Christopher B. Roberts

Preparation of budesonide and budesonide-PLA microparticles using supercritical fluid precipitation technology

The objective of this study was to prepare and characterize microparticles of budesonide alone and budesonide and polylactic acid (PLA) using supercritical fluid (SCF) technology. A precipitation with a compressed antisolvent (PCA) technique employing supercritical CO2 and a nozzle with 100-μm internal diameter was used to prepare microparticles of budesonide and budesonide-PLA. The effect of various operating variables (temperature and pressure of CO2 and flow rates of drug-polymer solution and/or CO2) and formulation variables (0.25%, 0.5%, and 1% budesonide in methylene chloride) on the morphology and size distribution of the microparticles was determined using scanning electron microscopy. In addition, budesonide-PLA particles were characterized for their surface charge and drug-polymer interactions using a zeta meter and differential scanning calorimetry (DSC), respectively. Furthermore, in vitro budesonide release from budesonide-PLA microparticles was determined at 37°C. Using the PCA process, budesonide and budesonide-PLA microparticles with mean diameters of 1 to 2 μm were prepared. An increase in budesonide concentration (0.25%–1% wt/vol) resulted in budesonide microparticles that were fairly spherical and less aggiomerated. In addition, the size of the microparticles increased with an increase in the drug-polymer solution flow rate (1.4–4.7 mL/min) or with a decrease in the CO2 flow rate (50–10 mL/min). Budesonide-PLA microparticles had a drug loading of 7.94%, equivalent to ∼80% encapsulation efficiency. Budesonide-PLA microparticles had a zeta potential of— 37±4 mV, and DSC studies indicated that SCF processing of budesonide-PLA microparticles resulted in the loss of budesonide crystallinity. Finally, in vitro drug release studies at 37°C indicated 50% budesonide release from the budesonide-PLA microparticles at the end of 28 days. Thus, the PCA process was successful in producing budesonide and budesonide-PLA microparticles. In addition, budesonide-PLA microparticles sustained budesonide release for 4 weeks.

Magnetism in dodecanethiol-capped gold nanoparticles: Role of size and capping agent

In gold nanoparticles (Au NPs) capped with dodecanethiol (DT), the authors report the observation of superparamagnetic blocking temperature TB≃50K in D≃5nm NPs but only diamagnetism in 12nm NPs. For T<TB=50K, the strong temperature dependence of coercivity Hc, saturation magnetization Ms, and exchange bias He (in the field-cooled sample) confirm the blocked state resembling ferromagnetism with Hc≃250Oe, He≃−40Oe, and Ms≃10−2emu∕g at 5K. The observed electron magnetic resonance line shows expected shift, broadening, and reduced intensity below TB. A magnetic moment μ≃0.006μB per Au atom attached to DT is determined using a model which yields Ms varying as 1∕D, with its source being holes in the 5d band of Au produced by charge transfer from Au to S atoms in DT.

Selective Fischer–Tropsch synthesis over an Al2O3 supported cobalt catalyst in supercritical hexane

Abstract Supercritical fluids (SCFs) offer several advantages as reaction media for catalytic reactions. These advantages include the ability to manipulate the reaction environment through simple changes in pressure to enhance solubility of reactants and products, to eliminate interphase transport limitations, and to integrate reaction and separation unit operations. Benefits derived from the SCF-phase Fischer–Tropsch synthesis (SCF-FTS) involve the gas-like diffusivities and liquid-like solubilities, which together combine the desirable features of the gas- and liquid-phase FT synthesis routes. In this paper, FT synthesis under SCF hexane conditions is examined in a continuous, high-pressure reactor by employing a traditional Co catalyst (15% Co–0.5% Pt/Al 2 O 3 ). Steady-state operation was quickly achieved under SCF conditions and the SCF-FT process has a marked effect on the hydrocarbon product distribution with a shift to higher carbon number products owing to enhanced heat and mass transfer from the catalyst surface. In addition, an obvious difference in the olefin content was observed where the 1-olefin content in the SCF phase was always higher than in the gas phase. Based on the experimental observations, a mechanistic explanation is provided for the difference of the reaction behavior under supercritical and gas-phase environments. Enhanced olefins readsorption and increased availability of active sites in the supercritical state contribute to the increased olefin selectivity and chain growth probability in the supercritical phase. In addition, the effect of pressure tuning in the supercritical phase reaction was investigated as well as the effect of the supercritical medium on heat transfer and temperature distribution within the reactor.

Size-selective fractionation of nanoparticles at an application scale using CO2 gas-expanded liquids

Size-based fractionation of nanoparticles remains a non-trivial task for the preparation of well-defined nanomaterials for certain applications and fundamental studies. Typical fractionation techniques prove to be inefficient for large nanoparticle quantities due to several factors including the expense of equipment, throughput constraints, and the amount of organic solvent waste produced. Through the use of the pressure-tunable physico-chemical properties of CO2-expanded liquids, a rapid, precise, and environmentally sustainable size-selective fractionation of ligand-stabilized nanoparticles is possible through simple variations in applied CO2 pressure. An apparatus capable of fractionating large quantities of nanoparticles into distinct fractions with the ability to control mean diameters and size distributions has been developed. This apparatus consists of three vertically mounted pressure vessels connected in series with needle valves. This process, at current design scales, operated at room temperature, and CO2 pressures between 0 and 50 bar, results in a batch size-selective fractionation of a concentrated nanoparticle dispersion. This paper presents this new apparatus and the separation results of various single pass fractionations as well as recursive fractionations.

Catalytic hydrodechlorination of trichloroethylene in water with supported CMC-stabilized palladium nanoparticles

In this work, we developed and tested a new class of supported Pd catalysts by immobilizing CMC (carboxymethyl cellulose) stabilized Pd nanoparticles onto alumina support. The alumina supported Pd nanoparticles were able to facilitate rapid and complete hydrodechlorination of TCE (trichloroethylene) without intermediate by-products detected. With a Pd mass loading of 0.33 wt% of the alumina mass, the observed pseudo first order reaction rate constant, k(obs), for the catalyst was increased from 28 to 109 L/min/g when CMC concentration was raised from 0.005 to 0.15 wt%. The activity increase was in accord with an increase of the Pd dispersion (measured via CO chemisorption) from 30.4% to 45.1%. Compared to the commercial alumina supported Pd, which has a lower Pd dispersion of 21%, our CMC-stabilized Pd nanoparticles offered more than 7 times greater activity. Pre-calcination treatment of the supported catalyst resulted in minor drop in activity, yet greatly reduced bleeding (<6%) of the Pd nanoparticles from the support during multiple cycles of applications. The presence of DOM (dissolved organic matter) at up to 10 mg/L as TOC had negligible effect on the catalytic activity. The alumina supported CMC-stabilized Pd nanoparticles may serve as a class of more effective catalysts for water treatment uses.

Self-Assembled Monolayer-Immobilized Gold Nanoparticles as Durable, Anti-Stiction Coatings for MEMS

Self-assembled monolayer (SAM) films of p-aminophenyl trimethoxysilane (APhTS) and 3-mercaptopropyl trimethoxysilane (MPTS) were used to immobilize gold nanoparticles (AuNPs) on silicon substrates and silicon-based microdevices, which created robust nanoparticle coatings that reduced microstructure adhesion. The terminal groups of APhTS and MPTS have both been previously shown to strongly interact and/or bind with metals and metallic nanoparticles. Scanning electron microscopy (SEM) analysis indicated that APhTS and MPTS monolayers improved the adhesion of gold nanoparticles deposited on silicon substrates and microstructures. SEM analysis also showed that the gold nanoparticle/organic monolayer (AuNP/APhTS or AuNP/MPTS) films were more robust than non-immobilized AuNP coatings toward both cantilever beam mechanical contact and water erosion testing. The combination of the rough, lower-energy surfaces of AuNP/APhTS and AuNP/MPTS films also effectively reduced the adhesion exhibited between microstructured surfaces by nearly two orders of magnitude as measured by the apparent work of adhesion. Smooth native oxide-coated Si(100) in-plane surfaces typically have an adhesion energy in excess of 30 mJ/m2 while AuNP/APhTS and AuNP/MPTS coatings reduced the adhesion energy to 0.655 and 1.66 mJ/m2, respectively.

A gas-expanded liquid nanoparticle deposition technique for reducing the adhesion of silicon microstructures

A gas-expanded liquid-based nanoparticle deposition technique was integrated with a critical point drying process to modify the surface of polysilicon microstructures in order to reduce the adhesion that ordinarily occurs due to dominant interfacial surface forces. Dodecanethiol-capped gold nanoparticles (AuNPs) were deposited onto arrays of cantilever beams using gas-expanded liquid technology in an effort to increase the surface roughness, thereby reducing the real contact surface area as well as changing the chemical constituents of the contacting areas. Both AuNP-coated and uncoated (native oxide surface) arrays were actuated electrostatically in order to determine the work of adhesion. The results of this study indicate that while cantilever beams with only their native oxide exhibit apparent adhesion energies of about 700 +/- 100 microJ m(-2), cantilever beam arrays coated with AuNPs exhibit an apparent adhesion energy of about 8 microJ m(-2) or less. These results indicate that metallic nanoparticle coatings can be successfully applied to micromachines and provide a drastic reduction in apparent adhesion energy.

Separation and Recovery of Nylon from Carpet Waste Using a Supercritical Fluid Antisolvent Technique

Abstract This article presents a new process for the selective separation and recovery of nylon material from carpet waste using a solvent-based selective dissolution technique combined with supercritical fluid antisolvent precipitation. The process is described in three primary stages: (1) selective dissolution of nylon up to 2.31 wt.% from the model carpet with an 88 wt.% liquid formic acid solution is performed at 40°C, (2) recovery of the nylon product powder with supercritical C02 antisolvent precipitation at pressures between 84 and 125 bar at 40°C, and (3) recycle of both the solvent and antisolvent by flashing into two phases. Detailed studies on the supercritical fluid antisolvent precipitation (stage 2) of the nylon material from carpet waste were performed in which the influences of operating conditions were examined. Effective recovery of the nylon material was achieved with control over the morphology and particle size of the nylon powder. The particles obtained were typically less than 20 μm...

Measurements and modeling of cloud point behavior for polypropylene/n-pentane and polypropylene/n-pentane/carbon dioxide mixtures at high pressure

Abstract The phase behavior of polypropylene (PP) in n -pentane and n -pentane/carbon dioxide solvent mixtures has been studied using a high-pressure variable volume view cell. Cloud point pressures for polypropylene ( M w =50,400) in near-critical n -pentane were studied at temperatures ranging from 432 to 470 K for polymer concentrations of 1 to 15 mass%. Furthermore, cloud point pressures for polypropylene ( M w =95,400) in near-critical n -pentane were studied at temperatures ranging from 450 to 465 K for polymer concentrations of 1 to 8 mass%. Cloud point pressures were also measured for PP ( M w =200,000, 3 mass%) in n -pentane at temperatures ranging from 450 K to 465 K. The cloud point pressures for PP ( M w =50,400) in n -pentane/CO 2 mixtures were determined for PP concentrations of 3.0 mass% and 9.7 mass% with CO 2 solvent concentrations ranging from 12.6 mass% to 42.0 mass% at temperatures ranging from 405 K to 450 K. All of the experimental cloud point isopleths were relatively linear with approximately the same positive slope indicating LCST behavior. The experimental cloud point pressures were relatively insensitive to the concentration and molecular weight of polypropylene. At a given temperature, the cloud point pressure of the PP/ n -pentane/carbon dioxide system increased almost linearly with increasing carbon dioxide solvent concentration (for carbon dioxide concentrations less than 30 mass%). The Sanchez–Lacombe (SL) equation of state was used to model the experimental data.

An overview to ‘Advances in C1 chemistry in the year 2002’

Abstract The current volume presents 19 papers that advance research and technology in C1 chemistry and fuel science technology. This introductory paper contains a brief outline of the material presented in those papers.