Dispersion polymerization of <Emphasis Type="Italic">N</Emphasis>-vinyl caprolactam in supercritical carbon dioxide

Dispersion polymerization of N-vinyl caprolactam (NVCL) was carried out in supercritical carbon dioxide (scCO₂) using three surfactants. The polymerization was performed in the presence of fluorine-based poly(heptadecafluorodecyl acrylate) (PHDFDA), poly(heptadecafluorodecyl methacrylate) (PHDFDMA) or siloxane-based PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA) as a surfactant. FE-SEM and image analyzer were used to characterize particle morphology, size, and size distribution. When fluorine-based surfactants were used, spherical PVCL particles were obtained. Using Monasil PCA resulted in agglomerated and irregular polymer particles. The effect of concentration of surfactants, initiators, and monomer, and reaction pressure on the particle morphology, average particle size and particle size distribution (PSD) was also investigated with fluorine-based surfactant, PHDFDA or PHDFDMA.     

Supercritical antisolvent micronization of PVP and ibuprofen sodium towards tailored solid dispersions

The supercritical antisolvent technology is used to precipitate polyvinylpyrrolidone (PVP) particles and crystallise ibuprofen sodium (IS) crystals separately and in the form of solid dispersion together. Supercritical carbon dioxide (scCO₂) is used as antisolvent. For PVP particle generation, ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 wt% and 1.5 wt%, the operation pressure between 10 MPa and 30 MPa and the composition of ethanol/acetone solvent mixtures between 100 wt% and 0 wt% of ethanol at a constant temperature of 313 K. Furthermore, the mean molecular weight of the polymer was varied between 40 kg mol⁻¹, 360 kg mol⁻¹ and 1300 kg mol⁻¹. An increase of the content of the poor solvent acetone in the initial solvent mixture as well as the usage of PVP with a higher molecular weight, leads to a significant decrease in mean particle size. At all the investigated parameters always fully amorphous PVP powder precipitates. For IS, only ethanol was used as the solvent, the initial IS concentration in the solution was varied between 1 wt% and 3 wt% and the operation pressure between 10 MPa and 16 MPa. A variation of these parameters leads to a manipulation of the size and the morphology of the crystallised IS crystals. Irrespective of the parameters used, always the same polymorphic form of ibuprofen sodium is produced. The solid dispersions were generated at different compositions of PVP to IS and with two different molecular weights of PVP at otherwise constant conditions. Fully amorphous solid dispersions consisting of IS and PVP together were generated at different ratios of PVP to IS.The mechanisms that control the final particle properties are discussed taking into account two different models for “ideal” and “non-ideal” solutes. Furthermore, the study of the “unconventional” SAS parameters, molecular weight and solvation power of the solvent shows that these parameters qualify to tailor polymer particle properties via SAS processing. Next to the investigation into the behaviour of both solutes separately, fully amorphous solid dispersions consisting of IS and PVP together were generated. While X-ray diffraction was used to analyze the crystalline structure of the particles, respectively, solid dispersions, their morphology was analysed using scanning electron microscopy (SEM).     

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1 W cm⁻² and then it was found to decrease with a further increase to 33.80 W cm⁻². The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40 nm.     

Formation of PVP hollow fibers by electrospinning in one-step process at sub and supercritical CO2

It was well known that electrospinning is one of the simple technical methods for the production of polymer nanoparticles and nanofibers. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years mostly in solvent solution and some in melt form. In this work, hollow fibers with walls made of organic polymer composites have been formed by electrospinning in a single processing step under pressurized carbon dioxide (CO₂). The experiments were conducted at 313 K and ∼8 MPa. The capability and feasibility of this technique was demonstrated by the production of polyvinylpyrrolidone (PVP) fibers whose size and wall thickness could be independently varied by controlling a set of experimental parameters. The PVP fibers had an average pore diameter 2–4 μm. At low pressures (<5 MPa; subcritical conditions), the solid fibers were formed, the baloon-like structures of PVP was formed with increasing pressure of CO₂ at 8 MPa (supercritical condition)     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Deposition of aromatic polyimide thin films in supercritical carbon dioxide

The deposition of aromatic polyimide (API) thin films was carried out in supercritical carbon dioxide (scCO₂) with 20 mol% of N,N-dimethylformamide (DMF) as a cosolvent, and using 4,4′-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) as monomers. A new apparatus based on a flow method that consisted of a cold-wall type reactor and two supply lines for each of the API monomers was used. The effect on the morphology of the films was investigated at feeding monomer concentrations and deposition temperatures ranging from 5 × 10⁻⁴ to 5 × 10⁻⁶ on a mole fraction basis and from 423 to 523 K, respectively. The results showed that increasing the monomer concentration and decreasing the deposition temperature increased the thickness of the films, and a smooth surface of the film was obtained at 423 K. Additionally, FT-IR study and thermogravimetric (TG) analysis of the film deposited at monomer mole fractions of 5 × 10⁻⁵ and at a deposition temperature of 473 K were also carried out. The FT-IR spectrum of the deposited film in scCO₂ with DMF represented imide structures although there was a small peak of amide carbonyl stretching that originated from the polyamic acid and DMF. The TG curve indicated the temperature of 5% weight loss was more than 800 K under an air atmosphere after complete imidization.     

Effect of operating parameters on PVP/tadalafil solid dispersions prepared using supercritical anti-solvent process

Supercritical anti-solvent (SAS) process was employed to produce tadalafil solid dispersion sub-micron particles. Three independent variables for the SAS process (temperature, pressure, and drug concentration) were varied in order to investigate the effects on particle size and morphology of PVP/tadalafil solid dispersion (drug to polymer ratio 1:4). The mean particle size decreased with decreasing temperature (50 → 40 °C) and concentration (15 → 5 mg/mL) and increasing pressure (90 → 150 bar). Depending on the experimental variable, the mean particle size varied from 200 nm to 900 nm, and the dominant experimental variable was determined to be the drug concentration. Moreover, at a concentration of 15 mg/mL with any other process conditions, tadalafil tended to partially aggregate in crystalline form with irregular particle shapes. The results of in vitro dissolution experiments showed good correlation with mean particle size and crystallinity of the SAS-processed particles, in that the highest drug concentration showed the least dissolution rate and vice versa. Therefore, among the three variables studied, the drug concentration is the major factor that produces sub-micron particles in the SAS process.     

On the effects of emulsion polymerization of furfuryl alcohol on the formation of carbon spheres and other structures derived by pyrolysis of polyfurfuryl alcohol

Carbon spheres were synthesized by emulsion polymerization and pyrolysis of polyfurfuryl alcohol. Pluronic F-127 was used as the structure-directing agent to synthesize polymer spheres that after pyrolysis led to carbon spheres with average sizes from 50 nm to few micrometers in diameter depending upon the conditions of polymerization. As-synthesized carbon spheres possess high surface areas of around 480 m²/g with an average mean pore size of 0.5 nm. These spheres can be activated using carbon dioxide to create much higher surface areas (>1500 m²/g). Different compositional regions of the pseudo-ternary phase diagram of surfactant/monomer/solvent were explored in order to determine the effects of changes in the emulsion polymerization variables on the kinds of carbon morphologies that could be derived from polyfurfuryl alcohol after pyrolysis. The diameter of the carbon spheres was found to be sensitive to monomer and surfactant concentrations, acid molarity and solvent composition. In general, the diameter of the spheres grew with increasing furfuryl alcohol concentration and decreasing surfactant concentration, respectively. By varying the acid concentration and solvent composition, a minimum diameter for spheres was found. The formation and size of the spheres are strongly influenced both by micelle growth and the polymerization mechanism.     

Electrochromic performance and ion sensitivity of a terthienyl based fluorescent polymer

A novel terthienyl based fluorescent polymer bearing strong electron-withdrawing substituents directly attached to the 3,4-positions of the central thiophene ring was synthesized by electrochemical polymerization of diethyl 2,5-di(3,4-ethylenedioxythiophen-2-yl)thiophene-3,4-dicarboxylate. The corresponding polymer was characterized by cyclic voltammetry, FT-IR and UV–vis spectroscopy. The polymer has a well-defined redox process (E_p,1/2 = 0.74 V) and demonstrates a reversible electrochromic behavior; lilac in the neutral state and transparent sky blue in the oxidized state. Also, the polymer had low band gap (E_g = 1.82 eV) and high redox stability (retaining 94.0% of its electro-activity after 500th switch). Moreover, the sensitivity of both the monomer and its polymer towards metal cations was investigated by monitoring the change in the fluorescence intensity. Among various common ions both the monomer and its polymer were found to be selective towards Cu²⁺ and Cu⁺ ions by quenching the fluorescence efficiency with a Stern–Volmer constant (K_sv) of (1.4–1.6 × 10³ M^?1) and (1.5–1.8 × 10² M^?1) for monomer and polymer solutions, respectively.     

Mechanical strength and damage tolerance of highly porous alumina ceramics produced from sintered particle stabilized foams

Highly porous alumina particle stabilized foams were prepared by combining the concepts of particle stabilized foams and gelcasting, using sulfonate surfactants and poly vinyl alcohol (PVA) as the gelcasting polymer. The ceramic samples sintered at 1500 °C for 2 h had porosities from 65% to 93%, with pore sizes in two categories: “big pore” around 300 μm and “small pore”, around 100–150 μm, depending on the type and amount of surfactant added. The mechanical behaviour of the foams (axial and diametral compression) depended on the overall porosity and pore size. On average, tensile and compressive strengths around 5 and 16 MPa respectively were measured for samples with bigger pore sizes and larger porosities. Samples with smaller pore sizes and lower porosities produced average values of 12 and 57 MPa for tensile and compressive strengths, respectively. The elastic modulus reached a maximum around 3GPa for “small pore” size samples. The effect of increasing amount of PVA in the samples had a strong effect on the green mechanical strength, but it did not significantly affect the mechanical response of the sintered alumina foams. Large and complex shape sintered components produced using this route showed a remarkable damage tolerance, due to crack tip blunting.     

Dense CO2 antisolvent precipitation of levothyroxine sodium: A comparative study of GAS and ARISE techniques based on morphology and particle size distributions

Morphology and particle size distribution of levothyroxine sodium are experimentally investigated by comparing gas antisolvent (GAS) and atomized rapid injection for solvent extraction (ARISE) techniques using dense CO₂. Precipitation of levothyroxine sodium from ethanol was carried out at 25, 40 and 50 °C, with pressure in the 90–120 bar range and different concentrations of the organic solution. Particles produced by the GAS process are nanospheres whereas ARISE processed particles are either spherical or rod-like micro and nanoparticles. Particle size and size distributions of GAS processed levothyroxine sodium are in the 370–500 nm range, while the ARISE process produced particles in the 360–1200 nm range. In most cases, both techniques produced bimodal size distributions, due to particle agglomeration. The different morphological characteristics and particle size distributions of levothyroxine sodium obtained using GAS and ARISE at different operating conditions can be useful depending on the type of drug formulation chosen, as well as the route of drug administration and delivery system.     

Supercritical carbon dioxide immobilization of glucose oxidase on polyurethane/polypyrrole composite

Glucose oxidase (GOX) was immobilized on polyurethane/polypyrrole (PU/PPY) composite foam via supercritical fluid immobilization (SFI) towards the preparation of biosensors. Buffer solution was used as the immobilization medium along with scCO₂. To provide insight into the relation between the scCO₂ and the GOX-buffer solution, the GOX-buffer solutions were subjected to scCO₂ and the protein amounts of the GOX-buffer solutions before and after scCO₂ exposure were determined at 80, 100 and 150 bar and 30, 40 and 50 °C for an exposure time of 24 h. The protein amount in GOX-buffer solution decreased in all cases after exposure to scCO₂. The lowest and highest loss in GOX amounts observed were 2.9 and 36.4 μg at 80 bar, 30 °C and 100 bar, 50 °C, respectively. The effects of immobilization pressure (80, 100 and 150 bar), temperature (30, 40 and 50 °C) and time (4, 24 and 72 h) on the activities of the GOX-immobilized PU/PPY composites were investigated. At 30 °C immobilization temperature, the activity values of the GOX-immobilized PU/PPY composites were slightly increased as the pressure was increased from 80 to 100 bar. Further increase in immobilization pressure from 100 to 150 bar at 30 °C caused a decrease in the activity values. At 40 °C immobilization temperature, increasing the immobilization pressure from 80 to 100 bar did not provide an increase in activity values, but further increase to 150 bar caused a decrease in the activity values. At 100 bar immobilization pressure, decrease in temperature enhanced the activity values of the samples. When immobilization was performed via SFI, the activity values were doubled compared to the immobilization at atmospheric conditions. Among all the immobilization pressures and temperatures investigated, both the highest activity (U/cm²) and the highest specific activity (U/mg) were obtained for the samples processed at 100 bar, 30 °C.     

Novel alkyl methylnaphthalene sulfonate surfactants: A good candidate for enhanced oil recovery

The surface tensions of various surfactant aqueous solution and the dynamic interfacial tensions between the Shengli oil field of China crude oil and the solution of novel surfactants, a series of single-component alkylmethylnaphthalene sulfonates (AMNS) including various the length of alkyl chains (hexyl, octyl, decyl, dodecyl and tetradecyl, developed in our laboratory), were measured. It is found that synthesized surfactants exhibited great capability and efficiency of lowering the solution surface tension. The critical micelle concentrations, CMC were: 6.1–0.018×10⁻³ mol L⁻¹, and the surface tensions at CMC, γ_CMC were: 28.27–35.06 mN m⁻¹. It is also found that the added surfactants are greatly effective in reducing the interfacial tensions and can reduce the tensions of oil–water interface to ultra-low, even 10⁻⁶ mN m⁻¹ at very low surfactant concentration without alkali. The addition of salt, sodium chloride, results in more effectiveness of surfactant in reducing interfacial tension and shows that there exist obviously both synergism and antagonism between the surfactant and inorganic salt. All of the synthesized surfactants, except for hexyl methylnaphthalene sulfonate, can reduce the interfacial tension to ultra-low at an optimum surfactant concentration and salinity. Especially Tetradec-MNS surfactant is most efficient on lowering interfacial tension between oil and water without alkaline and the other additives at a 0.002 mass% of very low surfactant concentration. Both chromatogram separation of flooding and breakage of stratum are avoided effectively, in addition to the less expensive cost for enhanced oil recovery, and therefore it is a good candidate for enhanced oil recovery.     

Microwave assisted hydrothermal synthesis of engineered cerium oxide nanopowders

Cerium oxide nanopowders have been prepared via microwave assisted hydrothermal technique in the presence of different amounts of poly vinyl pyrrolidone (PVP). The prepared nanopowders were characterized using XRD, TEM and SAED. The results showed that the particle size of the ceria nanopowders was decreased with the increase of PVP amount. The prepared ceria has nanocrystalline cubic fluorite structure with high purity. The influence of PVP content on the densification behavior of CeO₂ was investigated by means of dilatometer and scanning electron microscopy (SEM). It was found that the increase of PVP amount reduced sintering temperature. The cold-pressed powders can be sintered to full density at temperatures starting from 1070 °C in just 10 min.     

Formation and stabilization of submicron particles via rapid expansion processes

Submicron particles were produced by rapid expansion of supercritical solution into air (RESS) or an aqueous surfactant solution (RESSAS) to minimize particle growth and to prevent particle agglomeration. Thereby the effect of process conditions on the size of the particles precipitated was investigated. The obtained product was evaluated by measuring particle size by 3-wavelength extinction measurements, dynamic light scattering, specific surface areas by nitrogen gas adsorption, melting behaviour by differential scanning calorimetry, particle morphology by X-ray diffraction, scanning electron micrographs (SEM), and drug loading by high performance liquid chromatography.Prior to the particle formation experiments, the melting temperature of Salicylic acid under CO₂ pressure and the solubility of Salicylic acid in CO₂ were measured. The size of Salicylic acid particles produced via RESS decreased from 230 to 130 nm as the pre-expansion temperature decreased from 388 to 328 K and the specific surface area of the micronized particles was found to be up to 60 times higher than that of the unprocessed material. RESSAS experiments demonstrate that in 1 wt.% Tween 80 solutions Salicylic acid concentrations of 4.6 g/dm³ could be stabilized with particle diameters in the range of 180 nm. Additional experiments show that Ibuprofen nanoparticles with an average size of 80 nm and a drug concentration of 2.4 g/dm³ could be stabilized in 1 wt.% Tween^® 80 solutions. The use of a SDS solution instead of Tween^® 80 results in a stable aqueous suspension of phytosterol nanoparticles, where the average particle size is 50 nm at a drug concentration of 5.6 g/dm³.     

Monodisperse biopolymer nanoparticles by Continuous Supercritical Emulsion Extraction

In this work Continuous Supercritical Emulsions Extraction (SEE-C) has been tested to produce monodisperse biopolymer nanoparticles. The SEE-C technology allows an improved control of particle size distribution by reducing the emulsion processing times and preventing any droplet/particle aggregation. Biopolymers as, poly-lactic acid (PLA), poly-caprolactone (PCL) and poly-lactic-co-glycolic acid (PLGA) in different emulsion formulations were tested using acetone as oily-phase solvent. Emulsion formulation parameters, such as surfactant and/or polymer concentration and emulsification techniques (ultrasound or high speed emulsification) were analyzed in connection to SEE-C, to produce monodisperse nanoparticles. Operating at 38 °C and 80 bar, with an L/G ratio of 0.1, particles of PLA, PCL and PLGA with mean size of 233 nm, 342 nm and 212 nm, respectively, were produced. Poly-dispersity indexes lower to 0.1 nm were also obtained, confirming the possibility to obtain sharp distributions with monodisperse characteristics. Solvent residues as low as 500 ppm were also observed.     

Micronization and characterization of squid lecithin/polyethylene glycol composite using particles from gas saturated solutions (PGSS) process

Lecithin was isolated from squid viscera residues after supercritical carbon dioxide (SC-CO₂) extraction at 25 MPa and 45 °C. The particle formation of squid lecithin with biodegradable polymer, polyethylene glycol (PEG) was performed by PGSS using SC-CO₂ in a thermostatted stirred vessel. By applying different temperatures (40 and 50 °C) and pressures (20–30 MPa), conditions were optimized. Two nozzles of different diameters (250 and 300 μm) were used for PGSS and the reaction time was 1 h. The average diameter of the particles obtained by PGSS at different conditions was about 0.74–1.62 μm. The lowest average size of lecithin particle with PEG was found by the highest SC-CO₂ density conditions with the stirring speed of 400 rpm and nozzle size of 250 μm. The inclusion of lecithin in PEG was quantified by HPLC. Acid value and peroxide value was measured after micronization of lecithin.     

Precipitation kinetics of PMMA sub-micrometric particles with a supercritical assisted-atomization process

Sub-micrometric particles of PMMA were successfully prepared via a supercritical assisted-atomization (SAA) process using acetone as a solvent and supercritical carbon dioxide as a spraying medium. The effects of several key factors on the particle size were investigated. These factors included the concentration of polymer solution, temperature in saturator and volumetric flow rate ratio of carbon dioxide to polymer solution. The shape of the polymer's primary particles is spherical with the arithmetic mean size ranging from 82 nm to 176 nm and the mass-weighted mean size ranging from 127 nm to 300 nm. As evidenced from the experimental results, the lower concentrations of polymer solution, optimized volumetric flow rate ratios, and higher temperatures in saturator can effectively reduce the mean particle size. The precipitation kinetic parameters were determined from the particle size distributions with the aid of the population balance theory. This study found the primary nucleation to be dominant in the precipitation and diffusion may govern particle growth.     

Polymethylmethacrylate (PMMA) sub-microparticles produced by Supercritical Assisted Injection in a Liquid Antisolvent

A recently developed supercritical assisted process, called Supercritical Assisted Injection in a Liquid Antisolvent (SAILA) is proposed to produce polymer micro and nanoparticles in water stabilized suspensions. Polymethylmethacrylate (PMMA) has been selected as the model polymer for a systematic study of the influence of the SAILA operating parameters on particle morphology and diameter. The effect of expanded liquid injection pressure on particle size and distribution was studied and different expanded liquid temperatures and compositions were also explored. Successful precipitation of the polymer in a water stabilized suspension was obtained and narrow particle size distributions were obtained using 70 and 90 bar injection pressures. PMMA particles controlled diameter were produced ranging between 0.2 ± 0.04 μm and 0.9 ± 0.2 μm. Particles are formed from the expanded liquid solution as a consequence of very fast supersaturation produced by spraying it the liquid antisolvent.     

Preparation of Ni0.1Mg0.9O nanocrystalline powder and its catalytic performance in methane reforming with carbon dioxide

Ni_0.1Mg_0.9O nanocrystalline powders were prepared by surfactant assisted precipitation method and employed as catalyst in dry reforming. The powders were characterized by using XRD, BET, SEM, TGA/DSC and TPR techniques. The results showed that the surfactant to metal mole ratio affects the textural properties. Increasing in surfactant to metal mole ratio increased the specific surface area and decreased the crystallite and particle size. The Ni_0.1Mg_0.9O with the highest surface area (115.39 m² g^?1) was employed as catalyst in dry reforming. This catalyst showed a high catalytic activity and stability during 122 h time on stream without any decrease in methane conversion.