Aqueous Solutions Of Polyethylene Oxide Research Articles

Spontaneous absorption of viscous and viscoelastic fluids by capillaries and porous substrates

We have developed a new technique to monitor spontaneous absorption of fluids by porous substrates. The method is based on an optical electronic measuring system providing millisecond resolution. The method capabilities are demonstrated with the example of the absorption of millimeter-size droplets of water and aqueous solutions of polyethylene oxide and polyacrylamide by capillaries. It is shown that polymer additives even in a small amount reduce significantly the rate of absorption. We have introduced a generalized Lucas–Washburn equation to account for the fluid elasticity. This equation is shown to explain the observed kinetics quantitatively without invoking adjustable parameters. We have derived a modified Bosanquet equation for the initial velocity of penetration, which accounts for the fluid elasticity. This simple formula gives a reasonable estimate of the rate of absorption of small droplets. We report visualization experiments on absorption of water and polymer solutions by sugar cubes as an example of porous substrates. Although the kinetics of droplet adsorption by porous substrates is similar to the kinetics of droplet adsorption by capillaries, the interpretation of experimental data is more complex and requires a plausible hydrodynamic model for lateral spreading in pores.

SANS study of salt induced micellization in PEO–PPO–PEO block copolymers

Small-angle neutron scattering (SANS) measurements have been carried out from the aqueous solutions of polyethylene oxide (PEO)–polypropylene oxide (PPO)–PEO block copolymers of pluronics F88 and P84 in presence of salt KCl. It is seen that the effect of addition of salt is similar to that of increasing temperature. The pluronics exist as unimers at low temperatures and their micellization takes place when the salt is added or the temperature is increased. The measurements for different salts of the lyotropic series on the above pluronic systems show that micellar structure is sensitive to the sizes of the hydrated ions of these salts.

Interfacial compositions of cationic and mixed non-ionic micelles by chemical trapping: a new method for characterizing the properties of amphiphilic aggregates

A specially synthesized arenediazonium ion bound to amphiphilic aggregates decomposes spontaneously via rate determining loss of N 2 to give a highly reactive, unselective, aryl cation intermediate. This intermediate is trapped competitively by weakly basic nucleophiles in the interfacial region of aggregates such as micelles and other association colloids. Product yields, analyzed by HPLC with UV detection, are used to estimate, simultaneously, the interfacial concentrations of a number of different nucleophiles, including water, that are commonly found at the surfaces of biomembranes and in many commercial products. Two applications of the method are discussed. First, we show that the interfacial concentrations of X − ( X=Br, Cl) increase steadily with increasing cetyltrimethylammonium halide (CTA X) and tetramethylammonium halide (TMA X) concentrations and that the interfacial concentrations of these counterions increase continuously with their aqueous phase concentrations at a constant degree of micelle ionization. Interfacial Br − and Cl − concentrations also show marked increases at their respective sphere-to-rod transitions. This steady increase in interfacial counterion concentration with increasing aqueous counterion concentration contradicts a basic assumption of the pseudophase ion exchange (PIE) model of chemical reactivity in aggregates, i.e. that the total concentrations of ions at aggregate interfaces is constant and independent of the amphiphile and salt concentrations. The consequences for the PIE model are discussed. Second, the chemical trapping reaction is used to estimate: (a) distributions of terminal OH groups of non-ionic amphiphiles in mixed non-ionic micelles composed of amphiphiles with different lengths of oligoethylene oxide chains and (b) hydration numbers of the inner layers of interfacial region next to the hydrocarbon core in these mixed micelles. Terminal OH groups distributions are well fitted by a radial one-dimensional random walk model. The average hydration number for the inner layers at 40°C is about 3, in agreement with estimates from NMR water (D 2O) self-diffusion measurements and with the hydration number of 3 for aqueous solutions of polyethylene oxide. The results suggest that the hydration states of the ethylene oxide (EO) units near the micellar core are near their minimum value. Recent and potential applications of the chemical trapping method are briefly discussed.

Spread films of polymethyl methacrylate on aqueous solutions of polyethylene oxide

Polymethyl methacrylate has been spread on a 0.1% (w/v) aqueous solution of polyethylene oxide. The near surface organisation of both polymers and the water has been determined using neutron reflectometry. Both deuterio and hydrogenous forms of both polymers were available and the reflectivity data at the lower concentration of polymethyl methacrylate investigated (1.0 mg m −2) could be interpreted using the kinematic approximation. At this lower concentration both polymethyl methacrylate and polyethylene oxide regions require a two-layer model to fit the reflectivity data. The thickness of the denser methacrylate near the water surface is 22 Å, the less dense layer further into the air phase has a thickness of 28 Å but a concentration one-tenth of the dense layer. At the higher concentration of polymethyl methacrylate (3.0 mg m −2) the near surface water layer becomes very diffuse and broad, and the full kinematic approximation could only be used for the polymethyl methacrylate reflectivity data. A two-layer model again gave the best fit to the data with thicknesses not much greater than those at the lower surface concentration, however the total concentration of polymethyl methacrylate was now much lower than that dispensed, suggesting the existence of a third layer which was so low in concentration of polymer that it contributed but little to the reflectivity. Using the optical matrix analysis method, the near surface water layer was modelled as a single very diffuse layer to which the majority of the polyethylene oxide was confined. The thickness of this uniform layer of polyethylene oxide was 37 Å, almost double the thickness of the layer at the lower polymethyl methacrylate surface concentration. No polyethylene oxide was desorbed from the interface, the surface concentration was identical for both surface concentrations of polymethyl methacrylate and of the same value as that obtained in the absence of a spread polymethyl methacrylate film.

Viscosimetric study of high molecular weight polyethylene oxide

It is well known that polyethylene oxide (PEO) type polyethers are non-ionogenic polymers and behave as electrolytically neutral in aqueous medium [1, 2]. Direct and indirect data exist, however, that PEO can specifically bond the cations of some alkaline earth and transition metals [3-6]. Since PEO is generally synthesized using a catalyst containing calcium or zinc, it may be presumed that Ca 2+ and Zn 2+ ions can be specifically bonded with the oxygen atoms of the ethylene oxide groups; consequently, the macromolecules of the polymer behave as positively charged in aqueous medium. Investigation of the IR spectra of PEO in 4.8 M CaCI2 solutions shows that Ca 2+ is really a non-indifferent ion with respect to the ethylene oxide groups [ -EO--] [7, 8]. Literature data, however, provides no direct evidence for the presence of charges directly bonded to the PEO macromolecules. The present study is a part of our investigations aimed at determining whether the macromolecules of commercially available PEO are electrically neutral in aqueous media, an issue of paramount importance in cases when PEO is used as a brightener for the electroplating of bright copper coatings. Viscosimetric measurements were used for the resolution of this problem. The choice was based on the fact that charged polymers with a flexible chain have a larger size of the chaotic (Gaussian) sphere, due to the electrostatic repellent force among the identically charged links. Aqueous solutions of polyethylene oxide produced at NEOCHIM (Bulgaria) were used for the assessments. The molecular mass of the product, determined by us viscosimetrically was 1.6 × 10 o. The basic PEO solution with a concentration 1 g dm -3 was prepared by dissolving the dry product in double-distilled water cooled down to 4°C; this was done with continuous stirring using an electromagnetic stirrer at 300 r.p.m, for 24 h. The doubledistilled water was used for all cases of further measurements. The viscosimetric measurements were carried out with a modified Hoeppler viscosimeter at shear stress S within the range 0.736-1.96 kPa at 0.24 kPa steps. The temperature of the solutions during the study was kept within the limits 20 + 0.05 °C using a water thermostat. The concentration of the investigated polymer in the solutions was changed within the range 1.0-0.1 gdm -3 and the concentration of NaC1 within the range 0.05-1.2 M. The time t required for the shift of the piston (spherical ball) at a certain distance in the test tube containing the investigated solution was measured.

Rheological behavior of concentrated calcium halophosphate suspensions

Suspensions of electrostatically stabilized calcium halophosphate particles of four unimodal sizes were studied under steady shear Couette flow conditions. The particle size ranged from 8.4 to 16.8 μm. The suspensions were prepared in an aqueous polyethylene oxide solution containing an ammonium neutralized polyacrylic acid dispersant. Shear thinning, followed by shear thickening at higher shear rates, was observed for suspensions containing either the individual unimodal fractions or their blends. The polyelectrolyte dispersant is a necessary component for shear thickening and also for reduction in viscosities below the high shear limit. At a constant total volume fraction of 0.38, the dependence of viscosity on shear rate changed with blend composition. In the shear thinning region at low shear rates, the viscosity increased linearly with decreasing median particle diameter, with no observable polydispersity effect over the range of size distribution investigated by blending the halophosphate fractions. At shear rates within the shear thickening transition, a broader size distribution significantly reduces the viscosity and delays the onset of shear thickening, even for blends containing size ratios as low as 1.64:1. A scaling analysis of the relative importance of forces acting on the particles in the shear thinning and shear thickening regimes is presented.

Effect of polyethylene oxide on gas hydrate phase equilibria

Englezos P. and Ngan Y.T., 1994. Effect of polyethylene oxide on gas hydrate phase equilibria. Fluid Phase Equilibria, 92: 271-288. Incipient phase equilibrium data for methane, ethane and propane hydrate formation in aqueous solutions of polyethylene oxide (PEO) were measured. The experiments were performed in the temperature range of 273.55–285.3 K. The range of measured incipient equilibrium hydrate formation pressures was 0.187–9.961 MPa. Aqueous polyethylene oxide solutions at 5, 15 and 25 wt.% were used. The results indicate a very weak inhibiting effect compared with the effect of electrolytes and alcohols on the equilibrium hydrate formation conditions. The measured equilibrium hydrate formation pressures were compared with the predictions from the existing gas hydrate equilibria prediction method. The data were found to be in good agreement with the predicted values.

Viscoelastic effects in patterns between miscible liquids.

Water injected into aqueous solutions of polyethylene oxide in a Hele-Shaw cell shows a wide variety of patterns as four control parameters are independently varied. Despite the strong variation of patterns, both the initial unstable length scale and the mean and standard deviation of Fourier modes of averaged late-time patterns show a smooth variation with a dimensionless number constructed from the ratio of the imposed shear time scale to the polymer-relaxation time.

Bilayer Composite Hydrogels for Corneal Prostheses

ABSTRACTA two-layer composite material composed of a thin-layer of corneal tissue and a synthetic polyethylene oxide (PEO) hydrogel is described. The material is designed to provide a suitable substrate for corneal epithelial cell growth while maintaining the desirable characteristics of hydrogels, i.e. clarity, flexibility, and ability to allow diffusive flow of nutrients. The gels are synthesized via electron irradiation induced crosslinking of an aqueous solution of PEO onto a thin layer of collagenous tissue substrate. light microscopic studies indicate that the interface between the corneal tissue and PEO gel appears well adherent with no gaps in the interface. SEM studies of the material surface show an architecture similar to that of normal corneal tissue. Surface analytical techniques were used to identify amino-acids covalently bound to the gel at the gel/collagen interface after the proteinaceous material was removed. ESCA survey scans identified the presence of nitrogen on exposed gel/collagen interfaces and amino acid labelling confirmed the presence of amino acids. ATR-IR studies identifed increased absorption for the gel collagen interfaces at 1640 cm− 1and 1540 cm−1indicative of bound amino acids.

Flow of dilute polymer solutions through curved pipes. Flow in inlet region.

Developing flows of water and dilute aqueous solutions of polyethylene oxide in an inlet region of a curved pipe have been investigated by measuring velocity distributions in the Dean number range of 150 to 1200. The flows are visualized with small nylon particles having specific gravity of 1.02 and mean diameter of about 150μm. The particles are lighted by a stroboscope and photographed consecutively. Axial and secondary flow velocity distributions in the developing flow region are obtained from the picture of the particles. In addition, pictures of secondary flows in a cross section of curved pipes are taken in that region. It has been found as a result of the measurements that the flows of dilute solutions develop with the same process as water flow in laminar flow regions, but in the turbulent flow region the developing process of dilute solutions differs from that of water flow. Furthermore, the variation of boundary layer thickness and inlet length have been derived from velocity profiles.

Laser-doppler measurements of turbulence structure in a drag-reducing pipe flow with polymer injection.

Aqueous solutions of polyethylene oxide were injected into a pipe flow through a small tube at the center of a pipe. The turbulent characteristics in drag-reducing flow with polymer injection were measured by means of a Laser Doppler Velocimeter (LDV). The experimental results were compared with measurements both in a Newtonian fluid (water) flow and in a premixed flow with 300 ppm homogeneous polymer solution. The experimental results suggested that the polymer injection caused a thickening of the buffer layer, enlargement of macroscale turbulent eddy and suppression of fine turbulent eddy. A difference in turbulent characteristics between premixed and polymer injected systems was observed in the distributions of turbulent macroscale, skewness factor and flatness factor. The enlargement of macroscale was more significant in the turbulent core region in the case of polymer injection experiments. The measurements of skewness and flatness factors showed that the low-speed fluid element caused by the ejection process passed more clearly the measuring position near the outer boundary of the buffer layer in the case of polymer injection experiments.

Study of the mechanism of degradation of aqueous solutions of polyethylene oxide and polyacrylamide in a hydrodynamic field

Degradation of aquoues solutions of PEO and polyacrylamide ina hydrodynamic field has been studied by viscometry, fall in hydrodynamic resistance, radical trap and qualitative chemical reactions. It is assumed that the bulk of the radicals forms as a result of detachment of hydrogen atoms from the carbon chain and their stabilization occurs mostly through recombination leading to the formation of intra- and intermolecular crosslinks.

Formation of particles of a new phase in dilute aqueous solutions of polyethylene oxide

A new morphological form of PEO has been found formed from dilute aqueous solutions of the polymer when concentrated: this form represents fibrillar particles with a colloidal degree of dispersity which display the properties of crystalline particles. Thus, in the PEO-water system the liquidus-2 curve exists in the ranges 0·02< c<0·06 fractions by weight and 20°< T<80°C. These particles may play an essential role in different areas of application of aqueous PEO solutions and in methods of analysis sensitive to their presence.

An experimental study of the minimum fluidization velocity in a three-phase external-loop air-lift reactor

A study of the minimum fluidization velocity of the large particles (3–6 mm) in a three-phase external-loop air-lift reactor is reported. The results show that the minimum fluidization velocity depends on particle diameter, solids loading and the properties of the liquid phase. The addition of small quantities of n-butanol or polyethylene oxide (a drag-reducing agent) markedly reduced the minimum fluidization velocity. Hysteresis behaviour in a 0.5% butanol solution was observed, i.e. two fluidization velocities were determined: the higher one to reach fluidization and the lower one to maintain it. An essentially different behaviour of 3- and 6-mm particles in water and an aqueous solution of polyethylene oxide was noticed. The fluidization velocity in the 3-mm bed was larger than in the 6-mm bed. This phenomenon, being opposite to existing two- and three-phase investigations, was considered as a consequence of the hydrodynamics of the investigated type of reactor. A simple model is used to predict the gas holdup in the riser required for fluidization. A good agreement between the predicted and experimental data was obtained.

The water structure around the chloride ion in aqueous polyethylene oxide solutions

Neutron diffraction and nuclear magnetic relaxation yield complementary information on the interaction of ions and water molecules in solution. In the present study the two techniques are used to investigate the influence of poly (ethyleneoxide) on the Cl − hydration sphere. It is concluded that the important effect of PEO on the 35Cl relaxation rate is due to the occurrence of a long correlation time rather than structural changes.

Flow of dilute polymer solutions in a two-dimensional channel. 1st report. Turbulent friction factors and velocity distributions.

Turbulent friction factors of dilute aqueous solutions of polyethylene oxide measured in a two-dimensional channel. The influence of viscoelasticity on friction loss is considered by the method of dimensional analysis and the friction factor is correlated with the Reynolds number and the Weissenberg number. Velocity distributions also are measured by using a pitot tube. It is shown that the transition layer in the flow of dilute polymer solutions becomes thicker in comparison with that of Newtonian.

Flow of Dilute Polymer Solutions Through Curved Pipes : 2nd Report, Pressure Loss in 360°Bends

Experiments on flows of water and dilute aqueous solutions of polyethylene oxide are carried out in the Reynolds number range of 103 to 5× 104. Concentration of polymer solutions is varied from 1ppm to 100ppm. The ratios of curvature radius to pipe radius, R/a, are 18.7, 34.3 and 47.3. Measured pressure distributions along a bend axis are classified in three types by their patterns. Flow property of each pattern is clarified by using the method of flow visualization. Drag reduction in a bend flow is smaller than that in a straight pipe flow. Pressure loss coefficients are correlated with the Reynolds number, the ratio of radius R/a and the Weissenberg number. The empirical formulas presented for the bend loss coefficient are useful from an engineering viewpoint.

Transient Flow Viscometry

Theoretical relations are derived between material properties and the torque measured in transient flow experiments using the parallel‐plate and the cone‐and‐plate geometries. The formulas are similar to well‐known expressions from viscometric flow theory, except in the parallel‐plate case where the differentiation with respect to edge shear rate is taken at a fixed time. Shear stress growth σ+ and shear stress relaxation σ− functions were measured for two aqueous polyethylene oxide solutions and the NBS fluid 40 using both geometries attached to a Weissenberg rheogoniometer fitted with a piezoelectric load cell and interfaced to a microcomputer. The results show that σ+ and σ− can be measured in the parallel‐plate geometry if the appropriate formulas are used to transform measured torques to material properties. Data from both geometries clearly indicate the existence of primary overshoot and undershoot and that the strain at which the primary overshoot maximum is obtained is the same for all three fluids over the range of shear rates studied.Theoretical relations are derived between material properties and the torque measured in transient flow experiments using the parallel‐plate and the cone‐and‐plate geometries. The formulas are similar to well‐known expressions from viscometric flow theory, except in the parallel‐plate case where the differentiation with respect to edge shear rate is taken at a fixed time. Shear stress growth σ+ and shear stress relaxation σ− functions were measured for two aqueous polyethylene oxide solutions and the NBS fluid 40 using both geometries attached to a Weissenberg rheogoniometer fitted with a piezoelectric load cell and interfaced to a microcomputer. The results show that σ+ and σ− can be measured in the parallel‐plate geometry if the appropriate formulas are used to transform measured torques to material properties. Data from both geometries clearly indicate the existence of primary overshoot and undershoot and that the strain at which the primary overshoot maximum is obtained is the same for all three fluid...

Flow structure of aqueous solutions of polyethylene oxide in the inlet region of short capillaries

The article presents data on the visualization of the flow of aqueous solution of polyethylene oxide (PEO) in the inlet ection of a capillary. The times of structural relaxation in solutions of PEO are evaluated.

Flow of Dilute Polymer Solutions through Curved Pipes : 1st Report, Frictional Loss in the Fully Developed Flow Region

Experiments of the flow of dilute aqueous solutions of polyethylene oxide through curved pipes with circular cross-section are carried out over the Reynolds number range of 500 to 1×104. Concentration of the polymer solution is varied from 0.5ppm to 100ppm. The ratio of the curvature radius to the pipe radius, R/a, of curved pipes is set at 16.3, 28.8 and 46.0. These fluid are found to cause frictional drag reduction under the turbulent flow condition in a curved pipe as well as in a straight pipe. Experimental values of a frictional loss are correlated with the Weissenberg number, the Reynolds number and the radius ratio R/a. The empirical formulas for the frictional loss estimation are proposed separately for both the laminar and the turbulent flow regime. It is also shown that the transition to turbulent flow depends on the Weissenberg number as well as the Reynolds number.