Electrophoretic Mobility Measurements Research Articles

Dispersion of thulium-yttria nanoparticles to build up smart structures

The development of new materials for radiation dosimetry is a challenge to assure quality improvement practices related to radiation protection concept. On this context, colloidal stability provides conditions to build up smart structured materials from bottom-up perspective. The present work reports zeta potential characterization of thulium-yttria nanoparticles in aqueous medium. Thulium-yttria nanoparticles formed by a relative low temperature hydrotermal synthesis were characterized by XRD, PCS, and SEM. The stability of particles in aqueous medium was evaluated by electrophoretic mobility measurements, followed by zeta potential calculation. The results revealed that the isoelectric point of thulium-yttria suspensions shifted in accordance with thulium concentration from pH 8.5 (“pure” yttria) to pH 9.2 (2at.%Tm). Besides, most suspensions could be stabilized at pH 10.5, presenting zeta potential values around 30 mV. These results are substantial parameters to advance toward new materials for radiation dosimetry.

Molybdenite Flotation in the Presence of a Polyacrylamide of Low Anionicity Subjected to Different Conditions of Mechanical Shearing

Polyacrylamides (PAM) are used as flocculants in the copper-molybdenum mining industry to improve the settling rate of flotation tailings. These types of reagents are recirculated to flotation in the water that is recovered from the thickeners, and as a result of this practice they can cause depression of flotation of some important minerals such as molybdenite. The objective of this work was to study the effect of a PAM of 11.9% of degree of anionicity on the flotation of molybdenite. The effect of the anionic PAM on molybdenite flotation was studied under different levels (three) of flocculant mechanical shearing. The flotation data was discussed along with intrinsic viscosity, adsorption, induction time, and electrophoretic mobility measurements. It was found that the non-sheared PAM (NS–PAM) had the strongest depressing effect on molybdenite flotation, followed by the moderately sheared PAM (MS–PAM). The depressing effect of the strongly sheared PAM (SS–PAM) was negligible. The flotation data correlated with the induction time measurements that showed that molybdenite became more hydrophilic in the presence of the NS–PAM. The SS–PAM has no effect on the induction times. Further work is ongoing to understand the effect of PAM on molybdenite flotation in the presence of clay minerals and different aqueous media.

Aggregation and transport behavior of goethite colloids as affected by dissolved organic matter and pH: Electrostatic vs. hydrophilic interactions

Wettable surfaces in aqueous media experience hydrophilic repulsion forces, which have been thoroughly examined for interactions between biocolloids. However, there is no systematic assessment yet on the effects of hydrophilic repulsion on aggregation and transport behavior of soil mineral colloids. The aim of this study was to fill that gap in knowledge, with an emphasis on whether hydrophilic or electrostatic forces govern the respective interactions. For that, the interactions of hydrophilic goethite colloids were examined by batch aggregation experiments and colloid breakthrough experiments using columns filled with hydrophilic quartz sand. To induce electrostatic interactions ranging from attractive to repulsive, colloid zeta potential was modified via changes in dissolved organic matter concentration and pH. Classic DLVO and the extended DLVO (XDLVO) theory that includes hydrophilic interaction energies were applied using electrophoretic mobility measurements and sessile drop contact angle data. Results showed that for each case in which hydrophilic repulsion was predicted to be stronger than electrostatic attraction, the latter always controlled the colloid aggregation and transport behavior in the experiment. The likely reason was that the irregular shape and surface roughness of the colloids, as shown by SEM images, rendered the short-range hydrophilic repulsion ineffective, so that the more long-range electrostatic interactions predominated. We conclude that in contrast to biocolloids, hydrophilic repulsion did not have a relevant effect on the interactions between soil mineral colloids. Hence, our study clearly shows that for the aggregation and mobility of soil mineral colloids, soil parameters affecting their surface charge are more important than parameters affecting their wettability.

Dispersed liquid crystals as pH-adjustable antimicrobial peptide nanocarriers

HypothesispH-responsive nanocarriers have the potential to provide targeted delivery of antimicrobial peptides (AMPs) to sites of bacterial infection with typically abnormal pH levels in the body. However, the local pH of the infected sites varies substantially among different infection-related diseases, calling for the development of delivery systems capable of targeting local pathological conditions in an adjustable pH range. ExperimentsIn this study, a highly versatile pH-responsive nanocarrier platform, based on dispersions of oleic acid (OA) and glycerol monooleate (GMO) self-assemblies with the human cathelicidin AMP LL-37, was designed and characterized. FindingsA detailed pH-composition phase diagram was constructed from small angle X-ray scattering and cryogenic transmission electron microscopy data. In addition, the protonation state and apparent pKa of OA embedded in these nano-self-assemblies were investigated by electrophoretic mobility measurements at different pHs and found to be strongly dependent on nanocarrier composition. By varying composition of these nanocarriers, the apparent pKa of embedded OA molecules could be tuned from 7.8 to 6.3, shifting the range of nanocarriers' pH-response. The study advances our fundamental understanding of self-assembly and pH-responsiveness in lipid-peptide systems containing monounsaturated long-chain fatty acids. The results may guide the future design of highly adaptable nanocarriers for patient-optimized pH-targeted AMP delivery.

Investigating the binding measurements of human α-acid glycoprotein with chlorambucil and dacarbazine in the presence of imidazolium based -ionic liquid by affinity capillary electrophoresis

Human alpha (α1)-acid glycoprotein (AGP) is an acute phase protein whose plasma concentration increases several-folds in the presence of various diseases. The variability in AGP plasma concentration is expected to have a huge impact on the drug binding equilibrium. Therefore, a precise measurement of AGP-drug binding is of great demand for drug development. In the current study, an ionic liquid-based aqueous two-phase system combined with affinity capillary electrophoresis (ILATPS/ACE) was utilised in order to improve the accuracy of AGP-drug binding analysis through the measurements of electrophoretic mobilities. The utilisation of ILATPS has shown to have a positive impact on the stability of AGP activity solution during the storage for an extended period of time. In addition, the effect of various alkyl chains (C2-C10) of imidazolium-based ILs with concentrations ranging between 10.00 and 1000.0 μmol L−1 on the AGP binding with the anti-cancer drugs chlorambucil (CHL) and dacarbazine (DAC) was examined by the system developed (ILATPS/ACE). A 100.00 μmol L−1 1-ethyl-3-methylimidazolium chloride (EMImCl) prepared in the physiological buffer conditions containing AGP (5.00–100.00 µmol L−1) has provided an accurate apparent binding constant of 1.99 ± 0.11 and 6.95 ± 0.14 L mmol−1 with CHL and DAC respectively. Apart from the ACE analysis, EMImCl/phosphate buffer solution was found to be a distinguished system that could lengthen the stability of AGP activity for a period of time reaching 90 days during the solution storage at 4.00 °C. This effect is thought to be due to the easy conversion of one-phase EMImCl/phosphate buffer/AGP at the ambient lab temperature into the two-phase solution at refrigerator temperature, 4.00 °C, and vice versa. Therefore, the ILATP/ACE system could be used to enhance the accuracy for other AGP-drug bindings with a fast, easy to use, and cost-effective analysis.

Adenine Derivatives for Regenerable Antibacterial Surface Applications Based on A−T Base Pairing

AbstractSurface contamination is a major concern in the design, fabrication, and application of biomaterials. In this work, a series of new adenine derivatives were synthesized in a three‐step method with the goal of protecting the functional materials against microbial adhesion. Initially, 9‐(chloroalkyl)‐9H‐purin‐6‐amine compounds were synthesized from adenine. Then, these compounds were reacted with potassium thiocyanate or potassium selenocyanate. In the last step, adenine derivatives incorporating a tetrazole ring were synthesized via the cycloaddition of sodium azide with thiocyano or selenocyano derivatives. The antimicrobial activity of the compounds was evaluated by using the minimal inhibitory concentration method. Furthermore, the effect of the compounds on pBR322 plasmid DNA was studied using gel electrophoretic mobility measurements. The antimicrobial assay showed that some of the synthesized compounds exerted vigorous antibacterial and antifungal activities. Further experiments indicated that seleno‐adenine derivatives have higher antimicrobial and DNA effect than other derivatives. The surfaces activated by the adenine derivative demonstrated antibacterial activity resisting bacterial attachment in order to remove dead bacteria from the surface. All results showed that some of these adenine derivatives have an antibacterial activity and the potential for further applications, for example as a smart surface coating that prevents bacterial adhesion to biomaterials.

Effect of temperature on the association behavior in aqueous mixtures of an oppositely charged amphiphilic block copolymer and bile salt

The association in aqueous mixtures of a thermoresponsive cationic diblock copolymer composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(3-acrylamidopropyl)-trimethylammonium-chloride (PAMPTMA(+)) and the oppositely charged bile salt sodium deoxycholate (NaDC) is investigated at different compositions by light and X-ray scattering, calorimetry, and electrophoretic mobility measurements. Clouding reveals aggregation upon heating. The addition of NaDC to the copolymer solution lowers the temperature of the transition and increases its cooperativity. At high temperature and low NaDC fractions, mixed aggregates with a dehydrated PNIPAM-rich interior and a PAMPTMA(+)-rich shell partially neutralized by DC– anions are formed. At high NaDC fractions, the aggregates present internal regularly spaced segregated nanoregions of dehydrated PNIPAM and PAMPTMA(+)/DC– (microphase separation). The results suggest that the mixed aggregates have appealing composition-controlled thermoresponse. The system phase separates at body temperature and the highest NaDC fractions investigated, meaning in conditions accomplished when the use of the polymer as a bile salt sequestrant is hypothesized.

Determination of Protein Charge in Aqueous Solution Using Electrophoretic Light Scattering: A Critical Investigation of the Theoretical Fundamentals and Experimental Methodologies.

Studies are reported of the measurement of electrophoretic mobilities of bovine serum albumin (BSA) in aqueous potassium chloride solutions as a function of ionic strength and pH using electrophoretic light scattering (ELS). It is demonstrated that the use of palladium or platinum electrodes should be avoided and that platinized platinum electrodes are necessary to avoid interference from unwanted electrochemical phenomena at the electrode-liquid interface. Potentiometric acid titration was performed to quantify the amount of protonic charge per protein molecule at the same pH values as the electrophoretic mobility measurements. It is shown that appropriate selection of an electrokinetic model yields excellent agreement between predicted and experimental electrophoretic mobilities across the ranges of pH and ionic strength studied in accordance with the protonic charge values obtained by titration. The experimental results are explained in terms of protonation, chloride counterion binding, and protein molecule permeability. This work highlights specific requirements of using ELS for confident analysis of proteins in aqueous solutions.

Characterization of Human Glioblastoma versus Normal Plasma-Derived Extracellular Vesicles Preisolated by Differential Centrifugation Using Cyclical Electrical Field-Flow Fractionation.

Although many properties for small extracellular vesicles (sEVs, formerly termed "exosomes") isolated at ∼100 000g are known, a wide range of values are reported for their electrophoretic mobility (EM) measurements. This paper reports for the first time the effect of dilution on the EM of U87 glioblastoma cell-derived and plasma-derived sEVs and medium size EVs (mEVs, commonly termed "oncosomes") preisolated by differential centrifugation. Furthermore, the effect of resalting on the EM of sEVs and mEVs was evaluated. The EM of U87 sEVs and U87 mEVs showed an increase as the salt concentration decreased to 0.005% of the initial salt concentration. However, for the plasma sEVs and plasma mEVs, the electrophoretic mobility increased as the salt concentration decreased to 0.01% of the initial salt concentration and then increased to its initial value when the salt concentration decreased to 0.005% of the initial salt concentration. For both U87 and plasma sEVs and mEVs, the EM remained almost constant when the concentration of the particles changed and the salt concentration was kept the same as its initial value. This indicates that the EM of EVs is only a function of the salt concentration of the buffer and is independent of the concentration of the particles. The sEVs and mEVs were separated with cyclical ElFFF for the first time. The results indicate that ElFFF was able to fractionate the EVs, and a crescent-shaped trend was found for the retention time when the applied AC voltage was altered (increased).

How Low Can You Go? Molecular Details of Low-Charge Nanoemulsion Surfaces.

Negative charge accumulation at aqueous-hydrophobic interfaces and its pH-dependent behavior are routinely ascribed to special adsorption properties of hydroxide ions. Mounting experimental and computational evidence, however, indicates that this negative charge accumulation is the result of surface-active impurities. If true, these impurities would obfuscate our fundamental understanding of the molecular structure and bonding environment at aqueous-hydrophobic interfaces. In this work, we describe the preparation and characterization of bare low-charge nanoemulsions (LCNEs), nanosized droplets of oil-absent emulsifiers. Electrophoretic mobility measurements of LCNE droplets in varying pH environments suggest that trace surface-adsorbed impurities are contributing to the lingering negative surface charge that leads to their marginal stability. We then use vibrational sum-frequency scattering spectroscopy to support this claim and to study the molecular structure and bonding environment of the interfacial aqueous and hydrophobic phases on both the LCNE surface and the surface of nanoemulsions with increasing amounts of adsorbed surfactants. For LCNE samples, our results show that interfacial water bonds more strongly to the oil phase on the droplet surface compared to similar planar interfaces. Interfacial oil molecules are found to orient mostly parallel to the bare droplet surface and reorganize upon surfactant adsorption. In summation, the results reported here provide a new look at the molecular structure and bonding of bare nanoemulsion surfaces and contribute to our evolving understanding of bare aqueous-hydrophobic interfaces.

Non-invasive targeted iontophoretic delivery of cetuximab to skin

ABSTRACTBackground: Cetuximab (CTX) is a glycosylated anti-EGFR monoclonal antibody of great interest in the treatment of non-melanoma skin cancers. Its intravenous administration is associated with severe side effects. This is the first report on the noninvasive iontophoretic-targeted topical delivery of CTX to skin.Methods: Iontophoretic transport of CTX (0.5 mA/cm2) was studied as a function of formulation pH (4, 5.5 and 7) and duration of current application (2, 4 and 8 h). CTX cutaneous biodistribution was determined; electrotransport mechanisms and penetration pathways were investigated.Results: Electrophoretic mobility measurements of CTX isoforms and co-iontophoresis of acetaminophen at each pH demonstrated that CTX electrotransport was due to electroosmosis: despite an ~8-fold reduction in charge, CTX skin deposition was greater at pH 7 than pH 4 (8.974 ± 1.952 and 0.482 ± 0.165 μg/mm3) – consistent with the increased electroosmotic flow at pH 7. Iontophoresis of an Alex488-CTX conjugate showed that skin penetration occurred by the intercellular and follicular routes. Therapeutic concentrations of CTX in the viable epidermis, upper dermis and lower dermis were achieved following iontophoresis for 2, 4 and 8 h, respectively.Conclusion: The results demonstrate the topical delivery of a 152 kDa monoclonal antibody into skin in a targeted, controlled and entirely noninvasive manner.

Nanoparticle charging with mixed reverse micelles in apolar media

The charging of colloidal particles using mixed surfactants in apolar media is investigated. Previous work has shown that one can predict the sign and magnitude of particle charge by comparing the acid-base properties of an oil-soluble surfactant to the acid-base properties of a specific particle. The present work sought to tune the acid-base properties by using mixed surfactants. Unexpected mineral oxide particle charging results were obtained however, from mixing the acidic surfactant sorbitan monooleate (SPAN 80), with the basic surfactant polyisobutylene succinimide (OLOA 11000), requiring further investigation into the mixed reverse co-micelle particle charging mechanism. Conductometric titrations and small-angle neutron and x-ray scattering measurements showed that the surfactant mixtures formed spherical reverse co-micelles. Quartz crystal microbalance adsorption measurements demonstrated that both surfactants can adsorb to the particle surface. Lastly, electrophoretic mobility measurements showed that the surfactant mixture produced negative particle charging for nearly all surfactant ratios, and a greater magnitude of negative charging than that produced by the OLOA 11000 surfactant alone. It was discovered that in the mixed surfactant system studied, the basic surfactant would charge the hydroxyl groups on both the oxide surface, and the adsorbed acidic surfactant head groups. The results showed that particle charging behavior in apolar media using mixed micelles requires knowledge beyond that for the individual surfactants and their proportions in the mixture.

Charging of Oxide Nanoparticles in Media of Intermediate Dielectric Constant.

The use of surfactants to charge colloidal particles in solvents of intermediate dielectric constants (5 < ε < 40) is investigated. While particle charging mechanisms in aqueous (ε = 80) and apolar (ε < 5) media are well understood, the interplay of these different charging mechanisms, which can all occur in solvents of intermediate dielectric constants (sometimes referred to as "leaky dielectrics"), remains to be fully explored. Conductometric titrations determining the critical micelle concentration (CMC) of the surfactant (aerosol-OT) confirm the existence of reverse micelles in intermediate dielectrics and show that as the solvent dielectric constant decreases, the CMC decreases as well. Electrophoretic mobility measurements of three oxide particles (SiO2, TiO2, and MgO) highlight various charging mechanisms that arise from particle-solvent, particle-surfactant, and solvent-surfactant interactions in a solvent series of alcohols and ketones. The results show that a combination of donor-acceptor particle-solvent interactions, surfactant ion adsorption, and reverse micelle-mediated acid-base interactions can all charge oxide particles in intermediate dielectrics. Furthermore, the results show that the dielectric constant of the solvent affects the relative magnitudes of each charging mechanism.

Transparent layer-by-layer coatings based on biopolymers and CeO2 to protect wood from UV light

Wood is a renewable and abundant material with a high aesthetic appeal, but is heavily affected by weathering, particularly by UV-induced degradation in unprotected exposure. Here, we demonstrate a simple coating procedure of spruce wood with UV-protective CeO2 nanoparticles and biopolymers. Using a layer-by-layer approach, multilayers of the nanoparticles and biopolymers (chitosan or cationic starch) were deposited onto the wood surface by a simple dip coating process. The nanoparticle suspensions and biopolymer solutions were characterized by dynamic light scattering and electrophoretic mobility measurements. The coated wood surfaces were visualized by SEM and the successful nanoparticle deposition confirmed by EDX. The streaming potential data correlated strongly with the proposed layered build-up. The established coatings were transparent and did only lead to a minute alteration of the surface color. At the same time, they reduced the amount of UV light induced color change in all CIELAB dimensions.

Denatured lysozyme-coated carbon nanotubes: a versatile biohybrid material

Carbon nanotubes (CNTs) are among the most versatile nanomaterials, but their exploitation is hindered by limited dispersibility, especially in aqueous solvents. Here, we show that AP-LYS, a highly cationic soluble derivative of denatured hen egg lysozyme, is a very effective tool for the unbundling and solubilisation of CNTs. AP-LYS proved to mediate the complete and stable dispersion of CNTs at protein: CNT ratios ≥1: 3 (w:w) in very mild conditions (10–20 minutes sonication in ammonium acetate buffer, pH 5.0). Electrophoretic mobility and ζ-potential measurements confirmed that dispersed CNTs were coated by the protein, whereas molecular docking was used to study the interactions between AP-LYS and CNTs. AP-LYS-coated CNTs proved to be a very effective microbial cell-flocculating agent with an efficiency similar to that of chitosan, one of the best available flocculating agents, thus suggesting that this hybrid could find industrial applications in the treatment of wastewaters contaminated by microbial cells, or to remove microbial cells after fermentation processes. Moreover, we exploited the low stability of AP-LYS-coated CNT dispersions in eukaryotic cell culture media to prepare scaffolds with an extracellular matrix-like rough surface for the cultivation of eukaryotic cells.

Spectroscopic insights into the effect of pH, temperature, and stabilizer on erlotinib adsorption behavior onto Ag nanosurface.

In this study, surface - enhanced Raman spectroscopy (SERS) was applied at the first time for estimation of how pH, temperature, and nanoparticle (NP) stabilizer affect an adsorption behavior of erlotinib (drug approved in a non-small cell lung cancer therapy) onto citrate-stabilized silver nanoparticles (AgNPs). Novel approach to improve cancer therapy assumes application of NPs as an efficient drug delivery system. This strategy requires designing stable drug/nanocarrier conjugates that can effectively interact in the target site. It is also important to perform deeply characterization of a drug orientation on the potential carrier surface and estimation how stable the appeared interaction is. Performed analysis, indicates that pH, temperature, presence of NP stabilizers, and time of incubation have an influence on the occurring adsorption geometry of the drug. However, the observed erlotinib/AgNP interaction remains stable regardless of the applied conditions. These considerations were supported by insightful physicochemical characteristics of the AgNPs and the erlotinib/AgNP conjugates by conducting transmission electron microscopy (TEM) imaging, determination of colloid stability conducted with the use of dynamic light scattering technique (DLS) and measurements of electrophoretic mobility. Such complex approach allows a better understanding of the stability of the erlotinib/AgNP conjugates and provides information how the investigated interaction is affected by the induced perturbations.

Assessment of the use of lignosulfonates to separate chalcopyrite and molybdenite by flotation

Molybdenum is the most important by-product of Chile's copper mining industry, and during the last decade gained international relevance because of its high price At mining deposits, copper and molybdenum are extracted together and then separated in a process consisting of several stages of flotation using sodium hydrosulfide (NaHS) as key reagent. However, environmental issues related to the potential emissions of toxic hydrosulfide gas (H2S), and bad odors make necessary the development of new environmentally friendly processes that incorporate non-toxic reagents. In this work, we hypothesize that a selective separation of chalcopyrite and molybdenite by flotation can be achieved by using lignosulfonates instead of NaHS. This approach was evaluated by testing the effect of lignosulfonates, produced by reacting kraft lignin with sodium sulfite and formaldehyde, and commercially available lignosulfonates, on molybdenite and chalcopyrite flotation. Chemical characterization of lignosulfonates was performed by determination of molecular mass, elemental analysis, fourier transform infrared, and mass spectroscopy with inductively coupled plasma. Also, interactions between molybdenite and lignosulfonates were studied through measurements of electrophoretic mobility. The main conclusions of the work are that molybdenite flotation can be depressed by the action of lignosulfonates, and such depressing effect increases with pH because of the interactions between lignosulfonates with the metallic calcium sites existing on the surface of the mineral particles. The experimental results also indicate that lignosulfonates can depress chalcopyrite flotation when sodium isopropyl xanthate is used as a collector, but this effect can be completely mitigated by using potassium amyl xanthate as a collector, thus, making it possible the potential separation of both minerals.

Hyperthermia-Triggered Doxorubicin Release from Polymer-Coated Magnetic Nanorods.

In this paper, it is proposed that polymer-coated magnetic nanorods (MNRs) can be used with the advantage of a double objective: first, to serve as magnetic hyperthermia agents, and second, to be used as magnetic vehicles for the antitumor drug doxorubicin (DOX). Two different synthetic methodologies (hydrothermal and co-precipitation) were used to obtain MNRs of maghemite and magnetite. They were coated with poly(ethyleneimine) and poly(sodium 4-styrenesulfonate), and loaded with DOX, using the Layer-by-Layer technique. Evidence of the polymer coating and the drug loading was justified by ATR-FTIR and electrophoretic mobility measurements, and the composition of the coated nanorods was obtained by a thermogravimetric analysis. The nanorods were tested as magnetic hyperthermia agents, and it was found that they provided sufficiently large heating rates to be used as adjuvant therapy against solid tumors. DOX loading and release were determined by UV-visible spectroscopy, and it was found that up to 50% of the loaded drug was released in about 5 h, although the rate of release could be regulated by simultaneous application of hyperthermia, which acts as a sort of external release-trigger. Shape control offers another physical property of the particles as candidates to interact with tumor cells, and particles that are not too elongated can easily find their way through the cell membrane.

Anionic polyacrylamide as a substance strengthening the Pb(II) immobilization on the kaolinite surface

The main purpose of the study was to examine lead(II) ion immobilization on the kaolinite surface and determine the effect of soil flocculant (macromolecular compound) on this process. For this reason, the adsorption measurements of anionic polyacrylamide and/or Pb(II) ions on the kaolinite surface were performed. Moreover, the impact of heavy metal on electrokinetic and stability properties of kaolinite/polyacrylamide/supporting electrolyte system was determined. It was done based on the results of potentiometric titration, electrophoretic mobility, and absorbance measurements. The most important conclusions of the study were as follows: (1) kaolinite is an effective Pb(II) adsorbent when ion concentration in the environment equals 1 or 10 ppm (it adsorbs 80% and 72% of the ions, respectively), (2) when Pb(II) concentration in the environment is 100 ppm, kaolinite adsorbs only 29% of the ions, and (3) anionic polyacrylamide may strengthen the Pb(II) adsorption on the kaolinite surface (in the presence of 100 ppm AN PAM 30% and 1 ppm Pb(II), even 96% of the ions are adsorbed). Due to the above process, the bioavailability of heavy metal for organisms is considerably limited.Graphic

Surfactant-Like Behavior for the Adsorption of Mixtures of a Polycation and Two Different Zwitterionic Surfactants at the Water/Vapor Interface.

The bulk and interfacial properties of solutions formed by a polycation (i.e., poly(diallyl-dimethylammonium chloride), PDADMAC) and two different zwitterionic surfactants (i.e., coco-betaine (CB) and cocoamidopropyl-betaine (CAPB)) have been studied. The bulk aggregation of the polyelectrolyte and the two surfactants was analyzed by turbidity and electrophoretic mobility measurements, and the adsorption of the solutions at the fluid interface was studied by surface tension and interfacial dilational rheology measurements. Evidence of polymer–surfactant complex formation in bulk was only found when the number of surfactant molecules was closer to the number of charged monomers in solutions, which suggests that the electrostatic repulsion associated with the presence of a positively charged group in the surfactant hinders the association between PDADMAC and the zwitterionic surfactant for concentrations in which there are no micelles in solution. This lack of interaction in bulk is reflected in the absence of an influence of the polyelectrolyte in the interfacial properties of the mixtures, with the behavior being controlled by the presence of surfactant. This work has evidenced the significant importance of the different interactions involved in the system for controlling the interaction and complexation mechanisms of in polyelectrolyte–surfactant mixtures.