| 1. |
- Andersson, August, et al.
(författare)
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Magnetic resonance investigations of lipid motion in isotropic bicelles
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 21:7, s. 7702-7709
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of DMPC in different isotropic bicelles have been investigated by NMR and EPR methods. The local dynamics were obtained by interpretation of 13C NMR relaxation measurements of DMPC in the bicelles, and these results were compared to EPR spectra of spin-labeled lipids. The overall size of the bicelles was investigated by PFG NMR translational diffusion measurements. The dynamics and relative sizes were compared among three different bicelles: [DMPC]/[DHPC] = 0.25, [DMPC]/[DHPC] = 0.5, and [DMPC]/[CHAPS] = 0.5. The local motion is found to depend much more strongly on the choice of the detergent, rather than the overall size of the bicelle. The results provide an explanation for differences in apparent dynamics for different peptides, which are bound to bicelles. This in turn determines under what conditions reasonable NMR spectra can be observed. A model is presented in which extensive local motion, in conjunction with the overall size, affects the spectral properties. An analytical expression for the size dependence of the bicelles, relating the radius of the bilayer region with physical properties of the detergent and the lipid, is also presented.
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| 2. |
- Allouche, Joachim, et al.
(författare)
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Simultaneous Conductivity and Viscosity Measurements as a Technique To Track Emulsion Inversion by the Phase-Inversion-Temperature Method
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:6, s. 2134-2140
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Tidskriftsartikel (refereegranskat)abstract
- Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under const. stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphol. according to the so-called phase-inversion-temp. method. At a high water content, a multiple W/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion cond. and viscosity allows the identification of several phenomena that take place during the temp. decrease. In all cases, a viscosity max. is found on each side of the three-phase behavior temp. interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a not-too-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-compn. bidimensional map.
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| 3. |
- Abele, S, et al.
(författare)
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Reactive surfactants in heterophase polymerization. 10. Characterization of the surface activity of new polymerizable surfactants derived from maleic anhydride
- 1997
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 13, s. 176-181
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of the surface activity of previously obtained polymerizable dialkyl maleates is performed to find out the relation between the structure of surfactants and their performances. The given polymerizable surfactants were synthesized for using in the emulsion polymerization. Three groups of dialkyl maleates-nonionic, cationic and zwitterionic-with different chain lengths of hydrophobic alkyl groups are investigated. Critical micelle concentration (cmc) values are determined for water soluble surfactants. It is found that cmc decreases with increasing chain length of the hydrophobic alkyl group. For nonionic and cationic surfactants interfacial tension at the interface between water and dodecane is measured. Droplet size in oil-in-water (O/W) emulsions is determined for all given surfactants. Cationic and zwitterionic dialkyl maleates with the longest investigated alkyl chain (R=C16H33, C17H35) provide good stability of O/W emulsions. In order to compare the obtained results, measurements with well-known surfactants-nonionic nonylphenol-poly(ethylene oxide) (NPEO10) and cationic hexadecyltrimethyl ammonium bromide (CTAB)-are performed.
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| 4. |
- Aben, Simon, et al.
(författare)
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Rheological Investigations on the Creaming of Depletion-Flocculated Emulsions
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:21, s. 7967-7975
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Tidskriftsartikel (refereegranskat)abstract
- Preventing creaming or sedimentation by the addition of thickeners is an important industrial challenge. We study the effect of the addition of a "free" nonadsorbing polymer (xanthan gum) on the stability against creaming of sterically stabilized O/W emulsions. Therefore, we analyze our samples using microscopy and rheological measurements. At low xanthan concentrations, the emulsions cream. However, above a certain concentration a three-dimensional network of droplets is formed, which can prevent creaming. We attribute the formation of this structure to depletion attraction. The rheological behavior of an emulsion that is macroscopically stable should be elastic, while it should be viscous for a creaming emulsion. In order to distinguish between stable and unstable samples, we measure their relaxation time by mechanical rheology and find a good correlation to the visual observation. However, the measured relaxation times are much shorter than the time-scales, on which we observe creaming. We hypothesize that the measured relaxation time is related to the droplet-droplet interaction. This determines the frequency at which microscopic rearrangements occur, which weaken the network structure prior to creaming. Based on this interpretation, the relaxation time gives direct access to the microstructural processes involved in creaming. We therefore suggest using it as a predictive parameter of creaming stability.
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| 5. |
- Abitbol, Tiffany, et al.
(författare)
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Surface Charge Influence on the Phase Separation and Viscosity of Cellulose Nanocrystals
- 2018
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 34:13, s. 3925-3933
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Tidskriftsartikel (refereegranskat)abstract
- counterions in the suspensions. The results suggest that there is a threshold surface charge density (∼0.3%S) above which effective volume considerations are dominant across the concentration range relevant to liquid crystalline phase formation. Above this threshold value, phase separation occurs at the same effective volume fraction of CNCs (∼10 vol %), with a corresponding increase in critical concentration due to the decrease in effective diameter that occurs with increasing surface charge. Below or near this threshold value, the formation of end-to-end aggregates may favor gelation and interfere with ordered phase formation.
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| 6. |
- Abraham, T., et al.
(författare)
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Polyelectrolyte-mediated interaction between similarly charged surfaces : Role of divalent counter ions in tuning surface forces
- 2001
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:26, s. 8321-8327
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Tidskriftsartikel (refereegranskat)abstract
- The effects of divalent salts (CaCl2, MgCl2 and BaCl2) in promoting the adsorption of weakly charged polyelectrolyte (polyacrylic acid), PAA, Mw similar to 250000 g/mol) on mica surfaces and their role in tuning the nature of interactions between such adsorbed polyelectrolyte layers were studied using the interferometric surface forces apparatus. With mica surfaces in 3 mM MgCl2 solutions at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in a long-range attractive bridging force and a short-range repulsive steric force. This force profile indicates a low surface coverage and weak adsorption. The range of the force can be related to the characteristic length scale R-G of polyelectrolyte chains using a scaling description. An increase of the PAA concentration to 50 ppm changed the attractive force profile to a monotonic, long-range repulsive interaction extending up to 600 Angstrom due to the increased surface coverage of polyelectrolyte chains on the mica surfaces. Comparison of the measured forces with a scaling mean field model suggests that the adsorbed polyelectrolyte chains are stretched, which eventually give rise to the polyelectrolyte brush like structure. When the mica surfaces were preincubated in 3 mM CaCl2 at pH similar to8.0-9.0, in contrast to the case of 3 MM MgCl2, the addition of 10 ppm PAA resulted in a more complex force profile: long-range repulsive forces extending up to 800 Angstrom followed by an attractive force regime and a second repulsive force regime at shorter separations. The long-range electrosteric forces can be attributed to strong adsorption of polyelectrolyte chains on mica surfaces (high surface coverage) which is facilitated by the presence of Ca2+ ions, while the intermediate range attractive forces can be ascribed to Ca2+ assisted bridging between adsorbed polyelectrolyte chains. Also interesting is to note various relaxation processes present in this system. In contrast to both MgCl2 and CaCl2 systems, with mica surfaces in 3 mM BaCl2 solution at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in precipitation of polyelectrolyte chains on mica surfaces, resulting in an extremely long-range monotonic repulsive force profile. In summary, our study showed that divalent counterions (Mg2+, Ca2+, and Ba2+) exhibit significantly different behavior in promoting PAA adsorption on mica surfaces, modifying and controlling various surface interactions.
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| 7. |
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| 8. |
- 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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| 9. |
- Aggarwal, N., et al.
(författare)
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Effect of Molecular Composition of Heparin and Cellulose Sulfate on Multilayer Formation and Cell Response
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 29:45, s. 13853-13864
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Tidskriftsartikel (refereegranskat)abstract
- Here, the layer-by-layer method was applied to assemble films from chitosan paired with either heparin or a semisynthetic cellulose sulfate (CS) that possessed a higher sulfation degree than heparin. Ion pairing was exploited during multilayer formation at pH 4, while hydrogen bonding is likely to occur at pH 9. Effects of polyanions and pH value during layer formation on multilayers properties were studied by surface plasmon resonance ("dry layer mass"), quartz crystal microbalance with dissipation monitoring ("wet layer mass"), water contact angle, and zeta potential measurements. Bioactivity of multilayers was studied regarding fibronectin adsorption and adhesion/proliferation of C2C12 myoblast cells. Layer growth and dry mass were higher for both polyanions at pH 4 when ion pairing occurred, while it decreased significantly with heparin at pH 9. By contrast, CS as polyanion resulted also in high layer growth and mass at pH 9, indicating a much stronger effect of hydrogen bonding between chitosan and CS. Water contact angle and zeta potential measurements indicated a more separated structure of multilayers from chitosan and heparin at pH 4, while CS led to a more fuzzy intermingled structure at both pH values. Cell behavior was highly dependent on pH during multilayer formation with heparin as polyanion and was closely related to fibronectin adsorption. By contrast, CS and chitosan did not show such dependency on pH value, where adhesion and growth of cells was high. Results of this study show that CS is an attractive candidate for multilayer formation that does not depend so strongly on pH during multilayer formation. In addition, such multilayer system also represents a good substrate for cell interactions despite the rather soft structure. As previous studies have shown specific interaction of CS with growth factors, multilayers from chitosan and CS may be of great interest for different biomedical applications.
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| 10. |
- Aggarwal, Ruchi, et al.
(författare)
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From Bulk Molybdenum Disulfide (MoS 2 ) to Suspensions of Exfoliated MoS 2 in an Aqueous Medium and Their Applications
- 2023
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Ingår i: Langmuir. - 1520-5827 .- 0743-7463. ; 40:19, s. 9855-9872
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Forskningsöversikt (refereegranskat)abstract
- Two-dimensional (2D) layered materials like graphene, transition-metal dichalcogenides (TMDs), boron nitrides, etc., exhibit unique and fascinating properties, such as high surface-to-volume ratio, inherent mechanical flexibility and robustness, tunable bandgap, and high carrier mobility, which makes them an apt candidate for flexible electronics with low consumption of power. Because of these properties, they are in tremendous demand for advancement in energy, environmental, and biomedical sectors developed through various technologies. The production and scalability of these materials must be sustainable and ecofriendly to utilize these unique properties in the real world. Here, in this current review, we review molybdenum disulfide (MoS2 nanosheets) in detail, focusing on exfoliated MoS2 in water and the applicability of aqueous MoS2 suspensions in various fields. The exfoliation of MoS2 results in the formation of single or few-layered MoS2. Therefore, this Review focuses on the few layers of exfoliated MoS2 that have the additional properties of 2D layered materials and higher excellent compatibility for integration than existing conventional Si tools. Hence, a few layers of exfoliated MoS2 are widely explored in biosensing, gas sensing, catalysis, photodetectors, energy storage devices, a light-emitting diode (LED), adsorption, etc. This review covers the numerous methodologies to exfoliate MoS2, focusing on the various published methodologies to obtain nanosheets of MoS2 from water solutions and their use.
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