High interfacial activity of polymers "grafted through" functionalized iron oxide nanoparticle clusters.

The mechanism by which polymers, when grafted to inorganic nanoparticles, lower the interfacial tension at the oil-water interface is not well understood, despite the great interest in particle stabilized emulsions and foams. A simple and highly versatile free radical "grafting through" technique was used to bond high organic fractions (by weight) of poly(oligo(ethylene oxide) monomethyl ether methacrylate) onto iron oxide clusters, without the need for catalysts. In the resulting ∼1 µm hybrid particles, the inorganic cores and grafting architecture contribute to the high local concentration of grafted polymer chains to the dodecane/water interface to produce low interfacial tensions of only 0.003 w/v % (polymer and particle core). This "critical particle concentration" (CPC) for these hybrid inorganic/polymer amphiphilic particles to lower the interfacial tension by 36 mN/m was over 30-fold lower than the critical micelle concentration of the free polymer (without inorganic cores) to produce nearly the same interfacial tension. The low CPC is favored by the high adsorption energy (∼10(6) kBT) for the large ∼1 µm hybrid particles, the high local polymer concentration on the particles surfaces, and the ability of the deformable hybrid nanocluster cores as well as the polymer chains to conform to the interface. The nanocluster cores also increased the entanglement of the polymer chains in bulk DI water or synthetic seawater, producing a viscosity up to 35,000 cP at 0.01 s(-1), in contrast with only 600 cP for the free polymer. As a consequence of these interfacial and rheological properties, the hybrid particles stabilized oil-in-water emulsions at concentrations as low as 0.01 w/v %, with average drop sizes down to 30 µm. In contrast, the bulk viscosity was low for the free polymer, and it did not stabilize the emulsions. The ability to influence the interfacial activity and rheology of polymers upon grafting them to inorganic particles, including clusters, may be expected to be broadly applicable to stabilization of emulsions and foams.

Stereoelectronically-induced allosteric binding: shape complementarity promotes positive cooperativity in fullerene/buckybowl complexes.

A novel 2 : 1 host-guest complex forms between 8-tert-butyl-6b2-azapenta-benzo[bc,ef,hi,kl,no]corannulene (1) and C60 with positive cooperativity (α = 2.56) and high affinity (K1 × K2 = 2.8 × 106 M-2) at 25 °C. The C60 undergoes increasing shape complementarity toward 1 throughout the binding process.

Caudal Epidural Steroid Injections in the Setting of Remaining on Antithrombotics: A Retrospective Study.

BACKGROUND: The American Society of Regional Anesthesia currently recommends ceasing antithrombotic medications for all spinal epidural steroid injections, however there is a paucity of data on the true risk of spinal epidurals via various approaches versus the risk of cessation of an agent as it relates to the underlying medical condition. OBJECTIVE: This study evaluated the complication rate of caudal epidural steroid injections in patients who remain on antithrombotic medications. STUDY DESIGN: Retrospective chart review. SETTING: Physiatric Spine Clinic in Orthopedic Specialty Office and Surgical Center. METHODS: A retrospective chart review was performed identifying patients (n = 335) who received a caudal epidural steroid injection (n = 673) from June 2015 through April 2020. Patients were included if they had received the injection while taking an antithrombotic medication. Patients were excluded if they were not taking an antithrombotic. The patient's age, indication for the injection including magnetic resonance imaging or computed tomography findings, antithrombotic medication, the medical condition requiring an antithrombotic, and any complications following the injection were collected via chart review. RESULTS: Of the 443 injections included in the study, 51 encounters were lost to follow-up. Of the other 392 injections, there were no reported complications, regardless of the patient's imaging findings, age, the antithrombotic medication used, or the underlying medical condition for which an antithrombotic medication was indicated. LIMITATIONS: This is a retrospective study. Therefore, a prospective study may have yielded fewer encounters lost to follow-up. Patients were not contacted directly after the procedure and chart reviews were utilized to evaluate for complications, which was limited to a patient's reporting of perceived complications without any imaging. CONCLUSIONS: We conclude that caudal epidural steroid injections can be performed safely in patients while taking antithrombotic medications. Catastrophic events have been observed in patients who have discontinued antithrombotic agents preceding procedures. Thus, discontinuing antithrombotic medications may pose a greater risk than benefit for patients on an antithrombotic medication who have painful lumbar radiculopathy.

Advanced Silicon-on-Insulator: Crystalline Silicon on Atomic Layer Deposited Beryllium Oxide.

Silicon-on-insulator (SOI) technology improves the performance of devices by reducing parasitic capacitance. Devices based on SOI or silicon-on-sapphire technology are primarily used in high-performance radio frequency (RF) and radiation sensitive applications as well as for reducing the short channel effects in microelectronic devices. Despite their advantages, the high substrate cost and overheating problems associated with complexities in substrate fabrication as well as the low thermal conductivity of silicon oxide prevent broad applications of this technology. To overcome these challenges, we describe a new approach of using beryllium oxide (BeO). The use of atomic layer deposition (ALD) for producing this material results in lowering the SOI wafer production cost. Furthermore, the use of BeO exhibiting a high thermal conductivity might minimize the self-heating issues. We show that crystalline Si can be grown on ALD BeO and the resultant devices exhibit potential for use in advanced SOI technology applications.

Atomic-Layer Deposition of Single-Crystalline BeO Epitaxially Grown on GaN Substrates.

We have grown a single-crystal beryllium oxide (BeO) thin film on a gallium nitride (GaN) substrate by atomic-layer deposition (ALD) for the first time. BeO has a higher thermal conductivity, bandgap energy, and dielectric constant than SiO2. As an electrical insulator, diamond is the only material on earth whose thermal conductivity exceeds that of BeO. Despite these advantages, there is no chemical-vapor-deposition technique for BeO-thin-film deposition, and thus, it is not used in nanoscale-semiconductor-device processing. In this study, the BeO thin films grown on a GaN substrate with a single crystal showed excellent interface and thermal stability. Transmission electron microscopy showed clear diffraction patterns, and the Raman shifts associated with soft phonon modes verified the high thermal conductivity. The X-ray scan confirmed the out-of-plane single-crystal growth direction and the in-plane, 6-fold, symmetrical wurtzite structure. Single-crystalline BeO was grown on GaN despite the large lattice mismatch, which suggested a model that accommodated the strain of hexagonal-on-hexagonal epitaxy with 5/6 and 6/7 domain matching. BeO has a good dielectric constant and good thermal conductivity, bandgap energy, and single-crystal characteristics, so it is suitable for the gate dielectric of power semiconductor devices. The capacitance-voltage (C-V) results of BeO on a GaN-metal-oxide semiconductor exhibited low frequency dispersion, hysteresis, and interface-defect density.

Iron Oxide Nanoparticles Grafted with Sulfonated and Zwitterionic Polymers: High Stability and Low Adsorption in Extreme Aqueous Environments.

A facile "grafting through" approach was developed to tether tunable quantities of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) as well as zwitterionic poly([3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide) (PMPDSA) homopolymer onto iron oxide (IO) nanoparticles (NPs). In this case, homopolymers may be grafted, unlike "grafting to" approaches that often require copolymers containing anchor groups. The polymer coating provided steric stabilization of the NP dispersions at high salinities and elevated temperature (90 °C) and almost completely prevented adsorption of the NPs on silica microparticles and crushed Berea sandstone. The adsorption of PAMPS IO NPs decreased with the polymer loading, whereby the magnitude of the particle-surface electrosteric repulsion increased. The zwitterionic PMPDSA IO NPs displayed 1 order of magnitude less adsorption onto crushed Berea sandstone relative to the anionic PAMPS IO NPs. The ability to design homopolymer coatings on nanoparticle surfaces by the "grafting through" technique is of broad interest for designing stable dispersions and modulating the interactions between nanoparticles and solid surfaces.