Polymer conformation in mixed aqueous-polar organic solvents

Carboxymethyl hydroxypropyl guar gum physicochemical properties in dilute aqueous media

We investigate carboxymethyl hydroxypropyl guar gum (CMHPG) solution properties in water and NaCl, KCl, and CaCl2 aqueous solutions. The Huggins, Kraemer, and Rao models were applied by fitting specific and relative viscosity of CMHPG/water and CMHPG/salt/water to determine the intrinsic viscosity [η]. The Rao models yielded better results (R2 = 0.779-0.999) than Huggins and Kraemer equations. [η] decreased up to 84% in salt solution over the range 0.9-100 mM compared to water. Salt effects screened the CMHPG charged side groups chains leading to a compacted structure. In 0.9 mM NaCl(aq), the hydrodynamic coil radius (Rcoil) was 28% smaller and 45% smaller in 100 mM NaCl solution relative to water. Similar decreases were seen in KCl and CaCl2 solutions. KCl and CaCl2 were more effective than NaCl. CMHPG is salt-tolerant and shows comparatively less viscosity change than native guar gum, with modest reduced viscosity increases with CMHPG dilution at all salt concentrations. The electrostatic interactions were effective up to 100 mM salt. The activation energy of viscous flow for CMHPG solutions was computed and compared to measured xanthan gum and several literature values. These data show that the barrier to CMHPG flow is higher than for xanthan gum.

Dimension and Flexibility of Polystyrenesulfonate Chains in Methanol-Water

The influence of the relative permittivity of the solvent medium on the single-chain dimension and flexibility of sodium polystyrenesulfonate chains has been investigated in mixed solvent media of methanol and water using viscosity experiments. Particular attention has been paid to explore the effect of the added low-molar-mass electrolyte. The root-mean-square (rms) radii of gyration of the chains in the unperturbed state have been calculated by applying the Flory model, while the intrinsic persistence lengths by the Benoit-Doty equation on the basis of the Kratky-Porod worm-like chain model. Estimation of the expansion factors for the rms radius of gyration, and the electrostatic persistence length helps evaluate the rms radii of gyration and the total persistence length of polystyrenesulfonate chains in the presence of varying amount of the supporting electrolyte. The polyion chains are highly extended at low ionic strengths but exhibit coil-like behavior with small persistence lengths when an excess of the supporting electrolyte is added in all the methanol-water mixtures investigated. Specifically, in the investigated solvent media, the polystyrenesulfonate chains have been found to shrink by ∼63-65% in the θ-state from their expanded conformation in the presence of 0.0001 mol L-1 NaCl. The chain dimensions pass through a maximum as the medium becomes richer in methanol, which could be explained by the formation and breakup of internal rings involving the polyion chain and water and/or methanol molecules. The intrinsic persistence length of sodium polystyrenesulfonate in a methanol-water mixture containing 0.1 mole fraction of methanol is ca. 1.3 times that in a medium with 0.3 mole fraction of methanol, indicating that flexibility of the polyion depends appreciably on the relative permittivity of the medium.

Salt and Temperature Effects on Xanthan Gum Polysaccharide in Aqueous Solutions

Xanthan gum (XG) is a carbohydrate polymer with anionic properties that is widely used as a rheology modifier in various applications, including foods and petroleum extraction. The aim was to investigate the effect of Na+, K+, and Ca2+ on the physicochemical properties of XG in an aqueous solution as a function of temperature. Huggins, Kraemer, and Rao models were applied to determine intrinsic viscosity, [η], by fitting the relative viscosity (ηrel) or specific viscosity (ηsp) of XG/water and XG/salt/water solutions. With increasing temperature in water, Rao 1 gave [η] the closest to the Huggins and Kraemer values. In water, [η] was more sensitive to temperature increase (~30% increase in [η], 20-50 °C) compared to salt solutions (~15-25% increase). At a constant temperature, salt counterions screened the XG side-chain-charged groups and decreased [η] by up to 60% over 0.05-100 mM salt. Overall, Ca2+ was much more effective than the monovalent cations in screening charge. As the salt valency and concentration increased, the XG coil radius decreased, making evident the effect of shielding the intramolecular and intermolecular XG anionic charge. The reduction in repulsive forces caused XG structural contraction. Further, higher temperatures led to chain expansion that facilitated increased intermolecular interactions, which worked against the salt effect.

Structure of Cellulose Ether Affected by Ionic Surfactant and Solvent: A Small-Angle Neutron Scattering Investigation

Polysaccharides and their derivatives are commonly used in pharmaceutical and agricultural formulations as rheology modifiers. Their performance is related to their conformation in solution, which in turn is affected by other ingredients present in the formulation. This study focuses on modulating the conformation of relatively rigid cellulose chains in aqueous solutions. In particular, we have investigated the nonionic cellulose derivative ethyl(hydroxyethyl)cellulose (EHEC) in water in the presence of the ionic surfactant sodium dodecyl sulfate (SDS) and/or ethanol acting as modulating agents. We have used small angle neutron scattering (SANS) with contrast variation to determine the EHEC chain conformation in the presence of (but not masked by) ethanol and SDS. In dilute and semidilute aqueous solutions, EHEC exhibits worm-like chain conformation due to the rigid cellulose backbone. Addition of ethanol does not impact the polymer conformation to a great extent. Addition of SDS alters the EHEC chain conformation, resulting in polyelectrolyte-like scattering behavior due to repulsive interactions between bound charged micelles which show similar structure as the free SDS micelles in solution (in the absence of polymers). Ethanol affects the polymer + surfactant system primarily by acting on the surfactant (bound on polymer) which, in turn, affects the polymer conformation. At higher ethanol concentrations (20 wt %), EHEC regains the worm-like chain conformation because of the detachment of the bound SDS micelles. To the best of our knowledge, this is the only study providing details on chain conformation of the rigid polymer EHEC in dilute or semidilute aqueous solutions in the presence of surfactant and alcohol and one of very few papers utilizing SANS for the characterization of polymer + surfactant + water + alcohol interactions. Such fundamental understanding of interactions and structure in multicomponent mixtures supports the design of industrial formulations.

Effects of lower alcohols on nanocomposite particles for inhalation prepared using O/W emulsion

BACKGROUND

Inhalable nanocomposite particles using O/W emulsions were studied. The effect of the composition of the dispersed phase on the nanoparticles in the nanocomposite particles was reported, however, the effect on the inhalation characteristics of nanocomposite particles has not been investigated.

OBJECTIVE

The aim of this study was to study the effects of lower alcohols in the dispersed phase of O/W emulsions on inhalable nanocomposite particles.

METHODS

Nanocomposite particles were prepared using a spray dryer from O/W emulsion. A mixed solution of dichloromethane and lower alcohols in which rifampicin (RFP) and poly(L-lactide-co-glycolide) were dissolved was used as a dispersed phase, and an aqueous solution in which arginine and leucine were dissolved was used as a continuous phase.

RESULTS

We succeeded in preparing non-spherical nanocomposite particles with an average diameter of 9.01-10.91 μm. The results of the fine particle fraction (FPF) measurement showed that the higher the hydrophobicity of the lower alcohol mixed in the dispersed phase, the higher the FPF value. The FPF value of the nanocomposite particles was significantly increased by using ethanol and 1-propanol.

CONCLUSIONS

The results were revealed that mixing 1-propanol with the dispersed phase increased the amount of RFP delivered to the lungs.

Construction and Transition Metal Oxide Loading of Hierarchically Porous Carbon Aerogels

Hierarchically porous carbon aerogels (CAs) were prepared by organic condensation gelation method combined with atmospheric drying and pore-formation technology, followed by a carbonization process. With as-prepared CAs as substrate, the transition metal oxide nanoparticles loaded CAs composites (MnO2/Mn2O3@CA and Ni/NiO@CA) were achieved by means of liquid etching method combined with heat treatment, respectively. The catalyst, pore-forming agent and etching have important roles on the apparent density and pore structure of CAs. The hydrochloric acid (catalyst) significantly accelerates the gelation process and influences the size and distribution of macropores, whereas the addition of PEG2000 (pore-forming agent) and the etching of liquid solution leads to the formation of mesopore structure in CAs. Appropriate amounts of hydrochloric acid and PEG2000 allow the formation of hierarchically porous CAs with a BET surface area of 482.9 m2·g-1 and a macropore size of 11.3 μm. After etching and loading, the framework of CAs is etched to become a mesoporous structure, and the transition metal oxide nanoparticles can be uniformly loaded in CAs. These resultant composites have promising application in super capacitor, electrocatalysis, batteries and other fields.

Effect of the Conformation of Poly(L-lactide-co-glycolide) Molecules in Organic Solvents on Nanoparticle Size

Controlling the size of nanoparticles is important for drug delivery methods such as pulmonary administration, transdermal administration, and intravenous administration. In this study, we have investigated the effect of polymer conformation in organic solvents on the size of the nanoparticles. Poly(L-lactide-co-glycolide) (PLLGA), a promising nanoparticle carrier, was used as the polymer. A mixed solution of dichloromethane, which is a good solvent, and a lower alcohol (methanol, ethanol, and 1-propanol), which is a poor solvent, was used as the solvent for dissolving PLLGA. An oil-in-water emulsion was prepared by sonication using the mixed solution of organic solvents in which PLLGA was dissolved as a dispersed phase and an amino acid aqueous solution as a continuous phase. Nanocomposite particles were prepared from the emulsion using a spray dryer and redispersed in purified water to obtain the PLLGA nanoparticles. The conformation of PLLGA molecules in the organic solvents was evaluated by analyzing the results of the viscosity measurements. The polymer coil radius and the volume per polymer coil were observed to decrease with the increase in the ratio of the lower alcohol in the solvent, whereas these values tended to decrease with the use of more hydrophilic lower alcohols. In addition, based on the results of the calculated entanglement index, it was found that when the hydrophobicity of the dispersed phase is reduced, the polymers were hardly entangled with each other. These results were significant, specifically when the ratio of the lower alcohol in the solvent was low. Estimation of the Pearson's correlation coefficients indicated that there were positive correlations between these indices and the mean volume diameter of PLLGA nanoparticles. This study shows that changing the composition of the dispersed phase, in which the PLLGA is dissolved, can change the conformation of the PLLGA molecules and control the size of the PLLGA nanoparticles.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO₁₀₀PO₆₅EO₁₀₀) and Pluronic P123 (EO₁₉PO₆₉EO₁₉), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Holistically Engineered Polymer-Polymer and Polymer-Ion Interactions in Biocompatible Polyvinyl Alcohol Blends for High-Performance Triboelectric Devices in Self-Powered Wearable Cardiovascular Monitorings

The capability of sensor systems to efficiently scavenge their operational power from stray, weak environmental energies through sustainable pathways could enable viable schemes for self-powered health diagnostics and therapeutics. Triboelectric nanogenerators (TENG) can effectively transform the otherwise wasted environmental, mechanical energy into electrical power. Recent advances in TENGs have resulted in a significant boost in output performance. However, obstacles hindering the development of efficient triboelectric devices based on biocompatible materials continue to prevail. Being one of the most widely used polymers for biomedical applications, polyvinyl alcohol (PVA) presents exciting opportunities for biocompatible, wearable TENGs. Here, the holistic engineering and systematic characterization of the impact of molecular and ionic fillers on PVA blends' triboelectric performance is presented for the first time. Triboelectric devices built with optimized PVA-gelatin composite films exhibit stable and robust triboelectricity outputs. Such wearable devices can detect the imperceptible skin deformation induced by the human pulse and capture the cardiovascular information encoded in the pulse signals with high fidelity. The gained fundamental understanding and demonstrated capabilities enable the rational design and holistic engineering of novel materials for more capable biocompatible triboelectric devices that can continuously monitor vital physiological signals for self-powered health diagnostics and therapeutics.

Recent advances in organosolv fractionation: Towards biomass fractionation technology of the future

Organosolv treatment is among the most promising strategies for valorising lignocellulosic biomass and could facilitate the transition towards enhanced utilization of renewable feedstocks. However, issues such as inefficient solvent recycle and fractionation has to be overcome. The present review aims to address these issues and discuss the role of the components present during organosolv treatment and their influence on the overall process. Thus, the review focuses not only on how the choice of solvent and catalyst affects lignocellulosic fractionation, but also on how the choice of treatment liquor influences the possibility for solvent recycling and product isolation. Several organic solvents have been investigated in combination with water and acid/base catalysts; however, the lack of a holistic approach often compromises the performance of the different operational units. Thus, an economically viable organosolv process should optimize biomass fractionation, product isolation, and solvent recycling.

Investigating the self-assembly and shape transformation of poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PDLLA) polymersomes by tailoring solvent-polymer interactions

Different ratios between THF and dioxane were used to study the effect of organic solvent composition on the self-assembly and subsequent shape-change of poly(ethylene glycol)-b-poly(d,l-lactide) (PEG-PDLLA) polymersomes.

Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment

Fluorinated surfactants are used in a wide range of applications that involve aqueous solvents incorporating various additives. The presence of organic compounds such as urea is expected to affect the self-assembly of fluorinated surfactants, however, very little is known about this. We investigated the effect of urea on the micellization in water of the common fluorinated surfactant ammonium perfluorooctanoate (APFO), and on the structure and microenvironment of the micelles that APFO forms. Addition of urea to aqueous APFO solution decreased the critical micellization concentration (CMC) and increased the counterion dissociation. The observed increase in surface area per APFO headgroup and decrease in packing density at the micelle surface suggest the localization of urea at the micelle surface in a manner that reduces headgroup repulsions. Micropolarity data further support this picture. The results presented here indicate that significant differences exist between urea effects on fluorinated surfactant and on hydrocarbon surfactant micellization in aqueous solution. For example, the CMC of sodium dodecyl sulfate (SDS) increased with urea addition, while the increase in surface area per headgroup and packing density of SDS with urea addition are much lower than those observed for APFO. This study informs fluorinated surfactant fate and transport in the environment, and also applications involving aqueous media in which urea or similar additives are present.

Emulsifying properties of high methoxyl pectins in binary systems of water-ethanol

Pectin is widely distributed in plant cell wall, most of which have limited emulsifying properties. Ethanol could alter the solubility of pectin, and affect its emulsifying properties. No creaming and breaking of emulsion appeared in 21% (v/v) ethanol contained emulsion. This project investigated the influence of ethanol (0%-35%, v/v) on conformation and emulsifying properties of pectin. Results shown that ethanol could reduce the helix conformation and zeta potential of pectin chain, which leading to compact conformation and enhanced interaction among pectin molecules. Although emulsion droplet diameter increased with ethanol content, the most stable emulsion was found in 21% (v/v) ethanol. CLSM also indicated over-aggregated pectin have a poor adsorption capacity on the interface of O/W. All results manifested the emulsifying properties of pectin can be improved by 21% (v/v) ethanol. This study provides a new strategy to improve the emulsifying property of pectin by changing its conformation.

Dynamic High-Pressure Microfluidization-Treated Pectin under Different Ethanol Concentrations

We previously reported that dynamic high-pressure microfluidization (DHPM) can degrade pectin in aqueous solution. In this study, we further investigated the effect of DHPM on pectin in water-ethanol systems. In the absence of DHPM treatment, it was found that pectin exhibited increased average particle size and unchanged average molecular weight, but a decline in reducing-sugar-ends content with the increase of ethanol concentrations (0⁻10% v/v). These results indicated that the addition of ethanol induced aggregation of pectin. During DHPM treatment, pectin underwent disaggregation and degradation under all measured ethanol concentrations. Disaggregation was enhanced but degradation was weakened with the increase of ethanol concentration. FT-IR and UV spectra indicated that demethylation but no β-elimination occurred in the water-ethanol system during DHPM. Finally, the mechanism of DHPM-induced disaggregation and degradation of pectin under a water-ethanol system was updated. This work may help us to find a suitable condition for reducing the degradation of pectin during the process of homogenization.

Insight into Nanoscale Network of Spray-Dried Polymeric Particles: Role of Polymer Molecular Conformation

Poly(lactic- co-glycolic acid) (PLGA) microparticles represent a promising formulation approach for providing steady pharmacokinetic/pharmacodynamic profiles of therapeutic drugs for a long period. Understanding and controlling the supramolecular structure of PLGA microparticles at a molecular level is a prerequisite for the rational design of well-controlled, reproducible sustained-release profiles. Herein, we reveal the role of PLGA molecular conformation in particle formation and drug release. The nanoscale network of PLGA microparticles spray-dried using the solvents with distinct polarities was investigated by using NMR and neutron scattering. By employing chemometric method, we further demonstrate the evolution of nanoscale networks in spray-dried PLGA microparticles upon water absorption. Our results indicate that PLGA molecules form more chain entanglements during spray drying when using the solvents with low polarity, where PLGA molecule adopts a more flexible, extended conformation, resulting in the network being more resistant to water absorption in spray-dried PLGA microparticles. This work underlines the role of PLGA molecular conformation in controlling formation and evolution of nanoscale network of spray-dried PLGA microparticles and will have important consequences in achieving customized drug release from the PLGA microparticles.

Zymomonas mobilis exopolysaccharide structure and role in high ethanol tolerance

Bacterial cell surface exopolysaccharides (EPS) provide a protective barrier from the external milieu and participate in host-environment interactions. Zymomonas mobilis, an ethanologenic Gram negative bacterium, is used by the industry in bio-ethanol production process, due to its extraordinary resistance to a highly ethanolic environment. We found that Z. mobilis produces a mixture of two EPSs, an [α-(1→6)-D-Manp] mannose homopolymer and a galactose containing polysaccharide: [→2)-β-D-Galf-(1→3)-β-D-Galp-(1→]_n. A physico-chemical study, conducted with diffusion-ordered spectroscopy (DOSY) and Dynamic Light Scattering (DLS), allowed to demonstrate that, differently from the majority of polysaccharides, ethanol is a good solvent for the galactose containing EPS, revealing that its chemical structure is specifically connected with the Zymomonas mobilis high ethanol tolerance.

From polyelectrolyte complexes to polyelectrolyte multilayers: Electrostatic assembly, nanostructure, dynamics, and functional properties

Polyelectrolyte complexes (PECs) are three-dimensional macromolecular structures formed by association of oppositely charged polyelectrolytes in solution. Polyelectrolyte multilayers (PEMs) can be considered a special case of PECs prepared by layer-by-layer (LbL) assembly that involves sequential deposition of molecular-thick polyelectrolyte layers with nanoscale control over the size, shape, composition and internal organization. Although many functional PEMs with novel physical and chemical characteristics have been developed, the current practical applications of PEMs are limited to those that require only a few bilayers and are relatively easy to prepare. The viability of such engineered materials can be realized only after overcoming the scientific and engineering challenges of understanding the kinetics and transport phenomena involved in the multilayer growth and the factors governing their final structure, composition, and response to external stimuli. There is a great need to model PEMs and to connect PEM behavior with the characteristics of the PEC counterparts to allow for prediction of performance and better design of multilayered materials. This review focuses on the relationship between PEMs and PECs. The constitutive interactions, the thermodynamics and kinetics of polyelectrolyte complexation and PEM formation, PEC phase behavior, PEM growth, the internal structure and stability in PEMs and PECs, and their response to external stimuli are presented. Knowledge of such interactions and behavior can guide rapid fabrication of PEMs and can aid their applications as nanocomposites, coatings, nano-sized reactors, capsules, drug delivery systems, and in electrochemical and sensing devices. The challenges and opportunities in future research directions are also discussed.

Preparation and evaluation of posaconazole-loaded enteric microparticles in rats

OBJECTIVES

Posaconazole (POS) is an antifungal compound which has a low oral bioavailability. The aim of this study was to prepare POS enteric microparticles to enhance its oral bioavailability.

METHODS

POS enteric microparticles were prepared with hypromellose acetate succinate (HPMCAS) via the spray drying method. The solvent mixtures of acetone and ethanol used in the preparation of the microparticles were optimized to produce the ideal POS enteric microparticles. Multivariate data analysis using a principal component analysis (PCA) was used to find the relationship among the HPMCAS molecular characteristics, particle properties and drug release kinetics from the spray dried microparticles.

KEY FINDINGS

The optimal spray solvent mixtures were critical to produce the POS microparticles with the defined polymer entanglement index, drug surface enrichment, particle size and drug loading. The HPMCAS molecular characteristics affected the microscopic connectivity and diffusivity of polymer matrix and eventually influenced the drug release behavior, and enhanced the bioavailability of POS.

CONCLUSIONS

These studies suggested that the selection of suitable solvent mixtures of acetone and ethanol used in the spray drying of the microparticles was quite important to produce the entangled polymer structures with preferred polymer molecular properties of polymer coiling, overlap concentration and entanglement index. Additional studies on particle size and surface drug enrichment eventually produced HPMCAS-based enteric microparticles to enhance the oral bioavailability of POS.

Fundamental Study of Electrospun Pyrene-Polyethersulfone Nanofibers Using Mixed Solvents for Sensitive and Selective Explosives Detection in Aqueous Solution

Fluorescent pyrene-polyethersulfone (Py-PES) nanofibers were prepared through electrospinning technique using mixed solvents. The effects of mixed solvent ratio and polymer/fluorophore concentrations on electrospun nanofiber's morphology and its sensing performance were systematically investigated and optimized. The Py-PES nanofibers prepared under optimized conditions were further applied for highly sensitive detection of explosives, such as picric acid (PA), 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) in aqueous phase with limits of detection (S/N = 3) of 23, 160, 400, and 980 nM, respectively. The Stern-Volmer (S-V) plot for Py excimer fluorescence quenching by PA shows two linear regions at low (0-1 μM) and high concentration range (>1 μM) with a quenching constant of 1.263 × 10(6) M(-1) and 5.08 × 10(4) M(-1), respectively. On the contrary, S-V plots for Py excimer fluorescence quenching by TNT, DNT, and RDX display an overall linearity in the entire tested concentration range. The fluorescence quenching by PA can be attributed to the fact that both photoinduced electron transfer and energy transfer are involved in the quenching process. In addition, pyrene monomer fluorescence is also quenched and exhibits different trends for different explosives. Fluorescence lifetime studies have revealed a dominant static quenching mechanism of the current fluorescent sensors for explosives in aqueous solution. Selectivity study demonstrates that common interferents have an insignificant effect on the emission intensity of the fluorescent nanofibers in aqueous phase, while reusability study indicates that the fluorescent nanofibers can be regenerated. Spiked real river water sample was also tested, and negligible matrix effect on explosives detection was observed. This research provides new insights into the development of fluorescent explosive sensor with high performance.

Nanoparticles in ionic liquids: interactions and organization

Interactions between nanoparticles and ionic liquids can lead to a variety of organized structures.

Charging and uncharging a neutral polymer in solution: a small-angle neutron scattering investigation

Aqueous formulations containing polymers and surfactants find several applications in pharmaceutics, coatings, inks, and home products. The association between polymers and surfactants contributes greatly to the function of these complex fluids, however, the effects of polar organic solvents, ubiquitous in formulations, remain mostly unexplored. We have analyzed small angle neutron scattering (SANS) data to determine the conformation of a "model" nonionic polymer, poly(ethylene oxide) (PEO), in aqueous solutions as affected by the presence of an ionic surfactant, sodium dodecyl sulfate (SDS), and subsequent addition of short-chain alcohol (ethanol or 2-propanol). PEO chains (MW = 90,000) are Gaussian in dilute aqueous solutions, but become polyelectrolyte-like upon the addition of 30 mM SDS, with about 6 SDS micelles bound to each PEO chain. Micelles associated with polymer are similar in structure and interactions to micelles that form in aqueous solutions in the absence of polymer. Addition of alcohol alters both the polymer and micelle structure and interactions, leads to detachment of micelles from the polymer, and the PEO chains regain their Gaussian conformation. 2-Propanol is more effective than ethanol in influencing the polymer conformation and the properties of SDS micelles in aqueous solutions, either in the presence or in the absence of PEO. This study contributes fundamental insights on polymer and surfactant organization in solution, as well as new, quantitative information on systems that are widely used in practice.

Synthesis of water-soluble and water-insoluble amphiphilic derivatives of dextran in organic medium

Hydrophobically modified dextrans were prepared by reacting native polysaccharide with 1,2-epoxydodecane in dimethylsulfoxide. Epoxide oligomerization was shown to occur as a secondary reaction when hydroxide ions were used as base catalysts. By adjusting the amount of epoxide in the feed, dextran derivatives with degrees of substitution (DS) between 0% and 164% were obtained. Polymers with DS above 100% were readily soluble in organic solvents like tetrahydrofuran, dioxane and water-saturated chloroform and dichloromethane. Their solution properties in organic solvent were characterized by capillary viscometry. Water-soluble derivatives were compared to other amphiphilic dextrans obtained using a heterogeneous modification in aqueous medium. The effect of modification conditions on substitution pattern was evidenced.

Protective effect of polysaccharides on the stability of parenteral emulsions

The main purpose of this study is to investigate the influence of two polysaccharides (dextran, hydroxyethyl starch) on the stability of parenteral emulsions. All parenteral emulsions were prepared by high-pressure homogenization. The influence of polysaccharides concentration was studied. The stabilities of autoclaving sterilization, centrifugation and freeze-thawing process were investigated extensively. Following the addition of polysaccharides, the stabilities of the parenteral emulsions were improved. A high-concentration polysaccharides solution (13%, w/v) produced better protection than a low one (1.3%, w/v), especially during freeze-thawing process. The protective mechanisms of polysaccharides were attributed to increasing systematic viscosity, non-frozen water absorbed by polysaccharides, formation of a linear bead-like structure and thicker mixed emulsifier film. Overall, polysaccharides can offer greatly increased protection for parenteral emulsions, and represent a novel protective strategy for improving the stability of this delivery system.

Micellization of alkyl-propoxy-ethoxylate surfactants in water-polar organic solvent mixtures

The effects of cosolvents (glycerol, ethanol, and isopropanol) on the self-assembly of novel alkyl-propoxy-ethoxylate surfactants in aqueous solutions have been investigated with a focus on the (i) quantification of solvent effects on the critical micelle concentration (cmc), (ii) free-energy contributions to micellization, (iii) local environment in the micellar solution, and (iv) structure of the micelles. The introduction of the polar organic solvents considered in this work into water decreases cohesive forces in the solvent mixture, resulting in an increase in the solubility of the surfactant molecules. As a result, micelle formation becomes less favorable and the cmc increases. The contribution of the cosolvent to the free energy of micellization is positive, and the data for different mixed solvents collapse onto a single straight line when plotted versus a function of the solubility parameters of the surfactant alkyl chains and the mixed solvents. The behavior of the poly(propylene oxide) part of the alkyl-propoxy-ethoxylate surfactants is hydrophilic, albeit less so in the ethanol-water mixed solvent than in plain water. Pyrene fluorescence emission I(1)/I(3) data suggest that the microenvironment in micellar solutions is affected mainly by the cosolvent concentration, not the surfactant degree of ethoxylation. Small-angle X-ray scattering data for both water and ethanol-water surfactant solutions are consistent with oblate ellipsoid micelles and reveal that the introduction of 20% ethanol decreases the micelle long axis by 10-15%.