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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]