Polymerizable ionic liquid with state of the art transport properties.

The physicochemical properties of diallyldimethylammonium-bis(trifluoromethanesulfonyl)imide (DADMATFSI) and its binary mixture with LiTFSI are presented herein, also showing this novel compound as a polymerizable room temperature ionic liquid with excellent transport properties for Li(+) ions. In particular, results of pulsed field gradient (PFG)-NMR diffusion experiments and impedance measurements show that DADMATFSI exhibits state of the art properties of ionic liquids. Similar ionic diffusion coefficients and a similarly high conductivity as seen in the benchmark compound N-butyl-N-methylpyrrolidinium-bis(trifluoromethanesulfonyl)imide (PYR14TFSI) are observed. In accordance, the Li transference number in the binary mixture matches the trend seen for PYR14TFSI-LiTFSI mixtures. In addition to these impressive properties as ionic liquid, DADMATFSI was polymerized by UV treatment. The polymerization is demonstrated and the ion conducting properties of the resulting gel polymer electrolyte are investigated, showing that DADMATFSI can be transformed into an ionogel and may have applications where polymerization is desirable.

Activation of transport and local dynamics in polysiloxane-based salt-in-polymer electrolytes: a multinuclear NMR study.

We have investigated a new improved lithium ion conducting salt-in-polymer electrolyte system consisting of a polysiloxane backbone with oligoether side chains and added LiCF(3)SO(3) (LiTf), which has a conductivity at 30 degrees C of up to 1.3 x 10(-4) S cm(-1) and up to 6.9 x 10(-5) S cm(-1) after cross-linking, which is employed to enhance mechanical stability. The mechanisms governing local dynamics and mass transport have been studied on the basis of temperature dependent spin-lattice relaxation time and pulsed field gradient diffusion measurements for (7)Li, (19)F and (1)H, respectively. The correlation times characterizing the local ion dynamics reflect the complexation of the cations by the polyether side chains of the polymer and show the anion as the more mobile species. In contrast, (7)Li and (19)F diffusion coefficients and their activation energies are rather similar, suggesting the formation of ion pairs with similar activation barriers for cation and/or anion long-range transport. In general, the activation energies describing local reorientation are significantly smaller than those characterizing long range diffusion, suggesting that the long-range transport of both cations and anions is a much more complex process than a simple succession of free ion jumps, and involves (1) the coupling of conformational side-chain reorientations to the cation movement, and (2) the correlated diffusion of cations and anions within dimers or clusters. An important practical conclusion from our results is that the relatively high ionic conductivity in polysiloxane-based polymer electrolytes could even be increased if salt dissociation could be enhanced further.

Melting behavior and ionic conductivity in hydrophobic ionic liquids.

Four room-temperature ionic liquids (RTILs) based on the N-butyl-N-methyl pyrrolidinium (Pyr(14)(+)) and N-methyl-N-propyl pyrrolidinium cations (Pyr(13)(+)) and bis(trifluoromethanesulfonyl)imide (TFSI(-)) and bis(fluorosulfonyl)imide (FSI(-)) anions were intensively investigated during their melting. The diffusion coefficients of (1)H and (19)F were determined using pulsed field gradient (PFG) NMR to study the dynamics of the cations, anions, and ion pairs. The AC conductivities were measured to detect only the motion of the charged particles. The melting points of these ionic liquids were measured by DSC and verified by the temperature-dependent full width at half-maximum (FWHM) of the (1)H and (19)F NMR peaks. The diffusion and conductivity data at low temperatures gave information about the dynamics at the melting point and allowed specifying the way of melting. In addition, the diffusion coefficients of (1)H (D(H)) and (19)F (D(F)) and conductivity were correlated using the Nernst-Einstein equation with respect to the existence of ion pairs. Our results show that in dependence on the cation different melting behaviors were identified. In the Pyr(14)-based ILs, ion pairs exist, which collapse above the melting point of the sample. This is in contrast to the Pyr(13)-based ILs where the present ion pairs in the crystal dissociate during the melting. Furthermore, the anions do not influence the melting behavior of the investigated Pyr(14) systems but affect the Pyr(13) ILs. This becomes apparent in species with a higher mobility during the breakup of the crystalline IL.

Predictive factors of femtosecond laser flap thickness measured by online optical coherence pachymetry subtraction in sub-Bowman keratomileusis.

PURPOSE: To evaluate possible factors responsible for the difference between predicted and measured parameters during 100 microm flap creation with a femtosecond laser (IntraLase FS30) using online optical coherence pachymetry (OCP). SETTING: AugenVersorgungsZentrum, Weilheim, and the Technical University of Munich, Munich, Germany. METHODS: In this nonrandomized prospective interventional case study, 287 eyes of 146 consecutive patients were monitored by online OCP before and after flap creation with the femtosecond laser. The laser-specific settings were held constant during the study to attempt a 100 microm flap in all eyes. A multiple linear regression model with backward variable selection procedure was applied to evaluate possible multivariable explanatory powers of several covariates. In addition, very thin and very thick flaps (ie, lower and upper quartiles of flap thickness distribution) were analyzed separately in a logistic regression model. RESULTS: Central flap thickness measured with online OCP subtraction varied according to a Gaussian distribution from 57 to 138 microm, with a mean of 100.4 microm +/- 13.6 (SD). Regression analysis between predicted and measured flap thickness showed no predictive power of 11 variables including the keratometry value of the cornea, preoperative corneal thickness, and patient age. CONCLUSION: The plano applanation interface of the IntraLase FS30 femtosecond laser produced ultrathin flaps for sub-Bowman keratomileusis that were independent of some preoperative and surgical factors known to affect outcomes with mechanical microkeratomes.

Quartz crystal microbalance studies of the contact between soft, viscoelastic solids.

Mechanical contact between a viscoelastic lens and a viscoelastic film has been probed by means of a quartz crystal microbalance operated in the impedance analysis mode. The frequency shift induced by the formation of the contact decreases with increasing film thickness because of the finite penetration depth of the acoustic shear wave. The dependence of frequency and bandwidth on film thickness and contact area is described within a sheet-contact model, which can be employed to quantitatively analyze mechanical contact in a wide range of materials problems. The model was tested by bringing a quartz crystal coated with an elastomeric gel into contact with a hemispherical cap of a similar gel. Both gels consisted of the thermoreversible gel Kraton G swollen in mineral oil. The experiments support the model well.

Measurements of interfacial viscoelasticity with a quartz crystal microbalance: influence of acoustic scattering from a small crystal-sample contact.

We discuss the influence of a limited contact size on measurements of high-frequency interfacial viscoelasticity performed with a combination of a quartz crystal microbalance (QCM) and the Johnson-Kendall-Roberts (JKR) apparatus. In this instrument, a sphere-plate contact is established between an elastomeric lens and a quartz resonator. The analysis is carried out in the frame of the sheet-contact model, which states that both the shift of resonance frequency and the bandwidth are proportional to the contact area as long as the contact area is much smaller than the crystal itself. In particular, the ratio of the shift in bandwidth and the shift in frequency (termed the D-f ratio) is predicted to be constant and independent of geometry. However, the experiment does show a slight increase in the D-f ratio with the contact radius when the contact radius is comparable to the wavelength of sound inside the crystal. This effect can be explained by acoustic scattering.