Microstructures formed in aqueous solutions of a hydrophobically modified nonionic cellulose derivative and sodium dodecyl sulfate: a fluorescence probe investigation

Solution properties and aggregating structures for a fluorine-containing polymeric surfactant with a poly(ethylene oxide) macro-monomer

A polymeric surfactant (PFSA) was synthesized by the aqueous free-radical copolymerization using acrylamide, sodium 2-acrylamido-2-methylpropane sulfonate, allyl-capped octylphenoxy poly(ethylene oxide) (PEO) with the polymerization degree of 20 (AOP) and 1H,1H,2H,2H-perfluoro-1-decyl p-vinylbenzyl ether (VF). PFSA exhibited both the good surface and interfacial activities and the thickening behaviour. It could be used in enhanced oil recovery to increase both sweep and oil displacement efficiencies. The critical micelle concentration (CMC) of PFSA was 0.1 g l-1 in aqueous solution. The spherical micelles with the diameter of 100 nm were formed at CMC, and numerous compact worm-shaped micelles were observed above CMC. The interfacial tension was 0.027 mN m-1 for the 0.1 g l-1 PFSA solution containing 5 g l-1 NaCl and 0.209 g l-1 SDBS. The PFSA solutions still showed low interfacial tensions at high NaCl concentrations and temperatures, respectively, because of the incorporation of both VF and AOP containing long PEO.

Enzymic degradation of hydroxyethyl cellulose and analysis of the substitution pattern along the polysaccharide chain

The enzymatic degradation behavior of hydroxyethyl cellulose (HEC) samples with different molar substitutions (MS) values was investigated. The changes in the molecular structure of HEC treated with enzymatic approach in comparison to the native HEC were studied through nuclear magnetic resonance (NMR), fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques and kinetics of degradation was studied by viscometry. The cleavage of HEC chains could be observed from FTIR and kinetics results. Moreover, reduce in molecular weight (Mw) of polymer and liberated glucose concentration was investigated by gel permeation chromatography (GPC) analysis during enzymatic degradation. And all these results indicated that HEC with lower MS is more susceptible to degrade and provided a better understanding of the mechanism operating during enzymatic hydrolysis of HEC by cellulases. Furthermore, by complete degradation and quantification of liberated glucose, the substitution index (SI) and the distribution of substituents along the HEC chain were investigated. The results suggested that the HEC samples differed in hydroxyethyl molar substitutions (MS) and possible distribution of the hydroxyethyl groups. Impressively, our efforts established a facile analytical method for the elucidation of the distribution of substituents along the HEC chain.

Preparation and properties of propylene oxide and octenylsuccinic anhydride modified potato starches

Starch was dually chemically modified for developing food-grade ingredients of lower digestibility and their properties were compared to those of single modified and native starches. Hydroxypropylation with propylene oxide (HP) followed by esterification with octenylsuccinic anhydride (OSA) of potato starch (P-native) produced derivatives with lower digestibility than esterification solely with OSA. The dextrose equivalent, maltose and glucose contents, which were used as the main indicators for in vitro digestion, were lower for modified starches. P-HP_0.2-OSA_0.0200 derivative was the least digestible; the glucose and maltose contents were lowered by 28.3 and 42.1% compared to P-native. The aggregation behavior of enzymatically hydrolyzed starch derivatives was studied in aqueous solution by employing the fluorescence probe and dynamic light scattering techniques. The critical aggregation concentration for OSA modified and dually modified starches varied from 1.2 to 3 g/L and from 0.125 to 0.48 g/L, respectively, depending on the degree of OSA substitution. The study showed that above a critical concentration the hydrolyzates of modified starches tend to form the aggregates with different properties depending both on the degree of OSA substitution and chemical structure.

Phase behavior and molecular thermodynamics of coacervation in oppositely charged polyelectrolyte/surfactant systems: a cationic polymer JR 400 and anionic surfactant SDS mixture

Coacervation in mixtures of polyelectrolytes and surfactants with opposite charge is common in nature and is also technologically important to consumer health care products. To understand the complexation behavior of these systems better, we combine multiple experimental techniques to systematically study the polymer/surfactant binding interactions and the phase behavior of anionic sodium dodecyl sulfate (SDS) surfactant in cationic JR 400 polymer aqueous solutions. The phase-behavior study resolves a discrepancy in the literature by identifying a metastable phase between the differing redissolution phase boundaries reported in the literature for the surfactant-rich regime. Isothermal titration calorimetry analyzed within the framework of the simple Satake-Yang model identifies binding parameters for the surfactant-lean phase, whereas a calculation for polymer-bound micelles coexisting with free micelles is analyzed in the surfactant-rich redissolution regime. This analysis provides a preliminary understanding of the interactions governing the observed phase behavior. The resulting thermodynamic properties, including binding constants and the molar Gibbs free energies, enthalpies, and entropies, identify the relative importance of both hydrophobic and electrostatic interactions and provide a first approximation for the corresponding microstructures in the different phases. Our study also addresses the stability and metastability of oppositely charged polyelectrolytes and surfactant mixtures.

Sol-Gel Behavior of Hydroxypropyl Methylcellulose (HPMC) in Ionic Media Including Drug Release

Sol-gel transformations in HPMC (hydroxypropyl methylcellulose) are being increasingly studied because of their role in bio-related applications. The thermo-reversible behavior of HPMC is particularly affected by its properties and concentration in solvent media, nature of additives, and the thermal environment it is exposed to. This article contains investigations on the effects of salt additives in Hofmeister series on the HPMC gelation. Various findings regarding gelation with salt ions as well as with the ionic and non-ionic surfactants are presented. The gel formation in physiological salt fluids such as simulated gastric and intestine fluids is also examined with the interest in oral drug delivery systems. The processes of swelling, dissolution and dispersion of HPMC tablets in simulated bio-fluids are explored and the release of a drug from the tablet affected by such processes is studied. Explanations are provided based on the chemical structure and the molecular binding/association of HPMC in a media. The test results at the body or near-body temperature conditions helped in understanding the progress of the gelation process within the human body environment. The detailed interpretation of various molecule level interactions unfolded the sol-gel mechanisms and the influence of a few other factors. The obtained test data and the established mathematical models are expected to serve as a guide in customizing applications of HPMC hydrogels.

Physicochemical properties of methylcellulose and dodecyltrimethylammonium bromide in aqueous medium

Interactions between uncharged polymers and cationic surfactants are considered weaker than interactions with the anionic analogues. This work describes the binding occurring between methylcellulose (MC) and the cationic surfactant DTAB in aqueous medium. In the absence of salt, MC-DTAB exhibits a maximum in hydrodynamic radius, R(h,slow), with the increase in the surfactant concentration. Otherwise, in presence of salt the MC-DTAB system shows only a linear increase of R(h,slow). CAC is lower than the CMC, which is taken as an evidence of binding between the cationic surfactant and neutral polymer that induces the aggregation process. Static light scattering, rheology and micro-DSC results highlight the hydrophobic MC-DTAB association. Salt-out and the salt-in effects were observed in presence of DTAB, with a clear transition at concentration values close to the CMC, as judged from rheological and micro DSC measurements. Indeed, DTAB affects both the pattern of the sol-gel transition and the gel strength.

Xylan-based nanoparticles: prodrugs for ibuprofen release

Esterification of xylan with ibuprofen via activiation of the carboxylic acid with N,N'-carbonyldiimidazole (CDI) yields products of high drug loadings. Subsequent sulfation of xylan ibuprofen esters using the gentle agent SO(3)/DMF was successfully carried out in order to modify hydrophobicity of the xylan esters. The structure of the novel xylan esters was evaluated by means of NMR spectroscopy. The resulting xylan derivatives self assemble into spherical nanoparticles with mean diameters ranging from 162 to 472 nm. Preliminary stability measurements indicate that hydrolytic stability decreases with increase in degree of substitution of sulfate groups. Thus, a new concept toward improved drug delivery from polysaccharide-based nanoparticles can be established here.

Association of a hydrophobically modified polyelectrolyte and a block copolymer followed by fluorescence techniques

By using absorption and fluorescence (steady-state and time-resolved) techniques, the interaction between a poly(acrylic acid) (PAA), randomly grafted with pyrene (Py) units (PAAMePy55), and a triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) (EO(20)PO(68)EO(20), P123) was investigated. From the fluorescence data, it is shown that upon addition of P123 a decrease of the (pyrene-pyrene, Py-Py) intramolecular association, i.e., a decrease of dynamic and static excimer formation, is observed. Time-resolved fluorescence data reveal the existence of two types of monomers (monomers that are able to form excimer, MAGRE, and isolated monomers) and two excimers. Addition of P123 causes also an increase of the amount of isolated Py monomers. The overall fluorescence data suggest that the PAAMePy55 and the P123 block copolymer associate strongly at low pH, leading to the formation of P123 micelles surrounded by one PAAMePy55 chain, where the pyrene groups are located at the PPO/PEO interface of the P123 micelles. Steady-state fluorescence results also showed that an excess of P123 micelles in solution is required for the association to occur. At high pH (pH 9 and above) the situation is less clear. The steady-state (particularly in the I(1)/I(3) ratio) and time-resolved fluorescence results indicate a contact between the pyrene groups and PEO, which then would imply that there may be an interaction, but much weaker than at low pH.

Derivatizing weak polyelectrolytes—Solution properties, self-aggregation, and association with anionic surfaces of hydrophobically modified poly(ethylene imine)

The physical properties of weak polyelectrolytes may be tailored via hydrophobic modification to exhibit useful properties under appropriate pH and ionic strength conditions as a consequence of the often inherently competing effects of electrostatics and hydrophobicity. Pulsed-gradient spin-echo NMR (PGSE-NMR), electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS) surface tension, fluorescence, and pH titration have been used to examine the solution conformation and aggregation behavior of a series of hydrophobically modified hyperbranched poly(ethylene imine) (PEI) polymers in aqueous solution, and their interaction with sodium dodecylsulfate (SDS). PGSE-NMR gave a particularly insightful picture of the apparent molecular weight distribution. The presence of the hydrophobes led to a lower effective charge on the polymer at any given pH, compared to the (parent) nonmodified samples. Analysis of the SANS data showed that the propensity to form highly elliptical or rod-like aggregates at higher pHs, reflecting both the changes in protonation behavior induced by the hydrophobic modification and an hydrophobic interaction, but that these structures were disrupted with decreasing pH (increasing charge). The parent samples were not surface active yet the hydrophobically modified samples show pronounced surface activity and the presence of small hydrophobic domains. The surface activity increased with an increase in the degree of modification. On addition of SDS, the onset of the formation of polymer/surfactant complexes was insensitive to the degree of modification with the resultant PEI/SDS complexes resembling the size and shape of simple SDS micelles. Indeed, the presence of the SDS effectively nullifies the effects of the hydrophobe. Hydrophobic modification is therefore a viable option to tailor pH dependent properties, whose effects may be removed by the presence of surfactant.

Added surfactant can change the phase behavior of aqueous polymer-particle mixtures

The phase behavior of aqueous mixtures of the "clouding" polymer ethyl(hydroxyethyl)cellulose (EHEC) mixed with colloidal particles and surfactants has been studied. These types of mixtures are important in many technical formulations. Two types of particles, polystyrene latex and silica, and two types of EHEC, nonmodified EHEC (N-EHEC) and hydrophobically modified EHEC (HM-EHEC), were studied. The EHECs adsorb to both kinds of particles. Both the amount and the type of added surfactant were seen to dramatically influence the partitioning of the particles between the EHEC-rich and EHEC-poor phases of phase-separated mixtures (above the cloud point temperature). Surfactants that are known not to associate with the EHEC backbone, that is, nonionic surfactants and short-chain cationic surfactants, changed the interaction between EHEC and the colloidal particles from attraction to repulsion above a specific surfactant concentration, resulting in a change in the partitioning of the particles from the EHEC-rich to the EHEC-poor phase. No such particle inversion was observed for ionic surfactants that bind to the EHEC backbone. An analysis considering both the binding of surfactant to EHEC and the competitive adsorption of surfactant to the particle surfaces could rationalize all observations, including the large variations observed, among the studied mixtures, in the surfactant concentration required for particle inversion.