Supercritical carbon dioxide (scCO2) could be one aspect of a significant and necessary movement towards green chemistry, being a potential replacement for volatile organic compounds (VOCs). ...Unfortunately, carbon dioxide has a notoriously poor solubilising power and is famously difficult to handle. This review examines attempts and breakthroughs in enhancing the physicochemical properties of carbon dioxide, focusing primarily on factors that impact solubility of polar and ionic species and attempts to enhance scCO2 viscosity.
We present a new class of superhydrophobic surfaces created from low-cost and easily synthesized aluminum oxide nanoparticles functionalized carboxylic acids having highly branched hydrocarbon (HC) ...chains. These branched chains are new low surface energy materials (LSEMs) which can replace environmentally hazardous and expensive fluorocarbons (FCs). Regardless of coating method and curing temperature, the resulting textured surfaces develop water contact angles (θ) of ∼155° and root-mean-square roughnesses (R q) ≈ 85 nm, being comparable with equivalent FC functionalized surfaces (θ = 157° and R q = 100 nm). The functionalized nanoparticles may be coated onto a variety of substrates to generate different superhydrophobic materials.
The interfacial properties and water-in-CO2 (W/CO2) microemulsion (μE) formation with double- and novel triple-tail surfactants bearing trimethylsilyl (TMS) groups in the tails are investigated. ...Comparisons of these properties are made with those for analogous hydrocarbon (HC) and fluorocarbon (FC) tail surfactants. Surface tension measurements allowed for critical micelle concentrations (CMC) and surface tensions at the CMC (γCMC) to be determined, resulting in the following trend in surface activity FC > TMS > HC. Addition of a third surfactant tail gave rise to increased surface activity, and very low γCMC values were recorded for the double/triple-tail TMS and HC surfactants. Comparing effective tail group densities (ρlayer) of the respective surfactants allowed for an understanding of how γCMC is affected by both the number of surfactant tails and the chemistry of the tails. These results highlight the important role of tail group chemical structure on ρlayer for double-tail surfactants. For triple-tail surfactants, however, the degree to which ρlayer is affected by tail group architecture is harder to discern due to formation of highly dense layers. Stable W/CO2 μEs were formed by both the double- and the triple-tail TMS surfactants. High-pressure small-angle neutron scattering (HP-SANS) has been used to characterize the nanostructures of W/CO2 μEs formed by the double- and triple-tail surfactants, and at constant pressure and temperature, the aqueous cores of the microemulsions were found to swell with increasing water-to-surfactant ratio (W 0). A maximum W 0 value of 25 was recorded for the triple-tail TMS surfactant, which is very rare for nonfluorinated surfactants. These data therefore highlight important parameters required to design fluorine-free environmentally responsible surfactants for stabilizing W/CO2 μEs.
Foams: From nature to industry Hill, Christopher; Eastoe, Julian
Advances in colloid and interface science,
September 2017, 2017-Sep, 2017-09-00, 20170901, Letnik:
247
Journal Article
Recenzirano
Odprti dostop
This article discusses different natural and man-made foams, with particular emphasis on the different modes of formation and stability. Natural foams, such as those produced on the sea or by ...numerous creatures for nests, are generally stabilised by dissolved organic carbon (DOC) molecules or proteins. In addition to this, foam nests are stabilised by multifunctional mixtures of surfactants and proteins called ranaspumins, which act together to give the required physical and biochemical stability. With regards to industrial foams, the article focuses on how various features of foams are exploited for different industrial applications. Stability of foams will be discussed, with the main focus on how the chemical nature and structure of surfactants, proteins and particles act together to produce long-lived stable foams. Additionally, foam destabilisation is considered, from the perspective of elucidation of the mechanisms of instability determined spectroscopically or by scattering methods.
Foam image taken by author, Spittle bug photo reprinted with permission from David Iliff. License: CC-BY-SA 3, Túngara frog photo is free to use from the public domain (https://creativecommons.org/publicdomain/mark/1.0/), Fire man photo reprinted with permission from Angus Fire LTD. Display omitted
•Advances in stabilisation of aqueous foams by surfactants, proteins and particles•Discussion of modern methods for studying foams.•Natural foams provide protection, moisture and incubation during reproduction.•Overview of foams used for fire-fighting, mineral flotation and other advances.•Review of how production of undesirable foams is inhibited by defoaming agents.
The concentration-dependent aggregation of two surfactants, anionic sodium dioctylsulfosuccinate (Aerosol OT or AOT) and nonionic pentaethylene glycol monododecyl ether (C12E5), has been studied in ...cyclohexane-D12 using small-angle neutron scattering (SANS). A clear monomer-to-aggregate transition has been observed for both surfactants, spherical inverse micelles for AOT and hank-like micelles for C12E5. This suggests that a critical micelle concentration exists for surfactants of these kinds in nonpolar solvents. The nature of the transition is different for the two surfactants. AOT aggregates are the same size and shape with decreasing concentration until a sharp critical micelle concentration, after which they cannot be detected. However, C12E5 aggregates gradually decrease in size. These differences demonstrate that the strength of the solvophobic effect can influence the formation of surfactant aggregates in nonaqueous solvents.
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Here is presented a systematic study of the dispersibility of multiwall carbon nanotubes (MWCNTs) in natural rubber latex (NR-latex) assisted by a series of single-, double-, and ...triple-sulfosuccinate anionic surfactants containing phenyl ring moieties. Optical polarising microscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Raman spectroscopy have been performed to obtain the dispersion-level profiles of the MWCNTs in the nanocomposites. Interestingly, a triple-chain, phenyl-containing surfactant, namely sodium 1,5-dioxo-1,5-bis(3-phenylpropoxy)-3-((3-phenylpropoxy)carbonyl) pentane-2-sulfonate (TCPh), has a greater capacity the stabilisation of MWCNTs than a commercially available single-chain sodium dodecylbenzenesulfonate (SDBS) surfactant. TCPh provides significant enhancements in the electrical conductivity of nanocomposites, up to ∼10−2Scm−1, as measured by a four-point probe instrument. These results have allowed compilation of a road map for the design of surfactant architectures capable of providing the homogeneous dispersion of MWCNTs required for the next generation of polymer–carbon-nanotube materials, specifically those used in aerospace technology.
High-water-content water-in-supercritical CO2 (W/CO2) microemulsions are considered to be green, universal solvents, having both polar and nonpolar domains. Unfortunately, these systems generally ...require environmentally unacceptable stabilizers like long and/or multifluorocarbon-tail surfactants. Here, a series of catanionic surfactants having more environmentally friendly fluorinated C4–C6 tails have been studied in terms of interfacial properties, aggregation behavior, and solubilizing power in water and/or CO2. Surface tensions and critical micelle concentrations of these catanionic surfactants are, respectively, lowered by ∼9 mN/m and 100 times than those of the constituent single fluorocarbon-tail surfactants. Disklike micelles in water were observed above the respective critical micelle concentrations, implying the catanionic surfactants have a high critical packing parameter, which should be suitable for the formation of reverse micelles. Based on visual observation of phase behavior and Fourier transform infrared spectroscopic and small-angle neutron scattering studies, one of the three catanionic surfactants tested was found to form transparent single-phase W/CO2 microemulsions with a water-to-surfactant molar ratio of up to ∼50. This is the first successful demonstration of the formation of W/CO2 microemulsions by synergistic ion-pairing of anionic and cationic single-tail surfactants. This indicates that catanionic surfactants offer a promising approach to generate high-water-content W/CO2 microemulsions.
Spin State As a Probe of Vesicle Self-Assembly Kim, Sanghoon; Bellouard, Christine; Eastoe, Julian ...
Journal of the American Chemical Society,
03/2016, Letnik:
138, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A novel system of paramagnetic vesicles was designed using ion pairs of iron-containing surfactants. Unilamellar vesicles (diameter ≈ 200 nm) formed spontaneously and were characterized by cryogenic ...transmission electron microscopy, nanoparticle tracking analysis, and light and small-angle neutron scattering. Moreover, for the first time, it is shown that magnetization measurements can be used to investigate self-assembly of such functionalized systems, giving information on the vesicle compositions and distribution of surfactants between the bilayers and the aqueous bulk.
Two series of Aerosol-OT-analogue surfactants (sulfosuccinate-type di-BC n SS and sulfoglutarate-type di-BC n SG) with hyperbranched alkyl double tails (so-called “hedgehog” groups, carbon number n = ...6, 9, 12, and 18) have been synthesized and shown to demonstrate interfacial properties comparable to those seen for related fluorocarbon (FC) systems. Critical micelle concentration (CMC), surface tension at the CMC (γCMC), and minimum area per molecule (A min) were obtained from surface tension measurements of aqueous surfactant solutions. The results were examined for relationships between the structure of the hedgehog group and packing density at the interface. To evaluate A and B values in the Klevens equation for these hedgehog surfactants, log(CMC) was plotted as a function of the total carbon number in the surfactant double tail. A linear relationship was observed, producing B values of 0.20–0.25 for di-BC n SS and di-BC n SG, compared to a value of 0.31 for standard double-straight-tail sulfosuccinate surfactants. The lower B values of these hedgehog surfactants highlight their lower hydrophobicity compared to double-straight-tail surfactants. To clarify how hydrocarbon density in the surfactant-tail layer (ρlayer) affects γCMC, the ρlayer of each double-tail surfactant was calculated and the relationship between γCMC and ρlayer examined. As expected for the design of low surface energy surfactant layers, ρlayer was identified as an important property for controlling γCMC with higher ρlayer, leading to a lower γCMC. Interestingly, surfactants with BC9 and BC12 tails achieved much lower γCMC, even at low ρlayer values of <0.55 g cm–3. The lowest surface energy surfactant studied here was di-BC6SS, which had a γCMC of only 23.8 mN m–1. Such a low γCMC is comparable to those obtained with short FC-tail surfactants (e.g., 22.0 mN m–1 for the sulfosuccinate-type FC-surfactant with R = F(CF2)6CH2CH2−).
In some cases, surfactant adsorption at solid surfaces appears to show a two-stage kinetic profile, suggesting two distinct processes may occur.
A theoretical model is presented which accounts for ...two stages of surfactant adsorption onto a solid surface. The model incorporates both mass transfer (diffusion) and attachment terms, making it applicable to systems where mass transport and adsorption may occur on similar timescales. The model is tested against example systems which appear to show two-step adsorption processes, consisting of cationic ammonium bromide surfactants adsorbing onto silica from water and organic solvents. Kinetic parameters suggest that adsorption may occur in a broadly similar fashion from both water and low-dielectric solvents, and that the fast adsorption step appears to be transport-limited for organic solvents but may experience an adsorption barrier in aqueous systems.
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