The antimicrobial activity of oil-in-water microemulsions is predicted by their position within the microemulsion stability zone

It has been shown previously that thermodynamically stable oil-in-water microemulsions have significant antimicrobial activity against planktonic cells and biofilm cells over short periods of exposure. It was the aim of this study to identify whether the position of the microemulsion within the microemulsion stability zone of the pseudo-ternary phase structure predicts the efficiency of the antimicrobial action of the microemulsion. Microemulsions were formulated at different points within the microemulsion stability zone. Experiments were performed to observe the kinetics of killing of these microemulsions against selected test microorganisms (Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 10231, Staphylococcus aureus ATCC 6538 and Aspergillus niger ATCC 16404). The results indicated that the antimicrobial activity of the microemulsion is dependant upon its position within the zone of stability and is greater nearer the centre of that zone. The results indicate that significant antimicrobial activity can be observed at all points within the zone of microemulsion stability, but that maximal activity is to be found at the centre of that area

Formation and structure of the microemulsion phase in two-dimensional ternary AB+A+B polymeric emulsions

We present an analysis of the structure of the fluctuation-induced microemulsion phase in a ternary blend of balanced AB diblock copolymers with equal amounts of A and B homopolymers. To this end, graphical analysis methods are employed to characterize two-dimensional configuration snapshots obtained with the recently introduced Field-Theoretic Monte Carlo (FTMC) method. We find that a microemulsion forms when the mean curvature diameter of the lamellar phase coincides roughly with the periodicity of the lamellar phase. Further, we provide evidence to the effect of a subclassification of the microemulsion into a genuine and a defect-driven region.Comment: to appear in J. Chem. Phy

Nucleation in A/B/AB blends: Interplay between microphase assembly and macrophase separation

We study the interplay between microphase assembly and macrophase separation in A/B/AB ternary polymer blends by examining the free energy of localized fluctuation structures (micelles or droplets), with emphasis on the thermodynamic relationship between swollen micelles (microemulsion) and the macrophase-separated state, using self-consistent field theory and an extended capillary model. Upon introducing homopolymer B into a micelle-forming binary polymer blend A/AB, micelles can be swollen by B. A small amount of component B (below the A-rich binodal of macrophase coexistence) will not affect the stability of the swollen micelles. A large excess of homopolymer, B, will induce a microemulsion failure and lead to a macrophase separation. Between the binodal and the microemulsion failure concentration, macrophase separation in A/B/AB occurs by a two-step nucleation mechanism via a metastable microemulsion droplet of finite size. Our results illustrate a recently proposed argument that the two-step nucleation via a metastable intermediate is a general phenomenon in systems involving short-range attraction and long-range repulsion

Swollen Micelles Plus Hydrophobically Modified Hydrosoluble Polymers in Aqueous Solutions: Decoration Versus Bridging. a Small Angle Neutron Scattering Study

In this paper we examine the effective interactions introduced between the droplets of an oil in water microemulsion upon progressive addition of hydrophobically modified water soluble poly(ethylene oxide)-PEO using essentially small angle neutron scattering. To discuss the relative importance of decoration and bridging of the droplets we compare analogous samples with addition of a PEO grafted at both extremities with hydrophobic C12H 25 chains (PEO-2m) or addition of a PEO grafted at one extremity only with a C12H 25 chain (PEO-m). PEO-m or PEO-2m adsorb onto the droplets via their hydrophobic extremities and the droplets are found to retain their form and size upon addition of up to 40 hydrophobic C12H 25 chains per droplet. When the volume fraction of droplets is less than about 10%, the effective interactions introduced by PEO-m or PEO-2m are found to be very different: PEO-m introduces a repulsive interaction while PEO-2m introduces an effective attractive interaction. This attractive interaction leads to an associative phase separation in the range of low volume fraction when a sufficient amount of PEO-2m is added

Microemulsion breakdown by pervaporation technique: Effect of the alkyl chain length of n-alkanol, a cosurfactant of the microemulsion

Two sets of microemulsions, cyclohexane- and water-rich ones, were prepared with the following n-alkanols as cosurfactants: n-propanol, n-butanol, n-pentanol, and n-hexanol. The results showed the influence of the alkyl chain length of the n-alkanol on the permselectivity properties of the pervaporation technique in the breakdown of the microemulsions. The variations of the total flux rate J and the enrichment factor β were in parallel with the effect of the cosurfactant on the swelling extent of the PDMS membrane

Structure and rheological properties of model microemulsion networks filled with nanoparticles

Model microemulsion networks of oil droplets stabilized by non ionic surfactant and telechelic polymer C18-PEO(10k)-C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering. A Reverse Monte Carlo approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R=10nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%

Clean synthesis of adipic acid from cyclohexene in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant: From the laboratory to bench scale

Adipic acid, HOOC(CH2)4COOH, is a white crystalline solid used primarily in the manufacture of nylon-6,6 polyamide. In industry, adipic acid is mainly produced by oxidation of cyclohexane with air and nitric acidfollowing a homogeneous two-step route. However, this process leads to the formation of nitrous oxide, a greenhouse gas that has to be decomposed. The aim of this study was the development of a clean technology at pilot scale in order to obtain and recover pure adipic acid, and the evaluation of its industrial practicability. Adipic acid was synthesized from cyclohexene and hydrogen peroxide in microemulsions with stearyl dimethyl benzyl ammonium chloride as surfactant. The non-polluting catalyst sodium tungstate, which contains no heavy metal, was used and the reaction conducted under mild conditions (85 C, 8 h). Yields of up to 81% were reached at the 0.14 L scale. However at the end of the reaction the catalyst and the surfactant must be separated and recycled for subsequent cycles. The reuse of the reaction media enabled the conversion to be increased up to 92% but a loss of surfactant and/or catalyst through the cycles progressively reduced the yields. Yields at the bench scale (1.4 L) increased during the two first cycles and then decreased to conversions of between 60% and 70%. Globally the yield is a little lower at bench scale. The results obtained show that the synthesis of adipic acid by a heterogeneous one-step oxidation of cyclohexene in the presence of hydrogen peroxide is an attractive route for developing a future green industrial process

Self-Diffusion and Collective Diffusion of Charged colloids Studied by Dynamic Light Scattering

A microemulsion of decane droplets stabilized by a non-ionic surfactant film is progressively charged by substitution of a non-ionic surfactant molecule by a cationic surfactant. We check that the microemulsion droplets remain identical within the explored range of volume fraction (0.02 to 0.18) and of the number of charge per droplets (0 to 40) . We probe the dynamics of these microemulsions by dynamic light scattering. Despite the similar structure of the uncharged and charged microemulsions the dynamics are very different . In the neutral microemulsion the fluctuations of polarization relax, as is well known, via the collective diffusion of the droplets. In the charged microemulsions, two modes of relaxation are observed. The fast one is ascribed classically to the collective diffusion of the charged droplets coupled to the diffusion of the counterions. The slow one has, to our knowledge, not been observed previously neither in similar microemulsions nor in charged spherical colloids. We show that the slow mode is also diffusive and suggest that its possible origine is the relaxation of local charge fluctuations via local exchange of droplets bearing different number of charges . The diffusion coefficient associated with this mode is then the self diffusion coefficient of the droplets

Reaction Kinetics in the Production of Pd Nanoparticles in Reverse Microemulsions. Effect on Particle Size

In the synthesis of metallic nanoparticles in microemulsions, we hypothesized that particle size is mainly controlled by the reaction rate. Thus, the changes observed on the particle sizes as reaction conditions, such as concentrations, temperature, type of surfactant used, etc., are varied should not be correlated directly to the modification of those conditions but indirectly to the changes they produce on the reaction rates. By means of time resolved UV-vis spectroscopy, we measured the reaction rates in the production of Pd nanoparticles inside microemulsions at different reactant concentrations, keeping all the other parameters constant. The measured reaction rates were then correlated with the particle sizes measured by transmission electron microscopy (TEM). We found that nanoparticle size increases linearly as the reaction rates increases, independently of the actual reactant concentrations. We proposed that the kinetics is controlled mainly by the diffusion of the reducing agent through the surfactant monolayer covering the microemulsion membrane. With this model, we predicted that particle size should depend indirectly, via the reaction kinetics, on the micelle radius (v0 ~ r^-3), the water volume (v0~vw^3) and the total microemulsion volume (v0~vT^-3), and temperature (Arrhenius). Some of these predictions were explored in this article

Influence of process variables on the properties of simvastatin self-emulsifying granules obtained through high shear wet granulation

Improvements of the oral bioavailability of lipophilic drugs can be obtained using lipidic formulations such as the self-emulsifying drug delivery systems. The high shear wet granulation (HSWG), using microemulsions as binder, is a viable process to produce self-emulsifying granules. However only few information are present in the literature on the effect of process variables on the properties of the granules obtained with these binders. Consequently, this article compares the effects of some relevant experimental variables (impeller speed and massing time) on thefinal technological and pharmaceutical properties of the granules produced using simple water, or alternatively, a microemulsion as binder and containing simvastatin (SV) as model drug. The effects of the variables were determined by evaluating the granule median diameter, their particle size distribution, roundness, disintegration time and dissolution rate of SV. Results clearly demonstrated that the microemulsion-based process was less sensitive tooperating conditions than the water-based process. With microemulsion the nucleation process and growth regimes were more difficult to control, resulting in products with broader PSDs. At the same operatingconditions microemulsion-based granules were more brittle but rounder and showed smaller median diameter compared to water-based granules. The dissolution rate of simvastatin was not significantly affected by the operating conditions