| Abstract
| - Entropy of mixing is shown to be the driving interactionfor the endothermic physisorption process of organicvapor partitioning into seven systematically side-chain-modified (polar, acidic, basic, polarizable side groups andgroups interacting via H-bridges) polysiloxanes on thickness-shear mode resonators. Each sensor was exposedto seven analytes, selected for their diversity of functionalgroups. This systematic investigation of sorption yieldsbenchmarking data on physisorption selectivity: responsedata and modeling reveal a direct correlation of partitioncoefficients with interactions between specific polymerside chains and analyte functional groups. Partition coefficients were determined for every polymer/analyte pairingover the 273−343 K range at 10 K intervals; frompartition coefficient temperature dependence, overallabsorption enthalpies and entropies were calculated. Bysubtracting the enthalpy and entropy of condensation fora given pure analyte, its mixing entropy (primarily combinatorial) and mixing enthalpy (associated with intermolecular interactions) with each polymer matrix weredetermined. These two crucial thermodynamic parameters determine the chemical selectivity patterns of thepolymers for the analytes. Simple molecular modelingbased on the polymer contact surface share of the modified side group or the introduced functional group revealsa direct correlation between the partition coefficients andthe side-group variation.
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