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University of Twente Publications (49,892 recursos)
University of Twente Repository provides publications of UT scientific staff, in many cases full text and publicly available.

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Mostrando recursos 1 - 20 de 9,492

1. Microfluidic devices for kinetic studies of chemical reactions - Bula, W.P.

2. A capillary micro-reactor as a tool to study pressurised reactions: The influence of pressure on the stereoselectivity of the Diels-Alder reaction of 2- and 3-Furylmethanol with maleimides - Benito-Lopez, Fernando; Kettelarij, Albert J.; Egberink, Richard J.M.; Velders, Aldrik H.; Tiggelaar, Roald M.; Gardeniers, Han J.G.E.; Reinhoudt, David N.; Verboom, Willem
The influence of a pressure of 60 MPa on theconversion and the stereoselectivity of the Diels-Alderreaction of 2- and 3-furylmethanol with methyl-, benzyl-, andphenylmaleimide was studied in a capillary micro-reactor. Inthe case of 2-furylmethanol, a 1.7-fold higher conversion wasobtained at 60 MPa with respect to 0.1 MPa experiments.Pressure positively affects the formation of the exo isomer,whereas in the case of 3-furylmethanol pressure does notaffect the reaction.

3. Formation and prevention of fractures in sol-gel-derived thin films - Kappert, Emiel J.; Pavlenko, D.; Malzbender, J.; Nijmeijer, A.; Benes, N.E.; Tsai, P.A.
Sol–gel-derived thin films play an important role as the functional coatings for various applications that require crack-free films to fully function. However, the fast drying process of a standard sol–gel coating often induces mechanical stresses, which may fracture the thin films. An experimental study on the crack formation in sol–gel-derived silica and organosilica ultrathin (submicron) films is presented. The relationships among the crack density, inter-crack spacing, and film thickness were investigated by combining direct micrograph analysis with spectroscopic ellipsometry. It is found that silica thin films are more prone to fracturing than organosilica films and have a critical film thickness...

4. Temperature calibration procedure for thin film substrates for thermo-ellipsometric analysis using melting point standards - Kappert, Emiel J.; Raaijmakers, M.J.T.; Ogieglo, W.; Nijmeijer, A.; Huiskes, C.; Benes, N.E.
Precise and accurate temperature control is pertinent to studying thermally activated processes in thin films. Here, we present a calibration method for the substrate–film interface temperature using spectroscopic ellipsometry. The method is adapted from temperature calibration methods that are well developed for thermogravimetric analysis and differential scanning calorimetry instruments, and is based on probing a transition temperature. Indium, lead, and zinc could be spread on a substrate, and the phase transition of these metals could be detected by a change in the C signal of the ellipsometer. For water, the phase transition could be detected by a loss of signal...

5. Visualization and characterization of interfacial polymerization layer formation - Zhang, Yali; Benes, N.E.; Lammertink, R.G.H.
We present a microfluidic platform to visualize the formation of free-standing films by interfacial polymerization. A microfluidic device is fabricated, with an array of micropillars to stabilize an aqueous–organic interface that allows a direct observation of the films formation process via optical microscopy. Three different amines are selected to react with trimesoyl chloride: piperazine, JEFFAMINE®D-230, and an ammonium functionalized polyhedral oligomeric silsesquioxane. Tracking the formation of the freestanding films in time reveals strong effects of the characteristics of the amine precursor on the morphological evolution of the films. Piperazine exhibits a rapid reaction with trimesoyl chloride, forming a film up...

6. Young technologist entrepreneurial boot camp - Walsh, S.

7. The transport of Hydronium and Hydroxide Ions through Reverse Osmosis Membranes - Kezia, K.; Lee, J.; Ogieglo, W.; Hill, A.; Benes, N.E.; Kentish, S.E.
It is important to understand the fundamental behaviour of reverse osmosis membranes under a range of pH and salinity conditions. In this work, experiments and modelling are used in a complementary manner to better understand these fundamentals. We find experimentally that both pH and salinity can influence membrane charge, the fractional free volume (or pore size) and the membrane thickness. The thickness of the membrane is quantified using ellipsometry while the pore size is estimated through glucose filtration. The membrane swells marginally with increasing pH, but more so with increasing salt concentration up to 170 mM. The flux of hydronium...

8. Polymer relaxations in thin films in the vicinity of a penetrant or a temperature induced glass transition - Ogieglo, W.; Wessling, M.; Benes, N.E.
The transient properties of thin glassy polymer films in the vicinity of the glass transition are investigated. We compare the differences and similarities between sorption and temperature induced glass transitions, referred to as Pg and Tg, respectively. The experimental technique used is in situ spectroscopic ellipsometry, which allows for a very precise dynamic measurement of the changes in the thickness and the refractive index of the thin films. It is shown that significant differences exist between the penetrant- and temperature-induced transitions. The Tg is relatively well-defined with a sharp change in polymer dynamics, causing a well-known curvature change, a kink,...

9. Hermeneutische benadering: op zoek naar betekenissen - Scheer, A.M. van der

10. Guidelines for catalytic membrane reactor configuration selection - Mengers, H.J.; Benes, N.E.; Nijmeijer, D.C.

11. Hybrid Polyhedral Oligomeric Silsesquioxanes-Imides with Tailored Intercage Spacing for Sieving of Hot Gases - Raaijmakers, M.J.T.; Wessling, M.; Nijmeijer, A.; Benes, N.E.
Macromolecular network rigidity of synthetic membranes is essential for sieving of hot gases. Hyper-cross-linked polyPOSS−imide membranes with tailored intercage spacing are presented. The length and flexibility of their imide bridges enables tuning of gas permeability and selectivity in a broad temperature range. The facile synthesis allows for large-scale production of membranes designed for specific process conditions.

12. Oxygen Transport Membranes: A material science and process engineering approach - Chen, W.
The general consensus exists that the earth is experiencing rapid climate changes, which may cause a redistribution of the global climates. Although it is unknown whether this is beneficial or disastrous for human beings, it will undoubtedly affect human civilization. For example, global warming may cause ice melting in Antarctica and Greenland, which leads to a rise of the sea level and eventually some low altitude cities and countries may disappear. Although there is no universal agreement about the cause of global warming, many climate scientists assume that the anthropogenic emission of carbon dioxide (CO2) into the atmosphere is one of...

13. Modeling water flux and salt rejection of mesoporous γ-alumina and microporous organosilica membranes - Farsi, A.; Boffa, V.; Qureshi, H.F.; Nijmeijer, A.; Winnubst, A.J.A.; Lykkegaard Christensen, M.
The water and ion transport through a mesoporous γ-alumina membrane and a microporous organosilica membrane was simulated using the extended Nernst–Planck equation combined with models for Donnan, steric and dielectric interfacial exclusion mechanisms. Due to the surface charge within the pore, the electroviscous effect was introduced in the model. The modified model fits well the rejection and permeability data for both membranes. The organosilica membrane shows a higher selectivity compared to the γ-alumina membrane, but the permeate flux is lower. At low ionic strength the electroviscous effect lowers the water flux through the γ-alumina membrane. The electroviscous effect is negligible...

14. The precautionary principal and emerging technologies - Walsh, S.; Marinakis, Y.D.

15. PDMS grafting of mesoporous γ-alumina membranes for nanofiltration of organic solvents - Tanardi, C.R.; Pinheiro de Melo, A.F.; Nijmeijer, A.; Winnubst, A.J.A.
In this paper grafting of mesoporous γ-alumina membranes with monovinyl terminated polydimethyl- siloxane (PDMS), using 3-mercaptopropyltriethoxysilane (MPTES) as a linking agent, is described. The grafting performance of the organic moieties on γ-alumina powders was studied by FTIR. Contact angle measurements and solvent permeability tests were used to characterize the membrane properties. The results indicated that grafting reactions were successfully carried out. The toluene permeability of the membrane was reduced from 5.3 to 2.1 L/m2 h bar after grafting with the polymer. No degradation of the membrane material was observed after chemical stability tests in toluene for 6 days at room temperature...

16. The state of TSensor systems roadmap - Walsh, S.; Marinakis, Y.D.

17. Dynamic response of ultrathin highly dense ZIF-8 nanofilms - Cookney, J.; Ogieglo, W.; Hrabanek, P.; Vankelecom, I.; Fila, V.; Benes, N.E.
Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for nonequilibrium organic polymers.

18. Towards the fabrication of La0.98−xSrxCo0.2Fe0.8O3−δ perovskite-type oxygen transport membranes - Schulze-Küppers, F.; Baumann, S.; Tietz, F.; Bouwmeester, H.J.M.; Meulenberg, W.A.
La0.98−xSrxCo0.2Fe0.8O3−δ (LSCF) is a candidate material for use as an oxygen transport membrane (OTM). In this work, fabrication-relevant properties (sinteringbehaviour, thermal and chemical expansion) of LSCF (x = 0.2, 0.4, 0.6, 0.8) were investigated in order to select the preferred composition for fabricating a thin-film supported membrane able to withstand the thermochemical stresses encountered during manufacturing and operation with simultaneously high oxygen permeation flux. Partial substitution of La by Sr ions in LSCF is beneficial for increasing the oxygen permeation rate, but it causes drawbacks regarding manufacturing and operation. A Sr content of x ≥ 0.6 results in a swelling of...

19. Advances in Tsensor systems roadmap - Walsh, S.; Marinakis, Y.D.; Haak, R.

20. Oxygen-selective membranes integrated with oxy-fuel combustion - Chen, W.; Chen, Chusheng; Bouwmeester, H.J.M.; Nijmeijer, A.; Winnubst, A.J.A.
The perovskite-type oxide SrCo0.8Fe0.2O3 δ (SCF), a highly oxygen-permeable material, is restricted for application in the membrane-integrated oxy-fuel combustion process by its low tolerance to CO2. In the present work, we found that the CO2 tolerance of SCF is improved by increasing the oxygen partial pressure in the CO2-containing gas. Long term oxygen permeation experiments, at 950 1C, show that mixing 5% of oxygen into the CO2 sweep gas effectively prevents degradation of the SCF membrane. X-ray photoelectron spectroscopy indicates that the increase in CO2 tolerance of SCF is caused by a decrease in basicity of the material with increasing...

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