Evaluating the Baylis-Hillman reaction of cyclic enones using surfactants in water

Conjugated cyclic enones react smoothly in water with a variety of aldehydes (Baylis-Hillman reaction) in the presence of surfactants above their critical micelle concentrations (CMC).

Submicron dispersions of hexosomes based on novel glycerate surfactants

Glycerate-based surfactants are a new class of swelling amphiphiles which swell to a finite degree with water. Among this class of surfactants, oleyl (cis-octadec-9-enyl) glycerate is very similar in structure to a well characterized mesophase-forming lipid, glyceryl monooleate (GMO). Despite the similar structural characteristics, a subtle change in connectivity of the ester bond substantially alters the binary surfactant-water phase behaviour. Whereas the phase behaviour of GMO is diverse and dominated by cubic phases, the phase behaviour of oleyl glycerate and a terpenoid analogue phytanyl (3,7,11,15-tetramethyl-hexadecane) glycerate is much simplified. Both exhibit an inverse hexagonal phase (H-II), which is stable to dilution with excess water, and an inverse micellar phase (L-II) at ambient temperatures. The inverse hexagonal phases formed by oleyl glycerate and phytanyl glycerate have been characterized using SAXS. Analogous to GMO cubosomes, the inverse hexagonal phase of phytanyl glycerate has been dispersed to form hexagonally facetted particles, termed hexosomes, whose structure has been verified using cryo-TEM.

Peptide surfactants (Pepfactants) for switchable foams and emulsions

We have developed a series of sustainable peptide surfactants (Pepfactants) capable of stabilizing foams and emulsions in a stimuli-responsive manner, based on the reversible formation of a mechanically strong interfacial film. Under conditions where the interfacially adsorbed peptide forms a mechanically strong film state, foam or emulsion stabilization occurs as a direct result of the film strength. Under conditions where the interfacially adsorbed peptide forms a mobile detergent state, foam or emulsion stabilization is either reduced, or does not occur. Preformed foams or emulsions stabilized by Pepfactants undergo rapid phase coalescence when the film state is converted to the detergent state. Switching between film and detergent states is readily and reversibly achieved by a change in the bulk solution composition, such as a change in pH, or the addition or sequestering of metal ions. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

A novel method to prepare mesoporous nano-zirconia

A novel method to prepare mesoporous zirconia was developed. The synthesis was carried out in the presence of PEO surfactants via solid-state reaction. The materials exhibit strong diffraction peak at low 2-theta angle and their nitrogen adsorption/desorption isotherms are typical of IV type with H3 hysteresis loops. The pore structure examined by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniform in size (around 1.5nm) and their pores center at around 4.6nm. The zirconia nanocrystal growth is mainly via an aggregation mechanism. This study also reveals that the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stability of zirconia. The ratio of NaOH to ZrOCl2, crystallization and calcination temperature play an important role in the synthesis of mesoporous zirconia.

Synthesis and stabilization of nanocrystalline zirconia with MSU mesostructure

In the presence of nonionic block-copolymer surfactant, nanocrystalline zirconia particles with MSU mesostrucmre were synthesized by a novel solid-state reaction route. The zirconia particles possess a nanocrystalline pore wall, which renders higher thermal stability compared to an amorphous framework. To further enhance its stability, laponite, a synthetic clay, was introduced. Laponite acts as an inhibitor to crystal a growth and also as a hard template for the mesostructure. High surface area and ordered pore structure were observed in the stabilized zirconia. The results show that the formation of the MSU structure is attributed to reverse hexagonal micelles, which are the products of the cooperative self-assembly of organic and inorganic species in the solid-state synthesis system with crystalline water and hygroscopic water present.

Dynamic interfacial tension of aqueous solutions of PVAAs and its role in liquid-liquid dispersion stabilization

In liquid-liquid dispersion systems, the dynamic change of the interfacial properties between the two immiscible liquids plays an important role in both the emulsification process and emulsion stabilization. In this paper, experimentally measured dynamic interfacial tensions of 1-chlorobutane in the aqueous solutions of various random copolymers of polyvinyl acetate and polyvinyl alcohol (PVAA) are presented. Theoretical analyses on these results suggest that the adsorption of the polymer molecules is controlled neither by the bulk diffusion process nor the activation energy barrier for the adsorption but the conformation of polymer molecules. Based on the concept of critical concentration of condensation for polymer adsorption, as well as the observation that the rate at which the dynamic interfacial tension changes does not correlate to the PVAA's ability to stabilize a single drop, it is postulated that the main stabilization mechanism for the PVAAs is by steric hindrance, not the Gibbs-Marangoni effect offered by the small molecule surfactants.

The problem of purity in evaluating surfactant performance

Labeled surfactants have impurities in the form of un-reacted molecules or distributed products which is a constraint in evaluating its performance. This short review deals with the purity issue of surfactants and is divided into two parts. The first part deals with the methods of purification employed for obtaining a surface chemically pure surfactant for evaluation. In the second part the use of surface chemically impure surfactant in application areas of formulations is presented to highlight the impending impact on reproducibility of results.

The interlayer swelling and molecular packing in organoclays

Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl-ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles. (c) 2005 Elsevier Inc. All rights reserved.

Mesoporous bioactive glasses. I. Synthesis and structural characterization

Highly ordered mesoporous bioactive glasses (MBGs) with different compositions have been synthesized by a combination of surfactant templating, sol-gel method and evaporation-induced self-assembly (EISA) processes. The texture properties and compositional homogeneity of MBGs have been characterized and compared with conventional bioactive glasses (BGs) synthesized in the absence of surfactants by evaporation method. The formation mechanism (pore - composition dependence) and compositional homogeneity in the case of MBG materials are different from those in conventional BGs. Unlike conventional sol-gel-derived BGs that shows a direct correlation between their composition and pore architecture, MBGs with different compositions may possess similar pore volume and uniformly distributed pore size when the same structure-directing agent is utilized. The framework of MBG is homogeneously distributed in composition at the nanoscale and the inorganic species generally exists in the form of amorphous phase. MBGs calcined at temperatures

The in-vitro bioactivity of mesoporous bioactive glasses

Ordered mesoporous bioactive glasses (MBGs) with different compositions were prepared by using nonionic block copolymer surfactants as structure-directing agents through an evaporation-induced self-assembly process. Their in-vitro bioactivities were studied in detail by electron microscopy, Fourier-transform infrared spectroscopy, and inductively coupled plasma (ICP) atomic emission spectroscopy. The ICP element analysis results were further calculated in terms of the total consumption of Ca and P, Delta[Ca]/Delta[P] ratios, and ionic activity product (IP) of hydroxyapatite. Through the above analysis, it is clear that MBGs show a different structure-bioactivity correlation compared to conventional sol-gel-derivcd BGs. The in vitro bioactivity of MBGs is dependent on the Si/Ca ratio in the network when the other material parameters such as the mesostructure and texture properties (pore size, pore volume) are controlled. MBG 80S15C with relatively lower calcium content exhibits the best in vitro bioactivity, in contrast to conventional sol-gel-derived BGs where usually higher calcium percentage BGs (e.g. 60S35C) show better bioactivity. Calcination temperature is another important factor that influences the in vitro bioactivity. According to our results, MBGs calcined at 973 K may possess the best in vitro bioactivity. The influences of the composition and calcination temperature upon bioactivity are explained in terms of the unique structures of MBGs. (c) 2006 Elsevier Ltd. All rights reserved.

Dissolution of porcine incisor pulps in sodium hypochlorite solutions of varying compositions and concentrations

Background: The solubility of dental pulp tissue in sodium hypochlorite has been extensively investigated but results have been inconsistent; due most likely to variations in experimental design, the volume and/or rate of replenishment of the solutions used and the nature of the tissues assessed. Traditionally, the sodium hypochlorite solutions used for endodontic irrigation in Australia have been either Milton or commercial bleach, with Milton being the most common. Recently, a range of Therapeutic Goods Administration (TGA) approved proprietary sodium hypochlorite solutions, which contain surfactant, has become available. Some domestic chlorine bleaches now also contain surfactants. The purpose of this study was to perform new solubility assessments, comparing Milton with new TGA approved products, Hypochlor 1% and Hypochlor 4% forte, and with a domestic bleach containing surfactant (White King). Methods: Ten randomly assigned pulp samples of porcine dental pulp of approximately equal dimensions were immersed in the above solutions, as well as representative concentrations of sodium hydroxide. Time to complete dissolution was measured and assessed statistically. Results: White King 4% showed the shortest dissolution time, closely followed by Hypochlor 4% forte. White King 1% and Hypochlor 1% each took around three times as long to completely dissolve the samples of pulp as their respective 4% concentrations, while Milton took nearly 10 times as long. The sodium hydroxide solutions showed no noticeable dissolution of the pulp samples. Conclusions: The composition and content of sodium hypochlorite solutions had a profound effect on the ability of these solutions to dissolve pulp tissue in vitro. Greater concentrations provided more rapid dissolution of tissue. One per cent solutions with added surfactant and which contained higher concentrations of sodium hydroxide were significantly more effective in dissolution of pulp tissue than Milton.

Reversible active switching of the mechanical properties of a peptide film at a fluid-fluid interface

Designer peptides have recently been developed as building blocks for novel self-assembled materials with stimuli-responsive properties. To date, such materials have been based on self-assembly in bulk aqueous solution or at solid-fluid interfaces. We have designed a 21-residue peptide, AM1, as a stimuli-responsive surfactant that switches molecular architectures at a fluid-fluid interface in response to changes in bulk aqueous solution composition. In the presence of divalent zinc at neutral pH, the peptide forms a mechanically strong 'film state'. In the absence of metal ions or at acid pH, the peptide adsorbs to form a mobile 'detergent state'. The two interfacial states can be actively and reversibly switched. Switching between the two states by a change in pH or the addition of a chelating agent leads to rapid emulsion coalescence or foam collapse. This work introduces a new class of surfactants that offer an environmentally friendly approach to control the stability of interfaces in foams, emulsions and fluid-fluid interfaces more generally.

Investigation of spontaneous microemulsion formation in supercritical carbon dioxide using high-pressure NMR

NMR spectroscopy and relaxometry were used to investigate microemulsion formation in supercritical CO2. The droplets were stabilised by the salt of a perfluorinated polyether. Spontaneous microemulsion formation was observed over a period of 5 h in the absence of applied sheer. Time-resolved relaxation times of the surfactant tail showed a stepwise increase in mobility of the tail over this period. Conversely, the translational mobility of water confined within the droplet decreased over the same interval. This data is consistent with the gradual decrease in droplet size as time progressed. Indeed, NMR self-diffusion coefficients were used to show that droplets with a radius of approximately 5 nm were formed at equilibrium.

Foaming properties of a peptide designed to form stimuli-responsive interfacial films

We have designed an amphipathic peptide, AM1, that can self-assemble at the air-water interface to form an interfacial ensemble capable of switching between a mechanically strong cohesive film state and a mobile detergent state in response to changes in the solution conditions. The mechanical properties of the AM1 ensemble in the cohesive film state are qualitatively equivalent to the protein beta-LG, while in the mobile detergent state they are equivalent to the low molecular weight surfactant, SDS. In this work the foaming properties of AM1 are compared to those of beta-LG and SDS at the same weight concentration and it is found that AM1 adsorbs rapidly to the interface, initially forming a dense foam like that formed by SDS and superior to beta-LG. In addition, under solution conditions where interfacially adsorbed AM1 forms a cohesive film state the foam stability is high, comparable to beta-LG. However when the interfacially adsorbed AM1 forms a foam under detergent-state conditions, the foam stability is poor. We have achieved control of foam stability through the design of a peptide that exhibits stimuli-responsive changes in the extent of intermolecular interactions between peptide molecules adsorbed at the air water interface. These results illustrate the exciting potential of peptide surfactants to form a new class of stimuli-responsive foaming agents.