Browsing by Author "Jayakody, J.R.P."

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A Fundamental Study of the Transport Properties of Aqueous Superacid Solutions
(Journal of Physical Chemistry B, 2010) Suarez, S.N.; Jayakody, J.R.P.; Greenbaum, S.G.; Zawodzinski, T.; Fontanella, J.J.
An extensive investigation of the transport properties of aqueous acid solutions was undertaken. The acids studied were trifluoromethanesulfonic (CF3SO3H), bis(trifluoromethanesulfonyl)imide [(CF3SO2)2NH], and para-toluenesulfonic (CH3C6H4SO3H), of which the first two are considered superacids. NMR measurements of self-diffusion coefficients (D), spin?lattice relaxation times (T1), and chemical shifts, in addition to ionic conductivity (?), viscosity (?), and density measurements, were performed at 30 �C over the concentration range of 2?112 water to acid molecules. Results showed broad maxima in ? for all three acids in the concentration range of 12?20 water to acid molecules. This coincided with minima in anion Ds and is attributed to a local molecular ordering, reduced solution dielectric permittivity, and increased ionic interactions. The location of the maxima in ? correlates with what is observed for hydrated sulfonated perfluoropolymers such as Nafion, which gives a maximum in ionic transport when the ratio of water to acid molecules is about 15?20. Of the three acids, bis(trifluoromethanesulfonyl)imide was found to be the least dependent on hydration level. The occurrence of the anticorrelation between the ionic conductivity maximum and the anion self-diffusion minimum supports excess proton mobility in this region and may offer additional information on the strength of hydrogen bonding in aqueous media as well as on the role of high acid concentration in the Grotthuss proton transport mechanism.
A multinuclear NMR study of ion transport in P(EO)nLiBETI complexes
(Solid State Ionics, 2005) Suarez, S.N.; Abbrent, S.; Jayakody, J.R.P.; Greenbaum, S.G.; Shin, J.H.; Passerini, S.
A study of ion transport in P(EO)nLiBETI complexes was undertaken, using both AC impedance and nuclear magnetic resonance (NMR) spectroscopy. 1H, 7Li and 19F NMR techniques were used to investigate structure and dynamics as a function of temperature for n=3, 6, 8, 12 and 20. Spin?lattice relaxation times (T1) and spectral information were obtained from ?50 to 100 �C. Variable temperature self-diffusion coefficients (D) and ionic conductivity (?) measurements were also performed. Anion diffusion (DF) results displayed a dependence on available free volume, increasing with decreasing salt concentration. On the other hand, cation diffusion (DLi) results did not follow this trend. DLi for n=3 and 6 suggest the presence of ionic mobility in the crystalline phase, with a significant rise above the melting point. A transition from a crystalline to amorphous phase dominated ion transport occurs at n=8. This is supported by ? results, which exhibited a VTF type of behavior for n?8 that is associated with ion transport in the amorphous phase.
A Study of Temperature and Salinity Variations with Depth in Salt Pans at Palavi in North-West Region of Sri Lanka
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2000) Hewageegana, P.S.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
A Study of Wind Effects on Thermal Stability of Salt Pan Solar Ponds
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2001) Punyasena, M.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Perera, P.A.A.
An investigation of rain and wind effects on thermal stability of large-area saltpan solar ponds
(Solar Energy, 2003) Punyasena, M.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Perera, P.A.A.; Ehamparam, P.
An investigation of the thermal stability of large area saltpan solar ponds under different climatic conditions is presented. The study focuses on time taken by the pond to reach its stable conditions with heavy rainfall and the effect of wind-mixing process for the stability of the pond. Investigations were carried out over a period of 60 days on a large-area solar pond of 90 cm deep. The temperature and density profiles obtained 34 days after filling showed that the pond had attained its stability with a bottom temperature of 63 �C. Results reveal that heavy rainfall is the prime cause for the pond to reach stability in a time period of about 30 days. Strong wind-induced mixing prevailed during the second half of the investigation, which contributed to the erosion of the nonconvecting zone is the cause for observed destabilization of the pond. The estimated critical wind speed for complete destruction of the nonconvecting zone is about 25 km/h.
Characterization of single walled carbon nanotube: Polyvinylene difluoride composites
(Composites Science and Technology, 2006) Owensa, F.J.; Jayakody, J.R.P.; Greenbaum, S.G.
Composites of polyvinylene difluoride (PVdF) and single walled carbon nanotubes (SWNTs) produced by evaporation of suspensions of PVdF and SWNTs in acetone while being subjected to sonication are characterized. Raman measurements of the PVdF/SWNT composites showed sizable shifts of the radial breathing and tangential mode frequencies of the SWNT compared with the values in pristine SWNTs indicative of interaction between the PVdF and the SWNT. Changes of the frequencies and intensities of the CH stretching modes of PVdF were also observed. Variable temperature 19F NMR measurements show differences in the line widths of the PVdF/SWNT composite compared to the pristine polymer but no differences were observed in the spin-lattice relaxation time. Composites containing 6.7% SWNTs by weight showed a 30% increase in hardness and a resistivity of 3.38 ? cm. Ferromagnetic resonance and magnetization measurements indicated the composites were ferromagnetic due to presence of iron nanoparticles used as catalysts in the synthesis of the carbon nanotubes.
Construction and Filling of a Large-area Deep-tank Solar Pond for Harnessing Solar Energy
(Annual Research Symposium, Faculty of Graduate Studies, University of Kelaniya, 2002) Jayakody, J.R.P.; Punyasena, M.A.; Perera, P.A.A.; Amarasekara, C.D.; Kumarasinghe, M.A.S.
Construction and Filling of a Large-area Deep-tank Solar Pond for Harnessing Solar Energy
(Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2002) Jayakody, J.R.P.; Punyasena, M.A.; Perera, P.A.A.; Amarasekara, C.D.; Kumarasinghe, M.A.S.
Correlation Time for Polymer Chain Motion Near the Glass Transition in Nitrocellulose.
(MRS Proceedings, 1993) Jayakody, J.R.P.; Bulusu, S.; Marino, R.A.
The NMR chemical shift anisotropy (CSA) has a temperature dependence as a result of thermal motions of the NMR site. For slow motions of a polymer chain at or near the glass transition, Tg, the CSA begins to decrease, with the characteristic powder pattern features, shoulders and divergence, approaching one another. This motional narrowing can be interpreted to yield the correlation time of the thermal motions. If ? is the rigid-lattice shoulder to shoulder chemical shift anisotropy and ? is the correlation time of the slowmotion of the polymer chains, the total fractional shift, ?/?, for the general asymmetric case is found to be derived using Lee's theory. In this work, Nitrocellulose isotopically highly enriched with 15N was studied at four temperatures between 27� and 120� Celsius. To circumvent signal-to-noise problems in obtaining CSA data from a polycrystalline/amorphous sample, we used the Magic Angle Spinning (MAS) technique of Herzfeld and Berger. The principal values of the chemical shift tensor were then obtained from the relative intensities of the spinning sidebands in the MAS NMR spectrum. Correlation times were found to be of the order of 400 ms at 70�C, and 17 ms at 120�C.
Daytime Variation of Temperature and Salinity Profiles in Large-Area Saltpan Solar Ponds at Palavi, Sri Lanka
(Proceedings of the 18th Technical Session of the Institute of Physics - Sri Lanka, 2002) Perera, P.A.A.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Deuteron and Oxygen-17 NMR Studies of Molecular Motion in Methanol-Saturated Nafion Membranes
(MRS Proceedings, 1993) Chen, R.S.; Jayakody, J.R.P.; Greenbaum, S.G.
Deuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at ?75% and ?100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.
High Pressure NMR Study of Water Self-Diffusion in NAFION-117 Membrane
(Journal of Physical Chemistry B, 2004) Jayakody, J.R.P.; Stallworth, P.E.; Mananga, E.S.; Farrington-Zapata, J.; Greenbaum, S.G.
Measurements of the self-diffusion coefficient of water in NAFION-117 as a function of pressure have been carried out. The natural field gradient of a 7.3 T superconducting magnet was used for the diffusion measurement. The measurements were carried out at 288 K and variable pressure up to 0.25 GPa. The high-pressure diffusion data were obtained for four different water contents between 6.6 and 22 wt %. The calculated activation volume decreased from 13.2 to 2.7 cm3/mol as the water content increased from 6.6 to 22 wt %. These results agree with previously published activation volumes extracted from electric conductivity and NMR T1 measurements. It is suggested that segmental motions within the polymer play a significant role in the transport mechanism for low water content membranes, and that the transport mechanism for high water content membranes is similar to that in liquid bulk water.
High pressure studies of hydrated NAFION membranes: Dielectric relaxation and deuteron NMR
(Solid State Ionics, 1993) McLin, M.G.; Wintersgill, M.C.; Fontanella, J.J.; Chen, R.S.; Jayakody, J.R.P.; Greenbaum, S.G.
Audio frequency electrical conductivity/dielectric relaxation and nuclear magnetic resonance studies of NAFION-117 have been carried out at pressures up to 0.3 GPa (3 kbar). For some samples, the electrical conductivity exhibits dispersion typical of hopping conductivity in an amorphous material, ?=?0?m. The values of m are sample dependent and vary from about 0.55 to 0.75. In addition, the values of m are not strongly pressure sensitive. At a given frequency, the electrical conductivity tends to decrease as pressure increases and yield activation volumes on the order of 5 to 10 cm3/mol. The activation volume determined from the NMR spin-lattice relaxation time measurements are also sample dependent. The data shown correspond to an activation volume of about 8.6 cm3/mol. The results of the high pressure electrical conductivity studies also yield activation volumes on the order of that determined via NMR.
Investigation of temperature and density profile of brine in evaporating salt pans at Palavi in north-western Sri Lanka
(2001) Hewageegana, P.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
Measurements of temperature and density variations with depth in salt pans having a stable salinity gradient are presented. The density variation of brine has been correlated to the temperature variation with depth. The convective and nonconvective zones were identified. Gradients in salinity and temperature in the nonconvective zone were observed. Temperature and salinity were observed to remain the same throughout the convective bottom layer of brine in the ponds. The investigation has been extended to different ponds filled to different depths and storage periods of brine. A maximum temperature of around 55 0C was observed in the bottom layers while the surface remained as low as 29 0C. This is a consequence of positive salt-density gradient, which suppresses convection and allows a temperature gradient to develop downwards. The temperature measurements of different ponds filled to different heights indicate that the convective bottom layer temperature of a pond will increase if the pond is filled with brine to a higher level. These results indicate that the large area deep salt pans with long term storage periods can be used as solar ponds to collect and store solar energy in addition to the usual salt production. Based on our results we speculate that the bottom temperatures of these ponds could be increased to about 80 0C by filling the ponds to a height of about 1.5 meters. Thermal energy stored in the convective bottom layer of these ponds could be extracted for many applications. The moderate temperature desalination of seawater especially in the areas where fresh water is in short supply is identified as one of the promising applications of thermal energy stored in solar pond-salt pans.
Investigation of Temperature and Density Profiles of Brines in Evaporating Salt Pans at Palaviya in the North-Western Region of Sri Lanka
(Proceedings of the 16th Technical Session of the Institute of Physics - Sri Lanka, 2001) Hewageegana, P.S.; Amarasekara, C.D.; Jayakody, J.R.P.; Punyasena, M.A.
New membranes based on ionic liquids for PEM fuel cells at elevated temperatures
(Journal of Power Sources, 2008) Ye, H.; Huang, J.; Xu, J.J.; Kodiweera, N.A.C.; Jayakody, J.R.P.; Greenbaum, S.G.
Proton exchange membrane (PEM) fuel cells operating at elevated temperature, above 120 �C, will yield significant benefits but face big challenges for the development of suitable PEMs. The objectives of this research are to demonstrate the feasibility of the concept and realize [acid/ionic liquid/polymer] composite gel-type membranes as such PEMs. Novel membranes consisting of anhydrous proton solvent H3PO4, the protic ionic liquid PMIH2PO4, and polybenzimidazole (PBI) as a matrix have been prepared and characterized for PEM fuel cells intended for operation at elevated temperature (120?150 �C). Physical and electrochemical analyses have demonstrated promising characteristics of these H3PO4/PMIH2PO4/PBI membranes at elevated temperature. The proton transport mechanism in these new membranes has been investigated by Fourier transform infrared and nuclear magnetic resonance spectroscopic methods.
NMR investigation of water and methanol transport in sulfonated polyareylenethioethersulfones for fuel cell applications
(Journal of Power Sources, 2006) Jayakody, J.R.P.; Khalfana, A.; Mananga, E.S.; Greenbaum, S.G.; Dang, T.D.; Mantz, R.
We report an investigation of water and methanol transport in polymer electrolyte membranes based on highly sulfonated polyarelenethioethersulfones (SPTES) for direct methanol fuel cell (DMFC) applications. Measurements of both water and methanol self-diffusion coefficients of SPTES polymer as well as in a reference sample of Nafion-117 equilibrated in 2 M methanol solution have been carried out, using the pulsed gradient spin echo technique, over a temperature range of 20?140 �C. The selectivity of the membrane, defined as (DOH/DCH3), decreased from 6 to 2.4 as temperature increased from 20 to 140 �C in SPTES sample while in Nafion, the value decreased from 3.2 to 1.4 as temperature increased from 20 to 100 �C. These results indicate significantly lower fuel molecular permeability in SPTES compared to that of Nafion. All results suggest high-temperature stability in these materials, offering the possibility of fuel cell operation at temperatures >120 �C. High pressure NMR diffusion measurements were also carried out for three different water contents (between 20 and 55 wt.%) in a static field gradient in order to get supplemental information regarding water transport in SPTES materials. The calculated activation volume increased from 1.54 to 8.40 cm3/mol as the water content decreased from 55 to 20%. This behavior is qualitatively similar to previously reported results for Nafion-117.
NMR Studies of Ionic and Molecular Motion in Diglyme:LiCF3SO3 Complexes
(2004) Jayakody, J.R.P.; Suarez, S.; Greenbaum, S.G.; Petrowsky, M.; Frech, R.
Low molecular mass diglyme forms complexes with lithium salts similar to the high molecular mass and much-studied poly(ethylene oxide) (PEO), and thus serves as a useful model for investigating ion solvation,association, and transport in polymer electrolytes. NMR measurements of diglyme:LiCF3SO3 complexes were performed on all three mobile components (solvent, cation, and anion) at 1H, 7Li and 19F Larmor frequencies of 301.0, 116.9 and 283.2 MHz respectively. The diglyme/Li ratio varied from 5:1 to 40:1, and variable temperature measurements were carried out for a 20:1 sample. Spectra, spin-lattice relaxation times (T1) and self-diffusion coefficients (D) were obtained; D measured by standard pulsed field gradient methods. Spin-lattice relaxation times and self-diffusion coefficients for the anion (19F), cation (7Li) and solvent ( 1H) as a function of diglyme concentration at 20oC are displayed in Figures 1 and 2, respectively. As shown in Figure 1 the T1?s are observed to increase with decreasing salt concentration, consistent with the known increase in viscosity of electrolytes at high salt concentrations. The self-diffusion coefficient is a more direct indicator of mass transport, and thus also decreases with increasing salt concentration. At high salt concentrations (n = 5 and 6) all three species gave similar D?s, indicating strongly correlated motion. For diglyme/salt ratios greater than n=6, the proton (solvent) D's were higher than those of both the cation and anion. A comparison of the anions and cations shows the cations having greater D's than the anions above n = 20. These results will be discussed in the context of cation-anion association and cation-diglyme complexation information gained from vibrational spectroscopic data on the same system. Finally, variable pressure self-diffusion measurements were performed for the first time on any polymer electrolyte using a static magnetic field gradient. For the 10:1 diglyme/LiTf complex, diffusion activation volumes for the anion and host were the essentially the same, again indication strongly correlated motion.
NMR Studies Of Mass Transport In High Acid Content Fuel Cell Membranes Based On PBI/Phosphoric Acid
(2004) Chung, S.H.; Durantino, L.; Jayakody, J.R.P.; Zhang, H.; Xiao, L.; Benicewicz, B.; Greenbaum, S.G.
Acid doped polybenzimidazole (PBI) has emerged as a promising candidate for a low-cost and high performance fuel cell membrane material. It has been shown that this polymer electrolyte membrane exhibits high ionic conductivity at temperatures up to 200oC. However,additional progress is still needed for the large-scale application of PBI in fuel cells. Furthermore, the conventional method to prepare acid doped PBI membranes involves a multi-step process while the mechanical properties of the resulting membranes are largely limited by the low molecular weight of PBI used in previous studies. A novel process, previously reported and termed as the PPA process, has been developed to prepare pyridine-based PBI (PPBI) membranes loaded with high levels of phosphoric acid by direct casting of the PPA polymerization solution without isolation or redissolution of the polymers, followed by a sol-gel transition induced by the hydrolysis of PPA intophosphoric acid. In an attempt to understand the ion dynamics in these membranes, two samples of this material prepared in a different manner have been examined by using nuclear magnetic resonance (NMR) techniques over a range of temperatures from 290 to 383 K. The first sample BB1 was prepared by soaking the PBI films in phosphoric acid solutions whereas the second sample BB2 was produced by the new sol-gel process which allows for greater levels of phosphoric acid loading. Using experimental techniques described elsewhere3, 1H (I=�) and 31P (I=�) NMR linewidths, spin-lattice relaxation times T1, and self-diffusion coefficients D for these materials are reported. To obtain consistent and reproducible data, the samples were dried at 423K for 90 minutes. Significant differences in the diffusion coefficients and relaxations times before and after drying are noted. For all samples a single 31P peak centered close to the reference signal from 85% H3P04 was observed. There were no spectral indications of condensed phosphates. In BB1 the line widths and relaxation times show weak temperature dependence in contrast to the data for BB2 where there were indications of motional narrowing and a welldefined T1 minimum. The diffusion data show that protons diffuse faster than the phosphorus carrying species, which means that the inter-phosphate proton transfer is important in these materials. Proton NMR diffusion and T1 data for BB2 are shown at right.
NMR Studies of Mass Transport in High-Acid-Content Fuel Cell Membranes Based on Phosphoric Acid and Polybenzimidazole
(Journal of Electrochemical Society, 2007) Jayakody, J.R.P.; Chung, S.H.; Durantino, L.; Zhang, H.; Xiao, L.; Benicewicz, B.; Greenbaum, S.G.
Mass-transport studies of phosphoric acid (PA)-doped meta-polybenzimidazole (PBI) fuel cell membranes are described. In this study, the fundamental differences in transport properties between m-PBI/PA membranes prepared by conventional imbibing procedures and the polyphosphoric acid (PPA) process are explored. The membranes were characterized by proton conductivity and multinuclear (1H and 31P) magnetic resonance measurements. Both short-range and long-range dynamical processes were investigated by spin?lattice and spin?spin relaxation time measurements and by pulsed ?eld gradient diffusion, respectively. Comparative data for pure PA and PPA are included. The high proton conductivity(0.13 S/cm at 160�C) of the PPA-processed membranes is correlated with rapid proton self-diffusion (3 x 10?6 cm2/s at 180�C). The 31P results reveal the presence of both PA and the dimeric pyrophosphoric acid and indicate strong interaction between the phosphate groups and the m-PBI matrix, with negligible anionic transport for both kinds of membranes. The higher concentration of PA in the PPA-processed membranes and differences in membrane morphology may provide an additional proton-transport mechanism involving rapid exchange between the PA and pyrophosphoric acid species.