Calculation of the Grüneisen constant of glassy polymers from thermoelastic data

Thermoelastic measurements on a glassy polymer make it possible to measure directly the quantity αV/C_p where α is the coefficient of linear expansion, V the specific volume, and C_p the specific heat at constant pressure. By further measuring the bulk modulus (B_T) it is possible to derive a relatively accurate value of the thermodynamic Gruneisen constant (γ_T) where γ_T = 3B_TαV/C_v. The values obtained decrease only slightly with temperature.     

Measurement of the correlation radius in oil-in-water microemulsions by dynamic light scattering

The diffusion coefficient and correlation radius associated with the droplet particles in oil-in-water microemulsions (CTAB, octane, butanol, NaBr and water) were determined by dynamic light scattering- Unlike the case of CTAB micelles, there is a maximum in the correlation radius versus temperature plot.     

聚苯乙烯稀溶液的小角激光弹性和准弹性光散射

随着激光技术的发展,近年来出现了与散射光频加宽相应的光子相干光谱即准弹性光散射。于是,利用光散射(也称弹性光散射)法不仅能获得高聚物的各种物性参数如分子量(?),第二维利系数A_2和均方旋转半径(),而且还能得到大分子在溶液中的动态参数,即扩散系数D_0。由D_0求得流体力学半径R_H。本文只涉及小角度准弹性光散射(1°<θ<7°)对稀溶液范围的平动扩散系数的测定。与文献比较,表明方法是成功的。     

Polarized and depolarized dynamic light scattering of concentrated polystyrene solutions

Polarized and depolarized dynamic light scattering have been used to examine the dynamics of concentrated polystyrene solutions in dioctyl phthalate and toluene. Time-temperature superposition of the depolarized intensity correlation functions gave master curves covering more than 10 decades on the time scale. Polarized correlation functions are resolved into relaxational and diffusive components having different temperature dependences. When the relaxation rate of the concentration fluctuations approaches the reorientational relaxation rate, the concentration fluctuations become q-independent i.e. the diffusional relaxation is rate-determined by the backbone mobility. With a small molecule solvent as toluene, however, a part of the concentration fluctuations relaxes faster than the orientational relaxation, i.e., the diffusion occurs in the free volume within the “frozen” network.     

Ion distribution around electrostatically stabilized polystyrene latex particles studied by ellipsometric light scattering

The ion distribution around electrostatically stabilized polystyrene latex spheres for different ionic strengths is investigated by ellipsometric light scattering. This method is sensitive to the refractive index profile around colloidal particles, which is affected by the local salt content. At an average salt concentration of c* = 10(-4) mol L(-1), the ion concentration at the particle interface increases discontinuously, and a layer of high salt content with 20-30 nm thickness is built up. The observation cannot be explained within the framework of the Poisson-Boltzmann equation; it rather resembles a prewetting transition. Interactions that could possibly lead to a stabilization of the observed layer of high salt content are discussed.     

Use of a cooperative-motion domain model to analyze brillouin light scattering measurements of the dynamic modulus in triblock copolymers

The use of the relaxation function is widespread in the study of polymer dynamics. Since the popular empirical KWW relaxation function consistently underestimates dielectric loss at high frequency, several models dealing explicitly with intermolecular cooperativity have been proposed as alternatives. In this article, the domain model proposed by Matsuoka, previously used only to analyze dielectric relaxation results, is used to analyze Brillouin light scattering results from polystyrene–polybutadiene–polystyrene triblock copolymers. A single relaxation time analysis and the KWW model are both compared to the domain model. Neither of these models fits the Brillouin data well. The single relaxation time analysis gives a physically unrealistic results; the KWW analysis fits the data at low frequency, but fails in the high-frequency region by underestimating the attenuation. The domain model fits the Brillouin data well over the entire temperature/frequency range. The results show that in order to understand the full range of dynamics in these materials and in polymeric materials in general, the KWW model is insufficient due to its underestimation of attenuation at high frequency. A model including cooperative motion is crucial to fully understand polymer dynamics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2170–2178, 2000     

Studies of particle-particle interactions using polystyrene latices and time-average light scattering

Dilute dispersions of monodisperse negatively-charged polystyrene latex particles, radii 161 Å, have been examined by time-average light scattering at various latex volume fractions and electrolyte concentrations. The latter were varied from the low value produced by maintaining mixed bed ion-exchange resin beads in the systems (ca. 10^–5 mol dm^–3) to the value of 5×10^–3 mol dm^–3 obtained by the addition of sodium chloride. From angular scattering measurements determinations of the structure factors were made; these were produced as a consequence of the particle-particle interactions in the system. By extrapolation of the structure factor to zero scattering angle, values were obtained for the osmotic compressibility and hence the osmotic pressure of the systems as a function of the latex volume fraction. It was found that the experimental data obtained could be interpreted in terms of a hard-sphere model for the particle-particle interaction. Good agreement was obtained provided that the particles were assigned a hard-sphere radius which was determined by the electrostatic repulsion between the particles.     

Micelles of imidazolium-functionalized polystyrene diblock copolymers investigated with neutron and light scattering

We synthesize a series of block copolymers comprising a polystyrene (PS) block and an imidazolium-functionalized PS (IL) block and characterize their assembly properties. We use small-angle neutron scattering and dynamic light scattering to determine the micelle size and shape in dilute solutions and to assess the micelle interactions in concentrated solutions. By studying a series of copolymers with fixed PS block length, we find that the length of the IL block governs the micelle dimensions. Our data suggest that these copolymers form elongated micelle structures where the IL block is extended in the micelle core. We find that these micelles can sequester water and that interactions between the micelles lead to structure factor peaks at elevated concentrations.     

Light and X-ray scattering by polystyrene glasses

Summary Polarized and depolarized components of the light scattered by atactic polystyrene samples prepared from monomer of varying purity were investigated at 25 °C. In addition, small angle X-ray measurements were made on a well purified sample. These investigations show that the angular dependence and the magnitude of the scattered intensity are strongly influenced by dust-like solid impurities. The scattering observed with polystyrene glasses prepared from the purest monomer is consistent with a model in which the glass is a structureless liquid-like material. No evidence for any ordered regions is seen in these clean glasses by either light or X-ray scattering.Further consideration shows, however, that light and X-ray scattering are not very sensitive to the presence of small isotropic regions. While depolarized light scattering may be more sensitive to order through orientational correlations, quantitative interpretation of the H _v intensities is difficult. Nevertheless, from the observation that the light scattering is unaffected by thermal history, one can be reasonably certain that no structure is present beyond that expected in a supercooled liquid.

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Zusammenfassung Polarisierte und depolarisierte Komponenten des gestreuten Lichtes von ataktischen Polystyrol-Proben hergestellt von Monomeren mit verschiedenen Reinheitsgraden, wurden mit Hilfe eines Lichtstreuphotometers bei 25 °C untersucht. Ferner wurden Röntgenkleinwinkelmessungen an einigen Proben von höchster Reinheit durchgeführt. Diese Untersuchungen ergaben, daß sowohl die Winkelabhängigkeit als auch die Höhe der Intensität durch Staub und feste Verunreinigungen stark beeinflußt wird. Die Streuung von Polystyrolen im Glaszustand, die von höchstreinen Monomeren hergestellt wurden, stimmte mit dem Modell eines strukturlosen, flüssigkeitsähnlichen Glases überein. Licht- und Röntgenkleinwinkelstreuung zeigten keinen Hinweis auf geordnete Gebiete.Theoretische Überlegungen zeigen, daß die Lichtund Röntgenstreuung durch kleine isotrope Gebiete wenig beeinflußt wird. Während die depolarisierte Lichtstreuung empfindlicher gegen Ordnung durch Orientierungskorrelationen sein kann, sind quantitative Aussagen über dieH _v Intensitäten schwierig. Da die Lichtstreuung durch Wärmebehandlung nicht beeinflußt wurde, kann man mit ziemlicher Sicherheit sagen, daß es nicht mehr Struktur gibt als man es von einer unterkühlten Flüssigkeit erwarten würde.

     

Anisotropic light scattering and rheological study of the physical gelation of atactic polystyrene in carbon disulfide

The physical gelation of the solutions of atactic polystyrene (aPS) in carbon disulfide (CS₂) is studied by the excess of anisotropic light scattering δH_v and by the Theological properties. An abrupt jump of δH_v at gelation temperature shows that a part of the chains are stiffened upon gelation. This effect which is independent of aPS molecular weight strongly decreases with concentration. It is well correlated with an abrupt change of the plateau modulus ^GN which indicates the formation of additional entanglements in the gel phase with respect to the sol. The compatibility of these abrupt jumps with the thermodynamic theories used to interpret the concentration and molecular-weight dependence of the gelation temperature is discussed.     

Characterization of polystyrene networks by small-angle neutron scattering

Polystyrene networks prepared by anionic polymerization have been characterized by small-angle neutron scattering. Two kinds of systems have been examined: (A) networks with labelled branch points allowing characterization of the spatial distribution of crosslinking points; (B) networks containing a low proportion of chains labelled with perdeuterated polystyrene in order to characterize the conformation of individual elastic chains of the polymeric network. The dependence of the results on swelling and uniaxial extension is discussed.     

Brillouin light scattering studies of the mechanical properties of polystyrene/polyisoprene multilayered thin films

We have used Brillouin light scattering (BLS) to investigate the mechanical properties of thin polystyrene (PS) and polyisoprene (PI) films incorporated in a multilayer geometry consisting of alternating layers of the two polymers. All samples had a total thickness h ∼ 1600 Å, and consisted of between 2 and 10 individual polymer films; individual layer thicknesses were as small as 160 Å. Ellipsometry was used to determine the thickness of the PS and PI layers. The velocities of several high-frequency film-guided mechanical waves were measured using BLS and the results are compared with values calculated using an effective medium approach. The effective elastic constants of the multilayered films were obtained from those determined for thick films of PS and PI. Remarkable agreement was obtained between the measured and calculated velocities even for samples in which the individual layer thicknesses were much less than the unperturbed size of the polymer molecules. These results suggest that the mechanical properties of polymers change very little even when the molecules are forced into highly confined geometries. © 1996 John Wiley & Sons, Inc.     

Review of polystyrene diffusion studies in latex particles by small‐angle neutron scattering

This paper reviews small‐angle neutron scattering (SANS) and some results from direct nonradiative energy transfer (DET), for the observation of the diffusion coefficients of polystyrene chains at latex interfaces. To compare SANS with DET, doubly labeled polystyrene with deuterium and fluorescence groups were synthesized, showing that while SANS and DET produce comparable data in terms of diffusion coefficients, both results differ in detail, each having their own advantages. Chain confinement, ionic end groups, and short branch effects on interdiffusion were studied. Large polymer chains confined in small particles have non‐Gaussian shapes that store rubber elastic energy. Rapid, non‐diffusion relaxation is inhibited because the density would be required to become less than normal. Hence confinement effects on the diffusion rate are not significant. Using the DET method, ionic end‐groups were found to increase the early‐time apparent interdiffusion coefficients during film formation. The early‐time apparent diffusion coefficients of polystyrene with varying end‐groups were found to increase as follows: The higher apparent diffusion coefficients of the chains with ionic groups are presumably due to a surface segregation of the end‐groups caused by the polar, aqueous environment during latex synthesis. The interdiffusion behavior of sulfite‐ended polystyrene (M_n ? 300 000 g/mol) with H‐ends, one sulfite end, and two sulfite ends were compared via SANS and DET. The diffusion coefficients of polystyrene with one or two sulfite end groups were five times and ten times lower than that of polystyrene, respectively. The ionic end group effects on the reduced diffusion coefficients are interpreted as the competition between enhancement by the surface segregation of end groups and reduction by end group aggregation. Noting that sulfate end groups diffused faster, while sulfite end groups diffused slower, the effect is complex, and not yet fully resolved. Diffusion coefficients of polystyrene with branches were studied by DET. Short branches work to decrease the T_g and hence increase the diffusion coefficients. However, after the experimental temperature, T, is converted to a normalized temperature, T‐T_g, the diffusion coefficients are found to be almost independent upon the number of branches and the length of branches. The branch length ranged from one‐carbon to 40 carbons. Side chains of entanglement molecular weight or longer may be required to significantly reduce the diffusion coefficient. Copyright © 2002 John Wiley & Sons, Ltd.     

Study on interaction between cationic polystyrene nanoparticles and DNA, and the detection of DNA by resonance light scattering technology

Monodisperse cationic polystyrene nanoparticles (PS-NPs) were prepared through microemulsion polymerization. Photon correlation spectrometry and transmission electron microscopy revealed that these cationic PS-NPs have a z-average particle size of 30 nm. Size analysis, circular dichroism spectroscopy and transmission electron microscopy indicate that the PS-NPs nanoparticles undergo electrostatic interaction with DNA to form a PS–DNA complex that obviously enhances the resonance light scattering (RLS) signal. A method is presented where the PS-NPs act as a probe for the detection of DNA by RLS. The method is convenient, sensitive, reproducible, and enables high-throughput. The PS-NPs are inexpensive and exhibit low toxicity.