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 ν3-SO₄^-2 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 ofmixed 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.