The Experts below are selected from a list of 16836 Experts worldwide ranked by ideXlab platform
J.e. Castanheiro - One of the best experts on this subject based on the ideXlab platform.
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Methoxylation of α-pinene over poly(vinyl alcohol) containing sulfonic acid groups
Chemical Engineering Journal, 2008Co-Authors: D.s. Pito, Isabel Fonseca, Ana M. Ramos, Joaquim Vital, J.e. CastanheiroAbstract:Abstract The methoxylation of α-pinene was studied using poly(vinyl alcohol) (PVA) containing sulfonic acid groups as catalysts. These groups were introduced by the direct reaction between –OH groups of PVA and sulfosuccinic acid (SSA). Poly(vinyl alcohol) catalysts were prepared using sulfosuccinic acid by varying the amount of SSA (5–40 mol%). It was observed that the amount of acid sites increases with amount of SSA. It was also observed that the diffusivity of α-pinene through the Polymeric catalysts decreases with the increase of Crosslinking degree. The conversion of α-pinene increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5% to 40%. However, when the Crosslinking degree increases from 20% to 40%, the conversion of α-pinene increases only slightly. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained over poly(vinyl alcohol) with sulfonic acid groups. Catalytic stability of the PVA_SSA20 was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. Since the concentration profiles of the reagent and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reagents and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.
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Esterification of acetic acid by isoamylic alcohol over catalytic membranes of poly(vinyl alcohol) containing sulfonic acid groups
Applied Catalysis A: General, 2006Co-Authors: J.e. Castanheiro, Ana M. Ramos, Isabel Fonseca, Joaquim VitalAbstract:Abstract In this study, poly(vinyl alcohol) (PVA) membranes crosslinked with sulfosuccinic acid (SSA) were used for the esterification of acetic acid by isoamylic alcohol. In order to study the effects of the Crosslinking degree and, simultaneously, the amount of sulfonic groups, different membranes were prepared with SSA:PVA ratios in the range of 5–40 mol%. Aiming at to eliminate the dependence between the amount of acid sites and the Crosslinking degree, were also prepared PVA membranes in which the –SO 3 H groups were introduced by anchoring 5-sulfosalisilic acid (SA) on the PVA chains. The conversion of isoamylic alcohol increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5 to 20%. However, when Crosslinking degree increases from 20 to 40%, the conversion of isoamylic alcohol increases only slightly, probably due to the increase of molecules mobility restrictions, in the PVA matrix. In the case of the PVA membranes where the –SO 3 H groups were introduced by esterifying 5-sulfosalisilic acid on the PVA –OH groups, it was observed that membrane activity increases with the Polymer Crosslinking. It was also observed an increase of the activity of these membranes with the amount of –SO 3 H groups in the Polymeric matrix. Catalytic stability of PVA membranes, prepared with SSA and SA, was evaluated by performing consecutive batch runs with the same membrane being observed, after the third run, a trend to stabilization of catalytic activity. An experiment with a membrane reactor operating under sweep gas pervaporation conditions is described.
Joaquim Vital - One of the best experts on this subject based on the ideXlab platform.
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Methoxylation of α-pinene over poly(vinyl alcohol) containing sulfonic acid groups
Chemical Engineering Journal, 2008Co-Authors: D.s. Pito, Isabel Fonseca, Ana M. Ramos, Joaquim Vital, J.e. CastanheiroAbstract:Abstract The methoxylation of α-pinene was studied using poly(vinyl alcohol) (PVA) containing sulfonic acid groups as catalysts. These groups were introduced by the direct reaction between –OH groups of PVA and sulfosuccinic acid (SSA). Poly(vinyl alcohol) catalysts were prepared using sulfosuccinic acid by varying the amount of SSA (5–40 mol%). It was observed that the amount of acid sites increases with amount of SSA. It was also observed that the diffusivity of α-pinene through the Polymeric catalysts decreases with the increase of Crosslinking degree. The conversion of α-pinene increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5% to 40%. However, when the Crosslinking degree increases from 20% to 40%, the conversion of α-pinene increases only slightly. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained over poly(vinyl alcohol) with sulfonic acid groups. Catalytic stability of the PVA_SSA20 was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. Since the concentration profiles of the reagent and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reagents and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.
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Esterification of acetic acid by isoamylic alcohol over catalytic membranes of poly(vinyl alcohol) containing sulfonic acid groups
Applied Catalysis A: General, 2006Co-Authors: J.e. Castanheiro, Ana M. Ramos, Isabel Fonseca, Joaquim VitalAbstract:Abstract In this study, poly(vinyl alcohol) (PVA) membranes crosslinked with sulfosuccinic acid (SSA) were used for the esterification of acetic acid by isoamylic alcohol. In order to study the effects of the Crosslinking degree and, simultaneously, the amount of sulfonic groups, different membranes were prepared with SSA:PVA ratios in the range of 5–40 mol%. Aiming at to eliminate the dependence between the amount of acid sites and the Crosslinking degree, were also prepared PVA membranes in which the –SO 3 H groups were introduced by anchoring 5-sulfosalisilic acid (SA) on the PVA chains. The conversion of isoamylic alcohol increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5 to 20%. However, when Crosslinking degree increases from 20 to 40%, the conversion of isoamylic alcohol increases only slightly, probably due to the increase of molecules mobility restrictions, in the PVA matrix. In the case of the PVA membranes where the –SO 3 H groups were introduced by esterifying 5-sulfosalisilic acid on the PVA –OH groups, it was observed that membrane activity increases with the Polymer Crosslinking. It was also observed an increase of the activity of these membranes with the amount of –SO 3 H groups in the Polymeric matrix. Catalytic stability of PVA membranes, prepared with SSA and SA, was evaluated by performing consecutive batch runs with the same membrane being observed, after the third run, a trend to stabilization of catalytic activity. An experiment with a membrane reactor operating under sweep gas pervaporation conditions is described.
Bing Cao - One of the best experts on this subject based on the ideXlab platform.
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Tailoring the molecular structure of crosslinked Polymers for pervaporation desalination.
Nature communications, 2020Co-Authors: Yun Long Xue, Jin Huang, Cher Hon Lau, Bing CaoAbstract:Polymer Crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. Here in this work we deployed molecular dynamics simulations to optimise the selection of Crosslinking compounds that overcome this trade-off relationship. We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m−2 h−1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. Key to achieving this state-of-the-art desalination performance is the spray coating of 0.73 μm thick crosslinked dense, hydrophilic Polymers on to electrospun nanofiber mats. The desalination performances of our Polymer nanocomposites are harnessed here in this work to produce freshwater from brackish water, seawater and brine solutions, addressing the key environmental issue of freshwater scarcity. Polymer Crosslinking in desalination membranes adds stability on the cost of molecular transportation rates through the membrane. Here the authors tailor Crosslinking of desalination membranes to overcome the stability and transport trade-off, and demonstrate a pervaporation desalination thin-film composite membrane with high water flux.
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elucidating the impact of Polymer Crosslinking and fixed carrier on enhanced water transport during desalination using pervaporation membranes
Journal of Membrane Science, 2019Co-Authors: Yun Long Xue, Cher Hon Lau, Bing CaoAbstract:Abstract Crosslinking is a well-established technique to enhance chemical stability of Polymer membranes but at the expense of lower flux. We previously demonstrated that this trade-off between chemical stability and separation performance can be overcome through the judicious selection of a Crosslinking agent, 4-sulfophthalic acid (SPTA), which also functioned as a fixed carrier site. The mechanism underpinning this breakthrough remained unknown. Through molecular dynamic simulations and a series of complementary experiments, here we reveal that higher Crosslinking degree can increase local water concentration close to the sulfonic acid groups, and enhance both long-distance water-sulfonic acid-interactions and water molecule mobility. These underpinned the significant increase in water flux of crosslinked pervaporation membranes during desalination. These results show that the dependence of water diffusivity on water concentration is reduced with higher Crosslinking degree. More importantly, water diffusivity at the “dry membrane region” determined the overall water transport behaviour. These findings can potentially impact on the design of pervaporation membranes for production of potable water from brackish, sea and brine water.
Torsten Rossow - One of the best experts on this subject based on the ideXlab platform.
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single cell laden protease sensitive microniches for long term culture in 3d
Lab on a Chip, 2017Co-Authors: Torsten Rossow, Philipp S Lienemann, David J Mooney, Angelo S Mao, Queralt Vallmajomartin, Martin EhrbarAbstract:Single cell-laden three-dimensional (3D) microgels that can serve to mimic stem cell niches in vitro, and are therefore termed microniches, can be efficiently fabricated by droplet-based microfluidics. In this technique an aqueous Polymer solution along with a highly diluted cell solution is injected into a microfluidic device to create monodisperse pre-microgel droplets that are then solidified by a Polymer Crosslinking reaction to obtain monodisperse single cell-laden microniches. However, problems limiting this approach studying the fate of single cells include Poisson encapsulation statistics that result in mostly empty microniches, and cells egressing from the microniches during subsequent cell culture. Here, we present a strategy to bypass Poisson encapsulation statistics in synthetic microniches by selective Crosslinking of only cell-laden pre-microgel droplets. Furthermore, we show that we can position cells in the center of the microniches, and that even in protease-sensitive microniches this greatly reduces cell egress. Collectively, we present the development of a versatile protocol that allows for unprecedented efficiency in creation of synthetic protease-sensitive microniches for probing single stem cell fate in 3D.
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cell microencapsulation by droplet microfluidic templating
Macromolecular Chemistry and Physics, 2017Co-Authors: Torsten Rossow, Philipp S Lienemann, David J MooneyAbstract:Microgels are hydrogel particles with micro-scale dimensions in the range of 10–1000 µm. They have gained particular importance for cell microencapsulation, because they allow for highly specific creation of a myriad of discrete and miniaturized mimics of the three-dimensional natural extracellular matrix of tissues. This trend article highlights and critically reviews current droplet-based microfluidic approaches for the formation of such cell-laden microgels. It addresses the technical issues of particle formation, the most common Polymers used for microgel preparation, and the different types of Polymer Crosslinking. Furthermore, remaining technical challenges in the field are discussed and perspectives for further development and potential future applications are provided.
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Hybrid Polymer-Network Hydrogels with Tunable Mechanical Response.
Polymers, 2016Co-Authors: Sebastian Czarnecki, Torsten Rossow, Sebastian SeiffertAbstract:Hybrid Polymer-network gels built by both physical and covalent Polymer Crosslinking combine the advantages of both these Crosslinking types: they exhibit high mechanical strength along with excellent fracture toughness and extensibility. If these materials are extensively deformed, their physical crosslinks can break such that strain energy is dissipated and irreversible fracturing is restricted to high strain only. This mechanism of energy dissipation is determined by the kinetics and thermodynamics of the physical Crosslinking contribution. In this paper, we present a poly(ethylene glycol) (PEG) based material toolkit to control these contributions in a rational and custom fashion. We form well-defined covalent Polymer-network gels with regularly distributed additional supramolecular mechanical fuse links, whose strength of connectivity can be tuned without affecting the primary Polymer-network composition. This is possible because the supramolecular fuse links are based on terpyridine⁻metal complexation, such that the mere choice of the fuse-linking metal ion adjusts their kinetics and thermodynamics of complexation⁻decomplexation, which directly affects the mechanical properties of the hybrid gels. We use oscillatory shear rheology to demonstrate this rational control and enhancement of the mechanical properties of the hybrid gels. In addition, static light scattering reveals their highly regular and well-defined Polymer-network structures. As a result of both, the present approach provides an easy and reliable concept for preparing hybrid Polymer-network gels with rationally designed properties.
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hybrid microgels with thermo tunable elasticity for controllable cell confinement
Advanced Healthcare Materials, 2015Co-Authors: Sebastian Hackelbusch, Sebastian Seiffert, Torsten Rossow, Dirk Steinhilber, David A WeitzAbstract:Stimuli-responsive hydrogels are able to change their physical properties such as their elastic moduli in response to changes in their environment. If biocompatible Polymers are used to prepare such materials and if living cells are encapsulated within these networks, their switchability allows the cell‐ matrix interactions to be investigated with unprecedented consistency. In this paper, thermo-responsive macro- and microscopic hydrogels are presented based on azide-functionalized coPolymers of poly( N -(2-hydroxypropyl)methacrylamide) and poly(hydroxyethyl methacrylate) grafted with poly( N isopropylacrylamide) side chains. Crosslinking of these comb Polymers is realized by bio-orthogonal strain-promoted azide‐alkyne cycloaddition with cyclooctyne-functionalized poly(ethylene glycol). The resulting hybrid hydrogels exhibit thermo-tunable elasticity tailored by the Polymer chain length and grafting density. This bio-orthogonal Polymer Crosslinking strategy is combined with droplet-based microfl uidics to encapsulate living cells into stimuli-responsive microgels, proving them to be a suitable platform for future systematic stem-cell research.
Ana M. Ramos - One of the best experts on this subject based on the ideXlab platform.
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Methoxylation of α-pinene over poly(vinyl alcohol) containing sulfonic acid groups
Chemical Engineering Journal, 2008Co-Authors: D.s. Pito, Isabel Fonseca, Ana M. Ramos, Joaquim Vital, J.e. CastanheiroAbstract:Abstract The methoxylation of α-pinene was studied using poly(vinyl alcohol) (PVA) containing sulfonic acid groups as catalysts. These groups were introduced by the direct reaction between –OH groups of PVA and sulfosuccinic acid (SSA). Poly(vinyl alcohol) catalysts were prepared using sulfosuccinic acid by varying the amount of SSA (5–40 mol%). It was observed that the amount of acid sites increases with amount of SSA. It was also observed that the diffusivity of α-pinene through the Polymeric catalysts decreases with the increase of Crosslinking degree. The conversion of α-pinene increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5% to 40%. However, when the Crosslinking degree increases from 20% to 40%, the conversion of α-pinene increases only slightly. Good values of selectivity to α-terpinyl methyl ether (about 60% near complete conversion) were obtained over poly(vinyl alcohol) with sulfonic acid groups. Catalytic stability of the PVA_SSA20 was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch it was observed a stabilisation of the initial activity. A kinetic model was developed assuming that the α-pinene is consumed according to the parallel reaction network. Since the concentration profiles of the reagent and the products do not exhibit any pronounced initial inductive period, the external and internal diffusion of the reagents and products on the catalyst were not considered. It was observed that the kinetic model fits experimental concentration data quite well.
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Esterification of acetic acid by isoamylic alcohol over catalytic membranes of poly(vinyl alcohol) containing sulfonic acid groups
Applied Catalysis A: General, 2006Co-Authors: J.e. Castanheiro, Ana M. Ramos, Isabel Fonseca, Joaquim VitalAbstract:Abstract In this study, poly(vinyl alcohol) (PVA) membranes crosslinked with sulfosuccinic acid (SSA) were used for the esterification of acetic acid by isoamylic alcohol. In order to study the effects of the Crosslinking degree and, simultaneously, the amount of sulfonic groups, different membranes were prepared with SSA:PVA ratios in the range of 5–40 mol%. Aiming at to eliminate the dependence between the amount of acid sites and the Crosslinking degree, were also prepared PVA membranes in which the –SO 3 H groups were introduced by anchoring 5-sulfosalisilic acid (SA) on the PVA chains. The conversion of isoamylic alcohol increases when the amount of sulfosuccinic acid used in the Polymer Crosslinking is increased from 5 to 20%. However, when Crosslinking degree increases from 20 to 40%, the conversion of isoamylic alcohol increases only slightly, probably due to the increase of molecules mobility restrictions, in the PVA matrix. In the case of the PVA membranes where the –SO 3 H groups were introduced by esterifying 5-sulfosalisilic acid on the PVA –OH groups, it was observed that membrane activity increases with the Polymer Crosslinking. It was also observed an increase of the activity of these membranes with the amount of –SO 3 H groups in the Polymeric matrix. Catalytic stability of PVA membranes, prepared with SSA and SA, was evaluated by performing consecutive batch runs with the same membrane being observed, after the third run, a trend to stabilization of catalytic activity. An experiment with a membrane reactor operating under sweep gas pervaporation conditions is described.