| 1. |
- Sanchez-fernandez, Adrian, et al.
(författare)
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Micellization of alkyltrimethylammonium bromide surfactants in choline chloride:glycerol deep eutectic solvent
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9076. ; 18:48, s. 33240-33249
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Tidskriftsartikel (refereegranskat)abstract
- Deep eutectic solvents have shown the ability to promote the self-assembly of surfactants in solution. However, some differences have been found compared with self-assembly in pure water and other polar organic solvents. The behaviour of alkyltrimethylammonium bromides in choline chloride:glycerol deep eutectic solvent has been studied by means of surface tension, X-ray and neutron reflectivity and small-angle neutron scattering. The surfactants were found to remain surface active and showed comparable critical micelle concentrations to the same surfactants in water. Our scattering studies demonstrate that these surfactants form globular micelles with ellipsoidal shape in solution. The size, shape and aggregation number of the aggregates were found to vary with the chain length of the surfactant. Specific solvent-headgroup interactions were not found in this system, unlike those we have previously postulated for anionic surfactants in choline chloride deep eutectic solvents.
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| 2. |
- Afifi, Hala, et al.
(författare)
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Solubilization of Oils or Addition of Monoglycerides Drives the Formation of Wormlike Micelles with an Elliptical Cross-Section in Cholesterol-Based Surfactants : A Study by Rheology, SANS, and Cryo-TEM
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:12, s. 7480-7492
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Tidskriftsartikel (refereegranskat)abstract
- We report the formation of wormlike micelles (WLM) in poly(oxyethylene) cholesteryl ether (ChEO(10)) aqueous solutions by the addition of lipophilic monoglycerides at room temperature (monolaurin (ML), monocaprin (MC), and monocaprylin (MCL)) bearing 12-, 10-, and 8-carbon alkyl chains, respectively. A combination of rheology, small-angle neutron scattering (SANS), and cryo-TEM was used to study their viscoelastic properties and structure. With the successive addition of cosurfactant, a significant increase in viscosity and a clear solidlike behavior is obtained, suggesting the formation of a viscoelastic network of wormlike micelles. Only for MCL is typical Maxwellian behavior obtained. The onset of micellar growth, as detected by the occurrence of solidlike behavior and a significant increase in viscosity, is obtained for 0.30 (1 wt %), 0.34 (1 wt %), and 0.60 (1.5 wt %) cosurfactant/ChEO(10) molar ratios with ML, MC, and MCL, respectively. With ML and MC, extremely long relaxation times (exceeding 20 s) compared to those of MCL are obtained, and zero-shear viscosity values are more than 1 order of magnitude higher than with MCL. These results show that cosurfactants with longer alkyl chain lengths (ML and MC) induce the formation of longer wormlike micelles and do so at lower concentrations. SANS measurements on dilute solutions confirm that the viscoelastic behavior correlates with an increase in contour length and reveals an elliptical cross-section with an axial ratio of around 2. Cryo-TEM images provide visual evidence of the wormlike micelles and confirm the elliptical shape of the cross-section. The addition of small amounts of aliphatic oils (ethyl butyrate, EB, and ethyl caprylate, EC) and cyclic oils (peppermint, PP, and tea tree, TT, oils) to ChEO(10) solutions induces wormlike micelle formation at a lower cosurfactant concentration or even in its absence (for PP, TT, and EC) because of their probable localization in the palisade layer. The viscosity peak and height of the plateau modulus occur at increasing monoglyceride concentration following the order PP ≈ TT > EC > EB > no oil.
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| 3. |
- Afifi, Hala, et al.
(författare)
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Structural transitions in cholesterol-based wormlike micelles induced by encapsulating alkyl ester oils with varying architecture
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 378:1, s. 125-134
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Tidskriftsartikel (refereegranskat)abstract
- The effect of encapsulating oils on the phase behaviour and the microstructure of wormlike micelles formed by polyoxyethylene cholesteryl ether (ChEO10) and triethylene glycol monododecyl ether co-surfactant (C12EO3) was investigated using rheology, Cryo-TEM and small-angle neutron scattering measurements. Six alkyl ester oils bearing small, systematic variations in their molecular structure were encapsulated: ethyl butyrate (EB24), ethyl caproate (ECO26), ethyl caprylate (EC28), methyl enanthate (ME17), methyl caprylate (MC18) and butyl butyrate (BB44), where the subscripts refer to the length of the alkyl chain and fatty acid chain, respectively, on either sides of the ester link. The addition of alkyl ester oils to ChEO10/C12EO3 solutions promotes the longitudinal growth of the surfactant aggregates into wormlike micelles possessing an elliptical cross-section, with rminor 31 ± 2 Å and rmajor varying from 45 to 70 Å. At fixed alkyl chain length, oils with longer fatty acid chains were found to be more efficient in inducing wormlike micelle formation or their elongation, following the order: EC28 > ECO26 > EB24. Instead, at fixed fatty acid chain length, increasing the alkyl chain has a negative effect on the longitudinal micellar growth (MC18 > EC28 and EB24 > BB44). At high co-surfactant concentrations and in the presence of EB24, an unusual phase of ring-like micelles was detected. Overall, the orientation of the oil molecules within the micelles enables them to act as co-surfactants with a small head-group, decreasing the average cross-section area and promoting longitudinal growth of the micelles into worms.
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| 4. |
- Aili, Daniel, et al.
(författare)
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Polypeptide Folding-Mediated Tuning of the Optical and Structural Properties of Gold Nanoparticle Assemblies
- 2011
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Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 11:12, s. 5564-5573
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Tidskriftsartikel (refereegranskat)abstract
- Responsive hybrid nanomaterials with well-defined properties are of significant interest for the development of biosensors with additional applications in tissue engineering and drug delivery. Here, we present a detailed characterization using UV-vis spectroscopy and small angle X-ray scattering of a hybrid material comprised of polypeptide-decorated gold nanoparticles with highly controllable assembly properties. The assembly is triggered by a folding-dependent bridging of the particles mediated by the heteroassociation of immobilized helix-loop-helix polypeptides and a complementary nonlinear polypeptide present in solution. The polypeptides are de novo designed to associate and fold into a heterotrimeric complex comprised of two disulfide-linked four-helix bundles. The particles form structured assemblies with a highly defined interparticle gap (4.8 +/- 0.4 nm) that correlates to the size of the folded polypeptides. Transitions in particle aggregation dynamics, mass-fractal dimensions and ordering, as a function of particle size and the concentration of the bridging polypeptide, are observed; these have significant effects on the optical properties of the assemblies. The assembly and ordering of the particles are highly complex processes that are affected by a large number of variables including the number of polypeptides bridging the particles and the particle mobility within the aggregates. A fundamental understanding of these processes is of paramount interest for the development of novel hybrid nanomaterials with tunable structural and optical properties and for the optimization of nanoparticle-based colorimetric biodetection strategies.
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| 5. |
- Hellsing, Maja S., et al.
(författare)
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Structure of a large colloidal crystal : controlling orientation and three-dimensional order
- 2012
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:18, s. 7091-7098
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Tidskriftsartikel (refereegranskat)abstract
- The three-dimensional crystal structure of charge stabilised polystyrene latex in deionised water was investigated by small-angle neutron diffraction. Crystallisation with a grain size of approximately 1 x 1 cm(2) was observed when the sample was flowed gently in to a 2 mm path cell. Bragg scattering peaks arising from the structure were observed under rotation about three perpendicular axes of the sample. The diffraction patterns indicate clearly that there is a cubic close packed structure with a 110 axis perpendicular to the cell wall. Rotations in small steps show large changes and indicate that the crystal is well oriented and has three-dimensional order. The crystal orientation was controlled by the meniscus and direction of flow when filling the cell.
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| 6. |
- Rennie, Adrian R., et al.
(författare)
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Learning about SANS instruments and data reduction from round robin measurements on samples of polystyrene latex
- 2013
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 46:5, s. 1289-1297
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of a well-characterized `standard' sample can verify the performance of an instrument. Typically, small-angle neutron scattering instruments are used to investigate a wide range of samples and may often be used in a number of configurations. Appropriate `standard' samples are useful to test different aspects of the performance of hardware as well as that of the data reduction and analysis software. Measurements on a number of instruments with different intrinsic characteristics and designs in a round robin can not only better characterize the performance for a wider range of conditions but also, perhaps more importantly, reveal the limits of the current state of the art of small-angle scattering. The exercise, followed by detailed analysis, tests the limits of current understanding as well as uncovering often forgotten assumptions, simplifications and approximations that underpin the current practice of the technique. This paper describes measurements of polystyrene latex, radius 720 Å, with a number of instruments. Scattering from monodisperse, uniform spherical particles is simple to calculate and displays sharp minima. Such data test the calibrations of intensity, wavelength and resolution as well as the detector response. Smoothing due to resolution, multiple scattering and polydispersity has been determined. Sources of uncertainty are often related to systematic deviations and calibrations rather than random counting errors. The study has prompted development of software to treat modest multiple scattering and to better model the instrument resolution. These measurements also allow checks of data reduction algorithms and have identified how they can be improved. The reproducibility and the reliability of instruments and the accuracy of parameters derived from the data are described.
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| 7. |
- Sanchez-Fernandez, A, et al.
(författare)
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Micelle structure in a deep eutectic solvent : A small-angle scattering study
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:20, s. 14063-14073
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Tidskriftsartikel (refereegranskat)abstract
- In recent years many studies into green solvents have been undertaken and deep eutectic solvents (DES) have emerged as sustainable and green alternatives to conventional solvents since they may be formed from cheap non-toxic organic precursors. In this study we examine amphiphile behaviour in these novel media to test our understanding of amphiphile self-assembly within environments that have an intermediate polarity between polar and non-polar extremes. We have built on our recently published results to present a more detailed structural characterisation of micelles of sodium dodecylsulfate (SDS) within the eutectic mixture of choline chloride and urea. Here we show that SDS adopts an unusual cylindrical aggregate morphology, unlike that seen in water and other polar solvents. A new morphology transition to shorter aggregates was found with increasing concentration. The self-assembly of SDS was also investigated in the presence of water; which promotes the formation of shorter aggregates.
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