Julian Eastoe

Dynamic surface tension and adsorption mechanisms of surfactants at the air–water interface

Recent advances in understanding dynamic surface tensions (DSTs) of surfactant solutions are discussed. For pre-CMC solutions of non-ionic surfactants, theoretical models and experimental evidence for a mixed diffusion-kinetic adsorption mechanism are covered. For micellar solutions of non-ionics, up to approximately 100 x CMC, the DST behaviour can also be accounted for using a mixed mechanism model. Finally, the first reported measurements of the dynamic surface excess Gamma(t), using the overflowing cylinder in conjunction with neutron reflection, are described.

Design and optimization of a new self-nanoemulsifying drug delivery system

To improve the dissolution rate of ibuprofen, a model poorly water soluble drug, self-nanoemulsifying drug delivery systems (SNEDDS) were developed. Various surfactants and oils were screened as candidates for SNEDDS on the basis of droplet size of the resulting emulsions. The influence of the constituent structure, concentration and the composition of SNEDDS formulations, and the emulsifier HLB value, on the properties of the resulting emulsions was systematically investigated. Several SNEDDS formulations were employed to study the relationship between the emulsion droplet size and the dissolution rate of ibuprofen. The dissolution rate was accelerated by decreasing the nanoemulsion droplet size, and was significantly faster than that from a conventional tablet. The optimal SNEDDS formulation had a mean nanoemulsion droplet diameters of 58 nm in phosphate buffer, pH 6.8 (simulated intestinal fluid), and released ibuprofen more than 95% within 30 min. Therefore, these novel SNEDDS carriers appear to be useful for controlling the release rate of poorly water soluble drugs.

Self-assembly of light-sensitive surfactants

This review covers recent advances with an intriguing class of functionalised light-sensitive surfactants. The main chemical classes are described, and the photo-responses in interfacial and aggregation systems are discussed.

Magnetic Control over Liquid Surface Properties with Responsive Surfactants

are well known. Here we report for the first time ionicliquid surfactants that are magneto-responsive, thus offeringthe potential to perturb liquid emulsions simply by theapplication of an external magnetic field. Although ionicliquids(ILs)containingtransitionmetalcomplexeshavebeenknown for some time,

Applications of polymerizable surfactants

Abstract Polymerizable surfactants (‘surfmers’) offer potential for developing hybrid nanometer-sized reaction and templating media. There has been a significant literature devoted to polymerization of, or in organized amphiphilic assemblies. This has led to the formation of a number of unique nano-materials including open-cell polymer networks, ultra-fine polymer latexes and inorganic/organic nano-composites, which exhibit novel properties, and would be unobtainable through conventional techniques. Amongst other parameters, surfmer composition and molecular structure play an extremely important role in the polymerization process, and essentially govern the final properties of the polymer. This review focuses on three main areas including the polymerization of micelles, vesicles, lyotropic liquid crystals or mesophases and microemulsions.

Anionic Surfactant Ionic Liquids with 1-Butyl-3-methyl-imidazolium Cations: Characterization and Application

For the first time a series of anionic surfactant ionic liquids (SAILs) has been synthesized based on organic surfactant anions and 1-butyl-3-methyl-imidazolium cations. These compounds are more environmentally friendly and chemically tunable as compared to other common ionic liquids. A detailed investigation of physicochemical properties highlights potential applications from battery design to reaction control, and studies into aqueous aggregation behavior, as well as structuring in pure ILs, point to possible uses in electrochemistry.

Nanoparticle and polymer synthesis in microemulsions

Micellar and microemulsion phases can be used to synthesize and disperse nanometre-sized colloids. The self-organization of the parent surfactant phases can control the final size and, in some cases, shape of the particles. Metallic, semiconductor, superconductor and magnetic particles can be made as well as polymeric materials.

Stimuli-responsive surfactants

Recent progress in stimuli-responsive surfactants is reviewed, covering control of both interfaces and bulk solution properties. Particular attention is devoted to potential future directions and applications.

Anionic Surfactants and Surfactant Ionic Liquids with Quaternary Ammonium Counterions

Small-angle neutron scattering and surface tension have been used to characterize a class of surfactants (SURFs), including surfactant ionic liquids (SAILs). These SURFs and SAILs are based on organic surfactant anions (single-tail dodecyl sulfate, DS, double-chain aerosol-OT, AOT, and the trichain, TC) with substituted quaternary ammonium cations. This class of surfactants can be obtained by straightforward chemistry, being cheaper and more environmentally benign than standard cationic SAILs. A surprising aspect of the results is that, broadly speaking, the physicochemical properties of these SURFs and SAILs are dominated by the nature of the surfactant anion and that the chemical structure of the added cation plays only a secondary role.

Variation of surfactant counterion and its effect on the structure and properties of Aerosol-OT-based water-in-oil microemulsions

The sodium salt of the di-chained anionic surfactant bis-2-ethylhexylsulfosuccinate [Aerosol-OT or Na(AOT)] stabilises essentially monodisperse, spherical water-in-oil microemulsion (w/o) droplets in alkanes over a wide range of pressure, temperature and composition. In order to investigate the effect of change in counterion charge and size on the microemulsion properties, we have replaced the Na+ counterion by doubly charged ions. The surfactant is then M2+(AOT)2·nH2O: M is from the series Mg2+, Ca2+, Co2+, Ni2+, Cu2+ and Zn2+, and n is the number of water ligands associated with the surfactant molecule. The value of n was determined by FTIR and depends on M2+, but can be between 2 and 8 per molecule of M2+(AOT)2 depending on the nature of M. The ion replacement, assessed by UV–VIS spectrophotometry, is ca. 100% efficient. The effect of temperature on the phase stability of the single-phase M2+(AOT)2 water-in-oil (w/o) microemulsion systems is negligible, in contrast to that observed for the corresponding Na(AOT) system. The structure and properties of the microemulsion are found to be dependent on the counterion identity. Small-angle neutron scattering (SANS) and viscosity measurements provide evidence for the existence of rod-shaped aggregates for Co2+, Ni2+, Cu2+ and Zn2+ at low water constants given by w=[H2O]/[AOT]≈ 5, whilst for Mg2+ and Ca2+ spherical aggregates are present as for Na+. On further addition of water at constant surfactant concentration (w > 10) with Co2+, Ni2+, Cu2+ and Zn2+ the aggregates undergo a shape change, and a more spherical structure is favoured. The results may be explained in terms of the interaction of the different counterions with the SO–3 head group of the surfactant.