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Thermodynamic analysis of unimer-micelle and sphere-to-rod micellar transitions of aqueous solutions of sodium dodecylbenzenesulfonate

Valente, Artur J. M.; López Cascales, J. J.; Fernández Romero, Antonio J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Temperature dependence of specific conductivity of sodium dodecylbenzenesulfonate (NaDBS) aqueous solutions was analyzed. Two breaks on the plot appeared for all temperature, which suggest two micellar transitions. This has been corroborated by surface tension measurements. The first transition concentration occurs at the critical micelle concentration (CMC), whilst the second critical concentration (so-called transition micellar concentration, TMC) is due to a sphere-to-rod micelles transition. The dependence of CMC and TMC on the temperature allows the computation of the corresponding thermodynamic functions: Gibbs free energy, enthalpy and entropy changes. For the CMC, enthalpy and entropy increments were found that decrease with the temperature values. However, an anomalous behavior was obtained for the TMC, where both ΔS0 and ΔH0 values raised with the temperature increase. However, for both transitions, an (enthalpy + entropy) compensation is observed. These results will be compared with similar systems reported in the literature.

Potential tuberculostatic agent: Micelle-forming pyrazinamide prodrug

Silva, M.; Ricelli, N. L.; El Seoud, O.; Valentim, C. S.; Ferreira, A. G.; Sato, D. N.; Leitel, CQF; Ferreira, E. I.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 283-290
ENG
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Pyrazinamide was condensed with the poly(ethylene glycol)-poly(aspartic acid) copolymer (PEG-PASP), a micelle-forming derivative was obtained that was characterized in terms of its critical micelle concentration (CMC) and micelle diameter. The CMC was found by observing the solubility of Sudan III in Poly(ethylene glycol)-poly(pyrazinamidomethyl aspartate) copolymer (PEG-PASP-PZA) solutions. The mean diameter of PEG-PASP-PZA micelles, obtained by analyzing the dynamic light-scattering data, was 78.2 nm. The PEG-PASP-PZA derivative, when assayed for anti-Mycobacterium activity, exhibited stronger activity than the simple drug.

Oil wastes as unconventional substrates for rhamnolipid biosurfactant production by Pseudomonas aeruginosa LBI

Nitschke, Marcia; Costa, Siddhartha G. V. A. O.; Haddad, Renato; Gonçalves, Lireny A. G.; Eberlin, Marcos N.; Contiero, Jonas
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1562-1566
ENG
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Oil wastes were evaluated as alternative low-cost substrates for the production of rhamnolipids by Pseudomonas aeruginosa LBI strain. Wastes obtained from soybean, cottonseed, babassu, palm, and corn oil refinery were tested. The soybean soapstock waste was the best substrate, generating 11.7 g/L of rhamnolipids with a surface tension of 26.9 mN/m, a critical micelle concentration of 51.5 mg/L, and a production yield of 75%. The monorhamnolipid RhaC10C10 predominates when P. aeruginosa LBI was cultivated on hydrophobic substrates, whereas hydrophilic carbon sources form the dirhamnolipid Rha2C10C10 predominantly. © 2005 American Chemical Society and American Institute of Chemical Engineers.

A new insight about pharmaceutical dosage forms for benzathine penicillin G

Holanda E Silva, K. G.; Tabosa Do Egito, Eryvaldo Sócrates; Xavier-Júnior, F. H.; Farias, I. E G; Caldas Neto, J. A.; Silva, A. K A S; Nakashima-Júnior, T.; Araújo, I. B.; Oliveira, Anselmo Gomes de; Medeiros, A. C.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 21-26
ENG
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In this work, a micellar system of benzathine penicillin G (BPG) in sodium deoxycholate (NaDC) was developed and evaluated physicochemically. The solubility profile of the drug in water and buffer solutions at various pH was determined, as well as its n-octanol/water partition coefficient. The Critical Micellar Concentration of NaDC and its ability to incorporate BPG were also assessed. The study was carried out at low and high ionic strength which was adjusted by the addition of sodium chloride. The results demonstrated the ability of the micellar system to incorporate BPG, as well as to increase its apparent solubility in water. The enhancement of the solubility of BPG by the presence of NaDC micelles could be analyzed quantitatively within the framework of the pseudo-phase model. Concentration analysis showed that the micellar system could attain up to 90% incorporation of BPG. The incorporated drug is expected to exhibit improved stability, since the antibiotic enclosed in the hydrophobic core of micelles is rather shielded from the aqueous external environment.

Rhamnolipids Production by a Pseudomonas eruginosa LBI Mutant: Solutions and Homologs Characterization

Lovaglio, Roberta B.; Silva, Vincius L. da; Capelini, Tulio de Lucca; Eberlin, Marcos N.; Hausmann, Rudolf; Henkel, Marius; Contiero, Jonas
Fonte: Carl Hanser Verlag Publicador: Carl Hanser Verlag
Tipo: Artigo de Revista Científica Formato: 397-405
ENG
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 07/03983-4; This paper evaluates the effect of additives (NaCl and ethanol) on the solution properties of rhamnolipids. The properties are the surface activity, aggregate formations and emulsifying activity as well as the synergistic effects of additives and pH variations on the physical properties of rhamnolipids. Additionally, analysis of fatty acids and rhamnolipid homologues produced using different carbon sources was performed by mass spectrometry. The results indicate that this biosurfactant maintain its properties in the presence of additives. NaCl decreases the size and number of aggregates formed in solutions without pH control, while ethanol to rhamnolipid solutions reduces critical micelle concentration and favors aggregation of monomers. The profiles of fatty acids produced by P. aeruginosa LBI 2A1 varied according to the carbon source used, however for rhamnolipids there was no difference.

Isolation and functional characterization of a biosurfactant produced by Lactobacillus paracasei

Gudiña, Eduardo J.; Teixeira, J. A.; Rodrigues, L. R.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /03/2010 ENG
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In this study, the crude biosurfactant produced by a Lactobacillus paracasei strain isolated in a Portuguese dairy industry was characterized. The minimum surface tension (41.8mN/m) and the critical micelle concentration (2.5 mg/ml) obtained were found to be similar to the values previously reported for biosurfactants isolated from other lactobacilli. The biosurfactant was found to be stable to pH changes over a range from 6 to 10, being more effective at pH 7, and showed no loss of surface activity after incubation at 60 ◦C for 120 h. Although the biosurfactant chemical composition has not been determined yet, a fraction was isolated through acidic precipitation, which exhibited higher surface activity as compared with the crude biosurfactant. Furthermore, this isolated biosurfactant showed antimicrobial and anti-adhesive activities against several pathogenic microorganisms. In addition, L. paracasei exhibited a strong autoaggregating phenotype, which was maintained after washing and resuspending the cells in PBS, meaning that this attribute must be related to cell surface components and not to excreted factors. The autoaggregation ability exhibited by this strain, together with the antimicrobial and anti-adhesive properties observed for this biosurfactant opens the possibility for its use as an effective probiotic strain.; Fundação para a Ciência e a Tecnologia (FCT)under the scope of the Project BIOSURFA: Biosurfactants application for microbial adhesion inhibition in medical devices.

Determinação da concentração micelar crítica de ácidos húmicos por medidas de condutividade e espectroscopia

Moraes,Solange Leite de; Rezende,Maria Olímpia Oliveira
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2004 PT
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The aim of this study was the determination of the critical micelle concentration (CMC) of the sodium dodecyl sulfate (SDS) surfactant using spectroscopic and conductimetric determinations and to compare these methodologies in the determination of the CMC of different humic acids (HA). The CMC obtained by conductimetric determination was satisfactory. By spectroscopic determination two values of the CMC were obtained for HA. These values can be to due the intra and intermolecular interactions in the HA structure.

Efecto del catión, del anión y del co-ión sobre la agregación de líquidos iónicos en solución acuosa

Guzmán,Nólides Marina; Fernández,José Francisco; Parada,Mónica; Orbegozo,Carlos; Rodríguez,María Alejandra; Padrón,Alida; Thöming,Jorg
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 ES
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The aggregation behavior of thirteen 1-alkyl-3-methylimidazolium based ionic liquids in aqueous solution is presented, considering variations of the alkyl side chain length as well as the anionic moiety. Cation and anion molecular volumes are selected as appropriate molecular descriptors. Additionally, the existing relationship between critical micelle concentration (CMC) and electrolyte concentration in solution is established, aiming to clarify ion effects. CMC values were obtained by measuring electrical conductivity and surface tension. It was confirmed that aggregation of ionic liquids in aqueous solution and in presence of inorganic salts is affected by the factors developed in this study.

Solubilization of human erythrocyte membranes by ASB detergents

Domingues,C.C.; Malheiros,S.V.P.; de Paula,E.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2008 EN
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Understanding the membrane solubilization process and finding effective solubilizing agents are crucial challenges in biochemical research. Here we report results on the interaction of the novel linear alkylamido propyl dimethyl amino propanosulfonate detergents, ASB-14 and ASB-16, with human erythrocyte membranes. An estimation of the critical micelle concentration of these zwitterionic detergents (ASB-14 = 100 µM and ASB-16 = 10 µM) was obtained using electron paramagnetic resonance. The amount of proteins and cholesterol solubilized from erythrocytes by these detergents was then determined. The hemolytic activities of the ASB detergents were assayed and the detergent/lipid molar ratios for the onset of hemolysis (Re sat) and total lysis (Re sol) were calculated, allowing the determination of the membrane binding constants (Kb). ASB-14 presented lower membrane affinity (Kb = 7050 M-1) than ASB-16 (Kb = 15610 M-1). The amount of proteins and cholesterol solubilized by both ASB detergents was higher while Re sat values (0.22 and 0.08 detergent/lipid for ASB-14 and ASB-16, respectively) were smaller than those observed with the classic detergents CHAPS and Triton X-100. These results reveal that, besides their well-known use as membrane protein solubilizers to enhance the resolution of two dimensional electrophoresis/mass spectrometry...

Relationship of critical micelle concentrations of bacterial lipoteichoic acids to biological activities.

Courtney, H S; Simpson, W A; Beachey, E H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1986 EN
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The critical micelle concentration (CMC) of lipoteichoic acid (LTA) was investigated with two dyes, rhodamine 6G and Coomassie brilliant blue R-250. Both dyes gave similar values for the CMC of LTA. The CMC of LTA from several species of bacteria ranged from 28 to 60 micrograms/ml in phosphate-buffered saline. The CMC values for the LTAs are in the range expected for an amphiphile containing a single, 16-carbon fatty acid residue. Formation of micelles was not detected with deacylated LTA. Salt decreased the CMC of LTA from 380 micrograms/ml in distilled water to 37 micrograms/ml in 0.5 M NaCl. At concentrations greater than the CMC, LTA induced the lysis of sheep erythrocytes and was cytotoxic for Girardi heart cells. The data suggest that LTA in the micellar state may cause disruption of the erythrocyte membrane and may be cytotoxic for cells in culture.

Lanthanide-induced phosphorus-31 NMR downfield chemical shifts of lysophosphatidylcholines are sensitive to lysophospholipid critical micelle concentration.

Kumar, V V; Baumann, W J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1991 EN
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613.2966%
Lysophosphatidylcholine (lysoPC) monomers or micelles in water give rise to a narrow, isotropic phosphorus-31 NMR signal (40.6 ppm; v1/2 1.7 Hz; 32.2 MHz). Upon addition of praseodymium ions, the phosphorus signals are shifted downfield. However, the downfield shifts for the longer-chain lysophosphatidylcholines, which exist in the aggregated state, are far greater than those for the shorter-chain homologues, which exist as monomers. At a Pr3+/lysoPC molar ratio of 0.5, the signals of C12lysoPC through C18lysoPC were shifted by 12.1 ppm, whereas the signals of C6lysoPC and C8lysoPC were shifted by only 2.26 ppm. This very pronounced difference in lanthanide-induced downfield shifts between micelles and monomers can be utilized to determine with accuracy lysoPC critical micelle concentrations (CMC) from downfield shift-vs.-concentration plots. The CMC values we determined were 57 mM for C8lysoPC, 5.7 mM for C10lysoPC, and 0.6 mM for C12lysoPC. The shift reagent phosphorus-31 nuclear magnetic resonance technique particularly lends itself to the measurement of CMC values in the millimolar and high micromolar range. The method can equally be used for measuring critical micelle concentrations of short-chain phosphatidylcholines.

Effect of polyoxypropylene chain length on the critical micelle concentration of propylene oxide-ethylene oxide block copolymers*

Zhang, Zhi-guo; Yin, Hong
Fonte: Zhejiang University Press Publicador: Zhejiang University Press
Tipo: Artigo de Revista Científica
EN
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705.7558%
In this work, the surface activity of block copolymer nonionic surfactants (RPE) has been determined, i.e., critical micelle concentration (CMC), surface excess concentration (Γ), surface area demand per molecule (A), surface tension at CMC (γ CMC). A linear decrease of ln[CMC] vs number of oxypropylene units in copolymer molecule was observed. The change in the work of cohesion per oxypropylene group when passing from molecular into micellar state, calculated from the Shinoda equation, was 0.43kT for the studied compounds.

A facile surfactant critical micelle concentration determination

Cai, Lifeng; Gochin, Miriam; Liu, Keliang
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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702.22445%
Liquid surface curvature variations in microplate wells due to different liquid surface tension cause significant signal change in spectroscopic measurement using a plate reader with a vertical detecting light beam. The signals have been quantitated and used to develop a method for facile surfactant critical micelle concentration determination.

Alcohols Effect on Critic Micelle Concentration of Polysorbate 20 and Cetyl Trimethyl Ammonium Bromine Mixed Solutions

Sidim, Taliha; Acar, Gökhan
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
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609.9447%
In this research, the micellar behavior of a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB) and an nonionic surfactant, polysorbate 20 (Polyoxyethylene (20) sorbitan monolaurate) in different alcohol solutions media was investigated over the temperature range 293.15–313.15 K. The interaction between two surfactants in binary systems can be determined by calculating the values of their β parameters. The critical micelle concentrations (CMC) of the micelles were determined from the surface tension, the conductivity at different temperatures. The CMC behavior of CTAB and polysorbate 20 was analyzed in terms of the effect of temperature and the increase in the alcohol carbon chain. Changes in the critical micelle concentration of mixed surfactant systems of different alcohol solutions were measured. The CMC decreased sharply as the hydrocarbon chain length of the alcohols becomes larger. This shows that the more hydrophobic alcohols are, the more marked a decrease in CMC is observed.

Modelling of the Critical Micelle Concentration of Cationic Gemini Surfactants Using Molecular Connectivity Indices

Mozrzymas, Anna
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
EN
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595.4828%
Modelling of the critical micelle concentrations (cmc) using the molecular connectivity indices was performed for a set of 21 cationic gemini surfactants with medium-length spacers. The obtained model contains only the second-order Kier and Hall molecular connectivity index. It is suggested that the index 2χ includes some information about flexibility. The obtained model was used to predict log10 cmc of other cationic gemini surfactants. The agreement between calculated and experimental values of log10 cmc for the gemini surfactants that were not used in the correlation is very good.

Synthesis, thermal behavior, and aggregation in aqueous solution of poly(methyl methacrylate)-b-poly(2-hydroxyethyl methacrylate)

ACEVEDO, B.; MARTINEZ, F.; OLEA, A. F.
Fonte: 2014 Sociedad Chilena de Química Publicador: 2014 Sociedad Chilena de Química
Tipo: Artigo de Revista Científica
EN
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713.2966%
Indexación: Scielo; ABSTRACT Amphiphilic block copolymers of poly(methyl methacrylate) PMMA and poly(2-hidroxyethyl methacrylate) PHEMA were synthesized by a two-step atom transfer radical polymerization (ATRP). Copolymers with various degrees of polymerization and different relative block sizes were obtained. The structure of the resulting polymers have been characterized and verified by FT-IR and 1H-NMR, molecular weight were determined by size exclusion chromatography analyses. The thermal properties of these polymers were investigated by differential scanning calorimetry DSC and thermogravimetric analysis TGA. The glass transition temperature of mono halogenated PMMA increases from 116 °C to 123 °C with increasing molecular weight, whereas the glass transition temperature of block copolymers depends slightly on polymer structure. The derivatives of TGA curves indicate that thermal degradation occurs in one stage. The self-assembly of PMMA-b-PHEMA in aqueous solution have been investigated by fluorescence probing methods. The critical micelle concentrations are in the range 10-6 - 10-7 M. The micropolarity sensed by pyrene is higher than in aggregates formed by block copolymers based on polystyrene. Keywords: Block copolymers...

Label-Free Critical Micelle Concentration Determination of Bacterial Quorum Sensing Molecules

Davis, B.M.; Richens, J.L.; O'Shea, P.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 06/07/2011 EN
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A practical label-free method for the rapid determination of small-molecule critical micelle concentration (CMC) using a fixed-angle light-scattering technique is described. Change in 90° light scattering at a fixed wavelength of incident radiation with increasing bacterial quorum molecule concentration and the observation of a break point is used to determine CMC. In our study, this technique is utilized to investigate the aqueous CMC of previously uncharacterized Pseudomonas aeruginosa quorum sensing signaling molecules (QSSM) belonging to the n-acylhomoserine lactone and 2-alkyl-4-quinolone classes. Several were found to form micelles within a physiologically relevant concentration range and potential roles of these micelles as QSSM transporters are discussed. The influence of temperature and the presence of biological membranes or serum proteins on QSSM CMC are also investigated and evidence is obtained to suggest the QSSMs studied are capable of both membrane and serum protein interaction. This demonstrates that the fixed-angle light-scattering technique outlined can be used simply and rapidly to determine small-molecule CMC under a variety of conditions.

Surface tension model for surfactant solutions at the critical micelle concentration

Burlatsky, S. F.; Atrazhev, V. V.; Dmitriev, D. V.; Sultanov, V. I.; Timokhina, E. N.; Ugolkova, E. A.; Tulyani, S.; Vincitore, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/06/2013
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A model for the limiting surface tension of surfactant solutions (surface tension at and above the critical micelle concentration, cmc) was developed. This model takes advantage of the equilibrium between the surfactant molecules on the liquid/vacuum surface and in micelles in the bulk at the cmc. An approximate analytical equation for the surface tension at the cmc was obtained. The derived equation contains two parameters, which characterize the intermolecular interactions in the micelles, and the third parameter, which is the surface area per surfactant molecule at the interface. These parameters were calculated using a new atomistic modeling approach. The performed calculations of the limiting surface tension for four simple surfactants show good agreement with experimental data (~30% accuracy). The developed model provides the guidance for design of surfactants with low surface tension values.

Micelle formation in block copolymer/homopolymer blends: comparison of self-consistent field theory with experiment and scaling theory

Greenall, M. J.; Buzza, D. M. A.; McLeish, T. C. B.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We present a self-consistent field theory (SCFT) study of spherical micelle formation in a blend of poly(styrene-butadiene) diblocks and homopolystyrene. The micelle core radii, corona thicknesses and critical micelle concentrations are calculated as functions of the polymer molecular weights and the composition of the diblocks. Our results are compared with an earlier scaling theory and with X-ray scattering data. The agreement between self-consistent field theory and experiment for the micelle structure is sometimes quantitative and is generally more successful than scaling theory. For copolymers with relatively light core blocks, SCFT predictions for the critical micelle concentration improve over those of scaling theories by an order of magnitude. In the case of heavier core blocks, SCFT predicts the critical micelle concentration less well due to inaccuracies in the modelling of the bulk chemical potential. Overall, we find that SCFT gives a very good description of spherical micelle formation and hence demonstrate that a mean-field, equilibrium approach is valid for these systems.; Comment: accepted by Macromolecules; free energy minimisation method corrected

Adsorption Kinetics and Structural Arrangements of Cationic Surfactants on Silica Surfaces

Atkin, R; Craig, Vincent; Biggs, Simon
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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The adsorption of cetyltrimethylammonium bromide (CTAB) to the silica-aqueous interface has been studied using optical reflectometry. The effect of pH, salt, and surface preparation on the surface excess and adsorption kinetics has been studied. The adsorption kinetics have been measured and compared to the theoretical diffusion limited flux of surfactant, the quotient being the `sticking ratio'. Analysis of the sticking ratio as a function of CTAB concentration reveals that the adsorption process is cooperative above the critical micelle concentration (CMC). At the critical surface aggregation concentration (CSAC), adsorption proceeds slowly in the absence of salt and takes hours to reach an equilibrium value. At all other concentrations and even at the CSAC when salt is present, the adsorption is complete within minutes. These results indicate that, above the CMC, micelles adsorb directly to the silica surface, and this is reflected in the structure of the surface layer. At the CSAC the equilibrium surface structure is analogous to adsorbed micelles, but as only monomers are present in solution, the adsorption proceeds to equilibrium slowly.