The effect of CTAB on Na₂SO₄nucleation in mixed Na₂SO₄/CTAB aerosols by FTIR-ATR technology

FTIR-ATR technology is used to study the efflorescence kinetic of Na₂SO₄and mixed Na₂SO₄/CTAB aerosols. As the RH decreased linearly, the ν₃[Formula presented]₄²⁻band shifts from 1094 cm⁻¹to 1132 cm⁻¹, suggesting the phase transition of Na₂SO₄from solution to crystal phase (III). For pure Na₂SO₄aerosols, 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 Na₂SO₄crystals in mixed aerosols is only 62.7% and the heterogeneous nucleation rate of Na₂SO₄in Na₂SO₄/CTAB mixed aerosols is lower than that in pure Na₂SO₄aerosols. They showed that CTAB assembled into reversed micelle and part Na₂SO₄droplets are in the core to form core-shell structure, and CTAB shell prevents core Na₂SO₄solutions from crystallizing. However, the counter ion Br⁻for CTAB reversed micelle can interact with Na⁺ions, which decreases the crystallization rate of free Na₂SO₄droplets and ERH is delayed.