Mechanism of Conductivity Relaxation in Liquid and Polymeric Electrolytes: Direct Link between Conductivity and Diffusivity.

Combining broadband impedance spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance we analyzed charge and mass transport in two polymerized ionic liquids and one of their monomeric precursors. In order to establish a general procedure for extracting single-particle diffusivity from their conductivity spectra, we critically assessed several approaches previously employed to describe the onset of diffusive charge dynamics and of the electrode polarization in ion conducting materials. Based on the analysis of the permittivity spectra, we demonstrate that the conductivity relaxation process provides information on ion diffusion and the magnitude of cross-correlation effects between ionic motions. A new approach is introduced which is able to estimate ionic diffusivities from the characteristic times of conductivity relaxation and ion concentration without any adjustable parameters. This opens the venue for a deeper understanding of charge transport in concentrated and diluted electrolyte solutions.

Multinuclear NMR study of the effect of acid concentration on ion transport in phosphoric acid doped poly(benzimidazole) membranes.

(1)H and (31)P NMR spectra, line widths, spin-lattice relaxation times (T(1)), and (1)H self-diffusion coefficients (D) were determined for two distinct poly(benzimidazole) (PBI) proton exchange membranes (PEM), para-PBI and dihydroxy-PBI (2OH-PBI), both incorporating varying concentrations of phosphoric acid. The study was performed over the temperature range of 20-180 °C, for phosphoric acid concentrations of 30, 50, and 70 wt %. Of the two samples, less mobility was indicated for the 2OH-PBI compared with the para-PBI at all acid concentrations. It was also observed that increasing the acid content resulted in an increase in the temperature at which the T(1) minimum or plateau occurred. (31)P spectra reveal the presence of pyrophosphates and in the case of the 50 and 70 wt % para-PBI samples higher oligomers such as tripolyphosphates. (1)H D data showed the 30 wt % para-PBI having almost identical values as the 70 wt % 2OH-PBI over the entire temperature range. In general, stronger short- and long-range interactions were observed in the 2OH-PBI matrix, yielding reduced translational proton transport compared to that of para-PBI. While these stronger interactions hinder translational proton diffusion, they could enhance proton transport by the Grotthuss or structure diffusion mechanism, the more favorable transport mechanism. Activation energies obtained from the (1)H D data supports a proton-hopping mechanism, with possible assistance from fast exchange between phosphate groups.

Solid State Multinuclear Magnetic Resonance Investigation of Electrolyte Decomposition Products on Lithium Ion Electrodes.

Solid electrolyte interphase (SEI) formation in lithium ion cells prepared with advanced electrolytes is investigated by solid state multinuclear (7Li, 19F, 31P) magnetic resonance (NMR) measurements of electrode materials harvested from cycled cells subjected to an accelerated aging protocol. The electrolyte composition is varied to include the addition of fluorinated carbonates and triphenyl phosphate (TPP, a flame retardant). In addition to species associated with LiPF6 decomposition, cathode NMR spectra are characterized by the presence of compounds originating from the TPP additive. Substantial amounts of LiF are observed in the anodes as well as compounds originating from the fluorinated carbonates.

Solid-State NMR Studies of Chemically Lithiated CF.

Three types of fluorinated carbon, all in their original form and upon sequential chemical lithiations via n-butyllithium, were investigated by (13)C and (19)F solid-state NMR methods. The three starting CF(x) materials [where x = 1 (nominally)] were fiber based, graphite based, and petroleum coke based. The aim of the current study was to identify, at the atomic/molecular structural level, factors that might account for differences in electrochemical performance among the different kinds of CF(x). Differences were noted in the covalent F character among the starting compounds and in the details of LiF production among the lithiated samples.

Lithium-Ion-Conducting Electrolytes: From an Ionic Liquid to the Polymer Membrane.

This work concerns the design, the synthesis, and the characterization of the N-butyl-N-ethylpiperidinium N,N-bis(trifluoromethane)sulfonimide (PP(24)TFSI) ionic liquid (IL). To impart Li-ion transport, a suitable amount of lithium N,N-bis-(trifluoromethane)sulfonimide (LiTFSI) is added to the IL. The Li-IL mixture displays ionic conductivity values on the order of 10(-4) S cm(-1) and an electrochemical stability window in the range of 1.8-4.5 V vs Li(+)/Li. The voltammetric analysis demonstrates that the cathodic decomposition gives rise to a passivating layer on the surface of the working electrode, which kinetically extends the stability of the Li/IL interface as confirmed by electrochemical impedance spectroscopy measurements. The LiTFSI-PP(24)TFSI mixture is incorporated in a poly(vinylidene fluoride-co-hexafluoropropylene) matrix to form various electrolyte membranes with different LiTFSI-PP(24)TFSI contents. The ionic conductivity of all the membranes resembles that of the LiTFSI-IL mixture, suggesting an ionic transport mechanism similar to that of the liquid component. NMR measurements demonstrate a reduction in the mobility of all ions following the addition of LiTFSI to the PP(24)TFSI IL and when incorporating the mixture into the membrane. Finally, an unexpected but potentially significant enhancement in Li transference number is observed in passing from the liquid to the membrane electrolyte system.

Anhydrous proton-conducting polymeric electrolytes for fuel cells.

The need to design proton-conducting electrolytes for fuel cells operating at temperatures of 120 degrees C and above has prompted the investigation of various "water-free" polymeric materials. The present study investigates the properties of "water-free" proton-conducting membranes prepared from high-molecular-weight polymeric organic amine salts. Specifically, the properties of bisulfates and dihydrogenphosphates of poly-2-vinylpyridine (P2VP), poly-4-vinylpyridine (P4VP), and polyvinylimidazoline (PVI) have been investigated over the temperature range of 25-180 degrees C. Nanocomposites of these polymeric organic amine salts and hydroxylated silica have also been investigated in this study. These polymers are found to be stable and proton-conducting at temperatures up to 200 degrees C. In all the polymer examples studied herein, the phosphates are more conducting than the bisulfates. The activation energy for ionic conduction was found to decrease with increasing temperature, and this is associated with the increased polymer mobility and ionization of the proton. This is confirmed by the high degree of motional narrowing that is observed in proton NMR experiments. The measured values of conductivity and the differences in pKa values of the polymeric organic amine and the mineral acid are clearly correlated. This observation provides the basis for the design of other water-free acid-base polymer systems with enhanced proton conductivity. The results presented here suggest that anhydrous polymer systems based on acid-base polymer salts could be combined with short-range proton conductors such as nanoparticulate silica to achieve acceptable conductivity over the entire temperature range.

Iontophoresis as a tool for anesthesia in dermatologic surgery: an overview.

One of the biggest challenges of performing dermatologic surgery procedures is to minimize pain. Not only will the experience of each patient be enhanced by increased comfort, but the medical and aesthetic results achieved by the physician will be facilitated as well. Iontophoresis is the use of electrical impulses to drive molecules into the skin. Anesthetic agents are one type of medicine that can be delivered in such a way. There is a tremendous potential for the applications of iontophoresis to be expanded. As our understanding of the technique increases we will be able to modify the skin's surface as well as the individual agents we wish to transport.

Stellate purse-string closure.

BACKGROUND: There are fundamental concepts we use in managing surgical defects. Whether planning a primary closure or a local flap, we frequently modify the basic design to maximize aesthetic outcomes, taking into consideration a number of factors including the location of the defect and tissue availability. OBJECTIVE: We describe the stellate modified purse-string closure, a novel flap modification. METHOD: Report of an illustrated case. RESULT: A patient with vertex scalp defect was reconstructed using the stellate purse-string flap. CONCLUSION: Certain modifications of commonly used reconstructive techniques can be utilized in specific situations to enhance cosmesis. Advantages of this modification are discussed.

Modified Burow's wedge flap for upper lateral lip defects.

BACKGROUND: There are fundamental concepts we use in managing surgical defects. Whether planning a primary closure or a local flap, we frequently modify the basic design to maximize aesthetic outcomes, taking into consideration a number of factors including the location of the defect and tissue availability. OBJECTIVE: We describe a modified Burow's wedge flap for upper lateral lip defects. METHOD: Report of an illustrated case. RESULT: A patient with an upper lip defect was successfully reconstructed using the modified Burow's wedge flap, where the Burrow's wedge is placed on the mucocutaneous lip. CONCLUSION: Certain modifications of commonly used reconstructive techniques can be utilized in specific situations to enhance cosmesis. For the Burow's wedge flap, the dermatologic surgeon has several options in placing the Burow's triangle. This is an example of how alternatives in a closure can be used depending on the laxity of the skin and the size of the defect. Advantages and disadvantages of this alternative placement of the Burow's triangle are discussed.

A genetic investigation of E2A function in lymphocyte development.

Lymphocytes are derived from hematopoietic stem cells (HSC) following a series of regulated differentiation events. Multipotent HSCs become committed to the B cell lineage in bone marrow and the T cell lineage in the thymus after receiving appropriate signals from the corresponding microenvironment. These committed lymphoid cells must then undergo V(D)J recombination at the immunoglobulin gene or T cell receptor gene locus resulting in clonal production of functional B or T lymphocytes, respectively. Lymphocyte commitment and differentiation are accompanied by programmed gene expression or repression events which are driven by lineage and stage specific transcription factors. The basic-helix-loop-helix (bHLH) transcription factors encoded by the E2A gene are involved in several differentiation events during B and T cell development, including lineage commitment, initiation of V(D)J recombination, and antigen receptor mediated proliferation and differentiation. Several recent reviews have provided a comprehensive discussion of biochemical, cellular, and genetic research on E2A function in lymphocyte development (1,2). Here, we only discuss some of the genetic approaches our laboratory (except where it is noted) has undertaken to investigate the molecular pathways mediated by E2A transcription factors in lymphocyte development.

Modified purse-string closure for reconstruction of moderate/large surgical defects of the face.

BACKGROUND: Large surgical defects of the face can often be difficult to repair. Extensive adjacent tissue transfer may be necessary and may result in significant scars and possible flap compromise. Often there may be less donor tissue available than is necessary to achieve closure. The alternative is a split-thickness skin graft, which often has a poor cosmetic outcome with poor color match and contour irregularities. OBJECTIVE. A novel approach to closing large surgical defects of the face is described. This relies on a combination of side-to-side bilateral advancement and circumferential tissue recruitment utilizing the purse-string suture. METHODS: Report of illustrated cases. RESULTS: A 3.5 x 5.5 cm preauricular cheek defect, which could not be closed primarily side-to-side, was successfully completely closed in a curvilinear fashion by implementing both side-to-side bilateral advancement and circumferential tissue recruitment. A 3.8 x 5.5 cm cheek defect and a 6.0 x 8.0 cm temple defect were significantly decreased by using the modified purse-string closure. Healing by second intention in these two cases provided an excellent cosmetic result. CONCLUSION: The use of the purse-string closure utilizing circumferential tissue recruitment in combination with side-to-side bilateral adjacent tissue transfer allows seemingly large facial defects to be closed or significantly reduced in size. Such closure is evident even in cases where poor skin laxity and size of the defect would not appear to allow this. The modified purse string closure can result in an excellent cosmetic outcome.

Carbon dioxide laser resurfacing of peri-oral rhytids in scleroderma patients.

BACKGROUND: The short pulse duration high-energy carbon dioxide (CO2) lasers have been used in the past for treating cutaneous pathology and more recently for cosmetic improvements of rhytids, photo-aging, and acne. OBJECTIVE: This study was undertaken to determine the benefits of CO2 laser resurfacing on the severe peri-oral rhytidosis commonly seen in patients with systemic scleroderma. METHODS: Three patients were studied and evaluated for satisfactory wound healing, improved cosmetic result, and lack of complications. RESULTS: All three patients experienced significant improvement following laser resurfacing. CONCLUSION: The study demonstrated the safe and effective treatment for peri-oral rhytidosis in patients with generalized scleroderma utilizing CO2 laser resurfacing.

Intraoperative tissue expansion in eyelid reconstruction.

OBJECTIVE: Chronic tissue expansion is a well-accepted modality for increasing available tissue for reconstructive surgery. In rapid intraoperative tissue expansion (RITE), a tissue expander is used intraoperatively to increase the available tissue area for defect closure. The use of the ubiquitous and inexpensive Foley catheter has previously been reported as a tissue expander in RITE. In this paper, the authors examine the application of the Foley catheter for RITE in oculoplastic surgery. DESIGN: Case series. PARTICIPANTS: Twenty-six patients (ages 50 to 87) with eyelid defects from various causes underwent reconstruction using RITE. INTERVENTION: Using this technique, the tip of a #14 French Foley catheter is trimmed, keeping the balloon intact. The balloon is inserted under a skin-muscle flap. Counter traction is applied, and the balloon is filled with saline until the flap blanches. The balloon is inflated twice for 5 minutes with a 1- to 2-minute rest period between expansions. This provides increased tissue area for reconstruction of periocular defects. MAIN OUTCOME MEASURES: The linear extent of the eyelid defect was measured prior to and after expansion with RITE. A comparison was made between the two measurements. RESULTS: The linear extent of the eyelid margin defect decreased by 36% after RITE. CONCLUSIONS: Rapid intraoperative tissue expansion with a Foley catheter is a means of providing increased tissue area for reconstructive surgery of the eyelids and periorbital region. This technique provides excellent tissue match for color, texture, and thickness. The technique decreases the size of the incised and undermined skin-muscle flap and the tension needed for wound closure.

Bispecific monoclonal antibody complexes facilitate erythrocyte binding and liver clearance of a prototype particulate pathogen in a monkey model.

We used Anger camera imaging in a monkey model to investigate the organ localization of a prototype particulate pathogen, 131I-labeled bacteriophage phi X174, after it was bound to the primate erythrocyte complement receptor and then cleared from the circulation. This 131I-labeled phi X174 was infused into the circulation of an immunized monkey, and the nascently formed immune complexes showed rapid and quantitative binding to erythrocytes via the immune adherence reaction (complement-mediated binding). Alternatively, phi X174 was infused into the circulation of a naive animal, and then cross-linked bispecific mAb complexes (heteropolymers, anti-CR1 x anti-phi X174) were infused into the circulation. The infused heteropolymers also facilitated rapid and quantitative binding of phi X174 to erythrocytes. In both cases, after a short lag period, the erythrocyte-bound phi X174 was rapidly cleared from the circulation, and the vast majority of the radiolabel was cleared to the liver, with a small amount clearing to the spleen. Further liver imaging confirmed that within 24 h most of the bacteriophage previously cleared to the liver via the heteropolymer system was phagocytosed and destroyed. The findings in this model system provide additional evidence for the potential utility of heteropolymers to facilitate the safe and rapid clearance of blood-borne pathogens as a potential treatment for infectious diseases.