Aqueous Solutions Of Nonionic Surfactants Research Articles

Efficient β-carotene recovery from surfactant-based aqueous solutions: Advancing from experimental to process simulation

β-carotene is a carotenoid present in the human diet with numerous functions in the body. This work suggests a new platform for efficiently recovering this bioactive compound from aqueous solutions. For the first time, a ternary deep eutectic solvent (DES) is proposed to promote phase separation in aqueous solutions of non-ionic surfactants (Triton X-102 and Tween 20). The influence of temperature on the miscibility regions was investigated from 298.15 K to 308.15 K as a preliminary step. The obtained phase diagrams at three temperatures were accurately correlated using four empirical equations. The extraction capacity of these novel combinations was analysed by means of the Tie-Lines (TL) and their derived magnitudes: Tie-Line Length (TLL) and Slope (S). The reliability of the TLs was ascertained through three empirical equations. Analysis of the data showed that more than 99 % of the model carotene could be extracted using ChCl:U:Gly from a Triton X-102 aqueous solution at 308.15 K. Process simulation using SuperPro Designer confirmed that an effective and sustainable process for recovering β-carotene from algal biomass can be designed using a simple approach.

Studies on the properties and molecular dynamics simulations of nonionic surfactants based on succinic acid derivatives

AbstractNonionic surfactants have proven useful in various applications such as wastewater treatment, enhanced oil recovery, dyeing, and cosmetics. Novel nonionic surfactants such as PEMP, BEMP, HEMP and BEEP were synthesized based on succinic acid derivatives and using L‐isoleucine as the linking group and four polyether alcohols as the hydrophilic group. First, the structures of the four nonionic surfactants were studied using Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectra. Then the critical micelle concentration (CMC) and surface tension at CMC (γCMC) of the four nonionic surfactants in aqueous solution were tested. γ‐lg c curves determined the relationships of their surface properties as BEEP > PEMP > BEMP > HEMP. In order to expand the range of applications for nonionic surfactants, we evaluated the salt‐resistant properties of four such surfactants. Our findings demonstrated that this class of surfactants indeed has superior salt‐resistant properties. Molecular dynamics (MD) simulations were used to study how surfactant molecules aggregate in the interfacial film. The study investigated the trend of solvent accessible surface area (SASA) over time. Results showed that the surfactant molecules interacted well with solvent molecules in the equilibrium state. This study investigates the performance differences among four types of surfactants using the electrostatic potential (ESP) distribution of their molecules. The study employed both experimental and computational simulations to provide a more comprehensive understanding of surfactant properties. The results offer insights into the theoretical research and application extension of this class of surfactants.

Fabrication of high-flux PTFE hollow fiber membranes through nonionic surfactant infiltration coupled with mussel-inspired chemistry coating

Polytetrafluoroethylene (PTFE) hollow fiber membrane holds tremendous potential for the treatment of complex wastewater due to its outstanding chemical and thermal stability. However, its treatment efficiency is often hindered by the low water permeate flux arising from the inherent hydrophobicity of PTFE. Here, we present a gentle and convenient hydrophilic modification method that involves immersion in a nonionic surfactant aqueous solution, followed by dopamine self-polymerization. The nonionic surfactant facilitated the penetration of the dopamine solution into the membrane, where dopamine self-polymerized to form a hydrophilic layer on the surface and inner pores of the membrane. The hydrophilicity-modified PTFE hollow fiber membranes demonstrated an impressive increase in water permeate flux, reaching 10231.4 L m−2 h−1, nearly ten times that of the original membrane. Even after prolonged exposure to a strong acid solution (pH = 1) or an oxidant solution (1000 mg L−1 NaClO) for two weeks, this membrane still maintained its favorable water permeability. Furthermore, the modified PTFE membranes also exhibited remarkable resistance to fouling by humic acid. These results showcased a straightforward method for designing a hydrophilic layer on PTFE hollow fiber membranes, underscoring their significant potential for real wastewater treatment applications.

Prediction of the second critical micelle concentration of aqueous tween and span solutions via CPA EoS: Application of the quantitative theory in growth of wormlike micelles

A new combination of previously established molecular-thermodynamic methods was offered in conjunction with the Cubic Plus Association (CPA) equation of state (EoS) for the assessment of the second critical micelle concentration (SCMC), and curvature parameters in aqueous solutions of non-ionic surfactants encompassing Tween 80, Tween 60, Span 80, and Span 60. This combination will yield a quantifiable examination that adheres to creating the micelles resembling worms, enabling the optimization of critical curvature parameters, as well as the prediction of the SCMC. This previously well-known model is reliant upon theoretical components, including chain conformation, headgroup-steric effects, and interfacial tension pertaining to the energy of micelle-free systems. So, the optimized curvature parameters obtained because of these forces can be used as the input of CPA EoS to independently count the association interactions and predict the SCMC for the first time. For the aforementioned surfactants, the first critical micelle concentration (FCMC) data was previously used to modify five pure parameters of the CPA EoS. Consequently, applying the adjusted parameters, the SCMC of noted aqueous solutions has been predicted reasonably using CPA EoS.

Dynamic diffusive interfacial transport (D-DIT): A novel quantitative swelling technique for developing binary phase diagrams of aqueous surfactant systems.

Current methods to develop surfactant phase diagrams are time-intensive and fail to capture the kinetics of phase evolution. Here, the design and performance of a quantitative swelling technique to study the dynamic phase behavior of surfactants are described. The instrument combines cross-polarized optical and short-wave infrared imaging to enable high-resolution, high-throughput, and in situ identification of phases and water compositions. Data across the entire composition spectrum for the dynamics and phase evolution of a binary aqueous non-ionic surfactant solution at two isotherms are presented. This instrument provides pathways to develop non-equilibrium phase diagrams of surfactant systems-critical to predicting the outcomes of formulation and processing. It can be applied to study time-dependent material relationships across a diverse range of materials and processes, including the dissolution of surfactant droplets and the drying of aqueous polymer films.

Design of novel aqueous two-phase systems to be coupled in biological remediation processes

The ability of a biodegradable Deep Eutectic Solvent (DES) reline to induce phase segregation in aqueous solutions of polymeric non-ionic surfactants (Tween 20 and Tween 80) has been demonstrated as a preliminary step to be employed for assisting a biological degradation process of a model contaminant. The binodal curves for systems composed of (surfactants + reline + Water) have been determined at several temperatures, and the experimental data have been correlated using well-known equations. The equilibrium data have been analysed in the light of the operating temperature and the hydrophobicity of surfactants. Tie-lines of these systems have been determined, together with useful parameters such as tie-line length and tie-line slopes. Othmer-Tobias and Bancroft equations have been applied to provide an adequate description of the equilibrium data. Finally, the application of this new approach for the remediation of aqueous polluted effluent has proven to be highly efficient, with extraction percentages exceeding 99% for two model persistent contaminants (Acid Black 48 and Crystal Violet). Consequently, this ATPS is proposed as an extra-stage to enhance the remediation percentages achieved through biological methods. Furthermore, the process has been simulated using commercial software.

Effect of surfactants and interfacial rheology on equilibrium drop size in turbulent liquid-liquid dispersions

Surfactants are often required to stabilize liquid-liquid dispersions produced by high shear mixers. Due to the high power input, drops are deformed rapidly in the dispersion zone so the dynamic interfacial properties governed by the surfactant adsorption rate can have a significant impact on the resulting drop size. The objective of this work is to develop a fundamental link between surfactant adsorption dynamics, interfacial properties, and turbulent emulsification processes. To ensure constant bulk surfactant concentration during dispersion, equilibrium drop size for dilute dispersions produced by a batch rotor-stator mixer were studied. Silicone oils of various viscosity were dispersed in aqueous nonionic surfactant solutions. Drop size distributions (DSD) were measured via a video microscopy/automated image analysis technique. Equilibrium interfacial tension was measured via a pendant drop technique, as a function of surfactant concentration. The dynamic surface tension was similarly measured. The data were fit to the Langmuir adsorption isotherm and the long-times approximation to the Ward – Tordai equation and the adsorption parameters and surfactant diffusivities so obtained were employed, with an estimate of the drop deformation timescale, to estimate the surface dilational modulus (Esd) or Marangoni stress acting on the drop’ surface due to interfacial tension gradients. Trends observed in the measured equilibrium mean drop size and DSD are explained in terms of the interfacial and rheological properties. Below the CMC, Esd peaks and the drop size increases with bulk surfactant concentration, despite a decrease in equilibrium interfacial tension. Above the CMC, Marangoni stresses are small but the presence of the surfactant still modifies the rheology of the interface, increasing the effective viscosity of the drops. A comprehensive set of mechanistic models for drop size in turbulent flows, based on Kolmogorov-Hinze theory, was developed and modified to partially account for the effect of surfactants via an appropriately defined effective viscosity. The approach allows integration of surfactant phenomena into widely accepted correlations for drop size in surfactant free systems.

Effect of Surfactants on Reverse Osmosis Membrane Performance

The aim of this study was to evaluate the performance of a reverse osmosis (RO) membrane in surfactant removal using various surfactant model aqueous solutions. The separation tests were performed with laboratory scale units in a dead-end configuration. Cellulose Acetate (CA) and Polyamide (PA) RO membranes were used with nonionic, anionic, or cationic surfactants at a wide range of concentrations. Membrane performance was evaluated using permeate flux and total organic carbon (TOC) rejection. The effects of surfactant type and concentration on RO membranes were assessed. Permeate flux of the PA membrane depended on the surfactant type and concentration. The separation of cationic surfactant aqueous solutions yielded the lowest permeate flux, followed by nonionic and anionic surfactant aqueous solutions, respectively. Surfactant adsorption on the membrane surface occurred at very low concentration of cationic and nonionic surfactants due to electrostatic and hydrophobic interactions, respectively, which affected permeate flux, and micelles did not affect the permeate flux of PA membrane. However, for CA membrane the permeate flux was not affected by the feed solution. Both membranes exhibited satisfactory TOC rejection (92–99%). This study highlights the importance of assessing interactions between membrane material and surfactant molecules to mitigate membrane fouling and guarantee a better performance of the RO membrane.

Separation and Micro Determination of Zinc(II) and Cadmium(II) in Food Samples Using Cloud Point Extraction method

The cloud point extraction technique has become increasingly popular in recent years for trace metal separation and preconcentration. When heated to a specific temperature, cloud point extraction utilizes the property of nonionic surfactants in aqueous solutions to generate micelles and become turbid (so-called cloud point temperature). For analytical chemists, developing a simple and selective technology for the separation and determination of metals and medicinal drugs is a critical concern. Therefore, a sensitive, accurate, and green cloud point extraction (CPE) procedure was developed for the micro-determination of metal cations like zinc (II) and cadmium (II) in food samples. Triton X–114 and 1-(4-(Phenyldiazenyl) phenyl) azo naphthalene-2-ol (Sudan III) were used as extractants. Sudan III forms an ion-pair association complex with metal ions when the pH is 9. In the presence of 5 ppm zinc (II) or 4 ppm cadmium (II) in an aqueous solution, the maximum extraction efficiency should be achieved. In order to create Cloud Point Temperature (CPT) quantitatively, the extraction applications in this approach required heating at 85°C for 20 minutes. In this work, the impacts of different surfactants, pH, stoichiometry, and various organic reagents on interferences as well as spectrophotometric determination were explored. The linearity ranges of zinc (II) and cadmium (II) were 0.25-700 and 0.25-400 ppm, respectively. The results show low detection limits of 0.035 and 0.042 ppm for zinc (II) and cadmium (II), respectively. Also, the quantification limits for zinc (II) and cadmium (II) are 0.116 and 0.140 ppm, respectively.

Reliable assessment of carbon black nanomaterial of a variety of cell culture media for in vitro toxicity assays by asymmetrical flow field-flow fractionation

Carbon black nanomaterial (CB-NM), as an industrial product with a large number of applications, poses a high risk of exposure, and its impact on health needs to be assessed. The most common testing platform for engineered (E)NMs is in vitro toxicity assessment, which requires prior ENM dispersion, stabilization, and characterization in cell culture media. Here, asymmetric flow field-flow fractionation (AF4) coupled to UV–Vis and dynamic light scattering (DLS) detectors in series was used for the study of CB dispersions in cell culture media, optimizing instrumental variables and working conditions. It was possible to disperse CB in a non-ionic surfactant aqueous solution due to the steric effect provided by surfactant molecules attached on the CB surface which prevented agglomeration. The protection provided by the surfactant or by culture media alone was insufficient to ensure good dispersion stability needed for carrying out in vitro toxicity studies. On the other hand, cell culture media in combination with the surfactant improved dispersion stability considerably, enabling the generation of shorter particles and a more favourable zeta potential magnitude, leading to greater stability due to electrostatic repulsion. It was demonstrated that the presence of amino acids in the culture media improved the monodisperse nature and stability of the CB dispersions, and resulted in a turn towards more negative zeta potential values when the pH was above the amino acid isoelectric point (IEP). Culture media used in real cell culture scenarios were also tested, and in vitro toxicity assays were developed optimizing the compatible amount of surfactant.Graphical abstract

Thermodynamic modeling of density, viscosity and critical micelle concentration of aqueous Tween and Span solutions via Cubic plus association equation of state

The Cubic Plus Association (CPA) equation of state (EoS) has been offered to separately compute different thermodynamic properties of the aqueous non-ionic surfactant solutions, including Tween 80, Tween 60, Span 80, and Span 60. These surfactants have been modeled for the first time, and 5 pure components parameters of the CPA EoS have been fitted to the Critical Micelle Concentration (CMC) data at various temperatures. Tweens and Spans surfactant molecules have been modeled as associating constituents via considering 3 × 2B association scheme. Furthermore, applying the adjusted parameters, the liquid mixture density of the noted aqueous solutions has been predicted marvelously at various temperatures. Moreover, the liquid mixture viscosity has been compared reasonably using four different theories at ambient conditions. Besides, the effects of temperature have been investigated in the case of liquid mixture viscosity. Additionally, several new correlated equations have been introduced considering the optimized parameters of non-ionic surfactants.

Combining biodegradable surfactants and potassium inorganic salts for efficiently removing polycyclic aromatic hydrocarbons from aqueous effluents

The use of aqueous solutions of non-ionic surfactants like Tergitol 15-S7 and Tergitol 15-S9 is proposed for the first time to ex-situ remediation of Phenanthrene, Pyrene and Benzo[a]anthracene polluted soils, thus generating aqueous Polycyclic Aromatic Hydrocarbons (PAH)-polluted effluents. The effectiveness of several potassium based-inorganic salts (K3PO4, K2HPO4, K2SO4, K2S2O3 and K2CO3) to act as PAHs extractants was evaluated. The immiscibility region of the aqueous solutions was determined at room temperature, correlated by three empirical equations and compared with other non-ionic surfactants belonging to Tween and Triton families. The segregation capacity of the salts was analyzed in the light of their water-structuring degree and molar Gibbs free energy of hydration (ΔhydG). Tie-line determination was the tool used to determine the more viable PAHs removal strategy. Thus, the efficiency of combining K3PO4 to salt out Tergitol 15-S9 aqueous solutions polluted with the selected PAHs was investigated. The extraction percentage of the pollutants was 75% of Benzo[a]anthracene, 72% of Phenanthrene and 60.5% of Pyrene. The process was simulated at real scale through SuperPro Designer v.8.5 for the treatment of 156,000 tons/year of PAH-polluted soil.

Simultaneous addition of surfactant and oxidant to remediate a polluted soil with chlorinated organic compounds: Slurry and column experiments

The inadequate management of wastes associated with chlorinated organic compounds (COCs) has become a huge environmental problem. Surfactant Enhanced In-Situ Chemical Oxidation (S-ISCO) was studied as a successful technique to remediate polluted sites. This work investigated the reaction between an aqueous solution of nonionic surfactant (Emulse-3®) and an oxidant (sodium persulfate activated with NaOH) with a real polluted soil with a complex mixture of COCs from lindane liquid wastes. Two experimental setups were used. In the first one, the reactions were carried out in batch mode under slurry conditions using different surfactant concentrations (0–10 g·L−1), 210 mM of persulfate and 420 mM of NaOH with an aqueous to soil ratio VL/W = 10 L·kg−1. The runs were carried using a column loaded with the soil in the second experimental setup. The solution of surfactant, oxidant and activator was put in contact with soil in four pore volumes with a ratio aqueous to soil ratio VL/W = 0.2 L·kg−1. Under these experimental conditions, the surfactant addition improved the reduction of COCs compared with the application carried out without surfactant, from 40.1% to values of conversion of 64.8 – 90.4%. However, an excess of surfactant hindered the COCs oxidation and increased the unproductive consumption of the oxidant, resulting in an optimal value of surfactant in the aqueous phase (1–2 g·L−1). A remarkable drop in the surfactant concentration in the aqueous phase and COCs solubilized was noticed in column runs due to the surfactant adsorption.

Dual role of a natural deep eutectic solvent as lipase extractant and transesterification enhancer

The present work demonstrates the suitability of a natural deep eutectic solvent (DES) composed of glucose and cholinium chloride to act both as lipase extractant and biodiesel enhancer. After having demonstrated the viability of using this DES as segregation agent in aqueous solutions of non-ionic surfactants widely employed as lipase inducers in culture media (Tween 20 and Tween 80), the immiscibility gaps where characterized by ascertaining the binodal curves and tie-lines at several temperatures. Then, the effect of phase forming components concentration on Candida antarctica lipase B (CALB) extraction was investigated, concluding that a careful selection of feed composition allows reaching almost 100% of CALB extraction to the DES-rich phase. Additionally, the role of DES as coadjuvant in CALB-catalyzed glycerol-free transesterification was evaluated after an initial optimization of the reaction conditions (enzyme load and DMC:oil molar ratio). It was concluded that the use of the proposed natural DES led to biodiesel conversions 3 times higher than the levels attained with a conventional imidazolium-based ionic liquid (C2C1imC2SO4), or 20% higher than control transesterification reactions (without coadjuvant).

Experimental study on the characteristics of temperature dependent surface/interfacial properties of a non-ionic surfactant aqueous solution at quasi-thermal equilibrium condition

The surface/interfacial properties of liquid at elevated temperatures are fundamental issues for wide applications where the surface force matters. The dynamic characteristics of wetting behavior and surface tension (ST) of surfactant solutions remain unclear at thermal equilibrium, especially at high temperature. Utilizing a quasi-thermal equilibrium setup, the temperature dependence of the surface/interfacial properties of liquids (ultra-pure water and aqueous surfactant solutions) at temperature ranging from 10 to 90 °C (1 atm) are studied, by the sessile drop method and pendant drop method, respectively. A decreasing trend of the initial ST and contact angle (CA) is observed with the increase of temperature. During evaporation, the increase of the local relative humidity around the droplet has a crucial influence on CA. The obtained ST and CA are based on the thermodynamic model with modified coefficients, which can well describe the general trends for different temperatures and concentrations. For the ultra-pure water, the droplets will be pinned suddenly on the heating surface, until a sudden contraction occurs with evaporation. However, the surfactant-laden droplet shows different dynamical behaviors from ultra-pure water. Three different stages, named spreading-controlled Stage I, evaporation-controlled Stage II, and depinning-controlled Stage III are found for the dynamic evolution of surfactant-laden droplet. In what follows, the different droplet behaviors are also analyzed for surfactant solution and ultra-pure water.

Aggregates of Ethoxylated Surfactant with Added n-Octanol: Details of Corona Structure from a Molecular-Thermodynamic Model

Polar heads of many nonionic surfactants have complex chemical structure. In the micellar aggregates these heads are engaged in specific and nonspecific interactions with one another and with the hydration water. We present here a molecular-thermodynamic aggregation model that takes into account explicitly the hydrogen bonding and other specific interactions within the hydrated corona of a mixed nonionic aggregate. Apart from the aggregation characteristics that are usually obtained from the classical aggregation models – critical micelle concentration (CMC), the distribution of the aggregates over the size and shape and their composition - our model helps to establish a number of likely details of structure, including the corona thickness, hydration, and the partial penetration of the micelle components in the corona region. In this work the model is applied to describe the aggregation equilibrium in aqueous solutions of nonionic surfactants of the polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether family that is closely related to Tritons, the commercial surfactants of an extensive practical use. The model gives reasonable estimates of the CMCs and predicts correctly the trends in CMC and in the aggregation numbers vs the number of oxyethylene groups in the surfactant molecule. The hydration numbers and the fraction of water engaged in hydrogen bonds are calculated. For the hydration of the aggregate coronae, the predicted trend is in line with that found for other ethoxylated nonionic surfactants: poly(ethylene oxide) alkyl ethers and neonols. For surfactant solutions with added n-octanol, the model suggests that the tails of the octanol molecules are deeply buried in the cores of the mixed micelles with only one methylene group penetrating the coronae. We predict co-surfactant effect of added n-octanol: the depression of the CMCs is progressively stronger for more hydrophilic surfactants with larger EO heads.

Partition of a mixture of chlorinated organic compounds in real contaminated soils between soil and aqueous phase using surfactants: Influence of pH and surfactant type

The equilibrium between surfactant adsorption and contaminants desorption was studied. Two soil samples from a polluted site with residues from lindane production, compounded of a complex mixture of 28 chlorinated organic compounds (COCs) and different concentration of COCs in soil (2.27 and 34.69 mmolCOCs·kgsoil−1), were used. Soil was in contact with aqueous surfactant solutions (1–15 g·L−1) of nonionic (E-Mulse® 3, and Tween® 80) and anionic (sodium dodecylsulfate) surfactants. Due to alkaline pH promoting the dehydrochlorination of COCs, neutral pH and strongly alkaline pH (pH > 12) were studied. It was found that the higher the COCs concentration adsorbed in soil, the higher the adsorption of the surfactants, finding an irreversible adsorption in the case of nonionic surfactants. The desorption of COCs increased with the surfactant concentration in the aqueous phase and was not selective towards any contaminant. Although at neutral pH, higher COC desorption was found with nonionic surfactants, at alkaline pH surfactant the anionic surfactant improved its COCs desorption capacity significantly. Finally, the adsorption of the surfactants was well adjusted to Langmuir, and the apparent partition coefficient predicted the partitioning of COCs between the soil and aqueous phases, which changes with the surfactant concentration in the aqueous solution.

Synthesis and wettability of cellulose based composites by aqueous solutions of nonionic surfactant

The synthesis and characterization of the new UV-cured polymeric composites with microcrystalline cellulose (MCC) as a bio-filler are presented. The different contents of MCC from 0% to 20% wt. were applied. The polymeric parts of the composites were: bisphenol A glycerolate diacrylate (BPA.DA) as a cross-linking monomer and N-vinylpyrrolidone (NVP) as an active diluent. Due to the application of bulk polymerization method and UV-initiator (2,2-dimethoxy-2-phenylacetophenone), regular plates with the dimensions of 60 × 50 × 3 mm were obtained. The surface properties of the obtained solids were determined by the infrared spectra (ATR-FTIR) and optical profilometer as well as the values of the solid surface tension calculated from those of the contact angle of model liquids and van Oss et al. approach to the solid-liquid interface tension. Next the contact angle measurements of aqueous solutions of the nonionic surfactant Triton X-100 (TX100) (C = 10−6–10−3 M) were performed in the time range from 0 to 12 min for each drop. It was proved that with the MCC addition the composites become more hydrophobic and the TX100 adsorption at the solid-water interface as well as the surface structure are not the same as at the water-air one. Also the wetting and the spreading processes depend on the amounts of hydroxyl groups on the composites surface and the surface roughness as well as on the conformation and hydration of hydrophilic parts of TX100 molecules.

Formation of Double-Helical Structures by Silica Nanotubes Templated by Mixtures of Common Nonionic Surfactants in Aqueous Solutions.

Micelles of Pluronic F108 (EO132PO50EO132)/P104 (EO27PO61EO27) surfactant mixtures swollen with toluene were found to template silica nanotubes that formed double-helical structures under appropriately selected aqueous acidic solution conditions. In particular, the double-helical nanotube structure (DHNTS) formed as a main product at 15 °C for 30-37.5 wt % of Pluronic P104 in a surfactant mixture, with 35 wt % being particularly suitable. The formation of DHNTSs appears to involve a spontaneous wrapping of micelle-templated nanotubes around one another, while a similar structure was known to form only under confinement of anodic alumina pores of appropriate diameter. In addition to DHNTSs, other helical or circular structures, such as a helical nanotube tightly wrapped around a straight nanotube, or nanotube(s) wrapped around a sphere, were observed in many cases as minor components. DHNTSs formed as a major component at a well-defined proportion of silica precursor to surfactant at 15 °C, while the relative amount of the swelling agent and the hydrochloric acid concentration could be varied considerably. The hydrothermal treatment temperature was used to adjust the pore diameter of the DHNTS. However, structures formed without the hydrothermal treatment or with the treatment at a moderate temperature appeared very soft, while the treatment at excessively high temperature resulted in a development of significant gaps in the nanotube walls. Our results establish DHNTS as a well-defined ordered mesoporous silica with ultralarge (∼35 nm) helical mesopores of some degree of diameter adjustability, accessible under aqueous conditions using common nonionic surfactants as templating agents.

Phase separation of a nonionic surfactant aqueous solution in a standing surface acoustic wave for submicron particle manipulation.

Acoustic manipulation of submicron particles in a controlled manner has been challenging to date because of the increased contribution of acoustic streaming, which leads to fluid mixing and homogenization. This article describes the patterning of submicron particles and the migration of their patterned locations from pressure nodes to antinodes in a non-ionic surfactant (Tween 20) aqueous solution in a conventional standing surface acoustic wave field with a wavelength of 150 μm. Phase separation of the aqueous surfactant solution occurs when they are exposed to acoustic waves, probably due to the "clouding behavior" of non-ionic surfactant. The generated surfactant precipitates are pushed to the pressure antinodes due to the negative acoustic contrast factor relative to water. Compared with the mixing appearance in pure water media, the patterning behavior of submicron particles with a diameter of 300 nm dominated by acoustic radiation force is readily apparent in an aqueous solution with 2% volumetric concentration of Tween 20 surfactant, thanks to the suppression effect of acoustic streaming in inhomogeneous fluids. These submicron particles are first pushed to acoustic pressure nodes and then are migrated to antinodes where the surfactant precipitates stay. More attractively, the migration of acoustically patterned locations is not only limited to submicron particles, but also occurs to micrometer-sized particles in solutions with higher surfactant concentrations. These findings open up a novel avenue for controllable acoustic manipulation.