| 1. |
- Alves, Luis, et al.
(författare)
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On the role of hydrophobic interactions in cellulose dissolution and regeneration: Colloidal aggregates and molecular solutions
- 2015
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 483, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The development of strategies for dissolution and regeneration of cellulose constitutes an increasingly active research field due to the direct relevance for many production processes and applications. A wide variety of suitable solvents for cellulose are already available. However, cellulose solvents are of highly different nature reflecting the great challenges in the understanding of the subtle balance between the different interactions. Here, we report on the effect of two different solvents on the dissolution of cellulose on multiple length scales and its consequences for the characteristics of the regenerated material. While an aqueous tetrabutylammonium hydroxide solution gives rise to what appears to be dissolution down to the molecular level, a sodium hydroxide solution does not dissolve cellulose molecularly but rather leaves aggregates of high crystallinity stable in the cellulose dope. The dramatic difference between a small inorganic cation and an amphiphilic cation indicates a critical role of hydrophobic interactions between cellulose molecules and provides support for the picture that cellulose molecules have pronounced amphiphilic properties. (C) 2015 Elsevier B.V. All rights reserved.
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| 2. |
- Andersson, I. M., et al.
(författare)
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Impact of protein surface coverage and layer thickness on rehydration characteristics of milk serum protein/lactose powder particles
- 2019
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 561, s. 395-404
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Tidskriftsartikel (refereegranskat)abstract
- Spray-dried powders were produced from milk serum protein concentrate and lactose in varying ratios, and the rehydration characteristics of the powders were evaluated. The dissolution rate was estimated with a flow-cell based technique, and the external and internal distribution of the powder components were evaluated with X-ray photoelectron spectroscopy and confocal Raman microscopy, respectively. The surface of the powder particles is more or less covered by a thin protein layer. A phase segregation between protein and lactose is observed in the interior of the particle resulting in a protein rich layer in the vicinity of the surface. However, the protein layer in the vicinity of the particle surface tends to become thinner as the bulk protein concentration increases in the powders (from 10 to 60% w/w). The time for the spontaneous imbibition to occur show a linear correlation with the protein surface coverage. The dissolution rate of powders containing 0.1% w/w protein is around 60 times faster than for a powder containing 1% w/w protein but the dissolution rate of powders containing 1% and 100% w/w differ only by a factor of 2. Thus, it is suggested that the outer protein layer becomes denser at the interface as the protein content increases in the powders, thereby causing poorer rehydration characteristics of the powders (especially for low protein concentrations 0.1–1% w/w). This insight has relevance for the formulation of whey protein powders with improved rehydration characteristics. © 2018 Elsevier B.V.
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| 3. |
- 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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| 4. |
- Babakhani, Peyman, et al.
(författare)
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Comparison of a new mass-concentration, chain-reaction model with the population-balance model for early- and late-stage aggregation of shattered graphene oxide nanoparticles
- 2019
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Ingår i: Colloids and Surfaces A. - : ELSEVIER. - 0927-7757 .- 1873-4359. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation as an essential mechanism impacting nanoparticle (NP) functionality, fate, and transport in the environment is currently modelled using population-balance equation (PBE) models which are computationally expensive when combined with other continuum-scale reactive transport models. We propose a new simple mass-concentration-based, chain-reaction modelling (CRM) framework to alleviate computational expenses of PBE and potentially to facilitate combination with other fate, transport, and reaction models. Model performance is compared with analytical PBE solution and a standard numerical PBE technique (fixed pivot, FP) by fitting against experimental data (i.e., hydrodynamic diameter and derived count rate of dynamic light scattering used as a representative of mass concentration) for early- and late-stage, aggregation of shattered graphene oxide (SGO) NP across a broad range of solution chemistries. In general, the CRM approach demonstrates a better match with the experimental data with a mean Nash-Sutcliffe model efficiency (NSE) coefficient of 0.345 than the FP model with a mean NSE of 0.29. Comparing model parameters (aggregation rate constant and fractal dimension) obtained from fitting CRM and FP to the experimental data, similar trends or ranges are obtained between the two approaches. Computationally, the modified CRM is an order-of-magnitude faster than the FP technique, suggesting that it can be a promising modelling framework for efficient and accurate modelling of NP aggregation. However, in the scope of this study, reaction rate coefficients of the CRM have been linked to collision frequencies based on simplified and empirical relationships which need improvement in future studies.
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| 5. |
- Bayati, Solmaz, et al.
(författare)
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Complexes of PEO-PPO-PEO triblock copolymer P123 and bile salt sodium glycodeoxycholate in aqueous solution : A small angle X-ray and neutron scattering investigation
- 2016
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 504, s. 426-436
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Tidskriftsartikel (refereegranskat)abstract
- Small angle X-ray (SAXS) and neutron scattering techniques were combined to study mixed complexes formed between micelles of the nonionic amphiphilic PEO-PPO-PEO copolymer (P123) and the anionic bile salt (NaGDC) in aqueous solution. The purpose was to investigate the structural parameters of the charged complexes, such as size and internal structure, as well as their interparticle interactions in aqueous solution. The overall aim of this work was to gain understanding of how thermoresponsive PEO-PPO-PEO block copolymers interact with bile salts in order to make predictions as to whether they can be put forward as a new class of bile salt sequestrants in the treatment of bile-salt related diseases. The system was investigated at a constant P123 concentration of 1.74 mM and bile salt concentrations were varied up to a molar ratio [Formula presented] (MR) = 5.7. It was found that the NaGDC molecules preferentially associated to the PEO corona of the P123 micelle and due to their amphiphilic nature, close to the core/corona interface. Because of this association the micelles became charged causing their reciprocal interparticle repulsions in solution to increase. In parallel, the association caused a decrease in the core radius accompanied by dehydration, which in turn led to a decrease in total radius of the “P123 micelle-NaGDC” complexes. To elucidate the effect of the interactions on their diffusive motion, an interaction model based on a spherical particle with a hard-core interaction shell was employed using the fitted SAXS data. At higher molar ratios, the interparticle interaction was increasingly screened because of nonadsorbed bile salt in the surrounding solution. Meanwhile, a further decrease in total radial size of the P123 micelle-NaGDC complexes occurred due to a decrease in the aggregation number of P123 as the bile salt finally disintegrated the complexes. However, the micelles were found to be more stable and less prone to disintegration in D2O. This investigation demonstrated the importance of using small angle scattering techniques for studying intermolecular interactions in order to gain understanding of how natural surfactants influence the aggregation behavior of amphiphilic polymers.
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| 6. |
- Cao, Wen-Tao, et al.
(författare)
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Facile preparation of robust and superhydrophobic materials for self-cleaning and oil/water separation
- 2017
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 529, s. 18-25
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Tidskriftsartikel (refereegranskat)abstract
- Superhydrophobic coatings have broad applications owing to their excellent water-resisting and self-cleaning properties. In this study, we have successfully fabricated coated meshes with robust and superhydrophobic surface (i.e., water-repellent magnesium stearate powders on substrates made of phenol-formaldehyde resin). These coated meshes showed superhydrophobicity with water contact angles exceeding 150 degrees and excellent self-cleaning property both in air and oil circumstances. Additionally, the superhydrophobic surfaces also exhibited prominent mechanical stability, thermal stability, corrosion resistance, and oil/water separation properties (> 92%). Therefore, it is believed that the facile fabrication presented in this study may provide a novel methodology and these robust and superhydrophobic coated meshes have potential applications in oil/water separation.
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| 7. |
- Chatzidaki, Maria D., et al.
(författare)
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Formulation and characterization of food-grade microemulsions as carriers of natural phenolic antioxidants
- 2015
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 483, s. 130-136
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Tidskriftsartikel (refereegranskat)abstract
- Food-grade W/O microemulsions based on lecithin, caprylic/capric triglycerides, isopropyl myristate, alcohols and water were formulated and structurally characterized to be used as potential carriers of natural food antioxidants. Different well-known food antioxidants including gallic acid, p-hydroxybenzoic acid, protocatechuic acid and tyrosol were successfully encapsulated in the aqueous cores of the microemulsions. A pseudo-ternary phase diagram was constructed to determine the extent of the monophasic area that corresponds to an inverted type microemulsion. Apparent hydrodynamic diameter measurements of empty and loaded microemulsions were performed using dynamic light scattering (DLS) and swollen micelles with diameters smaller than 10 nm were detected. Interfacial properties of the microemulsions were studied by electron paramagnetic resonance (EPR) spectroscopy employing the nitroxide spin probe 5-doxylstearic acid (5-DSA). A small increase in spin probe mobility upon addition of the antioxidants was observed; whereas the rigidity of the surfactants was not affected. Cryogenic transmission electron microscopy (Cryo-TEM) indicated the existence of entangled thread-like reversed micelles. Finally, the investigated phenolics were assessed and compared for their radical scavenging activity using an EPR approach based on free radicals. The encapsulated gallic acid showed the highest antioxidant activity (0.93 mM trolox equivalents) as compared to other antioxidants assessed within the frame of this study.
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| 8. |
- Conley, Gaurasundar M., et al.
(författare)
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Superresolution microscopy of the volume phase transition of pNIPAM microgels
- 2016
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 499, s. 18-23
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchical polymer structures such as pNIPAM microgels have been extensively studied for their ability to undergo structural and physical transformations that can be controlled by external stimuli such as temperature, pH or solvent composition. However, a direct three-dimensional visualization of individual particles in-situ has so far been hindered by insufficient resolution, with optical microscopy, or contrast, with electron microscopy. In recent years superresolution microscopy techniques have emerged that can provide nanoscopic optical resolution. Here we report on the in-situ superresolution microscopy of dye-labelled submicron sized pNIPAM microgels revealing the internal density profile during swelling and collapse of individual particles. Using direct STochastic Optical Reconstruction Microscopy (dSTORM) we demonstrate a lateral optical resolution of 30 nm and an axial resolution of 60 nm.
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| 9. |
- de Escobar, Cícero Coelho, et al.
(författare)
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Molecularly imprinted TiO2 photocatalysts for degradation of diclofenac in water
- 2018
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 538, s. 729-738
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Tidskriftsartikel (refereegranskat)abstract
- In order to improve the selectivity in photocatalytic process, molecularly imprinted photocatalysts containing a low loading of TiO2 (from 6.6 to 16.6% of total mass) were prepared for photocatalytic degradation of an organic pollutant, diclofenac (DIC). The photocatalytic component TiO2 (P25), with and without being doped with Cu2O, was embedded in diclofenac-imprinted polymers. The molecularly imprinted polymers (MIPs) and the composite photocatalysts exhibited a superior specific target recognition for selective degradation of DIC over non-target reference molecules, fluoxetine (FLU) and paracetamol (PARA). In contrast to the non-selective commercial sample of TiO2, the average value of selectivity of the imprinted catalysts for photocatalytic degradation of DIC was estimated to be 2.8, which suggests that the specific binding sites created by the molecular imprinting are essential for gaining high catalytic selectivity and efficiency. After 6 cycles of testing under UV-light, the imprinted catalysts maintained almost the same efficiency for photo degradation of DIC. In addition, the morphology and the structure of the imprinted catalysts remained after repeated uses. The results suggest that it is feasible to use MIPs to control the selectivity of photocatalytic degradation of organic pollutants.
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| 10. |
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