Ultrasonic preparation, stability and thermal conductivity of a capped copper - methanol nanofluid

This paper describes a two-step method to prepare novel copper-methanol nanofluids capped with a short chain molecule, (3-Aminopropyl)trimethoxysilane (APTMS). Two commercial nanopowders were dispersed at various powers using a 20 kHz ultrasonic probe into solutions of methanol and the capping agent. Ultrasonic energy input was measured by calorimetry with z-average diameters, intensity and number size distributions recorded by a dynamic light scattering technique. The stability of the dispersion was monitored visually, and quantified by recording the zeta potential. Dispersions of the bare powder were used as a control. Absorption spectroscopy was used to confirm the presence of the capping agent. The thermal conductivities of 0 to 10% wt./vol. (1.1% vol.) dispersions of the capped copper-methanol nanofluid were determined using a C-Therm analyzer. Optimum ultrasonic de-agglomeration conditions gave dispersions with a z-average particle size of &lt;200 nm and a PdI of &lt;0.2. The capped particles showed good stability; up to six months in some instances, and an average zeta potential of +38 mV was recorded. The thermal conductivity of the nanofluid increased with concentration, and an enhancement of 9% over the base fluid was found at 10% wt./vol. (1.1% vol.). This innovative work has demonstrated the ultrasonic preparation and stability of copper nanoparticles protected with APTMS; a short chain molecule which binds to copper and prevents oxidation. The protected particles can enhance the thermal conductivity of methanol with no interference from the capping ligand.</p

Monotelechelic Poly(oxa)norbornenes by Ring-Opening Metathesis Polymerization Using Direct End-Capping and Cross-Metathesis

Two different methodologies for the synthesis of monotelechelic poly(oxa)norbornenes prepared by living ring-opening metathesis polymerization (ROMP) are presented. The first method, termed direct end-capping, is carried out by adding an internal cis-olefin terminating agent (TA) to the reaction mixture immediately after the completion of the living ROMP reaction. The second method relies on cross-metathesis (CM) between a methylene-terminated poly(oxa)norbornene and a cis-olefin TA mediated by the ruthenium olefin metathesis catalyst (H_(2)IMes)(Cl)_(2)Ru(CH-o-OiPrC_(6)H_4) (H_(2)IMes = 1,3-dimesitylimidazolidine-2-ylidene). TAs containing various functional groups, including alcohols, acetates, bromides, α-bromoesters, thioacetates, N-hydroxysuccinimidyl esters, and Boc-amines, as well as fluorescein and biotin groups, were synthesized and tested. The direct end-capping method typically resulted in >90% end-functionalization efficiency, while the CM method was nearly as effective for TAs without polar functional groups or significant steric bulk. End-functionalization efficiency values were determined by ^(1)H NMR spectroscopy

Process of end-capping a polyimide system

A process of endcapping a polyimide system with an endcapping agent in order to achieve a controlled decrease in molecular weight and melt viscosity along with predictable fracture resistance of the molded products is disclosed. The uncapped system is formed by combining an equimolar ratio of 4,4'-bis (3,4-dicarboxyphenoxy) diphenylsulfide dianhydride (BDSDA) and 1,-bis (aminophenoxy) benzene (APB) dissolved in bis (2-methoxyethyl)ether. The endcapped system is formed by dissolving APB in bis-(2-methoxyethyl)ether, adding the BDSDA. By varying the amount of endcapping from 0 to 4%, molecular weight is decreased from 13,900 to 8660. At a processing temperature of 250 C, there is a linear relationship between molecular weight and viscosity, with the viscosity decreasing by two orders of magnitude as the molecular weight decreased from 13,900 to 8660

Trade & Cap: A Customer-Managed, Market-Based System for Trading Bandwidth Allowances at a Shared Link

We propose Trade & Cap (T&C), an economics-inspired mechanism that incentivizes users to voluntarily coordinate their consumption of the bandwidth of a shared resource (e.g., a DSLAM link) so as to converge on what they perceive to be an equitable allocation, while ensuring efficient resource utilization. Under T&C, rather than acting as an arbiter, an Internet Service Provider (ISP) acts as an enforcer of what the community of rational users sharing the resource decides is a fair allocation of that resource. Our T&C mechanism proceeds in two phases. In the first, software agents acting on behalf of users engage in a strategic trading game in which each user agent selfishly chooses bandwidth slots to reserve in support of primary, interactive network usage activities. In the second phase, each user is allowed to acquire additional bandwidth slots in support of presumed open-ended need for fluid bandwidth, catering to secondary applications. The acquisition of this fluid bandwidth is subject to the remaining "buying power" of each user and by prevalent "market prices" – both of which are determined by the results of the trading phase and a desirable aggregate cap on link utilization. We present analytical results that establish the underpinnings of our T&C mechanism, including game-theoretic results pertaining to the trading phase, and pricing of fluid bandwidth allocation pertaining to the capping phase. Using real network traces, we present extensive experimental results that demonstrate the benefits of our scheme, which we also show to be practical by highlighting the salient features of an efficient implementation architecture.National Science Foundation (CCF-0820138, CSR-0720604, EFRI-0735974, CNS-0524477, and CNS-0520166); Universidad Pontificia Bolivariana and COLCIENCIAS–Instituto Colombiano para el Desarrollo de la Ciencia y la Tecnología “Francisco Jose ́ de Caldas”

Low temperature cross linking polyimides

A polyimide is formed by cross linking a prepolymer formed by reacting a polyfunctional ester, a polyfunctional amine, and an end-capping unit. By providing an end-capping unit, the prepolymer is curable at a relatively low temperature of about 175 to 245 C

Ultrasound- and microwave-assisted preparation of lead-free palladium catalysts: effects on the kinetics of diphenylacetylene semi-hydrogenation

The effect of environmentally benign enabling technologies such as ultrasound and microwaves on the preparation of the lead-free Pd catalyst has been studied. A one-pot method of the catalyst preparation using ultrasound-assisted dispersion of palladium acetate in the presence of the surfactant/capping agent and boehmite support produced the catalyst containing Pd nanoparticles and reduced the number of pores larger than 4 nm in the boehmite support. This catalyst demonstrated higher activity and selectivity. The comparison of kinetic parameters for diphenylacetylene hydrogenation showed that the catalyst obtained by using the one-pot method was seven times as active as a commercial Lindlar catalyst and selectivity towards Z-stilbene was high. Our work also illustrated that highly selective Pd/boehmite catalysts can be prepared through ultrasound-assisted dispersion and microwave-assisted reduction in water under hydrogen pressure without any surfactant

Impact of pulmonary exposure to gold core silver nanoparticles of different size and capping agents on cardiovascular injury

Background:The uses of engineered nanomaterials have expanded in biomedical technology and consumer manufacturing. Furthermore, pulmonary exposure to various engineered nanomaterials has, likewise, demonstrated the ability to exacerbate cardiac ischemia reperfusion (I/R) injury. However, the influence of particle size or capping agent remains unclear. In an effort to address these influences we explored response to 2 different size gold core nanosilver particles (AgNP) with two different capping agents at 2 different time points. We hypothesized that a pulmonary exposure to AgNP induces cardiovascular toxicity influenced by inflammation and vascular dysfunction resulting in expansion of cardiac I/R Injury that is sensitive to particle size and the capping agent. Methods: Male Sprague–Dawley rats were exposed to 200 μg of 20 or 110 nm polyvinylprryolidone (PVP) or citrate capped AgNP. One and 7 days following intratracheal instillation serum was analyzed for concentrations of selected cytokines; cardiac I/R injury and isolated coronary artery and aorta segment were assessed for constrictor responses and endothelial dependent relaxation and endothelial independent nitric oxide dependent relaxation. Results: AgNP instillation resulted in modest increase in selected serum cytokines with elevations in IL-2, IL-18, and IL-6. Instillation resulted in a derangement of vascular responses to constrictors serotonin or phenylephrine, as well as endothelial dependent relaxations with acetylcholine or endothelial independent relaxations by sodium nitroprusside in a capping and size dependent manner. Exposure to both 20 and 110 nm AgNP resulted in exacerbation cardiac I/R injury 1 day following IT instillation independent of capping agent with 20 nm AgNP inducing marginally greater injury. Seven days following IT instillation the expansion of I/R injury persisted but the greatest injury was associated with exposure to 110 nm PVP capped AgNP resulted in nearly a two-fold larger infarct size compared to naïve. Conclusions: Exposure to AgNP may result in vascular dysfunction, a potentially maladaptive sensitization of the immune system to respond to a secondary insult (e.g., cardiac I/R) which may drive expansion of I/R injury at 1 and 7 days following IT instillation where the extent of injury could be correlated with capping agents and AgNP size.This work was supported by the National Institute of Environmental Health Sciences U19ES019525, U01ES020127, U19ES019544 and East Carolina Universit