The effect of CTAB on Na2SO4 nucleation in mixed Na2SO4/CTAB aerosols by FTIR-ATR technology

FTIR-ATR technology is used to study the efflorescence kinetic of Na2SO4 and mixed Na2SO4/CTAB aerosols. As the RH decreased linearly, the ν3SO42− band shifts from 1094 cm−1 to 1132 cm−1, suggesting the phase transition of Na2SO4 from solution to crystal phase (III). For pure Na2SO4 aerosols, the ERH is 75.1% RH, whereas the efflorescence point of mixed Na2SO4/CTAB aerosols (74.2%) is lower. By further analysis of IR differential spectra, the ratio of Na2SO4 crystals in mixed aerosols is only 62.7% and the heterogeneous nucleation rate of Na2SO4 in Na2SO4/CTAB mixed aerosols is lower than that in pure Na2SO4 aerosols. They showed that CTAB assembled into reversed micelle and part Na2SO4 droplets are in the core to form core-shell structure, and CTAB shell prevents core Na2SO4 solutions from crystallizing. However, the counter ion Br− for CTAB reversed micelle can interact with Na+ ions, which decreases the crystallization rate of free Na2SO4 droplets and ERH is delayed.

The crystallization ratio of the Na2SO4 decreased greatly owing to CTAB addition, suggesting that CTAB assembled into the shell of the part Na2SO4 droplets. The kinetic of crystallization showed that the nucleation rate of the Na2SO4 in Na2SO4/CTAB mixing aerosols was lower, which should rise from the interaction between the counter ion Br− for CTAB and Na+ ions.Figure optionsDownload as PowerPoint slide