Statistical Mechanics of Glass Formation in Molecular Liquids with OTP as an Example

We extend our statistical mechanical theory of the glass transition from examples consisting of point particles to molecular liquids with internal degrees of freedom. As before, the fundamental assertion is that super-cooled liquids are ergodic, although becoming very viscous at lower temperatures, and are therefore describable in principle by statistical mechanics. The theory is based on analyzing the local neighborhoods of each molecule, and a statistical mechanical weight is assigned to every possible local organization. This results in an approximate theory that is in very good agreement with simulations regarding both thermodynamical and dynamical properties

Polymer-membrane pH electrodes as internal elements for potentiometric gas-sensing systems

The use of polymer-membrane pH electrodes as internal sensing elements for the fabrication of inexpensive ammonia and carbon dioxide gas sensing systems is reported. The pH-responsive polymer membranes are prepared by incorporating tridodecylamine as the neutral carrier in plasticized poly(vinyl chloride) membranes. Both static and continuous-flow gas-sensing arrangements are described. For miniature static gas sensors, the internal polymer pH electrode can be made with or without an internal reference solution. In the latter case, the polymeric membrane is coated directly onto a graphite substrate. The polymer pH electrode can also be prepaerd in tubular form and used in conjunction with a gas dialysis chamber for automated continuous-flow determinations of carbon dioxide and ammonia. Slopes, response times, and reproducibility of these new gas-sensing systems are evaluated using optimized internal electrodes, flow rates, and gas-permeable membrane materials. When appropriate reagents and materials ar used, the static sensors exhibit slopes in the range 48-62 mV/decace with potentials reproducible to less than +/-1.5 mV at gas concentrations greater than 10-3 M.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25336/1/0000782.pd

Theoretical predictions on the response properties of potentiometric gas sensors based on internal polymer membrane electrodes

The appropriate equilibrium expressions and known thermodynamic equilibrium constants are used in calculations on the expected response properties of polymer membrane electrode-based ammonia and carbon dioxide gas sensors. Slopes, detection limits, Nernstian response ranges and selectivities of such devices are shown to be a function of the initial pH, ionic strength and equilibrium constant of the internal electrolyte buffer used within these probes. Previously reported data for an ammonia sensor of this type correlate well with the theory. The poor response characteristics of carbon dioxide sensors based on internal carbonate-responsive membranes is also explained via the model presented. Future prospects and considerations for the development of other gas sensors of this type are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25338/1/0000784.pd