Mechanism Of Polymer Adsorption Research Articles

Optimisation of orthophosphate and turbidity removal using an amphoteric chitosan-based flocculant–ferric chloride coagulant system

Environmental contextThe fate and build-up of phosphate nutrients in aquatic environments is an urgent environmental problem affecting global water security. This study, guided by a statistical design method, optimises the flocculation properties of a biopolymer for removing orthophosphate from water. This improved technology has potential widespread applications for removal of orthophosphate from water and wastewater treatment systems. AbstractA coagulation-flocculation process was employed to remove turbidity (Ti) and orthophosphate (Pi) in aqueous media using a ferric chloride (FeCl3) and a grafted carboxymethyl chitosan (CMC) flocculant system. The amphoteric CMC-CTA flocculant was synthesised by grafting 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA) onto the biopolymer backbone of CMC. Here, CMC-CTA denotes the covalent grafting of CTA onto CMC. Optimisation of the variables for Pi and Ti removal was conducted using a jar test system based on the experimental design obtained from the response surface methodology (RSM). The Box–Behnken design was used to evaluate the individual and interactive effects of four independent variables: CMC-CTA dosage, FeCl3 dosage, pH and settling time. The RSM analysis showed that the experimental data followed a quadratic polynomial model with the following optimal conditions: [CMC-CTA]=3.0mgL−1, [FeCl3]=10.0mgL−1, pH 6.8 and settling time=35min. Optimum conditions led to a Pi removal of 96.4% and turbidity removal of 96.7% based on the RSM optimisation, in good agreement with experimental results with an initial concentration of 30.0mg PiL−1. The coagulation-flocculation process is characterised by a combination of electrostatic charge neutralisation, polymer bridging and a polymer adsorption mechanism.

Mechanism of polymer adsorption on shale surfaces: Effect of polymer type and presence of monovalent and divalent salts

This paper studies the adsorption behavior of representative guar-based polymers onto the surface of source rock outcrop samples to provide a better picture of the interaction(s) of polymers with these rocks. Outcrop samples from the Barnett, Eagle Ford, and Marcellus shales were collected, analyzed for mineralogy and total organic content, and then exposed to different polymer solutions under elevated temperature and moderately elevated pressure. Viscosities of these polymer solutions were measured before and after exposure to the rock samples to establish a correlation between polymer adsorption and rock mineralogy and/or organic content. Results indicate a direct correlation between polymer adsorption and both rock mineralogy. Cationic polymers are shown to be more prone to adsorption onto the surface of the rock than non-ionic polymers. The results from this work establish that fluid-rock interactions are significant and that further research regarding shale polymer interactions and its effects on hydrocarbon production is needed with representative downhole shale samples given the trends now shown with outcrop samples.

Impact of adsorption of poly(aspartic acid) and its copolymers with polyethylene glycol on thermal characteristic of Cr2O3

The polymer structure impact on the adsorption layer conformation formed on the chromium (III) oxide surface was investigated. As adsorbates, three macromolecular compounds were tested: poly(l-aspartic acid) homopolymer and two block copolymers containing the poly(amino acid) segments as well as the poly(ethylene glycol) ones in the chain structure. Due to the ionic nature of the poly(amino acid), all measurements were carried out as a function of solution pH value. The most probable polymer chain binding mechanism was determined on the basis of the values obtained from the adsorption, potentiometric titration, turbidimetry and thermogravimetry experiments. The acquired results indicate that the solution pH has a great influence on the adsorbed macromolecule conformation. Additionally, in the case of the block copolymers, the individual structural unit affinity for the solid particles can be modified by the pH changes. Therefore, a significant difference in the mass decrement measured for the systems at pH 3 and 10 can be explained by the contribution of electrostatic forces and hydrogen bond formation to the polymer adsorption mechanism. Structure of the adsorbed polymer layer determines also the suspension stability. The solid surface charge neutralization by the macromolecules bound to the Cr2O3 surface at pH 3 impairs the sample stability, whereas the presence of the extended polymer chains in the basic solution leads to the durability improvement.

Synthetic polyacrylamide as a potential flocculent to remove commercial chromium(III) oxide from aqueous suspension

The effects of solution pH and cationic group contents in polyacrylamide (PAM) macromolecules on the polymer adsorption mechanism on chromium(III) oxide surface were studied. The structure of PAM adsorption layer was also characterized to explain the changes in solid suspension stability. The following methods were applied: turbidimetry, spectrophotometry, potentiometric titration and microelectrophoresis. Thanks to them, the stability of the Cr2O3–polymer systems, polymer-adsorbed amount, surface charge density and zeta potential of solid particles were determined. The experimental results indicate that adsorption of cationic PAM increases with the rising pH. The larger the content of cationic groups in PAM chains is, the higher the adsorption level is observed. The most effective chromium(III) oxide removal is achieved at pH 9 after addition of PAM with the largest content of cationic groups (i.e. 80 %). The neutralization of solid surface negative charge by positively charged polymer chains (assuming more coiled conformation) is responsible for this.

Experimental Study and Modeling of Boundary Lubricant Polyelectrolyte Films

Strongly adsorbed polyelectrolytes are central in the conditioning properties of many personal care products. Whereas the mechanism of polymer adsorption is rather well understood, less is known about the actual mechanism of polyelectrolyte lubrication. We investigated the adsorption on mica and the lubricant properties of a strong polyelectrolyte, poly(diallyldimethylammonium chloride), polyDADMAC, in aqueous solutions of different salt concentrations. We found that the adsorption of the polymer was enhanced and the morphology of the adsorbed layer modified by increasing salt concentration. The lubricant properties of the adsorbed polyelectrolyte layer were good at low compressions but rapidly deteriorated at larger applied pressure. A complex velocity dependence of the friction was observed, with a maximum value at intermediate velocities and hysteresis in an acceleration/deceleration cycle. A progressive increase in separation between the rubbing surfaces with velocity was also observed. We developed a...

Impact of anionic and cationic polyacrylamide on the stability of aqueous alumina suspension—comparison of adsorption mechanism

In the present study, particular emphasis was put on the effects of the type of functional groups of anionic and cationic polyacrylamide (PAM) and solution pH on the mechanism of polymer adsorption on the surface of dispersed alumina. The polymer-adsorbed amount, surface charge density and zeta potential of solid particles without and with PAM, as well as the stability of Al2O3 suspension containing the polymer, were determined. For this purpose, the spectrophotometry, potentiometric titration, microelectrophoresis and turbidimetry were applied. It was shown that adsorption of anionic PAM decreases with the pH rise, whereas in the case of cationic PAM, it increases. High adsorption level is a result of more coiled structure of adsorbed macromolecules. The anionic PAM has greater impact on the suspension stability deterioration in comparison to the cationic polymer in the whole range of studied pH values. The more pronounced effect of alumina suspension destabilization in the anionic PAM presence was obtained at pH 6, at which solid surface charge neutralization occurs.

Influence of the solid type on the adsorption mechanism of nonionic polymers in the metal oxide/water solution system—temperature effect

Abstract The main purpose of the study was to determine the effect of adsorbent type (surface characteristics and pore size) on nonionic polymers adsorption mechanism on the solid surface in the temperature range 15–40 °C. Polyethylene glycol (PEG) and polyvinyl alcohol (PVA) were used in the experiments as adsorbates. The following metal oxides were applied: aluminum (III) oxide, silicon (IV) oxide, zirconium (IV) oxide and controlled porosity glass (CPG). Polymer adsorption mechanism and structure of its adsorption layer at the metal oxide-aqueous solution interface were proposed based on the data obtained from the techniques: spectrophotometry, viscometry, microelectrophoresis and potentiometric titration. They allowed the determination of the amount of adsorbed polymer, the linear dimensions of polymer chains in the solution, the thickness of the polymer adsorption layer, the free energy of polymer adsorption and the surface charge density of the adsorbent in the absence and presence of PEG and PVA. It was indicated that the polymer adsorption on the metal oxide surface increases with the rise of temperature. It is caused by conformational changes of adsorbing macromolecules expressed in the increase of linear dimension of polymer chain. Such specific conformation of the macromolecular compound influences the structure of its adsorption layer. Both PEG (containing only hydroxyl groups) and PVA (containing 2% of acetate groups besides hydroxyl ones) show the smallest adsorption on the silica surface. In the case of the other examined oxides, polymers demonstrate different behavior. PEG adsorption is the greatest on the CPG surface, whereas PVA is the highest on the zirconia surface. It can be caused by various pore sizes of the applied metal oxides whose adsorbing PEG and PVA chains are able to penetrate or not (depending on a macromolecule diameter).

Understanding the Role of ω-End Groups and Molecular Weight in the Interaction of PNIPAM with Gold Surfaces

Modification of nanoparticle surfaces by adsorption or grafting of polymers allows fine control of hybrid materials properties for diverse applications. To obtain such a control, it is of paramount importance to understand the impact of the polymer structure on the nature and strength of its interaction with the nanoparticle. We investigated here a simple model of hybrid materials made of poly(N-isopropylacrylamide) of different molar masses and end groups interacting with gold surfaces. A series of poly(N-isopropylacrylamide) with number-average molar masses ranging from 3700 to 10000 g·mol–1 were synthesized by reversible addition–fragmentation chain transfer/macromolecular design by interchange of xanthates (RAFT/MADIX). The terminal xanthate group was then reduced into either a thiol or a hydrogen group. Quartz crystal microbalance adsorption/desorption experiments demonstrated that the polymer termini have a strong impact on the mechanism of polymer adsorption on flat gold surfaces. These differences in polymer structure have, in return, a strong influence on the colloidal stability and growth mechanism of nanoparticles when directly synthesized in polymer solution. For those properties, the effect of xanthate group compared very favorably to the conventional thiol moiety. Interestingly, the properties of nanohybrids were poorly affected by the molar mass of the polymer.

Adsorption of a Low-Molecular-Weight Polyacrylic Acid on Silica, Alumina, and Kaolin

Polyelectrolytes are often used to prepare highly concentrated dispersions of particles of heterogeneous surfaces of controlled viscosity and stability. However, there is not a satisfactory understanding of the adsorption mechanism of polymers on the surface of heterogeneously charged particles such as kaolin. A systematic investigation of the interaction of silica, alumina, and kaolin, with Na–polyacrylic acid (PAA) polyelectrolyte was performed by conducting adsorption experiments and employing attenuated total reflection infrared spectroscopy (FTIR/ATR) techniques. Adsorption studies indicate that the adsorption density of Na–PAA on the surface of kaolin is considerably smaller than that on alumina particles and there is no indication of adsorption of PAA on the surface of silica particles. FTIR/ATR experiments confirmed that there are specific interactions between PAA and the surface of alumina and kaolin particles as the adsorption bands are shifted to higher wavenumbers.

Grafting γ-aminopropyl triethoxysilane onto silica: consequence on polyacrylic acid adsorption

A set of silica samples with various surface density of amine functions was prepared by grafting γ-aminopropyl triethoxysilane from carbon tetrachloride solutions. The surface concentration of APS grafted molecules was determined by a solution depletion method, whereas the irreversibility of grafting was checked by infrared measurements in solution as well as at the solid surface. The adsorption of a polymer and its representative monomer (polyacrylic acid and propionic acid, respectively) on these grafted samples were studied as a function of grafting density, by determining adsorption isotherms and adsorption enthalpies (by microcalorimetry). The surface concentrations of both molecules are strongly enhanced at the saturation plateau when the grafting density is increased. At high grafting density and intermediate coverage of the surface by the polymer, non-equilibrium phenomena are observed. At saturation, as shown by adsorption enthalpy measurements, the fraction of polymer units belonging to trains seems weakly modified. A mechanism of polymer adsorption is proposed.

Use of organic polymers in the flotation of polymetallic ores: A review

Organic polymers are used in flotation for a wide range of oxides, silicates and industrial minerals as dispersants, depressants and as flocculants. Most of the investigations with polymers were conducted in this area and theories were advanced to explain the mode of adsorption on non-metallic mineral surfaces. In the area of sulphide flotation, polymers have found only limited application, although there is a great potential for the application of polymers in the selective separation of sulphide minerals. The use of polymers in sulphide flotation was not studied extensively and consequently, there are few reliable data available to explain the adsorption mechanism of polymers on sulphides. Published data on the use of polymers in flotation of sulphide minerals is reviewed in the following sections.

Adsorption Mechanism(s) of Poly(Ethylene Oxide) on Oxide Surfaces

Adsorption of poly(ethylene oxide) (PEO) on various oxides and the flocculation behavior of PEO-coated particles was investigated to elucidate the polymer adsorption mechanism(s). It was determined that strong Bronsted acid sites on the surface interact with the ether oxygen of PEO, a Lewis base, to induce adsorption and subsequent flocculation of the substrate particles. In general highly acidic oxides of the type MO3, M2O5, and MO2are expected to adsorb and flocculate with PEO. Accordingly, MoO3, V2O5, and SiO2were found to strongly adsorb PEO and exhibit flocculation. On the other hand, no significant adsorption was observed on oxides with a point of zero charge (pzc) greater than that of silica such as TiO2, Fe2O3, Al2O3- and MgO thereby indicating specificity of PEO–surface bonding site interactions. The other possible mechanisms of PEO adsorption such as complexation with adsorbed ions and electrostatic interactions with a positively charged surface were found not to play a major role in the PEO adsorption onto oxide particles. In this investigation, the adsorption and flocculation behavior of oxides with PEO and the underlying adsorption mechanism(s) are discussed.

Investigation of the Mechanism of Polymer Adsorption on a Metal Oxide/Water Solution Interface

The results of investigations of polymer adsorption in dispersed solid/water solutions of a polymer are presented. Poly(vinyl alcohol) (PVA), polyacrylamide (PAM) and poly(acrylic acid) (PAA) were used as polymers and TiO2, Fe2O3, Al2O3 and polystyrene latex as adsorbents. All measurements were conducted with fractionated commercial polymers. Analysis of the experimental and theoretical data obtained proved that of the three kinds of structures created during macromolecule adsorption, i.e. trains, loops and tails, tails play the main role in determining the thickness of the adsorption layer.

The Mechanism of Flocculation of Coal Particles by Polyethyleneoxide

The flocculation of coal (anthracite) suspension by a high molecular weight polyethylene oxide (PEO) has been studied and the results correlated with the adsorption of PEO at the coal/water interface. The effects of pH, inorganic salts, H-bonding agents, methylation and oxidation on the adsorption and flocculation behaviour have been determined. The mechanism of polymer adsorption would appear to be through hydrophobic interactions between the -CH2- groups in the polymer molecule and the coal surface. However, the small decrease in polymer adsorption obtained in the presence of H-bonding competitors suggests that H-bonding may have a minor role in the adsorption process.

ADSORPTION OF POLYVINYL ALCOHOL ON COTTON AND POLYESTER FIBERS

Adsorption onto cotton and polyester fibers of two kinds of polyvinyl alcohols (PVA) having different amount of residual acetyl group is investigated. PVA-iodine complex method is applied for the determination of PVA concentration. The shapes of adsorption isotherms for these two PVA's at 40°C are clearly different. The amount of adsorbed PVA-I, having no residual acetyl group, is saturated once at lower concentration level and then increases linearly with the concentration in solution. While, that of PVA-II, having 20mol% of residual acetyl group, is saturated at certain low concentration without further increase. The adsorption behavior depends on the amount of residual acetyl group of PVA but not on the kind of fibers.Equilibrium adsorption constant k and the amount of saturated adsorption x∞ calculated from these adsorption data, as well as specific surface area obtained from N2-adsorption data in B. E. T. method, were discussed to elucidate the polymer adsorption mechanism.

Adsorption of Macromolecules from Solution

Abstract This publication arranges published papers on adsorption of polymers with special regard to experiment and theory. A summary is given of all investigated systems. Experimental methods are outlined and amounts adsorbed are discussed as a function of the system and experimental parameters (polymer, adsorbent, solvent, molecular weight, concentration, time, and temperature). Calculated and experimental amounts for saturation, number of contact points per molecule adsorbed, thickness of the adsorbed layer, adsorption isotherms, heats of adsorption, and effects of desorption are compared. Assumptions are made and discussed as to the structure of the adsorbed layer and the mechanism of polymer adsorption.