Adsorption Of Polyacrylic Acid Research Articles

Physical Adsorption of Polyacrylic Acid on Boron Nitride Nanotube Surface and Enhanced Thermal Conductivity of Poly(vinyl alcohol) Composites.

To fully tap into the potential of boron nitride nanotubes (BNNTs), addressing their inherent insolubility was imperative. In this study, a water-soluble polymer, poly(acrylic acid) (PAA), was employed as a surface-active reagent, using an accessible and scalable approach. The physical properties and structure of PAA-BNNT were meticulously confirmed through valuable characterization techniques, encompassing X-ray diffraction, scanning electron microscopy, Fourier-transform infrared, X-ray photoelectron spectroscopy, and thermogravimetric analysis. PAA-BNNT exhibited remarkable dispersion in water and demonstrated compatibility with the poly(vinyl alcohol) (PVA) matrix. When incorporating 30 wt % of PAA-BNNT (about 24.75 wt % net BNNT) into the PVA matrix, the thermal conductivity surged by over 21.7 times compared to pure PVA due to the uniform dispersion of high-concentration PAA-BNNT in the polymer matrix.

Robust silica-graphene oxide nanocomposite membrane for separating NaCl salt from seawater under atmospheric pressure

When graphene oxide (GO) based membranes are used to filter high concentration salt ion solutions at atmosphere pressure, flow of water molecules is easily blocked by the narrow spaces of graphene oxide membrane (GM), thus causing severely reduced permeability. To solve this problem, in this study, multilayer and composite framework membranes with multiple scale porous channels of sub-nanometer to tens of nanometers was designed and synthesized to promote effective flow of water molecules. These nanocomposite membranes were fabricated by crosslinking, condensation and self-assembly of polyacrylic acid (PAA), nanosized silica (SiO2) and GO onto nylon membrane substrates using a vacuum filtration method. Their permeance obtained using 35 g·L−1 NaCl solution at a pressure of 0.98 bar was 38.6 L∙m−2∙h−1∙bar−1, about 1400 times of that using GM only, and their average retention rate was 27 %. The mechanisms of effective salt removal using these nanocomposite membranes were identified. Firstly the nanoscale SiO2 increased the permeated flux of water by increasing the spacings and defects of GO sheets. The barrier structures and nanochannels formed by adding nanoscale SiO2 effectively block the salt ions. Finally electrostatic adsorption of GO sheets and PAA provided more ion adsorption and rejection rates using the GO sheets.

Performance influence of polyacrylic acid dispersant on nuclear grade anion exchange resin

Secondary circuit water chemistry control is vital for the safe operation of nuclear power plants. Polyacrylic acid (PAA) is used in the secondary circuit water system to reduce the fouling of the steam generator (SG) because of its good dispersion effect. However, PAA as a macromolecular organic matter possibly causes organic fouling for anion exchange resin of the water purification system and affects its performance. Some research reported that the performance of resin changes after PAA application. But it is not clear whether this change is related to PAA. In this research, the anion resins were performed for five cycles, and each cycle included batch PAA adsorption, dynamic PAA desorption and resin rinse. Results showed that NaOH solution could realize the desorption of PAA on anion resin, but desorption solution and rinse water consumption slightly increased with the cycle number. Meanwhile, residual PAA linearly increased with the cycle number, but the rate was relatively slow. Furthermore, the performance influence of PAA on anion resin was investigated. The exchange capacity and kinetic performance for anion resin slightly decreased after PAA cycle. The effluent conductivity of anion resin bed increased after PAA cycle, but it could not cause the adverse influence of sodium leakage. The contrast experiment of H2SO4 cycle showed that resin aging was the primary reason for the change of resin performance, rather than residual PAA. Within the fewer cycles, PAA and anion resin had better compatibility.

Influence of organic dispersant on nuclear grade anion exchange resin and their interaction behavior

ABSTRACT Polyacrylic acid (PAA) was used as an organic dispersant in the secondary circuit of nuclear power plants, which could interact with anion exchange resin and affect its properties in the condensate polishing treatment system. This study investigated the kinetics, isotherms, and thermodynamics characteristics of PAA adsorption on anion exchange resin. The results suggested that the inhibition of PAA adsorption on resin can be achieved by lowering the PAA concentration and temperature. In addition, the adsorption reversibility and influence of PAA on anion exchange resin were discussed. The chemical desorption agent (NaOH) can desorb 94.10% of the adsorbed PAA on resin. The physicochemical properties of anion exchange resin changed little after adsorbing and desorbing PAA. Furthermore, the interaction feature between PAA and anion exchange resin was revealed through analyzing the stoichiometry and ATR-FTIR spectra, which was partial ion exchange and most attachment. This feature caused the weak binding force between PAA and resin. Therefore, PAA was easily desorbed from the resin and the exchange capacity of resin can be restored after the chemical desorption process. In conclusion, PAA had little influence on the properties of anion exchange resin and did not cause nonreversible organic fouling.

Interactions between Nanoclay, CTAB and Linear/Star Shaped Polymers.

The influence of star-shaped (PAA-SS) and linear polyacrylic acid (PAA) with different molecular weights (high—PAA-HMW and low—PAA-LMW) on the structure of the adsorption layer, adsorption amount, electrokinetic and stabilizing properties of the PAA/CTAB/nanoclay suspensions was studied. The properties of the systems containing one of these polymers, the cationic surfactant—hexadecyltrimethylammonium bromide (CTAB) and the surface-modified nanoclay (N-SM) were analyzed using the following techniques: BET, CHN, FT-IR, ED-XRF, XRD, HRTEM, UV-Vis, tensiometry and zeta potential measurements. It was proved that PAA could be used as an effective stabilizer of N-SM. Moreover, the addition of CTAB caused a significant increase in the stability of the systems but decreased the adsorption of PAA on the N-SM surface and changed the structure of the adsorption layers. The largest stability was observed in the PAA-HMW/CTAB system. The PAA polymers and PAA/CTAB complexes adsorbed, especially on the clay surface, influenced the primary distribution of the layered sheets but kept the same basal d-spacing. The adsorption of PAA and the PAA/CTAB complexes took place mainly at the plate edges and on the contact space between the sheets. The obtained results will be used for the preparation of the PAA/CTAB/nanoclay composite for water purification.

Spindle-like-aggregating behavior of hydroxyapatite nanorods in polyacrylic acid aqueous system

The aggregating behavior of hydroxyapatite (HAP) nanorods plays a central role in the mechanism of biomimetic mineralization. In this study, the spindle-like aggregating behavior of hydroxyapatite (HAP) nanorods was studied by ultrasonically dispersing HAP in a polyacrylic acid (PAA) aqueous system. Unlike the quick aggregation and precipitation of HAP nanorods without PAA, the spindle-like primary aggregations formed herein could be suspended in water with good stability. The preferential adsorption of PAA on the side surface of HAP nanorods generated steric repulsion opposite to the van der Waals interaction in the radial direction. Accordingly, with an increase in the molar ratio of PAA[-COOH-]/HAP, the HAP nanorods showed a tendency to form spindle-like primary aggregations with decreased diameter and increased aspect ratio. The resulting aggregates possessed sufficient repulsion (steric repulsion and electric double layer repulsion) to overcome van der Waals interactions to remain suspended and dispersed. This study revealed the mechanism of aggregating HAP nanorods into spindle-like aggregates by extended Derjaguin–Landau–Verwey–Overbeek theory, including the steric stabilization mode. We believe that this study will facilitate the ordered structuring of minerals in hard-tissue mineralization processes.

Effect of AgNP distribution on the cotton fiber on the durability of antibacterial cotton fabrics

Silver nanoparticles (AgNPs) loaded on the cotton fiber can endow the fiber with good antibacterial activity, but the AgNPs on the surface of cotton fiber will leach out with the increase of washing times, which will not only greatly reduce the antibacterial properties of cotton fiber, but also cause pollution to the environment. In this paper, carboxyl groups were introduced into cotton fiber by three methods, namely selective oxidation, butane tetracarboxylic acid (BTCA) grafting and polyacrylic acid (PAA) adsorption. The silver ions (Ag+) were adsorbed on the cotton fibers through electrostatic attraction, and after reduction, the AgNPs were loaded onto the cotton fibers, and the AgNP distribution on the fiber and its effect to the washing resistance of AgNPs were studied. The results showed that the carboxyl groups can be introduced onto the cotton fibers by all the three methods, and the reaction only occurred in the amorphous region of the fibers. The selective oxidation and the BTCA grafting can introduce carboxylic groups into the interior of cotton fibers while the PAA adsorption only imports carboxyl groups on the surface of the fiber. As a consequence, AgNPs were formed inside of the cotton fiber when the selective oxidation and the BTCA grafting were employed, while AgNPs can only be loaded on the surface of the fiber by the PAA adsorption method. AgNPs inside of the fiber have high energetic adherence, resulting in silver-cotton fabric nanocomposites with strong slow-release property and long-term antibacterial ability. The fabric nanocomposites prepared by selective oxidation and BTCA grafting exhibited high AgNP retention rate and excellent antibacterial activity even after 80 washing cycles.

Influence of Magnetic Field on Adsorption of Polyacrylic Acid (PAA) on SiO2

The aim of this study was to investigate the influence the magnetic field on the adsorption of polyacrylic acid (PAA) on the silica (SiO2) surface as well as on the zeta potential of the PAA/SiO2 system. The magnetic field influences the amount of PAA adsorbed on silica. The highest adsorption of PAA was observed at pH 9 and the lowest at pH 3. This tendency is opposite to that for the adsorption of PAA on SiO2 in the absence of the magnetic field. This discrepancy occurs because magnetic field generates dipoles in the polymer macromolecules due to the presence of delocalized electrons in the ionized carboxylic groups. Consequently, the PAA molecules undergo polarization, which implies their adsorption on the negatively charged surface of silica. It was also observed that the magnetic field influences the zeta potential of the PAA/SiO2 system by changing the conformation of the adsorbed macromolecules accompanied by changes in the position of the slipping plane.

Effect of Polyacrylic Acid on Rheology of Cement Paste Plasticized by Polycarboxylate Superplasticizer.

Viscosity-enhancing agents (VEA) have been widely employed in high flowability cement-based materials, so as to ensure that no bleeding and segregation would occur. However, in most cases, interaction between VEA and superplasticizer would be unavoidable. In this study, the effect of polyacrylic acid (PAA), known as one of the most commonly used VEAs, on rheology performance of cement paste containing polycarboxylate superplasticizer (PCE), was studied. The initial fluidity was assessed with mini slump, and rheological behavior of cement paste was evaluated with rotor rheometer. Adsorption amount was examined with total organic carbon (TOC) analyzer, and the zeta potential was also tested. The interaction between PAA and PCE in the presence of calcium ion (Ca2+) was analyzed with conductivity, X-ray photoelectron spectroscope (XPS), and dynamic light scattering (DLS). The results illustrate that PAA can adsorb onto the surface of cement particles to plasticize cement paste, being similar to PCE. In the presence of Ca2+, PAA can be curled and crosslinked, as a result of the combination between carboxyl groups (COO−) and Ca2+, thereby affecting the adsorption performance and conformation behavior. It is interesting that negative impact of PAA on dispersion efficiency of PCE can be demonstrated; one reason is the reduced adsorption amount of PCE by PAA competitively adsorbing onto the cement surface, and another possible reason is the invalided PCE by adsorption of PAA. Additionally, molecular weight of PAA should be considered if being used as VEA in PCE system.

Armored Enzyme-Nanohybrids and Their Catalytic Function Under Challenging Conditions.

Synthesis and characterization of highly stable and functional bienzyme-polymer triads assembled on layered graphene oxide (GO) are described here. Glucose oxidase (GOx) and horseradish peroxidase (HRP) were used as model enzymes and polyacrylic acid (PAA) as model polymer to armor the enzymes. PAA-armored GOx and HRP covalent conjugates were further protected from denaturation by adsorption onto GO nanosheets. Structure and morphology of this enzyme-polymer-nanosheet hybrid biocatalyst (GOx-HRP-PAA/GO) were confirmed by agarose gel electrophoresis, zeta potential, circular dichroism, and transmission electron microscopy. The armored biocatalysts retained full enzymatic activities under challenging conditions of pH (2.5-7.4), warm temperatures (65°C), and presence of chemical denaturants, 4mM sodium dodecyl sulfate, while GOx/HRP physical mixtures without the armor had very little activity under the same conditions. Therefore, this novel combination of two orthogonal approaches, enzyme conjugation with PAA and subsequent physical adsorption onto GO nanosheets, resulted in super stable hybrid biocatalysts that function under harsh conditions. Therefore, this general and powerful approach may be used to design environmentally friendly, green, biocompatible, and biodegradable biocatalysts for energy production in biofuel cell or biobattery applications.

Surface nanomorphology of montmorillonite modified with polyacrylic acid

The effect of adsorption of polyacrylic acid (PAA) on the surface morphology of montmorillonite has been determined using atomic force microscopy (AFM). The analytical capabilities of this method for studying the initial stages of physicochemical transformations of the montmorillonite surface during coagulation structuring with an organic additive have been shown. It has been found that the surface structure of the original montmorillonite differs from that of the sample modified with an organic additive; the surface of the latter simultaneously contains molecular aggregates of various shapes and sizes, which depend on the suspension concentration. The surface roughness of the original and PAA-modified montmorillonite has been determined according to the derived longitudinal and transverse profiles of the samples.

Role of Cerium Oxide Surface Chemistry in Adsorption of Polyacrylic Acid in CMP Slurries

Chemical mechanical polishing (CMP) slurries formulated of cerium oxide nanoparticles (CNPs) and polyacrylic acid (PAA) are widely used in shallow trench isolation (STI) application. The critical parameter in slurry formulation is the amount of PAA which determines the extent of its adsorption on CNPs and the excess amount. The adsorption of PAA on CNPs results in a softer surface and prevents defects such as scratches on the wafer surface. The excess PAA selectively adsorbs on silicon nitride, slowing down its etching as compared to silicon dioxide.1 Therefore, the understanding of PAA adsorption on CNPs in a slurry formulation is critical to predict the CMP slurry characteristics. In previous studies the adsorption of PAA on CNPs has been widely studied;2 however there is still a lack of understanding between adsorption behavior of PAA and the interfacial properties of CNPs. Here, we have systematically investigated the PAA adsorption on ceria slurries and correlating it to the CNPs interfacial properties. Three different commercial ceria slurries were obtained having similar hydrodynamic size, but different surface area as determined using BET. The catalytic properties of CNPs is assessed from the ratio of Ce3+/Ce4+ on its surface, determined using XPS.3 The surface functionalization of CNPs is evaluated from FTIR and NMR depicting three different types of organic moieties resulting in different zeta potentials. Lattice strain and grain size are another important parameter which signifies the internal energy of CNPs. These parameters were calculated using Williamson-Hall plots obtained from the XRD curve. The adsorption isotherm of PAA on CNPs is determined by measuring the carbon content in the supernatant separated from the CNPs using centrifugation. The carbon content is measured using TOC analyzer and the amount of PAA adsorbed on CNPs is calculated by mass balance equation. 1. Ronay, M., Selective polishing with slurries containing polyelectrolytes. Google Patents: 2005. 2. (a) Saraf, S.; Neal, C. J.; Das, S.; Barkam, S.; McCormack, R.; Seal, S., Understanding the Adsorption Interface of Polyelectrolyte Coating on Redox Active Nanoparticles Using Soft Particle Electrokinetics and Its Biological Activity. ACS applied materials & interfaces 2014, 6 (8), 5472-5482; (b) Kim, S.; So, J.-H.; Lee, D.-J.; Yang, S.-M., Adsorption behavior of anionic polyelectrolyte for chemical mechanical polishing (CMP). Journal of colloid and interface science 2008, 319 (1), 48-52. 3. Pirmohamed, T.; Dowding, J. M.; Singh, S.; Wasserman, B.; Heckert, E.; Karakoti, A. S.; King, J. E.; Seal, S.; Self, W. T., Nanoceria exhibit redox state-dependent catalase mimetic activity. Chemical communications 2010, 46 (16), 2736-2738.

Adsorption of poly acrylic acid onto the surface of calcite: an experimental and simulation study.

Macromolecular binding to minerals is of great importance in the formation of biofilms, and carboxylate functional groups have been found to play a pivotal role in the functioning of these macromolecules. Here we present both fluorescence time-resolved anisotropy measurements and simulation data on the conformational behaviour and binding of a poly acrylic acid polymer. In solution the polymer exhibits a pH dependent behaviour, with a coiled conformation at a low pH and extended conformation at higher pH values. The polymer is readily adsorbed on the surface of calcite, preferring to bind in an extended conformation, with the strength of the adsorption dependent on the pH and presence of counter ions. We discuss the reasons why the calculated adsorption free energy differs from that obtained from a Langmuir isotherm analysis, showing that they refer to different quantities. The enhanced binding of the extended conformations shows the importance of flexibility in the binding of macromolecules.

Understanding the adsorption interface of polyelectrolyte coating on redox active nanoparticles using soft particle electrokinetics and its biological activity.

The application of cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in a biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. The coating of CNPs with polyacrylic acid (PAA) has increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analyzed using the change in the Gibbs free energy computed by the Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The change in Gibbs free energy was highest for CNPs coated with PAA of 250 kg/mol indicating the most stable coating. The change in free energy for PAA of 100 kg/mol coated CNPs was 85% lower than the PAA of 250 kg/mol coated CNPs. This significant difference is caused by the strong adsorption of PAA of 100 kg/mol on CNPs. Catalytic activity of PAA-CNPs is assessed by the catalase enzymatic mimetic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. This indicates that the catalase activity is also affected by the structure of the coating layer.

Comparison of adsorption affinity of polyacrylic acid for surfaces of mixed silica–alumina

The influence of solution pH (in the range 3–9) on the adsorption of polyacrylic acid (PAA) on the mixed silica–alumina surface (SA-3: SiO2 97 %–Al2O3 3 % and SA-96: SiO2 4 %–Al2O3 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.

Improving dispersibility of hafnium diboride in aqueous media using polyacrylic acid and ammonium citrate

It has been well accepted that polyacrylic acid (PAA) is an effective dispersant for metal diborides (such as ZrB2) in aqueous media. However, when dispersing HfB2 powder, the dispersing effect is reduced significantly. In this work, a second dispersant, ammonium citrate, was used to resolve this problem. It was found that a PAA–ammonium citrate binary dispersant system could effectively enhance the zeta potential, increase the PAA adsorption content, and improve the stability of HfB2. The apparent viscosities of the suspensions were also investigated. Results showed that the PAA–ammonium citrate binary dispersant system was effective for improving the dispersion of HfB2 particles in aqueous media.

Adsorption of polyacrylic acid and polyacrylamide on montmorillonite

The effect of process duration, temperature, and concentration on the adsorption of polyacrylic acid and polyacrylamide by montmorillonite is studied. It is shown that the pattern of interaction of the studied polyelectrolytes with the sorbent surface is determined by the nature of the polymers, the prevalence of acid-base sites, and the pore structure of the mineral.

Study of polyacrylic acid adsorption on the interface of hydroxyapatite – electrolyte solutions

The adsorption of polyacrylic acid (PAA) on hydroxyapatite (HAP) from HAP saturated solutions was studied in this work as a function of PAA concentration, temperature, pH and ionic strength. In all experiments, the adsorption was studied under conditions of negatively charged adsorbent and adsorbate, respectively. These conditions ensured that adsorption was not electrostatically favored. The solution composition was found to influence significantly the maximum of the adsorbed amount. In fact, the adsorption of PAA, was found to increase with ionic strength, due to the decrease of double layer thickness of HAP particles. The effect of temperature and ionic strength on the kinetics of adsorption are also reported. Adsorption isotherms obtained at 30oC were found to be Langmuirtype, while at higher temperatures they were of the Brunauer-Emmett-Teller (BET) type. The absorbed amount of PAA was found to decrease with temperature, while it increased with ionic strength. For pH values lower than 6.5, the adsorption increased while for pH between 6.5 and 9 the adsorbed amount remained almost constant.

Effect of the solid pore size on the structure of polymer film at the metal oxide/polyacrylic acid solution interface – Temperature impact

The goal of the study was to determine the effects of adsorbent type and its pore size on the polyacrylic acid (PAA) adsorption mechanism on the solid surface in the temperature range 15–40°C. The following metal oxides were applied: aluminum (III) oxide, silicon (IV) oxide, zirconium (IV) oxide and controlled porosity glass (CPG). PAA adsorption characteristics at the metal oxide-aqueous solution interface was proposed based on the data obtained from the techniques: spectrophotometry, viscometry and potentiometric titration. They allowed the determination of the following parameters: the amount of adsorbed polymer, the linear dimensions of polymer chains in the solution, the thickness of the polymer adsorption layer, as well as the surface charge density of the adsorbent in the absence and presence of PAA. It was shown, that the adsorption of polyacrylic acid on the metal oxide surface proceeds through both electrostatic and hydrogen bridge interactions. Moreover, the temperature increase leads to the increase of macromolecule size, which influences the polymer adsorbed amount and the structure of its adsorption layer. It results in the increase of polymer adsorption with the temperature rise in the case of alumina, silica and CPG. For zirconia the adsorption minimum in the temperature range 25–30°C was obtained. Such behaviour of the investigated systems is caused by various pore size of the applied metal oxides.

Stability of Colloidal Silica Modified by Macromolecular Polyacrylic Acid (PAA) – Application of Turbidymetry Method

The effect of anionic polyacrlic acid (PAA) adsorption on fumed silica (SiO2) surface on suspension stability was studied. The turbidymetry method was applied to monitor the changes in the suspension stability (using apparatus Turbiscan LabExpert with cooling module TLAb Cooler). PAA macromolecules contain dissociable carboxyl groups, therefore, all measurements were carried out at three pH values: 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the stability of the studied systems. The PAA adsorption has the greatest impact on the silica suspension stability at pH 3 (significant improvement of its stability). On the other hand, the presence of polyacrylic acid at pH 6 causes a noticeable deterioration of system stability conditions. At pH 9, polymer minimally influences the stability of SiO2 suspension.