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PubMed2000

[The adsorption on attapulgite and cross-linked agar beads entrapped attapulgite(CAA)].

The adsorption of four drugs with certain toxicity, i.e. chlorpromazine, quinidine, diazepam and phenobarbital on attapulgite and Cross-linked Agar Beads Entrapped Attapulgite(CAA) was determined in this study. The results revealed that attapulgite possessed high adsorption for the cation drugs(chlorpromazine and quinidine), moderate adsorption for diazepam, and slight adsorption for phenobabital. The adsorption in attapulgite was quite quick and came to equilibrium in about 30 min. No significant difference(P > 0.05) of adsorption on attapulgite was observed at 30 min and 60 min. The adsorbent selectivity on CAA was the same as that on attapulgite. The speed of the adsorption was slower on CAA than on attapulgite, but the quantity adsorpted on CAA and that on attapulgite had no marked difference(P > 0.05) after 60 min. CAA preserved the adsorption property of attapulgite fundamentally. CAA overcame the dispersibility of attapulgite distinctly and showed good hemocompatibility and a fair blood flow rate in hemoperfusion. It may play an important role in the separation of blood components and in hemopurification.

Adsorption↗
PubMed2001

Characteristics of new coccine dye adsorption onto digested sludge particulates.

The adsorption characteristics of an anionic azo dye (new coccine) onto digested sludge have been studied. Results show that the dye can effectively be removed by sludge. It was found that the adsorption rate is very rapid and the equilibrium can be reached in 10 min. The adsorption kinetics can be expressed by the modified Freundlich equation. Also, the solution pH, ionic strength, and temperature are the key factors affecting the adsorption. The effect of electrical double layer thickness on the adsorption was also discussed. The adsorption standard free energy, enthalpy, and entropy were determined. The adsorption follows a nonlinear multilayer adsorption isotherm. The specific surface area of sludge was determined as 82 to approximately 150m2/g on the basis of its monolayer dye adsorption capacity.

Adsorption↗
PubMedDate not supplied

Study of protein adsorption effects on crossflow filtration using BSA and milk protein.

Three membrane materials were tested under similar conditions to determine the effects of membrane material on the performance and cleanability of the filters. The membrane materials investigated were stabilized cellulose (Hydrosart, Sartorius Corporation), cellulose triacetate, and polyethersulfone; all having a 10 kilodalton molecular weight cutoff. Stabilized cellulose is a cellulose-based membrane material, modified for low non-specific protein adsorption combined with high pH-resistance. When analyzing the data, three phenomena were considered: adsorption of protein to the membrane, gel layer formation, and osmotic pressure due to concentration polarization. Throughout these studies, the effects of a gel layer and the osmotic pressure were approximately equivalent in all cassettes. However, the stabilized cellulose was resistant to protein adsorption while the other two membranes exhibited significant decreases in permeate flux due to adsorption. Using a 0.2% BSA (MW = 67,000 kD) solution with a crossflow rate of 5 L/min and transmembrane pressure of 35 psi, the permeate flux through the stabilized cellulose membrane was 3% lower than the baseline saline flux, whereas the cellulose triacetate and polyethersulfone membranes lost 33% and 60% of baseline flux, respectively. The decrease in flux occurring in the latter two membranes is due to adsorption. Another study evaluated adsorption by alternating between crossflow and static operation. After three cycles, the stabilized cellulose maintained the original crossflow flux level. The polyethersulfone lost cumulatively 17% of its crossflow flux after three cycles and the cellulose triacetate lost 13%. The stabilized cellulose and polyethersulfone membranes were also evaluated using a milk solution. The results indicate that the stabilized cellulose is not susceptible to adsorption of any of the milk components while the polyethersulfone permeate flux was limited by adsorption. The saline flux of the stabilized cellulose immediately after testing with the milk solution was 3% lower than the baseline flux, while the polyethersulfone membrane saline flux was 81% lower. The results consistently indicated that, unlike the cellulose triacetate and polyethersulfone membranes, the stabilized cellulose membrane was not subject to adsorption.

Adsorption↗
PubMed2003

Granular activated carbon (GAC) adsorption in tertiary wastewater treatment: experiments and models.

Wastewater treatment has always been a major concern in the developed countries. Over the last few decades, activated carbon adsorption has gained importance as an alternative tertiary wastewater treatment and purification process. In this study, granular activated carbon (GAC) adsorption was evaluated in terms of total organic carbon (TOC) removal from low strength synthetic wastewater. This paper provides details on adsorption experiments conducted on synthetic wastewater to develop suitable adsorption isotherms. Although the inorganics used in the synthetic wastewater solution had an overall unfavourable effect on adsorption of organics, the GAC adsorption system was found to be effective in removing TOC from the wastewater. This study showed that equation of state (EOS) theory was able to fit the adsorption isotherm results more precisely than the most commonly used Freundlich isotherm. Biodegradation of the organics with time was the most crucial and important aspect of the system and it was taken into account in determining the isotherm parameters. Initial organic concentration of the wastewater was the determining factor of the model parameters, and hence the isotherm parameters were determined covering a wide range of initial organic concentrations of the wastewater. As such, the isotherm parameters derived using the EOS theory could predict the batch adsorption and fixed bed adsorption results of the multi-component system successfully. The isotherm parameters showed a significant effect on the determination of the mass transfer coefficients in batch and fixed bed systems.

Adsorption↗
PubMed2003

[Synthesis of a novel starch derivative and its adsorption property for creatinine].

AIM: To prepare a novel creatinine adsorbent with anti-renal failure activity. METHODS: A novel starch ester was prepared under heterogeneous condition by the reaction of starch (ST) and 3, 5-dinitrobenzoyl chloride (DNBZ-Cl). The products were characterized by means of elemental analysis, FTIR, 13CNMR and UV-Vis spectra. The adsorption properties of DNBZ-ST were examined. RESULTS: The adsorption equilibrium is reached after 4 h, the adsorption capacity increases with the degree of substitution (DS) of adsorbent and creatinine concentration. When creatinine concentration is higher than 300 mg.L-1, concentration showed no apparent effect on adsorption capacity. As the adsorption temperature varied from 19 degrees C to 49 degrees C, adsorption capacity first decreases and then increases, and is lowest at 37 degrees C. The adsorption capacity first increases and then decreases as the pH value increase from 4 to 11 and is highest at pH 8. The highest adsorption capacity reached 25 mg.g-1 at 37 degrees C pH 7 and the creatinine concentration is 100 mg.L-1. CONCLUSION: Starch 3,5-dinitrobenzoate showed a better adsorption property for creatinine, and it is worthy to be studied more deeply.

Adsorption↗
PubMed2003

[The experimental study to Hg0 adsorption of fly ash in flue gas].

Through the simulation experimentation, the Hg adsorption characteristics of fly ash in flue gas were studied carefully in laboratory. From the experiment results it was found that Hg adsorption capacity of different porous medium in fly ash was different obviously. Unburned carbon had higher Hg adsorption capacity. The surface-area of BET sorbent had positive correlation with Hg adsorption capacity. Hg concentration in blend gas had non-linearity relationship with Hg adsorption capacity. Hg adsorption capacity of 5 x 10(-7) Hg concentration was only 1/2 compared to that of 5 x 10(-6). Adsorption temperature had negative correlation with it. C=O in unburnt carbon surface was beneficial to oxidation and chemic adsorption of Hg. It was obtained that the porous structure and huge surface-area of the unburned carbon was benefit to the Hg adsorption in flue gas.

Adsorption↗
PubMed2004

[Analysis of correlation degree between phase components and adsorptive amounts of serum proteins for DLC film].

In the present paper, the influence of carbon phase components of three kinds of diamond like carbon (DLC) films, viz. DLC, DLC rich in graphite and DLC rich in diamond films, on adsorption of human serum albumin (HSA), human serum fibrinogen (HFG) and immunoglobin (IgG) was quantitatively analyzed by use of T-type correlation degree in the grey system theory. Through the analysis, the rational explanation for adsorptive amounts variations of the serum proteins with phase components in the experiment is reached and some essential conclusions have been obtained: (1) The effect of graphite phase and C-H phase on HSA adsorption are greater than that of other phase components; with the increase of these two phase coumponents, the adsorptive amounts of HSA decrease; (2) The powerful influence on HFG adsorption stems from DLC phase and C-O phase; with the decrease of DLC phase or the increase of C-O phase, the adsorptive amounts of HFG increase; (3) All of the carbon phase components have only limited influence on IgG adsorption in positive or negative fashion with a little difference in degree; (4) DLC phase has both effects of enhancing adsorption for HSA and weakening adsorption for HFG and IgG, thus its influence on the hemocompatibility of DLC films is much more important than that of other phase components.

Adsorption↗
PubMed1991

Baboon fibrinogen adsorption and platelet adhesion to polymeric materials.

The role of fibrinogen in mediating platelet adhesion to polymers exposed to blood plasma was studied by comparison of the effect of plasma dilution on fibrinogen adsorption and platelet adhesion, and by the use of coagulation factor deficient plasmas. Polyetherurethane substrates were first preadsorbed with dilute plasma, then contacted with washed platelets suspended in a modified, apyrase containing Tyrode's buffer. Platelet adhesion was studied under static conditions in Multiwell dishes, and also under shearing conditions using a parallel plate perfusion chamber. Fibrinogen adsorption and platelet adhesion were measured using 125I radiolabeled baboon fibrinogen and 111In radiolabeled baboon platelets, respectively. Surfaces were characterized by electron spectroscopy for chemical analysis (ESCA). When fibrinogen adsorption to Biomer was measured after 2 h contact with a series of dilute plasma solutions under static conditions, a peak in adsorption was observed from 0.26% plasma, i.e., adsorption was greater from 0.26% plasma than from either more or less dilute plasma. A peak in subsequent platelet adhesion to the plasma preadsorbed surfaces, measured after 2 h static incubation with washed platelets, was also observed but occurred on Biomer preadsorbed with 1.0% plasma. When fibrinogen adsorption was measured after 5 min contact under shearing conditions, the fibrinogen adsorption peak occurred on surfaces that had been exposed to 1.0% plasma. A peak in platelet adhesion to these preadsorbed surfaces, measured after 5 min contact with the platelet suspensions under shearing conditions, was observed on Biomer preadsorbed with 0.1% plasma. Shifts between the positions of the peaks in protein adsorption and platelet adhesion occurred on other polymers tested as well. Platelet adhesion was almost completely inhibited when baboon and human plasmas lacking fibrinogen (i.e., serum, heat defibrinogenated plasma, and congenitally afibrinogenemic plasma) were used. Platelet adhesion was restored to near normal when exogenous fibrinogen was added to fibrinogen deficient plasmas. Adhesion was also inhibited completely when a monoclonal antibody directed against the glycoprotein IIb/IIIa complex was added to the platelet suspension. Platelet adhesion to surfaces preadsorbed to von Willebrand factor deficient plasma was the same as to surfaces preadsorbed with normal plasma. While it appears that surface bound fibrinogen does mediate the initial attachment of platelets to Biomer, the observation that the fibrinogen adsorption and platelet adhesion maxima do not coincide exactly also suggests that the degree of subsequent platelet adhesion is dictated not only by the amount of surface bound fibrinogen but also by its conformation.

Adsorption↗
PubMed1977

[Pasteurella multocida bacteriophage adsorption].

Studied was the adsorption of 8 strains of Pasteurella multocida bacteriophages presenting three groups of phages isolated in Bulgaria. With the bacteriophages of groups I and II the adsorption in broth in the first 10 minutes amounted to 50-65%, and at the 80 the minute reached its maximum value--98-99%. With the bacteriophages of group III adsorption started with a lower percent and by the 140th minute reached 96-97%. It was by 60 min slower as compared with the adsorption with group I and II phages. In a veronal-medinal buffer the adsorption of all investigated phages of the three groups set in with a prolonged time of 60 min as compared with the time elapsed using broth. At the cross testing of adsorption the phages of group I were adsorbed by the hosts of the other two groups to a maximum level, however, the phages of groups II and III were adsorbed to a negligible extent on the other hosts (except for the adsorption on their homologous one). The difference established in the adsorption for a 60 minutes time so far as the phages of group III were concerned was sufficiently persuasive to consider this group as an individual one by this feature too. Adsorption appeared as a subsidiary taxonomic characteristic in the classification of Pasteurella multocida bacteriophages.

Adsorption↗
PubMed1984

Effect of plasma dilution on adsorption of fibrinogen to solid surfaces.

The adsorption of various plasma proteins to three solid surfaces has been studied as a function of plasma concentration. Albumin adsorption on glass showed no dependence on plasma concentration and increased to a plateau value on both polyethylene and siliconized glass. Immunoglobulin G (IgG) adsorption showed no dependence on plasma concentration on any surface. Fibrinogen adsorption increased with plasma concentration and then decreased, the maximum occurring at about 1% normal plasma concentration and varying somewhat with the surface. On glass the kinetics of fibrinogen adsorption was dependent on plasma concentration: at concentrations less than the adsorption maximum, the kinetics was conventional, with adsorption increasing onto a plateau; at concentrations greater than the adsorption maximum, kinetics curves also showed maxima the position of which shifted to longer times as plasma concentration decreased. These data are interpreted in terms of competitive adsorption between fibrinogen and other, as yet unidentified species in plasma. The data reported are in general agreement with the model of Vroman (12) for plasma-surface interactions which holds that initially adsorbed fibrinogen is later replaced by high molecular weight kininogen (HMWK), the rate of replacement depending on the relative activity of the surface in promoting coagulation.

Adsorption↗
PubMed1978

Interaction of plasma proteins with artificial surfaces: protein adsorption isotherms.

A simple technique using a small disc which is dipped into a 125I-labeled protein solution has been devised to study the adsorption of human albumin, fibrinogen, and IgG onto Cuprophane or PVC. The purity of these human plasma proteins has been examined carefully with PAGE and immunochemical methods. The adsorption isotherms of albumin, fibrinogen, and IgG show a langmuir type adsorption. Delipidation of albumin did not alter the albumin affinity to Cuprophane and PVC. The surface saturation concentration (ng/cm2) for albumin, fibrinogen, or IgG were all found to be more on PVC (a hydrophobic surface) than on Cuprophane (a hydrophilic surface). The competitive adsorption of one protein species in a two- or three-protein mixture was also studied. Albumin and fibrinogen complete with each other for adsorption. The effects of IgG on the adsorption of albumin or fibrinogen were inconsistent and not predictable; the reason for this is unknown. The effect of laminar flow on albumin adsorption was studied with a specially designed Richardson flow chamber. In general caused an increase in albumin adsorption over that at static conditions. The increase of albumin adsorption was more pronounced also for PVC than for Cuprophane from 1 to 10 ml/min.

Adsorption↗
PubMedDate not supplied

Adsorption of recombinant human granulocyte colony stimulating factor (rhG-CSF) to polyvinyl chloride, polypropylene, and glass: effect of solvent additives.

The adsorption of recombinant-derived proteins to glass and polymeric materials used in their packaging and delivery remains a problem. Loss of these very expensive proteins to surface adsorption not only results in reduced yields during purification and scale-up, but also to decreased therapeutic efficacy. The purpose of the present investigation was to inhibit/minimize adsorption of a model protein, namely, recombinant human granulocyte colony stimulating factor (rhG-CSF) to glass, polyvinyl chloride (PVC), and polypropylene by inclusion of select solvent additives. Solvent additives used to inhibit/minimize surface adsorption included glycerin, U.S.P. (0.5%, 1%, 5%, and 25% v/v), Pluronic F-127 (0.005%, 0.05%, and 0.5% w/w), Pluronic F-68 (0.005%, 0.05%, and 0.5% w/w), Tween 80 (0.005% and 0.05% w/w) and Tween 20 (0.005%, 0.05%, and 0.5% w/w). Over the rhG-CSF concentration range of 0.0 ng/ml to 300 ng/ml, the amount of rhG-CSF bound per cm2 of PVC increased with an increase in the rhG-CSF concentration tested. At rhG-CSF equilibrium concentrations of 262 +/- 3.7 ng/ml and 136 +/- 1.9 ng/ml, the rhG-CSF bound/cm2 of PVC at 22 degrees C and 45 degrees C reached a maximum of 37.6 +/- 9.8 ng/cm2 and 165.2 +/- 11.7 ng/cm2, respectively. The adsorption isotherms determined at each temperature were described by the classic Freundlich equation. Moreover, the rate of adsorption of rhG-CSF to PVC was extremely rapid. The mean values of the percent of rhG-CSF bound to PVC after only 10 minutes of equilibration at 22 degrees C and 45 degrees C were 92.8 +/- 9.2 percent and 97.3 +/- 17.9 percent, respectively. The mean values of the percent of rhG-CSF bound to PVC at 22 degrees C and 45 degrees C after 24 hours were 52.4 +/- 10.9% and 70.0 +/- 9.7%, respectively, indicating that some desorption of rhG-CSF does occur during 24 hr. However, surface adsorption of rhG-CSF to PVC was shown to be irreversible over a 1 hr time period. Using viscometry, an estimate of the thickness of the adsorbed layer of rhG-CSF to glass was determined to be approximately 1 micron. The overall rank order of the solvent additives for minimizing adsorption of rhG-CSF to PVC was Tween 20 > Tween 80 > Pluronic F-127 > Pluronic F-68. Tween 20 was the most effective solvent additive for inhibiting surface adsorption of rhG-CSF to parenteral vials made of either glass or polypropylene.

Adsorption↗
PubMed1996

Evaluation of affinity and pseudo-affinity adsorption processes for penicillin acylase purification.

Affinity ligand (6-Aminopenicillanic acid, Amoxycillin, Ampicillin, Benzylpenicillin and 4-Phenylbutylanzine) of penicillin acylase (EC 3.5.1.11) were attached to hydrophilic gels like Sepharose 4B-CNBr and Minileak 'medium'. Ampicillin and 4-Phenylbutylamine were the affinity ligands that presented the higher concentrations attached to both gels. Penicillin acylase adsorption on these affinity gels was mainly dependent on the activated group of the gel, the affinity ligand attached and the experimental conditions of enzyme adsorption. Under affinity conditions only the ligands Amoxycillin, Ampicillin and 4-Phenylbutylamine, immobilized on Minileak, adsorbed the enzyme from osmotic shock extracts at different pH values. These affinity ligand systems were characterized by low adsorption capacities of penicillin acylase activity (1.2-2.1 IU mL-1 gel) and specific activity (1.5-2.9 IU mg-1 prot). Under pseudo-affinity conditions all the ligands attached both activated to gels (Sepharose 4B-CNBr and Minileak) adsorbed the enzyme. The affinity gels were characterized by higher values of adsorption capacity (3.7 and 55.6 IU mL-1 gel) and adsorbed specific activity (2.0 and 6.1 IU mg-1 prot) than those observed under affinity conditions. The space arm of Minileak gel, shown to be fundamental to enzyme adsorption under affinity conditions, preferentially adsorbed proteins in relation to the enzyme under pseudo-affinity conditions. However, this effect was partially minimized when the gel was derivatized by the affinity ligands at concentrations higher than 6 mumol mL-1 gel. Ampicillin was the affinity ligand that presented the best results for specific adsorption of penicillin acylase under affinity and pseudo-affinity adsorption processes. The Sepharose 4B-CNBr derivatized gel also presented a good adsorption capacity of enzyme activity (26.8 IU mL-1 gel) under pseudo-affinity adsorption processes.

Adsorption↗
PubMed2004

A molecular modeling study of the effect of surface chemistry on the adsorption of a fibronectin fragment spanning the 7-10th type III repeats.

Although it is well documented that proteins adsorb onto biomaterial surfaces, relatively little is quantitatively understood about the effects of adsorption on protein orientation and conformation. Because this is the primary determining factor of protein bioactivity, the ability to accurately predict a protein's orientation and conformation following adsorption will be essential for the rational design of biomaterial surfaces to control biological responses. Force field-based computational chemistry methods provide an excellent means to theoretically address this issue, with the nontrivial requirement that the force field must be tailored to appropriately represent protein adsorption behavior. Accordingly, we have modified an existing force field (CHARMm) based on semiempirical quantum-mechanical peptide adsorption data to enable it to simulate protein adsorption behavior in an implicit aqueous environment. This modified force field was then applied to predict the adsorption behavior of the 7-10 type III repeats of fibronectin on functionalized surfaces. Predicted changes in adsorption energy and adsorption-induced conformation as a function of surface chemistry were found to correlate well with experimentally observed trends for these same systems. This work represents a first attempt towards the development of a molecular mechanics force field that is specifically parameterized to accurately simulate protein adsorption to biomaterial surfaces.

Coated Materials, Biocompatible↗
PubMed1996

Experimental Simulation of Polymer Mixture Adsorption from Two-Phase Solutions

The simulation of segregation of two polymers near an interface has been realized by studying adsorption from concentrated solutions of incompatible polymers at concentrations above that for coil overlapping and corresponding to one-phase and two-phase states. For solutions that have separated into two phases with increasing component concentration, the adsorption from each phase has been studied separately and the total adsorption from two phases has been calculated. The polystyrene-poly(butyl methacrylate)-CCl4 system was investigated using fumed silica as adsorbent. Simultaneously the fraction of segments of each type immobilized by the surface was determined from NMR spectra. In all cases, poly(butyl methacrylate) is characterized by preferential adsorption. The main features of adsorption are similar in both one-phase and two-phase states; however, the values of adsorption and fraction of immobilized segments are different for adsorption from two separated phases because of the difference in the ratio of components and their concentration in each phase. The total adsorption of poly(butyl methacrylate) from the two-phase state is higher than from the one-phase state. It is concluded that in two-phase systems adsorption proceeds simultaneously from both phases, leading to higher segregation of one of the components.

Journal Article↗
PubMed1997

Studies on the Adsorption of Sulfapyridine at the Solution-Alumina Interface

The adsorption of Sulfapyridine (SP) onto the alumina surface has been carried out at room temperature to study the adsorption behavior of SP and its mode of interaction with the surface of alumina particles. It is found that various factors such as concentration of SP solution, required time for adsorption equilibrium, pH of the adsorbate solution, temperature of adsorption medium, presence of ions like PO43-, SO42-, and Cl- affect quantitatively the adsorption of SP. Various adsorption and kinetic parameters such as the adsorption isotherm, adsorption coefficient, rate constants for adsorption and desorption and surface coverage have also been evaluated. The present study is significant because knowledge of the exact interaction between the SP molecules and the alumina surface and the proper choice of experimental condition would be helpful in carrying out an optimum separation of sulfa drug compounds chromatographically.

Journal Article↗
PubMed1999

Surface Structural Ion Adsorption Modeling of Competitive Binding of Oxyanions by Metal (Hydr)oxides.

Spectroscopy has provided a progressive flow of information concerning the binding mechanism(s) of ions and their surface-complex structure. An important challenge in surface complexation models (SCM) is to connect the molecular microscopic reality to macroscopic adsorption phenomena. This is important because SCM alone provide insufficient insight in the binding mechanisms, and moreover, it is a priori not obvious that SCM, which describe the pH dependent adsorption correctly in simple systems, will predict the ion interaction under multicomponent conditions. This study elucidates the primary factor controlling the adsorption process by analysing the adsorption and competition of PO4, AsO4, and SeO3. We show that the structure of the surface-complex acting in the dominant electrostatic field can be ascertained as the primary controlling adsorption factor. The surface species of arsenate are identical with those of phosphate and the adsorption behavior is very similar. On the basis of the selenite adsorption, we show that the commonly used 2pK models are incapable to incorporate in the adsorption modeling the correct bidentate binding mechanism found by spectroscopy. The use of the bidentate mechanism leads to a proton-oxyanion ratio and corresponding pH dependency that are too large. The inappropriate intrinsic charge attribution to the primary surface groups and the condensation of the inner sphere surface complex to a point charge are responsible for this behavior of commonly used 2pK models. Both key factors are differently defined in the charge distributed multi site complexation (CD-MUSIC) model and are based in this model on a surface structural approach. The CD-MUSIC model can successfully describe the macroscopic adsorption phenomena using the surface speciation and binding mechanisms as found by spectroscopy. The model is also able to predict the anion competition well. The charge distribution in the interface is in agreement with the observed structure of surface complexes. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Adsorption Mechanism of Conventional and Dimeric Cationic Surfactants on Silica Surface: Effect of the State of the Surface.

The aim of this study was to investigate the effect of the state of the silica surface and of the surfactant molecular structure on the adsorption of cationic surfactants onto silica. Thus, the adsorption of DTAB (dodecyltrimethylammonium bromide) and of the dimeric surfactant 12-2-12 (ethanediyl-1,2-bis(dodecyldimethylammonium bromide)) on raw silica (SiNa) and on HCl-washed silica (SiH) has been investigated under "free" system conditions. The amount of surfactant adsorbed (adsorption isotherm), the sodium ion and bromide ion concentrations and the pH in the equilibrated supernatant, and the silica particle electrophoretic mobility have been measured along the isotherms. The adsorption mechanisms of the two surfactants on the raw and washed silica are qualitatively similar. Nevertheless, important quantitative differences are observed which are all due to (i) the larger number of surface sites present at the surface of SiNa with respect to SiH and (ii) the larger ionic strength of the supernatant in SiNa/surfactant systems with respect to SiH/surfactant systems, due to the much larger amount of sodium ions released by SiNa upon surfactant binding. Thus, the amounts of surfactant adsorbed at the point of zero charge and at saturation of the silica particles, of sodium ions released by the surface and the decrease of critical micelle concentration (cmc) in the supernatant with respect to pure water are all larger for the raw silica than for the treated silica. For the four silica/surfactant systems investigated, the first adsorption step corresponds to the adsorption of individual surfactant ions on the negative sites of the silica surface. It is driven by electrostatic interactions and strongly dependent on the number of surface sites and ionic strength associated to the released ions. At the end of the first adsorption step, which is clearly seen with SiH/surfactant systems, the second adsorption step starts. This step is driven by hydrophobic interaction between surfactant alkyl chains and results in the formation of surface aggregates. The surfactant adsorption on the surface is shown to continue even after the cmc in the supernatant is reached. Copyright 1999 Academic Press.

Journal Article↗