Poly Ethylene Oxide Solutions Research Articles

Shear wave velocity anisotropy of salt- and polymer-amended kaolinite

Shear wave velocity (Vs) anisotropy of kaolinite mixed with sodium chloride (NaCl) and organic polymer (polyethylene oxide, xanthan gum, and chitosan) solutions was investigated using a custom-made floating wall consolidometer-type bender element testing system. The addition of salt and polymers influenced the microfabric anisoopy of platy kaolinite particles, thus resulted in the increment or decrement in the Vs anisotropy. The Vs of kaolinite in all three orthogonal directions increased as the NaCl concentration increased; however, the Vs anisotropy decreased. PEO and chitosan increased the Vs of kaolinite, while xanthan gum exhibited counter-effects. Vs anisotropy (Vs−hh/Vs−vh and Vs−hv/Vs−vh) of polymer amended kaolinite was found to decrease. In addition, both salt- and polymer-modified kaolinite did not show Vs cross-anisotropy.

Special Features of Nonlinear Behavior of a Polymer Solution on Large Periodic Deformations

Study of the behavior of polymer solution flows in the region of nonlinear viscoelasticity allows one to more accurately evaluate the adequacy of rheological models and to describe the rheological properties of a material in more detail. The nonlinear viscoelastic properties manifesting themselves in the process of studying the behavior of a polymer material on significant deformations were investigated with the aid of time dependences of shear stresses calculated at different amplitudes. The present work considers the applicability of the modified Vinogradov–Pokrovskii rheological model to describing the oscillating shearing of polymer fluids with a large amplitude. It has been established that on increase of the deformation amplitude, the shear stresses cease to be a true harmonic, and one observes the appearance of a "step" on their left front, which speaks of the substantial nonlinearity in the behavior of the sample. The obtained theoretical dependences are compared with experimental data for a 5% solution of polyethylene oxide in dimethyl sulfoxide. The comparison was made as by plotting the time dependences of normalized stresses, so by analyzing Lissajous figures. Despite the simplicity, the modifi ed Vinogradov–Pokrovskii rheological model adequately describes the behavior of polymer materials on significant periodic deformations.

Simultaneous measurement of rheological properties in a microfluidic rheometer

Microfluidic rheometry is considered to be a potential alternative to conventional rheometry for the rheological characterization of viscoelastic solutions having relatively low viscoelastic properties. None of the microfluidic platforms introduced so far, however, can be used for the measurements of multiple rheological properties in the same device. In this work, I present the first microfluidic platform, named the “μ-rheometer,” which allows for the simultaneous measurement of zero-shear viscosity η0 and longest shear relaxation time λ. This is achieved by transforming the original “flow rate controlled” platform presented by Del Giudice et al., “Rheometry-on-a-chip: Measuring the relaxation time of a viscoelastic liquid through particle migration in microchannel flows,” Lab Chip 15, 783–792 (2015) into a “pressure drop controlled” microfluidic device, by replacing a syringe pump with a pressure pump. The novel device has been tested by measuring both η0 and λ for a number of polyethylene oxide solutions in glycerol–water 25 wt. % and pure water, respectively. Its effectiveness has been corroborated by means of a direct comparison with a conventional rotational rheometer.

Development and Characterization of Electrospun Nanostructures Using Polyethylene Oxide: Potential Means for Incorporation of Bioactive Compounds

The development of processes for stabilization of the properties of bioactive compounds has been studied in recent years, and the use of nanotechnology is among the most discussed routes. The present work addressed the assembly of nanostructures using polyethylene oxide (PEO), the production of core-shell nanofibers (NFs) with bioactive compounds, and the evaluation of their microscopic and physical characteristics. Aqueous solutions of PEO were electrospun by varying different process and solution parameters (PEO and NaCl concentrations, feeding rate, the tip-to-collector distance (TCD), and applied voltage) in order to optimize production of nanostructures. The best condition obtained was evaluated to form core-shell NFs composed by jussara pulp as a source of anthocyanins. To assess the production of NFs with PEO and jussara pulp, feed solutions were prepared in acetate buffer (pH 4.5) with 6% PEO and 10% lyophilized jussara pulp, at a feeding rate of 150 μL·h−1 and TCD of 15 cm using an applied voltage of 10 kV to form core-shell NFs. The results revealed the formation of core-shell NFs with a diameter of 126.5 ± 50.0 nm. The outcomes achieved represent a crucial step in the application of anthocyanins in food systems as pigments, establishing a basis for further research on the incorporation of nanomaterials into foodstuff.

Experimental study on different behaviors of spheres entering water and PEO solution

We conducted an experimental study on the formation of cavity and splash crown during the impact of superhydrophobic and hydrophilic spheres on water and polyethylene oxide solution (non-Newtonian liquid). We investigated the influences of falling speed of spheres on splash crown and cavity formation. In particular, we focused on the evolution time of splash and cavity when spheres with different contact angles fall into different liquids under various speeds and the different behavior of splash curtain. Results show that sphere contact angle and liquid viscosity have a great effect on cavity formation. The increase in contact angle and liquid viscosity induces cavity formation. However, viscosity has a certain inhibitory effect on crown evolution. The faster the falling speed is, the shorter the splash crown’s evolution time, but the greater the volume will be. A pinch-off model of cavity has a great impact on the formation of “Worthington jet.”

Early transition, relaminarization and drag reduction in the flow of polymer solutions through microtubes

Experiments are performed to investigate the onset of early transition and drag reduction in the flow of polymer (polyacrylamide and polyethylene oxide) solutions through rigid microtubes of diameters in the range 0.49–2.84 mm. We measure friction factor variation with Reynolds number for varying polymer concentrations and tube diameters, and the Reynolds number, , at which the experimental data deviate from the laminar value represents the onset of transition. Crucially, owing to the high shear rates encountered in our experiments, we show that it is important to account for shear thinning of the fluid in the theoretical estimation of the friction factor in the laminar regime. We accomplish this using a Carreau model, and show that the use of laminar friction factor calculated without shear thinning leads to an erroneous overestimation of . The obtained from friction factor data in the present study is in good agreement with that inferred using micro particle image velocimetry analysis in Chandra et al. (J. Fluid Mech., vol. 844, 2018, pp. 1052–1083). For smaller concentrations of the added polymer, there is a marginal delay in the onset of turbulence, but as the concentration is increased further, the transition Reynolds number decreases much below , the usual value at which transition occurs in Newtonian pipe flows. Thus, the present study further corroborates the phenomenon of early transition leading to an ‘elasto-inertial’ turbulent state in the flow of polymer solutions. For concentrations such that there is a delay in transition, if is maintained above the for Newtonian fluids, the flow is transitional or turbulent in the absence of polymers. At such a fixed , if the concentration of the polymer is increased gradually, the friction factor decreases and the flow relaminarizes. With further increase in polymer concentration, the flow undergoes a transition due to elasto-inertial instability. The effect of addition of small amounts of polymer on turbulent drag reduction in the flow of water through microtubes is also investigated. Increase in polymer concentration, molecular weight and decrease in tube diameter causes an increase in drag reduction. The friction factor data for different polymer concentrations, molecular weights, tube diameters and , when plotted with , show a reasonable collapse, where is the Weissenberg number defined as the product of the longest relaxation time of the polymer solution and the average shear rate in the tube and is the ratio of solvent to total solution viscosity. Interestingly, the onset of the maximum drag reduction asymptote, for experiments using varying tube diameters and polymer concentrations, appears to occur at .

Experimental Analysis of the Extensional Flow of Very Weakly Viscoelastic Polymer Solutions.

We study with ultra-high-speed imaging the thinning of the filament formed during the breakup of a pendant droplet of very weakly viscoelastic polymer solutions of polyvinylpyrrolidone (PVP) and polyethylene oxide (PEO). In the latter case, we consider two molecular weights: g/mol (PEO100K) and g/mol (PEO2M). The results allow us to measure with high reproducibility extensional relaxation times of the order of 10 s. Despite the noticeable differences between PVP and PEO100K, very similar values are obtained for the range of concentrations where the linear elasto-capillary is established. For PEO2M, the extensional relaxation time depends on the concentration even for values significantly smaller than the overlap one. The prediction for the concentration below which the linear elasto-capillary regime cannot be reached qualitatively agrees with the results for PVP and PEO2M, while it underestimates the critical concentration for PEO100K. The results for PEO2M are consistent with those reported in the literature for higher concentrations.

Microfluidic shear rheology and wall-slip of viscoelastic fluids using holography-based flow kinematics

In this study, we report microfluidic shear rheology and wall-slip using the 3D-resolved flow kinematics obtained from digital holography microscopy (DHM). We computationally reconstruct the recorded holograms to visualize the tracer imbued flow volume in linear microchannels, followed by the implementation of particle tracking velocimetry (PTV) to quantitate spatially resolved velocity fields in 3D. In order to select optimal parameters for DHM-PTV characterization of viscoelastic fluids, we studied the effect of the hologram recording distance, seeding density, and particle size. Using the optimal parameters, we show quantitative characterization of the shear rheology from the velocity fields without any a priori assumptions of wall boundary conditions or constitutive equation. The viscosity vs shear rate data for Newtonian and polyethylene oxide (PEO) solutions could be measured in the range of ≈0.05 to 20 000 s−1 with just three input pressures using sample volumes as low as 20 µl. These data from holographic shear rheometry were found to be in good agreement with computational fluid dynamics simulations and macrorheometry. With respect to the wall-slip, we find that highly viscoelastic PEO solutions can show slip lengths in the order of few microns. Finally, we discuss holographic visualization of particle migration in microfluidic flows, which can limit flow field access, whereas at the same time provide a fingerprint of the suspending fluid rheology.

Electro-osmotic flow of electrolyte solutions of PEO in microfluidic channels

HypothesisWe investigate if the shear-stress exerted on the wall of a glass microchannel can be a robust and accurate criterion for the safe electro-osmotic transfer of polyethylene oxide (PEO) chains dissolved in a NaCl aquatic solvent. To this end, a comprehensive multiscale formulation based on the rheological and electrochemical modeling of the PEO dynamics is proposed. Phenomena that occur in microscale, e.g., the migration of PEO to the core region of the channel and Polymeric Depletion Layer (PDL) formation, and in nanoscale, e.g., the development of an electric double layer on the glass surface and ionic steric effects, are included. Experimental arrangementWe study the electro-osmotic flow of PEO solutions (0.1–0.5%), flowing in a glass microchannel of rectangle shape, with dimensions of 300 μm in length and 75 μm in height. We vary the externally applied electric field (300–500 V/cm), and the bulk ionic concentration (0.001–10 mM). FindingsWe find that all features of our formulation are indeed essential to reproduce the experimental data of Huang, Chen, Wong, Liow, Soft Matter, (2016) precisely. Although the PDL formation preserves the fragile nature of biopolymers, the dominant stress is the normal stress, and the critical value is at the PDL interface. A new design criterion for microdevices is proposed.

Coil-Uncoiled Chain Transition of Polyethylene Oxide Solutions under Convergent Flow

Coil-Uncoiled Chain Transition of Polyethylene Oxide Solutions under Convergent Flow

Elastic instabilities in the electroosmotic flow of non-Newtonian fluids through T-shaped microchannels.

Electroosmotic flow (EOF) has been widely used to transport fluids and samples in micro- and nanofluidic channels for lab-on-a-chip applications. This essentially surface-driven plug-like flow is, however, sensitive to both the fluid and wall properties, of which any inhomogeneity may draw disturbances to the flow and even instabilities. Existing studies on EOF instabilities have been focused primarily upon Newtonian fluids though many of the chemical and biological solutions are actually non-Newtonian. We carry out a systematic experimental investigation of the fluid rheological effects on the elastic instability in the EOF of phosphate buffer-based polymer solutions through T-shaped microchannels. We find that electro-elastic instabilities can be induced in shear thinning polyacrylamide (PAA) and xanthan gum (XG) solutions if the applied direct current voltage is above a threshold value. However, no instabilities are observed in Newtonian or weakly shear thinning viscoelastic fluids including polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), and hyaluronic acid (HA) solutions. We also perform a quantitative analysis of the wave parameters for the observed elasto-elastic instabilities.

Effect of polyethylene oxide on flotation of molybdenite fines

The processing of low-grade deposits of molybdenite is becoming more urgent with the gradual depletion of high-grade molybdenite ores in China. Low flotation efficiency has been suffered due to finer sizes liberation resulted from finely disseminated nature of low-grade ores and crystal anisotropy. In this study, kerosene was used to collect the molybdenite fines with different sizes, but even high dosage of kerosene could not achieve high flotation recovery for molybdenite particles with finer sizes. However, the presence of polyethylene oxide (PEO) considerably increased the flotation efficiency of molybdenite. The mechanism of PEO effect on the molybdenite flotation was studied by molecular dynamics simulation, Atomic Force Microscopy (AFM), Focused Beam Reflectance Measurement (FBRM), etc. Molecular dynamics calculation shows PEO molecules were more susceptible to (010) plane than (001) plane, thereby promoting the adsorption of PEO on the finer molybdenite particles. The wettability results indicate molybdenite particles become more hydrophobic in the presence of PEO, especially for the edge planes. Thereby the attachment time between bubbles and molybdenite particles reduced significantly. Moreover, in PEO solution, larger attractive forces were detected between molybdenite surfaces at >100 nm, agreeing with the rapid formation of large flocs in the molybdenite suspension. Thus, PEO not only improves the surface hydrophobicity but also induces the flocculation of fine particles, both of which improve the flotation performances of molybdenite fine particles.

Experimental and theoretical investigation of the fluid behavior during polymeric fiber formation with and without pressure

The fabrication of polymeric micro/nanofibers is gaining attention due to their use in an array of applications including tissue engineering scaffolds, nanosensors, and fiber-reinforced composites. Despite their versatile nature, polymeric fibers are widely underutilized due to the lack of reliable, large-scale production techniques. Upon the discovery of centrifugal spinning and, recently, pressurized gyration techniques, new research directions have emerged. Here, we report a comprehensive study detailing the optimal conditions to significantly improve the morphology, homogeneity, and yield of fibers of varying diameters. A series of polymeric fibers was created using a 21 wt. % solution of polyethylene oxide in distilled water and the fluid behavior was monitored inside a transparent reservoir using a high-speed camera. Fabrication of the fibers took less than 1 s. Using centrifugal spinning, we studied the formation of the fibers at three different rotational speeds, and for pressurized gyration, one rotational speed was studied with three different nitrogen gas pressures. Using the pressurized gyration technique at a gas pressure of 0.3 MPa, there was significant improvement in the production yield of the fibers. We found a strong correlation between the variation of pressure and the rate of the solution leaving the reservoir with the improved morphology of the fibers. The use of reduced power techniques, like centrifugal spinning and pressured gyration, to yield high-quality nonwoven nanofibers and microfibers in large quantities is important due to their use in rapidly expanding markets.

Strain shifts under stress-controlled oscillatory shearing in theoretical, experimental, and structural perspectives: Application to probing zero-shear viscosity.

Rheological measurements in which the applied stress or strain is oscillated are widely used to interrogate viscoelastic properties due to the independent control over the time scale and length scale afforded by changes in amplitude and frequency. Taking a nontraditional approach, we treat stress-controlled oscillatory tests as creep tests with transiently varying stress and apply an analysis typically used for steady creep and recovery experiments. Defining zero strain as the state prior to external shearing, it is shown that strain responses to small-amplitude oscillatory stressing are naturally shifted from the starting point by an amount proportional to the phase of the applied stress. The phenomenology is experimentally observed with entangled polymerlike micelles and polyethylene oxide solutions. A theory of strain shifting in the steady alternating state is provided based on recovery rheology, where differences between total strain and recoverable strains are acknowledged. User-controlled variables, such as the amplitude of the stress, the angular frequency, and the phase of the stress, as well a lone material parameter, the zero-shear viscosity, are shown to dictate the amount of shifting. A rapid and efficient approach of determining the zero-shear viscosity is, therefore, presented. We investigate the microstructural evolution via in situ small-angle neutron scattering when strain shifting appears. The microscopic orientation is shown to correlate to the recoverable strain independent of the shifting. Additional measurements are carried out on collagen, pluronic-hyaluronic acid, alginate gels, and polystyrene melts to show the generic nature of the strain shift phenomenon. In addition, we demonstrate that the strain-shift knowledge can be applied to determine the horizontal shift factor in time-temperature superposition, free of any numerical fitting procedures.

Gamma Irradiated Synthesis of Polyethylene Oxide (PEO)-N, N-Dimethyacrylamide (DMA) Hydrogel and Chitosan

Hydrogel which can swell rapidly and retain large volumes of water in their swollen structure have shown a significant contribution for wound healing. More recently, hydrogel synthesized by radiation polymerization and grafting have been reported which did not require any crosslinking agent. In this study, Crosslinked Poly ethylene oxide (PEO) / N, N-dimethylacrylamide (DMA) hydrogel containing chitosan for wound dressing has been prepared by gamma radiation technique. Chitosan solutions with different concentration (0.5-1.5%,10%) have been blended with 5% aqueous solution of Poly ethylene oxide, N, N-dimethylacrylamide and irradiated at the doses 5-20 kGy by gamma rays. The copolymers were characterized by Fourier transform infra-red spectroscopy and their physical chemical properties of hydrogels were evaluated in terms of gel fraction, swelling ratio, elongation at break and mechanical properties (tensile Strength). It was found that under maximum condition of incorporation 1% chitosan with irradiation dose of 10 kGy, Poly ethylene oxide - N, N-dimethylacrylamide -chitosan hydrogels with high gel fraction (80%), swelling ratio (4152%) and elongation at break (110%) were obtained.

Electrokinetic instability in microchannel viscoelastic fluid flows with conductivity gradients

Electrokinetic instability (EKI) is a flow instability that occurs in electric field-mediated microfluidic applications. It can be harnessed to enhance sample mixing or particle trapping but has to be avoided in particle separation. Current studies on EKI have been focused primarily on the flow of Newtonian fluids. However, many of the chemical and biological solutions exhibit non-Newtonian characteristics. This work presents the first experimental study of the EKI in viscoelastic fluid flows with conductivity gradients through a T-shaped microchannel. We find that the addition of polyethylene oxide (PEO) polymer into Newtonian buffer solutions alters the threshold electric field for the onset of EKI. Moreover, the speed and temporal frequency of the instability waves are significantly different from those in the pure buffer solutions. We develop a three-dimensional preliminary numerical model in COMSOL, which considers the increased viscosity and conductivity as well as the suppressed electroosmotic flow of the buffer-based PEO solutions. The numerically predicted threshold electric field and wave parameters compare favorably with the experimental data except at the highest PEO concentration. We attribute this deviation to the neglect of fluid elasticity effect in the current model that increases with the PEO concentration.

Viscoelastic focusing of polydisperse particle suspensions in a straight circular microchannel

Flow cytometry is a technique for the analysis of cells and particles by coupling a sheath flow assisted focusing microfluidic device to an optical or electrical reader. In this context, polymer solutions can be employed to drive particle and cell focusing on the centreline of simple straight microfluidic channels. However, the change of the focusing efficiency due to polydispersity, which is a rule rather than the exception across cell populations, has not been extensively studied yet. In this work, the effect of particle polydispersity on the viscoelastic focusing in a straight cylindrical microchannel was studied by preparing two particle suspensions, containing different concentrations of particles with average diameters of 10,upmu hbox {m}, 15,upmu hbox {m} and 20,upmu hbox {m}, suspended in three solutions of polyethylene oxide with mass concentrations of 0.1 wt%, 0.25 wt% and 0.5 wt%. When the fluid explored the constant-viscosity region of the rheological curve, up to 95% of the particles were aligned on the channel centreline. When the fluid explored the shear-thinning region of the rheological curve, centreline focusing efficiency decreased, with the highest value of aligned particles being of 60%. For both mixtures, it was also observed that the fraction of aligned particles in a polydisperse system was not equivalent to that derived from the estimate of independent experiments with monodisperse particles.

Viscoelastic liquid curtains: experimental results on the flow of a falling sheet of polymer solution

We experimentally investigate the extensional flow of a sheet – or curtain – of viscoelastic liquid falling freely from a slot at constant flow rate under gravity. Extruded liquids are aqueous solutions of flexible polyethylene oxide (PEO) and of semi-rigid partially hydrolysed polyacrylamide (HPAM) with low shear viscosities. Velocimetry measurements reveal that the mean velocity field$U(z)$(where$z$is the distance from the slot exit) does not reduce to a free fall. More precisely, we show that the liquid falls initially with sub-gravitational accelerations up to a distance from the slot which scales as$g\unicode[STIX]{x1D70F}_{fil}^{2}$(where$g$is gravity and$\unicode[STIX]{x1D70F}_{fil}$is the extensional relaxation time of the liquid) due to the stretching of polymer molecules. Beyond this elastic length, inertia dominates and the local acceleration reaches the asymptotic free-fall value$g$. The length of the sub-gravitational part of the curtain is shown to be much larger than the equivalent viscous length$((4\unicode[STIX]{x1D702}/\unicode[STIX]{x1D70C})^{2}/g)^{1/3}$for Newtonian liquids of density$\unicode[STIX]{x1D70C}$and dynamic viscosity$\unicode[STIX]{x1D702}$which is usually small compared to the curtain length. By analogy with Newtonian curtains, we show that the velocity field$U(z)$rescales on a master curve. Besides, the flow is shown to be only weakly affected by the history of polymer deformations in the die upstream of the curtain. Furthermore, investigations on the curtain stability reveal that polymer addition reduces the minimum flow rate required to maintain a continuous sheet of liquid.

Evaluation of Abuse-Deterrent Characteristics of Tablets Prepared via Hot-Melt Extrusion.

In this study, the effect of formulation variables and process parameters on the abuse-deterrent (AD)characteristics of a matrix tablet manufactured using hot-melt extrusion (HME) was investigated. The formulation variables included polyethylene oxide (PEO) grades and its input level, while the HME process parameters varied were barrel temperature profile and die diameter. Depending on the diameter of the extrudate (2.5mm or 5.0mm), two different downstream processes were used to prepare the tablets: cryo-milling followed by compression for the 2.5mm extrudate, and cutting followed by compression for the 5.0mm extrudate. A D-optimal statistical design was used to evaluate the impact of formulation and process parameters on various responses, including tablet physical strength, particle size after manipulation, syringeability and injectability, solution viscosity, extractability in solvents, and dissolution rates. It was found that the post-HME extrusion processing method played a critical role in affecting the AD characteristics of abuse-deterrent formulations, likely through changing the tablet compactability and porosity. When the extrudates were cryo-milled-compressed, the tablets could be readily manipulated by milling, which led to high degree of extractability. Under high alcohol concentration, burst drug release was observed for the tablets compressed from cryo-milled extrudates. Additionally, heat exposure during HME process caused significant drop in PEO solution viscosity, likely due to thermal degradation.

Experimental research on the characteristics of drag reduction and mechanical degradation of polyethylene oxide solution

ABSTRACT Polymer drag reduction agents are easy to degrade during application. The drag reduction and mechanical degradation characteristics of polyethylene oxide were investigated in this research. A rotating disk apparatus evaluated the influence of molecular weight, concentration, temperature, mechanical degradation, and ultrasonic degradation. The experimental results showed that drag reduction property was influenced by the molecular formation, flow regime, and concentration. Rotating disk apparatus is similar to test circular system regarding reduction rate measurement for polyethylene oxide, where the rotating velocity was affected by the Reynolds number. The increase in temperature is not favorable for the drag reduction of polyethylene oxide, because of the more cluster formation caused by molecular motion strengthening. Simultaneously, polyethylene oxide with bigger molecular weight and hydraulic volume would show lower optimum concentration than smaller molecular weight. Also, the mechanical and ultrasonic degradation of polyethylene oxide solution were investigated. Due to the external transfer induced by free radical reaction energy, the polyethylene oxide with bigger molecular weight and longer chains are more likely to degrade, showing bad drag reduction effect.