Partitioning of an Enzyme-Polymer Surfactant Nanocomplex into Lipid-Rich Cellular Compartments Drives In Situ Hydrolysis of Organophosphates.

Most organophosphates (OPs) are hydrophobic, and after exposure, can sequester into lipophilic regions within the body, such as adipose tissue, resulting in long term chronic effects. Consequently, there is an urgent need for therapeutic agents that can decontaminate OPs in these hydrophobic regions. Accordingly, an enzyme-polymer surfactant nanocomplex is designed and tested comprising chemically supercharged phosphotriesterase (Agrobacterium radiobacter; arPTE) electrostatically conjugated to amphiphilic polymer surfactant chains ([cat.arPTE][S-]). Experimentally-derived structural data are combined with molecular dynamics (MD) simulations to provide atomic level detail on conformational ensembles of the nanocomplex using dielectric constants relevant to aqueous and lipidic microenvironments. These show the formation of a compact admicelle pseudophase surfactant corona under aqueous conditions, which reconfigures to yield an extended conformation at a low dielectric constant, providing insight into the mechanism underpinning cell membrane binding. Significantly, it demonstrated that [cat.arPTE][S-] spontaneously binds to human mesenchymal stem cell membranes (hMSCs), resulting in on-cell OP hydrolysis. Moreover, the nanoconstruct can endocytose and partition into the intracellular fatty vacuoles of adipocytes and hydrolyze sequestered OP.

Study on the Structure-Activity Relationship and Oil Displacement Characteristics of the Polysurfactant Agent.

This study examines a versatile polymer known as polysurfactant, which is synthesized by co-polymerizing flexible acrylamide and sodium acrylate hydrocarbon chain. The polymer serves as a backbone and possesses active functional groups. Notably, the polysurfactant exhibits superior plugging and flooding abilities compared to conventional polymers. The primary objective of this paper is to investigate the properties and oil displacement characteristics of the polysurfactant through indoor physical simulation experiments. The results demonstrate that the multi-branched structure of the polysurfactant enhances its ability to associate, leading to the formation of a unique spatial network structure. The inclusion of multi-branched structures notably amplifies the association effect. The critical concentration for the association is estimated to be around 800 mg/L, at which juncture the polysurfactant exhibits a viscosity retention rate surpassing 90% subsequent to shearing. Furthermore, this spatial network structure exhibits self-recovery capabilities after experiencing shear failure and displaying strong viscosity and shear resistance. In addition, the concentration of the polysurfactant can control the hydrodynamic feature size, which shows its adaptability in regulation and oil-repelling functions at reservoir permeabilities ranging from 500 to 2000 × 10-3 µm2 with resistance coefficients ranging from 108 to 320. During the microscopic oil displacement process, the polysurfactant exerts a significant impact on mobility control, while the elastic pull clearly demonstrates a commendable viscoelastic oil displacement effect. The polysurfactant exhibits a specific degree of emulsification capability towards crude oil, leading to the emulsion exhibiting typical pseudoplastic fluid characteristics. The utilization of emulsification transportation and emulsification blockage contributes to the enhancement of oil recovery. As a result, the polysurfactant exhibits multifaceted capabilities, encompassing profile control, flooding, and plugging, owing to its unique structural characteristics. Through the implementation of a field test focused on flooding in the Daqing Oilfield, a significant enhancement in the recovery rate of 10.85% is observed, accompanied by a favorable input-output ratio of 1:3.86, thereby generating significant economic advantages.

Remediation of multilayer soils contaminated by heavy chlorinated solvents using biopolymer-surfactant mixtures: Two-dimensional flow experiments and simulations.

To assess the efficiency of remediating dense non-aqueous phase liquids (DNAPLs), here heavy chlorinated solvents, through injection of xanthan solutions with or without surfactant (sodium dodecylbenzenesulfonate: SDBS), we conducted a comprehensive investigation involving rheological measurements, column (1D) and two-dimensional (2D) sandbox experiments, as well as numerical simulations on two-layers sand packs. Sand packs with grain sizes of 0.2-0.3 mm and 0.4-0.6 mm, chosen to represent the low and high permeable soil layers respectively, were selected to be representative of real polluted field. The rheological analysis of xanthan solutions showed that the addition of SDBS to the solution reduced its viscosity due to repulsive electrostatic forces and hydrophobic interactions between the molecules while preserving its shear-thinning behavior. Results of two-phase flow experiments depicted that adding SDBS to the polymer solution led to a reduced differential pressure along the soil and improvements of the DNAPL recovery factor of approximately 0.15 and 0.07 in 1D homogeneous and 2D layered systems, respectively. 2D experiments revealed that the displacement of DNAPL in multilayer zones was affected by permeability difference and density contrast in a heterogeneous soil. Simulation of multiphase flow in a multilayered system was performed by incorporating non-Newtonian properties and coupling the continuity equation with generalized Darcy's law. The results of modeling and experiments are very consistent. Numerical simulations showed that for an unconfined soil, the recovery of DNAPL by injection of xanthan solution can be reduced for more than 50%. In a large 2D experimental system, the combination of injecting xanthan with blocking the contaminated zone led to a promising remediation of DNAPL-contaminated layered zones, with a recovery of 0.87.

Effect of polymer/surfactant complexation on diffusiophoresis of colloids in surfactant concentration gradients.

HYPOTHESIS: A concentration gradient of surfactants in the presence of polymers that non-covalently associate with surfactants will exhibit a continually varying distribution of complexes with different composition, charge, and size. Since diffusiophoresis of colloids suspended in a solute concentration gradient depends on the relaxation of the gradient and on the interactions between solutes and particles, polymer/surfactant complexation will alter the rate of diffusiophoresis driven by surfactant gradients relative to that observed in the same concentration gradient in the absence of polymers. EXPERIMENTS: A microfluidic device was used to measure diffusiophoresis of colloids suspended in solutions containing a gradient of sodium dodecylsulfate (SDS) in the presence or absence of a uniform concentration of Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) nonionic triblock copolymers. To interpret the effect of P123 on the rate of colloid diffusiophoresis, electrophoretic mobility and dynamic light scattering measurements of the colloid/solute systems were performed, and a numerical model was constructed to account for the effects of complexation on diffusiophoresis. FINDINGS: Polymer/surfactant complexation in solute gradients significantly enhanced diffusiophoretic transport of colloids. Large P123/SDS complexes formed at low SDS concentrations yielded low collective solute diffusion coefficients that prolonged the existence of strong concentration gradients relative to those without P123 to drive diffusiophoresis.

Salt-Induced Transformations of Hybrid Micelles Formed by Anionic Surfactant and Poly(4-vinylpyridine).

Salt-induced structural transformation of charged hybrid surfactant/polymer micelles formed by potassium oleate and poly(4-vinylpyridine) was investigated by cryo-TEM, SANS with contrast variation, DLS, and 2D NOESY. Cryo-TEM data show, that at small salt concentration beads-on-string aggregates on polymer chains are formed. KCl induces the transformation of those aggregates into rods, which is due to the screening of the electrostatic repulsion between similarly charged beads by added salt. In a certain range of salt concentration, the beads-on-string aggregates coexist with the rodlike ones. In the presence of polymer, the sphere-to-rod transition occurs at higher salt concentration than in pure surfactant system indicating that hydrophobic polymer favors the spherical packing of potassium oleate molecules. The size of micelles was estimated by DLS. The rods that are formed in the hybrid system are much shorter than those in polymer-free surfactant solution suggesting the stabilization of the semi-spherical endcaps of the rods by embedded polymer. 2D NOESY data evidence that in the spherical aggregates the polymer penetrates deep into the core, whereas in tighter packed rodlike aggregates it is located mainly at core/corona interface. According to SANS with contrast variation, inside the rodlike aggregates the polymer adopts more compact coil conformation than in the beads-on-string aggregates. Such adaptive self-assembled polymer-surfactant nanoparticles with water-insoluble polymer are very promising for various applications including drag reduction at transportation of fluids.

Visualization of Polymer-Surfactant Interaction by Dual-Emissive Gold Nanocluster Labeling.

Polymer-surfactant interaction decides the performance of corresponding complexes, making its rapid and intuitionistic visualization important for enhancing the performance of products and/or processing in related fields. In this study, the fluorescence visualization of the interaction between cationic hyperbranched polyethyleneimine and anionic sodium dodecyl sulfonate surfactant was realized by dual-emissive gold nanocluster labeling. The sensing mechanism was due to the interaction-induced polymer conformation change, which regulated the molecular structure and subsequent photoradiation process of the gold nanoclusters. All three inflection points of the interactions between the polymers and the surfactants were obtained by the change in fluorescence emission ratio of the designed dual-emissive gold nanoclusters. Moreover, these inflection points are verified by the hydrodynamic diameter and zeta potential measurements.

Using Polymer-Surfactant Charge Ratio to Control Synergistic Flocculation of Anionic Particulate Dispersions.

This study investigates the flocculation induced destabilization of particulate dispersions by oppositely charged polymer−surfactant complexes, with a particular focus on controlling interactions by modulating the charge ratio Z, (where Z = [+polymer]/[−surfactant]) via [−surfactant] at fixed Cpolymer. Cationic hydroxyethyl cellulose (cat-HEC) polymer-sodium dodecylsulfate (SDS) complexes were prepared with either excess polymer (Z > 1) or surfactant (Z < 1) charges. Anionic particulate dispersions (Ludox and polystyrene-butadiene Latex) were then exposed to the complexes, and solvent relaxation NMR was used to characterize the particle surfaces before and after exposure. In both particulate dispersions, flocculation induced destabilization was enhanced after exposure to cat-HEC-SDS complexes with Z > 1, leaving any excess particle surfaces uncoated after gentle centrifugation. However, complexes with Z < 1 showed no adsorption and destabilization in the Ludox dispersions and only slight destabilization in the Latex dispersions due to possible hydrophobic interactions. Substituting SDS for non-ionic surfactant (C12E6) showed no additional destabilization of the dispersions, but post-centrifugation relaxation rates indicated preferential adsorption of C12E6 onto the particle surfaces. Since the dominant forces are electrostatic, this study highlights the possibility of controlling the interactions between oppositely charged polymer−surfactant complexes and particle surfaces by modulating Z through [−surfactant].

Thermo-Responsive Polyion Complex of Polysulfobetaine and a Cationic Surfactant in Water.

Poly(4-((3-methacrylamidopropyl)dimethylammonium)butane-1-sulfonate) (PSBP) was prepared via controlled radical polymerization. PSBP showed upper critical solution temperature (UCST) behavior in aqueous solutions, which could be controlled by adjusting the polymer and NaCl concentrations. Owing to its pendant sulfonate anions, PSBP exhibited a negative zeta potential of -7.99 mV and formed a water-soluble ion complex with the cationic surfactant cetyltrimethylammonium bromide (CTAB) via attractive electrostatic interaction. A neutral PSBP/CTAB complex was formed under equimolar concentrations of the pendant sulfonate group in PSBP and the quaternary ammonium group in CTAB. Transmittance electron microscopic images revealed the spherical shape of the complex. The stoichiometrically neutral-charge PSBP/CTAB complex exhibited UCST behavior in aqueous solutions. Similar to PSBP, the phase transition temperature of the PSBP/CTAB complex could be tuned by modifying the polymer and NaCl concentrations. In 0.1 M aqueous solution, the PSBP/CTAB complex showed UCST behavior at a low complex concentration of 0.084 g/L, whereas PSBP did not exhibit UCST behavior at concentrations below 1.0 g/L. This observation suggests that the interaction between PSBP and CTAB in the complex was stronger than the interpolymer interaction of PSBP.

Superanionic Solvent-Free Liquid Enzymes Exhibit Enhanced Structures and Activities.

The surface of a carboxylate-enriched octuple mutant of Bacillus subtilis lipase A (8M) is chemically anionized to produce core (8M)-shell (cationic polymer surfactants) bionanoconjugates in protein liquid form, which are termed anion-type biofluids. The resultant lipase biofluids exhibit a 2.5-fold increase in hydrolytic activity when compared with analogous lipase biofluids based on anionic polymer surfactants. In addition, the applicability of the anion-type biofluid using Myoglobin (Mb) that is well studied in anion-type solvent-free liquid proteins is evaluated. Although anionization resulted in the complete unfolding of Mb, the active α-helix level is partially recovered in the anion-type biofluids, and the effect is accentuated in the cation-type Mb biofluids. These highly active anion-type solvent-free liquid enzymes exhibit increased thermal stability and provide a new direction in solvent-free liquid protein research.

Peculiarities of the interaction of sodium dodecyl sulfate with chitosan in acidic and alkaline media.

In this work, the interaction between the negatively charged surfactant sodium dodecyl sulfate (SDS) and partially N-reacetylated chitosan (RA-CHI), which is soluble at pH range up to pH 12, is studied in a wide pH range including alkaline media by light scattering (LS) and isothermic titration calorimetry (ITC). It is shown that in the weakly alkaline medium (pH 7.4), RA-CHI/SDS interaction is exothermic and cooperative. This interaction is found to be coupled with proton transfer from the buffer substance to chitosan as it is revealed by the dependence of the measured heat release on the ionization enthalpy of the buffer. At higher pH values (pH > 8), another mechanism of interaction is observed that include SDS micellization induced by hydrophobic interactions with polymer segments, so that no phase separation occurred in these mixtures. The results obtained can contribute to expand the knowledge about application of chitosan for preparation of pharmaceutical and cosmetic compositions containing anionic surfactants.

A real-time and in-situ monitoring of the molecular interactions between drug carrier polymers and a phospholipid membrane.

The dynamic interactions between drug carrier molecules and a cell membrane can not be ignored in their clinical use. Here a simple, label-free and non-invasive approach, photo-voltage transient method, combined with the atomic force microscopy, dynamic giant unilamellar vesicle leakage assay and cytotoxicity method, was employed for a real-time monitoring of the interaction process. Two representative polymer molecules, polyoxyethylene (35) lauryl ether (Brij35) and polyvinylpyrrolidone (PVPk30), were taken as examples to interact with a phospholipid bilayer membrane in a low ionic strength and neutral pH condition. Brij35 demonstrated an adsorption-accumulation-permeabilization dominated process under the modulation of polymer concentration in the solution. In contrast, PVPk30 performed a dynamic balance between adsorption-desorption of the molecules and/or permeabilization-resealing of the membrane. Such difference explains the high and low cytotoxicity of them, respectively, in the living cell tests. Briefly, through combining the photo-voltage approach with conventional fluorescent microscopy method, this work demonstrates new ideas on the time and membrane actions of polymer surfactants which should be taken into account for their biomedical applications.

Molecular features of the interaction and antimicrobial activity of chitosan in a solution containing sodium dodecyl sulfate.

Molecular interaction of chitosan with sodium dodecyl sulfate (SDS) is a more complicated process than it has been imagined so far. For the first time it has been shown that the shorter chitosan chains are, the more preferably they interact with the SDS and the larger-in-size microparticles they form. The influence of ionic strength, urea and temperature on microparticles formation allows interpreting the mechanism of microparticles formation as a cooperative electrostatic interaction between SDS and chitosan with simultaneous decrease in the surface charge of the complexes initiating the aggregation of microparticles. It is shown that hydrogen bonding is mainly responsible for the aggregation while hydrophobic interaction has a lesser effect. Chitosan demonstrates a high bacteriostatic activity in the presence of SDS in solution and can be promising for preparation of microbiologically stable pharmaceutical hydrocolloids, cosmetic products and chitosan-based Pickering emulsions containing strong anionic surfactants.

An artificial membrane binding protein-polymer surfactant nanocomplex facilitates stem cell adhesion to the cartilage extracellular matrix.

One of the major challenges within the emerging field of injectable stem cell therapies for articular cartilage (AC) repair is the retention of sufficient viable cell numbers at the site of injury. Even when delivered via intra-articular injection, the number of stem cells retained at the target is often low and declines rapidly over time. To address this challenge, an artificial plasma membrane binding nanocomplex was rationally designed to provide human mesenchymal stem cells (hMSCs) with increased adhesion to articular cartilage tissue. The nanocomplex comprises the extracellular matrix (ECM) binding peptide of a placenta growth factor-2 (PlGF-2) fused to a supercharged green fluorescent protein (scGFP), which was electrostatically conjugated to anionic polymer surfactant chains to yield [S-]scGFP_PlGF2. The [S-]scGFP_PlGF2 nanocomplex spontaneously inserts into the plasma membrane of hMSCs, is not cytotoxic, and does not inhibit differentiation. The nanocomplex-modified hMSCs showed a significant increase in affinity for immobilised collagen II, a key ECM protein of cartilage, in both static and dynamic cell adhesion assays. Moreover, the cells adhered strongly to bovine ex vivo articular cartilage explants resulting in high cell numbers. These findings suggest that the re-engineering of hMSC membranes with [S-]scGFP_PlGF2 could improve the efficacy of injectable stem cell-based therapies for the treatment of damaged articular cartilage.

Peeling back the layers: Investigating the effects of polyelectrolyte layering on surface structure and stability of oil-in-water nanoemulsions.

HYPOTHESIS: Layer-by-layer deposition of polyelectrolytes is a useful technique for modifying surface functionalities. For drug delivery systems, alternating layers of biopolymers coat nanoemulsions, which house and protect the cargo until the time and destination of delivery. Here, we investigate molecular factors contributing to the stability and interfacial properties of nanoemulsions prepared by a co-adsorption of polymers poly(styrene sulfonate) and polyethylenimine (PEI), and surfactant dodecyltrimethylammonium bromide. We hypothesize the interplay between electrosteric and hydrophobic effects upon multi-polymer co-adsorption contributes to both macroscopic and molecular-level interfacial properties of nanoemulsions. EXPERIMENTS: To probe interfacial layering properties, we use vibrational sum frequency scattering spectroscopy with ζ-potential measurements to determine the adsorptive behavior and molecular conformational arrangement of the polymer layers. Complementing these interfacial studies are dynamic light scattering experiments measuring the nanoemulsion size distribution and polydispersity index over a 30-day period. FINDINGS: Our light scattering, ζ-potential, and spectroscopic results of the nanoemulsion surface show that the duration of droplet stability and the degree of molecular orientation of adsorbed polymers can be tuned by surfactant concentration, PEI concentration, and pH. These results illustrate how molecular surface properties of multi-polymer coated nanoemulsions contribute to synergistic effects and droplet stability, enabling advancements in applications surrounding biopharmaceuticals, cosmetics, and food sciences.

An Advanced Material with Synergistic Viscoelasticity Enhancement of Hydrophobically Associated Water-Soluble Polymer and Surfactant.

In order to prepare materials with controllable properties, changeable microstructure, and high viscoelasticity solution with low polymer and surfactant concentration, a composite is constituted by adding surfactant (sodium dodecyl sulfate, SDS) to hydrophobically associated water-soluble polymer (abbreviated as PAAC) solution. The viscoelasticity, aggregate microstructure, and interaction mechanism of the composite are investigated by rheometery, Cryo-transmission electron microscopy (Cryo-TEM), and fluorescence spectrum. The results show that when the mass ratio of polymer to surfactant is 15:1, the viscosity of the composite reaches the maximum. The viscosity of the composite system increases hundredfold. The viscosity plateau under dynamic shear is generated. The composite has the properties of high viscoelasticity, strong shear thinning behavior, and good salt tolerance, and temperature resistance. The maximum viscosity of the composite is shown at the salinity of 20000 mg L-1 . In addition, there is no phase separation in the composite with the increase of polymer and surfactant concentration, which indicates the good stability of the system. It is proposed a method to obtain a high viscoelasticity solution by adding surfactants without wormlike micelles to a hydrophobically associated water-soluble polymer solution.

Impact of polyelectrolyte-surfactant interactions on the rheology and wet lubrication performance of conditioning shampoo.

OBJECTIVE: The purpose of this study is to understand the impact of the cationic polymer merquat on the rheological behavior of the mixed surfactant system of sodium lauryl ether sulfate (SLES) and cocamidopropyl betaine (CapB) as well as the impact of varying formulation conditions on the wet lubrication performance of the SLES-CapB-Merquat system. METHODS: Rotation mechanical Rheometry was used to study the rheological response of the SLES-CapB-Merquat systems. Frequency sweeps were conducted to analyze the rheological properties of the system at low frequency ranges and bulk viscosity of the system was studied at high shear rates at varying salt and polymer concentrations. Wet combing tests and hair friction tests were run on the Dia-stron MTT175 flexible miniature tensile tester in order to evaluate the conditioning effects of the different formulations. RESULTS: The SLES-CapB system on its own exhibits very little viscosity. The bulk rheology results show that the addition of Merquat enhances the viscosity and viscoelastic properties of the SLES-CapB-Merquat system indicating the presence of electrostatic interactions between the surfactant and polyelectrolyte. Addition of salt had a significant impact on the system's rheological response due to the charge screening effect of salt. Wet combing force data indicate that the charged polyelectrolyte binds to the hair substrate resulting in reduced combing force values after the product was applied. The addition of silicone oil to the formulation seemed to greatly enhance the conditioning effect of the formulation. CONCLUSION: The charge interactions between SLES, CapB and Merquat results in the formation of an integrated gel like network, thus building the viscosity of the system. Variation of parameters like polymer and salt concentration has the potential to modify the bulk rheological properties and consequently the wet lubrication properties of the system.

OBJECTIF: Le but de cette étude est de comprendre l'impact du polymère cationique Merquat sur le comportement rhéologique du système de tensioactifs mixtes de sodium lauryl éther sulfate (SLES) et de cocamidopropyl bétaïne (CapB) ainsi que l'impact de diverses conditions de formulation sur la performance de lubrification en condition humide du système SLES-CapB-Merquat. MÉTHODES: La rhéométrie par rotation a été utilisée pour étudier la réponse rhéologique des systèmes SLES-CapB-Merquat. Des balayages de fréquence ont été effectués pour analyser les propriétés rhéologiques du système dans des gammes de basses fréquences et la viscosité en vrac du système a été étudiée à des taux de cisaillement élevés à des concentrations variables de sel et de polymère. Des tests de peignage humide et des tests de frottement capillaire ont été réalisés sur le testeur de traction miniature flexible Dia-stron MTT175 afin d'évaluer les effets de conditionnement des formulations différentes. RÉSULTATS: Le système SLES-CapB à lui seul présente très peu de viscosité. Les résultats de rhéologie de masse montrent que l'ajout de Merquat améliore la viscosité et les propriétés viscoélastiques du système SLES-CapB-Merquat indiquant la présence d'interactions électrostatiques entre le tensioactif et le polyélectrolyte. L'addition de sel a eu un impact significatif sur la réponse rhéologique du système en raison de l'effet de filtrage de charge du sel. Les données de force de peignage humide indiquent que le polyélectrolyte chargé se lie au substrat capillaire, ce qui réduit les valeurs de force de peignage après l'application du produit. L'ajout d'huile de silicone à la formulation a amélioré considérablement l'effet conditionneur de la formulation. CONCLUSION: Les interactions de charge entre SLES, CapB et Merquat aboutissent à la formation d'un réseau de type gel intégré, augmentant ainsi la viscosité du système. La variation de paramètres tels que la concentration de polymère et de sel a le potentiel de modifier les propriétés rhéologiques en vrac et par conséquent les propriétés de lubrification humide du système. MOTS CLÉS: Complexe polymère-tensioactif, rhéomètre rotatif, viscosité apparente, propriétés viscoélastiques, effet conditionneur, performances de lubrification par voie humide. REMERCIEMENTS: Nous reconnaissons la contribution de Lubrizol pour nous avoir fourni SLES (SulfochemTM ES-1 Surfactant, 25,5%), CAPB (ChembetaineTM ACB Surfactant, 36%), Merquat (Merquat 7SPR Polymer, 9%) et huile de silicone (SilSense® DW-18 silicone, 100%). Les auteurs remercient Constantina Drakontis pour la traduction du résumé.

Coacervation in Cationic Polyelectrolyte Solutions with Anionic Amino Acid Surfactants.

Coacervates formed by cationic polyelectrolytes and anionic surfactants are utilized to improve the user's tactile perception of shampooing hair during washing and after drying. In this study, we investigated the formation and structure of coacervates in aqueous systems containing anionic amino acid surfactants. The phase behaviors at constant temperature were investigated in aqueous systems combining cationic polyelectrolyte JR-400 with potassium cocoyl glutamate (CoGluK) or potassium cocoyl glycinate (CoGlyK) for a qualitative depiction of coacervate formation. The composition range of coacervate formation varied with the hydrophilic group of the surfactant. The surface tension was measured at different surfactant concentrations and constant polyelectrolyte concentration. The surface tension behavior revealed the critical association concentrations and critical micelle concentrations, indicating that coacervate was produced via complex formation through electrostatic interaction between opposite charges. Optical microscopy and small-angle X-ray scattering measurements revealed that the coacervates were composed of fibrous aggregates, a few microns thick, and those formed in the CoGlyK system had thicker fibers.

Synergy, competition, and the "hanging" polymer layer: Interactions between a neutral amphiphilic 'tardigrade' comb co-polymer with an anionic surfactant at the air-water interface.

Understanding the structure of polymer/surfactant mixtures at the air-water interface is of fundamental importance and also of relevance to a variety of practical applications. Here, the complexation between a neutral 'tardigrade' comb co-polymer (consisting of a hydrophilic polyethylene glycol backbone with hydrophobic polyvinyl acetate grafts, PEG-g-PVAc) with an anionic surfactant (sodium dodecyl sulfate, SDS) at the air-water interface has been studied. Contrast-matched neutron reflectivity (NR) complemented by surface tension measurements allowed elucidation of the interfacial composition and structure of these mixed systems, as well as providing physical insights into the polymer/surfactant interactions at the air-water interface. For both polymer concentrations studied, below and above its critical aggregation concentration, cac, (0.2 cac and 2 cac, corresponding to 0.0002 wt% or 0.013 mM and 0.002 wt% or 0.13 mM respectively), we observed a synergistic cooperative behaviour at low surfactant concentrations with a 1-2 nm mixed interfacial layer; a competitive adsorption behaviour at higher surfactant concentrations was observed where the polymer was depleted from the air-water interface, with an overall interfacial layer thickness ~1.6 nm independent of the polymer concentration. The weakly associated polymer layer "hanging" proximally to the interface, however, played a role in enhancing foam stability, thus was relevant to the detergency efficacy in such polymer/surfactant mixtures in industrial formulations.

Control of the colloidal depletion force in nonionic polymer solutions by complexation with anionic surfactants.

HYPOTHESIS: Charge, size and concentration of depletants control the magnitude and range of depletion and structural forces. Noncovalent association of nonionic polymers with ionic surfactants may therefore synergistically enhance these forces to an extent that depends on the structure and composition of the resulting complexes. EXPERIMENTS: Forces were measured between a silica sphere and a silica plate in solutions of Pluronic F108 nonionic poly(ethylene oxide - block - propylene oxide - block - ethylene oxide) triblock copolymers and anionic sodium dodecylsulfate (SDS) surfactants using colloidal probe atomic force microscopy as a function of polymer, surfactant and NaCl background electrolyte concentrations. Trends in the magnitudes of the depletion attraction minimum and the first repulsive maximum in the oscillatory structural force were interpreted with the aid of pyrene solubilization assays, sodium ion-selective electrode analysis, and dynamic light scattering measurements that characterized the formation, charge, and hydrodynamic radius of F108/SDS complexes respectively. FINDINGS: Synergistic enhancement of the depletion force and first repulsive maximum occurred within a finite range of SDS concentrations, to an extent that depended on F108 and NaCl concentrations. This was due mainly to charging of F108/SDS complexes. Size effects were important at low NaCl concentration. Forces measured above the synergistic SDS concentration range were indistinguishable from those in polymer-free SDS solutions due to the appearance of excess unbound SDS micelles.

Probing the molecular interactions between pharmaceutical polymeric carriers and bile salts in simulated gastrointestinal fluids using NMR spectroscopy.

The number of poorly soluble new drugs is increasing and one of the effective ways to deliver such pharmaceutically active molecules is using hydrophilic polymers to form a solid dispersion. Bile salts play an important role in the solubilisation of poorly soluble compounds in the gastrointestinal tract (gut) prior to absorption. When a poorly water-soluble drug is delivered using a hydrophilic polymer based solid dispersion oral formulation, it is still unclear whether there are any polymer-bile salt interactions, which may influence the drug dissolution and solubilisation. This study, using two widely used hydrophilic model polymers, Hydroxypropyl methylcellulose (HPMC) and polyvynilpirrolidone (PVP), and sodium taurocholate (NaTC) as the model bile salt, aims to investigate the interactions between the polymers and bile salts in simulated fed state (FeSSIF) and fasted state (FaSSIF) gut fluids. The nature of the interactions was characterised using a range of NMR techniques. The results revealed that the aggregation behaviour of NaTC in FaSSIF and FeSSIF is much more complex than in water. The addition of hydrophilic polymers led to the occurrences of NaTC-HPMC and NaTC-PVP aggregation. For both systems, pH and ionic strength strongly influenced the aggregation behavior, while the ion type played a less significant role. The outcome of this study enriched the understanding of the aggregation behaviour of bile salts and typical hydrophilic pharmaceutical polymers in bio-relevant media. Due to the high surface-activity of the bile salts and their ability to interact with polymers, such aggregation behaviour is expected to play a role in drug solubilisation in the gut when the drug is delivered by hydrophilic polymer based dispersions.