Sorption of Carbon Dioxide and Nitrogen on Porous Hyper-Cross-Linked Aromatic Polymers: Effect of Textural Properties, Composition, and Electrostatic Interactions.

Porous hyper-cross-linked aromatic polymers are one of the emerging classes of porous organic polymers with the potential for industrial application. Four different porous polymeric materials have been prepared using different precursors (indole, pyrene, carbazole, and naphthalene), and the composition and textural properties were analyzed. The materials were characterized in detail using different physicochemical techniques like scanning electron microscopy, transmission electron microscopy, nitrogen adsorption at 77 K, Fourier transform infrared spectroscopy, X-ray diffraction, etc. The effect of textural properties and nitrogen species on carbon dioxide and nitrogen adsorption capacities and selectivity was studied and discussed. The carbon dioxide and nitrogen adsorption capacities were measured using a volumetric gas adsorption system. The adsorption data were fitted into different adsorption models, and the ideal absorbed solution theory was used to calculate adsorption selectivity. Among the studied samples, POP-4 shows the highest carbon dioxide and nitrogen adsorption capacities. While POP-1 shows maximum CO2/N2 selectivity of 78.0 at 298 K and 1 bar pressure. It is observed that ultra-micropores, which are present in the prepared materials but not measured during conventional surface area measurement via nitrogen adsorption at 77 K, play a very important role in carbon dioxide adsorption capacity and determining the carbon dioxide selectivity over nitrogen. Surface nitrogen also increases the CO2 selectivity in the dual mode by increasing carbon dioxide adsorption via the acid-base interaction as well as by decreasing nitrogen adsorption due to N-N repulsion.

Relating the marginal fit of the castings to the accuracy of the impressions made from laminated hydrocolloid impression technique: a comparative study.

AIM: Relating the marginal fit of the castings, to the accuracy of the impression produced using laminated hydrocolloid impression technique, alginate and double-mixed polyvinyl siloxane. Basic objective of the study is to check the feasibility of the use of laminated hydrocolloid impression technique in the fixed partial denture. MATERIALS AND METHODS: The precisely machined metal die was designed to simulate standard complete metal crown preparation. The preparation was mounted on cylindrical base of 20 mm length and diameter of 10 mm. Seven impressions were made from the each impression material onto the metal die, and total 21 impressions were obtained from all three impression materials, which were poured by the die stone, and stone die was prepared. Wax patterns were fabricated on stone dies obtained from each impression and then casting was done. All the castings were checked for the marginal fit on metal die after applying a uniform standardized load of 30 pounds using measuring microscope. RESULTS: Result revealed that the marginal fit of the castings obtained from group II (laminated hydrocolloid technique) and group III (double-mix polyvinyl polysiloxane) did not show the significant difference between the two of them. Marginal gap of the castings obtained from group I are significantly greater in comparison to the castings obtained from groups II and III (p > 0.01). CONCLUSION: Group II (laminated hydrocolloid technique) impression material may be the choice of many clinicians over group III (double-mix polyvinyl polysiloxane) impression material. Group I (alginate impression material), though very cost-effective and easy to handle may not able to produce accurate results. CLINICAL SIGNIFICANCE: The study gives overview of the best impression material that can be used clinically. Laminated hydrocolloid technique is the technique of choice.

Dental plaque pH variation with regular soft drink, diet soft drink and high energy drink: an in vivo study.

BACKGROUND: A high incidence of dental caries and dental erosion associated with frequent consumption of soft drinks has been reported. The purpose of this study was to evaluate the pH response of dental plaque to a regular, diet and high energy drink. METHODOLOGY: Twenty subjects were recruited for this study. All subjects were between the ages of 20 and 25 and had at least four restored tooth surfaces present. The subjects were asked to refrain from brushing for 48 hours prior to the study. At baseline, plaque pH was measured from four separate locations using harvesting method. Subjects were asked to swish with 15 ml of the respective soft drink for 1 minute. Plaque pH was measured at the four designated tooth sites at 5, 10 and 20 minutes intervals. Subjects then repeated the experiment using the other two soft drinks. RESULTS: pH was minimum for regular soft drink (2.65 ± 0.026) followed by high energy drink (3.39 ± 0.026) and diet soft drink (3.78 ± 0.006). The maximum drop in plaque pH was seen with regular soft drink followed by high energy drink and diet soft drink. CONCLUSION: Regular soft drink possesses a greater acid challenge potential on enamel than diet and high energy soft drinks. However, in this clinical trial, the pH associated with either soft drink did not reach the critical pH which is expected for enamel demineralization and dissolution.