scCO2 Processing Research Articles

Enhancing Carrier Mobilities in Organic Thin-Film Transistors Through Morphological Changes at the Semiconductor/Dielectric Interface Using Supercritical Carbon Dioxide Processing.

Charge-carrier mobilities in poly(3-hexylthiophene) (P3HT) organic thin-film transistors (OTFTs) increase 5-fold when OTFTs composed of P3HT films on trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane (FTS) monolayers supported on SiO2 dielectric substrates (P3HT/FTS/SiO2/Si) are subjected to supercritical carbon dioxide (scCO2) processing. In contrast, carrier mobilities in P3HT/octadecyltrichlorosilane (OTS)/SiO2 OTFTs processed using scCO2 are comparable to mobilities measured in as-cast P3HT/OTS/SiO2/Si devices. Topographical images of the free and buried interfaces of P3HT films reveal that scCO2 selectively alters the P3HT morphology near the buried P3HT/FTS-SiO2 interface; identical processing has negligible effects at the P3HT/OTS-SiO2 interface. A combination of spectroscopic ellipsometry and grazing-incidence X-ray diffraction experiments indicate insignificant change in the orientation distribution of the intermolecular π-π stacking direction of P3HT/FTS with scCO2 processing. The improved mobilities are instead correlated with enhanced in-plane orientation of the conjugated chain backbone of P3HT after scCO2 annealing. These findings suggest a strong dependence of polymer processing on the nature of polymer/substrate interface and the important role of backbone orientation toward dictating charge transport of OTFTs.

Electrochemically triggered release of acetylcholine from scCO2 impregnated conductive polymer films evokes intracellular Ca2 + signaling in neurotypic SH-SY5Y cells

Implantable devices for electronically triggered drug release are attractive to achieve spatial and temporal control over drug concentrations in patients. Realization of such devices is, however, associated with technical and biological challenges. Among these are containment of drug reservoirs, lack of precise control cues, as well as the charge and size of the drug. Here, we present a method for electronically triggered release of the quaternary ammonium cation acetylcholine (ACh) from an impregnated conductive polymer film. Using supercritical carbon dioxide (scCO2), a film of PEDOT/PSS (poly(3,4)-ethylenedioxythiophene doped with poly(styrenesulfonate)) is impregnated with the neurotransmitter acetylcholine. The gentle scCO2 process generated a dry, drug-impregnated surface, well suited for interaction with biological material, while maintaining normal electrochemical properties of the polymer. Electrochemical switching of impregnated PEDOT/PSS films stimulated release of ACh from the polymer matrix, likely due to swelling mediated by the influx and efflux of charged and solvated ions. Triggered release of ACh did not affect the biological activity of the drug. This was shown by real-time monitoring of intracellular Ca2+ signaling in neurotypic cells growing on the impregnated polymer surface. Collectively, scCO2 impregnation of conducting polymers offers the first one-step, dopant-independent drug impregnation process, potentially facilitating loading of both anionic and cationic drugs that can be dissolved in scCO2 on its own or by using a co-solvent. We foresee that scCO2-loaded devices for electronically triggered drug release will create novel opportunities when generating active bio-coatings, tunable for specific needs, in a variety of medical settings.

Highly Stable Bonding of Thiol Monolayers to Hydrogen-Terminated Si via Supercritical Carbon Dioxide: Toward a Super Hydrophobic and Bioresistant Surface.

Oxide-free silicon chemistry has been widely studied using wet-chemistry methods, but for emerging applications such as molecular electronics on silicon, nanowire-based sensors, and biochips, these methods may not be suitable as they can give rise to defects due to surface contamination, residual solvents, which in turn can affect the grafted monolayer devices for practical applications. Therefore, there is a need for a cleaner, reproducible, scalable, and environmentally benign monolayer grafting process. In this work, monolayers of alkylthiols were deposited on oxide-free semiconductor surfaces using supercritical carbon dioxide (SCCO2) as a carrier fluid owing to its favorable physical properties. The identity of grafted monolayers was monitored with Fourier transform infrared (FTIR) spectroscopy, high-resolution X-ray photoelectron spectroscopy (HRXPS), XPS, atomic force microscopy (AFM), contact angle measurements, and ellipsometry. Monolayers on oxide-free silicon were able to passivate the surface for more than 50 days (10 times than the conventional methods) without any oxide formation in ambient atmosphere. Application of the SCCO2 process was further extended by depositing alkylthiol monolayers on fragile and brittle 1D silicon nanowires (SiNWs) and 2D germanium substrates. With the recent interest in SiNWs for biological applications, the thiol-passivated oxide-free silicon nanowire surfaces were also studied for their biological response. Alkylthiol-functionalized SiNWs showed a significant decrease in cell proliferation owing to their superhydrophobicity combined with the rough surface morphology. Furthermore, tribological studies showed a sharp decrease in the coefficient of friction, which was found to be dependent on the alkyl chain length and surface bond. These studies can be used for the development of cost-effective and highly stable monolayers for practical applications such as solar cells, biosensors, molecular electronics, micro- and nano- electromechanical systems, antifouling agents, and drug delivery.

Conversion of sustained release omeprazole loaded buccal films into fast dissolving strips using supercritical carbon dioxide (scCO2) processing, for potential paediatric drug delivery

This study involves the development of thin oral solvent cast films for the potential delivery of the proton pump inhibitor, omeprazole (OME) via the buccal mucosa for paediatric patients. OME containing films were prepared from ethanolic gels (1% w/w) of metolose (MET) with polyethylene glycol (PEG 400) (0.5% w/w) as plasticiser, and L-arginine (l-arg) (0.2% w/w) as a stabilizer and dried in an oven at 40°C. The blank and drug loaded films were divided into two groups, one group was subjected to supercritical carbon dioxide (scCO2) treatment and the other group untreated. The untreated and scCO2 treated films were then characterised using differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, hydration (swelling), mucoadhesion and in vitro drug dissolution studies. Treatment of the solvent cast films with scCO2 caused significant changes to the functional and physical properties of the MET films. The original drug loaded MET films showed a sustained release of OME (1h), whereas scCO2 treatment of the formulations resulted in fast dissolving films with >90% drug release within 15min.

Study on the effects of pressure and material characterization in thin film and TSV fabricated by supercritical carbon dioxide electrolyte

Supercritical CO2 (sc-CO2), post sc-CO2 and traditional electroplating are used to fabricate Cu metal thin films. The effects of adjusting electroplating pressure over grain size, preferred grain orientation, mechanical properties and sheet resistance are discussed in this work. Additionally, through silicon vias (TSV) with an aspect ratio of 1:4 were fabricated by the three methods presented, and their influence over electrical resistance of the Cu pillar was observed. From the results it was clear that sc-CO2 process provides the fastest micro-hole filling at 4h, followed by post sc-CO2 process at 5h and lastly, traditional process at 36h. Moreover, grain size produced by the sc-CO2 process was smallest, calculated at 20nm; second smallest was by post sc-CO2 process at around 27nm, and the largest was traditional process at around 38nm. Fabrication process had an evident effect over grain size, hence affecting the mechanical and electrical properties of the structures. It is revealed that thin films produced by sc-CO2 process have highest hardness, highest internal stresses and lowest roughness at 64–67Hv, 45–54MPa, and 0.68–0.85µm, respectively; traditional process had the lowest values at 57Hv, 30MPa and 1.15µm respectively; and post sc-CO2 process was intermediate at 58–62Hv, 33–41MPa and 0.95–1.10µm, respectively. In sheet resistance measurements, the trend persists and the highest values were displayed by the sc-CO2 process at 1.3–1.5µΩ-cm, the lowest by traditional process at 1.1µΩ-cm, and post sc-CO2 process was intermediate at 1.2–1.3µΩ-cm. For TSV Cu pillars, the sc-CO2 process displayed the highest electrical resistance at 5mΩ, second largest was post sc-CO2 process at 1.5mΩ and the smallest was traditional process at 1.1mΩ. Sc-CO2 electroplating described in this work was performed without any additives, and still produced a high degree of grain refinement and excellent filling capabilities.

Effects of deposition and supercritical CO2 treatment parameters on physical and electrical properties of pentacene thin films

The purpose of this work is to investigate the effects of deposition and post-deposition supercritical carbon dioxide (scCO2) processing parameters on physical and electrical properties of pentacene thin films. Pentacene, a common polycyclic aromatic hydrocarbon, has been studied for its potential applications in organic thin film (OTF) transistors used for electronic devices, bio- and chemical sensors. One of the primary challenges is controlling thin film quality, which is driven by processing techniques. Here, organic vapor phase deposition was used to deposit OTF at three temperatures (623K, 643K, and 648K) and two pentacene sources (singly-sublimed and triply-sublimed). The film surface was subsequently treated with benzene-1,4-diboronic acid (BDBA), in scCO2 for further electrical property improvement. ScCO2 film treatment was performed at 313K and 323K, for a nominal range of pressures, and with up to 5mol% of methanol added as co-solvent. Results show that triply-sublimed pentacene deposited at a slower rate compared to singly-sublimed pentacene, especially at lower temperatures. Triply-sublimed pentacene films also exhibited a surface microtexture with more crystalline features and lower sheet resistivity after scCO2/methanol/BDBA treatment. BDBA sorption at the film surface depends on both film thickness and surface morphology, but not processing temperature alone.

Supercritical processing of CO2-philic polyhedral oligomeric silsesquioxane (POSS)-poly(l-lactic acid) composites

High molecular weight and semicrystalline poly(l-lactic acid) (PLLA) films were processed with supercritical carbon dioxide (scCO2) for environmentally friendly formation of porous films. The polymeric matrix was processed with supercritical CO2 and the system was rapidly depressurized to cause supersaturation of the polymer, leading nucleation and growth of the pores in the matrix. Even though saturation temperatures close to the melting points of the polymers are required to form porous matrices of semicrystalline polymers, we obtained porous PLLA with porosity up to 40% by using CO2-philic trifluoropropyl polyhedral oligomeric silsesquioxane (TFPOSS) as an additive to induce formation of pores at 313K that is about 130K lower than PLLA’s melting point. This is the first time that PLLA with crystallinity greater than 30% foamed with the supercritical fluid at a temperature close to its critical temperature. PLLA without the additive did not result in a porous matrix once it was processed under the same conditions. A non-CO2-philic POSS was also used to observe the influence of CO2-philicity, which did not induce formation of pores in the matrix under the same conditions. Additive concentration (10–30wt%), saturation temperature (313–393K), saturation pressure (10.3–20.7MPa), venting rate (0.2–10.3MPamin−1), and saturation time (2–24h) were among the studied process parameters. Saturation temperature and additive concentration were observed to have significant effects on the porosity and the average pore size of the polymeric matrix, while venting rate had an effect only on the average pore size. The indentation hardness values of the PLLA films were increased by at least 60% after the scCO2 processing. A model antibiotic, Ceftriaxone Sodium, was loaded into the samples and about 85–95% of the loaded drug released in the first hour in in vitro conditions, which can be a preferable rate in local hard tissue antibiotic applications.

Effects of supercritical carbon dioxide treatment on the morphology of poly(l‐lactide)

ABSTRACTSynthetic l‐lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO2), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO2 processing, three types of poly(l‐lactide) having different properties were assessed. The Tm of one poly(l‐lactide) sample (H‐100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H‐440) also showed a constant value of approximately 152 °C. In contrast, the poly(l‐lactide) REVODE exhibited a Tm of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H‐100 and H‐440, the Tm value of the REVODE tended to decrease with increasing pressure. The Tg values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the Tg values for the H‐440 and REVODE increased by 4 °C and 5 °C, respectively. All Tg values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χc DSC of the H‐100 was 18% initially but increased to 20% upon scCO2 processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χc DSC values for the H‐440 showed the same trend as observed with the H‐100, a different trend was seen for the REVODE. The Χc XRD values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO2 treatment. ATR FT‐IR analyses identified peaks due to semicrystalline regions in poly(l‐lactide) samples treated with scCO2, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44006.

Enhanced dispersion of nanoclays in poly(ethylene terephthalate)/clay nanocomposites using supercritical carbon dioxide

Nanoclays were prepared using supercritical carbon dioxide (scCO2) as a medium, and then blended with polyethylene terephthalate (PET) via conventional melt blending processing. The structure and morphology of nanoclays were investigated using wide‐angle X‐ray diffraction (WAXD) and scanning electron microscopy (SEM). It was found that, compared with the original organically modified layer silicates, smaller nanoclay tactoids and individual platelets morphology could be obtained after they were processed by scCO2, indicating scCO2 processing could enhance exfoliation of nanoclays. WAXD and transmission electron microscopy measurements were used to evaluate the dispersion of nanoclays in the nanocomposites. The results indicated the conventional blending extrusion processing could help to improve the dispersion of nanoclays, and the nanocomposites containing scCO2 pretreated nanoclays formed a looser clay stack and an improved intercalation structure, compared with those containing as‐received nanoclays. Thermal and mechanical properties of the nanocomposites were also studied by differential scanning calorimetry (DSC) and dynamic mechanical analysis, and the results showed that crystallization rate, crystallinity, and storage modulus of the well‐dispersed nanocomposites containing scCO2 pretreated nanoclays were increased, compared with the neat PET and nanocomposites containing as‐received nanoclays or nanoclays prepared by conventional organomodification process in water. J. VINYL ADDIT. TECHNOL., 23:E58–E67, 2017. © 2016 Society of Plastics Engineers

Formation of solid lipid microparticles from fully hydrogenated canola oil using supercritical carbon dioxide

A simple and green process based on supercritical carbon dioxide (SC–CO2) technology was used to produce solid lipid microparticles from fully hydrogenated canola oil (FHCO). The effects of pressure (122, 211 and 300 bar) and nozzle diameter (0.1, 0.3 and 14.3 mm) on the particle size, morphology, thermal properties and polymorphism were investigated. Then, the essential oil loading capacity of the particles obtained under optimum conditions was evaluated. Smaller nozzle diameter (0.1 mm) and lower pressure (122 bar) produced spherical particles with narrower particle size distribution and a mean diameter of 1.27 μm. Melting point of all particles decreased to 65 °C from 69 °C for the FHCO. The main polymorphic form of the particles obtained at lower pressures and larger nozzle diameters was α, whereas it was β at higher pressures and smaller nozzle diameters. Essential oil loading efficiency of 96% was achieved when FHCO blended with 40% essential oil was used as the feed material. SC-CO2 process is a promising technology for solid lipid particle formation as delivery vehicles for bioactives.

Impregnation of Fenofibrate on mesoporous silica using supercritical carbon dioxide

Low oral bioavailability can be circumvented by the formulation of the poorly water soluble drug in ordered mesoporous silica (OMS-L-7). Fenofibrate is an orally administered, poorly water-soluble active pharmaceutical ingredient (API), used clinically to lower lipid levels. Fenofibrate was loaded into silica using two methods: incipient wetness and supercritical impregnation. This study investigates the impact of loading and the impact of varying supercritical carbon dioxide (scCO2) processing conditions. The objective is to enhance Fenofibrate loading into silica while reducing degree of the drug crystallinity, so as to increase the drug's dissolution rate and its bioavailability. The comparison of both impregnation processes was made in terms of impregnation yields and duration as well as physical characterization of the drug.While incipient wetness method led to a Fenofibrate loading up to 300mgdrug/gsilica in 48h of impregnation, the supercritical impregnation method yielded loading up to 485mgdrug/gsilica in 120min of impregnation duration, at 16MPa and 308K, with a low degree of crystallinity (about 1%) comparable to the crystallinity observed via the solvent method. In addition to the enhancement of impregnation efficiency, the supercritical route provides a solvent-free alternative for impregnation.

Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. 3D porous architectures featured by higher specific surface areas and larger pore volumes have received great interest, which not only maximize the availability of electron transfer within nanosized electrocatalyst surface area but also provide better mass transport of reactants to the electrocatalyst. Supercritical CO2 (scCO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials. Herein, we developed the scCO2 technique to synthesize boron-doped 3D graphene and low Pt group metal-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability for the ORR, holding great promise for the development of PEMFCs.

Supercritical CO2 sorption kinetics and thymol impregnation of PCL and PCL-HA

The potential of supercritical carbon dioxide (scCO2) processing of polycaprolactone (PCL) and polycaprolactone-hydroxyapatite (PCL-HA) composites for obtaining functional porous scaffolds at moderate temperatures (35–40°C) was analyzed and quantified. The effect of scCO2 sorption kinetics on the swelling, foam morphology and thermal behavior of the PCL and PCL-HA composites was studied. Sorption isotherms were determined using magnetic suspension balance at 10–30MPa and 35–40°C. Influence of the pressure, HA amount (10–20%) and procedure for HA powder preparation on the sorption kinetics was discussed. Supercritical solvent impregnation (SSI) of PCL and PCL-HA with thymol was investigated as environmentally friendly way to produce functional scaffolds with controlled microstructure. Moderately high pressures (13–17MPa) and 10% of HA were proven to be favorable for creation of the PCL scaffolds with satisfying foam microstructure (mean pore size ∼200–300μm), filler distribution and thymol impregnation yields (12–18%). This was due to the satisfactory high scCO2 solubility (0.25–0.30g/g) and mass transfer rate (∼10−10m2/s) in the polymer phase as well as its great plasticizing effect (−ΔTm=26.4–27.4°C). Higher saturation of the polymer phase with scCO2 (0.30–0.55g/g), filler amount (20%) and thymol solubility in scCO2 (>5.5g/kg) at pressures above 20MPa resulted in decreased mass transfer rate and SSI efficiency.

Facile Synthesis of Three-Dimensional Graphene Nanomaterials via Supercritical Fluid for Oxygen Reduction Reaction

The considerable interest in polymer electrolyte membrane fuel cells (PEMFCs) has sparked a sustained research effort on more active and reliable oxygen reduction reaction (ORR) electrocatalyst. Although great progress has been made on ORR catalysts in recent decades, the further development of PEMFCs is severely restrained by high-priced Pt in the cathode catalysts and the slow kinetics of the ORR. Control of nanostructures at the atomic level can precisely and effectively tune catalytic properties of materials, optimizing the structural and compositional effect and further enabling enhancement in both activity and durability. Besides, most electrochemical systems consist of porous electrode materials. These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes, not only maximizing the availability of electron transfer within nanosized electrocatalyst surface area but also providing better mass transport of reactants to the electrocatalyst. Fabricating interconnected mesoporous arrays/superstructures is critical to achieve both high surface area and fast mass transfer. Under the circumstances, constructing novel 3D porous nanostructures with non- and low Pt group metal (PGM) nanocatalysts have received significant attention to further enhance ORR electrocatalytic performance. Supercritical CO2 (sc-CO2) process offers an elegant and efficient route for the synthesis and processing of novel nanocomposite materials, consisting of active nanocarbon and nanocrystals. Herein, we developed the sc-CO2 technique to synthesize boron-doped 3D graphene and low PGM-based graphene/PtFe with 3D porous nanostructures. Significantly, these 3D nanocomposites show excellent electrocatalytic activity and high stability toward the ORR, holding great promise for the development of PEMFCs.

Investigation of factors influencing the hydrolytic degradation of single PLGA microparticles

Poly lactide-co-glycolide (PLGA) is an important polymer matrix used to provide sustained release across a range of active pharmaceutical ingredients (APIs) and works by hydrolytic degradation within the body, thereby releasing entrapped drug. Processing and sterilisation can impact on the morphology and chemistry of PLGA therefore influencing the hydrolysis rate and in turn the release rate of any entrapped API. This paper has looked at the effect of supercritical carbon dioxide (scCO2) processing, gamma irradiation, comonomer ratio and temperature on the hydrolysis of individual PLGA microparticles, using a combination of Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) imaging, Scanning Electron Microscopy (SEM), Differential Scanning Calorimetery (DSC) and Gel Permeation chromatography (GPC) to facilitate a better understanding of the physiochemical factors affecting the hydrolysis rate. This work has shown that scCO2 processing influences hydrolysis rates by increasing the porosity of the PLGA microparticles, increasing the lactide comonomer ratio decreases hydrolysis rates by reducing the hydrophilicity of the PLGA microparticles and increasing the gamma irradiation dose systematically increases the rate of hydrolysis due to reducing the overall molecular weight of the polymer matrix via a chain scission mechanism. Moreover this work shows that ATR-FTIR imaging facilitates the determination of a range of physicochemical parameters during the hydrolysis of a single PLGA microparticle including water ingress, water/polymer interface dimensions, degradation product distribution and hydrolysis rates for both lactide and glycolide copolymer units from the same experiment.

Complete glutaraldehyde elimination during chitosan hydrogel drying by SC-CO2 processing

Chitosan (CH) is one of the polymers most frequently proposed in form of hydrogels for tissue engineering (TE) applications. It is often crosslinked with the aim of improving its stability and mechanical properties. In this work, a supercritical carbon dioxide (SC-CO2) gel drying process was proposed to obtain CH scaffolds and, for the first time, the simultaneous elimination of unreacted glutaraldehyde (GTA), taking advantage of its solubility in supercritical mixtures.SC-CO2 gel dried crosslinked CH aerogels showed a nanofibrous structure characterized by an average diameter of about 100nm. No collapse of the nanostructure was observed in the aerogels, due to the peculiarities of supercritical fluids (e.g., near zero surface tension). Moreover, crosslinked CH showed a thermally stable structure, as determined by TGA analysis. The hypothesis that a supercritical mixture is able to efficiently extract GTA residues entrapped in the gel matrix was also verified: negligible residues of GTA were found at the end of release experiments; in particular, at the best operating conditions, a GTA concentration equal to 0.013ppm was detected. Therefore, the produced crosslinked CH aerogels can be effectively and safely used for TE applications.

Electroless Copper Plating on Polyester Fabric Modified with Silane through Supercritical Carbon Dioxide Process

Polyester fabric was pretreated with 3-aminopropyltrimethoxysilane (APTMS) through supercritical carbon dioxide (scCO2) process before electroless copper plating. APTMS pretreated polyester fibers were characterized by contact angle. Deposit weight, surface morphology and electromagnetic interference (EMI) shielding effectiveness (SE) of electroless copper plated polyester fabrics were investigated. The results show that polyester fibers are covered with APTMS after APTMS modification in scCO2 medium. Copper coatings on the polyester fibers are uniform after copper plating. Electromagnetic interference shielding effectiveness of the copper plated polyester fabric arrives at 60-80dB at frequencies ranging from 2 to 18 GHz.

Solubility of all-trans retinoic acid in supercritical carbon dioxide

All-trans retinoic acid (ATRA) is a derivative of retinol (or vitamin A) presenting similar benefits but considerable lower adverse toxicity, mainly in cases of high or long-term therapeutic doses. ATRA showed to be effective in the treatment and/or chemoprevention of several epithelial and hematological malignancies and diverse dermatological and eye diseases however, its low solubility in aqueous media and photosensitivity hinder its wider usage by the conventional administration methods. Supercritical fluids technologies are being widely used to enhance the in vivo bioactivity of this type of drugs both by improving their dissolution rate (using particle size reduction processes) and/or by controlling their release into the media after incorporation into solid polymeric/inorganic matrices (using supercritical impregnation/foaming processes). In both cases the solubility of the drug in the supercritical fluid (usually scCO2) is required for process optimization purposes. Therefore, in this work the solubility of ATRA in scCO2 was measured at different isotherms (308.2, 318.2 and 328.2K) and pressures that ranged from 10 up to 30MPa using a static analytical method. Solubility data were correlated using three commonly used density-based models, namely the Bartle, Chrastil and Méndez-Santiago–Teja models. The solubility of ATRA in scCO2 was found to be between 1.52×10−6 and 1.84×10−5 in terms of ATRA mole fraction and between 7.50×10−3 and 1.07×10−1 in terms of amount of solid solute per unit of volume of scCO2. Fairly good correlation agreement was obtained with all the applied models being the lowest deviations obtained with the Chrastil model. ATRA particles obtained after scCO2 processing (dissolution in scCO2 followed by re-precipitation) were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and in vitro dissolution studies. The results showed that the processed particles maintained their chemical structure and presented enhanced dissolution in aqueous media (PBS:ethanol, 80:20, v/v) when compared with commercial (non-processed) ATRA.

Enhanced electrical properties of polycarbonate/carbon nanotube nanocomposites prepared by a supercritical carbon dioxide aided melt blending method

Polycarbonate/carbon nanotube (CNT) nanocomposites were generated using a supercritical carbon dioxide (scCO2) aided melt blending method, yielding nanocomposites with enhanced electrical properties and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Baytubes® C 150 P CNTs were benignly deagglomerated with scCO2 resulting in 5 fold (5X), 10X and 15X decreases in bulk density from the as-received CNTs. This was followed by melt compounding with polycarbonate to generate the CNT nanocomposites. Electrical percolation thresholds were realized at CNT loading levels as low as 0.83 wt% for composites prepared with 15X CNT using the scCO2 aided melt blending method. By comparison, a concentration of 1.5 wt% was required without scCO2 processing. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO2 processing compared to direct melt blending, but was significantly worse than that of twin screw melt compounded nanocomposites reported in the literature. A rheologically percolated network was observed near the electrical percolation of the nanocomposites. The importance of maintaining longer carbon nanotubes during nanocomposite processing rather than focusing on dispersion alone is highlighted in the current efforts.

Influence of physical state of intercalating agents on intercalation process of high speed airflow pretreated montmorillonite in supercritical carbon dioxide

The work aimed at studying the effect of scCO2 processing technology on basal spacing, surface morphology and thermal stability of sodium montmorillonite (MMT) that were pretreated with high speed airflow pulverization method and then modified using myristyltrimethylammonium bromide (MTAB) and tetradecyltrihexylphosphonium chloride (TDTHP) with scCO2 as the medium. X-ray diffraction (XRD) showed that physical state of intercalating agents played an important role on the intercalation process in scCO2. Solid-state MTAB could hardly intercalate into the interlayer of pretreated MMT (PMMT), though addition of co-solvent benefited the intercalation to some extent. However, liquid TDTHP could intercalate into the interlayer of PMMT easily even without co-solvent and the basal spacing of TDTHP-modified PMMT was larger than that of MTAB-modified PMMT. Scanning electron micrographic (SEM) showed the large compact structure for MMT broke into small random structures after airflow processing and some smaller tactoids and more dispersed structures can be observed for both MTAB-modified PMMT and TDTHP-modified PMMT compared to unprocessed MMT. For TDTHP–PMMT, many clay platelets that were separated from the tactoidal structure and more dispersed structure were observed, which may be helpful for MMT exfoliation and dispersion in polymers. Thermogravimetric analysis (TG) demonstrated that TDTHP-modified PMMT was up to 100°C more stable than MTAB-modified PMMT. These results are very important and relevant to the preparation and application of MMT/polymer nanocomposites.