TY - JOUR
T1 - Hofmeister effects in micromolar electrolyte solutions
AU - Enami, Shinichi
AU - Mishra, Himanshu
AU - Hoffmann, Michael R.
AU - Colussi, Agustn J.
N1 - Funding Information:
This work was financially supported by the Japan Science and Technology Agency (JST) PRESTO program. We are grateful to Dr. Drew Parsons and Professor Barry Ninham for a helpful discussion. S.E. is grateful to Professor K. Takahashi, Professor M. Shiotani, and Ms. A. Hatano of Kyoto University for assisting the startup of a new laboratory. Valuable discussions with Professor William Goddard and Dr. Tod Pascal of California Institute of Technology are also acknowledged.
PY - 2012/4/21
Y1 - 2012/4/21
N2 - Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I -Br -, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH 4, and N(C 4H 9) 4) and NaY (Y OH, Cl, NO 3, and ClO 4) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I - and Br - are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.
AB - Ions induce both specific (Hofmeister) and non-specific (Coulomb) effects at aqueous interfaces. More than a century after their discovery, the origin of specific ion effects (SIE) still eludes explanation because the causal electrostatic and non-electrostatic interactions are neither local nor separable. Since direct Coulomb effects essentially vanish below ∼10 M (i.e., at 50 nm average ion separations in water), we decided to investigate whether SIE operate at, hitherto unexplored, lower concentrations. Herein, we report the detection of SIE above ∼0.1 M in experiments where relative iodidebromide populations, I -Br -, were determined on the surface of aqueous (NaI NaBr) jets by online electrospray mass spectrometry in the presence of variable XCl (X H, Na, K, Cs, NH 4, and N(C 4H 9) 4) and NaY (Y OH, Cl, NO 3, and ClO 4) concentrations. We found that (1) all tested electrolytes begin to affect below ∼1 M and (2) I - and Br - are preferentially suppressed by co-ions closely matching their interfacial affinities. We infer that these phenomena, by falling outside the reach of even the longest ranged electrostatic interactions, are dynamical in nature.
UR - http://www.scopus.com/inward/record.url?scp=84860153532&partnerID=8YFLogxK
U2 - 10.1063/1.4704752
DO - 10.1063/1.4704752
M3 - Article
C2 - 22519343
AN - SCOPUS:84860153532
SN - 0021-9606
VL - 136
JO - JOURNAL OF CHEMICAL PHYSICS
JF - JOURNAL OF CHEMICAL PHYSICS
IS - 15
M1 - 154707
ER -