Coupling of mutual diffusion to viscoelasticity in moderately concentrated polyisobutylene solutions

The normalized intensity autocorrelation function g⁽²⁾(t) were obtained by dynamic light scattering for moderately concentrated entangled solutions of polyisobutylene in n-heptane at 25.0 °C and in isoamyl isovalerate (IAIV) at 25.0 °C (Θ). The obtained data have been successfully analyzed by the ‘procedure X’ familiar for determination of mechanical relaxation spectra on the basis of the recent theory for g⁽²⁾(t). The results have shown that while the mutual diffusion coefficient D increases in the n-heptane solutions and decreases in the IAIV solutions with increasing polymer mass concentration c, the friction coefficient ζ for both solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M_w and solvent quality. It has been found that the instantaneous longitudinal modulus L₀ for n-heptane solutions increases in proportion to c², obeying the familiar relation for the plateau value (4/3)G_N of the longitudinal stress relaxation modulus, but L₀ for the IAIV solutions becomes progressively smaller than the values predicted from the relation with decreasing c. The terminal relaxation time τ_m has been found to follow the power-law τ_m∝M_w^3.4 established by rheological measurements.     

Viscoelastic characterization of moderately concentrated polystyrene solutions by dynamic light scattering

The dynamic light scattering measurements were performed for moderately concentrated entangled solutions of atactic polystyrene in benzene (BZ) at 25.0 °C, in cyclohexane (CH) at 34.5 °C (Θ), and in diethyl malonate (DEM) at 35.0 °C (Θ) to characterize their viscoelastic properties. The results have shown that while the mutual diffusion coefficient D increases in the BZ solutions and decreases in the CH and DEM solutions with increasing polymer mass concentration c, the friction coefficient ζ for the three solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M_w and solvent quality. It has been found that the instantaneous longitudinal modulus L₀ for the CH and DEM solutions increases in proportion to c², obeying the familiar relation for the plateau value (4/3)G_N of the longitudinal stress relaxation modulus, but the L₀ values for these solutions are somewhat smaller than the values predicted from the relation. The terminal relaxation time τ_m for the two Θ solvent systems has been found to follow the power-law τ_m∝c^2.7, showing good correspondence to the relation established by rheological measurements.     

Structure and dynamics of a pentablock copolymer of polystyrene-polybutadiene in a butadiene-selective solvent

We have examined solutions of a polystyrene-polybutadiene pentablock copolymer in n-heptane, a strongly selective solvent for polybutadiene. Small angle neutron scattering from 7 to 15% samples reveals domains about 10 nm in radius formed by the association of 200 polystyrene blocks. Dynamic light scattering measurements on 8 and 9% samples showed three modes: a fast diffusive mode related to the collective diffusion in semidilute solutions/gels; a relaxational mode related to the local dynamics of polystyrene domains trapped in the gel formed by bridging the domains with the polybutadiene chains; and a very slow diffusive mode. The relaxational dynamics persisted over the entire temperature range, becoming faster with increasing temperature, indicating a decreased microviscosity at higher temperatures. The slow dynamics seems to be connected with heterogeneities in the physical gel due to microsyneresis and almost disappeared above 50 °C. Macroscopic phase separation into two liquid phases was observed in a dilute solution of the un-associated copolymer, and into a liquid and gel phase at higher concentrations. The absence of flower-like micelles in dilute solutions and the macroscopic phase seperation suggest that the gels in the pentablock are formed by random association of multiplet domains and not by bridging of micellar domains.     

Zeta potential of Nafion molecules in isopropanol‐water mixture solvent

Structure of Nafion in isopropanol/water mixture solvent has been investigated using zeta potential. It was found that zeta potential of Nafion strongly depends on the concentration. When the concentration of Nafion varied from 0.5 to 1 wt %, zeta potential increased significantly from about 0 to ?12 mV, corresponding to the change of structure of Nafion molecules from true solution to dispersion of aggregates. While the concentration is above 5 wt %, micelle‐like structure of Nafion aggregates was proposed. The dependence of zeta potential of Nafion on pH value at concentration of 5 wt % shows a nonmonotonic function and isoelectric point of Nafion‐Na of 8.0 was observed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Solution properties of polyaniline

Solution properties of polyaniline (PANI) synthesized at various temperatures were studied using static light scattering (SLS), intrinsic viscosity, and dynamic light scattering (DLS). We demonstrated that average radius of gyration 〈R_g〉, intrinsic viscosity [η], and average hydrodynamic radius 〈R_H〉, of polyaniline molecules in dilute N‐methyl‐2‐pyrrolidinone (NMP) solutions increased with decreasing synthesis temperatures, i.e.; increasing molecular weight. SLS data demonstrate that second virial coefficient (A₂) decreased with increasing particle sizes suggesting that solubility of PANI in NMP decreased with increasing particle sizes. We also find that the polymers extend as the polymer concentration is lowered and that the increase in the hydrodynamic radius can be expressed by a power law of the electrostatic screening length. This behavior is typical of polyelectrolytes in dilute solution, providing a basis for understanding the conformation changes of this metallic polymer in solution. Copyright © 2009 Society of Chemical Industry     

Solution thermal properties of a family of thermo-responsive N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide copolymers - Aspects intrinsic to the polymers

A family of (N-isopropyl acrylamide-co-N-hydroxymethyl acrylamide) copolymers, p(NIPAAm-co-HMAAm), was synthesised and characterised with respect to solution thermal behaviour. A notable increase in cloud point (CP) was observed as the concentration of the polymer solutions was lowered, though the effect of concentration on CP of pure p(NIPAAm), was relatively small. In all cases, the elevation of CP was most evident at low concentration between 0.1 wt.% and 0.01 wt.%. Both at fixed and decreasing concentrations of p(NIPAAm) solutions, a direct relationship between molecular weight and CP was observed, where CP shifted to higher temperatures as the molecular weight increased. The polymer coil size in solution below the CP in the concentration range studied was between 4 and 11 nm for all the polymers in this study, irrespective of the concentration and of the fraction of hydroxy monomer incorporated, but increased dramatically above the CP. CPs obtained by Dynamic Light Scattering (DLS) were lower than those obtained by UV absorbance as the latter is less sensitive. Copolymer compositions with more than 13% hydroxy monomer showed no thermal hysteresis, in contrast to pure p(NIPAAm). The rate of heating/cooling had almost no effect on the CP values recorded.     

Aspects of the conducting properties of nafion doped polyaniline

The Nafion doped polyaniline blends are prepared by a one-step method based on the codis-solution of a proton exchanged Nafion powder and polyemeraldine base in NMP. As determined by elemental analysis, the doping level of PAni is dependent on the number of sulphonate groups per aniline unit and reaches a maximum value of 0.4. TEM pictures reveal the electronic conducting polymer dispersion in the Nafion matrix. Ionic conduction and electronic transfers are examined by ac impedance spectroscopy. The dependence of the electronic conductivity of the material on the composition, the swelling rate and the temperature leads us to suggest the contribution to the bulk conductivity of transverse polarons and bipolarons stabilised by sulphonate groups.     

Determination of polystyrene-carbon dioxide-decahydronaphthalene solution properties by high pressure dynamic light scattering

The diffusion coefficients of polystyrene (PS) in decahydronaphthalene (DHN) and in solutions of carbon dioxide (CO₂) and DHN were measured for dilute PS solutions over a range of temperatures and CO₂-DHN ratios using high pressure dynamic light scattering. Infinite dilution diffusion coefficients (D₀) of PS and dynamic second virial coefficients (k_D) were determined for essentially monodisperse 308 kDa PS. At a system pressure of 20.7 MPa, PS diffusion coefficients increased by a factor of 2.5, and the activation energy of diffusion decreased by approximately 16% when DHN was “expanded” with 44 mol% CO₂. However, the hydrodynamic radius of PS at a given temperature was not particularly sensitive to the CO₂ concentration. Solvent quality, as measured by k_D, decreased at higher CO₂ concentrations. The addition of CO₂ to polymer solutions may offer a way to “tune” the properties of the solution to facilitate the heterogeneous catalytic hydrogenation of polymers.     

Characterization of spatial inhomogeneities and dynamic properties of random cross-linked polystyrene networks by dynamic light scattering

The network inhomogeneity and the cooperative motion of the network chains of random cross-linked poly(styrene-co-maleic anhydride) gels were investigated by dynamic light scattering. Measurements were performed for gels in the preparation state as well as in the swelling equilibrium. Network inhomogeneities and cooperative motion were analyzed at varying the cross-linker concentration and the polymer volume fraction. While the cross-linker concentration has only a minor influence on the inhomogeneity and the diffusion constant D_coop, the polymer volume fraction clearly influences both measured properties. The concentration dependence of D_coop can be well described by a power law, as known for semi-dilute polymer solutions. In the preparation state the networks appear homogeneous, exhibiting dynamic contributions to the scattering intensity of 70-90%. Swollen to equilibrium stage, significant heterogeneities emerge, reducing the dynamic contributions to 10-20%.     

Static and dynamic light scattering study of strong intermolecular interactions in aqueous solutions of PVP/C60 complexes

The investigations of the dilute aqueous solutions of polyvinylpyrrolidone/fullerene (PVP/C₆₀) complexes by static (SLS) and dynamic (DLS) light scattering showed that strong intermolecular interactions, effective on the distances of about 45-50 nm, take place in the solutions. Two concentration ranges are well distinguished in these solutions. Above a critical concentration (c_cr) the fluctuations in the solutions are hindered and only one, diffusive, mode is observed in DLS experiments. Upon dilution (c<c_cr) this unified structure divides into large fragments (domains) and the slow mode attributed to long-range concentration fluctuations, gradually appears. The angular and concentration dependencies of the diffusion coefficient of the slow mode indicate the existence of strong intermolecular interactions.     

Methanol-Water Solution Transport in Nafion Membranes with Different Cationic Forms

Measurements of liquid transport were made with a Nafion membrane at different cationic forms. The experimental data are used to estimate the alcohol permeability when the membrane is separating water and water-methanol solutions. The obtained permeability coefficient values were useful for analyzing the influence of the substituted cations on the transport process in the membranes. In the present article, the permeability coefficient of methanol in Nafion substituted by Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Fe³⁺, and Al³⁺ were reported at different methanol concentration values. The analysis of the results revealed that, in general, for ions with the same period in the periodic table, the alcohol permeability decreases with increasing the valence. In contrast, when ions with the same valence are compared, the alcohol permeability decreases when the atomic mass increases, with the exception of the Mg²⁺. As a general trend, similar alcohol permeability variation with the concentration is observed for all the cationic forms of the membrane. There is an initial increase in the permeability, and, when the methanol concentration in the solutions is about 60%, the permeability decreases with the alcohol concentration. However, in the case of trivalent ions, the methanol permeability decreases with the methanol concentration.     

Dynamic light scattering of dilute PVA-borax aqueous solutions

Poly(vinyl alcohol)-borate (PVA-borate) complexes in dilute aqueous solutions were investigated by dynamic light scattering (DLS). Two relaxation modes obtained, were scattering vector-q² dependent and diffusive. The amplitude of slow mode was independent of borax concentration. In the very dilute PVA concentration regime ( [PVA] < 5 g/L), the PVA di-diol-borate complexation was dominated by intra-molecular reaction, and the fast mode correlation length ς_f which corresponds to the polymer chain dimension increased rapidly with borax concentrations lower than 0.06 M, and reached an asymptote in the higher borax concentration regime. However, for a dilute PVA aqueous solution with higher PVA content (i.e., [PVA] = 9 g/L), both intra-and inter-molecular PVA di-diol-borate complexations might happen. The chain expansion and shrinkage of PVA-borate complex with increasing borax concentration was observed due to the balance between the electrostatic repulsion of the charged diol-borate complexes and the intra-molecular crosslink induced by the intra-molecular di-diol-borate complexation.     

光散射技术及其在高分子溶液研究中的应用

从重均分子量,均方旋转半径及平均扩散系数等高分子溶液中较为重要的几个物理量入手介绍了近十几年来光散射技术在高分子溶液领域的应用。同时,对静态光散射和动态光散射的几个重要参数以及其较为重要的公式也做了介绍。最后,还综述了光散射的发展简史、基本原理、有关实验的技术方法等内容。     

Behaviour of poly(N-vinylcaprolactam) macromolecules in the presence of organic compounds in aqueous solution

Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa–non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl.

The behaviour of ternary systems PVCa macromolecules–ionic surfactant–pyrogallol and PVCa macromolecules–ionic surfactant–NaCl was studied. The addition of pyrogallol leads to the suppression of the intermacromolecular aggregation induced by temperature increase that is still observed at low surfactant concentrations and to the decrease of macromolecular hydrodynamic diameter. Also, the addition of NaCl to the PVCa/ionic surfactant systems results in the increase of the macromolecular hydrodynamic diameter. It is speculated that these results are due to the suppression of the cross-linking role of surfactant aggregates upon the addition of NaCl and pyrogallol.     

Aggregation behavior of new cyclic saturated copolymers synthesized via ring-opening metathesis polymerization

Cyclic saturated copolymers were prepared from 8-methyl-8-methoxycarbonyltetracyclo[4.4.0.1^2,5.1^7,10]dodec-3-ene (MMT) with polar ester group and dicyclopentadiene (DCP) without polar group. This procedure consisted of ring-opening metathesis polymerization (ROMP) followed by hydrogenation. Monomer reactivity of DCP was higher than that of MMT; the monomer reactivity ratio r_DCP/r_MMT varied from 2.135 to 1.159 in a temperature range from 80 to 130 °C. These kinetic results indicated that the copolymer had distribution of DCP composition in a macromolecule chain, which could provide the interesting aggregation behavior. The aggregation behaviors of the hydrogenated copolymer and the homopolymer in various solvents were also examined using dynamic light scattering (DLS) and static light scattering (SLS). DLS analysis indicated that the fast mode in each polymer is attributed to the diffusive motion of each single polymer chain, while the slow mode in the copolymer is caused by aggregated polymer. The aggregation degree of the copolymer decreased with increasing hydrophobicity of solvent, decreasing polymer concentration, decreasing molecular size of solvent and increasing temperature. Based on these findings, the mechanism of aggregation behavior was clarified that the DCP-rich unit in a macromolecule might be acting as core to give the aggregation in poor solvent.     

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 °C were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R_g and hydrodynamic radius, R_h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 °C were discussed according to the scaling relationships between R_g, R_h and M and the ρ-ratio (ρ=R_g/R_h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.     

Light scattering study on the dynamic behaviour of cellulose inclusion complex in LiOH/urea aqueous solution

In our previous study, the rapid dissolution of cellulose in alkali/urea aqueous solution at low temperature induced by a dynamic self-assembly process has been demonstrated [1]. The cellulose solution was meta-stable, and its stability could be influenced by system fluctuations (temperature, concentration or time). In the present work, cellulose dissolved in 4.6wt% LiOH/15.0wt% urea aqueous solution pre-cooled to −12 °C was studied by means of dynamic light scattering (DLS). The results revealed that cellulose existed as single inclusion complexes (ICs) associated with LiOH and urea hydrate which could surround the ICs at their surface. And the ICs were stiff, as revealed by results from transmission electron microscopy (TEM) and light scattering (LS). When there was a system fluctuation, the self-association of cellulose with each other took place, resulted from the destruction of the urea shell, and leading to the aggregation of the ICs. For that reason, the ICs stability could be evaluated by the aggregation behaviour. In our findings, the hydrodynamic radius (R_h,app) for the cellulose dispersion in dilute solution shifted to higher values with an increase of the temperature, the concentration or the storage time, indicating an IC aggregation phenomenon.     

Solvents effect on the physical properties of semi-dilute poly(N-isopropyl acryl amide) solutions

The physical properties of 5 wt% poly(NIPAM) (M_v=3.22×10⁵) semi-dilute solutions in H₂O, D₂O, and THF (tetrahydrofuran) solvents were studied using dynamic light scattering (DLS) and dynamic shear viscosity (DSV) measurements. The DLS data showed that there were poly(NIPAM) slow mode inter-polymer chains associations in H₂O and D₂O solvents. However, no DLS slow mode was observed in poly(NIPAM)/THF solutions. The DSV data showed that there are shear thickening behavior in these three poly(NIPAM) solutions, resulting in a maximum shear viscosity η_peak in the viscosity η′(ω) versus shear frequency ω curve. The slow mode hydrodynamic radius 〈R_hs〉 of DLS measurements and the zero shear rate viscosity η₀ and maximum viscosity η_peak data of DSV measurements from poly(NIPAM)/H₂O and poly(NIPAM)/D₂O solutions show two critical transition temperatures with T_cr1=30-32 °C and T_cr2=32-34 °C. Poly(NIPASM)/D₂O has higher T_cr1 and T_cr2 than poly(NIPASM)/H₂O. However, no transition temperatures of poly(NIPAM)/THF solution were observed. The different temperature dependencies of these three solutions were attributed to the ‘solubility’ and ‘hydrogen bonding’ effects between poly(NIPAM) with H₂O, D₂O, and THF solvents. Without considering the polymer-solvent hydrogen bonding, the solubility of poly(NIPAM) in solvents decreases in the following sequence: THF>H₂O>D₂O and the degree of polymer-solvent hydrogen bonding increases in the following sequence: THF<H₂O<D₂O. The effects of the degree of ‘hydrogen bonding’ and the ‘solubility’ of polymer in solvents on the physical properties of poly(NIPAM) solutions are discussed.     

Dynamic light scattering and viscoelasticity of semidilute polystyrene/cyclohexane solutions

In the present work, dynamic light scattering (DLS) measurements from polystyrene in cyclohexane semidilute solutions were carried out at 60 °C with scattering angles varied from 30° to 120°. The correlation functions were analyzed with the double KWW function and the CONTIN program. The amplitude of the fast mode A_f of the field correlation function g¹(t) was used to calculate the longitudinal stress modulus M_o using Wang’s theory. A comparison between M_o calculated from DLS data and the shear stress modulus G obtained from mechanical measurement was made.     

Dynamic light scattering studies on random cross-linking of polystyrene in semi-dilute solution

The random cross-linking of appropriately functionalized polystyrene in semi-dilute toluene solution (c = 0.01–0.05 g/mL) was studied by time-dependent measurements of dynamic light scattering. Macroscopic gelation occurred from concentrations as low as 0.02 g/mL. The gelation time, determined from the first appearance of fluctuations of the scattering intensity and the initial amplitude of the intensity correlation function (ICF), decreases markedly from about 100 min to 10 min with an increase of polymer concentration or cross-linker content. After the gel point, the ICFs display a characteristic power-law decay. The power-law exponent, n = 0.75 ± 0.06, does not change with (i) extent of reaction, (ii) polymer concentration, and (iii) cross-linker concentration, within the inspected ranges. This universal behavior is traced back to the fact that gelation took place as a result of random cross-linking of existent macromolecules, whose state of solution does not change markedly during conversion.