TY - JOUR
T1 - Surface-charge-induced orientation of interfacial water suppresses heterogeneous ice nucleation on α-alumina (0001)
AU - Abdelmonem, Ahmed
AU - Backus, Ellen H.G.
AU - Hoffmann, Nadine
AU - Sánchez, M. Alejandra
AU - Cyran, Jenée D.
AU - Kiselev, Alexei
AU - Bonn, Mischa
PY - 2017/6/29
Y1 - 2017/6/29
N2 - Surface charge is one of the surface properties of atmospheric aerosols, which has been linked to heterogeneous ice nucleation and hence cloud formation, microphysics, and optical properties. Despite the importance of surface charge for ice nucleation, many questions remain on the molecular-level mechanisms at work. Here, we combine droplet-freezing assay studies with vibrational sum frequency generation (SFG) spectroscopy to correlate interfacial water structure to surface nucleation strength. We study immersion freezing of aqueous solutions of various pHs on the atmospherically relevant aluminum oxide α-Al2O3 (0001) surface using an isolated droplet on the surface. The high-pH solutions freeze at temperatures higher than that of the low-pH solution, while the neutral pH has the highest freezing temperature. On the molecular level, the SFG spectrum of the interfacial water changes substantially upon freezing. At all pHs, crystallization leads to a reduction of intensity of the 3400 cm-1 water resonance, while the 3200 cm-1 intensity drops for low pH but increases for neutral and high pHs. We find that charge-induced surface templating suppresses nucleation, irrespective of the sign of the surface charge. Heterogeneous nucleation is most efficient for the nominally neutral surface.
AB - Surface charge is one of the surface properties of atmospheric aerosols, which has been linked to heterogeneous ice nucleation and hence cloud formation, microphysics, and optical properties. Despite the importance of surface charge for ice nucleation, many questions remain on the molecular-level mechanisms at work. Here, we combine droplet-freezing assay studies with vibrational sum frequency generation (SFG) spectroscopy to correlate interfacial water structure to surface nucleation strength. We study immersion freezing of aqueous solutions of various pHs on the atmospherically relevant aluminum oxide α-Al2O3 (0001) surface using an isolated droplet on the surface. The high-pH solutions freeze at temperatures higher than that of the low-pH solution, while the neutral pH has the highest freezing temperature. On the molecular level, the SFG spectrum of the interfacial water changes substantially upon freezing. At all pHs, crystallization leads to a reduction of intensity of the 3400 cm-1 water resonance, while the 3200 cm-1 intensity drops for low pH but increases for neutral and high pHs. We find that charge-induced surface templating suppresses nucleation, irrespective of the sign of the surface charge. Heterogeneous nucleation is most efficient for the nominally neutral surface.
UR - http://www.scopus.com/inward/record.url?scp=85021650493&partnerID=8YFLogxK
U2 - 10.5194/acp-17-7827-2017
DO - 10.5194/acp-17-7827-2017
M3 - Article
AN - SCOPUS:85021650493
SN - 1680-7316
VL - 17
SP - 7827
EP - 7837
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 12
ER -