903 research outputs found
Transparent, Stimuli‐Responsive Films from Cellulose‐Based Organogel Nanoparticles
No full textThe use of bio‐based nanoscaled cellulose for the construction of novel functional materials has progressed rapidly over the past years. In comparison to most of studies starting with the hydrophilic nanoscaled cellulose, surface‐stearoylated cellulose nanoparticles (SS‐CNPs) are used in this report for the construction of multifunctional, responsive films. SS‐CNPs with an average size of 115 ± 0.5 nm are obtained after the surface‐modification of cellulose under heterogeneous conditions. Crystalline cellulose core is present within SS‐CNPs according to solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy. SS‐CNPs show excellent dispersibility in nonpolar solvents and form temperature‐responsive organogels in tetrahydrofuran (THF) at low temperature or after long time storage at room temperature. Moreover, transparent and self‐standing films of SS‐CNPs from their THF‐suspension show solvent‐responsive surface wettability and responsive shape‐memory property. SS‐CNPs can also be used for the fabrication of nanocomposite films together with nonpolar compounds, such as (2‐stearoylaminoethyl) rhodamine B. Thus, these novel SS‐CNPs derived from sustainable cellulose fibers are promising candidates for the construction of novel functional materials
Dr. Gerd J. Horten Professor of History - Concordia University Portland
No full textGerd Horten, author of the book \u27Radio Goes to War: The Cultural Politics of Propaganda during World War II\u27, discusses World War II propaganda and censorship. Recorded by Phil Sedgwick.
Video uploaded by Phil Sedgwick under Standard YouTube Licensehttps://commons.cu-portland.edu/humfacultymedia/1000/thumbnail.jp
Multi-responsive cellulose nanocrystal–rhodamine conjugates: an advanced structure study by solid-state dynamic nuclear polarization (DNP) NMR
No full textMulti-stimuli responsive materials based on cellulose nanocrystals (CNCs), especially using non-conventional stimuli including light, still need more explorations, to fulfill the requirements of complicated application environments. The structure determination of functional groups on the CNC surface constitutes a significant challenge, partially due to their low amounts. In this study, rhodamine spiroamide groups are immobilized onto the surface of CNCs leading to a hybrid compound being responsive to pH-values, heat and UV light. After the treatment with external stimuli, the fluorescent and correlated optical color change can be induced, which refers to a ring opening and closing process. Amine and amide groups in rhodamine spiroamide play the critical role in this switching process. Solid-state NMR spectroscopy coupled with sensitivity-enhanced dynamic nuclear polarization (DNP) was used to measure 13C and 15N in natural abundance, allowing the determination of structural changes during the switching process. It is shown that a temporary bond through an electrostatic interaction could be formed within the confined environment on the CNC surface during the heat treatment. The carboxyl groups on the CNC surface play a pivotal role in stabilizing the open status of rhodamine spiroamide groups
Superhydrophobic surfaces from surface-hydrophobized cellulose fibers with stearoyl groups
No full textEndogenous Fixprices and Sticky Price Adjustment of Risk-averse Firms
Full text linkA risk-averse price-setting firm which knows the quantity demanded at the status quo price but has imperfect information otherwise may choose not to change it although an otherwise identical risk-neutral firm would do so, provided the variance of the firm's subjective probability distribution over quantities demanded as a function of price displays a kink at the status quo. This is equivalent to risk aversion of order one. When no such endogenous fixprice exists, the size of price adjustment still tends to zero as risk aversion tends to infinity, and to any arbitrarily small menu cost there exists a degree of risk aversion so that the firm will not adjust.fixed prices, price adjustment, risk aversion, menu cost
Thermoreversible Self-Assembly of Perfluorinated Core-Coronas Cellulose-Nanoparticles in Dry State
No full textSelf-assembly of nanoparticles (NPs) forming unique structures has been investigated extensively over the past few years. However, many self-assembled structures by NPs are irreversible, because they are generally constructed using their suspensions. It is still challenging for NPs to reversibly self-assemble in dry state, let alone of polymeric NPs with general sizes of hundreds of nm. Herein, this study reports a new reversible self-assembly phenomenon of NPs in dry state, forming thermoreversible strip-like supermolecular structures. These novel NPs of around 150 nm are perfluorinated surface-undecenoated cellulose nanoparticles (FSU-CNPs) with a core-coronas structure. The thermoreversible self-assembled structure is formed after drying in the air at the interface between FSU-CNP films and Teflon substrates. Remarkably, the formation and dissociation of this assembled structure are accompanied by a reversible conversion of the surface hydrophobicity, film transparency, and anisotropic properties. These findings show novel feasibility of reversible self-assembly of NPs in dry state, and thereby expand our knowledge of self-assembly phenomenon
Efficient, Self‐Terminating Isolation of Cellulose Nanocrystals through Periodate Oxidation in Pickering Emulsions
No full textMany efforts have been made to isolate native nanocrystals from raw materials in the last two decades, such as cellulose nanocrystals (CNCs), but existing methods still suffer from low yields, complicated synthesis processes, and nonuniform sizes of obtained CNCs. This study concerns a facile, self-terminating, and efficient method for the formation of uniform CNCs in high yields during the periodate oxidation process within Pickering emulsions. A biphasic system containing hexane with dissolved hexylamine and an aqueous solution of sodium periodate (NaIO4 ) was used as the reaction medium. Regulated by hexylamine, owing to its limited solubility in water, the pH value of the aqueous phase was enhanced to around 9.8, leading to the precipitation of sodium orthoperiodate (Na2 H3 IO6 ) nanoplates and thus the formation of the initial Pickering emulsions. During the gradual formation of cellulose nanofibers and then CNCs, CNCs were attracted to stabilize the interface of the Pickering emulsions, which prevented further decomposition of CNCs by the oxidizing agent in aqueous suspensions. Thus, this isolation strategy secured the efficient separation of CNCs based on their own particular amphiphilic properties and achieved a high yield of up to 56 wt %
Untersuchung von Metallkomplexen und metallaktivierten Reaktionen durch schwingungsspektroskopische Methoden
Full text linkEnzymatische Prozesse sind in der Natur ubiquitär. Ihre Selektivität und Ausbeute liegt oft deutlich über dem, was in der organischen Synthese möglich ist. Ein detailliertes Verständnis der Struktur-Eigenschafts- und Struktur-Dynamik-Beziehungen in enzymatischen Prozessen wie der Photosynthese kann helfen, neuartige Materialien zu entwickeln und chemische Prozesse effizienter zu gestalten. In der vorliegenden Arbeit wurden einerseits Ruthenium{Komplexe untersucht, die ähnlich wie Chlorophyll als Lichtsammelkomplexe dienen können. Derartige Komplexe haben das Potential, in farbstoffsibilisierten Solarzellen, OLEDs oder als schaltbare Katalysatoren eingesetzt zu werden
Ultra-light nanocomposite aerogels of bacterial cellulose and reduced graphene oxide for specific absorption and separation of organic liquids
No full textNovel materials based on sustainable materials with high absorption capacity are still rare for the separation of organic liquids or oil spills and water. In this report, ultra-light nanocomposite aerogels consisting of sustainable bacterial cellulose (BC) and graphene oxide (GO) were constructed after an eco-friendly freeze-drying process for the first time. Due to the hydrophilic properties of both materials and the highly porous structure, BC/GO aerogels could highly absorb not only organic liquids, such as cyclohexane and DMF, but also water. Specific absorption for organic liquids was achieved after the reduction of GO using H-2 gas, which led to nanocomposite aerogels of BC and reduced GO. They could specifically absorb 135-150 g organic liquids per g of their own weight, even with a high content of 80 BC in the nanocomposite aerogel
Treating gastro-oesophageal reflux disease (GERD) with sense
No full textGastro-esophageal reflux disease (GERD) is a common disorder that affects an estimated 5 % to 7 % of the global population. Management of GERD often poses a number of challenges. In this article, the author presents a number of management modalities for this condition.peer-reviewe
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