Polystyrene In Dioctyl Phthalate Research Articles

Extensional flow of low-viscosity fluids in capillary bridges formed by pulsed surface acoustic wave jetting

Forming capillary bridges of low-viscosity (≲10 mPa s) fluids is difficult, making the study of their capillary-thinning behavior and the measurement of the fluid's extensional viscosity difficult as well. Current techniques require some time to form a liquid bridge from the stretching of a droplet. Rapidly stretching a liquid bridge using these methods can cause its breakup if the viscosity is too low. Stretching more slowly allows the bridge to thin and break up before a suitable bridge geometry can be established to provide reliable and accurate rheological data. Using a pulsed surface acoustic wave to eject a jet from a sessile droplet, a capillary bridge may be formed in about 7.5 ms, about seven times quicker than current methods. With this approach, capillary bridges may be formed from Newtonian and non-Newtonian fluids having much lower viscosities—water, 0.04% by weight solution of high-molecular-weight (7 MDa) polystyrene in dioctyl phthalate and 0.25% fibrinogen solution in demineralized water, for example. Details of the relatively simple system used to achieve these results are provided, as are experimental results indicating deviations from a Newtonian response by the low-viscosity non-Newtonian fluids used in our study.

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).

Molecular orientation in non-Newtonian flow of dilute polymer solutions around spheres

A novel approach is presented to study the benchmark problem of flow around spheres in model dilute solutions of monodisperse samples of atactic polystyrene in di-octyl phthalate. Spheres are held “stationary” on flexible cantilevers of known spring-constant, k, while the polymer solutions are pumped past at controlled flow rates, allowing access to a wide range of Deborah number. In this way the non-Newtonian forces experienced by the spheres can be measured as a function of Deborah number, while detailed observations and measurements of birefringence are made, enabling assessment of macromolecular strain and orientation. In addition the flow field around a sphere has been measured in an a-PS solution. Experiments have been performed on a single sphere and on two spheres axially aligned in the direction of flow. The extensional flow around the downstream stagnation point of the single sphere is found to play a pivotal role in the development of molecular strain and stress, resulting in flow modification and subsequent non-Newtonian behaviour. The flow birefringence in the wake is found to modify severely the flow around a second, downstream, sphere, affecting the non-Newtonian forces encountered by the second sphere. This provides an explanation for the time interval dependent terminal velocity often observed when two spheres follow the same path through viscoelastic liquids.

Two-fluid demixing theory predictions of stress-induced turbidity of polystyrene solutions in dioctyl phthalate

Stress induced demixing of a polymer solution is predicted by a two fluid theory reformulated to be able to impose all the interface boundary conditions required. The theory has now been applied to the data on solutions of polystyrene in dioctylphthalate of Rangel-Nafaile et al. [Macromolecules 17, 1187–1195 (1984)] at one molecular weight at various temperatures, to additional unpublished data at various molecular weights, and to various published experiments in which there was evidence for phase separation. The dependence of elastic compliance on concentration was approximated by an equation which permitted the analytic differentiations and integrations required for the equations of the theory. The prediction of visual cloud point stresses at various temperatures were excellent within the concentration range over which the compliances had been fitted. The calculated demixing stresses were somewhat higher than those measured by extrapolation of photometric data to onset of turbidity, possibly because the...

Shear-induced effects on miscibility in polymer solutions

Methods of macromolecular integral equation theory are employed to calcuate the correlation functions of flexible linear homopolymers deformed by shear flow. The extent of coil deformation is calculated from bead-spring models that include corrections for finite chain extensibility and pre-averaged hydrodynamic interactions. The spinodal boundaries for sheared polymer solutions are obtained from the compressibility route under conditions of constant strain rate. It is shown that accounting for changes in the cohesive energy arising from flow-induced coil deformation may lead to non-monotonic shifts in the cloud point as a function of applied shear, even in the absence of nonlinear viscoelastic response. These model calculations are compared with experimental measurements of the cloud point for sheared solutions of polystyrene in dioctyl phthalate.

Structures in a Semidilute Polymer Solution Induced under Steady Shear Flow As Studied by Small-Angle Light and Neutron Scattering

Structures induced by a steady shear flow in a semidilute polymer solution of high molecular weight deuterated polystyrene in dioctyl phthalate are investigated. By a combined use of small-angle light scattering (SALS) and small-angle neutron scattering (SANS), we are able to obtain scattering functions of the shear-induced structures over 3 orders of magnitude in wavenumber (q) and 7 orders of magnitude in intensity. The changes in the structures with shear rate (γ) at a given temperature and with temperature at a given γ are explored. At a given temperature, the shear flow induces a structural change in the solution at γ larger than a critical shear rate γc, giving rise to a scattering pattern called “butterfly pattern” in the low q region of SANS, while keeping the same pattern as that in the quiescent state in the q region of SALS. As γ increases, the butterfly patterns evolved not only in the low q region of SANS but also in the q region of SALS. This indicates that the shear-induced structures ...

Light Scattering and Small-Angle Neutron Scattering Studies of Structures in a Semidilute Polymer Solution Induced under Oscillatory Shear Flow

Oscillatory-shear-flow-induced structures of a semidilute polymer solution of ultrahigh molecular weight deuterated polystyrene in dioctyl phthalate were investigated by using the small-angle light scattering (SALS) and the small-angle neutron scattering (SANS). Under a fixed strain amplitude of oscillatory shear flow at 4.8, we observed the shear-induced structures as a function of the angular frequency (ω) and the strain-phase. At low ω, butterfly patterns, which are the scattering patterns unique to the shear-induced structures formed in semidilute polymer solution, were observed by SALS and isotropic patterns with weak scattered intensities were obtained by SANS. At high ω, on the other hand, SANS showed butterfly patterns and SALS showed almost isotropic patterns. These results indicate that the anisotropic structures developed under oscillatory shear flow become smaller with increasing ω. From the SALS and SANS patterns, we obtained scattering profiles parallel and perpendicular to the flow directio...

Time-Resolved Small-Angle X-ray Scattering Studies of Spinodal Decomposition Kinetics in a Semidilute Polystyrene−Dioctyl Phthalate Solution

Synchrotron-based time-resolved small-angle X-ray scattering was used to measure the early-stage spinodal decomposition kinetics in a highly viscous semidilute solution of polystyrene in dioctyl phthalate. Although strong nonlinearities in the kinetics were observed, a linear theory analysis could fit the evolution of the structure factor at short times and low wavenumbers. Nonlinearities become significant earlier at higher wavenumbers, which is consistent with recent computer simulation studies. From the linear theory analysis, the exponential relaxation rate of the structure factor R(q) was found to be linear in q2 in the low-wavenumber region of the experiments, in agreement with mean-field theory for spinodal decomposition in polymer solutions. The wavenumber-dependent Onsager transport coefficient Λ(q), which is the Fourier transform of the nonlocal mobility in a polymer system, was determined to scale as q-4. This q dependence, which is stronger than that predicted by existing theory, may be related to entanglement effects.

A rheo‐optical study of near‐critical polymer solutions under oscillatory shear flow

The flow‐induced structure and dynamics of concentration fluctuations in a near‐critical polymer solution have been investigated using the technique of polarimetry. Specifically, this article presents scattering dichroism of a single‐phased, semidilute solution of polystyrene in dioctyl phthalate (PS/DOP) subjected to small amplitude oscillatory shear flow. The measured frequency response is compared to results obtained using the Onuki–Doi theory, which relates dichroism to structure factor, and the Helfand–Fredrickson model, from which the structure factor is calculated. The predictions are in good qualitative agreement with the experimental data when stress relaxation is taken into account in the constitutive equation relating stress to strain in the system. Our results demonstrate that the strength of the coupling between viscoelastic stress and flow governs the behavior of concentration fluctuations in semidilute polymer solutions under oscillatory shear flow.

Cooperative diffusion in concentrated polymer solutions

Concentrated solutions of polystyrene in dioctylphthalate have been examined as a function of temperature over the concentration range 0.2 to 0.9 g/ml. The static screening length and the hydrodynamic screening length evaluated from the cooperative-diffusion coefficient are compared with the predictions of current models.

A neutron scattering study of shear induced turbidity in polystyrene dissolved in dioctyl phthalate

The influence of shear on the small angle neutron scattering from a semidilute solution of polystyrene (PS) dissolved in dioctyl phthalate (DOP) is examined in the limit of strong shear (γ̇≥100 s−1). These experiments are restricted to room temperature, which is close to the theta point of PS/DOP. The fraction of deuterated PS chains is varied, while the total polymer weight fraction is fixed at 3%. This is near the critical composition of hydrogenated PS in DOP. The increased scattering at high shear rates (‘‘shear induced turbidity’’) is interpreted in terms of a critical temperature shift. Scattering along the flow direction is distorted and the scattering data normal to flow is uninfluenced by shear above a wave vector cutoff q*, which is independent of shear rate. This cutoff is found to correspond to the Debye length, characterizing the average intermolecular potential range.

Concentration fluctuation enhancement in polymer solutions by extensional flow

The growth of concentration fluctuations of poor and near-θ semidilute solutions of polystyrene in dioctyl phthalate (PS/DOP) subject to plane extensional flow at temperatures above the quiescent cloud point was investigated. Scattering dichroism and SALS indicate that concentration fluctuations grow perpendicular to the principal axis of entension for low strain rates. For higher extensional rates, fourfold symmetry is predicted appears in the structure factor, with intensity maxima on the axes at 45° to the principal axes

Viscoelastic properties of polymer solutions at temperatures lower than Θ points (abstract)

Zero‐shear viscosity η0 and steady‐state compliance Je of poly(α‐methylstyrenes) in benzyl n‐butyl phthalate (Θ=4.6 °C) and polystyrene in dioctyl phthalate (Θ=22 °C) were measured at temperatures lower than the Θ points. Moreover, stress developments after onset of steady shear flow were measured and the strength of entanglement was estimated on the basis of network rupture model. The concentration and the molecular weight dependences of η0 at temperatures lower than the Θ points are almost the same as those at the Θ temperatures, but the magnitude of η0 increases with decreasing temperature. This suggests that the strength of entanglement increases with decreasing solvent power. On the other hand, Je values at the temperatures lower than the Θ points are almost the same as those in good and Θ solvents. This result indicates that the entangled structure of polymer solution effective to Je is almost independent of solvent power. Therefore, it is concluded that the gel‐like behavior of polymer solution at ...

Time-dependent small-angle light scattering of shear-induced concentration fluctuations in polymer solutions

A small-angle light-scattering experiment probing the time-dependent behavior of a semidilute polymer solution under simple shear is presented. Specifically, this paper investigates time-dependent anisotropic growth and orientation of concentration fluctuations in a semidilute solution of polystyrene in dioctyl phthalate above the quiescent cloud-point temperature. Two flow cells, which permitted investigation of the structure and dynamics of concentration fluctuations in both the flow-shear and the flow-vorticity planes, were used. Concentration fluctuations were found to be enhanced anisotropically by the shear flow in both planes. In the flow-vorticity plane, shear-enhanced concentration fluctuations orient along the vorticity direction, while in the flow-shear plane, the axis of average orientation is at an angle between 135° and 45° to the direction of flow. Qualitative trends of this anisotropic growth of concentration fluctuations are in agreement with the predictions of the Helfand–Fredrickson model in the flow-shear plane. Furthermore, the Onuki–Doi theory relating the scattering dichroism to the structure factor has been verified experimentally by comparing scattering dichroism calculated from scattering patterns with previous experimentally measured dichroism. Scattering dichroism, both calculated from structure factors and experimentally determined over a range of shear rates and temperatures, is demonstrated to depend only on the Weissenberg number. Relaxation of shear-enhanced fluctuations on cessation of flow allowed for the calculation of a diffusion coefficient.

Small-angle neutron scattering from deuterated polystyrene in dioctyl phthalate solution under shear

Small-angle neutron scattering measurements were taken from high molecular weight (1.95 X lo6) deuterated polystyrene in dioctyl phthalate solution at low concentration (3 % weight fraction) under steady shear with rates ranging from the quiescent condition (0 s-l) to 1100 s-l at room temperature (22 OC). The scattered intensity increased drastically beyond a characteristic shear rate (+c = 57 9-1) similar to the increase following a temperature drop from the one-phase region (ambient temperature) to the two-phase region in this upper critical solution temperature system. The cloud point is estimated to be a few degrees lower than 14 OC which is the cloud point for protonated polystyrene in dioctyl phthalate at this molecular weight and concentration. On the basis of this analogy, the random-phase approximation (RPA) approach (the Zimm inverse scattering formula) was used along with a swollen radius of gyration in the Debye function to analyze the data and extract a statistical segment length b and a polymer-solvent interaction parameter xp. The segment length was seen to increase slightly, indicating a slight increase in chain volume beyond +c, while the interaction parameter showed a dramatic increase up to the 'spinodal value +* = 280 8-1 where the RPA breaks down, therefore giving nonreliable values. This data treatment method has no justification on physical grounds: it is merely a way to quantify our observations since specific models that could explain our data are not available at this time.

Viscous finger narrowing at the coil-stretch transition in a dilute polymer solution

We present results of an experimental study of Saffman-Taylor fingers in dilute solutions of polystyrene in dioctyl phthalate (DOP). While fingers in pure DOP obey classical scaling laws, we observe transitions to narrow fingers in polysterene solutions of concentrations as low as 1 part per million. The onset of narrowing occurs at a shear rate which roughly equals the inverse of the polymer Zimm relaxation time and depends only weakly on concentration. The onset of instability occurs earlier than in Newtonian fluids and is often initiated by small-amplitude oscillations.

Viscoelastic Properties of Polymer Solutions at Temperatures Lower than _??_ Points

Zero-shear viscosity η0 and steady-state compliance Je of poly(α-methylstyrenes) in benzyl n-butyl phthalate (_??_=46°C) and polystyrene in dioctyl phthalate (_??_=22°C) were measured at temperatures lower than the _??_ points. Moreover, stress developments after onset of steady shear flow were measured and the strength of entanglement was estimated on the basis of network rupture model.The concentration and the molecular weight dependences of η0 at temperatures lower than the _??_ points are almost the same as those at the _??_ temperatures, but the magnitude of η0 increases with decreasing temperature. This suggests that the strength of entanglement increases with decreasing solvent power.On the other hand, Je values at the temperatures lower than the _??_ points are almost the same as those in good and _??_ solvents. This result indicates that the entangled structure of polymer solution effective to Je is almost independent of solvent power. Therefore, it is concluded that the gel-like behavior of polymer solution at temperatures lower than the _??_ points is caused by the long relaxation times due to the high viscosity.

Calculation of hole pressure:: II. Viscoelastic Fluids

Numerical calculations using the finite element method are reported for the pressure hole problem caused by flow between two flat plates interrupted by a slit. Predicted are the effects of flow rate and geometry for viscoelastic fluids modeling solutions of polystyrene in dioctylphthalate. Model results are compared to experimental data from the literature for corotational and codeformational differential models having one time constant, when the models are adjusted empirically to give exact shear stress and first normal stress differences in viscometric flows.

Fluid elasticity measurements from hole pressure error data

A slit die of variable height H (0.135 in., 0.1975 in., or 0.2488 in.) width W 2.5 in., and variable length Le (12.0 in., 12.5 in., or 13.5 in.) has been designed and constructed for measuring the wall shear stress σw and the hole pressure error PH. Values of PH and σw are obtained directly and rapidly on a chart recorder from three commercial pressure transducers by means of an electronic differencing technique. The reliability of PH measurements is established by the excellent agreement between viscosity η values obtained from this apparatus and a rheogoniometer and by measuring negligible values of PH for the New tonian fluid, glycerine, for σw 0 for σw ≥ 800 dyn/cm2 and values of PH < 0 for a low-elasticity solution of polystyrene in dioctyl phthalate (DOP). Values of PH are found to be independent of the distance E of the transducers from the die exit and the die height which indicated that PH is independent of the undisturbed wall pressure Pw for constant values of σw. Our values agree well with those measured by Higashitani for a similar Separan solution in a different slit die. Using this new slit die, it is shown the PH is sensitive to changes in molecular weight (MW) for a series of solutions of polystyrene in DOP and that PH could be used to monitor continuously the changes in molecular structure which occured during the mechanical degradation of a 2.0% aqueous poly(ethylene oxide) solution. The simple relation between PH and N1 (PH = −cN1, where c is a constant) is verified for solutions of polystyrene in DOP and aqueous Separan solutions over a large range of flow conditions (⋅ = 1000 sec−1). Because c is found to vary slightly with polymer type, concentration, and molecular weight, a method is presented for obtaining N1 directly from PH data.

Normal Stress Effect in Dilute Polymer Solutions. I. Polystyrene in Dioctyl Phthalate

Normal Stress Effect in Dilute Polymer Solutions. I. Polystyrene in Dioctyl Phthalate