| 1. |
- Kehoe, Laura, et al.
(author)
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Make EU trade with Brazil sustainable
- 2019
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Journal article (other academic/artistic)
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| 2. |
- Abitbol, Tiffany, et al.
(author)
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Nanocellulose-Based Hybrid Materials for UV Blocking and Mechanically Robust Barriers
- 2020
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In: ACS Applied Bio Materials. - : American Chemical Society (ACS). - 2576-6422. ; 3:4, s. 2245-2254
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Journal article (peer-reviewed)abstract
- Nanocellulose (NC)-based hybrid coatings and films containing CeO2 and SiO2 nanoparticles (NPs) to impart UV screening and hardness properties, respectively, were prepared by solvent casting. The NC film-forming component (75 wt % of the overall solids) was composed entirely of cellulose nanocrystals (CNCs) or of CNCs combined with cellulose nanofibrils (CNFs). Zeta potential measurements indicated that the four NP types (CNC, CNF, CeO2, and SiO2) were stably dispersed in water and negatively charged at pH values between 6 and 9. The combination of NPs within this pH range ensured uniform formulations and homogeneous coatings and films, which blocked UV light, the extent of which depended on film thickness and CeO2 NP content, while maintaining good transparency in the visible spectrum (∼80%). The addition of a low amount of CNFs (1%) reduced the film hardness, but this effect was compensated by the addition of SiO2 NPs. Chiral nematic self-assembly was observed in the mixed NC film; however, this ordering was disrupted by the addition of the oxide NPs. The roughness of the hybrid coatings was reduced by the inclusion of oxide NPs into the NC matrix perhaps because the spherical oxide NPs were able to pack into the spaces between cellulose fibrils. We envision these hybrid coatings and films in barrier applications, photovoltaics, cosmetic formulations, such as sunscreens, and for the care and maintenance of wood and glass surfaces, or other surfaces that require a smooth, hard, and transparent finish and protection from UV damage.
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| 3. |
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| 4. |
- Álvarez-Asencio, Ruben, et al.
(author)
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Molecular-scale shear response of the organic semiconductor β -DBDCS (100) surface
- 2017
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 96:11
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Journal article (peer-reviewed)abstract
- In this work we present friction-force microscopy (FFM) lattice-resolved images acquired on the (100) facet of the semiconductor organic oligomer (2Z,2′Z)-3,3′-(1,4-phenylene)bis(2-(4-butoxyphenyl)acrylonitrile) (β-DBDCS) crystal in water at room temperature. Stick-slip contrast, lateral contact stiffness, and friction forces are found to depend strongly on the sliding direction due to the anisotropic packing of the molecular chains forming the crystal surface along the [010] and [001] directions. The anisotropy also causes the maximum value of the normal force applicable before wearing to increase by a factor of 3 when the scan is performed along the [001] direction on the (100) face. Altogether, our results contribute to achieving a better understanding of the molecular origin of friction anisotropy on soft crystalline surfaces, which has been often hypothesized but rarely investigated in the literature.
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| 5. |
- Álvarez-Asencio, Rubén, et al.
(author)
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Nanomechanical properties of human skin and introduction of a novel hair indenter
- 2016
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In: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier. - 1751-6161 .- 1878-0180. ; 54, s. 185-193
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Journal article (peer-reviewed)abstract
- The mechanical resistance of the stratum corneum, the outermost layer of skin, to deformation has been evaluated at different length scales using Atomic Force Microscopy. Nanomechanical surface mapping was first conducted using a sharp silicon tip and revealed that Young’s modulus of the stratum corneum varied over the surface with a mean value of about 0.4 GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4 μN). The latter effect was further demonstrated using nanomechanical imaging in which the obtained depth profiles clearly illustrate the effects of increased normal force on the elastic/plastic surface deformation. Force measurements utilizing the single hair fiber probe supported the nanoindentation results of the stratum corneum being highly elastic at the nanoscale, but revealed that the lateral scale of the deformation determines the effective elastic modulus.This result resolves the fact that the reported values in the literature vary greatly and will help to understand the biophysics of the interaction of razor cut hairs that curl back during growth and interact with the skin.
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| 6. |
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| 7. |
- Álvarez Asencio, Rubén, et al.
(author)
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Nanotribology : Tribotronics, ionic liquids and control of surface interactions
- 2013
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In: 5th World Tribology Congress, WTC 2013. ; , s. 3106-3108
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Conference paper (peer-reviewed)abstract
- The interfacial ordering of Ionic liquids leads to interesting nanotribological properties as revealed by colloid probe studies. The first of these is the clear correlation between the number of ion pairs trapped in the tribological contact and the friction coefficient displayed. The second is the fact that the surface electrical potential can be used to control the composition of the boundary layer and thus tune the friction. Thirdly, the interfacial ordering appears to significantly affect the fluid dynamics over large distances.
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| 8. |
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| 9. |
- Álvarez-Asencio, Rubén, 1978-
(author)
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Nanotribology, Surface Interactions and Characterization : An AFM Study
- 2014
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Doctoral thesis (other academic/artistic)abstract
- When two surfaces achieve contact, then contact phenomena such as adhesion, friction and wear can occur, which are of great interest in many disciplines, including physics, physical chemistry, material chemistry, and life and health sciences. These phenomena are largely determined by the nature and magnitude of the surface forces such as van der Waals, capillary and hydration forces. Moreover these forces are length-dependent, and therefore when the system scales down, their contribution scales up, dominating the interaction between the surfaces.A goal of my PhD work was to investigate fundamental contact phenomena in terms of the surface forces that regulate their properties. The primary tool applied in this PhD thesis work has been the atomic force microscopy (AFM), which (with all of its sub-techniques) offers the possibility to study such forces with high resolution virtually between all types of materials and intervening media. Therefore, in this work it was possible to study the long ranged interactions presented in air between different industrially relevant materials and how these interactions are shielded when the systems are immersed in an ionic liquid.Also investigated was the influence of microstructure on the tribological properties of metal alloys, where their good tribological properties were related with the vanadium and nitrogen contents for a FeCrVN tool alloy and with the chromium content for a biomedical CoCrMo alloy. Moreover, the effect of the intervening media can significantly affect the surface properties, and when the biomedical CoCrMo alloy was immersed in phosphate buffer saline solution (PBS), repulsive hydration forces decreased the friction coefficient and contact adhesion. On the other hand, with the immersion of the FeCrVN tool alloy in the NaCl solution, small particles displaying low adhesion were generated in specific regions on the surface with low chromium content. These particles are assumed to be related to a prepitting corrosion event in the tool alloy.The mechanical properties of stratum corneum (SC), which is the outermost layer of the skin, were also studied in this work. The SC presents a highly elastic, but stiff surface where the mechanical properties depend on the nanoscale. A novel probe has been designed with a single hair fibre in order to understand how the skin deforms locally in response to the interaction with such a fibre probe. This study revealed that is mostly the lateral scale of the deformation which determines the mechanical properties of the SC.Finally, important achievements in this work are the developments of two new techniques - tribological property mapping and the Hybrid method for torsional spring constant evaluation. Tribological property mapping is an AFM technique that provides friction coefficient and contact adhesion maps with information attributed to the surface microstructure. The Hybrid method is an approach that was originally required to obtain the torsional spring constants for rigid beam shaped cantilevers, which could not be previously determined from their power torsional thermal spectra (conventional method). However, the applicability is shown to be general and this simple method can be used to obtain torsional spring constants for any type of beam shape cantilever.
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| 10. |
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| 11. |
- Álvarez-Asencio, Ruben, et al.
(author)
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Note : Determination of torsional spring constant of atomic force microscopy cantilevers: Combining normal spring constant and classical beam theory
- 2013
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:9
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Journal article (peer-reviewed)abstract
- A technique has been developed for the calculation of torsional spring constants for AFM cantilevers based on the combination of the normal spring constant and plate/beam theory. It is easy to apply and allow the determination of torsional constants for stiff cantilevers where the thermal power spectrum is difficult to obtain due to the high resonance frequency and low signal/noise ratio. The applicability is shown to be general and this simple approach can thus be used to obtain torsional constants for any beam shaped cantilever.
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| 12. |
- Alvarez-Asencio, Ruben, et al.
(author)
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Role of microstructure on corrosion initiation of an experimental tool alloy : A Quantitative Nanomechanical Property Mapping study
- 2014
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In: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 89, s. 236-241
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Journal article (peer-reviewed)abstract
- The adhesion properties of a FeCrVN experimental tool alloy immersed in pure water and sodium chloride solution have been studied by Quantitative Nanomechanical Property Mapping to understand the influence of microstructure on corrosion initiation of this alloy. The approach used here allows early observation and identification of pre-pitting events that may lead to passivity breakdown of the alloy. Adhesion provides a good distinction between the different regions and we ascribe this to their vanadium and nitrogen contents. Finally, the prepitting is characterized by generation of small particles in specific regions of the surface with low chromium content.
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| 13. |
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| 14. |
- Alvarez-Asencio, Ruben, et al.
(author)
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Solventless synthesis of cerium oxide nanoparticles and their application in UV protective clear coatings
- 2020
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:25, s. 14818-14825
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Journal article (peer-reviewed)abstract
- Colloidal dispersions of cerium oxide nanoparticles are of importance for numerous applications including as catalysts, chemical mechanical polishing agents and additives for UV protective and anticorrosion coatings. Here, concentrated oleate-coated cerium oxide nanoparticles (CeO2 NPs) with a uniform size have been produced by solventless thermolysis of cerium-oleate powder under low pressure at 320 °C and subsequently dispersed in hexane. Unlike any previously reported colloidal synthesis process for ceria nanoparticles, this process does not involve any toxic high boiling point organic solvent that requires subsequent removal at high cost. Although the process is very simple, highly concentrated cerium oxide nanoparticles with more than 17 wt% solid content and 70% of the theoretical yield can be easily obtained. Moreover, the size, shape and crystallinity of cerium oxide nanoparticles can be tailored by changing the thermal decomposition temperature and reaction time. Moreover, the new synthesis route developed in this study allows the synthesis of clean and dispersible ceria nanoparticles at a relatively low cost in a single step. The prepared ceria nanoparticles have an excellent UV absorption property and remain transparent to visible light, thus having the potential to replace potentially hazardous organic compounds in UV absorbing clear coatings. As a proof of concept, the prepared dispersions of cerium oxide nanoparticles in hexane were formulated into a solvent borne binder base to develop clear UV protecting coatings for light sensitive substrates. The general synthesis strategy presented in this study is generally applicable for the low-cost production of a concentrated dispersion of metal oxide nanoparticles with minimal environmental impact.
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| 15. |
- Alvarez-Asencio, Rubén, et al.
(author)
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Tribological Properties Mapping : Local Variation in Friction Coefficient and Adhesion
- 2013
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In: Tribology letters. - : Springer Science and Business Media LLC. - 1023-8883 .- 1573-2711. ; 50:3, s. 387-395
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Journal article (peer-reviewed)abstract
- Tribological properties mapping is a new technique that extracts friction coefficient and adhesion maps obtained from lateral atomic force microscope (LAFM) images. By imaging the surface systematically as a function of load, a series of images can be tiled, and pixelwise fitted to a modified Amontons' Law to obtain friction coefficient and adhesion maps. This removes the ambiguity of friction contrast in LAFM imaging which can be a function of the load used for imaging. In ambient laboratory, air and tetradecane, a sample of Vancron(A (R))40, commercial powder metallurgical tool alloy containing nitrogen, have been scanned using a standard silicon cantilever in order to obtain tribological data. The tribological properties mapping provides unique information regarding the heterogeneous alloy microstructure as well as shedding light on the tribological behavior of the alloy.
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| 16. |
- Asencio, Rubén Alvarez, et al.
(author)
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Ionic Liquid Nanotribology : Stiction Suppression and Surface Induced Shear Thinning
- 2012
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:26, s. 9967-9976
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Journal article (peer-reviewed)abstract
- The friction and adhesion between pairs of materials (silica, alumina, and polytetrafluoroethylene) have been studied and interpreted in terms of the long-ranged interactions present. In ambient laboratory air, the interactions are dominated by van der Waals attraction and strong adhesion leading to significant frictional forces. In the presence of the ionic liquid (IL) ethylammonium nitrate (EAN) the van der Waals interaction is suppressed and the attractive/adhesive interactions which lead to "stiction" are removed, resulting in an at least a 10-fold reduction in the friction force at large applied loads. The friction coefficient for each system was determined; coefficients obtained in air were significantly larger than those obtained in the presence of EAN (which ranged between 0.1 and 0.25), and variation in the friction coefficients between systems was correlated with changes in surface roughness. As the viscosity of ILs can be relatively high, which has implications for the lubricating properties, the hydrodynamic forces between the surfaces have therefore also been studied. The linear increase in repulsive force with speed, expected from hydrodynamic interactions, is clearly observed, and these forces further inhibit the potential for stiction. Remarkably, the viscosity extracted from the data is dramatically reduced compared to the bulk value, indicative of a surface ordering effect which significantly reduces viscous losses.
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| 17. |
- Bergquist, Helen, et al.
(author)
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Disruption of Higher Order DNA Structures in Friedreich's Ataxia (GAA)(n) Repeats by PNA or LNA Targeting
- 2016
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In: PLOS ONE. - : PLOS. - 1932-6203. ; 11:11
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Journal article (peer-reviewed)abstract
- Expansion of (GAA)(n) repeats in the first intron of the Frataxin gene is associated with reduced mRNA and protein levels and the development of Friedreich's ataxia. (GAA)(n) expansions form non-canonical structures, including intramolecular triplex (H-DNA), and Rloops and are associated with epigenetic modifications. With the aim of interfering with higher order H-DNA (like) DNA structures within pathological (GAA)(n) expansions, we examined sequence-specific interaction of peptide nucleic acid (PNA) with (GAA)(n) repeats of different lengths (short: n= 9, medium: n= 75 or long: n= 115) by chemical probing of triple helical and single stranded regions. We found that a triplex structure (H-DNA) forms at GAA repeats of different lengths; however, single stranded regions were not detected within the medium size pathological repeat, suggesting the presence of a more complex structure. Furthermore, (GAA) 4-PNA binding of the repeat abolished all detectable triplex DNA structures, whereas (CTT) 5-PNA did not. We present evidence that (GAA) 4-PNA can invade the DNA at the repeat region by binding the DNA CTT strand, thereby preventing non-canonical-DNA formation, and that triplex invasion complexes by (CTT) 5-PNA form at the GAA repeats. Locked nucleic acid (LNA) oligonucleotides also inhibited triplex formation at GAA repeat expansions, and atomic force microscopy analysis showed significant relaxation of plasmid morphology in the presence of GAA-LNA. Thus, by inhibiting disease related higher order DNA structures in the Frataxin gene, such PNA and LNA oligomers may have potential for discovery of drugs aiming at recovering Frataxin expression.
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| 18. |
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| 19. |
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| 20. |
- Besharat, Zahra, et al.
(author)
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In-situ evaluation of dye adsorption on TiO2 using QCM
- 2017
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In: EPJ Photovoltaics. - : EDP Sciences. - 2105-0716. ; 8
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Journal article (peer-reviewed)abstract
- We measured the adsorption characteristics of two organic dyes; triphenylamine-cyanoacrylic acid (TPA-C) and phenoxazine (MP13), on TiO2, directly in a solution based on quartz crystal microbalance (QCM). Monitoring the adsorbed amount as a function of dye concentration and during rinsing allows determination of the equilibrium constant and distinction between chemisorbed and physisorbed dye. The measured equilibrium constants are 0.8 mM(-1) for TPA-C and 2.4 mM(-1) for MP13. X-ray photoelectron spectroscopy was used to compare dried chemisorbed layers of TPA-C prepared in solution with TPA-C layers prepared via vacuum sublimation; the two preparation methods render similar spectra except a small contribution of water residues (OH) on the solution prepared samples. Quantitative Nanomechanical Mapping Atomic Force Microscopy (QNM-AFM) shows that physisorbed TPA-C layers are easily removed by scanning the tip across the surface. Although not obvious in height images, adhesion images clearly demonstrate removal of the dye.
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| 21. |
- Ghalgaoui, Ahmed, et al.
(author)
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Monolayer Study by VSFS : In Situ Response to Compression and Shear in a Contact
- 2014
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:11, s. 3075-3085
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Journal article (peer-reviewed)abstract
- Self-assembled octadecyltrichlorosilane ((OTS), CH3(CH2)(17)SiCl3) layers on hydroxyl-terminated silicon oxide (SiO2) were prepared. The monolayers were characterized with atomic force microscopy (AFM) and contact angle measurements; their conformation was studied before, during, and after contact with a polymer (either PDMS or PTFE) surface using the vibrational sum frequency spectroscopy (VSFS) technique. During contact, the effect of pressure was studied for both polymer surfaces, but in the case of PTFE, the effect of shear rate on the contact was simultaneously studied. The VSFS response of the monolayers with pressure was almost entirely due to changes in the real area of contact with the polymer and therefore the Fresnel factors, whereas sliding caused disorder in the previously all-trans monolayer, as evidenced by a significant increase in the population of gauche defects.
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| 22. |
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| 23. |
- Karlsson, Mikael, 1978, et al.
(author)
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Characterization of paint formulated using secondary TiO2 pigments recovered from waste paint
- 2019
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In: JCT Research. - : Springer Science and Business Media LLC. - 1547-0091 .- 2168-8028 .- 1935-3804. ; 16:2, s. 607-614
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Journal article (peer-reviewed)abstract
- The paint industry is continuously striving to reduce its environmental impact, especially when it comes to the major virgin white pigment, titanium dioxide (TiO2). In this work, recycled TiO2 pigment was used in a paint formulation as a replacement for pigment made from virgin raw materials. The paint was evaluated based on pH, Stormer and ICI viscosities, gloss, hiding power, and color characteristics. The paint films were also characterized by LVSEM–EDS, AFM, and profilometry. The most significant difference between a paint based on recycled pigments and a paint based on virgin pigments was the agglomeration of pigment particles which gave a reduction in gloss and a rougher surface of the dried paint film based on recycled pigment, and it could be concluded that the recycled pigment could not be used without accepting a small decrease in paint quality. This points toward two main directions: (1) the use of recycled pigment in applications with less demand on surface finish and gloss, such as ceiling paints, and (2) that further work on formulation should be carried out with the recycled pigment as for any other new pigment introduced in a paint formulation to optimize its performance. © 2018, The Author(s).
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| 24. |
- Naranjo, Teresa, et al.
(author)
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Hydrogen-bonded host–guest systems are stable in ionic liquids
- 2020
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In: Scientific Reports. - : Nature Research. - 2045-2322. ; 10
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Journal article (peer-reviewed)abstract
- We show that H-bonded host–guest systems associate in ionic liquids (ILs), pure salts with melting point below room temperature, in which dipole–dipole electrostatic interactions should be negligible in comparison with dipole-charge interactions. Binding constants (Ka) obtained from titrations of four H-bonded host–guest systems in two organic solvents and two ionic liquids yield smaller yet comparable Ka values in ionic liquids than in organic solvents. We also detect the association event using force spectroscopy, which confirms that the binding is not solely due to (de)solvation processes. Our results indicate that classic H-bonded host–guest supramolecular chemistry takes place in ILs. This implies that strong H-bonds are only moderately affected by surroundings composed entirely of charges, which can be interpreted as an indication that the balance of Coulombic to covalent forces in strong H-bonds is not tipped towards the former. © 2020, The Author(s).
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| 25. |
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| 26. |
- Nyström, Lina, et al.
(author)
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Electrostatic Swelling Transitions in Surface-Bound Microgels
- 2016
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 8:40, s. 27129-27139
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Journal article (peer-reviewed)abstract
- Herein, electrostatic swelling transitions of poly (ethyl acrylate-co-methacrylic acid) microgels covalently bound to silica surfaces are investigated. Confined at a solid surface, microgel swelling is anisotropically hindered and the structure is flattened to an extent dictated by pH and microgel composition. Microgel deformation under applied load is also shown to depend on microgel charge density, with the highest deformation observed at intermediate charge densities. Two modes of microgel deformation under load were observed, one elastic and one viscoelastic, related to polymer strand deformation and displacement of trapped water, respectively. Results on polymer strand dynamics reveal that the microgels are highly dynamic, as the number of strand-tip interaction points increases 4-fold during a 10 s contact time. Furthermore, finite element modeling captures these effects qualitatively and shows that stress propagation in the microgel network decays locally at the rim of contact with a solid interface or close to the tip probe. Taken together, the results demonstrate a delicate interplay between the surface and microgel which determines the structure and nanomechanical properties of the latter and needs to be controlled in applications of systems such as pH-responsive surface coatings in biomaterials.
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| 27. |
- Nyström, Lina, et al.
(author)
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Factors affecting peptide interactions with surface-bound microgels
- 2016
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 17:2, s. 669-678
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Journal article (peer-reviewed)abstract
- Effects of electrostatics and peptide size on peptide interactions with surface-bound microgels were investigated with ellipsometry, confocal microscopy, and atomic force microscopy (AFM). Results show that binding of cationic poly-l-lysine (pLys) to anionic, covalently immobilized, poly(ethyl acrylate-co-methacrylic acid) microgels increased with increasing peptide net charge and microgel charge density. Furthermore, peptide release was facilitated by decreasing either microgel or peptide charge density. Analogously, increasing ionic strength facilitated peptide release for short peptides. As a result of peptide binding, the surface-bound microgels displayed pronounced deswelling and increased mechanical rigidity, the latter quantified by quantitative nanomechanical mapping. While short pLys was found to penetrate the entire microgel network and to result in almost complete charge neutralization, larger peptides were partially excluded from the microgel network, forming an outer peptide layer on the microgels. As a result of this difference, microgel flattening was more influenced by the lower Mw peptide than the higher. Peptide-induced deswelling was found to be lower for higher Mw pLys, the latter effect not observed for the corresponding microgels in the dispersed state. While the effects of electrostatics on peptide loading and release were similar to those observed for dispersed microgels, there were thus considerable effects of the underlying surface on peptide-induced microgel deswelling, which need to be considered in the design of surface-bound microgels as carriers of peptide loads, for example, in drug delivery or in functionalized biomaterials.
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- Safdari, Majid, et al.
(author)
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Investigation of cobalt redox mediators and effects of TiO2 film topology in dye-sensitized solar cells
- 2016
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:61, s. 56580-56588
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Journal article (peer-reviewed)abstract
- One-electron outer-sphere redox couples, such as cobalt metal-organic complexes, represent an interesting alternative as redox mediators in dye-sensitized solar cells since they show weak visible light absorption and available redox potentials may lead to higher open circuit voltage values. Here, we have studied the effect of using different substituents on bipyridyl and phenanthroline ligands in cobalt redox shuttles, giving the following complexes: Co[tris(4,4'-dimethoxy-2,2'-bipyridine)(PF6)(2)], Co[tris(4,4'-dichloro-2,2'-bipyridine)(PF6)(2)] and Co[tris(4,7-dichloro-1,10-phenanthroline)(CF3SO3)(2)], displaying a range of CoII/CoIII redox potentials from +0.37 to +0.79 V vs. NHE. The regeneration kinetics of the organic dye D35 was found to depend systematically on the redox mediator potential, which was explained using Marcus theory. The mass transport of cobalt mediators in dye-sensitized solar cells is highly dependent on the porosity, effective surface area and roughness of the mesoporous TiO2 films. Therefore, films with different TiO2 pore sizes were prepared and investigated to gain an insight into the topological effects of TiO2 film preparation in order to obtain optimum solar cell performance.
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| 32. |
- Shimizu, Michiko, et al.
(author)
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Preparation and characterization of cellulose acetate membranes with TEMPO-oxidized cellulose nanofibrils containing alkyl ammonium carboxylates
- 2020
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In: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 27:3, s. 1357-1365
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Journal article (peer-reviewed)abstract
- Cellulose acetate (CA) membranes have been widely used for water purification owing to several advantages, e.g., biocompatibility and low fouling rate. However, they suffer from a lower water flux compared to the other polymeric membranes. Therefore, in this study, CA membranes were blended with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (T-CNFs) containing quaternary alkyl ammonium (QA) carboxylates to improve their water flux. When increasing the alkyl chain length of the QAs, the positron lifetime and intensity of the CA membranes increased and decreased respectively, as revealed via positron annihilation lifetime spectroscopy. This indicated that the CA membranes had larger and fewer pores when using the T-CNFs containing QAs with longer alkyl chains. The pure water flux of these membranes also increased with the alkyl chain lengths of QAs although their rejection rate (Rj) decreased accordingly. However, they revealed a potentiality to be used as ultrafiltration membranes, allowing a 99% Rj for albumin. The tensile strength, strain to failure, and work of fracture of the CA membranes increased when blended with T-CNFs. Force measurements using the AFM colloidal probe technique showed that the adhesion between the membrane constituents depends on their surface chemistry. This indicated that the structural differences observed among the blended membranes may be due to the affinity between CA and T-CNF containing QAs with different alkyl chain lengths. This study demonstrates that the properties of CA membranes can be tailored by the addition of T-CNFs with different surface chemistries.
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