24,678 research outputs found
In-situ cross linking of polyvinyl alcohol
A method of producing a crosslinked polyvinyl alcohol structure, such as a battery separator membrane or electrode envelope is described. An aqueous solution of a film-forming polyvinyl alcohol is admixed with an aldehyde crosslinking agent a basic pH to inhibit crosslinking. The crosslinking agent, perferably a dialdehyde such as glutaraldehyde, is used in an amount of from about 1/2 to about 20% of the theoretical amount required to crosslink all of the hydroxyl groups of the polymer. The aqueous admixture is formed into a desired physical shape, such as by casting a sheet of the solution. The sheet is then dried to form a self-supporting film. Crosslinking is then effected by immersing the film in aqueous acid solution. The resultant product has excellent properties for use as a battery separator
Cross-linked polyvinyl alcohol and method of making same
A film-forming polyvinyl alcohol polymer is mixed with a polyaldehyde-polysaccharide cross-linking agent having at least two monosaccharide units and a plurality of aldehyde groups per molecule, perferably an average of at least one aldehyde group per monosaccharide units. The cross-linking agent, such as a polydialdehyde starch, is used in an amount of about 2.5 to 20% of the theoretical amount required to cross-link all of the available hydroxyl groups of the polyvinyl alcohol polymer. Reaction between the polymer and cross-linking agent is effected in aqueous acidic solution to produce the cross-linked polymer. The polymer product has low electrical resistivity and other properties rendering it suitable for making separators for alkaline batteries
In situ self cross-linking of polyvinyl alcohol battery separators
A battery separator was produced from a polyvinyl alcohol sheet structure which was subjected to an in situ, self crosslinking process by selective oxidation of the 1,2 diol units present in the polyvinyl alcohol sheet structure. The 1,2 diol units were cleaved to form aldehyde end groups which subsequently crosslink through acetalization of the 1,3 diol units of the polyvinyl alcohol. Selective oxidation was achieved using a solution of a suitable oxidizing agent such as periodic acid or lead tetraacetate
Inexpensive cross-linked polymeric separators made from water soluble polymers
Polyvinyl alcohol (PVA) crosslinked chemically with aldehyde reagents produces membranes which demonstrate oxidation resistance, dimensional stability, low ionic resistivity, low zincate diffusivity, and low zinc dendrite penetration rate which make them suitable for use as alkaline battery separators. They are intrinsically low in cost and environmental health and safety problems associated with commercial production appear minimal. Preparation, property measurements, and cell test results in Ni/Zn and Ag/Zn cells are described and discussed
Alkaline battery containing a separator of a cross-linked copolymer of vinyl alcohol and unsaturated carboxylic acid
A battery separator for an alkaline battery is described. The separator comprises a cross linked copolymer of vinyl alcohol units and unsaturated carboxylic acid units. The cross linked copolymer is insoluble in water, has excellent zincate diffusion and oxygen gas barrier properties and a low electrical resistivity. Cross linking with a polyaldehyde cross linking agent is preferred
Method of cross-linking polyvinyl alcohol and other water soluble resins
A self supporting sheet structure comprising a water soluble, noncrosslinked polymer such as polyvinyl alcohol which is capable of being crosslinked by reaction with hydrogen atom radicals and hydroxyl molecule radicals is contacted with an aqueous solution having a pH of less than 8 and containing a dissolved salt in an amount sufficient to prevent substantial dissolution of the noncrosslinked polymer in the aqueous solution. The aqueous solution is then irradiated with ionizing radiation to form hydrogen atom radicals and hydroxyl molecule radicals and the irradiation is continued for a time sufficient to effect crosslinking of the water soluble polymer to produce a water insoluble polymer sheet structure. The method has particular application in the production of battery separators and electrode envelopes for alkaline batteries
Polyvinyl alcohol cross-linked with two aldehydes
A film forming polyvinyl alcohol resin is admixed, in aqueous solution, with a dialdehyde crosslinking agent which is capable of crosslinking the polyvinyl alcohol resin and a water soluble acid aldehyde containing a reactive aldehyde group capable of reacting with hydroxyl groups in the polyvinyl alcohol resin and an ionizable acid hydrogen atom. The dialdehyde is present in an amount sufficient to react with from 1 to 20% by weight of the theoretical amount required to react with all of the hydroxyl groups of the polyvinyl alcohol. The amount of acid aldehyde is from 1 to 50% by weight, same basis, and is sufficient to reduce the pH of the aqueous admixture to 5 or less. The admixture is then formed into a desired physical shape, such as by casting a sheet or film, and the shaped material is then heated to simultaneously dry and crosslink the article
Baryon resonances and hadronic interactions in a finite volume
In a finite volume, resonances and multi-hadron states are identified by
discrete energy levels. When comparing the results of lattice QCD calculations
to scattering experiments, it is important to have a way of associating the
energy spectrum of the finite-volume lattice with the asymptotic behaviour of
the S-matrix. A new technique for comparing energy eigenvalues with scattering
phase shifts is introduced, which involves the construction of an exactly
solvable matrix Hamiltonian model. The model framework is applied to the case
of decay, but is easily generalized to include
multi-channel scattering. Extracting resonance parameters involves matching the
energy spectrum of the model to that of a lattice QCD calculation. The
resulting fit parameters are then used to generate phase shifts. Using a sample
set of pseudodata, it is found that the extraction of the resonance position is
stable with respect to volume for a variety of regularization schemes, and
compares favorably with the well-known Luescher method. The model-dependence of
the result is briefly investigated.Comment: 7 pages, 3 figures. Talk presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), June 24-29, 2012, Cairns,
Australi
Interpenetration as a Mechanism for Liquid-Liquid Phase Transitions
We study simple lattice systems to demonstrate the influence of
interpenetrating bond networks on phase behavior. We promote interpenetration
by using a Hamiltonian with a weakly repulsive interaction with nearest
neighbors and an attractive interaction with second-nearest neighbors. In this
way, bond networks will form between second-nearest neighbors, allowing for two
(locally) distinct networks to form. We obtain the phase behavior from analytic
solution in the mean-field approximation and exact solution on the Bethe
lattice. We compare these results with exact numerical results for the phase
behavior from grand canonical Monte Carlo simulations on square, cubic, and
tetrahedral lattices. All results show that these simple systems exhibit rich
phase diagrams with two fluid-fluid critical points and three thermodynamically
distinct phases. We also consider including third-nearest-neighbor
interactions, which give rise to a phase diagram with four critical points and
five thermodynamically distinct phases. Thus the interpenetration mechanism
provides a simple route to generate multiple liquid phases in single-component
systems, such as hypothesized in water and observed in several model and
experimental systems. Additionally, interpenetration of many such networks
appears plausible in a recently considered material made from nanoparticles
functionalized by single strands of DNA.Comment: 12 pages, 9 figures, submitted to Phys. Rev.
Unitarity and the Hilbert space of quantum gravity
Under the premises that physics is unitary and black hole evaporation is
complete (no remnants, no topology change), there must exist a one-to-one
correspondence between states on future null and timelike infinity and on any
earlier spacelike Cauchy surface (e.g., slices preceding the formation of the
hole). We show that these requirements exclude a large set of semiclassical
spacetime configurations from the Hilbert space of quantum gravity. In
particular, the highest entropy configurations, which account for almost all of
the volume of semiclassical phase space, would not have quantum counterparts,
i.e. would not correspond to allowed states in a quantum theory of gravity.Comment: 7 pages, 3 figures, revtex; minor changes in v2 (version published in
Class. Quant. Grav.
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