Robert L. Karlinsey

Design of organic–inorganic solid polymer electrolytes: synthesis, structure, and properties

This paper reports the synthesis, structure, and properties of novel hybrid solid polymer electrolytes (SPEs) consisting of organically modified aluminosilica (OM-AlSi), formed within a poly(ethylene oxide)-in-salt (Li triflate) phase. To alter the structure and properties of these polymer electrolytes, we used functionalized silanes containing poly(ethylene oxide) (PEO) tails or CN groups. The SPEs described here were studied using differential scanning calorimetry, Raman spectroscopy, X-ray powder diffraction, and AC impedance spectroscopy. The size of the OM-AlSi domains was estimated using transmission electron microscopy and comparing the sizes of AlSi nanoparticles, obtained via calcination of the hybrid SPE. The conductivity enhancement, caused by incorporation of PEO tails or CN groups in the hybrid materials based on 600 Da poly(ethylene glycol), can be ascribed to a decrease of OM-AlSi domain size accompanied by an increase of the OM-AlSi/PEO + LiTf interface. For the CN modifier, increase of this interface increases the amount of CN groups exposed to PEO + LiTf phase, thus increasing the effective dielectric constants of the materials and their conductivity, although this dependence is not linear. In the case of the PEO modifier, different effects are observed for 600 Da PEG and 100 kDa PEO. For 100 kDa PEO, incorporation of the silane with a PEO tail caused a decrease of conductivity. Here, AlSi particle size remains basically unchanged with addition of silane-modifier, and the decrease of conductivity can be attributed to formation of a crystalline phase at the OM-AlSi/PEO + LiTf interface.

Ice nucleation on BaF2(111).

The mechanism of heterogeneous ice nucleation on inorganic substrates is not well understood despite work on AgI and other materials over the past 50 years. We have selected BaF(2) as a model substrate for study since its (111) surface makes a near perfect match with the lattice of the basal face of I(h) ice and would appear to be an ideal nucleating agent. Two series of experiments were undertaken. In one, nucleation of thin film water formed from deposition of vapor on BaF(2)(111) faces was explored with the finding that supercooling to -30 degrees C was required before freezing occurred. In the other series, nucleation of liquid water on submerged BaF(2) crystals was studied. Here supercooling to -15 degrees C was needed before ice formed. The reason why BaF(2) is such a poor nucleating agent contains clues to realistic mechanisms of heterogeneous nucleation. Our explanation of these results follows the model of Fletcher [J. Chem. Phys. 29, 572 (1958)] who showed that heterogeneous ice nucleating ability depends on how well ice wets a substrate. In this view, a smooth BaF(2)(111) face is poor at nucleation because ice only partially wets its surface. In an extension of Fletchers model, our calculations, consistent with the experimental results demonstrate that the pitting of a submerged BaF(2) crystal dramatically improves its ice nucleating ability.