Absence Of Diluent Research Articles

Low molecular weight poly((D,L)-lactide-co-caprolactone) liquid inks for diluent-free DLP printing of cell culture platforms.

Digital light processing (DLP) printing offers the possibility of fabricating complex objects in a fast and reproducible manner. A main requirement for DLP printing is the use of inks with low viscosities that can flow under the printing platform in a short period of time. Its exploitation in tissue engineering applications has been centered on the use of hydrogel forming materials diluted in aqueous solutions or the use of polyesters in combination with diluents and heating platforms that aid in the reduction of their viscosity. The use of diluents, however, modifies the mechanical properties and reduces the shape fidelity of the printed objects and, the use of heating platforms results in vats with heterogeneous temperatures and ink viscosities. Here, we report on the synthesis of a library of methacrylated low molecular weight (<3000 g mol-1) homopolymers ((P(D,L)LA and PCL) and copolymers (P((D,L)LA-co-CL)) of 2- and 3-arms based on (D,L)-lactide and ε-caprolactone. The resulting inks possessed low viscosity that made them printable in the absence of diluents and heating elements. DLP printing of cubical and cylindrical patterns resulted in objects with a higher shape fidelity than their counterparts fabricated using diluents and with printed features on the order of 300 μm. The printed materials were biocompatible and supported the growth of human mesenchymal stem cells (hMSCs). Moreover, the variations in the composition resulted in polymers that enabled the attachment of hMSCs to different extents, leading to the formation of well-adhered cell monolayers or loosely adhered cell aggregates.

Combustion of zirconium powders in oxygen

The combustion of zirconium powders in air and oxygen was investigated as a function of gas pressure, level of dilution, and relative green density. The dilution (with ZrO 2) was varied from 0 to 80% and the pressure of the gas was varied from 1 to 12 atm. The combustion process involves two stages, one related to the propagation of the wave and the other is an after-burn process. In the absence of diluent, the first stage dominates, as reflected by temperature profiles. The combustion temperature and wave velocity increased with increasing gas pressure, leading to compaction of the temperature profiles. Changing the relative green density had a strong influence on the combustion process as judged by the temperature profiles. Profiles of undiluted lower density samples exhibit the typical steep initial rise, but those of higher density samples show a slow rise to the maximum.

Chitin–cellulose blends: phase properties in dimethylacetamide–LiCl

AbstractChitin–cellulose blends dissolved in dimethylacetamide containing LiCl (7% w/w) have been studied in a wide concentration range, from very dilute solutions to medium concentrations and up to solid films (absence of diluent).The intrinsic viscosities at various chitin–cellulose ratios, as well as the phase diagram behavior, imply a good compatibility between the components. The result is confirmed by the infrared measurements on solid films. The lack of anisotropic phase formation in chitin–diluent binary solutions and the anomalous trend of v′CH–CE line on the phase diagram are both interpreted on the basis of aggregation phenomena.

A study of radiation effects on the extraction of americium(III) with acidic organophosphates

Radiation effects on the extraction of americium(III) with several dialkylphosphoric and monoalkylphosphoric acids have been studied comparatively. The extractants were exposed to60Co γ-rays in the absence and presence of diluent and HNO3. The Df of Am(III) was measured and the yield of radiolytic products was determined after γ-irradiation as a function of the absorbed dose. Di(hexoxyethyl)phosphoric acid was the most susceptible to radiation among the extractants studied and its extractability was weakened by radiation regardless of the presence or absence of diluent or HNO3. Diisodecylphosphoric acid itself showed an enhancement upon irradiation but incurred a depressant effect upon intimate contact with HNO3·Mono(2-ethylhexyl)phosphoric acid showed a decrease of the Df of Am(III), similarly to DIDPA in the presence of HNO3 during γ-irradiation. All the above extractants gave H3PO4 as the principal radiolytic product upon γ-irradiation upon intimate contact with HNO3 causing decreasing solely the extraction of Am(III). Di(2-ethylhexyl)phosphoric acid proved to be the most stable extractant to radiation among those studied.

The polymerization of phenylacetylene in the presence of ferric acetylacetonate and triethylaluminum

AbstractThe polymerization of phenylacetylene initiated by ferric acetylacetonate and triethylaluminum was studied over the temperature range −30°−70°, in bulk as well as in the presence of diluents, and over a range of catalyst compositions and concentrations. The product consisted of four major fractions: crystalline polymer of molecular weight about 7000 and a very narrow molecular‐weight distribution (MWD), (fraction I); somewhat lower‐molecular‐weight amorphous polymer with a broader MWD (fraction II); linear oligomer (fraction III); and the asymmetric cyclic triphenyl‐benzene (fraction IV). The average degree of polymerization, of fraction I (65–70) is independent of all polymerization variables, that is, temperature from −30° to 70°C, the presence or absence of diluent (tetralin or benzene), and catalyst concentration and composition. The MWD is narrow with M̄w/M̄n equal to 1.05 or less. The results suggest that thermodynamic rather than kinetic factors limit the size of the polymer. A possible mechanism is proposed.

Stress-Strain Behavior of Swollen Polymeric Networks

Abstract The network parameters of swollen, solution-crosslinked polymer filaments can be collected from deswelling measurements in solutions of nonpermeating polymer or, as shown in this paper, from the stress—strain relation when in equilibrium with the surrounding solvent. The degree of swelling, at which the partial molar free energy of elasticity equals zero, is found to vary with solvent power in agreement with earlier findings on other systems. Comparison with results of studies on rubber networks crosslinked in the absence of diluent, show that previously observed discrepancies between theory and experiment can be attributed to the deficiency of the single term involving the one-third power of the volume fraction of polymer in the swollen network to describe the contribution of the partial elastic free energy.

Swelling Ratios and Rates of Sulfonation of Solvent Modified Copolymers of Styrene Cross-Linked with Pure m-and Pure p-Divinylbenzene

Abstract Solvent-modified (toluene) copolymers have been prepared from styrene cross-linked with commercial divinylbenzene, m-divinylbenzene, and p-divinylbenzene at divinyl monomer contents of 16 mole % and 32 mole % at FM = 0.50. The resultant copolymers have been characterized by swelling-ratio determinations and rates of sulfonation at 60 and 80°C. The solvent-modified 16 mole % cross-linked copolymers sulfonated at rates slightly greater than those characterizing the 8 mole % cross-linked copolymers prepared in the absence of diluent. The order of decreasing sulfonation rates for both the conventional 8 mole % cross-linked systems and for the solvent-modified 16 mole % cross-linked copolymers is commercial divinylbenzene/styrene, p-divinylbenzene/styrene, m-divinylbenzene styrene. The 32 mole % cross-linked systems exhibit a different order of decreasing sulfonation rates: commercial divinylbenzene/styrene, m-divinylbenzene/styrene, p-divinylbenzene/styrene. The swelling ratios of the 32 mole % solve...

Low-Temperature Internal-Friction Study of Diluent Effect in Some Polymethacrylates

A transverse resonance acoustic spectrometer was used to investigate the effect of diluents on the dynamic mechanical properties of poly-2-hydroxypropyl methacrylate (PHPMA) and poly-2-hydroxyethyl methacrylate (PHEMA) down to −196°C. Samples were prepared by polymerizing the monomer-diluent mixtures through ultraviolet radiation. In the dry sample of PHPMA, below the glass transition temperature, there is an internal friction peak at −90°C (gamma peak). With the introduction of 0.5 vol % water, the gamma peak broadens into a shoulder, with the concomitant appearance of a new ``diluent peak'' at −25°C. Addition of higher water content causes the internal friction curve to exhibit only one single peak, the position of which shifts to lower temperatures while the strengths of the loss peaks increase with increasing diluent concentration. Similar observations were made for other hydrogen-bonding diluents, i.e., deuterium oxide, methanol, and glycerol. For nonhydrogen-bonding diluents, chloroform and cyclohexane, the gamma peak was retained while a shoulder appears around −20°C. Isoproponal, on the other hand, produces an internal friction curve that appears to be ``borderline'' between the above two cases. For PHEMA, which has a gamma peak at −100°C in the absence of diluents, the addition of 0.5 vol % water produced an internal friction curve that possesses a doublet near −60°C. Again, at higher water concentration one observes only a single peak. When cyclohexane was used as the diluent, the doublet character persists up to 5% diluent concentration. These observations were examined in the light of the molecular motion hypothesis. A dual mechanism is suggested that attributes the new diluent peak to the composite of displaced beta and gamma processes. It is postulated that beta transition is lowered due to the plasticizing action of the diluents, while the gamma transition is elevated on account of the hindering effect of the immobilized diluent molecules. At sufficiently high diluent concentration, these two peaks merge into the single observed peak.