Relations Between Dynamic Localization and Solute Diffusion in Polymers

It is well known that a number of compound superconductors with the A15 structure undergo a martensite transformation when cooled to the superconducting state. Nb3Sn is one of those compounds that transforms, at least partially, from a cubic to tetragonal structure near 43 K. To our knowledge this transformation in Nb3Sn has not been studied by TEM. In fact, the only low temperature TEM study of an A15 material, V3Si, was performed by Goringe and Valdre over 20 years ago. They found the martensite structure in some foil areas at temperatures between 11 and 29 K, accompanied by faults that consisted of coherent twin boundaries on {110} planes. In pursuing our studies of irradiation defects in superconductors, we are the first to observe by TEM a similar martensite structure in Nb3Sn.Samples of Nb3Sn suitable for TEM studies have been produced by both a liquid solute diffusion reaction and by sputter deposition of thin films.

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Solute redistribution during in-situ irradiation of alloys in the high voltage electron microscope

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108994 ◽

1978 ◽

Vol 36 (1) ◽

pp. 370-371

Author(s):

P. R. Okamoto ◽

N.Q. Lam ◽

R. L. Lyles

Keyword(s):

Electron Microscope ◽

High Voltage ◽

Driving Forces ◽

Solute Diffusion ◽

Solute Redistribution ◽

Voltage Electron ◽

High Voltage Electron Microscope ◽

High Voltage Electron ◽

Thin Foils ◽

Solute Atoms

During irradiation of thin foils in a high voltage electron microscope (HVEM) defect gradients will be set up between the foil surfaces and interior. In alloys defect gradients provide additional driving forces for solute diffusion since any preferential binding and/or exchange between solute atoms and mobile defects will couple a net flux of solute atoms to the defect fluxes. Thus, during irradiation large nonequilibrium compositional gradients can be produced near the foil surfaces in initially homogeneous alloys. A system of coupled reaction-rate and diffusion equations describing the build up of mobile defects and solute redistribution in thin foils and in a semi-infinite medium under charged-particle irradiation has been formulated. Spatially uniform and nonuniform damage production rates have been used to model solute segregation under electron and ion irradiation conditions.An example calculation showing the time evolution of the solute concentration in a 2000 Å thick foil during electron irradiation is shown in Fig. 1.

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Effects of solute-solvent and solvent-solvent attractive interactions on solute diffusion

Molecular Physics ◽

10.1080/002689700419789 ◽

2000 ◽

Vol 98 (19) ◽

pp. 1553-1563 ◽

Cited By ~ 1

Author(s):

T. Yamaguchi, Y. Kimura

Keyword(s):

Solute Diffusion ◽

Solvent Solvent

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Synthesis of Smart Mesoporous Materials

MRS Proceedings ◽

10.1557/proc-775-p7.8 ◽

2003 ◽

Vol 775 ◽

Author(s):

G.V.Rama Rao ◽

Qiang Fu ◽

Linnea K. Ista ◽

Huifang Xu ◽

S. Balamurugan ◽

...

Keyword(s):

Mesoporous Silica ◽

Mesoporous Materials ◽

Fluorescent Dyes ◽

Thermo Gravimetric Analysis ◽

Molecular Transport ◽

Solute Diffusion ◽

Gravimetric Analysis ◽

Stimuli Responsive ◽

Porous Network ◽

Hybrid Mesoporous Materials

AbstractThis study details development of hybrid mesoporous materials in which molecular transport through mesopores can be precisely controlled and reversibly modulated. Mesoporous silica materials formed by surfactant templating were modified by surface initiated atom transfer radical polymerization of poly(N-isopropyl acrylamide) (PNIPAAm) a stimuli responsive polymer (SRP) within the porous network. Thermo gravimetric analysis and FTIR spectroscopy were used to confirm the presence of PNIPAAm on the silica surface. Nitrogen porosimetry, transmission electron microscopy and X-ray diffraction analyses confirmed that polymerization occurred uniformly within the porous network. Uptake and release of fluorescent dyes from the particles was monitored by spectrofluorimetry and scanning laser confocal microscopy. Results suggest that the presence of PNIPAAm, a SRP, in the porous network can be used to modulate the transport of aqueous solutes. At low temperature, (e.g., room temperature) the PNIPAAm is hydrated and extended and inhibits transport of analytes; at higher temperatures (e.g., 50°C) it is hydrophobic and is collapsed within the pore network, thus allowing solute diffusion into or out of the mesoporous silica. The transition form hydrophilic to hydrophobic state on polymer grafted mesoporous membranes was determined by contact angle measurements. This work has implications for the development of materials for the selective control of transport of molecular solutes in a variety of applications.

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