Adsorption Of Polyethylene Oxide Research Articles

Interaction between PEO and Kaolinite in Flocculating: An Experimental and Molecular-Simulation Study

In this paper, the flocculation properties of polyethylene oxide (PEO) on kaolinite and the mechanism of adsorption on kaolinite anisotropic substrates were explored. As revealed by the experimental results, the settling rate and removal rate of kaolinite increased with increasing PEO concentration, but too high PEO concentration would cause the small particles to stabilize and become difficult to settle. Furthermore, to probe deep into the interactions between PEO and kaolinite anisotropic substrates, the morphology of adsorbed PEO, interfacial adsorption structure, and dynamic behavior of water molecules were determined by quartz crystal microbalance with dissipation (QCM-D) and molecular dynamics (MD) simulations. The adsorption amount of PEO on different mineral surfaces is in the order of kaolinite > alumina > silica, and the thickness of the adsorption structure formed by alumina is greater than that of silica. As illustrated by the MD simulation results, the adsorption of PEO reduces the concentration of water molecules attached to the kaolinite surface. The PEO forms a double-layer adsorption structure on the 001 surface, while forming a tight monolayer adsorption structure on the 001¯ surface, weakening the interaction between the surface and the water molecules. The above results demonstrate that the adsorption of PEO effectively weakened the hydration dispersion of kaolinite and promoted the agglomeration of kaolinite particles.

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.

Spectroscopic, Electrochemical and Quantum Chemical Studies for Adsorption Action of Polyethylene Oxide on Copper Surface in NaCl Solution

Abstract The adsorption action of polyethylene oxide (PEO) on copper surface in 3.5 wt.% NaCl solution was tested using electrochemical frequency modulation (EFM), atomic absorption spectrometry (AAS), UV- visible spectrometry and the morphology of copper surface was investigated by attenuated total reflectance spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Results obtained show that PEO is effective in preventing the corrosion of copper in NaCl solution. The adsorption of PEO onto copper surface was found to follow Langmuir isotherm model. ATR-FTIR, SEM and EDX spectroscopy techniques confirmed the adsorption of protective film of PEO on copper surface. Further, quantum chemical calculations were in agreement with inhibition efficiency (%I) of PEO that were obtained experimentally.

Structural and elastic properties and stability characteristics of oxygenated carbon nanotubes under physical adsorption of polymers

The importance of covalent and non-covalent functionalization approaches for modification the properties of carbon nanotubes is being more widely recognized. To this end, elastic properties and buckling behavior of oxygenated CNT with atomic oxygen and hydroxyl under physical adsorption of PE (Polyethylene) and PEO (Poly (ethylene oxide)) are determined through employing the molecular dynamics (MD) simulations. The results demonstrate that non-covalent bonding of polymer on the surface of oxygenated CNT causes reductions in the variations of critical buckling load and critical strain compared to oxygenated CNTs. Critical buckling load and critical strain of oxygenated CNT/polymer are higher than those of oxygenated CNT. Also, it is demonstrated that critical buckling load and critical strain values in the case of oxygenated CNT/polymer are independent of polymer type unlike the value of Young's modulus. It is shown that variations of Young's modulus decrease as PE adsorbed on the surface of oxygenated CNT. Moreover, the presence of oxygen atom on PEO chain leads to bigger variations of Young's modulus with weight percentage of chemisorbed component, i.e. atomic oxygen and hydroxyl. It is also demonstrated that Young's modulus reduces more considerably in the presence of PEO chain compared to PE one.

Self-Consistent Colloidal Energy and Diffusivity Landscapes in Macromolecular Solutions

We report a dynamic analysis to simultaneously measure colloidal forces and hydrodynamic interactions in the presence of both adsorbed and unadsorbed macromolecules. A Bayesian inference method is used to self-consistently obtain the position-dependent potential energy (i.e., energy landscape) and diffusivity (i.e., diffusivity landscape) from measured colloidal trajectories normal to a wall. Measurements are performed for particles and surfaces with adsorbed polyethylene oxide (PEO) copolymer as a function of unadsorbed PEO homopolymer concentration. Energy landscapes are well described by a steric repulsion between adsorbed brushes and depletion attraction due to unadsorbed macromolecules. Diffusivity landscapes show agreement with predicted short-range permeable brush models and long-range mobilities determined by the bulk solution viscosity. Lower than expected mobilities in the vicinity of overlapping depletion layers are attributed to interactions of adsorbed and unadsorbed macromolecules altering nonconservative lubrication forces.

The pivotal role of polymer adsorption and flocculation conditions on dewaterability of talcaceous dispersions

In this study, the links between interfacial chemistry, polyethylene oxide (PEO) flocculant adsorption behaviour, orthokinetic flocculation and dewatering behaviour of talc mineral dispersion have been investigated. The effect of Mg(II) ions, suspension conditioning time, solid loading, PEO dosage and shear was probed. Unflocculated dispersion of weakly charged, polydispersed talc particles at pH 7.5 displayed very poor settling rate but good sediment consolidation (∼47 wt.% solid). PEO polymer adsorption rate and density were greater at higher than lower Mg(II) ion concentration. The adsorption propensity also decreased with increasing suspension conditioning time. An inverse correlation was observed between PEO adsorption rate/affinity and settling rate where slower adsorption kinetics led to larger and faster settling flocs. At equivalent PEO dosages (e.g., 200 g polymer t −1 solid), 8 wt.% solid dispersion solid produced both superior supernatant clarity and greater sediment consolidation than the markedly faster settling, dilute (2 and 4 wt.% solid) suspensions. The influence of Mg(II) ions and conditioning time on settling rate was PEO dosage dependent, however, these factors had no noticeable effect on sediment consolidation. Dramatic enhancement of flocculated sediment compaction (from 38 to 52 ± 2 wt.% solid) was achieved in secondary dewatering under moderate shear. The results provide useful fundamental knowledge of polymer adsorption rate, adsorption affinity and interparticle bridging behaviour which underpin the flocculation and dewatering of talcaceous clay suspensions for significant improvement.

Adsorption of poly(ethylene oxide) at the air/water interface: A dynamic and static surface tension study

The adsorption of polyethylene oxide (PEO) homologues in a wide range of molecular weight (from M PEO = 200 to 10 6) at the air/aqueous solution interface was investigated by dynamic and static surface tension measurements. An approximate estimate for the lower limit of PEO concentration was given at which reliable equilibrium surface tension can be determined from static surface tension measurements. It was shown that the observed jump in the earlier published σ – lg ( c PEO ) curves is attributable to the nonequilibrium surface tension values at low PEO concentrations. The adsorption behavior of short chain PEO molecules ( M PEO ⩽ 1000 ) is similar to that of the ordinary surfactants. The estimated standard free energy of PEO adsorption, Δ G 0 , increases linearly with the PEO molecular weight until M PEO = 1000 . In this molecular weight range, Δ G 0 was found to be approximately the fifth of the hydrophobic driving force related to the adsorption of a surfactant with the same number of methylene groups. In the case of the longer chain PEOs the driving force of adsorption is so high that the adsorption isotherm is near saturation in the experimentally available polymer concentration range. Above a critical molecular weight the PEO adsorption reveals universal features, e.g., the surface tension and the surface density of segments do not depend on the polymer molecular weight.

Aging properties of semidilute aqueous solutions of polyethylene oxide seeded with silica nanoparticles

Rheological properties of semidilute aqueous solutions of polyethylene oxide (PEO) seeded with silica nanoparticles are studied as a function of aging time. The viscosity, dynamic moduli, and extensional properties of solutions of 0.5% PEO of 4milliong∕mol molecular weight seeded with 10–20 nm silica particles in concentrations of 1%, 2%, and 3% by weight are greatly enhanced by the nanoparticles. The aforementioned properties were measured every week over a period of up to 18 weeks. The degradation of rheological properties with aging time in this period is greatly reduced and, in some cases is completely suppressed, by nanoparticles. The evolution of properties of these nanosolutions is not perfectly understood but is possibly determined in a resolution of the competing effects of adsorption of PEO onto the silica with cleavage of the polymers due to oxidation and other effects at work in static samples.

Adsorption of commercial, filtrated and fractionated polyethylene oxide onto hematite

Polyethylene oxide (PEO) was purified by a filtration process and fractionation on a chromatographic column. The influence of impurities present in the polymer solutions on the adsorption of PEO 100,000 and PEO 300,000 onto synthesised hematite at pH 3, 6 and 9 was analysed. Both electrokinetical properties (surface charge density and zeta potential) and thickness of the adsorption layer (calculated from viscosity and zeta potential measurements) were also analysed. X-ray fluorescence spectroscopy was used to estimate the quality and quantity of the impurities in the polyethylene oxide solutions. The adsorption amount as well as the shape of the adsorption isotherms of PEO is significantly influenced by impurities. PEO as a non-ionic polymer does not change the surface charge density. Nevertheless, commercial PEO (non-purified) does change the surface charge density as well as shift the point of zero charge because of the presence of various impurities. Those impurities also affect the zeta potential and isoelectric point of the analysed system. The adsorption layer thickness decreases with improvement of the quality of the used polymer solution.

Effects of Polymer Bridging and Electrostatics on the Rheological Behavior of Aqueous Colloidal Dispersions†

AbstractEffects of a low molecular weight physically adsorbed polyethylene oxide (PEO) and the range of the electrostatic repulsion on the rheological behavior of silica dispersions (as a model system) has been investigated. Particular attention is given to the evolution of the rheological behavior with increasing the polymer concentration in the system and also effectiveness of the polymer as a dispersant under extreme conditions (high ionic strength). Results indicate that at small separation distances and low polymer coverage, the polymer chains are long enough to adsorb on the surface of two particles simultaneously causing bridging flocculation in the system and hence increasing the viscosity and linear viscoelastic functions of the dispersion. A significant increase was observed in the viscosity of the dispersion at salt concentrations high enough to eliminate electrostatics between the particles. Under these conditions,the viscosity of the system increased significantly when PEO was added to the dispersion showing that at high electrolyte concentrations, a neutral polymer such as PEO is not able to stabilize the system.

Adsorption of polymeric additives and their effect on the deposition of wood materials in paper production

The objective of this study is to understand how adsorbed synthetic polymers affect deposition kinetics of dissolved and colloidal wood materials. The synthetic polymers were characterised by means of static and dynamic light scattering, and their adsorption on silica was studied by means of optical reflectometry. Deposition kinetics of colloidal wood resin, compounds in model process water, as well as adsorption of anionic carbohydrates was then studied on the surface layers formed by synthetic polymers. It was found that neither wood resin nor anionic carbohydrates have affinity for adsorbed polyethylene oxide. However, wood resin deposited readily on adsorbed cationic polyacryl amides. Both polyethylene oxide and cationic polyacryl amides formed multilayers with compounds in the model process water.

Measurement of long-range steric repulsions between microspheres due to an adsorbed polymer.

We have measured the interparticle potential between pairs of micron-sized silica spheres induced by adsorbed polyethylene oxide polymer using a line-scanned optical tweezer. We found this long-range steric repulsion to be exponential over the range of energies (0.1k(B)T-5k(B)T) and polymer molecular weights (452,000-1,580,000) studied, and that the potential scaled with the polymer's radius of gyration R(G). The potential's exponential decay length was about 0.6R(G) and its range was about 4R(G), although both parameters varied significantly from one pair of spheres to another. The potential's exponential prefactor was greater than mean-field predictions.

Effect of polyethylene oxide on the viscosity of dispersions of charged silica particles: interplay between rheology, adsorption, and surface charge

In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer molecular weight, and adsorbed layer thickness at different salt concentrations (range of the electrostatic repulsion between particles) is presented and discussed. Adsorption and rheological studies were performed on suspensions of silica particles dispersed in solutions of 10−2 M and 10−4 M NaNO3 containing PEO of molecular weights 7,500 and 18,500 of different concentrations. Adsorption measurements gave evidence of a primary plateau in the adsorption density of 7,500 MW PEO at an electrolyte concentration of 10−2 M NaNO3. Results indicate that the range of the electrostatic repulsion between the suspended particles affects both adsorption density of the polymer onto the surface of the particles and the viscosity behavior of the system. The adsorbed layer thickness was estimated from the values of zeta potential in the presence and absence of the polymer and was found to decrease with decreasing the range of the electrostatic repulsive forces between the particles. Experimental results show that even though there is a direct relation between the viscosity of the suspension and the adsorption density of the polymer onto the surface of the particles, variation of viscosity with adsorption density, equilibrium concentration of the polymer, and range of the electrostatic repulsion cannot be explained just in term of the effective volume fraction of the particles and needs to be further investigated.

Use of Pyrene Spectroscopic Probes in the Study of Colloidal Systems

The interfacial behavior of polyethylene oxide (PEO) end-labeled with the often-used fluorescent probe pyrene was monitored to asess the effect of use of such hydrophobic probes on system behavior. Mixtures of labeled and unlabeled PEO were adsorbed on silica and the resulting suspension properties noted. The suspension behavior was found to be markedly different, depending on the ratio of labeled-to-unlabeled PEO employed. While it was “safe” to use pyrene probes in amounts of 3% or less for spectroscopic investigation of PEO effects, it was found that ratios equal to, or greater than, 1 : 3 produced anomalous behavior of the silica suspensions. This was manifested in the form of decreased suspension stability, as evidenced by significantly higher settling rates. Similar experiments using free pyrene revealed that these effects could be attributed to the chemical attachment of the pyrene probe to the polyethylene oxide chain. Fluorescence spectroscopy was used to simultaneously monitor the behavior of the adsorbed polyethylene oxide molecules. These results were used to explain the observed suspension behavior as a function of the labeled-to-unlabeled polymer mixing ratio. Bridging effects facilitated by hydrophobic interaction between pyrene end groups is proposed as the reason for the observed phenomena.

Effect of Adsorbed Polyethylene Oxide on the Rheology of Colloidal Silica Suspensions

The viscosity behavior of aqueous suspensions of silica particles with physically adsorbed polyethylene oxide (PEO) molecules was investigated in relation to the adsorbed layer density and concentration of nonadsorbed polymer in the suspending fluid. Adsorption studies revealed the presence of two plateaus in the adsorption isotherm, which was attributed to a change in conformation from a flat, “pancake”-type, to a more elongated “brush”-type conformation of the adsorbed polymer, where the terminal hydroxyl groups remained bound to the silica surface. Adsorption and rheological studies were performed on suspensions of silica particles of three different sizes dispersed in solutions of 0.01 M NaNO3 containing PEO of different concentrations and different molecular weights. The variation of shear viscosity with the adsorbed layer density, concentration of free polymer in the suspending media (depletion forces), and particle size are discussed. Results on the role of particle size on the viscosity of electrostatically and sterically stabilized suspensions indicate that sterically stabilized systems may be treated as hard spheres at high shear rates depending upon the adsorbed layer density and concentration of nonadsorbed polymer in the suspending media. Electrostatically stabilized suspensions may show deviation from hard sphere behavior even at high shear rates depending on the range of electrostatic repulsion between the suspended particles. Further investigation must be performed to be able to explain the difference between the behavior of electrostatically and sterically stabilized systems in terms of the deformability of the layers, i.e., “softness” of the electrical double layers around the particles as compared with the “stiffness” of the adsorbed layers of the polymer.

Solvatochromic studies on the hydrogen-bond donating and dipolarity/polarizability properties of the polyethylene oxide/silica interface

The polarity of the polyethylene oxide(PEO)/silica interface in 1,2-dichloroethane as solvent is classified by means of linear solvation energy (LSE) relationships . The properties of the bare silica particle surface and the silica/PEO interface is expressed by two terms: the dipolarity/polarizability (π*) of the interface and the hydrogen-bond donating ability (α) of the surface silanols. These terms can be defined by using the Kamlet–Taft solvent parameters α and π* as a reference system. The interfacial polarity parameters α and π* were calculated by means of correlation analyses of the energy of the UV/vis absorption maxima of the surface polarity indicators: di-cyano-bis(1,10-phenanthroline) iron II, bis-4,4′-(N,N-dimethylamino) benzophenone, and 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate when adsorbed onto the PEO/silica particle surface. The experimental values of the ET(30) parameter of the PEO/silica interface are compared with independently calculated values employing specific LSE relations derived for well-behaved regular solvents and functionalized silicas. PEO adsorption on silica causes a decrease in the value of the α parameter of the silica surface and an evident increase in the dipolarity/polarizability of the interface.

Adsorption of polyethylene oxide on surface modified silica - stability of bare and covered particles in suspension

The adsorption of poly-ethylene oxide (PEO) on modified colloidal silica and the stability of the aqueous suspension was investigated. With octanol some silanol groups at the silica surface were replaced by octylgroups. The size of the modified silica particles and the charge and chemical groups on the surface were charaterized by ultracentrifugation, photon correlation spectrometry, polyelectrolyte titration and IR spectrometry. The adsorbed amounts of polyethylene oxides of different molar mass were determined on the modified silica in water. With photon correlation spectrometry (PCS) the hydrodynamic layer thickness of the PEO layers on the particles were measured. The dependences of the layer thicknesses on molar mass of the PEO, polymer concentration and adsorption time were determined. The aggregation of the suspended PEO coated and uncoated modified silica particles was examined with PCS by the time dependence of the diffusion coefficient at different salt concentrations. The influence of molar mass and concentration of PEO as well as of the age of the dispersion was explored. The measured dependences are discussed and compared with the behavior of unmodified silica- and latex-particles.

Temperature‐dependent behavior of polyethylene oxide in papermaking suspensions

AbstractThe adsorption of polyethylene oxide (PEO) on chemi‐thermo‐mechanical pulp (CTMP), clay, and chalk suspensions was investigated at 303 and 343 K. These conditions corresponded to points below and above the critical solution temperature (CST) of a 0.005 mass % polyethylene oxide solution in the presence of 2 mol/L of KCl. The PEO adsorption on CTMP and clay particles was also studied at different initial PEO concentrations up to 50 mg/L. PEO adsorbed onto papermaking furnish particles at both temperatures, but the adsorbed amount was found to be larger above the CST in all systems. At 303 K it increased with the increase in PEO added to the system until it reached a plateau, but at 343 K it increased with the increase in PEO added in all the range of PEO concentrations up to 50 mg/L. The state of aggregation of PEO‐clay and PEO‐chalk suspensions was also studied by monitoring fluctuations in the intensity of light transmitted through the suspension. These measurements indicated a strongly temperature‐dependent aggregation. It was concluded that the entropically driven phase separation leads to enhanced aggregation, which in turn favors the retention of fiber fines and clay filler.

Surface activity and property of polyethyleneoxide (PEO) in water

We have studied the surface activity of polyethyleneoxide (PEO) by measuring the reduction of the surface tension of an aqueous solution. The surface adsorption of PEO is strongly dependent on the polymer molecular weight and the concentration. These findings are confirmed with the results of the ellipsometry measurement which provides the total adsorbed amount of the polymer. Furthermore, the changes of surface waves due to the adsorbed layers is detected by surface wave spectroscopy.

Coagulation and flocculation measurements by photon correlation spectroscopy ? colloidal SiO2 bare and covered by polyethylene oxide

With photon correlation spectrometry (PCS) the diffusion coefficients, average diameters and polydispersities of colloidal particles can be determined in dilute aqueous suspensions. In this study PCS is used to follow the coagulation and flocculation of silica particles. Electrolyte solution added to suspensions of bare particles and of particles covered with adsorbed polyethylene oxide layers induces aggregation. The rate constants of aggregation are evaluated by the second-order Smoluchowski theory with the assumptions of spherical aggregated particles and volume proportional light-scattering amplitude. Adsorbed PEO layers of molar mass lower thanMw=160000 decrease the critical flocculation concentration and the flocculation states and rate constants for bare and covered particles are the same at high electrolyte concentrations. Polymer layers of high molar mass (Mw=325000, 900000) reducved at full coverage the rate constants and stabilize the suspensions even at high electrolyte concentrations. At low coverage adsorption of high molar mass polymers results in the same values as of low molar mass PEO. The correlation between rate constants and hydrodynamic PEO layer thicknesses demonstrates the steric influence of the tails of the adsorbed macromolecules on stability and flocculation.