Interaction of cationic surfactants with carboxymethylcellulose in aqueous media

Colloidal interactions between nanochitin and surfactants: Connecting micro- and macroscopic properties by isothermal titration calorimetry and rheology

This study elucidates the intricate interactions between chitin nanocrystals (ChNC) and surfactants of same hydrophobic tail (C12) but different head groups types (anionic, cationic, nonionic): sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and polyoxyethylene(23)lauryl ether (Brij-35). Isothermal Titration Calorimetry (ITC) and rheology are used to study the complex ChNC-surfactant interactions in aqueous media, affected by adsorption, self-assembly and micellization. The ITC results demonstrate that the surfactant head group significantly influences the dynamics and nature of the involved phenomena. Cationic DTAB's reveal minimal interaction with ChNC, non-ionic Brij-25's interact moderately at low concentrations driven by hydrophobic effects while SDS's interacts strongly and show complex interaction patterns that fall across four distinct regimes with SDS addition. We attribute such behavior to initiate through electrostatic attraction and terminate in surfactant micelle formation on ChNC surfaces. ITC also elucidates the impact of ChNC concentration on key parameters including critical aggregation concentration (CAC) and saturation concentration (C2). Dynamic rheological analysis indicates the molecular interactions translate to non-linear variations in the elastic modulus (G') upon SDS addition mirroring that observed in ITC experiments. Such a direct correlation between molecular interactions and macroscopic rheological properties provides insights to aid in the creation of nanocomposites with tailored properties.

Control of the Colloidal and Adsorption Behaviors of Chitin Nanocrystals and an Oppositely Charged Surfactant at Solid, Liquid, and Gas Interfaces

Chitin has a unique hierarchical structure, spanning the macro- and nanoscales, and presents chemical characteristics that make it a suitable component of multiphase systems. Herein, we elucidate the colloidal interactions between partially deacetylated chitin nanocrystals (cationic ChNC) and an anionic surfactant, sodium dodecyl sulfate (SDS). We investigate charge neutralization and association (electrophoretic mobility, surface tensiometry, and quartz crystal microgravimetry) and their role in the stabilization of Pickering emulsions. We find SDS adsorption and association with ChNC under distinctive regimes: At low SDS concentration, submonolayer assemblies form on ChNC, driven by the hydrophobic effect and electrostatic interactions. With the increased SDS concentration, bilayers or patchy bilayers form, followed by adsorbed hemimicelles and micelles. We further suggested the role of hydrophobic effects in the observed colloidal transitions and complex conformations. At the highest SDS concentration tested, charge neutralization and SDS/ChNC flocculation take place. Remarkably, at given concentrations, adsorbed SDS endows the chitin nanoparticles with an effective hydrophobicity that opens the opportunity to achieve tailorable Pickering stabilization. Hence, a facile route is proposed by in situ modification by SDS physisorption, which extends the potential of renewable nanoparticles in the formulation of complex fluids, for instance, those relevant to household and healthcare products.

Green-step assembly of the supramolecular amphiphile constructed by sodium carboxymethyl cellulose and calixarene for facile loading of hydrophobic food bioactive compounds

The use of biologically active compounds is often limited due to their poor aqueous solubility, which generally reduces their bioavailability and useful efficacy. In this regard, a wide search is currently underway for colloidal systems capable of encapsulating these compounds. In the creation of colloidal systems, long-chain molecules of surfactants and polymers are mainly used, which in an individual state do not always aggregate into homogeneous and stable nanoparticles. In the present work, cavity-bearing calixarene was used for the first time to order polymeric molecules of sodium carboxymethyl cellulose. A set of physicochemical methods demonstrated the spontaneous formation of spherical nanoparticles by non-covalent self-assembly contributed by macrocycle and polymer, and formed nanoparticles were able to encapsulate hydrophobic quercetin and oleic acid. The preparation of nanoparticles by supramolecular self-assembly without use of organic solvents, temperature and ultrasound effects can be an effective strategy for creating water-soluble forms of lipophilic bioactive compounds.

Effect of Surfactant Tail Length on the Hydroxypropyl Cellulose-Mediated Premicellar Aggregation of Sodium n-Alkyl Sulfate Surfactants

Polymer/surfactant composites have emerged as a subject of interest for their diverse applications. The improved solution properties in polymer/surfactant composites have been correlated to the formation of premicellar surfactant aggregate-polymer complexes (PS) at a surfactant concentration well below their critical micelle concentrations. Using different physicochemical and spectroscopic techniques here we have studied PS formed by hydroxypropyl cellulose, a nonionic-biocompatible polymer, and alkyl sulfate surfactants of different tail lengths. Our study shows that an increase in surfactant tail length eases PS formation and enhances PS-induced polymer cross-linking and, correspondingly, solution viscosity. PS consisting of shorter tail surfactants and those with longer tail surfactants differ microscopically as the former offers more polar interior than the later as evidenced from fluorescence measurements. Our study establishes that shorter tail surfactants intend to stay loosely packed inside PS and allow larger water penetration, which creates a relatively polar hydrophobic core compared to the PS with longer tail surfactants. The stronger packing of PS with longer tail surfactants is an outcome of favorable interaction between polymer polar groups and surfactant headgroups, which further creates strongly hydrogen-bonded water in their hydration shell.

Aggregation behavior and thermodynamic properties of the mixture of sodium carboxymethyl cellulose and cetyltrimethylammonium bromide in numerous temperatures and mixed solvents

Interaction of sodium carboxymethylcellulose (SCMC) with cetyltrimethylammonium bromide (CTAB; cationic in nature) in H2O and additives (alcohols and diols) media has been investigated using conductivity technique. The micellar parameters such as critical micelle concentration (cmc), fraction of counter ion binding (β), thermodynamic parameters, transfer properties, and enthalpy-entropy compensation parameters of CTAB + SCMC mixture have been assessed in water and aq. alcohols/diols media. One cmc value was achieved for CTAB + SCMC mixtures in the entire circumstances and the attendance of SCMC disfavors the CTAB micellization. The cmc values were obtained to be greater in alcohols and diols media compared to H2O medium. The cmc values also exhibit a dependency on the solvent composition and temperature variation. In all the cases, the ΔG 0 m values were achieved to be negative which signifying the spontaneous formation of micelles while the extent of spontaneity is decreased in alcohols and diols media. Both the ΔH 0 m and ΔS 0 m reveal that hydrophobic, ion-dipole as well as electrostatic interactions are the proposed binding forces between CTAB and SCMC. The compensation parameters (ΔH 0* m and T c ) are in decent agreement with the biological fluid.

Colloidal systems of surface active ionic liquids and sodium carboxymethyl cellulose: physicochemical investigations and preparation of magnetic nano-composites

Carboxymethyl cellulose-surface active ionic liquid colloidal formulations for preparation of magnetic nano-composites.

On the rheology of mixed systems of hydrophobically modified polyacrylate microgels and surfactants: Role of the surfactant architecture

HYPOTHESIS

The rheological control of suspensions is of key interest in the formulation design. A chemically cross-linked hydrophobically modified poly(acrylic acid) (HMCL-PAA), used as rheology modifier, is pH sensitive and shows swelling behavior above a critical pH due to the ionization of the acrylic acid groups. At low pH, HMCL-PAA suspensions are liquid and turbid. The binding of surfactants to HMCL-PAA, at low pH conditions, can result in significant changes on rheology and transparency of the polymeric suspensions, due to the swelling of the microgel particles.

EXPERIMENTS

The influence of surfactants addition on the rheological properties and transparency of HMCL-PAA suspensions was determined. A systematic study was performed using different types of surfactants (ionic, non-ionic and zwitterionic).

FINDINGS

The gelation efficiency of HMCL-PAA suspensions at low pH is strongly dependent on surfactant architecture: ionic surfactants are found to be much more efficient than non-ionic or zwitterionic surfactants. Ionic surfactants lead to a liquid-to-gel transition accompanied by an increase of transparency of the suspensions. Among the ionic surfactants, anionics show stronger interactions with the polymer. Also the surfactant hydrophobicity is relevant; the more hydrophobic the surfactant, the stronger is the binding to the polymer and thus the larger the particle swelling.

Tear fluid-eye drops compatibility assessment using surface tension

OBJECTIVE

To evaluate the compatibility of commercially available eye drop surface tension with the tear film physiological range and to characterize commonly used ophthalmic excipients in terms of their surface activity under eye-biorelevant conditions.

SIGNIFICANCE

There are a number of quality requirements for the eye drops (e.g. tonicity, pH, viscosity, refractive index) that needs to comply with the physiological parameters of the eye surface. However, the adjustment of surface tension properties of the eye drops to the normal range of surface tension at the air/tear fluid interface (40-46 mN/m) has received rather less attention thus far. Yet, the surface tension at the air/tear fluid interface is of vital importance for the normal function of the eye surface.

METHODS

The surface tension compatibility of the isotonic aqueous solutions of commonly used ophthalmic excipients as well as 18 approved eye drops with the tear fluid have been evaluated using surface tension method.

RESULTS

Each ophthalmic ingredient including the preservatives, solubilizing agents and thickening agents can influence the surface tension of the final formulation. In case of complex ophthalmic formulations one should also consider the possible interactions among excipients and consequent impact on overall surface activity. Out of 18 evaluated eye drops, three samples were within, 12 samples were below and three samples were above the physiological range of the tear fluid surface tension.

CONCLUSIONS

Our results provide a rationale for clinical studies aiming to assess the correlation between the eye drops surface tension and the tear film (in)stability.

Interaction of cationic gemini surfactant tetramethylene-1,4-bis(dimethyltetradecylammonium bromide) with anionic polyelectrolyte sodium carboxymethyl cellulose, with two different molar masses, in aqueous and aquo-organic (isopropanol) media

Interactions of the cationic gemini surfactant, 14-4-14 with anionic polymer, NaCMC.

Interactional behavior of the polyelectrolyte poly sodium 4-styrene sulphonate (NaPSS) with imidazolium based surface active ionic liquids in an aqueous medium

The present study aims to develop an understanding of the interactions between an anionic polyelectrolyte, poly sodium 4-styrene sulphonate (NaPSS), and cationic surface active imidazolium based ionic liquids (SAILs), [Cnmim][Cl] (n = 10, 12, 14) using a multi-technique approach. Various physicochemical and electrochemical techniques such as surface tension, conductivity, fluorescence, isothermal titration calorimetry (ITC), dynamic light scattering (DLS), turbidity, potentiometry, cyclic voltammetry (CV), and differential pulse voltammetry (DPV) are employed to obtain comprehensive information about NaPSS-SAIL interactions. Different stages of interaction, corresponding to the critical aggregation concentration (cac), critical saturation concentration (Cs) and critical micelle concentration (cmc) have been observed owing to the strong electrostatic and hydrophobic interactions, and the results obtained from different techniques complement each other very well. The results extracted from DLS and turbidity measurements clearly indicated that the size of the micelle like aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using potentiometry show a concentration dependence and the highly co-operative nature of the interactions which is attributed to aggregation of the polyelectrolyte-SAIL complexes. The diffusion coefficients (Dm) of the electroactive probe in the pure and NaPSS-SAIL mixed systems were obtained, which were further used to obtain the values of the micellar self-diffusion coefficients (D) and inter-micellar interaction parameters (kd).

Electronic polymers in lipid membranes

Electrical interfaces between biological cells and man-made electrical devices exist in many forms, but it remains a challenge to bridge the different mechanical and chemical environments of electronic conductors (metals, semiconductors) and biosystems. Here we demonstrate soft electrical interfaces, by integrating the metallic polymer PEDOT-S into lipid membranes. By preparing complexes between alkyl-ammonium salts and PEDOT-S we were able to integrate PEDOT-S into both liposomes and in lipid bilayers on solid surfaces. This is a step towards efficient electronic conduction within lipid membranes. We also demonstrate that the PEDOT-S@alkyl-ammonium:lipid hybrid structures created in this work affect ion channels in the membrane of Xenopus oocytes, which shows the possibility to access and control cell membrane structures with conductive polyelectrolytes.

Controlling the aggregation of sodium dodecylsulphate in aqueous poly(ethylene glycol) solutions

The role of PEG's of different molecular weights on the self-assembly of SDS and the role of added NaCl has been addressed opening new scopes for further studies.

PEG-coumarin based biocompatible self-assembled fluorescent nanoaggregates synthesized via click reactions and studies of aggregation behavior

HYPOTHESIS

Click chemistry has found wide application in drug discovery, bioconjugation reactions, polymer chemistry and synthesis of amphiphilic materials with pharmaceutical and biomedical applications. Triazole substitution via a click reaction alters photophysical properties of coumarin. Both coumarin and triazole moieties participate in π-π stacking interactions. Hence it should be possible to prepare fluorescent self-assembly systems by conjugation of coumarin to poly (ethylene glycol) (PEG) via click reactions exhibiting hydrophilic, hydrophobic and π-π stacking interactions. Moreover, the materials can be suitable platforms to assess fluorescence modulation effect of triazole substitution on coumarins.

EXPERIMENTS

PEG supported coumarin conjugates were synthesized and the fluorescence modulation effect of the formation of triazole on coumarin was assessed. Their aggregation properties were studied by surface tension measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM), fluorescence and (1)H NMR spectroscopy.

FINDINGS

The conjugates were found to form nanoaggregates in the size range of 100-120 nm with a negative free energy of micellization (~-27 kJ mol(-1)) confirming aggregation and self-assembly. The Quantum yield of 4-methyl-7-propargylcoumarin (7P4MC) was enhanced after triazole formation with azide functionalized PEG (methoxy-PEG350 azide). The conjugates were found to exhibit π-π stacking interactions in addition to hydrophilic and hydrophobic interactions. They were found to be biocompatible with human pancreatic cancer cells.

Rheological Study on ATBS-AM Copolymer-Surfactant System in High-Temperature and High-Salinity Environment

Experimental studies were conducted to evaluate the rheological properties of surfactant-polymer (SP) system. This SP system consists of a copolymer of acrylamide (AM) and acrylamido tertiary butyl sulfonate (ATBS) and sodium dodecyl sulphate (SDS) surfactant. Effects of surfactant concentration, temperature, polymer concentration, and salinity on rheological properties of SP system were investigated by means of oscillation and shear measurements. Comparison with classical partially hydrolyzed polyacrylamide (HPAM) was made. For the same temperature range, the viscosity drop for HPAM was about four times higher than the viscosity drop for ATBS-AM copolymer. In deionized water, viscosity of both polymers and SP systems was very high as compared to viscosity in saline water. Viscosity reduction of ATBS-AM copolymer was higher for salts having divalent cations. The SP system showed precipitation in presence of divalent cations. It worked well with monovalent cations even at relatively high salinities. The addition of 0.1% surfactant to the polymer resulted in a 60% decrease in the viscosity. Some interfacial rheological experiments were also carried out to investigate the behaviors on the interface between SP solutions and oil. Addition of 0.1% surfactant showed a 65% decrease inG′at SP solution-oil interface. SP system consisting of ATBS-AM and SDS showed better performance at high temperature compared to HPAM-SDS system. Due to precipitation, the SP system should be restricted to environment having low divalent cations.

Internal organisation in polyelectrolytes/oppositely charged surfactants colloidal complexes anticipating precipitated nanostructures

In this paper, we relate the periodic nanostructures found in the colloidal complexes and the concentrated phases obtained with polyelectrolyte/surfactant aqueous solutions. We present small-angle X-ray scattering studies of the self-organisation of the anionic polymer carboxymethylcellulose with three cationic quaternary ammonium surfactants with different head and tail groups: hexadecyl trimethyl, hexadecyl ethyl dimethyl and didodecyl dimethyl ammonium bromides. We investigated the mesophases obtained above a precipitation threshold. The mixed solutions with the double-chained surfactant led to lamellar phases, in which the repeat distance only depends on the surfactant/carboxyl charge molar ratio. We show that an internal lamellar organisation already takes place in the dilute phase containing colloidal complexes found below the precipitation threshold.

Interaction of gums (guar, carboxymethylhydroxypropyl guar, diutan, and xanthan) with surfactants (DTAB, CTAB, and TX-100) in aqueous medium

The interaction of surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), and p-tert-octylphenoxypolyoxyethylene (9.5) ether (TX-100) with guar (Gr), carboxymethylhydroxypropyl guar (CMHPG), diutan (Dn), and xanthan (Xn) gums has been studied employing conductometry, tensiometry, microcalorimetry, viscometry, and atomic force microscopy (AFM) techniques. Both weak and strong interactions were observed. CTAB interacted stronger than DTAB with the gums. The surfactant-gum interaction process was enhanced by the presence of borate ions in the solution; the borate ion itself also manifested interaction with the surfactants comparable with that of water-soluble polymers polyvinyl alcohol, polyoxyethylene, and so forth. Viscometric results supported configurational changes of the gum molecules by interaction with surfactants. The geometry of the pure gums and their CTAB interacted products in the dried states was ascertained from AFM measurements; spherical and prolate shapes were observed for pure gums, and distorted states were observed for their surfactant complexed species. Detailed topological features of these entities were ascertained.

Mechanisms underlying the cholesterol-lowering properties of soluble dietary fibre polysaccharides

A number of studies have shown a positive relationship between diets rich in soluble dietary fibres (SDF) such as β-glucan, pectin, guar gum and psyllium, and reduced serum cholesterol and thus a decreased risk of cardiovascular disease (CVD). Three major biological mechanisms have been proposed to explain the cholesterol-reducing effects of SDF: prevention of bile salt (BS) re-absorption from the small intestine leading to an excess faecal BS excretion; reduced glycemic response leading to lower insulin stimulation of hepatic cholesterol synthesis; and physiological effects of fermentation products of SDF, mainly propionate. Evidence for the latter mechanism is inconclusive, whereas in vivo, ex vivo and in vitro experiments suggest that BS micelles "bind" to SDF preventing their re-absorption. Whereas, glycemic responses to SDF have been studied extensively, the nature of interactions between bile salt micelles and SDF that lead to incomplete BS re-absorption are poorly defined. Three potential physicochemical mechanisms are proposed together with suggestions for in vitro experiments to test them.

A study of interaction of cationic dyes with anionic polyelectrolytes

The interactions of Acridine Orange with Sodium Alginate and Pinacyanol Chloride with Heparin have been investigated by spectrophotometric method. The polymers induce metachromasy in the dye as evidenced from the considerable blue shift in the absorption maxima of the corresponding dyes. The interaction constant and thermodynamic parameters of polymer-dye interactions have been determined. The effect of additives such as alcohols, and urea on the reversal of metachromasy has been studied. The data has been used to determine the stability of the metachromatic complex and the nature of binding. The thermodynamic parameters of interaction revealed that binding between Acridine Orange and Sodium Alginate involved only electrostatic forces while that between Pinacyanol Chloride involved both electrostatic and hydrophobic forces. The reversal studies using surfactants indicated the involvement of both electrostatic and hydrophobic forces in binding. Based on the results it can be concluded that Pinacyanol Chloride is more effective inducing metachromasy than Acridine Orange.

A comparative study of polyelectrolyte-dye interactions

The interaction of Azure B with sodium alginate and heparin in aqueous solution has been studied by spectrophotometric method. Absorbance of Azure B at 645 nm decreases and a new band appeared at 545 nm and at 556 nm respectively which indicated that a new metachromatic complex formed. A linear decrease in absorbance is noted. It was found that sodium alginate is more effective than heparin in decreasing the absorbance of Azure B at 645 nm. The stoichiometry of sodium alginate or heparin with Azure B was determined by spectrophotometry. The results suggested that the interaction between Azure B with sodium alginate or heparin was a result of electrostatic forces and the difference between heparin and sodium alginate were attributed to the different negative charge number on repetitive disaccharides unit. Studies on the effect of alcohol or urea indicated that sodium alginate and heparin interacted with the aggregates of Azure B. Thermodynamic parameters of interaction has been evaluated to determine the stability of the metachromatic complex. The effect of surfactants on reversal of metachromasy has also been studied.

Complexation of oppositely charged polyelectrolytes and surfactants in aqueous solutions. A review

Addition of surfactants to aqueous solutions of polyelectrolytes causes the spontaneous formation of complexes in a certain range of concentrations. In some conditions, compact monodisperse multichain complexes are obtained (short surfactant chain length and polymer rigid enough). The size of the complexes can be varied in controlled way from nanometers up to micrometers, but depends on the mixing procedure, whereas the shape of the complexes depends on the polymer backbone rigidity. These complexes exhibit microstructures analogue to that of the precipitates formed at higher concentrations. In most cases, however, the complexes are large, soft and polydisperse.

Nanostructures formed by self-assembly of negatively charged polymer and cationic surfactants

The formation of nanoparticles by interaction of an anionic polyelectrolyte, sodium polyacrylate (NaPA), was studied with a series of oppositely charged surfactants with different chain lengths, alkyltrimethylammonium bromide (CnTAB). The binding and formation of nanoparticles was characterized by dynamic light scattering, zeta-potential, and self-diffusion NMR. The inner nanostructure of the particles was observed by direct-imaging cryogenic-temperature transmission electron microscopy (cryo-TEM), indicating aggregates of hexagonal liquid crystal with nanometric size.

Polymer-surfactant interactions: binding mechanism of sodium dodecyl sulfate to poly(diallyldimethylammonium chloride)

The binding mechanism of poly(diallyldimethylammonium chloride), PDAC, and sodium dodecyl sulfate, SDS, has been comprehensively studied by combining binding isotherms data with microcalorimetry, zeta potential, and conductivity measurements, as well as ab initio quantum mechanical calculations. The obtained results demonstrate that surfactant-polymer interaction is governed by both electrostatic and hydrophobic interactions, and is cooperative in the presence of salt. This binding results in the formation of nanoparticles, which are positively or negatively charged depending on the molar ratio of surfactant to PDAC monomeric units. From microcalorimetry data it was concluded that the exothermic character of the interaction diminishes with the increase in the surfactant/polymer ratio as well as with an increase in electrolyte concentration.

Aggregate formation in aqueous solutions of carboxymethylcellulose and cationic surfactants

The addition of cationic surfactants to an aqueous solution of an anionic polymer, carboxymethylcellulose (carboxyMC), causes the spontaneous formation of aggregates in a certain range of concentrations. Here we studied two surfactants, dodecyl and hexadecyl trimethylammonium bromide (DTAB and CTAB, respectively). Using different techniques (light scattering, potentiometry, viscosimetry, and zetametry), we found that a simple lengthening of the surfactant tail length by four CH2 groups drastically changes the aggregate morphology, size, and charge. We explored in detail how the surfactant and polymer concentrations act on these systems.

Nanostructures of colloidal complexes formed in oppositely charged polyelectrolyte/surfactant dilute aqueous solutions

Small-angle neutron scattering measurements were performed on dilute solutions of carboxymethylcellulose/DTAB complexes in water in order to determine their size, shape and internal structures. At low polymer content, the complexes are spherical, rather monodisperse and probably made of polymer chains intercalated between surfactant micelles. Moreover, we show that these micelles have a similar cubic arrangement than found in polymer/surfactant precipitates formed at higher surfactant concentrations. At larger polymer content, in the semi-dilute polyelectrolyte regime, the complexes are larger, softer and polydisperse. However, they possess a similar internal structure in both regimes. Carboxymethylcellulose/CTAB complexes are also large, soft and polydisperse but do not seem to exhibit well-defined internal structures.