Some preliminary acoustical considerations in the design for the proposed Wellington (New Zealand) town hall

The preliminary design for Wellington Town Hall, New Zealand, is an evolution from the successful design for Christchurch Town Hall. It includes, however, the results of a decade of experimental work on the effects of early lateral reflections on listener preference for orchestral music. The basic form of the auditorium remains an arena, roughly elliptical in plan, and containing within its boundaries large suspended surfaces to ensure appropriate reflection sequences. The acoustical design objectives include the combination of a long reverberation time, “envelopment” due to the lateral reflections and clarity as encourtered in Christchurch Town Hall. Advances in the provision of diffusion and understanding of the acoustical requirements for ensemble are included in the proposals. The experimental work and other advances in knowledge relating to concert hall design are reviewed, and their application in the design of Wellington Town Hall is discussed.     

New Zealand Developments in Earth's Field NMR

We review here two decades of development of Earth's field nuclear magnetic resonance (NMR), starting with the first demonstration of resonant refocusing and the generation of spin echoes, the first measurement of diffusion using Earth's field NMR, and its application to Antarctic research, the adaptation of the apparatus to allow its use indoors, in a conventional laboratory setting, and finally, the construction of a flexible laboratory-based Earth's field NMR system capable of not only a range of relaxation and spectroscopy applications but also the straightforward demonstration of NMR Imaging. Authors' address: Paul T. Callaghan, MacDiarmid Institute, Victoria University of Wellington, PO Box 600, Wellington, New Zealand     

Premicellar and micelle formation behavior of aqueous anionic surfactants in the presence of triphenylmethane dyes: protonation of dye in ion pair micelles

The premicellar and micelle formation behaviors of four cationic triphenylmethane dyes, viz, Pararosaniline (RN), Crystal violet (CV), Ethyl violet (EV), and Malachite green (MG), in aqueous anionic surfactant solutions of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), and sodium dodecyl sulfonate (SDSN) have been studied by spectral and surface tension measurements. The study was carried out within a pH range where the dyes are stable in their quinoid forms. The dyes have been found to form dye–surfactant ion pairs (DSIPs) with the surfactants, at the surfactant concentrations well below their critical micelle concentration, CMC*. The DSIPs behave like nonionic surfactants and form an air–water interfacial monolayer. The DSIPs have a lower critical micelle concentration (CMC_IP), greater efficiency, and lower effectiveness than the corresponding pure surfactants. As the surfactant concentration is increased below the CMC*, the DSIPs start forming micelles of their own where the dye gets protonated and exists as a protonated dye–surfactant ion pair (PDSIP) in the ion pair micelles. As the concentration of the surfactant exceeds the CMC* of the pure surfactant, the protonation reverses gradually with the dye remaining in the micelles in solubilized form and the DSIPs in the air–water interfacial monolayer are replaced by pure surfactants. The distorted helical isomeric form (isomer B) of the dyes is favored in the PDSIPs. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization of Preparation Techniques for Poly(Lactic Acid-Co-Glycolic Acid) Nanoparticles

Microparticles and nanoparticles of poly(lactic acid-co-glycolic acid) (PLAGA) are excellent candidates for the controlled release of many pharmaceutical compounds because of their biodegradable nature. The preparation of submicron PLAGA particles poses serious challenges that are not necessarily present when preparing microparticles. We have evaluated several combinations of organic solvents and surfactants used in the formulation of PLAGA nanoparticles. Critical factors such as the ability to separate the nanoparticles from the surfactant, the ability to re-suspend the nanoparticles after freeze-drying, formulation yield and nanoparticle size were studied. The smallest particles were obtained using the surfactant/solvent combination of sodium dodecyl sulfate and ethyl acetate (65 nm) and the largest particles were obtained using poly(vinyl alcohol) and dichloromethane (466 nm). However, the optimal nanoparticles were produced using either acetone or ethyl acetate as the organic solvent and poly(vinyl alcohol) or human serum albumin as the surfactant. This is because the most critical measure of performance of these nanoparticles proved to be their ability to re-suspend after freeze-drying.     

Lattice-Boltzmann simulations of dynamic interfacial tension due to soluble amphiphilic surfactant

An amphiphilic Lattice-Boltzmann approach is adopted to model dynamic interfacial tension due to non-ionic surfactant. In the current system, the surfactant adsorption kinetics is diffusion dominated and the interface separates two immiscible fluids. A rotational relaxation time and a diffusive/viscous relaxation time are associated with the surfactant. The model results are compared with experimental data for the dynamic interfacial tension of a pendant oil droplet in water, with oil soluble surfactant. We demonstrate how to adapt and calibrate the model to capture the adsorption timescale of the surfactant and the magnitude of interfacial tension reduction due to surfactant. A scheme to overcome numerical instabilities due to the relatively low surfactant concentration, is devised. We are able to qualitatively match the Frumkin equation of state for the interfacial tension.     

Nanostructures of colloidal complexes formed in oppositely charged polyelectrolyte/surfactant dilute aqueous solutions

Small-angle neutron scattering measurements were performed on dilute solutions of carboxymethylcellulose/DTAB complexes in water in order to determine their size, shape and internal structures. At low polymer content, the complexes are spherical, rather monodisperse and probably made of polymer chains intercalated between surfactant micelles. Moreover, we show that these micelles have a similar cubic arrangement than found in polymer/surfactant precipitates formed at higher surfactant concentrations. At larger polymer content, in the semi-dilute polyelectrolyte regime, the complexes are larger, softer and polydisperse. However, they possess a similar internal structure in both regimes. Carboxymethylcellulose/CTAB complexes are also large, soft and polydisperse but do not seem to exhibit well-defined internal structures.     

Microphase separation in polymer solutions containing surfactants

A microphase separation in solutions containing a polymer and a mixture of two solvents, one of which consists of amphiphilic molecules (surfactant), is considered theoretically in the weak-segregation regime. A surfactant molecule is described as a dimer consisting of hydrophobic and polar parts. The energy gain due to the orientation of surfactant molecules can lead to the appearance of non-homogeneities in the solution, where density fluctuations cause the orientational ordering of surfactant molecules. The difference in the interaction energies of hydrophobic and polar groups of a surfactant with solvent is considered as a main reason for orienting surfactant molecules. The free energy is calculated for various morphologies (lamellar, cylindrical hexagonal, spherical particles arranged at different cubic lattices). The phase diagrams are presented. With worsening the solvent quality, the transitions from disordered to a macro-separated state at low polymer and surfactant concentrations or to a body-centered-cubic, then hexagonal, and then lamellar structure at high polymer and surfactant concentrations are predicted. The amphiphilicity degree of surfactant molecules should exceed a certain critical value to make a microstructure formation possible. The period of the lamellar microstructure decreases with increasing the surfactant and polymer concentrations.     

Physicochemical properties of nanoparticles affect translocation across pulmonary surfactant monolayer

Interaction between nanoparticles (NPs) and pulmonary surfactant monolayer is one of the most important parts in NP-based pulmonary drug delivery system, which can affect the result of the inhaled nano-drugs and their potential efficacy. Here, we show how surface charge of NPs affects translocation across pulmonary surfactant monolayer with coarse-grained molecular dynamics simulations. The results reveal that the surface charge position of NPs can determine the fate of the inhaled NPs about whether they can have the ability of translocation across the pulmonary surfactant monolayer, which is that NPs with face surface charge can penetrate the pulmonary surfactant monolayer and NPs with edge surface charge cannot. Besides, dynamic process, phase state and the potential of mean force profiles further confirm this result. Moreover, compared to anionic NPs, there is a greater chance for cationic NPs to be adsorbed on the surface of the pulmonary surfactant monolayer, which can further decrease the thickness of the pulmonary surfactant monolayer and reduce the distance between charged NPs and the pulmonary surfactant monolayer. Our researches provide a novel simulation model of NPs on translocation across pulmonary surfactant monolayer and the study of NP-based pulmonary drug delivery system should consider the surface charge of NPs.     

A conservative SPH method for surfactant dynamics

In this paper, a Lagrangian particle method is proposed for the simulation of multiphase flows with surfactant. The model is based on the multiphase smoothed particle hydrodynamics (SPH) framework of Hu and Adams (2006) [1]. Surface-active agents (surfactants) are incorporated into our method by a scalar quantity describing the local concentration of molecules in the bulk phase and on the interface. The surfactant dynamics are written in conservative form, thus global mass of surfactant is conserved exactly. The transport model of the surfactant accounts for advection and diffusion. Within our method, we can simulate insoluble surfactant on an arbitrary interface geometry as well as interfacial transport such as adsorption or desorption. The flow-field dynamics and the surfactant dynamics are coupled through a constitutive equation, which relates the local surfactant concentration to the local surface-tension coefficient. Hence, the surface-tension model includes capillary and Marangoni-forces. The present numerical method is validated by comparison with analytic solutions for diffusion and for surfactant dynamics. More complex simulations of an oscillating bubble, the bubble deformation in a shear flow, and of a Marangoni-force driven bubble show the capabilities of our method to simulate interfacial flows with surfactants.     

The influence of cysteamine and counterion concentrations on the properties of CdSe/ZnS quantum dots

The influence of the cysteamine surfactant concentration on the stability of CdSe/ZnS nanoparticles (NPs) solubilized by this compound at the phase interface between two immiscible liquids is considered. The steady-state and time-resolved fluorescence spectroscopy data show that the fluorescence quantum yield of cysteamine-coated NPs and their stability to aggregation in a potassium phosphate buffer are determined by the balance between the concentrations of surfactant in the aqueous phase and hydrophobic NPs in the nonpolar phase (chloroform, toluene, etc.). It is found that the brightest and most stable hydrophilic NPs can be obtained by completely coating them by cysteamine molecules without a surfactant deficit or excess in the reaction at the phase interface.     

Self-diffusion in microemulsions and micellar size

Self-diffusion of all components of two different microemulsions have been measured. Application of Stokes-Einstein equations for surfactant and oil gives a simple relation connecting their size and self-diffusion coefficients. Using the measured self-diffusion coefficients and dimensions of oil molecules known from elsewhere, the size of the surfactant droplets was estimated. This approach turns out to be advantageous in practical determination of droplet size in microemulsions.     

Numerical investigation of the effect of insoluble surfactant on drop formation in microfluidic device

Surfactants are commonly used in droplet-based microfluidics to stabilize the droplet interface. In this study, we investigate the effect of insoluble surfactant on drop formation in a capillary microfluidic device. We use a diffuse-interface method to describe the evolution of interface involving insoluble surfactant. The Navier-Stokes/Cahn-Hilliard equations and the surfactant conservation equation are solved by a finite element method along with a grid deformation method. As the surfactant has a non-uniform distribution during the drop formation in general, the surface tension has a gradient on the interface, which affects the flow field and interface evolution. The surfactant effect is discussed for dripping and jetting regimes.     

The role of excluded volume and electrostatics from coarse-grain modeling of the interaction of gemini surfactants with like-charged membranes

Cationic systems composed of lipids and/or surfactants are of paramount importance in a variety of applications. Within these, gemini have attracted particular attention, mainly due to their improved aggregation properties and to the possibility of tuning offered by the presence of a spacer. In this work, a Monte Carlo simulation study with a coarse-grained model was employed to assess the interaction of cationic gemini surfactants with a like-charged model membrane. Separating the contribution of the excluded volume and that of the electrostatic effects in the organization of gemini–lipid membranes was the first goal of this work and the role of these factors was assessed varying the concentration, the spacer length and the headgroup charge of gemini surfactants. The results provide a new insight on the organization of lipid headgroups in the vicinity of gemini surfactants. It was found that the surfactant–lipid interaction is strongly affected by the surfactant spacer length, being controlled by an overall balance between excluded volume and surfactant–lipid and surfactant–surfactant electrostatic effects. It is also seen that the out-of-plane motion of the spacer has a significant effect upon membrane organization and counterion condensation. Good agreement was found with results previously obtained from atomistic simulation.     

Recent developments and applications of the thermodynamics of surfactant mixing

In their diverse domestic, industrial and technological applications surfactants are invariably used as mixtures which optimise different aspects of their performance. The neutron scattering techniques of reflectivity and small-angle scattering have recently transformed our ability to probe surfactant mixing at interfaces and in self-assembly. This has in part stimulated developments in the application of different thermodynamic approaches, and in particular the pseudophase approximation, to quantify the mixing behaviour. In this paper, we present some recent applications of developments of the pseudo phase approximation to the surface mixing of nonionic, anionic-nonionic, and cationic – nonionic mixtures. These examples provide new insights into the factors controlling surfactant mixing. They highlight the importance of accounting for asymmetry in the mixing, the advantages of co-refining surface and micelle data, and the importance of determining the mixing properties over a wide concentration and composition range.     

Protonated dye-surfactant ion pair formation between neutral red and anionic surfactants in aqueous submicellar solutions

Spectral and surface tension behavior of aqueous neutral red in the presence of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfonate (SDSN) have been studied to understand the nature of the interactions in their submicellar concentration ranges. The variations in spectra and surface tension with variation in the concentrations of the surfactants suggest the formation of a 1:1 close-packed dye-surfactant ion pair, HNR⁺S⁻ between the acid form, HNR⁺ of the dye and the surfactant anion at very low concentrations of the surfactant below critical micelle concentration (cmc) of the pure surfactant. The dye-surfactant ion pair behaves like a nonionic surfactant having higher efficiency and lower cmc than that of the corresponding pure anionic surfactant. The ion pairs are adsorbed on the air/water interface at very low concentrations of the surfactant. As the concentration of the surfactant increases and the ion pairs form micelles of their own, the dye in the ion pair is protonated to form H₂NR²⁺S⁻. As the cmc of the pure surfactant is approached, the protonation equilibrium gradually reverses and pure surfactant ions gradually replace the ion pairs at the interface. Finally, a homogeneous monolayer of pure surfactant anions exists at the air/water interface and the dye remain solubilized in pure micelles above the cmc of the pure surfactant. The equilibrium constants, K_c for the close-packed protonated dye-surfactant ion pair (PDSIP) formation have been determined at varying pH. The submicellar interaction has been found to be stronger with SDS than SDBS. The plots of logarithm of K_c vs. pH have been found to be quite linear which consolidates the assumption of formation of the species, H₂NR²⁺S⁻. The interaction is driven by enthalpy as well as entropy.     

Influence of Synthetic Polymer on Aqueous Anionic Surfactant (SDBS) Micelle Investigated by FT-IR and Ultrasonic Study

The ultrasonic velocity, absorption, density and viscosity measurements were used to study the interaction of PEG, PVP and PVA with anionic surfactant — sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions of different concentrations and temperatures, namely, 303, 313 and 323 K. The properties of SDBS with increasing polymer concentration (0.2–1.2%) were investigated. Interaction of SDBS with polymer was found to involve the binding of surfactant with the polymer molecule followed by the usual micellization; from the observed values the related acoustical parameters are calculated and their variation are discussed. The FT-IR spectrum was also used to characterize these samples.     

过渡金属元素氢化物发生-原子荧光增敏效应研究

基于反应介质酸度对Zn,Cd,Cu和Ni的氢化物发生影响的考察,揭示了氢转移过渡中间态[H+BH-₄]*分解反应氢化物生成机理。分别考察了Co2+离子、Ni2+离子、邻菲咯啉、羟基喹啉对Zn,Cd,Cu和Ni氢化物发生原子荧光信号的影响,探讨了其增敏机理。由于Co和Ni的挥发性物种分解抑制了Cd和Zn氢化物在传输过程中的分解损失,明显提高了Cd和Zn氢化物的传输效率。邻菲咯啉与Co2+离子或8-羟基喹啉与Co2+离子对Zn和Cd信号均具有协同增敏效应,8-羟基喹啉和邻菲咯啉对Zn和Cd信号则没有协同增敏效应。考察了阳离子、阴离子和非离子表面活性剂对氢化物发生的促进作用。结果证实阳离子和非离子表面活性剂均对分析物信号有明显的增敏效果,其原因在于表面活性剂的存在引起溶液的表面张力显著的降低。以石墨炉原子吸收法进一步考察了分析物从表面活性剂吸收液中逸出特性,提出了表面活性剂在氢化物发生和传输过程中的增敏机理。     

Self-propelled droplets

Self-propelled droplets are a special kind of self-propelled matter that are easily fabricated by standard microfluidic tools and locomote for a certain time without external sources of energy. The typical driving mechanism is a Marangoni flow due to gradients in the interfacial energy on the droplet interface. In this article we review the hydrodynamic prerequisites for self-sustained locomotion and present two examples to realize those conditions for emulsion droplets, i.e. droplets stabilized by a surfactant layer in a surrounding immiscible liquid. One possibility to achieve self-propelled motion relies on chemical reactions affecting the surface active properties of the surfactant molecules. The other relies on micellar solubilization of the droplet phase into the surrounding liquid phase. Remarkable cruising ranges can be achieved in both cases and the relative insensitivity to their own ‘exhausts’ allows to additionally study collective phenomena.     

Study of surface and solution properties of gemini-conventional surfactant mixtures and their effects on solubilization of polycyclic aromatic hydrocarbons

The aqueous solubility enhancement of the polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene and pyrene by micellar solutions of single gemini surfactant hexanediyl-1,6-bis(dimethylcetylammonium bromide) (G6) and its mixtures with cationic cetyltrimethylammonium bromide (CTAB), anionic sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and nonioinic polyoxyethylene (20) cetyl ether (Brij 58) have been investigated. Above the cmc, maximum solubilization occurs in the Brij 58 surfactant micelles whereas the solubilization is least in presence of AOT. The PAHs are solubilized synergistically in mixed gemini-conventional surfactant solutions, which is attributed to the formation of mixed micelles, their lower cmc values, and the increase of the solvents' molar solubilization ratios or micellar partition coefficients because of the lower polarity of the mixed micelles.     

Self-assembled and fluorescence enhancement of semiconductor nanoparticles induced by surfactant adsorption

When semiconductor colloidal CdS nanoparticles and nonylphenol are mixed together in dimethyl sulfoxide at room temperature, a self-assembling process is induced. In the course, the size tunable properties of CdS nanoparticles are amplified. A blue shift in the emission spectrum and a strong photoluminescence enhancement are observed without significant change in the absorption features of the colloidal nanoparticles. These results are attributed to the adsorption of nonylphenol onto the nanoparticles surface and to the association process of the surfactant molecules. The surfactant adsorption process provides a nanoparticle surface passivation and induces an associative phase that enlarges the photoluminescence stability. This strategy opens the possibility to improve simultaneously physicochemical and photoluminescence properties of nanocrystals in solution as well as to control their deposition on two-dimensional surfaces.