the spatial distribution of steady-state birefringence and is verified with fluorescence measurements of DNA distribution. The stress-optic coefficient of 1% agarose gel is measured by mechanical compression and used to evaluate the magnitude of the induced strain on the gel during electrophoresis.

Birefringent and electro-optic effects in poled polymer films: steady-state and transient properties

Expansion of the orientational distribution function f(θ, t) of molecular dipoles in terms of Legendre polynomials with spherical modified Bessel functions in(μE/kT) as coefficients yields an analytic relation between the steady-state birefringence Δnz(ω) and the electro-optic coefficient χxxz(2)(-ω;ω,0) for a poled nonlinear optical system. A rotational diffusion equation, with the diffusion constant D, for the distribution function describing the onset and the decay of the induced optical and electro-optic properties is solved, with the help of the recurrence relation for spherical modified Bessel functions. It is found that the onset of birefringence involves at least two time constants, with rise times of 1/2D and 1/6D, while the onset of the electro-optic effect is dominated by the rise time of 1/2D. After removal of the dc poling field, the birefringence and the electro-optic effect are found to relax in time with different decay time constants, 1/6D and 1/2D, respectively. This is due to the difference in the tensor rank describing the birefringence and the electro-optic effect.