Semi-quantitative determination of ion transfers at an interface between water and quaternary ammonium polybromide droplets through stochastic electrochemical analysis

Abstract

In this article, we present stochastic electrochemical analyses for the semi-quantitative determination of ion transfers (ITs) at an interface between water and electrochemically generated quaternary ammonium polybromide (QBr(2n+1)) droplets (water vertical bar QBr(2n+1)) in QBr aqueous solutions containing different acids (HAs). The concentration of Br- in QBr(2n+1), CBr-(QBr2n+1) is linearly proportional to CA-(aq) with the proportionality constant, which was estimated from the difference between the two partition coefficients of H+ and A(-) from water toward QBr(2n+1), KH+ - KA-, and the ratio of the mean activity coefficient of the aqueous over that of the QBr(2n+1) phase, gamma(+/-,aq)/gamma(+/-),(QBr2n+1). CBr-(QBr2n+1) also shows the linear function of CQ+(aq) with (gamma(+/-,aq)/gamma(+/-,QBr2n+1))KQ+ as its proportionality constant. The stochastic chronoamperometric analyses of QBr(2n+1) droplets during their particle-impacts on Pt UME in acidic solutions containing either N-methyl-N-ethyl pyrrolidinium bromide (MEPBr) or ethyl-pyridinium bromide (EPyBr) as model QBrs can provide indirect information about CBr-(QBr2n+1), and we estimated the relative order to be KC+(Li+ or Na+), KH+, and KA- : KC+(Li+ or Na+) < KH+ < KA-, where KHSO4- < KClO4- < KCl- in KA- and KNa+ < KLi+ in KC+. Also, we found that Br--IT at water vertical bar QBr(2n+1) is effectively limited by A(-)-IT in the acidic solutions, and Cl- is most significantly transferred to QBr(2n+1), leading to the complete inhibition of Br--IT into QBr(2n+1).