| 1. |
- Asaro, Fioretta, et al.
(författare)
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Micellar crowding and branching in a versatile catanionic system
- 2016
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 506, s. 202-209
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Tidskriftsartikel (refereegranskat)abstract
- The catanionic system didodecyldimethylammonium bromide (DDAB)-sodium taurodeoxycholate (STDC)-D2O is characterized by an exceptionally extended L1 region. The comparison of self-diffusion coefficient of the solvent and the DDAB embedded in the micelles provided information about hydration of the aggregates. Moreover, correlating self-diffusion and 14N NMR relaxation measurements new insight could be obtained regarding the translational and rotational micellar motions in the crowded solutions of systems with 0.2 DDAB-STDC molar ratio. 1H 2D NMR spectra gave some hints about the mutual arrangement of DDAB and STDC within the aggregates. For samples with 1.8 and 2.6 DDAB/STD molar ratios the 14N data were in agreement with the presence of somewhat branched, interconnected micelles. 23Na and 81Br dynamic parameters resulted particularly sensitive to the surrounding environment. The peculiar rheological behaviour of the, highly concentrated, branched micelles samples, namely the steady oscillations in the step tests, was found to be an example of instability originated by the combined effect of material elasticity and slippage at the fixed wall.
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| 2. |
- Gentile, Luigi, et al.
(författare)
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Phase Coexistence in a Dynamic Phase Diagram.
- 2015
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 16:11, s. 2459-2465
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Tidskriftsartikel (refereegranskat)abstract
- Metastability and phase coexistence are important concepts in colloidal science. Typically, the phase diagram of colloidal systems is considered at the equilibrium without the presence of an external field. However, several studies have reported phase transition under mechanical deformation. The reason behind phase coexistence under shear flow is not fully understood. Here, multilamellar vesicle (MLV)-to-sponge (L3 ) and MLV-to-Lα transitions upon increasing temperature are detected using flow small-angle neutron scattering techniques. Coexistence of Lα and MLV phases at 40 °C under shear flow is detected by using flow NMR spectroscopy. The unusual rheological behavior observed by studying the lamellar phase of a non-ionic surfactant is explained using (2) H NMR and diffusion flow NMR spectroscopy with the coexistence of planar lamellar-multilamellar vesicles. Moreover, a dynamic phase diagram over a wide range of temperatures is proposed.
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| 3. |
- Andersson, Erika, et al.
(författare)
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A contrast variation SANS and SAXS study of soil derived dissolved organic matter, and its interactions with hematite nanoparticles
- 2023
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Ingår i: JCIS Open. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Soil derived dissolved organic matter (DOM) is an important component of the carbon cycle and influences numerous biogeochemical processes, including the formation of mineral-organic associations. DOM ranges in size from small organic molecules to macromolecules and colloidal aggregates. In this study we have used small angle neutron (SANS) and X-ray (SAXS) scattering to characterize the colloidal DOM fraction from the organic layer of a boreal forest soil, and its interactions with hematite (α-Fe2O3) mineral nanoparticles. Comparison between SAXS and contrast variation SANS patterns revealed that the scattering form factor of the colloidal DOM aggregates was essentially independent of the scattering contrast, implying that the colloidal aggregates have an essentially homogeneous chemical composition, down to the nanometre length scale. Variation of the D2O/H2O ratio of the solvent yielded a SANS intensity minimum at ca. 40 vol % D2O, which was consistent with colloids composed of mainly polysaccharides. At pH 5.5 the pure hematite nanoparticles were colloidally stable in water and characterized by a ζ-potential of +25 mV and a hydrodynamic radius of ca. 70 nm. In the presence of DOM, the hematite nanoparticles lost the colloidal stability and aggregated into larger clusters, displaying a negative ζ-potential of ca. −25 mV. The charge reversal suggested that negatively charged polyanions of DOM adsorbed onto the hematite particles, possibly leading to bridging flocculation. Our results suggested that mainly low molecular weight components induced hematite aggregation because no or very limited interactions between DOM colloids and hematite were detected.
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| 4. |
- Andersson, Erika, et al.
(författare)
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Generation and properties of organic colloids extracted by water from the organic horizon of a boreal forest soil
- 2023
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061. ; 432
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Tidskriftsartikel (refereegranskat)abstract
- Organic colloids are an important part of dissolved organic matter (DOM) yet many of their properties remain elusive. The main aims of this study were to assess how the colloidal properties of DOM extracted with water from an organic boreal soil horizon varied with the extraction protocol, and thereby provide insight into the nature of the DOM colloids and develop a mechanistic understanding of how the colloids were generated from the parent soil aggregates. This was accomplished by systematic variations of extraction temperature (4 °C–100 °C), time, mechanical agitation, and pH, together with a combination of chemical analyses, and light and X-ray scattering. Our results agreed with the previous identification of two main colloidal DOM species, one fractal cluster and a second, smaller colloidal DOM species described as chains or coils. Fractal clusters completely dominated the colloidal DOM in extracts from our soil at room temperature and below. Colloidal coils only existed in DOM extracted above room temperature, and their amount increased significantly between 50 °C–100 °C. Moreover, the temperature variation indicated that the fractal clusters partly dissolved into colloidal coils at elevated temperatures. Mechanical agitation at 4 °C significantly increased the amount of DOM extracted, increasing the concentrations of both fractal clusters and low-molecular weight organic compounds. While the clusters were extracted from agitated and non-agitated soil suspensions, the low molecular weight organics were mainly released by agitation. Based on the experimental observations, we propose a conceptual model where parent soil aggregates contain the fractal clusters in mobile and occluded forms, and that the occluded clusters co-exist with occluded low molecular weight organics. These occluded forms may be released by mechanical forces, increasing pH and temperature. At higher temperatures, the soil aggregates and the fractal clusters start to break up, and subsequently individual colloidal coils, presumably carbohydrates, disperse in the water phase. The model explains the origin and properties of the fractal clusters that completely dominate the colloidal DOM extracted from our soil at room temperature and below.
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| 5. |
- Colafemmina, Giuseppe, et al.
(författare)
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The cooling process effect on the bilayer phase state of the CTAC/cetearyl alcohol/water surfactant gel
- 2020
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 597
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Tidskriftsartikel (refereegranskat)abstract
- Gel formation by surfactant molecules is generally controlled by thermodynamics rather than kinetics. Mixtures of long-chain alcohols and surfactants are widely used in various cosmetic and pharmaceutical products. The cooling rate used to produce the products is known to be a key parameter to control the rheological properties and the final texture. However, the physical-chemistry links between the cooling process and the rheological properties are still unknown. Here, we investigated the mechanical properties and microstructure of a surfactant gel formulated with cetyltrimethylammonium chloride (CTAC) and cetearyl alcohol in water by using a multi-technique approach involving rheology, small-angle X-ray scattering (SAXS) and diffusion NMR. The gels, formed by two cooling processes fast and slow cooling, respectively from a high-temperature mixture, have locally a lamellar structure with periodic repeat distances of 31.4 and 28.5 nm for fast and slow cooling, respectively. The cross-polarized microscopy images reveal the presence of multilamellar vesicles (MLVs). These data on the supramolecular aggregates allow rationalizing the mechanical behavior of the two samples. In fact, the elastic, G′, and the viscous, G′′, moduli were detected to be ca. 4 times higher for the fast-cooling (quenched) sample than for the slow-cooling (relaxed) sample.
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| 6. |
- Dabkowska, Aleksandra P., et al.
(författare)
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Non-lamellar lipid assembly at interfaces : controlling layer structure by responsive nanogel particles
- 2017
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Ingår i: Interface Focus. - : ROYAL SOC. - 2042-8898 .- 2042-8901. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Biological membranes do not only occur as planar bilayer structures, but depending on the lipid composition, can also curve into intriguing three-dimensional structures. In order to fully understand the biological implications as well as to reveal the full potential for applications, e.g. for drug delivery and other biomedical devices, of such structures, well-defined model systems are required. Here, we discuss the formation of lipid non-lamellar liquid crystalline (LC) surface layers spin-coated from the constituting lipids followed by hydration of the lipid layer. We demonstrate that hybrid lipid polymer films can be formed with different properties compared with the neat lipid LC layers. The nanostructure and morphologies of the lipid films formed reflect those in the bulk. Most notably, mixed lipid layers, which are composed of glycerol monooleate and diglycerol monooleate with poly(N-isopropylacrylamide) nanogels, can form films of reverse cubic phases that are capable of responding to temperature stimulus. Owing to the presence of the nanogel particles, changing the temperature not only regulates the hydration of the cubic phase lipid films, but also the lateral organization of the lipid domains within the lipid self-assembled film. This opens up the possibility for new nanostructured materials based on lipid-polymer responsive layers.
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| 7. |
- Floudas, Dimitrios, et al.
(författare)
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X-ray scattering reveals two mechanisms of cellulose microfibril degradation by filamentous fungi
- 2022
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 88:17
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Tidskriftsartikel (refereegranskat)abstract
- Mushroom-forming fungi (Agaricomycetes) employ enzymatic and nonenzymatic cellulose degradation mechanisms, the latter presumably relying on Fenton-generated radicals. The effects of the two mechanisms on the cellulose microfibrils structure remain poorly understood. We examined cellulose degradation caused by litter decomposers and wood decomposers, including brown-rot and white-rot fungi and one fungus with uncertain wood decay type, by combining small- and wide-angle X-ray scattering. We also examined the effects of commercial enzymes and Fenton-generated radicals on cellulose using the same method. We detected two main degradation or modification mechanisms. The first characterized the mechanism used by most fungi and resembled enzymatic cellulose degradation, causing simultaneous microfibril thinning and decreased crystalline cellulose. The second mechanism was detected in one brown-rot fungus and one litter decomposer and was characterized by patchy amorphogenesis of crystalline cellulose without substantial thinning of the fibers. This pattern did not resemble the effect of Fenton-generated radicals, suggesting a more complex mechanism is involved in the destruction of cellulose crystallinity by fungi. Furthermore, our results showed a mismatch between decay classifications and cellulose degradation patterns and that even within litter decomposers two degradation mechanisms were found, suggesting higher functional diversity under current ecological classifications of fungi.IMPORTANCE Cellulose degradation by fungi plays a fundamental role in terrestrial carbon cycling, but the mechanisms by which fungi cope with the crystallinity of cellulose are not fully understood. We used X-ray scattering to analyze how fungi, a commercial enzyme mix, and a Fenton reaction-generated radical alter the crystalline structure of cellulose. Our data revealed two mechanisms involved in crystalline cellulose degradation by fungi: one that results in the thinning of the cellulose fibers, resembling the enzymatic degradation of cellulose, and one that involves amorphogenesis of crystalline cellulose by yet-unknown pathways, resulting in a patchy-like degradation pattern. These results pave the way to a deeper understanding of cellulose degradation and the development of novel ways to utilize crystalline cellulose.
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| 8. |
- Gentile, Luigi, et al.
(författare)
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A novel X-ray diffraction approach to assess the crystallinity of regenerated cellulose fibers
- 2022
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Ingår i: IUCrJ. - 2052-2525. ; 9, s. 492-496
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Tidskriftsartikel (refereegranskat)abstract
- Here, a new accurate approach is presented to quantify the degree of crystallinity of regenerated cellulose textile fibers using wide-angle X-ray scattering. The approach is based on the observation that the contributions to the scattering from crystalline and amorphous domains of the fibers can be separated due to their different degree of orientation with respect to the fiber direction. The method is tested on Ioncell-F fibers, dry jet wet spun with different draw ratios from an ionic liquid solution. The analysis output includes, apart from an accurate estimate of the fiber crystallinity, the degrees of orientation of the cellulose nanocrystals and the cellulose chains in the amorphous domains.
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| 9. |
- Gentile, Luigi, et al.
(författare)
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Cellulose–solvent interactions from self-diffusion NMR
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:4, s. 2753-2758
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Tidskriftsartikel (refereegranskat)abstract
- Molecular self-diffusion coefficients were measured in solutions of microcrystalline cellulose (MCC) and dissolving pulp, in 40 wt% aqueous tetrabutylammonium hydroxide (TBAH), using pulsed field gradient stimulated echo NMR. From the cellulose diffusion coefficients, a weight averaged radius of hydration h>w = 6.1 nm for MCC and h>w = 15 nm for pulp were obtained. Water and TBA+ ions show a significantly different dependence on the cellulose concentration, revealing different molecular interactions with the polymer. Water-cellulose are essentially excluded volume. TBA+ ions, on the other hand, bind to cellulose with approximately 1.2 TBA+ ions per glucose unit.
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| 10. |
- Gentile, Luigi, et al.
(författare)
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Dynamic Phase Diagram of a Nonionic Surfactant Lamellar Phase
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:13, s. 3622-3629
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic phase diagram of triethylene glycol dodecyl ether (C12E3) in D2O was determined for 40, 50, and 60 wt % of surfactant. The shear flow effect on the nonionic lamellar phase was investigated as a function of temperature and concentration. The transition from planar lamellae (L-alpha)-to-multilamellar vesicles (MLVs) was characterized by means of rheology, rheo-small-angle neutron and light scattering. New insight into the nature of the transition region between L-alpha and the MLVs state is provided. A disorder-order transition was also observed by SANS. This is attributed to a transition from disordered MLVs to a close-packed array of MLV's with slightly higher order than before. Moreover flow instability was observed in the shear-thickening regime at 40 degrees C.
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