Fabrication of zeolite/polymer multilayer composite membranes for carbon dioxide capture: Deposition of zeolite particles on polymer supports.

Membranes, due to their smaller footprint and potentially lower energy consumption than the amine process, offer a promising route for post-combustion CO2 capture. Zeolite Y based inorganic selective layers offer a favorable combination of CO2 permeance and CO2/N2 selectivity, membrane properties crucial to the economics. For economic viability on large scale, we propose to use flexible and scalable polymer supports for inorganic selective layers. The work described in this paper developed a detailed protocol for depositing thin zeolite Y seed layers on polymer supports, the first step in the synthesis of a polycrystalline zeolite Y membrane. We also studied the effects of support surface morphology (pore size and surface porosity) on the quality of deposition and identified favorable supports for the deposition. Two different zeolite Y particles with nominal sizes of 200 nm and 40 nm were investigated. To obtain a complete coverage of zeolite particles on the support surface with minimum defects and in a reproducible manner, a vacuum-assisted dip-coating technique was developed. Images obtained using both digital camera and optical microscope showed the presence of color patterns on the deposited surface which suggested that the coverage was complete. Electron microscopy revealed that the particle packing was dense with some drying cracks. Layer thickness with the larger zeolite Y particles was close to 1 µm while that with the smaller particles was reduced to less than 0.5 µm. In order to reduce drying cracks for layers with smaller zeolite Y particles, thickness was reduced by lowering the dispersion concentration. Transport measurement was used as an additional technique to characterize these layers.

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.

Influence of prior activity on residual limb volume and shape measured using plaster casting: results from individuals with transtibial limb loss.

The purpose of this research was to determine whether prior activity affected the shape of a plaster cast taken of a transtibial residual limb. Plaster casts were taken twice on one day in 24 participants with transtibial limb loss, with 5 s between doffing and casting in one trial (PDI-5s) and 20 min in the other trial (PDI-20m). The ordering of the trials was randomized. The mean +/- standard deviation radial difference between PDI-20m and PDI-5s was 0.34 +/- 0.21 mm when PDI-5s was conducted first and -0.02 +/- 0.20 mm when PDI-20m was conducted first. Ordering of the trials had a statistically significant influence on the mean radial difference between the two shapes (p = 0.008). The result shows that prior activity influenced the residual limb cast shape. Practitioners should be mindful of prior activity and doffing history when casting an individual's limb for socket design and prosthetic fitting.

Influence of crystallite size on cation conductivity in faujasitic zeolites.

The influence of particle size on the ionic conductivity of ceramic materials is an active area of research, and novel effects are observed as particles approach the nanoscale in size. Zeolites are crystalline aluminosilicates with ion-exchangeable cations that are responsible for ionic conductivity at high temperatures. In this paper, we present systematic results for the first time of ionic conductivity in alkali metal ion-exchanged faujasitic zeolites with morphologies ranging from a zeolite membrane, micrometer-sized, submicrometer, and nanoparticles of zeolite. Using impedance spectroscopy in the range of 10 MHz to 0.1 Hz, we have obtained the activation energy (E(act)) of cation motion with these various morphologies in the temperature range of 525-625 °C. Overall, the E(act) decreases with Si/Al ratio. Surface modification of the zeolite particles was carried out with a silylating agent, which upon high temperature calcination should lead to the formation of a monolayer Si-O-Si film on the particle surface. This surface modification had minimal influence on the E(act) of micrometer-sized zeolites. However, E(act) increased rapidly as the zeolite particle approached the nanoscale. These observations led us to propose that, for the high-temperature, low-frequency (10(4)-10(5) Hz), long-range ionic conduction in zeolites, cation hopping across grain boundaries is relevant to ion transport, especially as the size of the crystallite approaches the nanoscale. Intergrain boundaries are more defective in the nanosized zeolite and contribute to the higher E(act).

Synthesis and visible-light photochromism of a new composite based on polymolybdate enclosed in magadiite.

A new composite based on polymolybdate incorporated in layered magadiite has been synthesized via a exfoliation/self-assembly process. Various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), Raman spectroscopy, thermogravimetric (TG) analysis, UV-vis spectroscopy, and transmission electron microscopy (TEM), have been employed to characterize the composite. Results indicated that the polymolybdate particles were incorporated into the layered magadiite. Upon the irradiation of visible light (420-630 nm), the composite changed color from yellow to dark blue; moreover, the color can be bleached upon exposure to a 15% H2O2 solution. The visible-light illumination and H2O2 treatment can be repeated in excess of 10 times. The mechanism of photochromism has been investigated, and the reversibility is attributed to the hydration property of host magadiite and oxidative ability of H2O2 solution.

Computer-socket manufacturing error: how much before it is clinically apparent?

The purpose of this research was to pursue quality standards for computer-manufacturing of prosthetic sockets for people with transtibial limb loss. Thirty-three duplicates of study participants' normally used sockets were fabricated using central fabrication facilities. Socket-manufacturing errors were compared with clinical assessments of socket fit. Of the 33 sockets tested, 23 were deemed clinically to need modification. All 13 sockets with mean radial error (MRE) greater than 0.25 mm were clinically unacceptable, and 11 of those were deemed in need of sizing reduction. Of the remaining 20 sockets, 5 sockets with interquartile range (IQR) greater than 0.40 mm were deemed globally or regionally oversized and in need of modification. Of the remaining 15 sockets, 5 sockets with closed contours of elevated surface normal angle error (SNAE) were deemed clinically to need shape modification at those closed contour locations. The remaining 10 sockets were deemed clinically acceptable and not in need modification. MRE, IQR, and SNAE may serve as effective metrics to characterize quality of computer-manufactured prosthetic sockets, helping facilitate the development of quality standards for the socket manufacturing industry.

Physicochemical and toxicological properties of commercial carbon blacks modified by reaction with ozone.

Ozonation of two commercial carbon blacks (CBs), Printex 90 (P90) and Flammruss 101 (F101), was carried out and changes in their morphology, physical properties, and cytotoxicity were examined. The hypothesis examined was that different methods of manufacture of CBs influence their chemical reactivity and toxicological properties. Structural changes were examined by X-ray photoelectron spectroscopy, infrared spectroscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy (EPR). Introduction of surface oxygen functionality upon ozonation led to changes in surface charge, aggregation characteristics, and free radical content of the CBs. However, these changes in surface functionality did not alter the cytotoxicity and release of inflammation markers upon exposure of the CBs to murine macrophages. Interaction of macrophages with F101 resulted in higher levels of inflammatory markers than P90, and the only structural correlation was with the higher persistent radical concentration on the F101.

Contrast of the biological activity of negatively and positively charged microwave synthesized CdSe/ZnS quantum dots.

Quantum dots (QDs) are semiconductor nanocrystals that have found use in bioimaging, cell tracking, and drug delivery. This article compares the cytotoxicity and cellular interactions of positively and negatively charged CdSe/CdS/ZnS QDs prepared by a microwave method using a murine alveolar macrophage-like cell culture model. Keeping the core semiconductor the same, QD charge was varied by altering the surface capping molecule; negatively charged QDs were formed with mercaptopropionic acid (MPA-QDs) and positively charged QDs with thiocholine (THIO-QDs). The size and charge of these two QDs were investigated in three types of media (RPMI, RPMI + FBS, and X-VIVO serum-free media) relevant for the biological studies. MPA-QDs were found to have negative zeta potential in RPMI, RPMI + FBS, and serum-free media and had sizes ranging from 8 to 54 nm. THIO-QDs suspended in RPMI alone were <62 nm in size, while large aggregates (greater than 1000 nm) formed when these QDs were suspended in RPMI + FBS and serum-free media. THIO-QDs retained positive zeta potential in RPMI and were found to have a negative zeta potential in RPMI + FBS and nearly neutral zeta potential in serum-free media. In a cell culture model, both MPA-QDs and THIO-QDs caused comparable levels of apoptosis and necrosis. Both QDs induced significant tumor necrosis factor-alpha (TNF-α) secretion only at high concentrations (>250 nM). Both types of QDs were internalized via clathrin-dependent endocytosis. Using real-time, live cell imaging, we found that MPA-QDs interact with the cell surface within minutes and progress through the endocytic pathway to the lysosomes upon internalization. With the THIO-QDs, the internalization process was slower, but the pathways could not be mapped because of spectroscopic interference caused by QD aggregates. Finally, MPA-QDs were found to associate with cell surface scavenger receptors, while the THIO-QDs did not. This study indicates that the surface charge and aggregation characteristics of QDs change drastically in biological culture conditions and, in turn, influence nanoparticle and cellular interactions.

Assessment technique for computer-aided manufactured sockets.

This article presents an assessment technique for testing the quality of prosthetic socket fabrication processes at computer-aided manufacturing facilities. The assessment technique is potentially useful to both facilities making sockets and companies marketing manufacturing equipment seeking to assess and improve product quality. To execute the assessment technique, an evaluator fabricates a collection of test models and sockets using the manufacturing suite under evaluation, then measures their shapes using scanning equipment. Overall socket quality is assessed by comparing socket shapes with electronic file (e-file) shapes. To characterize carving performance, model shapes are compared with e-file shapes. To characterize forming performance, socket shapes are compared with model shapes. The mean radial error (MRE), which is the average difference in radii between the two compared shapes, provides insight into sizing quality. Interquartile range (IQR), the range of radial error for the best-matched half of the points on the compared socket surfaces, provides insight into regional shape quality. The source(s) of socket shape error may be pinpointed by separately determining MRE and IQR for carving and forming. The developed assessment technique may provide a useful tool to the prosthetics community and industry to help identify problems and limitations in computer-aided manufacturing and give insight into appropriate modifications to overcome them.

Central fabrication: carved positive assessment.

BACKGROUND: It is estimated that only 24% of practitioners use CAD/CAM regularly. Socket manufacturing error may be a source of the limited use of central fabrication. OBJECTIVES: The purpose of this study was to investigate the differences in shape between computer-manufactured, centrally fabricated carved models and electronic file shapes, to determine if carving was a major source of socket manufacturing error in central fabrication. STUDY DESIGN: Experimental, mechanical assessment. METHODS: Three different trans-tibial model shapes were sent electronically to each of 10 central fabrication facilities for the fabrication of positive foam models. A custom mechanical digitizer and alignment algorithm were used to measure the model shapes and then compare them with the electronic file shapes. RESULTS: Volume differences between the models and the electronic file shapes ranged from -4.2% to 1.0%, and averaged -0.9 (SD = 1.1)%. Mean radial error ranged from -1.2 mm to 0.3 mm and averaged -0.3 (SD = 0.3) mm. Inter-quartile range was between 0.3 mm and 2.7 mm and averaged 0.6 (SD = 0.5) mm. The models were significantly smaller than sockets made from the same electronic file shapes (p < 0.01), but the range of mean radial error and the interquartile range were not significantly different between the models and sockets. CONCLUSIONS: The results demonstrated that there was considerable variability in model quality among central fabricators in the industry, and that carving was not the sole source of socket fabrication error. CLINICAL RELEVANCE: The results provide insight into the severity and nature of carving error by central fabrication facilities. Because we found a wide range of model quality, there is not a consistent fabrication problem across the industry, but instead some central fabrication facilities practice the art of model fabrication better than others.

Measuring foam model shapes with a contact digitizer.

BACKGROUND AND AIM: It is difficult to measure foam model shapes using contact digitizers because the stylus contact tends to get stuck in the soft foam. The aim of this paper is to describe a technique to overcome this challenge and to assess its effect on digitizer error. TECHNIQUE: A controlled laboratory study was conducted. Thirty trans-tibial socket models were measured using a custom mechanical digitizer. Models were coated with a thin layer of resin, and then the resin thickness measured and subtracted from the digitizer data. Error introduced to the measurement from presence of the resin was determined. RESULTS AND DISCUSSION: The technique did not introduce meaningful error to the digitizer data beyond that already present from other sources in the instrument. The total instrument error for the contact digitizer used was 0.1% for model volume and 0.05 mm for mean radii. The root-mean-square error for individual measurement points was 0.08 mm. While resin coating introduced error to the digitizer measurements, the effect on volume, mean radii and interquartile range accuracies was minimal. CLINICAL RELEVANCE: Accurate model measurements can assist clinical service providers in the identification of problems and the repair of carving equipment. This facilitates the delivery of high quality sockets to practitioners and patients.