211 research outputs found
Erratum: Redox Switchable Thianthrene Cavitands (Synthesis (Germany) DOI: 10.1055/s-0036-1588659)
No full textThere is a mistake in Figure 8 and 9 (protonated sulfur). The correct Figures are shown below. (Figure presented). There is also a mistake in the HRMS data of cavitand 1. It should read: HRMS (MALDI) m/z calculated for C108H89N8O8S8 [M+H]+: 1882.46; found: 1882.61
Cavitand-Functionalized SWCNTs for N-Methylammonium Detection
No full textSingle-walled carbon nanotubes (SWCNTs) have been functionalized with highly selective tetraphosphonate cavitand receptors. The binding of charged N-methylammonium species to the functionalized SWCNTs was analyzed by X-ray photoelectron spectroscopy and confirmed by [superscript 31]P MAS NMR spectroscopy. The cavitand-functionalized SWCNTs were shown to function as chemiresistive sensory materials for the detection of sarcosine and its ethyl ester hydrochloride in water with high selectivity at concentrations as low as 0.02 mM. Exposure to sarcosine and its derivative resulted in an increased conductance, in contrast to a decreased conductance response observed for potential interferents such as the structurally related glycine ethyl ester hydrochloride.European Union. Project BION (ICT-2007-213219)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (DAAD-19-02-0002
Hartslagsensor voor 7 T MRI Cardiac Triggering
No full textVoor het maken van scans van het cardiovasculair gebied is het noodzakelijk de MRI-scanner te synchroniseren met de hartslagcyclus. Dit wordt cardiac triggering genoemd. Door de hoge magnetische veldsterkte treden synchronisatiefouten op, waardoor de scans erg onduidelijk en daardoor onbruikbaar worden. Het doel van dit onderzoek was het verbeteren van de hartslagsensor die bij cardiac triggering wordt toegepast. De meettechnieken pulse oxymetrie, ECG-meting en akoestische meting zijn gedetailleerd uitgewerkt. Uiteindelijk is gekozen voor een akoestisch ontwerp. Voor dit ontwerp zijn twee technieken geanalyseerd. Het gebruik van een Elektromechanical Film (EMFi) en een MR-stethoscoop. De EMFi viel buiten het budget, dus is voor de MR-stethoscoop als implementatie gekozen. Het uiteindelijke prototype voldeed niet aan alle gestelde eisen. De akoestische meting van de hartslag is veelbelovend, maar een aantal verbeteringen op het gebied van de waveguide, microfoon en elektronica is benodigd om het tot een bruikbaar product te maken.BachelorafstudeerthesisTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Triptycene Polyimides: Soluble Polymers with High Thermal Stability and Low Refractive Indices
No full textA series of soluble, thermally stable aromatic polyimides were synthesized using commercially available five- and six-membered ring anhydrides and 2,6-diaminotriptycene derivatives. All of these triptycene polyimides (TPIs) were soluble in common organic solvents despite their completely aromatic structure due to the three-dimensional triptycene structure that prevents strong interchain interactions. Low solution viscosities (0.07−0.47 dL/g) and versatile solubilities allow for easy solution processing of these polymers. Nanoporosity in the solid state gives rise to high surface areas (up to 430 m[superscript 2]/g) and low refractive indices (1.19−1.79 at 633 nm), which suggest very low dielectric constants at optical frequencies. Polymer films were found to be amorphous. The decomposition temperature (T[subscript d]) for all of the polymers is above 500 °C, and no glass transition temperatures can be found below 450 °C by differential scanning calorimetry (DSC), indicating excellent prospects for high-temperature applications. This combination of properties makes these polymers candidates for spin-on dielectric materials.National Science Foundation (U.S.). Graduate Research Fellowship ProgramMassachusetts Institute of Technology. Institute for Soldier Nanotechnologie
Side chain rigidity and backbone flexibility: new microporous materials for gas separation
No full textUnveiling Local Dynamics of a Triptycene-Based Porous Polymer by Solid-State NMR
No full textMembrane-based technologies for gas separation and capture are promising low-energy alternatives to the most common energy-consuming processes such as distillation and absorption. In this frame, porous polymers are attracting considerable interest, but issues related to a trade-off between permeability and selectivity as well as to the long-term stability of the membrane performances need to be overcome. To this end, the study of local dynamics is crucial as it directly correlates with the transport and separation characteristics of polymer-based membranes while also shedding light on plasticization and physical aging phenomena. This work presents a comprehensive characterization of the dynamic properties of a triptycene-based porous polymer with potential application in membrane-based gas separation technology by means of molecular dynamics (MD) simulations and solid-state NMR (SSNMR). The investigated polymer has triptycene-based structural repeating units bearing t-butyl groups that are connected by perfluorinated biphenyl repeats. The combination of different SSNMR variable temperature experiments including measurements of 1H, 13C, and 19F spin-spin and spin-lattice relaxation times, 1H-13C and 19F-13C dipolar chemical shift correlation experiments, and 2H experiments provided selective and detailed information on the molecular motions involving the t-butyl, triptycene, and perfluorinated biphenyl groups. A synergistic analysis of the acquired data, employing theoretical dynamic models and comparisons with MD simulations and calculated potential energy scans (PES), has enabled the determination of motion parameters, including activation energies and correlation times. This approach also yielded insights into the motion amplitudes and geometry. These findings can be valuable for future research aimed at elucidating the molecular origins of membrane performance, not only for the polymer under investigation but also for similar polymer-based membranes
Factors affecting the dispersion of MWCNTs in electrically conducting SEBS nanocomposites
No full textThe accessible concentration of exfoliated and undamaged multi-walled carbon nanotubes (MWCNTs) in polymer nanocomposites is an essential issue to the future of these materials. In this work, we report two methodologies directed at obtaining electrically conducting poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) nanocomposites with different MWCNT contents. The first depends on the time modulation of ultrasonication of toluene mixtures, whereas the second relies on the use of alkyl-functionalized MWCNTs (f-MWCNTs). UV‚Äìvis spectroscopy investigations and thermogravimetric analyses allowed the quantification of exfoliated CNTs incorporated in the SEBS mixture. TEM micrographs denoted that a prolonged sonication time (40 min) induced an extensive MWCNTs degradation (average length decreased of 40%), which affected the electrical conductivity of the nanocomposites. The f-MWCNTs appeared to be more effective in preparing SEBS nanocomposites due to the higher dispersion efficiency, negligible nanotube degradation and higher electrical conductivity. The temperature dependence of the resistance of the SEBS/MWCNT system was investigated in the range 20 - 60 °C to explore its potential for sensor development
One-Pot Regiodirected Annulations for the Rapid Synthesis of Ï-Extended Oligomers
No full textWe demonstrate the broad applicability of the annulation protocol combining, in one pot, a direct arylation and cross aldol condensation for the straightforward synthesis at gram-scale of Ï-extended thiophene-based scaffolds. The regiospecific direct arylation drives the subsequent cross-aldol condensation proceed under the same basic conditions, and the overall protocol has broad applicability in the synthesis of extended aromatics wherein the thiophene ring is annulated with furans, pyridines, indoles, benzothiophenes, and benzofurans. These scaffolds can be further elaborated into Ï-extended, highly fluorescent oligomers with a central deficient benzothiadiazole unit with up to nine aromatic rings through coupling reactions
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