PS Solutions Research Articles

Effect of Anionic Surfactants on the Oil-Water-Rock Interactions by an Improved Washburn Method.

The complex and variable structure of subsurface oil reservoirs as well as the small pore throat size of reservoirs make it extremely important to investigate the effect of oil-water-rock interactions for enhancing oil recovery. In this paper, the powder wettability of oil sand with different polar solvents was investigated using the improved Washburn capillary rise method, and the surface free energy of oil sand was calculated in combination with the OWRK method. In addition, the wettability of anionic surfactants HABS and PS solutions on the surface of oil sand was determined, and it showed that their wetting rates showed different trends after CMC (critical micelle concentration). The C×cosθ value of HABS decreased significantly with increasing concentration, whereas PS showed little changes. This may be related to the aggregate structure formed by HABS on the oil sand surface. Meanwhile, the interfacial free energy between crude oil and oil sand was obtained by crude oil-to-oil sand wetting experiments, and found that the wetting rate of crude oil to oil sand was much lower than that of solvents and surfactants. In combination with the above results and the oil-water interfacial tension (IFT), the oil-water-rock three-phase contact angle and the work of adhesion between the crude oil and the solid were obtained by Young's equation. From the three-phase contact angle results, it can be found that the contact angle values of both HABS and PS are obviously higher than that of the simulated water, and both HABS and PS have the ability to significantly reduce the work of adhesion, which shows a strong ability to strip the oil film on the surface of the solid. The research results of this paper are helpful to understand the oil displacement mechanism of chemical flooding in reservoir pores, which is of great significance for improving oil recovery.

The effects of online simulation-based collaborative problem-solving on students’ problem-solving, communication and collaboration attitudes

Despite national curricula and instructional reforms calling for collaborative problem-solving skills (CPS), however, there is an absence of a theory-laden model showing how to effectively construct CPS for science learning. We therefore developed and validated a simulation-based CPS model that exploits its constructs, sequences, and causal relationships, and evaluating its effectiveness on students’ problem-solving. Over the span of a two-week physics science course, 57 ninth-grade students were recruited from two intact middle school classes to engage in this online simulation-based collaborative problem-solving (CPS) program. This program consisted of nine electrochemistry problem-solving lessons spread across four class sessions, each lasting 45 min. Results indicated that the simulation-based CPS model was validated and proven to contribute to effective problem-solving by linking PS solution proposing, peer communication, implementing PS solutions with simulation, and providing evidence-based explanations. The simulation-based CPS model successfully improved the performance of both high- and low-achieving students. With the support and presence of high-achievers, low-achievers’ collaboration attitude was boosted, which lead them to achieve similar learning success.

Decolorization Kinetics of Ponceau S Dye by Chemical Chlorination: A Comparison with Sunlight/ Chlorine and UV/Chlorine Processes

Aqueous chlorination of Ponceau S dye (PS) was kinetically investigated through a classical method and under solar or UV radiations. For the classical method, the kinetics of PS chlorination was established by varying concentration ratios R = [Free chlorine (Cl(+I))]/[PS], pH, temperature, and bromide ions concentration. The decolorization reactions exhibited pseudo-first-order kinetics with respect to Ponceau S dye and their apparent rate constants (kapp ) increased when R increased, in fact, kapp reaches 0.205 min-1 when R=10. Important removal levels were obtained when pH= 10, 100% of decolorization obtained at only 5 minutes which means that the hypochlorite ion (ClO-) was more reactive than hypochlorous acid (HClO) for decolorizing PS dye. Otherwise, the apparent rate constant of PS disappearance increased with increasing medium temperature and led to the activation energy of 39.64 Kj/mol. When bromide ions were present in the medium, the decolorization of the PS solutions was more important than the simple chlorination when R=2.5 and at pH 7.20 following an oxidation result of bromide ions by sodium hypochlorite to hypobromite and/or hypobromous acid, the addition to the N=N double bond of dye is easier in the case of Br(+I) than Cl(+I). Under UV or solar radiations, and when R=1 and at pH 4.5, the decolorization rates of PS solutions were clearly increased in comparison with dark chlorination. Thus, the comparative order obtained in terms of apparent rate constant was kapp (Cl(+I)/UV)> kapp (Cl(+I)/Sunlight)> kapp (Cl(+I)). The disappearance efficiencies were 47.6%, 52.4% and 99.2% respectively when using dark chlorination, Cl(+I)/Sunlight and Cl(+I)/UV processes. Thus, it was clear that the advanced oxidation processes have proven to be more effective in terms of water treatment by chlorination. Thus, compared with dark chlorination, the enhanced decolorization of PS could be attributed to the formation of reactive radicals that adopt essentially radical mechanisms that are faster compared to molecular attack.

Effect of polystyrene molecular weight and zinc oxide concentration on dewetting behavior of polymeric thin films

The separation between ultra-thin polymer film on metal oxide substrate is called dewetting. Dewetting causes the polymer films to loss their stability and other important properties, for example, the films may short circuit or reduce their transparency. Therefore, the stability of polymer thin films on substrate need to be improved. Addition of nanoparticles is one of the most popular technique used to increase the stability of polymer thin films. The correlation between the different of molecular weight and ZnO concentration on dewetting behavior was studied in this research. The appropriate concentration of ZnO on dewetting suppression in each molecular weight was examined. Furthermore, the variation of dewetting pattern in each molecular weight system was analyzed. In this research, PS (13K and 30K) solutions mixed with ZnO suspension in toluene were prepared. The concentrations of ZnO in PS solution were 0-1.0 wt%. All composite thin films were coated by spin-casting technique and annealed at a temperature of 100°C in a vacuum oven to induce dewetting behavior. The topographies of annealed thin films were studied by using Optical microscope (OM) and Scanning electron microscope (SEM). The thicknesses of thin films were examined by Atomic force microscope (AFM). The surface energies of PS and PS-ZnO composite films were measured and calculated by using contact angle measurement. From the results, we found that addition of ZnO nanoparticles at concentrations 0.7 and 1.0 wt% are the optimum concentration for dewetting inhibition of PS13K and PS30K films, respectively.

Quantitative Structural Analysis of Polystyrene Nanoparticles Using Synchrotron X-Ray Scattering and Dynamic Light Scattering.

A series of polystyrene nanoparticles (PS-1, PS-2, PS-3, and PS-4) in aqueous solutions were investigated in terms of morphological structure, size, and size distribution. Synchrotron small-angle X-ray scattering analysis (SAXS) was carried out, providing morphology details, size and size distribution on the particles. PS-1, PS-2, and PS-3 were confirmed to behave two-phase (core and shell) spherical shapes, whereas PS-4 exhibited a single-phase spherical shape. They all revealed very narrow unimodal size distributions. The structural parameter details including radial density profile were determined. In addition, the presence of surfactant molecules and their assemblies were detected for all particle solutions, which could originate from their surfactant-assisted emulsion polymerizations. In addition, dynamic light scattering (DLS) analysis was performed, finding only meaningful hydrodynamic size and intensity-weighted mean size information on the individual PS solutions because of the particles’ spherical nature. In contrast, the size distributions were extracted unrealistically too broad, and the volume- and number-weighted mean sizes were too small, therefore inappropriate to describe the particle systems. Furthermore, the DLS analysis could not detect completely the surfactant and their assemblies present in the particle solutions. Overall, the quantitative SAXS analysis confirmed that the individual PS particle systems were successfully prepared with spherical shape in a very narrow unimodal size distribution.

Rhodamine B-decorated poly(hydroxypropyl acrylate) and their effects on the self-assembly of breath figure arrays

Novel poly(hydroxypropyl acrylate)-co-poly(hydroxypropyl acrylate)-rhodamine B (PHPA-co-PHPA-RhB) hydrophilic copolymers were synthesized via radical polymerization in this paper. And then the honeycomb-structured porous films were fabricated by dropping the (PHPA-co-PHPA-RhB) copolymers and PS solution on glass substrates by breath figure method (BFM). The effects of solvent, hydrophilic copolymers’ molecular weight, the proportion of hydrophilic copolymers and hydrophobic polymers on the formation of porous films were investigated. The porous films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), spectrofluorometer and confocal laser scanning microscope (CLSM). The results show that PHPA-co-PHPA-RhB and PS solutions can form regular honeycomb porous films; the average diameter of the films pore decreases with the proportion of hydrophobic polystyrene increased. Similar regular was also found when the molecular weight of PHPA-co-PHPA-RhB was enhanced. Furthermore, the fluorescence properties of the porous films were also investigated in this study.

Effect of magnetic field on phase transitions in solutions and melts of flexible polymers

The effect of the magnetic field on the phase diagrams of flexible-chain polymer–solvent systems is observed for the first time. Phase transitions in systems with the crystalline-phase separation (PE–o-xylene, PE–n-hexane, PE–chloroform, PE–o-dichlorobenzene, PEG–1,4-dioxane, PEG–toluene) and the amorphous demixing (PS–methyl acetate, PVA–ethanol, PDMS–butanone) are studied. The magnetic field increases the temperatures of crystallization of PE and PEG from solutions and melts but has no effect on phase transitions in PS, PVA, and PDMS solutions. The structures of polymer entities isolated from solutions and melts are studied. Under application of the magnetic field to PEG solutions, spherulites of substantially smaller sizes than those formed outside the field appear. The magnetic field increases the degree of crystallinity of PEG, but the degree of crystallinity and size of PE spherulites remain unchanged.

Enhanced Thermal and Electrical Properties of Polystyrene-Graphene Nanofibers via Electrospinning

Polystyrene- (PS-) graphene nanoplatelets (GNP) (0.1, 1, and 10 wt.%) nanofibers were successfully produced via electrospining of dimethyformamide- (DMF-) stabilized GNP and PS solutions. Morphological analysis of the composite nanofibers confirmed uniform fiber formation and good GNP dispersion/distribution within the PS matrix. The good physical properties of GNP produced by liquid exfoliation were transferred to the PS nanofibers. GNP modified PS nanofibers showed a 6-fold increase in the thermal conductivity and an increase of 7-8 orders of magnitude in electrical conductivity of the nanofibers at 10 wt.% GNP loading.

Primitive Chain Network Simulation of Elongational Flows of Entangled Linear Chains: Stretch/Orientation-induced Reduction of Monomeric Friction

Well-entangled monodisperse linear polystyrene melts exhibit monotonic thinning of the steady state elongational viscosity with increasing the strain rate ε̇ even beyond the Rouse relaxation frequency, τR-1. This behavior is quite different from the thinning followed by hardening at ε̇ > τR-1 observed for entangled semidilute solutions. We attempt to elucidate the molecular origin of this difference by focusing on the concept of stretch/orientation-dependent monomeric friction ζ recently proposed by Ianniruberto and co-workers. Specifically, literature data of the stress relaxation after cessation of transient elongational flow, reported for both PS melts and solutions, are analyzed to evaluate the stretch/orientation-dependent decrease of ζ. In our working hypothesis, ζ is expressed as a function of the factor Fso = λ̃2S̅, where λ̃ is the normalized stretch ratio of entangled subchains defined with respect to the fully stretched state, and S̅ is an average orientational anisotropy of the components (polymer plus solvent if any) in the system. The factor Fso was estimated from the stress decay data after flow cessation. The resulting functional form of ζ(Fso) was then used in the primitive chain network (PCN) simulation including finite extensible nonlinear elasticity (FENE) to examine the elongational behavior of melts and solutions. For melts the simulation indicates that ζ decreases significantly under fast elongation because the entangled subchains are short and approach the fully stretched (and fully oriented) limit rather easily. Hence, the steady elongational viscosity ηE follows this decrease of ζ to exhibit the monotonic thinning even at ε̇ > τR-1. In contrast, for solutions, the simulated ηE exhibits thickening at ε̇ > τR-1 because the average anisotropy S̅ is governed by the solvent and remains small, thus overwhelming the increase of the subchain stretch λ̃. The simulated results proved to be in satisfactory agreement with the experiments.

Studies on the electrospun submicron fibers of SIS and its mechanical properties

AbstractThe submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The Influence of Solvent Properties and Functionality on the Electrospinnability of Polystyrene Nanofibers

AbstractSummary: In order to produce nanometer‐sized fibers at an industrial scale, not only the morphology but also the production rate of fibers is important. The effect of solvent properties and functionality on the production rate of electrospun PS nanofibers was investigated using eighteen different solvents. The solution concentration was varied between 10 and 30% w/v. Electrospinning of PS solutions was carried out at various applied voltages and tip‐to‐collector distances The production rate of the obtained PS nanofibers was quantified in terms of electrospinnability. We found that the chance for the resulting PS solution to be spinnable is greater for solvents with high dipole moment and low viscosity. The solvent that provided the highest electrospinnability for polystyrene was DMF and the functionalities that promoted high dipole moment and thus high spinnability were the carbonyl group and the nitrogen group with free electrons. General guidelines for choosing suitable solvents for successful production of electrospun nanofibers have also been proposed.SEM image of PS 685D at 200× magnification and the %‐coverage of the fibers obtained by using DMF, chloroform, and 1,4‐dioxane.magnified imageSEM image of PS 685D at 200× magnification and the %‐coverage of the fibers obtained by using DMF, chloroform, and 1,4‐dioxane.

Dynamics of Flexible Polymer Chains in Elongational Flow

This paper focuses on the recent developments achieved in our group in the field of flexible polymer chain dynamics in elongational flow. Stress-induced orientation and deformation in flowing polymer solution is being surveyed in a wide variety of manifestations. Two types of flow fields have been investigated: the opposite-jet flow with a stagnation point, and the abrupt contraction flow with open flowlines. Emphasis has been placed on the latter geometry due to its widespread occurrence. Degradation experiments performed with dilute PS solutions in abrupt contraction flow demonstrate a distinct propensity for midchain scission, a feature apparently consistent with highly extended chains. On the other hand, the critical strain-rate for chain fracture (ἐf) determined under the same experimental conditions scales with M-1. The inverse relationship with polymer MW is characteristic of partly uncoiled chains but not of highly extended chains, for which a stronger MW dependence (ἐf) ∝ M-2 is expected. The 'yo-yo' model, which could rationalize these findings, is refuted by fluorescence depolarisation measurements which indicated that central orientation is more progressive than the average segmental orientation. For the first time, polarization-modulated birefringence was used to determine the state of local chain orientation in abrupt contraction flow. Axisymmetric contraction flow is complicated by the large variations in local molecular orientation along different streamlines. To account for this effect, a numerical inverse Abel transform has been devised to compute local birefringence (Δn) from experimental retardation (δ). Results show a steep decrease in birefringence with axial distance. Birefringence profiles determined in a direction perpendicular to the flow show a maximum, not at the centre, but in the vicinity of the orifice walls. This observation is in accord with flow simulation results which indicated the presence of extreme strain rates near re-entrant corners. Molecular extension ratios calculated with the Kuhn-Grün theory gives a qualitative description of polymer uncoiling up to about one third of the chain contour length at the approach of capillary entrance. A notable departure from the affine deformation model is, however, observed with multiple birefringence saturation levels changing with flow rate conditions. This behaviour could be explained by the presence of transient molecular conformations. Efforts are underway to visualize these metastable states by single chain fluorescence video microscopy using UHMW polystyrene randomly grafted with anthracene chromophores.

Birefringence of dilute PS solutions in transient elongational flow

Transient elongational flow, created by forcing a polymer solution across a narrow contraction, is characterized by a high strain rate of limited duration. Due to an inherent short residence time, this type of flow generally is considered as being less efficient in extending isolated flexible molecular coils than “stagnation” point elongational flow. Rheo-optical measurements revealed, nevertheless, a readily detectable birefringence zone above a critical strain rate in the immediate orifice entrance. Birefringence was studied for dilute PS solutions (100–400 ppm) in decalin as a function of fluid strain rate (\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon $\end{document} = 1000–38,000 s−1) and polymer molecular weight (M = 1.93–10.2·106). Transient elongational flow is complicated by the presence of local orientation distribution along the different streamlines. To account for this effect, a numerical technique has been devised to compute local birefringence (Δn) from experimental retardation (δ). Results show a uniform birefringence distribution across the capillary entrance and a steep decrease with the axial distance. Molecular extension ratio calculated with the Kuhn-Grün theory suggests that polymers may uncoil up to one third of the chain contour length at the approach of capillary entrance. Although extension ratio determined at the inlet could be fitted with an affine deformation model, notable departure from this simple representation is observed when molecular strain is calculated along the streamline. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1483–1500, 1998

Birefringence of dilute PS solutions in transient elongational flow

Transient elongational flow, created by forcing a polymer solution across a narrow contraction, is characterized by a high strain rate of limited duration. Due to an inherent short residence time, this type of flow generally is considered as being less efficient in extending isolated flexible molecular coils than “stagnation” point elongational flow. Rheo-optical measurements revealed, nevertheless, a readily detectable birefringence zone above a critical strain rate in the immediate orifice entrance. Birefringence was studied for dilute PS solutions (100–400 ppm) in decalin as a function of fluid strain rate (\documentclass{article}\pagestyle{empty}\begin{document}$\dot \varepsilon $\end{document} = 1000–38,000 s−1) and polymer molecular weight (M = 1.93–10.2·106). Transient elongational flow is complicated by the presence of local orientation distribution along the different streamlines. To account for this effect, a numerical technique has been devised to compute local birefringence (Δn) from experimental retardation (δ). Results show a uniform birefringence distribution across the capillary entrance and a steep decrease with the axial distance. Molecular extension ratio calculated with the Kuhn-Grün theory suggests that polymers may uncoil up to one third of the chain contour length at the approach of capillary entrance. Although extension ratio determined at the inlet could be fitted with an affine deformation model, notable departure from this simple representation is observed when molecular strain is calculated along the streamline. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1483–1500, 1998

Birefringence of a Polystyrene Solution in Elongational Flow: Effects of Molecular Weight and Solvent Quality

Elongational flow was created by forcing dilute PS solutions across two jets in exact opposition. The retardation signal was mapped across the birefringence domain as a function of fluid strain rate, polymer concentration, MW, and solvent quality. The use of a fast polarization-modulation technique in conjunction with signal averaging increased the detection limit by over 1 order of magnitude in comparison to static-polarization experiments. Retardation could be determined at polymer concentrations down to the ppm level. The critical strain rate (e c ) for molecular coil orientation was corrected for polymer dispersity by combining the birefringence curves with the MWD obtained by gel permeation chromatography. In contrast with previous investigations, it was found that e c depended on the solvent quality and scaled with polymer molecular weight (M) as ∼M -1.5 in a poor solvent (decalin) and as ∼M -1.8 in good solvents (toluene and 1-methylnaphthalene). The possibility of using flow birefringence to determine polymer molecular weight distribution has been assessed and compared to the more conventional technique of gel permeation chromatography. The large dispersion in the birefringence curves suggested a gradual increase in segmental orientation with the fluid strain rate instead of an abrupt coil-to-stretch transition.

Effect of precipitants on the phase equilibrium of solutions of polystyrene close to the upper and lower critical solution temperatures

The effect of precipitants (propanol, butanol, hexane) on the phase equilibrium of PS solutions in decaline, cyclohexane and tert-butyl acetate close to the upper and lower critical solution temperatures has been studied. Employing the Prigogine-Flory-Patterson theory the author calculates the temperature dependences of the interaction parameter χ for binary (PS-decalin, PS-cyclohexane) and tertiary (PS-decalinbutanol, PS-cyclohexane-propanol) systems.

Solvent reorientation in polystyrene/A1248 and polystyrene/DOP systems

The depolarized Rayleigh spectra IVH( omega ) of the solvents di-2-ethylhexylphthalate (DOP) and polychlorinated biphenyl (A1248) in undiluted state and of the solutions A1248/polystyrene (PS) (cPS up to 15%) and DOP/PS (cPS up to 75%) were measured over the temperature range 30-140 degrees C using Fabry-Perot interferometry (FPI). The experimental IVH( omega ) of the undiluted solvents were well represented by a single Lorentzian whereas two Lorentzians were found necessary to fit the IVH( omega ) of the PS solutions. The variation of the intensity ratio of the two Lorentzians with temperature and the increase of the orientation time tau 0 of the solvents, upon addition of PS, show evidence of polymer-induced modification of solvent mobility. The rate of change of tau (c,T)/ tau 0 with cPS, which is a measure of the solvent local friction assumes similar values for both DOP/PS and A1248/PS solutions at high temperatures.

Stress-Optical Coefficient of the Compatible Poly(styrene)-Poly(methyl methacrylate)-Benzene Solution System

A ternary solution of poly(styrene)-poly(methyl methacrylate)-benzene has been studied rheo-optically. Shear viscosity of the PS-PMMA solutions measured by a capillary measuring apparatus is well fitted by the Hashin’s blending rule. Flow birefringence Δn and orientation angle χ of the solution in the steady shear flow is measured by the phase modulated flow birefringence (PMFB) technique. By comparing the shear viscosities measured in a capillary apparatus with the optical data from the PMFB, the stress-optical coefficients of the solution and of the pure PS and PMMA solutions are obtained. In a blend state, the value of stress-optical coefficient is able to be predicted as a simple linear additive relation with the values of two pure polymer species and the compositions. The stress-optical law is turned out to be applicable to compatible PS-PMMA-benzene solution system.

Aspects of the rheological behaviour of polymer solutions in conditions of phase separation

Change in viscosity on exposure to shear deformation and temperature in the region of phase separation is examined for concentrated PS and PMMA solutions. Below the temperature of phase separation depending on the shear rate the viscosity of the system as a function of temperature has different values: at low shear rates the viscosity is higher. Viscosity abruptly diminishes with rise in the shear rate which characterizes the destruction of the structure of a heterogeneous system and the phase separation process.

Self Diffusion of Polymers in the Concentrated Regime I. Temperature Dependence of the Self Diffusion Coefficient and the Steady Viscosity of Polystyrene in Dibutyl Phthalate

The role of the segment friction coefficient in slow chain dynamics in concentrated polymer solutions was studied from temperature dependence of the self diffusion coefficient Ds, and the steady viscosity η. Concentrated solutions of two polystyrene samples (code F4; Mw=43900 and F40; Mw=355000) in dibutyl phthalate with concentration of 40 and 50 wt% were used as test samples. Solutions of their blend containing 1 wt% of labeled F40 were also studied at total concentration of 40 wt%. For unentangled PS (F4) solutions, temperature dependence of Ds and η at each concentration was found to be in good agreement with each other and the functional form was well described in terms of the free volume theory. The function with the same values of the free volume parameters at each concentration is also applicable for description of T dependence of Ds of entangled PS (F40) solutions and also of Ds of F40 in the blend solution. The same segment friction coefficient was concluded to be operative in mass and momentum transports in concentrated solutions irrespective of the entanglement coupling.