Concentrated Polystyrene Solutions Research Articles

Elongational rheology of polystyrene melts and solutions: Concentration dependence of the interchain tube pressure effect

The elongational viscosity data of Bach et al. [Macromolecules 36, 5174–5179 (2003)] and Huang et al. [ACS Macro Lett. 2, 741–744 (2013); Macromolecules 48, 4158–4163 (2015); Macromolecules 46, 5026–5035 (2013)] on monodisperse polystyrene melts and concentrated polystyrene solutions in oligomeric styrene represent a unique benchmark for improving the tube model of Doi and Edwards with respect to its predictive capabilities of nonlinear viscoelasticity and especially chain stretch. By relaxing one of the basic assumptions of the original tube model of Doi and Edwards [J. Chem. Soc., Faraday Trans. 2 Mol. Chem. Phys. 74, 1802–1817 (1978); J. Chem. Soc., Faraday Trans. 2 Mol. Chem. Phys. 74, 1818–1832 (1978)], i.e., the assumption of a constant tube diameter, and assuming that chain stretch is inversely proportional to a deformation-dependent tube diameter, the extended interchain pressure (EIP) theory [Wagner and Rolon-Garrido, AIP Conf. Proc. 1152, 16–31 (2009); Wagner and Rolon-Garrido, Korea Aust. Rheol. J. 21, 203–211 (2009)] allowed a parameter-free modeling of the elongational viscosity of monodisperse polystyrene melts. Here, we demonstrate that when the dependence of the interchain pressure effect on polymer concentration and molar mass of the oligomeric solvent is considered, the EIP model agrees with experimental evidence that at low Weissenberg numbers W i R = e ˙ τ R < 1 melts and solutions show extension thinning behaviors, while at W i R ≅ 1 solutions switch to extensional thickening or show a more or less constant steady-state elongational viscosity and melts continue with extension thinning behavior with a scaling of η E ∝ W i R − 0.5. We explain quantitatively the effects of molar mass of solvent and of polymer concentration on the elongational viscosity in the investigated concentration range from 10% to 100% (melt), based solely on the linear-viscoelastic characterization. For polystyrene dissolved in oligomeric styrene with molar mass larger than a quarter of the entanglement molar mass of the melt, M o s ≥ M e m / 4 = 3.3 kg / mol, we predict a universal relation for the steady-state elongational stress at W i R ≫ 1, which is independent of polymer concentration and molar mass of the solvent, while the stretch potential of polystyrene dissolved in oligomeric styrene with M o s < 3.3 kg / mol increases with decreasing molar mass of solvent and decreasing polymer concentration in agreement with available experimental evidence.The elongational viscosity data of Bach et al. [Macromolecules 36, 5174–5179 (2003)] and Huang et al. [ACS Macro Lett. 2, 741–744 (2013); Macromolecules 48, 4158–4163 (2015); Macromolecules 46, 5026–5035 (2013)] on monodisperse polystyrene melts and concentrated polystyrene solutions in oligomeric styrene represent a unique benchmark for improving the tube model of Doi and Edwards with respect to its predictive capabilities of nonlinear viscoelasticity and especially chain stretch. By relaxing one of the basic assumptions of the original tube model of Doi and Edwards [J. Chem. Soc., Faraday Trans. 2 Mol. Chem. Phys. 74, 1802–1817 (1978); J. Chem. Soc., Faraday Trans. 2 Mol. Chem. Phys. 74, 1818–1832 (1978)], i.e., the assumption of a constant tube diameter, and assuming that chain stretch is inversely proportional to a deformation-dependent tube diameter, the extended interchain pressure (EIP) theory [Wagner and Rolon-Garrido, AIP Conf. Proc. 1152, 16–31 (2009); Wagner and Rolon-Garrido, Korea Aust. Rheol...

From melt to solution: Scaling relations for concentrated polystyrene solutions

The scaling relations established for the relaxation modulus of concentrated solutions of polystyrene (PS) in oligomeric styrene [Wagner, Rheol. Acta 53, 765–777 (2014); Wagner, J Non-Newtonian Fluid Mech. (2015)] are applied to the solutions of PS in diethyl phthalate (DEP) investigated by Bhattacharjee et al. [Macromolecules 35, 10131–10148 (2002)] and Acharya et al. [AIP Conf. Proc. 1027, 391–393 (2008)]. The scaling relies on the difference ΔTg between the glass-transition temperatures of the melt and the glass-transition temperatures of the solutions. ΔTg can be inferred from the reported zero-shear viscosities, and the Baumgaertel, Schausberger, and Winter (BSW) spectra of the solutions are obtained from the BSW spectrum of the reference melt with good accuracy. Predictions of the extended interchain pressure (EIP) model, which is based on the assumption that the relative interchain pressure in the melt and in the solutions is identical, are compared to the steady-state elongational viscosity data of PS/DEP solutions. The Rouse stretch relaxation times as calculated from the respective scaling relation are a factor of 2–3 higher than the Rouse time defined by the experimentally observed upturn of the elongational viscosity at WiR=ε̇ τR→1. This may be caused by DEP being a good solvent at room temperature and/or polymer degradation. Using the experimentally determined Rouse times, quantitative agreement is obtained between experimental data and model. Except for a possible influence of solvent quality, linear and nonlinear viscoelasticity of entangled PS solutions can thus be obtained from the linear-viscoelastic characteristics of a reference polymer melt and the shift of the glass-transition temperature between melt and solution.

Modeling of Polystyrene under Confinement: Exploring the Limits of Iterative Boltzmann Inversion

We explore the limits of a purely structure based coarse-graining technique, the iterative Boltzmann inversion (IBI), in the coarse-graining of a confined concentrated polystyrene solution. In the first place, some technical considerations and challenges encountered in the course of the optimization process are represented. The concepts of the choice of the initial potentials and the cross-dependency of the interactions as well as the order of optimization are discussed in detail. Furthermore, the transferability of a previously developed CG confined polystyrene solution model, the “parent CG confined model”, to different degrees of confinement at constant concentration and temperature is examined. We investigate if a CG force field developed for a confined polymer solution by IBI is sensitive to changes in the degree of localization or arrangement of polymers near the surfaces although the concentration is kept constant. For this purpose, reference atomistic simulations on systems of different confinemen...

ATR IR spectra and structure of boundary layers of atactic polystyrene

The ATR IR spectra of solutions of atactic polystyrene in chloroform at the boundary with KRS-5 glass in the ranges 2800–3100 and 1550–1650cm−1 are studied. It is shown that the parameters of orientation Σ and polarizability anisotropy α′ p − α′ s of macromolecules estimated from the absorption and refractive indexes and the average complex polarizability of polystyrene boundary layers on KRS-5 vary in an extremum manner with the concentration of polystyrene in a solution. For dilute polystyrene solutions, a high degree of orientation of chains adsorbed on the glass surface is found. The inversion of the sign of polarizability anisotropy α′ p − α′ s and an increase in orientation parameter Σ of macromolecules in boundary layers on KRS-5 are associated with the compression and interpenetration of coils during the transition from semidilute to concentrated solutions of polystyrene.

Complete Suppression of Blinking and Reduced Photobleaching in Single MEH-PPV Chains in Solution

We report photophysical properties of individual chains of the conjugated polymer MEH-PPV in a concentrated solution of polystyrene. MEH-PPV chains diffusing freely in the solution show no fluorescence blinking and reduced photobleaching. Adsorption of the chains onto a substrate in the solution leads to 34% decrease in fluorescence intensity (quantum efficiency), five-fold increase in the rate of photobleaching and appearance of blinking. The blinking is often a two-state process caused by a reversible interaction with a single quencher. The interaction causes quenching of a substantial length of the extended MEH-PPV chain.

Surface modification of silica, titania, and zinc oxide micro particles with epoxidized soybean oil for preparation of polystyrene composite films

AbstractA novel and convenient procedure is presented for bilayered encapsulation of silica, ZnO, and TiO2 microparticles using highly adhesive unsaturated polyester, poly (2‐hydroxy propylene maleate) (PHM) and epoxidized soybean oil (ESO). Thus, adsorption of PHM onto the particle surfaces from acetone solution (under sonication) and followed curing at 180°C resulted in self crosslinking of the polyester layer by thermally induced addition of its free‐hydroxy groups to the maleate double bonds. The adsorption of the polyester onto particle surfaces was demonstrated to obey typical Langmuir isotherms. The oil was tethered onto particle surfaces through residual hydroxy groups of the crosslinked polyester layer at 180°C. Thermo gravimetrical analyses (TGA), FTIR spectra, and transmission electron microscopy (TEM) images of the oil‐modified pigments clearly indicated presence of organic layers (26.4–37.3% w/w) with 0.1–0.15 μm thicknesses. The resulting organically modified particles were demonstrated to give fairly stable and homogenous dispersions in concentrated polystyrene solutions. Those dispersions were employed for preparing nearly transparent cast films on glass substrates. Scanning electron microscopy (SEM) images of the freestanding films did not show any phase separation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Critical assessment of diffusion coefficients in semidilute to concentrated solutions of polystyrene in toluene

We have measured collective diffusion coefficients of dilute, semidilute, and concentrated solutions of polystyrene in toluene up to a polymer concentration of 0.832 mass fractions at T=25 degrees C. The three employed experimental techniques of photon correlation spectroscopy, thermal diffusion forced Rayleigh scattering, and optical beam deflection cover four orders of magnitude with respect to their characteristic diffusion lengths (200 nm-2.9 mm), corresponding to more than 8 decades of the diffusion time constants. Contrary to existing literature data, which suggest a length scale dependent anomalous diffusion at high concentrations, all our techniques yield identical diffusion coefficients and purely Fickian diffusion, irrespective of their characteristic length scale.

A SLOW RELAXATION MODE OF POLYMER CHAINS IN A SEMIDILUTE SOLUTION

Dust-free semidilute and concentrated polystyrene (PS) solutions in different solvents were prepared by slow evaporation and in situ anionic polymerization, which removes the effects of troublesome artifacts such as dust contamination and concentration gradient. The dynamics was reexamined by a combination of static and dynamic laser light scattering. In benzene and toluene (good solvents for PS), only one fast diffusive mode of polymer chains can be observed when the concentration (c) is up to 20%, which is attributed to thermally agitated fluctuation of "blobs" or chain segments. Static and dynamic correlation lengths (ξS and ξD) are scaled with c as ξS (or ξD) ~ c −0.72 ± 0.02 . In cyclohexane, whose quality decreases with temperature in the range 32−50°C, an additional slow mode of polymer chains can be observed. Such a slow mode is viewed more obviously at a large scattering angle even in a concentrated solution with high chain entanglement. The present study indicates that the slow mode is due to the solvent quality.

Reexamination of the Slow Mode in Semidilute Polymer Solutions: The Effect of Solvent Quality

Dust-free semidilute and concentrated polystyrene (PS) solutions in two solvents were prepared by conventional slow evaporation and in situ living anionic polymerization that removes previously troublesome artifacts, such as dust contamination and a concentration gradient. Their dynamics was reexamined by a combination of static and dynamic laser light scattering. As expected, only one fast diffusive mode was observed in benzene (an athermal solvent for PS) up to 20% concentration (C), attributed to thermally agitated fluctuation of chain segments (“blobs”) confined in a noninteracting “tube” made of its surrounding chains. In cyclohexane, whose quality as a solvent for PS decreases with the temperature in the range 32−50 °C, we observed an additional slow mode. The slow mode is enhanced as the solvent quality decreases. The scaling exponent (αs) between its related line-width (Γslow) and the scattering vector (q), i.e., Γslow ∼ qαs, decreases from 3 to 0 as C increases, which suggests that the slow mode has different natures, depending on C. When C is only a few times larger than the overlap concentration (C*) but lower than the entanglement concentration (Ce), i.e., not all the chains are entangled together, the slow mode is related to transient interchain segment−segment interaction-induced clusters. When C/Ce > 1, it is attributed to the confinement of each chain inside an inhomogeneous tube with a “band”-like structure due to relatively stronger segment−segment interaction near the entanglement points.

Viscosity of concentrated solutions of polystyrene and poly(vinyl acetate) (empirical equations)

The viscosity of solutions of polystyrene with Mw from 2.8 × 104 to 7.8 × 105 in toluene and of poly(vinyl acetate) with Mw from 2 × 104 to 1.4 × 105 in butyl acetate at 30–80°C is measured. The dependence of the activation energy of the viscous flow of the solutions on the molecular weight of the polymers and solution concentration is examined. This dependence is approximated by a cubic polynomial for polystyrene solutions and by a quadratic polynomial for poly(vinyl acetate) solutions. The dependences of the solution viscosity on the concentration, molecular weight, and temperature are approximated by exponential equations in which the exponents are sums of polynomials. The coefficients of the polynomials are determined.

Moderately concentrated solutions and gels of atactic polystyrene in solvent mixtures of carbon disulfide and tricresyl phosphate

Viscoelastic properties are followed during the formation of gels by moderately concentrated solutions of atactic polystyrene (aPS) in a mixed solvent of carbon disulfide and tri-m-tolyl phosphate (TCP). This mixture is a thermodynamically “good” solvent for aPS and with solution glass transition temperatures far below the temperatures used in the study. Gel formation is driven by the CS2 component, at temperatures and polymer concentrations similar to those observed in solutions of aPS in pure CS2. The TCP adjusts the viscoelastic response to a convenient range. The results show appreciable hysteresis in the melting and formation temperatures of gels, with the gel formation being a slow process, permitting dynamic mechanical or creep and creep recovery studies as a function of ageing during gel formation, as well as on the solutions prior to permit gel formation. These data reveal systematic behavior analyzed using the linear viscoelastic constitutive relation to obtain the viscosity and a measure of the...

Protuberant Morphology of Electrospun Polymeric Fibers

A highly concentrated solution of polystyrene (PS) in N,N-dimethyl formamide (DMF) was electrospun and the surface morphology of the electrospun PS fibers was investigated. Unlike the porous morphology observed on the surface of the fibers electrospun from the PS solution in a volatile solvent, e.g. tetrahydrofuran, a regular protuberance morphology was found on the surface of the fibers electrospun from the PS solution in the non-volatile solvent, DMF. This unique surface morphology was formed due to the presence of residual DMF solvent inside the electrospun PS fiber. Due to the large diameter of the PS fibers (~5 to ~10 μm) formed from the highly viscous PS solution, the DMF could not evaporate completely from inside them during the electrospinning process. Therefore, the extrusive force of the residual solvent inside the fiber induced the formation of a unique surface morphology. We believe that this unique surface morphology increases the surface area of the electrospun fibers, thus making it possible to control their wetting or adsorption behavior.

Study of interfacial tension in poly(ethylene oxide)/polystyrene/diblock copolymer system by electric deformation method

We investigated the interfacial tension γ between poly(ethylene oxide) (PEO) and polystyrene (PS) focusing our attention on the dependence of γ on the molecular weight (M) of PEO and the surfactant effect of poly(ethylene oxide-b-styrene) diblock copolymer [P(EO-b-S)]. Measurements of γ were carried out by observing electric deformation of droplets of PEO suspended in bulk PS or in a concentrated solution of PS in dioctylphthalate (DOP). The results indicate that γ between PEO and PS is almost independent of M of PEO in the high molecular weight region, but exhibits a minimum around M=500. Addition of 1wt% of P(EO-b-S) to the PEO/PS system causes a decrease of γ due to the surfactant effect of the copolymer, but γ is almost independent of further addition of the copolymer. The decrement of the interfacial tension Δγ increases with increasing molecular weight of P(EO-b-S).

New supramolecular crystalline polymer structure of syndiotactic polystyrene

AbstractSemi-crystalline polymers such as polyethylene and isotactic polypropylene are known to yield lamellar meso-structures through macromolecular chain folding upon solidification from the molten state. The lamellae typically assemble to form microscopic spherulitic or ‘shish-kebab’ super structures depending on the cooling condition being either quiescent or induced during flow. Cooling experiments with concentrated solutions of syndiotactic polystyrene, however, unexpectedly yielded a novel microscopic superstructure resembling a ‘bird nest’. These super structures can be made reproducibly under specific conditions. They reflect the impact of a chiral centre on the molecular organisation on the meso and micro level during a solidification process.

Rheofluorescence Technique for the Study of Dilute MEH-PPV Solutions in Couette Flow

A novel rheofluorescence technique has been developed that permits the study of fluorescent polymers in a near-uniform shear field. The system has been used to examine the effects of shear flow on dilute solutions of two commercially available samples of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) in toluene and xylene. A detailed description of the instrument is provided, along with data that confirm a small probe molecule, Rhodamine 6G, is not affected by simple shear flow. MEH-PPV solutions were examined over two decades of concentration for rheochromism indicative of changes in segment length, and shear-induced orientation revealed by measurements of the steady state emission anisotropy. It is demonstrated that these dilute samples were not influenced by shear rates in the range 100-1000 s(-1). In contrast, MEH-PPV dispersed in a concentrated polystyrene solution showed evidence of shear-induced orientation and rheochromism. This new technique shows promise for investigating the impact of shear flow on the conformation of conjugated polymers employed in organic optoelectronic devices.

Validity of the linear stress optical rule in mono-, bi- and polydisperse systems of entangled linear chains

The influence of the molecular weight distribution (MWD) of bidisperse entangled linear polymer systems on the critical stress at which the stress-optical rule (SOR) fails for uniaxial extensional flows is investigated numerically. The model predictions show that the critical extensional stress where the SOR fails, Δ τ FSOR , depends on the molecular weight distribution and the extension rate. The variation in Δ τ FSOR results primarily from the change in the mass fraction of stretched chains. In addition, the interplay between the contribution from the non-stretched and stretched chains to the stress and birefringence is significant for the magnitude of Δ τ FSOR . The latter is the reason why Δ τ FSOR is larger compared to that expected from the mass fraction of stretched chains alone. A comparison of the model predictions with experimental data for a nearly monodisperse concentrated polystyrene (PS) solution, reported in the literature, shows that the SOR fails for a chain stretch of about one-third of the maximum stretch ratio. For bidisperse PS melts, the critical stretch ratio varies with the MWD. For monodiperse PS melts, the critical stretch ratio is about two-fifth of the maximum value. A simplified procedure is proposed to analyze polydisperse melts. Compared to experimental data reported in the literature, the trend is qualitatively correct, but the predicted magnitude of Δ τ FSOR is too low.

Calorimetric Study of Dynamical Heterogeneity in Toluene Solutions of Polystyrene

In an effort to clarify the effect of dynamical heterogeneity on the glass transition in binary systems, we measured the heat capacity Cp on concentrated toluene solutions of polystyrene (PS) using an adiabatic calorimeter. We also carried out dielectric measurements on the same system. Results indicate that the Cp vs temperature T curve of the solvent toluene/xylene(90/10) exhibits a sharp stepwise increase of Cp at the glass transition temperature Tg (= 115 K). In contrast, the Cp curves of PS/toluene solutions exhibit a double-sigmoidal shape. The configurational heat capacity ΔCp around Tg has been determined by subtracting the heat capacity due to the lattice vibrations and intramolecular vibrations. We have further resolved ΔCp into two sigmoidal curves using an empirical function. The Tgs corresponding to the two sigmoids are denoted as Tg1 and Tg2 (Tg1 > Tg2). Two dielectric loss peaks termed α and β are assigned to segmental motions of PS and rotation of the toluene molecules, respectively. The dielectric glass transition temperatures Tα and Tβ are defined as the temperatures at which the dielectric relaxation times for the α and β processes become 103 s, respectively. Tα and Tβ agree well with the calorimetric Tg1 and Tg2, respectively.

Dielectric Study of Concentration Fluctuation in Solutions of Polystyrene

The effect of the solvent quality on local concentration fluctuation was studied for concentrated solutions of polystyrene (PS) in toluene (Tol), ethylbenzene (EtBz), n-propylbenzene (PrBz), and n-butylbenzene (BuBz) by using dielectric spectroscopy. The exponents of the Mark−Houwink−Sakurada equation of those solutions indicate that the solvent quality deteriorates in the order of Tol, EtBz, PrBz, and BuBz. Three dielectric relaxations designated as α, β, and γ are observed in the temperature dependence curves of the dielectric loss in the order of decreasing temperature. According to our previous study on PS/Tol solution, the α, β, and γ relaxations have been assigned to local segmental motions of PS, rotation of the solvent molecules, and the secondary relaxation in the glassy state, respectively. The half-width of the dielectric loss curve Λα for the α relaxation of PS/Tol solutions is independent of temperature, but the values of Λα for solutions in EtBz, PrBz, and BuBz increase with decreasing tempe...

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 L 0 for the CH and DEM solutions increases in proportion to c 2, obeying the familiar relation for the plateau value (4/3) G N of the longitudinal stress relaxation modulus, but the L 0 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.

Chain dynamics of concentrated polystyrene solutions studied by depolarized photon-correlation and viscosity measurements

Concentrated solutions of nearly monodisperse polystyrene samples in cyclohexane in the theta condition and in the entanglement-free region have been studied by means of the depolarized photon-correlation spectroscopy and viscosity measurements. It is shown that the viscoelastic behavior of the studied systems is described by the Rouse theory and that in agreement with the theoretical analysis the main polymer dynamic process probed by the depolarized Rayleigh scattering is basically the reorientational motion associated with a Rouse segment of the polymer chain, whose relaxation is independent of the scattering angle and the molecular weight. In addition to the main dynamic process, the tail region of a very fast process associated with the sub-Rouse-segmental motions can be observed, whose existence is expected from the theoretical analysis.