Molecular dimensions and chain conformation in glassy syndiotactic polystyrene

For the first time the small-angle neutron scattering (SANS) from mixtures of protonated and totally deuterated syndiotactic polystyrene (sPS) has been studied. Two amorphous samples with similar molecular weights have been measured at various concentrations of the protonated part. All measurements were performed at room temperature using the scattering equipment of two different laboratories. The molecular weight M_w evaluated from SANS data agreed with those obtained by gel permeation analysis (GPC). In the Kratky representation the scattering contribution due to the contrast scattering shows a plateau behavior up to q = 0.45 Å^?1, where q is magnitude of the scattering vector. This observation is in evident contrast to what is expected from the rotational isomeric state (RIS) model. In addition the characteristic ratios C_∞, derived either from the plateau height or from radii of gyration of the Zimm regime and being in reasonable agreement with each other, show strong deviations from the predictions of the RIS model. © 1994 John Wiley & Sons, Inc.     

UNMIXING KINETICS AND ITS MORPHOLOGY OF POLY ( ETHYLENE OXIDE) WITH POLYETHERSULPHONES BLENDS

Unmixing kinetics in a binary polymer mixture of polyethersulphones with poly (ethylene oxide) by spinodal decomposition has been investigated with time-resolved light scattering and microscope methods. The results showed that time evolution of scattered light intensity is of an exponential growth The maximum growth rate R(qm) of phase separation has been obtained. The experimental data did not satisfy the condition that the plot of R(q)/q~2 vs q~2 should be linear For unmixing system annealing at 30℃for three hours, its morphology manifested dish structure The experimental data of the Bragg spacing D_m can be correlated with a straight line which expresses the power-law relation, D_m=bl~α     

Dependence of nanophase separated structure of epoxy hydrogels on swelling conditions investigated by SANS

A hydrophilic non-stoichiometric epoxy network was prepared by end-linking reaction of α,ω-diamino terminated poly(oxypropylene)-b-poly(oxyethylene)-b-poly(oxypropylene) (POP-POE-POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA) at the excess of amino groups. Series of epoxy hydrogels swollen to various degrees was prepared by swelling of the epoxy network in D₂O and solutions of inorganic salt (KNO₃) in D₂O, respectively, and investigated by small-angle neutron scattering (SANS). Degree of swelling was controlled in two ways: by partial evaporation of the solvent and by KNO₃ concentration in the swelling solution. Nanophase separated structure of all hydrogels was confirmed by SANS. Scattering data were fitted to the Teubner-Strey model assuming bicontinuous locally lamellar structure of the hydrogels. Changes in SANS profiles induced by the presence of KNO₃ in swelling solutions reflect a refinement of the nanophase separated structure of hydrogels caused by improvement of POE-D₂O interaction by means of breakage of deuterium-bonded structure of D₂O by nitrate anions.     

Polydispersity effects in polymer self-diffusion measured by small-angle neutron scattering

The small-angle neutron scattering (SANS) method for measuring the self-diffusion coefficient D has been analyzed for effects of polydispersity in degree of polymerization for the case of linear polymers diffusing by reptation. Polydispersities corresponding to M_w/M_n = 1.0?10 were considered. It is shown that in all cases a meaningful effective diffusion coefficient D_e can be obtained from the short time recovery of the SANS intensity. This quantity D_e ≤ 1.3 D(M_w), where D(M_w) is the diffusion coefficient of a monodisperse polymer having molecular weight M = M_w. The method relies on SANS intensities extrapolated to zero scattering angle; realistic extrapolation is shown to give rise to quite acceptable errors on the order of 0.05 D_e.     

A New View of the Anionic Diene Polymerization Mechanism

We investigated the anionic polymerization of butadiene in d-heptane solvent using tert-butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: ¹H NMR and small angle neutron scattering (SANS). The time resolved ¹H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator --- at about 10% monomer conversion --- signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non-polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining ¹H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large-scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with N_agg >>1000 and R_g ≈ 1000Å were found.     

The response of microstructure to processing in a series of poly(siloxaneimide) copolymers

Poly(siloxaneimide) (PSI) segmented copolymers exhibit organized microdomains if the blocks are sufficiently incompatible. As with neat diblock and triblock copolymers, the processing route employed to prepare films of PSI materials is expected to influence the dimensions and/or morphology of the resultant microstructure. In this work, small-angle neutron scattering (SANS) is utilized to characterize the disordered microstructure found in films of a series of PSI copolymers which are subjected to solvent casting and various thermal treatments. Microstructural dimensions such as the periodicity and correlation length are deduced from the Teubner-Strey (TS) model for disordered microemulsions. The scattering intensity of each copolymer up to q = 5.0 nm^?1, where q is the scattering vector, is found to scale as q^?2.8+?0.1. Results indicate that processing the materials as cast films or as melt-pressed films allowed to cool slowly has a small, but discernible, effect on microstructural characteristics. SANS profiles of films quenched from elevated temperatures reveal a clear transition in microdomain periodicity, which correlates well with the glass transition temperature of the imide microphase in these and other materials of similar chemical structure. © 1993 John Wiley & Sons, Inc.     

Characterization of physical structure of silica nanoparticles encapsulated in polymeric structure of polyamide films

Polyamide nanocomposite films were prepared from nanometer sized silica particles and trimesoyl chloride–m-phenylene diamine based polyamides. The type of silica nanoparticles used is commercial LUDOX^® HS-40 and the particle size characterized by the radius of gyration (R_g) is about 66 Å. The immediately prepared films were easily broken into particles to form colloidal-like dilute suspension of the silica–polyamide composite particles in D₂O–H₂O solutions for SANS measurements, that in this dilute system SANS data the complication of scattering data from the interacting particles is minimized. At about 60% D₂O of the sample solution, the silica is contrasted out, therefore the SANS profiles are predominantly from the organic polyamide scattering. The SANS profile of the sample solutions measured at 90% D₂O clearly indicates scattering from both silica and polymer. The scattering heterogeneities for two-phase system were evident from the validity of the Debye–Bueche expression in case of the nanocomposite with high silica loading. At limited silica loading of the nanocomposite, interaction between the silica and polymer chains forming core–shell morphology was observed. The transport properties of the membranes made from the nanocomposite films were measured on a batch type test kit with an aqueous solution of 500 ppm dioxane concentration at pressures ranging from 50 to 200 psig, and correlated to their composite structure.     

Dynamic light scattering of CTAB:NaSal threadlike micelles in the semidilute regime. II. effect of surfactant concentration

Dynamic light scattering measurements are made on networks formed by elongated threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at 25°C. The surfactant concentrationC _D of the samples is varied from 0.006 to 0.3 M and the ratio of the salt concentrationC _s toC _D is fixed at unity. The time correlation functionA _q (t) of light intensity scattered from the solutions exhibits transition from the unimodal to the bimodal distribution of the decay rate at aroundC _D=0.05 M. The dependence of the first cumulant _e on the scattering vectorq for the samples withC _D0.03 M is described by the dynamic scaling law. The cooperative diffusion coefficientD _c is obtained from extrapolation of _e/q² for the samples withC _D0.03 M and of _f/q² forC _D0.05 M where _f is the first cumulant from the fast mode. TheD _c is found in proportion toC _D ^0.45, being in agreement with the theoretical prediction for a rigid rod in the semidilute regime by the scaling law. The decay rate _s characteristic of the slow mode is independent ofq, and _s ^–1 roughly agrees with the mechanical relaxation time estimated from a fit of the dynamic viscoelastic data of the same samples by a Maxwell type of model with the single relaxation time .     

Kinetics Characterization of Ion Release under Dynamic and Batch Conditions. I. Weak Acid and Weak Base Ion Exchange Resins

The aim of the present work is concerned with a study of the kinetics of release of both Ca²⁺ and F⁻ from the corresponding loaded ion-exchange resins (weak acid and weak base character for Ca²⁺ for F⁻, respectively), using both dynamic and batch experimental conditions with an artificial saliva solution as the ion-exchange media at 293 and 310 K. The influence of resin particle size and the temperature were evaluated by the kinetics parameters for the effective rate of release (B) and diffusion coefficient (D). The rate of ion release increases with temperature and decreases with particle size. The experimental data were well fitted by models based on intraparticle diffusion-controlled processes. In dynamic studies, the linear dependence of −log ₁₀(B) with the diameter of the resin particles can be applied for the estimation of B values when resins of low particle size are considered. In batch processes, although resins of low particle size can be studied, a linear relationship was only attained for the case of slow ion-exchange kinetic systems.     

Micellization of sodium dodecyl sulfate and polyoxyethylene dodecyl ethers in solution

The effect of polyoxyethylene type nonionic surfactants (C₁₂E _n n = 3, 4, 5, 6, 7 and 8) on the aqueous solution of sodium dodecyl sulfate (SDS) in absence and presence of NaCl was examined using small-angle neutron scattering (SANS), dynamic light scattering (DLS), and viscosity measurements. Upon addition of C₁₂E _n , micellar size of SDS was found to increase significantly, and such micellar elongation was further enhanced in the presence of NaCl. Micellar growth is most significant in presence of shorter moieties of C₁₂E _n (e.g., n = 3, 4) as compared to higher ethereal oxygen content. The results of structural investigations with SANS and DLS to confirm this assumption are reported. The cloud point of C₁₂E _n has increased upon addition of SDS and decrease with NaCl, and a typical behavior is observed when both SDS and NaCl were present.     

Small-Angle Neutron Scattering Study on Aggregation of 1-Alkyl-3-methylimidazolium Based Ionic Liquids in Aqueous Solution

Aggregation structures of 1-alkyl-3-methylimidazolium based ionic liquids (ILs) in aqueous solution were investigated by small-angle neutron scattering (SANS) from the viewpoint of alkyl chain length, n, and anions (Cl^?, Br^? and trifluoromethanesulfonate, $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ). In [C₄mIm⁺]-based IL systems, no noticeable SANS intensity was observed for all of the systems examined here, although aqueous [C₄mIm⁺][ $ {\text{BF}}_{4}^{ - } $ ] solutions show a significant SANS profile originating from concentration fluctuations in the solution (Almasy et al. J Phys Chem B 112:2382–2387, 2008). This suggests that [C₄mIm⁺][Cl^?], [C₄mIm⁺][Br^?] and [C₄mIm⁺][ $ {\text{CF}}_{3} {\text{SO}}_{3}^{ - } $ ] homogeneously mix with water, unlike the [C₄mIm⁺][ $ {\text{BF}}_{4}^{ - } $ ] system, due to preferential hydration of the ions. In the case of the C _n mIm cations with longer alkyl chain lengths (n = 8 and 12), SANS profiles were clearly observed in the aqueous solutions at IL concentrations of C _IL > 230 and 20.0 mmol·dm^?3, respectively. For aqueous [C₈mIm⁺][Br^?] solutions, the asymptotic behavior of the scattering function varied largely from I(q) ~ q ^?2 to ~q ^?4 with increasing C _IL, indicating that the solution changes from an inhomogeneous mixing state to a nano-scale micelle state. Aqueous [C₁₂mIm⁺][Br^?] solutions show a typical SANS profile for micelle formation in solution. It was found from a model-fitting analysis that the structure of the [C₁₂mIm⁺][Br^?] micelle is ellipsoidal, not spherical, in solutions over the C _IL range examined here.     

Interaction of blockcopolymer micelles as probed by small-angle neutron and by small-angle X-ray scattering

 The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm) in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle scattering data (SANS: q≤0.4 nm^-1; SAXS: q≤0.6 nm^-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled by a square-step potential. Received: 12 May 1997 Accepted: 9 July 1997     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). I. Kinetics of spinodal decomposition

The kinetics of phase separation via the spinodal decomposition of poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) from a delay time period to late stages were investigated with a light scattering technique. The standard procedure for identifying four stages of spinodal decomposition, based on the characteristics of concentration fluctuations, was clearly introduced with the light scattering method. The spinodal limits were divided into four stages: the delay time, the early stage, the intermediate stage, and the late stage. The validity of the linearized theory was reviewed because it was used as an indicator of the limit of the early stage of spinodal decomposition, which divided the delay time period from the early stage and the early stage from the intermediate stage. The linearized theory fit the experimental results very well after the delay time. The scaled structure function of the melt‐mixed blend was analyzed. The universality of the scale structure function, F(x) = S(q,t)q_m³(t) (where S is the structure function, x is equal to q/q_m, q is the scattering wave vector, q_m is the maximum wave vector, and t is the time in seconds), indicated the late stage of phase separation and divided the late stage from the intermediate stage. The simple normalized scaling function profile for the cluster region proposed by Furukawa described the experimental data very well, whereas the profile for deep quenching, which was recently suggested, showed some discrepancies. As a result of the phase separation, the processing of this blend may be able to be developed to provide the most suitable morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 871–885, 2004     

Rheological and structural properties of aqueous solutions of a hydrophobically modified polyelectrolyte and its unmodified analogue

Rheological methods and small angle neutron scattering (SANS) were used in the characterization of dilute and semidilute aqueous solutions, both with and without added salt, of anionic poly(vinyl alcohol) (PVA⁻) and its hydrophobically modified analogue (HM-PVA⁻). The rheological measurements showed that the concentration induced viscosification effect and elastic responses are considerably stronger for solutions of HM-PVA⁻ than in solutions of the unmodified polyelectrolyte. Over the considered polymer concentration domain, the solutions of PVA⁻ exhibit virtually Newtonian behavior, whereas strong shear thinning effects are observed in the HM-PVA⁻ solutions. The SANS results for HM-PVA⁻ solutions reveal a pronounced peak in the plot of scattering intensity versus scattering wavevector q at intermediate q values and the position of the maximum scales with polymer concentration as q_max∼c^0.28±0.02. This peak is suppressed in solutions of the unmodified polyelectrolyte and merely a shoulder in the scattering curve appears. Additionally, an “upturn” in the scattered intensity is observed at small q values and the magnitude of this effect depends on polymer concentration, hydrophobicity and salt addition. At large q values, the SANS results from HM-PVA⁻ solutions suggest morphological changes, from rod-like chains to a network of semiflexible chains, as the polyelectrolyte concentration increases.     

Die Schwingungsspektren einiger Pentadeuterophenylphosphorverbindungen

The vibrational spectra of C₆D₅PX ₂, (C₆D₅)₂PX (X=H, Cl), (C₆D₅)₃P and of the Cyclophosphanes (PC₆H₅) _n and (PC₆D₅) _n (n=5, 6) are reported. The spectra of the phenylphosphorouscompound D (the structure beeing unknown) are given too. The C₆H₅/C₆D₅ isotopic shift data in the lower frequency-region (600–100 cm^–1) (facilitating the recognition of vibrational coupling effects) are used for vibrational assignments.

     

Thermodynamics of ion exchange of H<Superscript>+</Superscript> by Na<Superscript>+</Superscript> or NH<Subscript>4</Subscript><Superscript>+</Superscript> on ion-exchange resins based on <Emphasis Type="Italic">C</Emphasis>-tetramethylcalix[4]resorcinarene

The corrected selectivity coefficients of the ion exchange H⁺-Na⁺ and H⁺-NH₄ ⁺ on ion-exchange resins based on C-tetramethylcalix[4]resorcinarene were calculated from the experimental data obtained from studying ion-exchange equilibria. The preference of the ion-exchange resins for cations increases in the sequence: Na⁺ < NH₄ ⁺ < < H⁺, and the ion-exchange resin based on (2-furyl)hydroxymethyltetramethylcalix[4]resorcinarene has a higher preference for ammonium cations. According to the results of microcalorimetric measurements, the exchange H⁺-Na⁺ on this ion-exchange resin is accompanied by the highest change in the differential enthalpy. It follows from the quantum-chemical calculations that the introduction of a (2-furyl)hydroxymethyl group into the structure of the polymer induces additional electrostatic interactions between an ammonium cation and an elementary unit of the ion-exchange resin.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2560–2563, December, 2004.     

Small-angle neutron scattering study of homopolymer blends and blockcopolymers of polystyrene/polyparamethylstyrene

Small angle neutron scattering (SANS) experiments were carried out at one mixture and two block copolymers of polystrene (PS) and poly(p-methylstyrene)(PpMS) at different temperatures ranging from 107 to 295°C. Both block copolymers show a maximum in scattering intensity, which increases with decreasing temperature approaching the spinodal point. Theoretical curves from Leibler's mean field theory agree very well with the experimental points with (XN) as the only fitting parameter, where χ is the Flory-Huggins interaction parameter and N is the degree of polymerization. The reciprocal value of I(q_m)⁻¹ of the maximum intensity for the block copolymers as well as the reciprocal intensity at zero scattering vector (I(q=0)⁻¹) for the mixture obey well the ansatz I = A + B/T within the experimental temperature range. The spinodal values of (X^N)_S are in good agreement with the theoretical values from Leibler.     

Neutron Scattering Studies of Structure and Self-Assembly of Star-Shaped Polymers with Fullerene Centres in Solutions

Protonated star-shaped polystyrenes with single and double fullerene C₆₀ core and the hybrid stars with pairs of polar and non-polar arms (tertbuthylmetacrylate, polystyrene) have been studied in deuterated toluene (20 °C) by small-angle neutron scattering at low and moderate polymer concentrations (c₁ ∼ 1 g/dl, c₂ ∼ 3–6 g/dl) to evaluate the peculiarities of fullerene centre action on polymers self-assembly in solutions. As we found, the cores composed of two fullerenes, linked via Si(CH₃)₂-bridge, induce stars' anisotropic interactions and association into chain-like structures (correlation radius ∼400–600 nm). Meanwhile, the single-core stars of polystyrene and hybrids organize globular clusters (size ∼ 10³ nm) those geometry do not change significantly by polymer content variation.     

Small-angle neutron scattering study of sodium cholate and sodium deoxycholate interacting micelles in aqueous medium

Small angle neutron scattering (SANS) measurements of D₂O solutions (0.1 M) of sodium cholate (NaC) and sodium deoxycholate (NaDC) were carried out atT= 298 K. Under compositions very much above the critical micelle concentration (CMC), the bile salt micelle size growths were monitored by adopting Hayter-Penfold type analysis of the scattering data. NaC and NaDC solutions show presence of correlation peaks atQ = 0.12 and 0.1 ?_-1 respectively. Monodisperse ellipsoids of the micelles produce best fits. For NaC and NaDC systems, aggregation number (9.0, 16.0), fraction of the free counterions per micelle (0.79, 0.62), semi-minor (8.0 ?) and semi-major axes (18.4, 31.7 ?) values for the micelles were deduced. Extent of micellar growth was studied using ESR correlation time measurements on a suitable probe incorporating NaC and NaDC micelles. The growth parameter (axial ratio) values were found to be 2.3 and 4.0 for NaC and NaDC systems respectively. The values agree with those of SANS.