Adsorption Of Polyacrylic Acid Research Articles

Development of a mineralogical matrix at the adsorption of polyelectrolytes on soil minerals and soils

The formation of the adsorption layers of polyelectrolytes (PEs) with the development of a mineralogical matrix on the surface of soil minerals and soils (kaolinite, montmorillonite, quartz sand, gray forest soil, and a chernozem) were established on the basis of direct measurements and IR spectroscopy. The differences in the adsorption kinetics of polyacrylamide (PAM) and polyacrylic acid (PAA) were revealed depending on the mineral nature, which were confirmed by the calculated values of the effective adsorption constants. It was found that the limit values of the PAM and PAA adsorption derived from experimental measurements for all the minerals were significantly higher than the values calculated for the formation of a monomolecular layer, which indicated adsorption on the surface of not only separate macromolecules but also secondary PE structures such as packets or fibrils. The IR spectroscopy studies confirmed the differences in the adsorption mechanism of PEs on soil minerals (from physical adsorption to chemisorption with the formation of surface compounds due to polar groups of PEs and surface groups of mineral particles). As a result, a cluster-matrix structure controlling the physicochemical properties of the modified surface was developed on the surface of natural aluminosilicates and soils.

Enhanced stability of polyacrylate-coated magnetite nanoparticles in biorelevant media

Magnetite nanoparticles (MNPs) were prepared by alkaline hydrolysis of Fe(II) and Fe(III) chlorides. Adsorption of polyacrylic acid (PAA) on MNPs was measured at pH=6.5±0.3 and I=0.01M (NaCl) to find the optimal PAA amount for MNP stabilization under physiological conditions. We detected an H-bond formation between magnetite surface groups and PAA by ATR-FTIR measurements, but bonds of metal ion–carboxylate complexes, generally cited in literature, were not identified at the given pH and ionic strength. The dependence of the electrokinetic potential and the aggregation state on the amount of added PAA at various pHs was measured by electrophoretic mobility and dynamic light-scattering methods. The electrokinetic potential of the naked MNPs was low at near physiological pH, but PAA adsorption overcharged the particles. Highly negatively charged, well-stabilized carboxylated MNPs formed via adsorption of PAA in an amount of approximately ten times of that necessary to compensate the original positive charge of the magnetite. Coagulation kinetics experiments revealed gradual enhancement of salt tolerance at physiological pH from ∼0.001M at no added PAA up to ∼0.5M at 1.12mmol/g PAA. The PAA-coated MNPs exert no substantial effect on the proliferation of malignant (HeLa) or non-cancerous fibroblast cells (MRC-5) as determined by means of MTT assays.

Dipole potential as a driving force for the membrane insertion of polyacrylic acid in slightly acidic milieu

In this work, we report on the interaction of polyacrylic acid with phosphatidylcholine bilayers and monolayers in slightly acidic medium. We found that adsorption of polyacrylic acid on liposomes composed of egg lecithin at pH 4.2 results in the formation of small pores permeable for low molecular weight solutes. However, the pores were impermeable for trypsin indicating that no solubilization of liposomes occurred. The pores were permeable for both positively charged trypsin substrate N-benzoyl-l-arginine ethyl ester and negatively charged pH-indicator pyranine. Two lines of evidence were obtained confirming the involvement of the membrane dipole potential in the insertion of polyacrylic acid into lipid bilayer. (i) Addition of phloretin, a molecule which is known to decrease dipole potential of lipid bilayer, reduced the rate of a polyacrylic acid induced leakage of pyranine from liposomes. (ii) Direct measurements of air/lipid monolayer/water interface surface potential using Kelvin probe showed that adsorption of polyacrylic acid at pH 4.2 induced a decrease in both boundary and dipole potential by 37 and 62mV for ester lipid dioleoylphosphatidylcholine (DOPC). Replacement of DOPC by ether lipid 1,2-di-O-oleyl-sn-glycero-3-phosphocholine (DiOOPC) which is known to form monolayers and bilayers with only minor dipole component of membrane potential showed that addition of PAA produced similar response in the boundary potential (by 50mV) but negligible response in dipole potential of monolayer. These observations agree with our assumption that dipole potential is an important driving force for the insertion of polyacids into biological membranes.

Self-localization of polyacrylic acid molecules on polar ZnO(0001)–Zn surfaces

The adsorption of single polyacrylic acid (PAAc) molecules was investigated on stepped hydroxide-stabilized polar ZnO(0001)-Zn surfaces using atomic force microscope (AFM) topography and force distance spectroscopy. Stepped surfaces of ZnO(0001)-Zn were prepared by a wet chemical etching procedure and PAAc molecules were adsorbed from aqueous NaClO(4) solutions. AFM single molecule topography studies could be utilized to show that polyacrylic acid molecules specifically adsorb on the non-polar (10-10) step edge faces at low ionic strengths. The radius of gyration of the dissolved PAAc in aqueous solution was measured by means of static light scattering experiments yielding a radius of gyration of R(g)=136 nm at pH 7.4 in 50 mM NaClO(4)/NaOH solution, which is in good agreement with the size of the adsorbed PAAc molecules as measured using AFM. The obtained results could be rationalized in terms of binding-site configurations at step edges and the effect of the chemical environment on both local electric double layer charge and molecular conformation of the PAAc molecules. The point of zero charge of the ZnO(10-10) surface was measured with chemical force microscopy to be pH(PZC)=10.2 ± 0.2. The specific adsorption of polyacrylic acid at non-polar ZnO step-edges can be explained by coordinative bonds formed between the carboxylic acid group and the Zn-surface atoms. On the hydroxide stabilized polar surface only weak hydrogen bonds can be formed in addition to van-der-Waals forces. Thus a "diffusion and trapping" mechanism keeps the adsorbed PAAc molecules mobile on the ZnO(0001)-Zn surface terraces due to small interaction forces until they are trapped at the (10-10) step faces by stronger coordinative bonds from the carboxylic groups to zinc atoms located in the first atomic layer of the crystal structure.

Temperature effect on adsorption properties of silica-polyacrylic acid interface

The temperature influence on the adsorption mechanism of anionic polyacrylic acid (PAA) macromolecules on the silica surface was studied. For this purpose, the following techniques were applied: spectrophotometry, thermogravimetry, potentiometric titration and microelectrophoresis. This method allowed to determine the adsorbed amounts of polymer, changes in thermal characteristic of silica surface with adsorbed PAA, surface charge density of the solid as well as zeta potential of SiO2 particles in the presence and absence of polyacrylic acid. All measurements were carried out in the temperature range 15-35 °C. The free energies of adsorption were calculated from the adsorption data fitted by the Langmuir model. The obtained results of increase of PAA adsorption and its adsorption free energies with the rising temperature suggest that adsorbed polymer conformation changes from the coiled structure to more stretched one. Moreover, the polymer adsorption on the silica surface at 25 °C leads to changes in the course of thermogravimetric curves as a result of surface properties modification of the solid by bonded macromolecules.

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

Molecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects.

Interaction and dispersion stability of alumina suspension with PAA in N,N′-dimethylformamide

The alumina suspension in N,N′-dimethylformamide (DMF) was studied in the presence of a polyacrylic acid (PAA) dispersant. The sedimentation measurements of the suspensions show that PAA can impart favorable dispersion stability to alumina in DMF over a wide apparent pH (pH a) range. The adsorption of PAA on alumina and the zeta potential of the suspension are pH a dependent. FTIR-ATR spectroscopic studies reveal that the different interaction mechanisms between PAA and alumina work as a function of pH a. But the observable difference of dispersion between pH a values of 2.6–12.7 is small according to the sedimentation experiments. This can be explained by a combination of the static effect of PAA dispersant and different sizes of steric barrier resulting from the configurational variation of PAA with changing pH a values.

Influences of polyacrylic acid adsorption and temperature on the alumina suspension stability

The temperature influence on the alumina (Al 2O 3) suspension stability in the absence and presence of polyacrylic acid (PAA) was studied. The investigated temperature range was 15–35 °C. Stability measurements were carried out by the use of Turbiscan Lab Expert with a thermostatic system. Additionally, at 25 °C the suspension stability was determined from the spectrophotometric data. The obtained data and calculated values of Turbiscan Stability Indexes (TSI) suggest that for the alumina suspensions without polymer, the values of TSI and the rates of solid particles settling as well as the thickness of sediment were the lowest at all investigated temperatures. Moreover the PAA adsorption causes pronounced decrease of system stability at 15 and 35 °C while at 25 °C polyacrylic acid adsorption slightly improves the alumina stability. The conformational changes of adsorbed polymer macromolecules are responsible for such behaviour of the investigated systems. At all investigated temperatures the solid suspension is not stable in the presence of PAA. In the case of PAA 2 000 the coagulation by charge neutralization takes place, whereas in the case of PAA 240 000 the bridging flocculation is the most probable process. The destabilization of systems by the adsorbed polymer occurs with the lowest effectiveness at 25 °C.

Adsorption and thermodynamic properties of the alumina–polyacrylic acid solution system

Free energies of polyacrylic acid (PAA) adsorption (ΔG ∘) on an alumina (Al 2O 3) surface in the temperature range 15–35 °C were estimated on the basis of adsorption–desorption measurements of the inorganic radioactive ions 36Cl, 45Ca, and 55Fe. Adsorbing polymer macromolecules caused the desorption process of previously adsorbed radioactive ions. The free energy of Ca-PAA surface complex formation (ΔG ∘) was estimated to be close to the free energy of Ca 2+ ions adsorption (polymer causes about 50% desorption of these ions). Moreover, a free energy of polymer molecule adsorption increase with the increasing temperature was observed. The obtained values of ΔG ∘ were compared with those calculated from the adsorption data. Additionally, the amount of polymer adsorbed and the thicknesses of polymer adsorption layers were determined in the temperature range 15–35 °C. The changes of polymer chain conformation with the temperature increase are responsible for the increase of PAA adsorption as well as thickness of polymer adsorption layers in the studied temperature range.

Comparison of the influence of a kind of electrolyte and its ionic strength on the adsorption and electrokinetic properties of the interface: Polyacrylic acid/MnO 2/electrolyte solution

The influence of a kind of electrolyte and its ionic strength on the adsorption of polyacrylic acid (PAA) 2000 and 60 000 on the surface of manganese dioxide (MnO 2) was measured. As background electrolytes NaCl, KCl, CaCl 2 and MgCl 2 were used. It was proved that PAA adsorption amount is the highest in the presence of CaCl 2 in comparison to PAA adsorption amount in the presence of other electrolytes. Polyacrylic acid adsorption amount increases with the increase of electrolyte ionic strength in all measured systems. The influence of a kind of electrolyte and its ionic strength on the zeta potential in the presence of polyacrylic acid of different concentrations was also measured. It was observed, that the zeta potential of MnO 2 is higher when CaCl 2 is used as a background electrolyte in comparison to the zeta potential of MnO 2 in the presence of NaCl or KCl. What is more, the zeta potential of MnO 2 increases with the increase of ionic strength for all measured systems. Potentiometric titrations of MnO 2 suspensions in the presence of polymer and chosen electrolyte prove the large impact of polymer presence on MnO 2 surface charge density. Other factors which also have the influence on the surface charge density are: a kind of used electrolyte and its ionic strength. Free energies of PAA adsorption in the presence of different electrolytes and ionic strengths were also calculated.

Investigation of the Effect of Temperature on the Structure of the Polyacrylic Acid Adsorption Layer at a Controlled Porosity Glass/Polymer Solution Interface

The influence of temperature on the structure of polyacrylic acid (PAA) adsorption layers on the surface of controlled porosity glass (CPG) was studied. For this purpose, adsorption, surface charge, zeta potential and viscosity measurements were carried out over the 15-35°C temperature range. The amounts of adsorbed polymer and the thickness of the polymer adsorption layer increase with increasing temperature. This is caused by conformational changes in the polymer macromolecules with increasing temperature, changing from a coiled structure at lower temperature to a more stretched structure at higher temperature. The free energies of the PAA segments adsorbed onto the CPG surface at 25°C were calculated from the adsorption data. Decreases in the charges on the surface and diffuse layers of CPG particles were observed in the presence of PAA. On the basis on these data, proposals have been made regarding the main factors causing the changes in the zeta potential and surface charge of CPG in the presence of ...

Adsorption of anionic polyelectrolyte and comb polymers onto lead magnesium niobate

This paper presents the results concerning the adsorption mechanism of polyacrylic acid (PAA) and polyacrylic acid/polyethylene oxide (PAA/PEO) comb polymer onto lead magnesium niobate (PMN) powders. In the study adsorption behavior of PAA and PAA/PEO onto PMN surface were determined in aqueous solutions and the influence of pH and ionic strength was investigated. Results showed that adsorption of PAA or PAA/PEO increased with decreasing pH of the suspensions. The increase in the ionic strength or the presence of divalent cations caused an increase in the adsorption of both polyelectrolytes. It was observed that the adsorption reaches a maximum when PAA is fully complexed in solution. On the other hand, the increase in the adsorption of PAA/PEO onto PMN in the presence of monovalent or divalent salt was attributed to the decrease in the electrostatic forces rather than complex formation with the divalent metal ions in solution. Turbidity measurements showed that there is no complex formation between the divalent metal ions and PAA/PEO comb polymers due to shielding effect of the PEO teeth.

Adsorption of PAA on the α‐Al2O3 Surface

The specific system of interest is the polyacrylic acid (PAA) and (0001) α‐Al2O3 surface, which was modeled and simulated by Cerius2 4.9 software with empirical potentials. The simulation predicted that the adsorbed conformations of PAA with a molecular weight (Mw) of 5000 were train and tail at pH <4 and >10, respectively. After gradually inserting additional PAA molecular chains, the adsorption reached a saturated amount. Gel permeation chromatography experimental results showed that the adsorption amount at pH 3.6 was three times greater than that at pH 11. Based on the results from simulations and experiments, a successively increasing pH environment was modeled to illustrate the possibility of optimizing electro‐steric effects by combining the higher adsorption density at a lower pH and strong steric repulsion of tail‐adsorbed configuration at a higher pH.

Influence of Temperature and Purity of Polyacrylic Acid on its Adsorption and Surface Structures at the ZrO2/Polymer Solution Interface

The influence of temperature and the effect of the purity of polyacrylic acid (PAA) on its conformation on the zirconium oxide surface were studied. Spectrophotometric measurements, potentiometric titrations, electrokinetic and viscosity measurements allowed the determination of the amounts of polymer adsorbed, the surface charge and the zeta potential of solid particles in the absence and presence of the polymer together with the thickness of the polymer adsorption layers. All measurements were carried out over the temperature range 15–40°C.The occurrence of a minimum in the adsorption of PAA between 25–30°C was caused by conformational changes of the polymer macromolecules. For non-filtered PAA, a decrease in polymer adsorption and an increase in the thickness of the adsorbed polymer layers were observed. These result from changes in the polydispersity index of filtered PAA and the blocking of some active sites on the oxide surface by inorganic contamination present in the non-filtered PAA samples.The f...

Influence of the ionic strength on the adsorption properties of the system dispersed aluminium oxide–polyacrylic acid

The influence of ionic strength, pH of the solution and molecular weight of polyacrylic acid (PAA) on its adsorption and the electrical double layer (Al2O3/polyelectrolyte solution) properties have been examined. The measurements show that the adsorption increases with increasing ionic strength and molecular weight of the polymer, whereas the increase in pH reduces the adsorption. The thickness of the PAA adsorption layer onto aluminium oxide and the expansion coefficient were also calculated. The increase in ionic strength, pH of the solution and polymer molecular weight causes an increase in adsorption layer thickness and expansion coefficient of PAA.

Influence of polymer functional group architecture on titania pigment dispersion

The influence upon adsorption of polymers containing different functional groups on the dispersion behaviour of titania pigment particle has been investigated at pH 6.0 and 9.5. The polymers chosen are polyacrylic acid and modified polyacrylamides including homo and copolymers modified with carboxylate and/or hydroxyl groups. A range of experimental methods including polymer adsorption isotherms, zeta potential, rheology and particle size measurements were used to assess the dispersion effect of the polymers. Adsorption of polyacrylic acid and anionic polyacrylamide copolymers onto the titania pigment surface is greatest when electrostatic repulsion is absent. At low pH values, below the pigment isoelectric point (iep), the adsorption density of the anionic polymers on titania pigment was high whilst at higher pH values, above the pigment iep, the adsorption density decreased. However, the adsorption of non-ionic polymers on titania pigment was less influenced by the pH. The presence of carboxylate functional groups in both polyacrylic acid and anionic polyacrylamide copolymer altered the titania pigment dispersion behaviour, reducing the suspension yield stress and mean particle size. The polyacrylamide homopolymer had negligible effect on the pigment dispersion properties at pH 9.5, while it caused pigment particle aggregation at pH 6.0. The hydroxyl-modified polyacrylamide had also a de-stabilisation effect on the pigment dispersion at pH 6.0, but decreased the yield stress and the mean particle size at pH 9.5. The stabilisation effect of both anionic and non-ionic polymers was pH-dependent. The dispersion properties of the pigment particles are largely predicted by DLVO theory.

Dispersion of alumina-coated TiO 2 slurries in the presence of poly(acrylic) acid influence of monovalent counterions

The rheological behavior of concentrated alumina-coated TiO 2 slurries has been investigated in connection with the type of surface counterions (monovalent cations: X = Li +, Na +, TMA +) in the absence and in the presence of polyacrylic acid (PAA). The study has been conducted in a pH range of 4–10 and with ionic strengths lower than 0.01 M. The pH and ionic strength were adjusted with XOH and XCl, respectively. The surface properties have been investigated by titration of surface counterions and the apparent yield stress has been measured using a dynamic stress rheometer. It appears from the results that the pH at the maximum yield stress and the magnitude of the yield stress depend on the nature of the counterion. The yield stress measurements were also conducted in the presence of PAA (0.5 segment/nm 2) adsorbed on the particle surface. In that case, the mineral surface and adsorbed polymer were neutralized with XOH. The results show that the dispersion efficiency depends on the polymer counterion. In general, it is found that the maximum yield stress and the corresponding counterion surface density both follow the sequence TMA + < Na + < Li +. The adsorption of PAA apparently amplifies the effects observed with the corresponding cation. An electrostriction effect of the hydration layer at the interface is suggested in order to explain the increasing yield stress as the surface density of Li + increases. The so-called structure-making/structure-breaking model explains the yield stress reduction with the TMA + surface density.

Adsorption of polyacrylic acid on self-assembled monolayers investigated by single-molecule force spectroscopy

Single-molecule force spectroscopy was used to study the adsorption and desorption processes of individual polyacrylic acid (PAA) chains from self-assembled monolayers (SAMs) with different terminal groups (CH3, OH, COOH). PAA was grafted to the tip of an AFM cantilever and all measurements were recorded with the same tip. For the OH- and the COOH-SAM, the desorption force was found to be independent of the salt concentration for NaCl, as well as for CaSO4. On CH3-SAM, a repulsive electrostatic interaction was found with NaCl in solution whereas a slightly attractive electrostatic interaction occurred with CaSO4 in solution. On the OH- and the COOH-terminated SAM, the non-electrostatic contributions to the desorption forces are of comparable magnitude (∼50–65 pN) whereas the non-electrostatic contribution for the CH3-terminated SAM is significantly higher (∼80–90 pN). Additional experimental findings concerning the length, the total number of adsorption events and the number of multiple polymer strands adsorbed in parallel, support the assumption that this difference in adsorption force is due to a different quality of the solvent for the polyacrylic acid chains at the SAM–water interface. Comparative surface pressure measurements at the air–water interface revealed a surface energy for polyacrylic acid of 30 mJ m2 which would correspond to a force contribution of ∼10 pN to the desorption force. This is in good agreement with the experimental results on hydrophobic SAMs. For further characterization of the surfaces the pH was varied from 3 to 11 at constant salt concentration (for a NaCl concentration of 100 mM and a CaSO4 concentration of 5 mM, respectively). In the presence of NaCl, the desorption force was found to be independent of the pH for all three substrates. For CaSO4, the desorption force was pH-independent for the OH- and the CH3-SAM. In the case of the COOH-SAM, a jump from 60 to 90 pN was recorded at pH 8, which we attribute to the formation of salt bridges between the polyacrylic acid chain and the COOH-SAM at higher pH.

Influence of the acid–basic character of oxide surfaces in dispersants effectiveness

Physical–chemical surface character has been described as a determinant factor in adsorbing polyelectrolytes onto oxide surfaces. Since basically composed by hydroxyl groups, the acidity or basicity induced by the bulk lattice in such groups seems to be of great relevance in the adsorption process. The influence of such properties in the adsorption of polyacrylic acid derivated polymers onto SnO 2 and Al 2O 3 surfaces is, therefore, studied in this paper. Polyacrylate acid molecules are observed to hardly adsorb onto the SnO 2 surface but strongly adsorb, as reported previously, onto the alumina surface. This behavior is explained based on the pronounced difference in relation to the acidity of both surfaces and, in this sphere of thought, a basic polymer (Chitosan; CS) is discussed as a functional dispersant for powders with acid surface character, such as SnO 2. Zeta potential measurements showed that this polymer raises the SnO 2 potential to +30 mV without pH variations.

Application of the SAXS method and viscometry for determination of the thickness of adsorbed polymer layers at the ZrO 2–polymer solution interface

The authors studied the influence of the molecular weight of polyacrylic acid (PAA) and polyacrylamide (PAM), solution pH and ionic strength, and the background electrolyte type on adsorption and the thickness of polyelectrolyte adsorption layers formed on ZrO 2 surface. Carboxyl groups distributed along PAA and PAM chains were shown to be responsible for their interface conformation, which directly influences the thickness of the adsorbed polyelectrolyte layers. Bonding of macromolecules with solid surface occurs through the hydrogen bridges of these groups. Two methods were applied to determine the PAA and PAM adsorption layer thickness on ZrO 2, i.e., SAXS (small angle X-ray scattering) and viscometry. Despite some limitations of the SAXS method resulting from the relationship between the size of solid pores, polymer molecular weight, and conformation of the adsorbed macromolecule, all obtained SAXS results were very close to those calculated from viscometry data.