Chemical Equilibrium Unique to Nano-Systems: Confinement vs. Quasi-Confinement Effects

M. Polak, L. Rubinovich
Ben-Gurion University of the Negev, IL

Keywords: nanochemical equilibrium, statistical-mechanical modeling, quasi-confinement, nano-space


A remarkable nano-confinement entropic effect on chemical equilibrium (NCECE) was predicted by us using a novel lattice-gas based statistical-mechanical modeling. The study was motivated by the increasing experimental research of confined nanospaces where selective chemical reactions can take place efficiently. The NCECE was modeled for two classes of experimentally studied reactions: (i) hydrogen-bonded nucleotide dimers stabilized inside molecular cages; (ii) the enhanced deuteration commonly observed for interstellar molecules reacting on tiny dust grain surfaces. In both cases, the theoretical predictions are in line with the observed trends. The broad outcome of the modeling concerns a remarkable stabilization of weakly exothermic reaction products, as reflected in augmented “equilibrium constant”, in comparison to macroscopic systems. The modeling has been extended to presumably more realistic “quasi-confined” systems exchanging matter with an equilibrated macroscopic environment. But the number of molecules capable of populating nano-space sites is limited by its small size due to spatial exclusion. Being intermediate between open and closed system conditions, quasi-confinement is unique to nanoscale systems. The peculiar entropic stabilization of products is anticipated for a wide range of other nanospaces (nanotubes, fullerenes, micelles), and thus can have implications for the growing nanotechnological utilization of chemical syntheses conducted within confined nanoreactors.