Interaction of sodium polyacrylate adsorbed on TiO2 with cationic and anionic surfactants

Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify the structures formed during the adsorption of sodium polyacrylate (NaPA) on charged TiO2 particles and to determine the subsequent interaction of the adsorbed polymer structure with cationic and anionic surfactants. The nature of the polymer structure was deduced from the adsorbed amount in tandem with the information obtained from monitoring the change in the relative intensity of the COO- and COOH infrared bands. In particular, it is found that the relative number of COO- and COOH groups on the polymer backbone for the adsorbed state differs from that of the same polymer in solution. This difference is due to a shift in the population of COO-/COOH groups on the polymer backbone that arises when the COO- groups bind to positively charged sites on the surface. A change in the number COO-/COOH groups on the polymer is thus related to a change in the bound fraction of polymer. It is shown that the initial NaPA approaching the bare surface adopts a flat conformation with high bound fraction. Once the bare sites on the surface are covered, the accommodation of additional polymer on the surface requires the existing adsorbed layer to adopt a conformation with a lower bound fraction. When the adsorbed NaPA is probed with a solution containing the anionic surfactant sodium dodecyl sulfate (SDS), the SDS competes for surface sites and displaces some of the bound NaPA segments from the surface, giving rise to an polymer layer adsorbed with an even lower bound fraction. In contrast, addition of a solution containing the cationic surfactant cetyltrimethylammonium bromide (CTAB) results in the binding of the surfactant directly to the free COO- sites on the adsorbed polymer backbone. Confirmation of a direct interaction of the CTAB headgroup with the free COO- groups of the polymer is provided by intensity changes in the headgroup IR bands of the CTAB.     

Colloidal stability of calcite dispersion treated with sodium polyacrylate

The stabilising action of sodium polyacrylate on colloidal dispersions of calcite has been investigated through measurement of viscosity, ion concentration and electrophoretic mobility. The dose of sodium polyacrylate was in the range 0 to 28 mg per g of calcite and the dispersions were prepared at a sodids content of 70% (by weight). The ionic strength of the dispersions, ca. 0.005 to 0.5, increased with dose. An increase in divalent ion concentration with dose was attributed to sodium polyacrylate-ion exchange.The stabilising action of sodium polyacrylate was evident from the sharp fall in viscosity observed at low levels of addition, and the invariance of this low viscosity throughout the remainder of the dose range. The stability of the dispersions at low doses was quantified by DLVO theory and attributed to electric double layer (EDL) repulsion. However, at higher doses, and with the resultant EDL compression, DLVO theory was found inadequate. Instead, recourse was made to steric stabilisation theories in order to explain the observed stability. A model was formulated to characterise the observed multilayer uptake of polyacrylate at higher doses. The steric repulsion evaluated using this model increased with dose and explained the observed higher dose stability. The stability over the dose ranges <2, 2 to 6, and >6 mg per g is best described as arising from, respectively, electrostatic, electrosteric and steric repulsions.     

Temperature influence of nonionic polyethylene oxide and anionic polyacrylamide on flocculation and dewatering behavior of kaolinite dispersions

Nonionic polyethylene oxide (PEO) and anionic polyacrylamide (PAM) flocculation of kaolinite dispersions has been investigated at pH 7.5 in the temperature range 20-60 degrees C. The surface chemistry (zeta potential), particle interactions (shear yield stress), and dewatering behavior were also examined. An increase in the magnitude of zeta potential of kaolinite particles, in the absence of flocculant and at a fixed PEO and PAM concentration, with increasing temperature was observed. The zeta potential behavior of the flocculated particles indicated a decrease in the adsorbed polymer layer thickness, while at the same time, however, the adsorbed polymer density showed a significant increase with increasing temperature. These results suggest that polymer adsorption was accompanied by temperature-influenced conformation changes. The hydrodynamic diameter and supernatant solution viscosity of both polymers decreased with increasing temperature, consistent with a change in polymer-solvent interactions and conformation, prior to adsorption. The analysis of the free energy (DeltaG(ads)) of adsorption showed a strong temperature dependence and the adsorption process to be more entropically than enthalpically driven. The polymer conformation change and increased negative charge at the kaolinite particle surface with increasing temperature resulted in decreased polymer bridging and flocculation performance. Consequently, the shear yield stress and the rate and the extent of dewatering (consolidation) of the pulp decreased significantly at higher temperatures (>40 degrees C). The temperature effect was more pronounced in the presence of PEO than PAM, with 40 and 20 degrees C indicated as the optima for enhanced performance of the latter and former flocculants, respectively. The results demonstrate that a temperature-induced conformation change, together with polymer structure type, plays an important role in flocculation and dewatering behavior of kaolinite dispersions.     

Regularities of flocculation of aqueous kaolinite dispersions with binary compositions of cationic polyelectrolytes

The regularities of the flocculation of kaolin suspensions with binary mixtures of cationic polyelectrolytes are studied. The relationship between the viscosity of flocculant solutions and the conditions of efficient flocculation is studied. It is established that an increase in the sedimentation rate upon the application of binary mixtures of flocculants results form their synergistic effect. The synergistic effect is assumed to be due to a reduction in the swelling coefficient of adsorbed polyelectrolyte macromolecules, which gives rise to the formation of floccules with enhanced density and strength.     

Adsorption of complexes formed by cationic starch and anionic surfactants on quartz studied by QCM-D

The adsorption of complexes of cationic starch, (CS) and a series of homologous sodium alkanoates on silica was studied with the quartz crystal microbalance with dissipation (QCM-D) instrument. The systems were chosen so as to represent CS/surfactant ratios below and above the critical association concentrations of the surfactants but below their critical micelle concentrations. It was found that

– surfactants did not adsorb on cationic polymers that were very tightly bound to the surface;

– surfactants did adsorb on polyelectrolytes forming layers with loops and tails extending into the solution, provided the concentration of surfactant was at least around the critical association concentration (cac) of the surfactant/polymer system;

– adsorption of surfactant was promoted by increasing the surfactant chain length and by adding simple electrolyte that weakened the electrostatic polymer/surface interaction and

– multilayers were formed when the surfactant concentration in solution was well above the cac; their formation was promoted by increasing hydrophobic interactions, e.g. by increasing the surfactant chain length.

Substituent effect on the emission behavior of thiazolidinedione derivatives in cationic and anionic micellar media

Thiazolidinedione (TZD) derivatives have been found to possess potent immunostimulatory properties as well as antiarthritic, antidiabetic and oncostatic activities. These compounds are free radical scavengers. Photophysical properties of the compounds have been studied in different aqueous micellar environments using steady state and time resolved emission spectroscopy. Appreciable hypsochromic shifts with enhancement in the fluorescence intensities have been observed in the ionic micellar media. The binding constants and energy changes during probe-micelle binding have been evaluated from relevant fluorescence data. Polarity of the microenvironment surrounding the probe molecules has been determined in the micellar systems.     

Novel investigation based on cationic modified starch with residual anionic polymer for enhanced oil recovery

Cationic modified starch polymer (CMSP) is a newly developed green chemical agent designed to reutilize the residual anionic polymer found in reservoirs for enhanced oil recovery (EOR). In this study, a series of experiments were conducted to investigate the phase behavior of the residual anionic polymer, CMSP solution, and the flocculation generated from the mixture in plugging capacity and capability of enhancing oil recovery in heterogeneous reservoirs. The experiment results show that the phase behavior of the residual anionic polymer and CMSP solution could be divided into two parts: rapid flocculation reaction and dispersion reaction. The main mechanisms of the rapid flocculation reaction were charge neutralization and bridging. Based on the above results, an optimal amount of CMSP was chosen for plugging capacity, stability, and EOR study. Plugging tests in both parallel cores and EOR in three-layer heterogeneous square cores illustrate that the injected CMSP slug after polymer flooding can effectively block the high-permeability zone and initiate the remaining oil in middle- to low-permeability zones. The investigation results prove that the CMSP solution, injected after polymer flooding, reduces the pollution of produced fluid and further improves oil recovery.     

Clouding behavior of nonionic–cationic and nonionic–anionic mixed surfactant systems in presence of carboxylic acids and their sodium salts

The study is focused on evaluation of clouding phenomena of the aqueous single nonionic surfactant system Triton X-100 (TX-100) and its mixed systems with anionic aerosol-OT (AOT) and cationic dodecylpyridinium chloride (DPC) in presence of hydrophobic ions furnished by sodium salts of carboxylic acids, viz., sodium ethanoate, sodium propanoate, sodium butanoate, and sodium hexanoate and the respective carboxylic acids [ethanoic acid, propanoic acid, butanoic acid, and hexanoic acid]. The influence of salts on the cloud point (CP) has been explained on the basis of salt effect as well as the solubilization of higher alkyl chain hydrophobic ions furnished by these salts. Moreover, the co- and counterion effect has been taken into account to explain the variation of the CP in the mixed systems. However, the effect of acids on CP has been explained in the light of their aqueous solubility and their partitioning ability between octanol and water as reflected by their K _OW values.     

The effects of some electrolytes on flocculation with a cationic polyacrylamide

The effects of sodium chloride, sodium sulfate, and alum (aluminum sulfate) on the performance of a cationic polyacrylamide flocculant in a papermaking suspension consisting of bleached (hardwood: softwood, 50∶50) kraft wood-pulp fibres and anatase (TiO₂) were investigated. Sodium chloride and sodium sulfate, 1×10^?5 to 1×10^?2 M, in the presence of polymer, caused negligible changes in the electrophoretic mobility of the TiO₂ and in the first-pass retention of TiO₂ (heteroflocculation of TiO₂ and fibres). Alum at concentrations from 1×10^?5 to 1×10^?4 M at pH 4.0 and 4.5 increased retention with polymer; higher alum concentrations resulted in lower retentions. At pH 4.0 the electrophoretic mobility of the TiO₂ was positive over the entire range of alum concentrations investigated (1×10^?5?3.2×10^?3 M) whereas at pH 4.5 the mobility was negative at 1×10^?5 M alum and charge reversal was observed at about 4×10^?5 M alum. The intrinsic viscosity of the cationic polyacrylamide was decreased by the addition of alum, sodium chloride or sodium sulfate. The effect of alum on the polymer conformation appeared to be that of the non-specific interaction of sulfate ions with a cationic polyelectrolyte. Retention results are discussed in terms of the colloidal stability of TiO₂, the adsorption of polyacrylamide on TiO₂ and the conformation of adsorbed polymer.     

Thermotropic phase behavior of cationic gemini surfactants and their equicharge mixtures with sodium dodecyl sulfate

The lyotropic phase behavior for the neat cationic gemini surfactants alkanediyl-alpha,omega-bis(alkyldimethylammonium bromide), designated here as m-s-m, has been investigated previously in several works, but the thermotropic behavior has not been well characterized. Only for 15-s-15 and 14-s-12 have thermotropic liquid crystals (Lc) been reported. In this work, for the first time and in contrast to previous reports, we observe thermotropic Lc formation for m-2-m geminis with m = 12, 14, 16, and 18, by means of polarizing microscopy and differential scanning calorimetry (DSC). Furthermore, we investigate mixtures of m-2-m and SDS, m-2-m Br2.2SDS, which exhibit crystal-to-crystal phase transitions at lower temperature and, at high temperature, smectic Lc phases. The transition temperatures and enthalpies for Lc phases, obtained by DSC, present clear trends upon increase of the chain lengths. Combining Langmuir film experiments, possible lamellar arrangements for the different phases are tentatively discussed.     

The calcite/water interface II. Effect of added lattice ions on the charge properties and adsorption of sodium polyacrylate

The origin of the surface potential of calcium carbonate in aqueous dispersions and the dissolution of calcite in systems containing excess Ca(2+) and CO(3)(2-) have been the subjects of this study. In addition, stabilization of calcite particles with an anionic polyelectrolyte (sodium polyacrylate (NaPA)) and the effect on surface potential and dissolution of calcite have been studied. Preferential dissolution of either Ca(2+) or CO(3)(2-) from the surface, which is governed by the partial pressure of CO(2) in solution and the pH of the solution, mainly determines the surface potential. Both lattice ions (Ca(2+) and CO(3)(2-)) adsorb onto the surface and thus alter the surface potential. NaPA adsorbs strongly onto the calcite surface regardless of background electrolyte concentration, and reverses the surface potential to negative values. Chelation of the surface due to NaPA can be partly prevented by adding Ca(2+) to the dispersion.     

Synthesis of hydrophobic association cationic starch and its flocculation application on containing algae water of Dianchi Lake

The hydrophobic formation cationic starch (PSOAMDA) was prepared from starch (St), octadecyl acrylate (OA), acrylamide (AM) and dimethyl diallyl ammonium chloride (DMDAAC) by means of inverse suspension polymerization with redox initiator. Water with algae from Dianchi Lake was tested with PSOAMDA. Results show that when the molar ratio of St: AM: DMDAAC: OA is 4:8:1.5:0.6 and the reaction temperature is 40°C with a reaction time of 3 h, the monomer conversion yield, graft percentage and cationic degree is 92.4%, 63.8% and 7.3%, respectively, and M _η = 3.26×10⁶ g/vmol. It had been found from the flocculation of disposed water with algae from Dianchi Lake that the transparency and COD elimination reach to 93.5% and 70.3%, respectively, with 15 mg/L PSOAMDA and at pH 6, vs. 91.3% and 69.2% obtained with the commercial cationic polyacrylamide (PAM-C). When PSOAMDA dosage is 10–25 mg/L and the pH of aqueous solution is 6–10, the flocculation performance is well capable of dealing with the water with algae from Dianchi Lake. __________ Translated from Journal of Yunnan University (Natural Sciences Edition), 2007, 29(2): 177–182 [译自: 云南大学学报(自然科学版)]     

The effect of anionic and cationic surfactants on indicators and measurement of dissociation constants with two different methods

The effects of cationic cetyltrimethylammonium bromide (CTAB), hexadecylpyridinum chloride (HDPC) and anionic sodium dodecylsulphate (SDS) surfactants on dissociation constants and transition intervals of methyl red, methyl orange and cresol red were studied spectrophotometrically. The results show that all studied indicators strongly interacted with cationic micelles (CTAB and HDPC). In the case of methyl red, relatively strong interaction with anionic surfactant (SDS) was obtained. However, no effect of SDS on dissociation constants of cresol red and methyl orange was observed. The dissociation constants of indicators were calculated with both the proposed and known chemometric (DATAN) method with a reasonable agreement on the data achieved.     

Particulate hematite diffusion in sodium polyacrylate solutions. The effect of ionic strength

The diffusion coefficients of hematite particles in polyelectrolyte solution have been investigated using dynamic light scattering. Two apparent diffusion coefficients, a fast and a slow diffusional mode, are observed for the hematite particles in high-molecular-weight sodium polyacrylate solution at pH 10.5. The slow diffusion coefficient (Dslow) shows a decrease with increase in polyelectrolyte concentration. The fast diffusion coefficient (Dfast) shows an increase to a maximum with increasing polyelectrolyte concentration and then a rapid decrease as the polyelectrolyte concentration increases further. With an increase in ionic strength from 10(-4) to 0.1 M NaNO3, the maximum value of Dfast increased in magnitude, while the polyacrylate concentration at which the maximum occurs is seen to increase. The dependence of Dfast on the measurement angle indicates that it is coupled to the fluctuations of the chains. The observed behavior is attributed to the hematite probe particle sensing both macroscopic (viscous) and elastic fluctuations associated with the polyelectrolyte motion.     

Comparative activity of aqueous dispersions of CdS nanocrystals stabilized by cationic and anionic polyelectrolytes in photocatalytic hydrogen production from water

The results of a study on the photocatalytic activity of aqueous dispersions of Ni-doped CdS nanocrystals (NCs) covered with an amphiphilic polyelectrolyte (PE) shell, i.e., a polycation (NC-PC) or polyanion (NC-PA), are presented for the first time. The H₂ evolution rate measured under identical conditions served as a measure of activity. The NC-PC and NC-PA samples were characterized by similar PE content (~40%) and monomodal size distribution. According to our calculations based on the NC dimensions and lattice parameters, about one macromolecule of the PE is required to stabilize one NC. The average hydrodynamic diameter of the NC-PC was found to be 1.5 times larger than that of the NC-PA due to the difference between their chemical structures and different abilities of ionogenic groups to dissociate. The photocatal ytic activity of the PE-stabilized CdS nanocrystals was significantly influenced by the type of the PE, while the H₂ evolution rate depended on the reducing medium used during the process. When the medium contained Na₂S or when the PE-stabilized NCs were pretreated with Na₂S, the effect of the shell type was more pronounced and the activity of NC-PA was 2 to 14 times higher than that of NC-PC.     

Adsorption of cationic starch on cellulose studied by QCM-D

The adsorption of cationic starch (CS) from aqueous electrolyte solutions onto model cellulose film has been investigated by the quartz crystal microbalance with dissipation monitoring (QCM-D) and X-ray photoelectron spectroscopy (XPS). The influence of the electrolyte composition and charge density of CS was examined. The adsorption of CS onto cellulose followed the general trends expected for polyelectrolyte adsorption on oppositely charged surfaces, with some exceptions. Thus, as result of the very low surface charge density of the cellulose surface, highly charged CS did not adsorb in a flat conformation even at low ionic strength. The porosity of the film, however, enabled the penetration of coiled CS molecules into the film at high electrolyte concentrations. Differences between the adsorption behavior of CS on cellulose and earlier observations of the adsorption of the same starches on silica could be explained by the different morphologies and acidities of the hydroxyl groups on the two surfaces.     

The flocculation of kaolin suspensions with cationic polyacrylamides of varying molar mass but the same cationic character

Cationic polyacrylamides of varying molar masses but of similar charge density were tested as flocculants for kaolin suspensions. Flocculant performance was assessed by determining the extent of polymer adsorption, the subsidence rates of the flocculated suspensions and the residual turbidities of the resulting supernatants. The sol concentration was kept constant at 20 g kaolin dm⁻³ in 10⁻³ mol dm⁻³ NaCl solution; pH was varied from 3 to 10. It was found that the subsidence rates did not reflect the trends of polymer adsorption. Polymer adsorption decreased while subsidence rates increased as the molar mass of the polymers increased. Increased adsorption of polymer with pH did not result in higher rates of subsidence. The principal effect of the quaternary cationic charge is to produce a partially extended polymer molecule at all values of the pH. The positive polymeric charge is of secondary importance to the length of the molecule in determining the efficacy of flocculation by polymer bridging and does not counteract the increasing self-repulsion of the clay particles with increasing pH which produced poor floc formation.     

Adsorption behavior of cationic and anionic species on chitosan resins possessing amino acid moieties.

Chitosan resins modified with amino acids, such as glycine, valine, leucine, and serine, were synthesized for investigating the adsorption behavior of cationic and anionic species, and showed good abilities for the adsorption of trace elements in aquatic media as follows: glycine for lanthanoids at pH 7, leucine for molybdenum at pH 1-5, serine for uranium at pH 2-7, and amino acids for bismuth at pH 1-7. Cationic and anionic species could be adsorbed by a chelating mechanism and an anion-exchange mechanism.     

阴/阳离子表面活性剂复配体系的中相微乳液研究

阴离子表面活性剂双-2-乙基己基磺化琥珀酸钠(简称AOT), 和阳离子表面活性剂十六烷基三甲基溴代铵(简称CTAB), 在有醇、正辛烷、盐水存在的情况下,能形成多相微乳液。本文系统地研究了阴/阳离子表面活性剂配比、醇的种类、醇的浓度对该体系的中相微乳液的形成及特性的影响, 得到了中相微乳液的特性参数(最佳含盐量S^*, 最佳中相微乳液体积V^*, 界面张力r~E、盐宽△S等)。这些性质对与阴/阳离子表面活性剂复配体系, 三次采油及日用化工上的应用开发具有重要意义。最后还开展单独阴离子表面活性剂体系和阴/阳离子表面活性剂复配体系进行了比较, 得到一些有价值规律, 并从理论上进行了探讨。