PERFLUOROALKYL PHOSPHONIC AND PHOSPHINIC ACID ELECTROLYTES FOR PROTON EXCHANGE MEMBRANE FUEL CELLS

Perfluorinated sulfonic acid polymers have been considered as the state-of-art membrane materials for proton exchange membrane fuel cells. A major technical issue with these polymers is that they do not function well at temperatures above 80 °C and at low humidities. Therefore, research has been focused on developing PEM materials that can operate independent of hydration requirements. The operation of fuel cells at high temperature (e.g. 120 oC) increases fuel cell system efficiency due to faster electrode kinetics and better CO tolerance. This dissertation will describe a study of proton-transport rates and mechanisms under anhydrous and aqueous conditions using a series of acid model compounds analogous to comb-branch perfluorinated ionomers functionalized with phosphonic, phosphinic, sulfonic and carboxylic acid protogenic groups. Model compounds were synthesized and characterized with respect to proton conductivity, viscosity, proton and anion (conjugate base) self-diffusion coefficients, and Hammett acidity and as a function of increasing perfluoroalkyl chain length. The highest conductivities and also the highest viscosities were typically observed for the phosphonic and phosphinic acid model compounds. The results of the study collectively supported the hypothesis that anhydrous proton transport in the phosphonic and phosphinic acid model compounds occurs primarily by a structure-diffusion, hopping-based mechanism rather than a vehicle mechanism. Further analysis of ionic conductivity and ion self-diffusion rates using the Nernst-Einstein equation reveals that the phosphonic and phosphinic acid model compounds are relatively highly dissociated even under anhydrous conditions. In contrast, sulfonic and carboxylic acid-based systems exhibit relatively low degrees of dissociation under anhydrous conditions. Investigations of these model acids under low hydration levels (3 mols of acid per a mole of acid) indicate that the proton conductivity of these phosphonic and phosphinic acids can be improved by more than an order of magnitude relative to the water-free conditions. These findings suggest that fluoroalkyl phosphonic and phosphinic acids are good candidates for further development as anhydrous, high temperature proton conductors. The chapter 5 describes the synthesis, characterization and ion transport of lithium polymer electrolytes that resist concentration polarization. Investigation of the purity of the ionic-melt by HPLC analysis and electrospray ionization mass spectrometry indicated that the ionic-melt is free of non-ionic impurities. The highest ionic conductivity of 7.1 × 10−6 S/cm at 30 °C was obtained for the sample consisting of a lithium salt of an arylfluorosulfonimide anion attached to a polyether oligomer with an ethyleneoxide (EO) to lithium ratio of 12. The conductivity order of various ionic melts having different polyether chain lengths suggests that at higher EO:Li ratios the conductivity of the electrolytes at room temperature is determined in part by the amount of crystallization of the polyether portion of the ionic melt. The chapter 6 describes the synthesis and characterization of a new room-temperature ionic liquid based on a alkylimidazolium cation and new fluoro anion [(CF3)2PO2-]. Investigation of its thermal stability, viscosity, voltage window, and conductivity suggests that it may be a useful as an electrolyte in batteries

INVESTIGATION OF STRUCTURE AND PROPERTIES OF NOVEL MULTI-LAYER CLAY NANOCOMPOSITE FILMS PRODUCED CONTROLLABLY BY CONTINUOUS CHAOTIC ADVECTION BLENDING

Polymer nanoclay composites have been studied extensively in the past decade due to the excellent combination of properties they can offer at low loadings of clay. Despite robust research, the potential enhancements that nanoclays are theoretically predicted to offer have not been achieved. Such potential improvements in mechanical and gas barrier properties are realized only when the internal structure of the nanocomposite is optimized in terms of arrangement and orientation of nanoclay within the matrix. The mixing-based approach and the accompanying complex flow fields of conventional processing techniques widely used to produce nanoclay composites are unable to control the internal structure. This has also impeded the documentation and verification of the effect of orientation and arrangement of clay platelets on the matrix and the nanocomposite properties. Hence, a unique processing technique based on chaotic advection developed at Clemson University and shown to controllably produce structured materials in the past was employed to produce structured nanocomposites with a high degree of clay orientation as well as localization of platelets within layers of nanoscale thicknesses. Continuous lengths of nanocomposites with different clay contents were extruded in the form of films by feeding separately melts of virgin polyamide-6 polymer and polyamide 6-clay masterbatch into a continuous chaotic advection blender. A variety of composite structures were producible at fixed clay compositions. The internal structure was characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Nanocomposites with novel in-situ multi-layered structures and a high degree of platelet orientation were formed by the recursive stretching and folding of the melt domains due to chaotic advection. Clay platelets were localized within discrete regions to form alternating virgin and platelet-rich layers leading to a hierarchical structure with multiple nano-scales. The thicknesses of the layers reduced with prolonged chaotic advection, eventually leading to nanocomposites in which the multi-layering was no longer discernible. The oriented platelets appeared to be homogenously dispersed through the bulk of the nanocomposite. Investigation of the morphology of the matrix by XRD showed that the homogeneity of the crystalline phase and the orientation of polymer chains parallel to the film surface increased with increased chaotic advection. Also, as the layer thickness reduced, the number of polymer chains restricted by clay platelets increased causing the γ-crystalline fraction to increase. While XRD results suggested a change in total crystallinity with chaotic advection and clay content but without a specific trend, no change in crystallinity was measured by DSC. Such contradictions are consistent with results of other investigators. Concentrating and orienting the clay platelets within layers increases the path length of the diffusing molecule and hence may improve barrier properties. The effect of multi-layering and platelet orientation on the gas permeability of the nanocomposite films was investigated both experimentally and theoretically. Experimental measurements of 2% clay films showed that a multi-layered structure with oriented clay platelets gives a 40% greater reduction in oxygen permeability compared to a structure with a homogenous dispersion of oriented clay platelets. Also, the nanocomposite films with homogenous dispersion of platelets produced by chaotic advection due to their high degree of platelet alignment exhibited improved barrier properties than nanocomposites produced by mixing. The combination of high degree of orientation and multi-layering conferred to the 2 wt% clay film produced with the chaotic advection blender a relative permeability lower than a 6 wt% clay film produced with a single screw extruder. A theoretical model was formulated to explore the barrier properties of nanocomposites comprising a wide range of clay contents and platelet aspect ratio. The model showed the importance of orientation and layered structure. Permeabilities close to the intrinsic platelet permeability (i.e., near zero) can be realized by localizing and orienting a relatively low volume fraction (4%) of very high aspect ratio platelets (≥350) in the matrix or high volume fractions (20%) of platelets with aspect ratios around 100 (typical of the montmorillonite (MMT) clay). The chaotic advection blender was unable, however, to process such masterbatches due to limitations of available screw extruders intended for polyolefins. Experiments considered low volume fractions of MMT clay less than 4%. Other physical properties of the films important for packaging applications were also evaluated. The presence of die lines, particulate contaminations and variations in thicknesses of the films led to data scatter of measured properties. However, even with film quality substantially less than obtained in industry, the nanocomposites of this study showed a slight increase in tensile strength with clay content without sacrificing impact toughness and resistance to tear. In addition, due to the high degree of orientation parallel to the film surface, the clay platelets were able to reinforce the material in both machine and transverse directions. The nanocomposites also retained the optical clarity of the pure polymer matrix. Experimental and modeling results suggest that high barrier properties may be attainable if improvements to the chaotic advection blending system are made such that higher quality films can be produced with only slightly higher clay content or higher aspect ratio clay platelets than considered in this study

Tropical, Coastal Aquifer Management - A Case Study

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

SMEs in Developing Countries Need Support to Address the Challenges of Adopting e-commerce Technologies

Although research indicates e-commerce offers viable and practical solutions for organizations to meet challenges of a predominantly changing environment, the few available studies related to SMEs in developing countries reveal a delay or failure of SMEs in adopting ICT and e-commerce technologies. The various factors identified as causes for the reticence can be broadly classified as Internal Barriers and External Barriers. This paper presents a model for barriers to adoption of ICT and e-commerce based on the results of an exploratory pilot study and survey. It identifies support for SMEs in Sri Lanka at different distinct levels of sophistication in SMEs with regard to ICT and e-commerce. It also determines a strong need for necessary support and discusses the availability of the support. Finally it proposes an initial framework to eTransorm SMEs

Retrograde intramedullary nailing for fractures of distal femur: a prospective study

Background: The objective of the present study was to evaluate the clinical and functional outcome of retrograde intramedullary interlocking nailing for fractures of distal femur.Methods: This two-year prospective observational study includes all patients with fractures of distal femur who underwent retrograde intramedullary interlocking nailing.  The patient was placed supine on fracture table with the affected limb flexed to 60o.  Through a transpatellar approach, the nail was introduced in a retrograde method after serial reaming. Postoperatively knee range of motion was started immediately and weight-bearing was progressed after signs of fracture union were noted on x-rays.  The outcome was evaluated for time taken for fracture union, complications and secondary procedures, knee range of motion and function at 1 year follow up using modified knee-rating scale of the hospital for special surgery.Results: There were 21 patients who underwent retrograde intramedullary nailing for fractures of distal femur during the study period. According to AO/ASIF system, fractures were classified as A1 (n=15), A2 (n=3), and A3 (n=3). In 17 patients, fracture united without complications or secondary procedures. Fractures united at a mean time of 19.4 weeks. There were no varus or valgus malalignments but one patient had significant limb shortening. At the end of 1 year, excellent to good functional outcome was noted in 81% of patients. Conclusions: Retrograde intramedullary nail fixation is a reliable method for treatment of fractures of distal femur. It promotes high rates of fracture union with minimal complications. This method does not interfere significantly with the knee function postoperatively

Effects of thermal buoyancy and variable thermal conductivity on the MHD flow and heat transfer in a power-law fluid past a vertical stretching sheet in the presence of a non-uniform heat source

The paper considers the flow of a power-law fluid past a vertical stretching sheet. Effects of variable thermal conductivity and non-uniform heat source/sink on the heat transfer are addressed. The thermal conductivity is assumed to vary linearly with temperature. Similarity transformation is used to convert the governing partial differential equations into a set of coupled, non-linear ordinary differential equations. Two different types of boundary heating are considered, namely Prescribed power-law Surface Temperature (PST) and Prescribed power-law Heat Flux (PHF). Shooting method is used to obtain the numerical solution for the resulting boundary value problems. The effects of Chandrasekhar number, Grashof number, Prandtl number, non-uniform heat source/sink parameters, wall temperature parameter and variable thermal conductivity parameter on the dynamics are shown graphically in several plots. The skin friction and heat transfer coefficients are tabulated for a range of values of the parameters. Present study reveals that in a gravity affected flow buoyancy effect has a significant say in the control of flow and heat transfer. © 2008 Elsevier Ltd. All rights reserved

Differential partitioning of Gαi1 with the cellular microtubules: a possible mechanism of development of Taxol resistance in human ovarian carcinoma cells

BACKGROUND: Taxol binds to the cellular microtubules and suppresses their dynamic instability. Development of tumor cell resistance to taxol is typically associated with increased expression of the drug efflux pump P-glycoprotein and/or alterations in the microtubules. Recently, changes in the dynamic instability of the microtubules have also been associated with development of taxol resistance in a lung cancer cell line. We have established a 250-fold taxol-resistant human ovarian carcinoma subline (2008/13/4) that does not display the typical alterations associated with development of drug resistance. RESULTS: Utilizing the mRNA differential display technique, we observed increased expression of an alpha subunit of the guanine nucleotide-binding protein, Gαi1, in the taxol-resistant human ovarian carcinoma cell lines compared to the parental 2008 cells. Several isoforms of the α-subunit of the G protein have been identified and the Gαi (inhibitory) are so named because they inhibit the activity of adenylate cyclase leading to inactivation of the cAMP-dependent protein kinase A (PKA) pathway. In addition, Gαi1 is also known to bind to microtubules and activates their GTPase activity and thus induces depolymerization of the microtubules. In the present study we demonstrate that the intracellular level of cAMP and the PKA activity were higher in the taxol-resistant 2008/13/4 and the 2008/17/4 cells despite the increased expression of Gαi1 in these cells. Moreover, Gαi1 was found to be localized not on the cell membrane, but in intracellular compartments in both the taxol-sensitive and -resistant human ovarian carcinoma cells. Interestingly, increased association of the Gαi1 protein and the microtubules in the taxol-resistant cells compared to the parental 2008 cells was observed, both prior to and after treatment of these cells with taxol. CONCLUSION: Based on the opposing effects of taxol and the Gαi1 protein on the microtubule dynamic instability (taxol suppresses microtubule dynamic instability whilst the Gαi1 protein inhibits the suppression) our results indicate the operation of a novel pathway that would enable the cells to escape the cytotoxic effects of taxol

Numerical Solution of the Momentum and Heat Transfer Equations for a Hydromagnetic Flow Due to a Stretching Sheet of a non-uniform Property Micropolar Liquid

A study of the hydromagnetic flow due to a stretching sheet and heat transfer in an incompressible micropolar liquid is made. Temperature-dependent thermal conductivity and a non-uniform heat source/sink render the problem analytically intractable and hence a numerical study is made using the shooting method based on Runge-Kutta and Newton-Raphson methods. The two problems of horizontal and vertical stretching are considered to implement the numerical method. The former problem involves one-way coupling between linear momentum and heat transport equations and the latter involves two-way coupling. Further, both the problems involve two-way coupling between the non-linear equations of conservation of linear and angular momentums. A similarity transformation arrived at for the problem using the Lie group method facilitates the reduction of coupled, non-linear partial differential equations into coupled, non-linear ordinary differential equations. The algorithm for solving the resulting coupled, two-point, non-linear boundary value problem is presented in great detail in the paper. Extensive computation on velocity and temperature profiles is presented for a wide range of values of the parameters, for prescribed surface temperature (PST) and prescribed heat flux (PHF) boundary conditions