| 11. |
- Gentile, Luigi, et al.
(författare)
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Effect of Shear Rates on the MLV Formation and MLV Stability Region in the C12E5/D2O System: Rheology and Rheo-NMR and Rheo-SANS Experiments
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:6, s. 2088-2092
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Tidskriftsartikel (refereegranskat)abstract
- At high temperatures, pentaethylene glycol monododecyl ether (C12E5) in D2O forms a swollen lamellar phase. This letter reports the shear induced multilamellar vesicle (MLV) formation in a sample that contains 40 wt % C12E5 dissolved in D2O at 55 degrees C. This transition has been investigated by time-resolved rheo-nuclear magnetic resonance, rheo small angle neutron scattering, and rheometry. The typical transient viscosity behavior of MLV formation has been discovered at 1 s(-1). For the first time, it has been found that MLVs are not stable over time when subjected to high shear rates. Our results show that the MLV stability is confined in a narrow region in the range 1-10 s(-1) shear rates. This is not observed for other CnEm surfactants.
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| 12. |
- Gentile, Luigi, et al.
(författare)
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Ferrihydrite Nanoparticle Aggregation Induced by Dissolved Organic Matter
- 2018
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 122:38, s. 7730-7738
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Tidskriftsartikel (refereegranskat)abstract
- Ferrihydrite (Fh) nanoparticles are omnipresent in nature and often highly mobile because of their colloidal stability. Thus, Fh serves as a vector for iron as well as associated nutrients and contaminants. Here, we demonstrate, using small-angle X-ray scattering combined with cryo-transmission electron microscopy (cryo-TEM), that dissolved organic matter (DOM), extracted from a boreal forest soil, induce aggregation of Fh nanoparticles, of radius 3 nm, into fractal aggregates, having a fractal dimension D = 1.7. The DOM consists of both fractal-like colloids (>100 nm) and small molecular DOM, but the attractive Fh interparticle interaction was mediated by molecular DOM alone as shown by cryo-TEM. This highlights the importance of using soil extracts, including all size fractions, in studies of the colloidal behavior of DOM-mineral aggregates. The Fh nanoparticles also self-assemble during synthesis into aggregates with the same fractal dimension as the DOM-Fh aggregates. We propose that, in both the absence and presence of DOM, the aggregation is controlled by the Fh particle charge, and the process can be viewed as a linear polymerization into a self-avoiding random walk structure. The theoretical D value for this is 5/3, which is in close agreement with our Fh and DOM-Fh results.
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| 13. |
- Gentile, Luigi, et al.
(författare)
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Fungal decomposition and transformation of molecular and colloidal fractions of dissolved organic matter extracted from boreal forest soil
- 2024
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Ingår i: Soil Biology and Biochemistry. - 0038-0717. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic matter (DOM) plays a central role in soil carbon (C) dynamics, serving as both a substrate for microbial decomposers and a source of material stabilised via physical protection in molecular aggregates and associations with mineral particles. It is well established that soil microorganisms play a key role in mineral-associated C aggregates; however, their impacts on molecular aggregates is not clearly understood. Here, we examined the ability of an ectomycorrhizal fungus (Paxillus involutus) and a saprotrophic fungus (a strain of Gloeophyllum), two major functional groups of fungal decomposers in forest ecosystems, to decompose and process the molecular and colloidal size fractions of DOM. DOM was extracted by water from boreal forest soil, and the chemical composition and colloidal properties were followed over 11 days using nuclear magnetic resonance (NMR) spectroscopy and small-angle light and X-ray scattering techniques. Both fungi decompose various organic compounds into their molecular fractions in the presence of an energy source (i.e. glucose). The decomposition rate was significantly higher for Gloeophyllum than for P. involutus. When glucose was depleted, Gloeophyllum continued to decompose more complex carbohydrates, whereas the decomposition activity of P. involutus almost stopped. A large proportion of the C in the DOM was found in organic colloids. At later stages, Gloeophyllum but not P. involutus, significantly affected the colloids by promoting the formation of larger aggregates. Thus, saprotrophic fungi activity can significantly influence the colloidal properties of DOM. Our results support the view that ectomycorrhizal fungi decompose some of the soil organic C however, their overall capacity for DOM decomposition and transformation is significantly lower than that of saprotrophic fungi.
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| 14. |
- Gentile, Luigi, et al.
(författare)
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Multi-lamellar vesicle formation in a long-chain nonionic surfactant: C16E4/D2O system
- 2011
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 362:1, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependent theological and structural behavior of a long-chain C16E4 (tetraethylene glycol monohexadecyl ether) surfactant in D2O has been studied within the regime of low shear range. In the absence of shear flow, the system forms a lamellar liquid crystalline phase at relatively high temperatures. The present paper reports on the shear-induced multi-lamellar vesicle (MLV) formation in C16E4/D2O at 40 wt.% of surfactant in the temperature range of 40-55 degrees C. The transition from planar lamellar structure to multi-lamellar vesicles has been investigated by time-resolved experiments combining rheology and nuclear magnetic resonance (rheo-NMR), rheo small-angle neutron scattering (rheo-SANS) and rheometry. The typical transient viscosity behavior of MLV formation has been discovered at low shear rate value of 0.5 s(-1). (C) 2011 Elsevier Inc. All rights reserved.
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| 15. |
- Gentile, Luigi, et al.
(författare)
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Multilamellar Vesicle Formation from a Planar Lamellar Phase under Shear Flow
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:28, s. 8316-8325
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Tidskriftsartikel (refereegranskat)abstract
- The formation of multilamellar vesicles (MLVs) from the lamellar phase of nonionic surfactant system C12E5/D2O under shear flow is studied by time-resolved small angle neutron and light scattering during shear flow. A novel small angle neutron scattering sample environment enables the tracking of the lamellae alignment in the velocity-velocity gradient (1-2) plane during MLV formation, which was tracked independently using flow small angle light scattering commensurate with rheology. During the lamellar-to-multilamellar vesicle transition, the primary Bragg peak from the lamellar ordering was observed to tilt, and this gradually increased with time, leading to an anisotropic pattern with a primary axis oriented at similar to 25 degrees relative to the flow direction. This distorted pattern persists under flow after MLV formation. A critical strain and critical capillary number based on the MLV viscosity are demonstrated for MLV formation, which is shown to be robust for other systems as well. These novel measurements provide fundamentally new information about the flow orientation of lamellae in the plane of flow that cannot be anticipated from the large body of previous literature showing nearly isotropic orientation in the 2,3 and 1,3 planes of flow. These observations are consistent with models for buckling-induced MLV formation but suggest that the instability is three-dimensional, thereby identifying the mechanism of MLV formation in simple shear flow.
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| 16. |
- Gentile, Luigi, et al.
(författare)
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Rheochaos and flow instability phenomena in a nonionic lamellar phase
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:4, s. 1133-1140
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report on instability phenomena in a solution where shear induces multilamellar vesicles (MLVs) from a lamellar phase. A shear-thickening regime has been observed for hexadecyl tetraethylene glycol ether (C16E4) dissolved in D2O at 40 degrees C. In this regime, unstable temporal viscosity behavior, i.e. periodic oscillations, has been observed at 2, 5 and 10 s(-1). Moreover at a shear rate of 10 s(-1) shear banding manifests itself as the occurrence of transparent and turbid bands stacked along the vorticity direction. We perform time-resolved-rheo-small angle neutron scattering (rheo-SANS) experiments to understand the nature of the viscosity oscillations and spatial-resolved experiments to obtain a structural characterization of vorticity bands.
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| 17. |
- Gentile, Luigi, et al.
(författare)
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Rheological and rheo-SALS investigation of the multi-lamellar vesicle formation in the C12E3/D2O system
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 367, s. 537-539
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Tidskriftsartikel (refereegranskat)abstract
- Usually in nonionic surfactant aqueous systems of the CnEm type, a lamellar phase occurs over a wide temperature and concentration range. For some CnEm surfactants, multi-lamellar vesicle (MLV) formation has been observed when the lamellar phase is subjected to shear flow. This communication reports the shear flow behavior at different shear rate values of a CnEm (where "n" is 12 and "m" is 3) aqueous system at 34 degrees C. The typical transient viscosity behavior of the shear-induced MLV formation in C12E3/D2O at 50 wt% of surfactant has been observed. The MLV formation is confirmed by time-resolved rheo-small angle light scattering (SALS) experiments. The experimental data show an intermediate structure that has been attributed to a multi-lamellar cylinders (MLCs). (C) 2011 Elsevier Inc. All rights reserved.
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| 18. |
- Gentile, Luigi, et al.
(författare)
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Soft-MS and computational mapping of oleuropein
- 2017
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 18:5
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Forskningsöversikt (refereegranskat)abstract
- Olive oil and table olives are rich sources of biophenols, which provides a unique taste, aroma and potential health benefits. Specifically, green olive drupes are enriched with oleuropein, a bioactive biophenol secoiridoid. Olive oil contains hydrolytic derivatives such as hydroxytyrosol, oleacein and elenolate from oleuropein as well as tyrosol and oleocanthal from ligstroside. Biophenol secoiridoids are categorized by the presence of elenoic acid or its derivatives in their molecular structure. Medical studies suggest that olive biophenol secoiridoids could prevent cancer, obesity, osteoporosis, and neurodegeneration. Therefore, understanding the biomolecular dynamics of oleuropein can potentially improve olive-based functional foods and nutraceuticals. This review provides a critical assessment of oleuropein biomolecular mechanism and computational mapping that could contribute to nutrigenomics.
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| 19. |
- Gentile, Luigi, et al.
(författare)
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Structural transitions induced by shear flow and temperature variation in a nonionic surfactant/water system
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 372, s. 32-39
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate structural transitions of tetraethylene glycol monohexadecyl ether (C16E4) in D2O as a function of shear flow and temperature. Via a combination of rheology, rheo-small-angle neutron scattering and rheo-small-angle light scattering, we probe the structural evolution of the system with respect to shear and temperature. Multi-lamellar vesicles, planar lamellae, and a sponge phase were found to compete as a function of shear rate and temperature, with the sponge phase involving the formation of a new transient lamellar phase with a larger spacing, coexisting with the preceding lamellar phase within a narrow temperature-time range. The shear flow behavior of C16E4 is also found to deviate from other nonionic surfactants with shorter alkyl chains (C10E3 and C12E4), resembling to the C16E7 case, of longer chain. (C) 2012 Elsevier Inc. All rights reserved.
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| 20. |
- Gubitosi, Marta, et al.
(författare)
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On cellulose dissolution and aggregation in aqueous tetrabutylammonium hydroxide
- 2016
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 17:9, s. 2873-2881
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous tetrabutylammonium hydroxide, TBAH(aq), has been found to dissolve cellulose and to be a potential solvent for chemical processing or fiber spinning. In this paper, we have investigated the dissolution state of cellulose in 40 wt % TBAH(aq) solvent, and present an extensive study of rheology, combined with static light and small-angle X-ray scattering, to correlate cellulose aggregation with changes in the rheological parameters. Two cellulose molecular weights are compared. Microcrystalline cellulose (MCC), with a degree of polymerization of ca. 260, and a dissolving pulp with an approximately ten times higher molecular weight. Scattering data demonstrate that cellulose is molecularly dissolved at lower cellulose concentrations, while aggregates are present when the concentration exceeds a certain value. The onset of the aggregate formation is marked by a pronounced increase in the scattering intensity at low q, shear thinning behavior and violation of the empirical Cox-Merz rule. Additionally, the SAXS data suggest the presence of a solvation shell enriched in TBA+ ions, compared to the bulk solvent. The results are consistent with the recent suggestion that while native cellulose I may still dissolve, solutions are, above a particular concentration, becoming supersaturated with respect to the more stable crystal form cellulose II.
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