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The dynamics of the α-relaxtion in three glass-forming polymeric systems has been studied by means of quasielastic neutron scattering as well as by relaxation techniques. By using these techniques, we have covered a wide time-scale ranging from mesoscopic to macroscopic times (10−10-101 s). All relaxation data have been interpreted in terms of a Havriliak-Nagami relaxation function, ΦHN. Neutron scattering data were described in terms of a scattering law S(Q, ω) which was also built starting from ΦHN. The results obtained indicate that the dynamics of the α-relaxation in a wide timescale can be well described by means of the same spectral shape, i.e. the same Havriliak-Negami parameter values. Moreover, the Havriliak-Negami characteristic times deduced from the fitting of the experimental data can also be described using only one Vogel-Fulcher functional form. Then, this implies a self-consistent description of the dynamics of the α-relaxation obtained by very different probes. [ABSTRACT FROM AUTHOR]

Local dynamics of a chain in the bulk state is strongly controlled by the immediate environment of the chain. The excessive friction exerted by the environment precludes large scale kinetic displacements of the chain atoms. In the presence of strong constraining effects of the environment, a transition from one configuration to the other is expected to take place by strongly correlated and relatively small range rearrangements of torsional motions. In the present study, local dynamics of the chain is analyzed as a succession of configurational rearrangements such that the change in the chain radius of gyration at each step is minimum. The degree of cooperativity among neighboring bonds along the chain resulting from the constraint of the environment is found to be highly localized. A 120° rotation of an internal bond is observed to be possible by cooperative adjustments of a few bonds in its immediate neighborhood along the chain. Changes in the mean-square anisotropic polarizability tensor when the ends of a relatively short chain (n≤50) are subject to a prescribed deformation, are also calculated. Calculations show that changes in the mean-square anisotropic polarizability depend strongly on chain length. [ABSTRACT FROM AUTHOR]

The synthesis, characterization, and some studies of the dynamics of a new rod/sphere composite liquid are discussed here. The composite liquid consists of silica spheres (39.4 and 60.4 nm radius) and poly(γ-benzyl-α,L-glutamate) rods (102 000 and 249 700 g/mol molecular weight) dispersed without aggregation in dimethylformamide (DMF) or a mixture of DMF and pyridine. The solvent mixture was used to refractive-index-match dilute solutions of spheres. Dynamic light scattering (DLS) was used to measure the diffusion constants of both the rods and the spheres simultaneously in the solution. Two dynamical regimes were observed for the diffusion of the rods with or without the spheres. The transition point between these two regimes was attributed to the change from dilute to semidilute dynamics. Sphere diffusion constants up to a value two times larger than expected from the Stokes-Einstein equation were measured for the composite liquid containing the large rod (249 700 g/mol) and the small sphere (39.4 nm) in accordance with the argument of Langevin and Rondelez [17]. The sphere diffusion constants measured for the liquid containing the large sphere (60.4 nm) and the small rod (102 000 g/mol) followed a stretched exponential decay with increasing polymer concentration: D/D0=exp (−0.16 c0.81). The c0.81 dependence compares well to experimental results using coil polymers but not to the theories for rod solutions which predict a c0.5 dependence. The similar concentration dependence found for rod and coil solutions suggests that polymer flexibility alone does not account for the deviation from the theoretical c0.5 predictions. Instead, rod-rod hydrodynamic interactions may play an important role in this deviation. [ABSTRACT FROM AUTHOR]

The relation between main- and normal-mode relaxation is studied on poly(propyleneoxide) of different molecular weights by dielectric measurements in a very large frequency range. The evaluation by a special technique shows a merging of α-relaxation and of normal-mode relaxation at an essential higher temperature than the Vogel temperature of the α-relaxation. This means the Rouse model is not applicable to the normal-mode relaxation near the glass transition temperature. [ABSTRACT FROM AUTHOR]

The basic notions of dynamic light scattering (DLS) on non-ergodic media are presented and discussed. We present the results, obtained by DLS, for the intermediate scattering function of polystyrene latex particles that are dispersed in aqueous polyacrylamide gels. It is shown that these systems display non-ergodic features, implying that the time-averaged intensity correlation function (ICF) is not equal to the ensemble-averaged ICF. [ABSTRACT FROM AUTHOR]

Static and dynamic laser light scattering and viscometry have been used to study the dynamics and structure of coil-to-globule transition. With the prism-cell laser light scattering spectrometer, very small scattering angles of the order of 3o could be reached which enabled us to determine the pure translational motion of large polymer chains. The contraction size of a polymer chain during the collapse process has been measured in terms of the radius of gyration, the hydrodynamic radius and the intrinsic viscosity. In the thermodynamically stable region, the coil size obeyed the scaling theory. However, a kinetic study of the collapse has demonstrated a two-stage collapse process in agreement with the theoretical prediction of Grosberg et al. Experimental results of the coil-to-globule transition from polystyrene in cyclohexane and from a polyelectrolyte (sodium polystyrene solfonate) in aqueous solution are presented. [ABSTRACT FROM AUTHOR]

The dynamic light-scattering spectrum from a polymer solution is shown to be related to the cooperative diffusion and longitudinal stress relaxation modes. Experimental results are presented to corroborate the theoretical analysis. [ABSTRACT FROM AUTHOR]

We discuss experimental results on molecular motion in polymer melts, obtained by neutron spin-echo spectroscopy (NSE). For longer times we observe systematic deviations from the Rouse model, revealing the presence of a well-defined intermediate dynamical length scale beyond which density fluctuations within a given chain are strongly reduced. Its value is found to be in excellent agreement with the entanglement distance obtained from rheological measurements. Measurements of the temperature dependence and polymer volume fraction dependence of the entanglement distance give an insight into the molecular origin of entanglement constraints. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of two polystyrene-polymethylmethacrylate (PS-PMMA) diblock copolymers has been studied in toluene by quasielastic light scattering in the vicinity and above the overlap concentration C* of the copolymer chains. At the macromolecular scale two relaxation modes have been found near C*. The slow mode has been ascribed to the classical cooperative motion of the transient physical network formed by the copolymer molecules. It is identical to the motion that is observed in the equivalent binary PS/toluene solution where PS has the same molecular weight as the molecular weight of the whole copolymer and where the PS and the PS-PMMA concentrations are equal. The fast mode is a structural mode that reflects the fluctuations of concentration of one species with respect to the other. Above C* a third motion appears that is not anticipated by the theories. The frequency of this mode is very low and decreases when the copolymer concentration increases. This mode is attributed to the formation of aggregates that can occur even at relatively low concentrations (4C*) for the systems under investigation. [ABSTRACT FROM AUTHOR]

Concentrated solutions (volume fraction 0.1-0.9) of polystyrene (PS) in toluene and of polybutylacrylate (PBA) in dioxane have been examined using dynamic light scattering (DLS) as a function of angle and temperature. With PS there is a pronounced maximum in the cooperative diffusion coefficient (Dc) at about Φ=0.5 as the glassy state is approached. By contrast, with PBA, which has a very low Tg, there is a crossover to a stronger concentration dependence for Dc, which is attributed to an increase in solvent mobility. In the PS/toulene system at Φ=0.78 a transition is noted between the diffusion mode and the main relaxational mode. At 17°C q-independence is observed and at 50 °C q2-dependence. At Φ=0.89, both relaxations are observed simultaneously in the DLS time window, the slower process being a structural relaxation. [ABSTRACT FROM AUTHOR]

The dynamic scattering properties of ternary mixtures made up of two polymer components and a solvent are considered. Examples of symmetrical and nonsymmetrical mixtures are examined. Particular attention is focused on the interpretation of the eigenmodes. It was recently shown that the eigenmodes for ternary mixtures could be rigorously identified with the cooperative and interdiffusive modes only if the two polymer components are identical, except for their optical properties. Here, we consider several mixtures made up of different polymer constituents and compare the variations of the relaxation frequencies with the scattering wave vector q. In all the examples considered, the behavior of (Γ, ΓT) and (Γ′, Γ1) are found to be qualitatively the same. This leads to the conclusion that, although the eigenmodes can be identified rigorously as the cooperative and interdiffusive dynamical processes only for symmetrical mixtures with a finite χ-parameter, they can still be so-identified approximately even in the case of different polymers and nonsymmetrical mixtures under certain experimental conditions. [ABSTRACT FROM AUTHOR]

Neutron-scattering experiments have been performed on elongated polystyrene melts consisting of relatively short labelled chains (M<100 000) dispersed in a matrix of very long ones (M>106), which were not labelled. Important anomalies with respect to the theoretical predications have been observed. In particular, the iso-intensity lines exhibit, in a large range of relaxation times, striking butterfly shapes and an unexpected orientation: the long axis of these patterns is oriented parallel to the stretching direction. As a working assumption, we propose to relate this phenomenon to a non-homogeneous arrangement of chain entanglements in the melts. As a matter of facts, it has been proposed that elongated gels should exhibit butterfly patterns (The whole solvent being labelled) as a result of a sort of anisotropic unscreening of cross-linking heterogeneities. Experiments were performed on samples synthesized specially in order to match the assumptions of the model and butterfly patterns have effectively been observed. The same type of mechanism can be driven by an heterogeneity of chain entanglement in the case of assymetrical melts: the short labelled chains may behave as a kind of polymeric solvent and accumulate, during the relaxation, in the less entangled regions (which should be also regions of lower constraint). [ABSTRACT FROM AUTHOR]

A diblock copolymer of poly(styrene-block-para-emthylstyrene) (PS-b-PMS) is investigated near its microphase separation temperature with respect to the formation of organized structures in thin films. A contract between components is achieved by deuteration of the PS-block, and the surface-induced order is detected by neutron reflectometry and 15N nuclear reaction analysis. While the PMS component is always enriched at the surface, an exponentially decaying lamellar order of alternating layers of PS and PMS parallel to the surface is observed depending on annealing time. Those observations are discussed with respect to the influence of surface and substrate on the development of organized structures in a block copolymer melt. [ABSTRACT FROM AUTHOR]

The ordering of thin films of symmetric diblock copolymers of polystyrene and polymethylmethacrylate has been investigated by neutron reflectivity. It is shown that the order-disorder transition temperature depends strongly on the film thickness, increasing as the film thickness decreases. The transition is shown to lose all its first-order characteristics in the thin films. For films thinner than ∼2000 Å it is not possible to obtain the copolymer flms in the disordered state at temperatures below the decomposition temperature. A transition is observed where the copolymer goes from a partially to a fully ordered state. For thick specimens, this transition corresponds to the bulk order-disorder transition temperature. However, for thinner specimens this transition temperature depends on the film thickness in a power law manner. [ABSTRACT FROM AUTHOR]

We investigated diffusion between deuterated and protonated polystyrene films at short times using neutron reflectometry (NR) and nuclear reaction analysis (NRA). We covered six orders of magnitude in time and identified two time regimes of diffusion with a crossover at the reptation time τrep. Below τrep the interfacial profile can be described by two superposed error functions attributed to the Rouse-type mobility and reptation. The contribution due to reptation shows a discontinuity at the position of the interface. There are some strong indications for an enhanced concentration of chain ends at the interface. The reliability of the results is supported by the agreement of the three values of τrep obtained by the use of the two complementary techniques. [ABSTRACT FROM AUTHOR]

The morphology of thin films of symmetric diblock copolymers has been investigated by neutron and X-ray reflectivity and X-ray photoelectron spectroscopy, for thicknesses less than 3L/2, where L is the long period of the lamellar morphology in the bulk. The constrains placed on a copolymer film by the presence of the two surfaces can produce severe perturbations on the morphology, due to the interactions of the copolymer blocks with the air and the substrate interfaces. It is possible to induce variations in the chain extension and in the interfacial mixing, and to force a normally microphase separated copolymer into a homogenecous state. [ABSTRACT FROM AUTHOR]

We report results on adsorbed layers of polystyrene (PS)-polyethylene oxide (PEO) diblock and PEO-PS-PEO triblock copolymers at the solid/liquid interface. The volume fraction profiles of the adsorbed PS-PEO diblock copolymers at the the quartz/toluene interface determined by neutron reflectometry are consistent with a parabolic profile as predicted by theory. Ellipsometry was used to investigate the adsorption kinetics of PS-PEO diblock copolymer chains on SiO2 from toluene. The results show a rapid diffusion-controlled process, characterized by a linear increase in the adsorbed amount with the square-root of time, at the early stages of adsorption, while at late times adsorption is slow and appears to be governed by an exponential time behavior. Studies of the PEO-PS-PEO copolymer, using the surface-force apparatus, reveal conformational rearrangements for the adsorbed triblock chains between mica surfaces. When two such surfaces are in close proximity to each other, triblock chains originally adsorbed in a "loop" conformation may open into a "bridge" conformation with both PEO blocks of a given chain adsorbing onto opposing mice surfaces. This is indicated by the appearance of clearly detectable attractive forces and their evolution with compression-decompression cycles. The time evolution of these forces reflects the dynamics of the rearrangement of chains between the two surfaces. [ABSTRACT FROM AUTHOR]

Mechanical measurements in the glass transition zone were carried out on a series of polydienes to study the effect of chemical structure on the segmental relaxation. The breadth of the glass transition dispersion in the mechanical spectrum increased with increasing concentration of pendant vinyl groups on the main chain. The broader relaxations exhibited stronger temperature dependences. Both observations are consistent with the compling model of relaxation. Enhanced intermolecular coupling arises due to steric interferences among the vinyl moieties, and the coupling model predicts that more cooperative relaxations will be both broader and more temperature sensitive. In miscible blends the glass transition dispersion is further broadened due the distribution of local environments engendered by concentration fluctuations. The coupling model is extended to consider the effect of concentration fluctuations on the local variation in the degree of intermolecular cooperativity. The shape of the relaxation spectra of miscible blends in the glass transition zone, as well as both composition and temperature dependencies of the dispersion, are markedly influenced by the concentration fluctuations specific to miscible blends. Application of the model to two blends is demonstrated to successfully describe the prominent features of the measurements. [ABSTRACT FROM AUTHOR]

A series of polystyrene/(cis 1-4)polyisoprene diblock copolymers is studied using small-angle x-ray scattering (SAXS), real-time SAXS, photon correlation spectroscopy (PCS) and dielectric spectroscopy (DS). The static structure of concentration fluctuations is found to deviate from the Gaussian coil assumption in a temperature regime above the microphase separation transition (MST). The dynamic experiments in this temperature regime test concentration fluctuations (real-time SAXS) as well as single-block dynamics (PCS and DS) making use of the intrinsic labelling properties of this specific diblock copolymer. They provide evidence for the existence of partially ordered domains above the MST. The assumption of a weakly segregated state is, therefore, questionable. [ABSTRACT FROM AUTHOR]

It has been reported by us, for the first time, that segmented polyurethanes (SPUs) based on 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment could form spherulite structures upon melt-quenching to an annealing temperature (TA) above 120°C. Synchrotron small-angle x-ray scattering (SAXS) experiments were performed to investigate the microphase separated structures corresponding to the spherulite formation. With increasing hard-segment content, both the integrated scattered intensity (Q) and the interdomain spacing (d) increased first and then decreased when the hard segment was above 50%, possibly due to phase inversion. With increasing TA, the Q values increased first, reached a maximum at ∼107°C, and then decreased with further increase in TA; the d values showed a monotonic increase. The kinetics of phase separation was investigated after the samples were quenched from the melt to 140°C. Interdomain spacing remained unchanged throughout the whole process. The results indicated that the hard-segment mobility and the system viscosity were the two key factors controlling the phase structure. [ABSTRACT FROM AUTHOR]

We examine the relevance of the strong-fragile classification scheme for glass-forming polymeric systems using results from Brillouin and photon correlation spectroscopy. The dynamics of salt doped polypropylene oxide (PPO) have been investigated in relation to induced local structural ordering. It is accomplished by forming complexes of NaCF3SO3-PPO in which the cations act as transient cross-links between chains. The amount of cross-links depends on salt concentration and temperature. This allows for a test of the suggested relation between structural properties and some characteristics of the relaxation function such as its non-exponential time decay and non-Arrhenius temperature dependence. [ABSTRACT FROM AUTHOR]

By measuring the complex dielectric susceptibility over 15 decades, we compare the scaling behavior of the α-relaxation for low-molecular-weight glass-forming liquids and polymers. The characteristic differences found for these both classes of substances are discussed in terms of segmental dynamics. [ABSTRACT FROM AUTHOR]

The cluster growth dynamics and the equilibrium cluster correlation length were studied in 1,1-di(4′-methoxy-5′-methyl-phenyl)-cyclohexane (BMMPC also called BKDE in previous papers) in the temperature range from 40°C to 70°C by means of static light scattering (SLS) and photon correlation spectroscopy (PCS). The equilibrium cluster correlation length obtained from PCS and SLS using the Ornstein Zernike formula are in a good agreement with each other. The analysis of the SLS data based on the Debye formula results in much lower values of the cluster correlation length. The relaxation processes in BMMPC were studied using depolarized Rayleigh spectroscopy (DRS). The relaxation times obtained from DRS exhibit an Arrhenius behaviour and with decreasing temperature diverge from the relaxation times of the primary α process measured by means of dielectric spectroscopy which follow the usual Williams-Landel-Ferry temperature dependence. [ABSTRACT FROM AUTHOR]

Translational diffusion coefficients D of photochronic dye molecules have been measured by forced Rayleigh scattering in polymer diluent systems at compositions from pure polymer to pure diluent. D could be measured down to below the glass transition temperature Tg. In the pure diluent, D(Tg) was found typically about two decades below that in the pure polymer but still far above the Stokes-Einstein prediction extrapolated from high temperatures. Some experimental results are in contrast with predictions from free-volume theory. [ABSTRACT FROM AUTHOR]

The relaxation processes in the glass-transition temperature range of bulk PIMA and PIMA-PMMA copolymer have been studied by means of Photon Correlation Spectroscopy (PCS) and dielectric spectroscopy (DR). The experimental results were treated in a conistent way employing an inverse Laplace transform analysis of the density Cϱ(t) and dipole moment ϕμ(t) autocorrelation functions. The latter was obtained from the ɛ″ (ω) data utilizing a recently developed algorithm. For bulk PIMA, Cϱ(t) clearly shows two distinct relaxation processes, whereas ϕμ(t) is dominated by the slower (α-) relaxation mode. The fast process in Cϱ(t) is probably related to the rotation of the rigid isobornyl group about the C-O bond. The copolymer displays a β-relaxation process and a slower α-relaxation dielectric process in agreement with the PCS results. The molecular origin of these processes is outlined. [ABSTRACT FROM AUTHOR]

In this paper it is shown, on the basis of a simple mean field approach to the dynamics of concentration and density fluctuations, that the interdiffusion coefficient Dint(ϕ) in a blend (A/B) of composition ϕ can be related to the self-diffusion coefficients D*A/B of the pure melts. However, the relation is predicted to be a linear combination of the so-called fast and slow modes: Dint−1=(1−U){Dslow*}−1+ U{Dfast*}−1. The parameter U=U(T) is given and is shown to be a measure of the nearness of the glass transition to the experimental temperature T. Far above the glass transition (U→0) the interdiffusion coefficient reduces to D*slow and should show the simple linear dependence on concentration according to {Dslow*}−1={ϕDA*}−1+{(1−ϕ) DB*}−. [ABSTRACT FROM AUTHOR]

Dynamic rotational isomeric state formalism is used to compute dipolar correlation functions for cis-polyisoprene in the bulk state. Transitions between rotational isomeric states take place through coupled motion of triplets of neighboring bonds in a given repeat unit, as follows from the study of intramolecular conformational energetics in the polymer. The intermolecular effect on local chain dynamics is included in two stages. First the relaxation in a homogeneous environment is treated through adoption of a local effective frictional resistance increasing with the size of the kinetic segment. Secondly, free-volume or density fluctuations of the medium are approximated by a bistate environment. The frequency distribution of relaxational modes is found to broaden with increasing number of bonds cooperatively participating in the segmental mode process. From a comparison with recent dielectric measurements of bulk cis-polyisoprene, the experimentally observed Kohlrausch-Williams-Watts (KWW) exponent of 0.39 is attributed to the cooperative relaxation of a kinetic segment of about three repeat units in a fluctuating environment. [ABSTRACT FROM AUTHOR]

In recent years we have developed a new method for the determination of liquid/liquid interfacial mass transfer in solvent extraction systems by use of the Beckman Model E Analytical Ultracentrifuge (AUC). We improved both optical systems of the AUC by use of modern technical equipment like A/D converter, PC data handling, video recording and digitizing. Software has been developed with respect to the evaluation of kinetic data and a diffusion controlled solvent extraction model was applied for the determination of transfer coefficients. [ABSTRACT FROM AUTHOR]

This paper presents alternative light sources to the rather unreliable high pressure mercury lamps, commonly used for the schlieren optical system of Analytical Ultracentrifuges. The alternatives are an ultra-bright light emitting diode (LED) and a halogen lamp, which are both commonly available and very cheap. The non-uniform light emitted by these light sources is either transformed to uniform diffuse light with a ground glass or only the uniform parts of the light beam are used. This maintains a sufficient picture quality with constant light intensities for the lifetime of the light source which is much higher than that of a mercury lamp. For the example of a Beckman Model E ultracentrifuge, it is demonstrated that only minor alterations to the original lamp housing are necessary to transform the mercury light source into a halogen or LED one. The modified light source can be used in the same way as the original one and original alignment procedure of the Schlieren optical system can still be applied. Comparative Schlieren patterns are presented to demonstrate the picture quality achieved with each light source. The advantages and disadvantages of both light sources are discussed. [ABSTRACT FROM AUTHOR]

Recently (H. Cölfen and S.E. Harding, Progr Colloid Polym Sci 99: 167-186 (1995), it was discovered that sedimentation velocity experiments using the Beckman Optima XL-A ultracentrifuge, scanning at wavelengths where the macro-molecules did not absorb, yielded typical Schlieren-like traces. Evaluation of the apparent sedimentation coefficient of these traces at a finite concentration for a number of polymers gave results which agreed to within ±0.05 S with results from experiments performed simultaneously on the Beckman Model E equipped with a ‘classical' Svensson-Philpott phase-plate Schlieren optical system. The aim of this present study was to investigate the concentration dependence of the sedimentation coefficient of three polysaccharides (xanthan, locust bean gum and arabinoxylan) using the Beckman Optima XL-A equipped with absorption optics and Model E with Schlieren optics to compare the values for the (infinite dilution) sedimentation coefficient, s°20,w and the sedimentation concentration dependence regression coefficient, ks. The values obtained by both methods for the three biopolymers compare very well (to within approximately 10% for s°20,w and 20% for ks). The Beckman Optima XL-A enabled concentrations as low as 0.041 mg/ml (in the case of xanthan) to be measured and gave more precise data than the Model E. This work provides further evidence that the Beckman Optima XL-A may be used as a potential Schlieren optical system based analytical ultracentrifuge, hence broadening its range of applications to include non-absorbing macromolecular systems such as polysaccharides and synthetic polymers. [ABSTRACT FROM AUTHOR]

This study describes how typical "Toepler" Schlieren patterns can be derived with the UV-absorption optics of the Beckman Optima XL-A ultracentrifuge without any modification of the optical system. Such a Schlieren effect can greatly enhance the application range of the XL-A ultracentrifuge which cannot yet be used to its possible full potential due to the present lack of a refractometric optical system and — not only for sedimentation velocity experiments — particularly the Schlieren optical system. It is shown that the Schlieren patterns detected with the UV-absorption optical system are caused by light refraction and not by light scattering or experimental artefacts. Two possible explanations for the generation of the Schlieren effect are given. Both explanations have in common that the refracted light cannot be detected by the photomultiplier system and is hence lost for detection. The intensity of the refracted light which can be registered with the photodetector of the optical system is dependent on the angle of incidence of the light, e.g., the local slope of the sedimenting boundary, and hence leads to a detection of the refractive index change with radial position: i.e., a Schlieren pattern. The advantages, disadvantages and differences of the XL-A Schlieren effect compared to conventional "Philpot-Svensson" Schlieren optics are discussed demonstrating that both optical systems deliver the same results for examples of sedimentation velocity experiments on several polysaccharides and bovine serum albumin. An estimation of the sensitivity of the Schlieren effect as a function of the wavelength selected is given as well as suggestions of how the Schlieren effect can be increased for suppressed. Considerations about the quantitative evaluation of XL-A Schlieren patterns show that the Schlieren effect is dynamic with respect to the concentration dependence. This creates some potential for new applications but is also a serious warning to those people who want to derive quantitative information from XL-A absorption traces as these can be superimposed by a Schlieren effect at certain wavelengths. [ABSTRACT FROM AUTHOR]

Establishment of an accurate extinction coefficient is often of interest when a precise amount of material is required for a biochemical reaction or when converting an association constant from absorbance units into concentration units. Although a gravimetric approach can provide a quick estimate of the concentration, the presence of salts or impurities can adversely affect its accuracy. Analytical ultracentrifugation is often used when more accurate estimates of the extinction coefficient are required. This technique has been applied to prostate specific antigen (PSA), and the value of the extinction coefficient estimated by amino acid analysis is confirmed by sedimentation analysis. The extinction coefficient of PSA was measured by analytical ultra-centrifugation using the method of sedimentation boundary analysis. This method utilizes centrifugal force to form a solvent boundary by layering a reference buffer onto a sample via a thin capillary connecting both sectors of the centerpiece i.e., a synthetic boundary centerpiece. The plateau formed by the boundary is then optically measured as it decreases over time due to diffusional effects. By using a combination of absorbance and interference optics, the OD and concentration (from the fringe displacement) can be sequentially measured and used in Beer's Law to directly solve for the extinction coefficient. A value for the extinction coefficient of PSA at 280 nm of 1.71 L/g-cm was obtained. This is in close agreement with a literature value of 1.84 L/g-cm using a concentration estimated by amino acid analysis. [ABSTRACT FROM AUTHOR]

A new method for the investigation of gels in the Analytical Ultracentrifuge is proposed and used. During the measurements only small changes in the concentration profiles of the gel phases occur. Therefore, a differential relation can be used for the evaluation of the Schlieren patterns. Real equilibria could be shown by the path independence of the obtained gradients. [ABSTRACT FROM AUTHOR]

Fourteen nearly monodisperse aqueous poly-n-butylmethacrylate (PBMA) dispersions with diameters of about 60 nm were prepared by emulsion polymerization. These PBMA-dispersions contain different amounts of the crosslinker methallylmethacrylate (MAMA), pMAMA=0/0, 02/0, 04/0, 06/0, 08/0, 1/0, 2/…/10 wt.%. First, these aqueous dispersions were characterized by light scattering (LS) and analytical ultracentrifugation (AUC). Particle size distributions, diffusion coefficients, sedimentation coefficients and particle densities were determined. Then these PBMA/MAMA-particles were transferred directly into the organic PBMA-solvent tetrahydrofuran (THF). Particles with small amounts of MAMA are completely dissolved, whereas particles with high amounts of MAMA are completely crosslinked and exist as swollen microgel particles with varying volume swelling ratios, q. Particles with medium amounts of MAMA consist of both dissolved macromolecules and crosslinked, extremely swollen microgels. Also by LS and AUC, the molecular masses, diffusion coefficients, sedimentation coefficients and densities of the dissolved macromolecules and the microgel particles were measured. Further, both the wt.%-ratio of dissolved macromolecules/microgel particles and the swelling ratio q of the microgel particles were determined. The measured quantities are discussed in relation to existing crosslinking theories. The hydrodynamic behavior of microgel particles in the interesting transition region from dissolved macromolecules to crosslinked particles is also discussed. [ABSTRACT FROM AUTHOR]

We developed a substitute for the dynography/multiplexer unit of the Beckman Model E Analytical Ultracentrifuge (AUC) consisting of a high-speed analog-to-digital converter and a personal computer. With this combination, we determine directly the intensity of light pulses measured at the photomultiplier. The computer program is written in the C + + programming language under DOS. It measures peak heights, relates them to the cell numbers they belong to, calculates optical densities from sample and reference sector, and displays the optical densities as a function of radius on the computer screen. Thus, it is possible to measure simultaneously all five concentrations that can be carried by the six-hole rotor of the Beckman Model E AUC during one scan. A multiplexer or flash lamp is no longer necessary. After a short description of the method, some general comments on requirements of sedimentation velocity experiments and on noise problems are made. The hardware and software for direct digitizing is presented and a further enhancement is proposed using a high-speed, two-channel recording system and one additional photomultiplier recording the primary intensity. [ABSTRACT FROM AUTHOR]

The polycation Poly[(dimethyleneimino)ethylene-(dimethyleneimino)-methylene-1,4-phenylene-methylenedichloride], Poly(XDC/TED), was synthesized of the monomers Dichloro-p-Xylylene (XDC) and Tetramethyl-ethylenediamine (TED). The molar mass averages Mn, Mw and Mz, and the molar mass distribution (MMD), w(M), were determined by equilibrium-ultracentrifugation. The resulting MMD was compared with the theoretical expected distribution. By considering the reaction kinetics we found a distribution which predicts the MMD of any Poly(XDC/TED) synthesis. [ABSTRACT FROM AUTHOR]

The resolutions of size exclusion chromatography (SEC) and sedimentation fractiometry (SF) are compared with mixtures of nearly monodisperse polystyrenes. It has been pointed out that the resolution, i.e., the precision of the molar mass distribution of the SF is as good as for the SEC. A new easy to handle procedure is suggested for the determination of molar mass distribution by SF and demonstrated with narrow and broad distributed polymers. [ABSTRACT FROM AUTHOR]

An alternate procedure, the run time integral method, is suggested for precise determinations of molar mass distributions of polymers. The method is based on the fact that modern analytical ultracentrifuges directly measure the variable angular velocity ω as a function of time. This allows an exact calculation of the run time integral ∫ ω2dt and replaces the physically uncorrect zero time correction t0 by ∫ ω2dt. The procedure is demonstrated by narrow and broad distributed polymers. [ABSTRACT FROM AUTHOR]

Mixtures of dispersions and grafted latices are of great importance in industry. These products are usually chemically heterogeneous and have not only a distribution in particle size but also in particle density. The analysis of such products can be carried out by analytical ultracentifugation. This is done by determining sedimentation coefficient distributions of the sample in two isorefractive dispersing media which have different densities. In this way it is possible to determine the particle size distribution and particle density distribution simultaneously, i.e., for each particle size of the size distribution the correlated particle density can be determined. This is demonstrated by a number of samples. This method represents a major advancement in the study of the structure of more complicated dispersions. So the composition of latex mixtures can be analysed and valuable insight into the mechanism of grafting reactions is available. [ABSTRACT FROM AUTHOR]

Velocity sedimentation and other hydrodynamic properties were studied for water soluble methyl cellulose (MC) samples (with the substitution degree 1.7) in molecular weight range 19≤M · 10−3≤408. The correlations between hydrodynamic characteristics and molecular weights are obtained. The values of persistence length and hydrodynamic diameter of MC chains were estimated. The comparison of investigations of concentration dependence of sedimentation coefficient S0 for real samples and graphic fractions was carried out. It was shown that use of S0 and concentration coefficient ks leads to adequate estimates of equilibrium rigidity of MC chains. [ABSTRACT FROM AUTHOR]

Relationship between the sedimentation coefficient S0 and its concentration coefficient KS obtained in experiments on velocity sedimentation are discussed. The values of S0, KS, and independently determined molecular masses reported by different researchers for different linear unchanged polymers are considered. It was established that the scaling index K ∼ S{ie101-1} unambiguously related to scaling index S0 ∼ Mb. The generalization of experimental data, which is based on Svedberg's equation for S0 and on the expression KS=B(h2)3/2M−1 made it possible to introduce the dimensionless sedimentation parameter βS. The average experimental values of βS were calculated for different polymer types and, to the first approximation, do not depend on molecular mass. Therefore, it is possible to write the generalized Wales-van Holde equation MKS=(NA/βS)3/2[S]3/2KS1/2. The adequacy of evaluation of M is illustrated taking as an example the determination of equilibrium rigidity of a polymer chain (flexible-chain polymers under ϑ-conditions and flexible-chain polymers in a thermodynamically good solvents) and of the unit length mass of the polymer chain (rigid-chain polymers). A rigorous theory of the concentration dependence of the sedimentation coefficient should take into account quantitatively the relationship between polymer chain draining and the solvent counterflow in the sedimentation of macromolecules. [ABSTRACT FROM AUTHOR]

The soluble bovine eye lens cytoplasm has been separated in its α-, β- and γ-crystallin fractions, using size exclusion chromatography. The individual α-crystallin fractions have been characterized using moving boundary and equilibrium sedimentation and photon correlation spectroscopy. The α-crystallin fractions represent a very broad distribution in molar mass from 500 000 to 1 100 000 g/mole, with a maximum at 650 000 g/mole. This population contains also a broad distribution of hydrodynamic structures, ranging from compact to more asymmetric structures; the main population has a frictional coefficient f/f0 ratio of (1.45±0.05). These structural properties perfectly fit the micellar model. [ABSTRACT FROM AUTHOR]

As determined by hydrodynamic measurements the small heat shock protein Hsp25 isolated from Ehrlich ascites carcinoma cells occurs in the form of monomers with a molecular mass of 23 kDa and a diameter of about 3.8 nm as well as in the form of highly associated complexes with molecular masses of about 180 kDa up to 740 kDa. Electron microscopic investigation of Hsp25 complexes shows ring-like particles with a diameter of about 16 nm and a probably eightfold symmetry. Considering different arrangements of the monomers and using the program HYDRO [Garcia de la Torre et al. Biophysical J. 67:530-531 (1994)] theoretical sedimentation and diffusion coefficients were calculated which are in consensus with the experimental data when assuming ring-like structures. From these data a model for the 3D structure of Hsp25 complexes is derived which consists of four stacked rings each containing eight Hsp25 molecules. [ABSTRACT FROM AUTHOR]

A great deal of work has been done to further the understanding of the solution conformation of the 6 S myosin monomer. Less extensively studied is the 10 S conformer in which part of the tail is observed to be attached to the heads. In this paper existing hydrodynamic data are further interpreted. A model for 10 S myosin is proposed which is more compact than previously reported structures. [ABSTRACT FROM AUTHOR]

By chemical cross-linking and analytical ultracentrifugation the dimer is shown to be the predominant quaternary structure of HBsu, the major histone-like protein from Bacillus subtilis, at protein concentrations up to 1 mM. At low ionic strength between 0 and 100 mM Nacl, higher-order structures up to the hexamer are also found. A double-stranded 10-basepair DNA oligomer is demonstrated to prevent the aggregation of HBsu molecules as does an increase in ionic strength. The complex formed between HBsu and the DNA decamer is determined to consist of two protein dimers and the DNA. The association constant is about 106 M−1. [ABSTRACT FROM AUTHOR]

Applying procedures originally suggested for water-soluble proteins (Osborne JC, Powell GM, Brewer HB (1980) Biochim Biophys Acta 619:559-571), our group has studied the association of the intrinsic membrane protein band 3 (from human erythrocytes) with other proteins for which band 3 represents a binding site. In all cases, the association was studied by sedimentation equilibrium analysis on detergent-solubilized band 3 and dye-labeled ligand proteins, under conditions where the proteins show ideal sedimentation behavior. During these studies, a standard step-by-step procedure has developed which allows the determination of the stoichiometry of the predominant heterologous complex and the detection of complexes of different band 3 or ligand content. Application of the procedure to aldolase, erythrocyte band 4.1 protein and hemoglobin as ligand proteins is demonstrated. It is shown that, in all cases studied, the band 3 tetramer represents the predominant or even the exclusive binding site. The number of ligand proteins bound per band 3 tetramer can reach 4 for aldolase and hemoglobin or nearly 8 for band 4.1. [ABSTRACT FROM AUTHOR]

The interaction of bovine adrenodoxin reductase with adrenodoxin was investigated by means of sedimentation equilibrium technique using the analytical ultrancentrifuge XL-A. From the radial concentration distributions recorded at sedimentation equilibrium the partial concentrations of the free proteins and the complex were obtained using the program Polymol. Independent of the ratios of proteins used in the experiments a 1:1 complex was formed. The association constant amount to about 2·106 M−1 at low phosphate concentration (10-50 mM). The value drops to about 103 M−1 at 500 mM phosphate. For successfu. crystallization the complex was stabilized by cross-linking experiments with carbodiimide to prevent dissociation at higher ionic strength. [ABSTRACT FROM AUTHOR]

It is known that oligonucleosomal chromatin fragments from chicken erythrocytes enriched in inactive genes can self-associate into pseudo-higher-order structures. In this paper, we demonstrate the similar aggregation phenomenon for another type of repressed cells, sea urchin spermatozoa. Like the inactive part of erythrocyte chromatin, sea urchin sperm chromatin is characterized by the long linker DNA (100 base pairs) and the presence of specific histones typical for the repressed state of chromatin. It seems that these two factors determine the specific association of oligonucleosomes. The aggregates of sea urchin sperm oligonucleosomes resemble those of the erythrocyte chromatin in the following features: the range of the sizes of oligonucleosomes that are able to associate into pseudo-higher-order structures is limited; such self-association takes place at a low extent of the chromatin digestion by micrococcal nuclease; the aggregates undergo salt-induced compaction. Similarity in the properties of chromatin aggregates from two types of terminally repressed cells makes it possible to consider the specific association into pseudo-higher-order structures as a characteristic feature of chromatin from the inactive part of the genome. [ABSTRACT FROM AUTHOR]

Sedimentation velocity techniques have been used to study the effect of the antibiotic drug netropsin (Nt) on the structural properties of different forms of closed circular DNA. Nt removes supercoils upon interaction with positively supercoiled DNA and introduces negative supercoils upon binding to relaxed DNA. Applying the classic assay of DNA unwinding by ethidium to complexes of negatively supercoiled DNA with Nt, we found that, compared with naked DNA, more ethidium is needed to convert the Nt-DNA complex into a superhelix-free form. From the shift in the critical ethidium/nucleotide binding ratio, a Nt-mediated decrease in the linking number difference and superhelix density (or increase in the number of superhelical turns) of negatively supercoiled DNA is calculated, synonymous with an increase in the linking number and a decrease in the helical repeat of the relaxed form. A significant influence of the presence of intrinsic bends in the DNA duplex on the magnitude of the drug-induced alterations in DNA supercoiling could not be detected. Although it is unclear whether the primary action of netropsin consists of changes in writhe or twist of DNA, or both, the measurable effects can be described by a Nt-induced overwinding of the DNA doulbe helix. Nt-specific DNA overwinding angels can also be derived from the (positive) linking number difference observed in literature upon relaxation of supercoiled Nt-DNA complexes by topoisomerase I and subsequent removal of Nt. A compilation of the data available from literature and our own work shows that the average Nt-mediated DNA overwinding angle exhibits a strong decrease with increasing Nt/nucleotide ratio. This finding suggests that Nt exerts the strongest effects on DNA supercoiling when interacting with DNA binding sites which have the highest affinity and, hence, primarily are occupied by Nt. [ABSTRACT FROM AUTHOR]

Sedimentation velocity and synthetic boundary diffusion studies have been undertaken for aqueous solutions of the branched microbial polysaccharide welan gum. Centrifugation and filtration to remove insoluble material from the crude gum is shown also to remove a proportion of soluble high molar mass material. Purified welan which has been dialysed exhaustively against distilled water to remove low molar mass impurities exhibits typical polyelectrolyte behaviour in saltfree solution: an enhanced apparent diffusion coefficient and diminished sedimentation coefficient at modest polymer concentrations, and a dramatic drop in apparent diffusion coefficient at concentrations below 0.6 g dm−3. In the presence of a salt, welan solutions exhibit ‘weak gel' behaviour. At NaCl concentrations greater than about 0.1 mol dm−3, sedimentation velocity shows no evidence of charge effects or conformational change. The solution behaviour may reflect a stable double-helical structure, stabilized by interactions between side chains and carboxylate groups in the polysaccharide backbone, coupled with weak association between double-helices. [ABSTRACT FROM AUTHOR]