Samuel P. Sawan

Interaction of supercritical carbon dioxide with polymers. I: Crystalline polymers

Supercritical fluid (SCF) technology involving carbon dioxide is recently receiving wide attention due to its vast potential application in various fields such as cleaning, extraction, synthesis, etc., in addition to its environmental benefits. To fully exploit the use of SCFs in new technologies, it is important to understand how SCFs interact with materials. To this end, we have undertaken a systematic study involving a wide pressure and temperature range to investigate the interaction of supercritical carbon dioxide (SC CO2) with nine different crystalline polymers, namely, substituted and unsubstituted polyethylene (four varieties), polypropylene, nylon 66, poly(ethylene terephthalate), poly(oxymethylene), and poly(vinylidine fluoride). Critical factors such as changes in appearance and weight, temperature, pressure and time of the supercritical fluid treatment, and dimension of samples have been observed. The influence of SC CO2 on the thermal properties of treated polymers has been investigated through TGA analysis. Further, changes in the mechanical properties such as yield strength, ultimate elongation, and modulus of elasticity of the investigated crystalline polymers were also observed. A discussion has been included to show the possible implications of the observed changes in realizing various applications.

Interaction of supercritical carbon dioxide with polymers. II. Amorphous polymers

In continuation of our goal to implement supercritical fluid (SCF) technology for various applications such as precision cleaning, foaming, and impregnation of materials, a systematic study has been performed involving amorphous polymers. Eleven different polymers of amorphous nature have been subjected to supercritical carbon dioxide (SC CO2) treatment under a wide pressure and temperature range (1000–3000 psi and 25–70°C, respectively). The influence and impact of such treatment on the appearance, weight change, and thermal and mechanical properties were followed systematically. In addition, the effect of treatment conditions and dimension of the samples on weight changes were also monitored. It has been found that amorphous polymers can absorb carbon dioxide to a greater extent than crystalline polymers and, in turn, the phenomenon of plasticization was also very high. In addition to morphology, the polarity of the polymer is also crucial in determining the solubility in carbon dioxide. Comparison was also made with the behavior of crystalline polymers.

Role of Si-H and Si-H2 in the photoluminescence of porous Si

FTIR spectra reported by Brandt et al. [Solid State Commun. 81, 307 (1992)], Tischler et al. [Appl. Phys. Lett. 60, 639 (1992)], and Tsai et al. [Appl. Phys. Lett. 59, 2814 (1991), and 60, 1700 (1992)] have shown the presence of Si‐H and Si‐H2 lines in porous Si which Canham [Appl. Phys. Lett. 57, 1046 (1990)], Tischler and Tsai have considered essential to the observation of visible photoluminescence (PL). Hydrogen has been ascribed as a surface passivating agent which eliminates nonradiative transitions thus enabling PL to occur. Photo‐oxidation has been described as replacing some of the surface passivants with oxygen, generating nonradiative transitions which quench the PL. We have markedly reduced the Si‐H and Si‐H2 content of anodized samples by treatment with CCl4 vapor. Comparison of the photoluminescent emission and excitation spectra for CCl4 treated and untreated samples show very similar results. Comparison of the FTIR spectra of photo‐oxidized samples which exhibit no PL and as‐anodized sampl...

UV curable bioadhesives: Copolymers of N‐vinyl pyrrolidone

A series of UV curable bioadhesives was prepared from copolymers of N-vinyl pyrrolidone with four different comonomers: 2-acrylamido methyl 1-propane sulfonic acid, vinyl succinimide, glycidyl acrylate, and 2-isocyanatoethyl methacrylate. The developed bioadhesives demonstrated a fast UV-induced setting with a set time of about 3 min. Bond strength between the bioadhesive and porcine intestine specimen was determined by the peel test. These bioadhesives can provide improved adhesion values up to 4.6 N/m of 180 degrees peel strength compared to five different commercial bioadhesives (values ranging from 0.52 to 3.04 N/m). In addition, the fully hydrated UV curable bioadhesives have shown a high water uptake ranging from 25 to 350 wt% and equilibrium water content ranging from 20 to 100 wt%. Because N-vinyl pyrrolidone is a monomer all these copolymers are expected to retain good biocompatibility. Obtained promising results of peel strength and water uptake clearly suggest that the developed bioadhesives have a strong potential for many medical applications such as single-layered hydrogel wound dressings and tissue adhesives.

Residual stability of lipase from Candida rugosain hexane, supercritical CO , and supercritical SF

Lipase from Candida rugosa (EC 3.1.1.3) lost only 15% of its activity when held in supercritical CO and about 10% activity in both supercritical SF and hexane even after two days of incubation at up to 60°C and 82 atm.A pressure of 680 atm resulted in up to 15% loss of enzyme activity in supercritical CO and only about 5% loss of activity in supercritical SF 6 even at 410 atm. There was about 60% decrease in enzyme activity even at 1% water content in supercritical CO . Supercritical SF is a better solvent than supercritical CO and hexane.

Development of an ionic 68Ge68Ga generator III. Chelate resins as chromatographic substrates for germanium

A synthetic chelate resin, a polycondensation product of pyrogallol and formaldehyde, has been developed and characterized for use as a substrate for a 68Ge68Ga generator. The distribution constants between this resin and 0.3 N HCl are 0.5 for gallium and higher than 5000 for germanium. The potential 68Ge68Ga generator system reproducibly delivers 60% of the 68Ga in ionic form, while the breakthrough of germanium remains lower than 10−3% per collection volume after 600 elutions of the generator. Preliminary toxicity studies indicate that the eluate from the generator is safe for the preparation of intravenous injectates.

The Supercritical State

Publisher Summary This chapter describes the the phenomenon of supercritical fluid (SCF) solubility and supercritical state. Supercritical fluid technology is widely used in extraction and purification processes in the food and pharmaceuticals industry and also for techniques such as supercritical fluid chromatography. It is mentioned that there has been a significant increase in interest of the use of sub- as well as supercritical (SC) carbon dioxide (CO2) as a substitute for chlorofluorocarbons (CFCs) for a variety of specific and specialized applications in which the choices of environmentally acceptable alternatives are quite limited. It is stated that SCFs have emerged as revolutionary industrial solvents. In addition to its unique solubility characteristics, a SCF possesses certain other physiochemical properties that add to its attractiveness. For example, even though it possesses a liquid-like density over much of the range of interest, it exhibits gas-like transport properties of diffusivity and viscosity. Additionally, the very low surface tension of SCFs allows facile penetration into microporous materials. It shows the relationship of a complete range of pressure-temperature-density for SC CO2. One can conclude that a SCF treatment system can be tailored to realize most desired applications by adjusting pressure and/or temperature and other influencing parameters. They are mentioned as ideal environmental friendly candidates to replace ozone depleting chlorofluorocarbons.

Conductivities of polysilanes

Measurements of the electrical conductivities of three types of polysilanes were carried out over a range of dc fields and temperatures. These polymers are varied in substituents and structures with formulas of [C 6 H 5 SiCH 3 ] n , [(C 6 H 5 SiCH 3 ) 70 (CH 3 SiH) 30 ] n , and [(C 6 H 5 SiCH 3 ) 50 (C 6 H 5 SiH) 30 (CH 3 Si) 20 ] n . Undoped polysilanes behaved as insulators since their conductivities were observed in the range of 10 -10 to 10 -13 S cm -1 , while SbF 5 -doped polysilanes of all kinds behaved as semiconductors with conductivities in the range of 10 -2 to 10 -4 S cm -1 . No significant difference in conductivities was observed among three SbF 5 -doped polysilanes although these polymers are very different in chemical properties. These experimental results suggest that electrical conductivities of polysilanes are associated with the Si-Si main-chain backbone rather than with the side groups. It is evident that the dopant is able to diffuse throughout the bulk of the polymer and the conductivity of the doped polymer is a function of the dopant concentration from the result of in situ monitoring of the resistance of the silane homopolymer during SbF 5 doping at room temperature. The conductivities of polysilanes appeared to be temperature-dependent. The activation energy for the conduction of SbF 5 -doped silane copolymer was found to change at its glass transition temperature.

Studies of residual alkali on intraocular lenses sterilized with NaOH

We measured the effects of pH changes after water washings of polymethylmethacrylate (PMMA) intraocular lenses sterilized in 10% sodium hydroxide (NaOH). Whereas inserting the base-sterilized lens directly into the eye causes a large pH change in the local area of the implant, three separate washings of the NaOH-treated implant in 15 ml of water eliminates this change. No buffer is required.

Solution Behavior of Modified Polyethylenimine (PEI) Polymers by Light Scattering Investigations

The eight average molecular weights, as well as other characteristics such as the second virial coefficients and root-mean-square (RMS) radii of gyration of poly (ethyleneimine) (PEI) and various derivatives, have been determined in solution light scattering studies. The solution dynamics of PEI and carboxylated and phosphorylated derivatives were studied a pH of 3.3, 7.0 and 10.0. Measurements were made in freshly distilled and de-ionized water as well as in 0.1 M, 1 M and 5-M solutions of sodium chloride in water. Molecular weights were calculated from Berry plots. The purified polymer, PEI-1, gave a molecular weight of 39,600 g/mol., while the same polymer, which was not purified, PEI-2, has MW of 43,100 g/mol.