Chaotrope vs. kosmotrope: which one has lower friction?
We examine the frictional properties of zwitterionic surfaces and explore whether chaotropic or kosmotropic charged groups are preferred to achieve lower friction. Self-assembled monolayers of carboxybetaine (CB-SAMs) and sulfurbetaine (SB-SAMs) are used as model surfaces as they contain the same positively charged group, but different negatively charged ones. The negatively charged groups are kosmotropic carboxylates in the CB-SAM surfaces and chaotropic sulfonate groups in the SB-SAM surfaces, respectively. The results show that the friction of the SB-SAM surfaces is even lower than that of the CB-SAM surfaces although both surfaces have low friction. This suggests that chaotropic charged groups are better in reducing friction than kosmotropic groups. The lower friction of the SB-SAM surfaces over the CB-SAM can be explained by the higher mobility of water near the SB-SAM surfaces, as shown in the survival autocorrelation function and the dipole autocorrelation function of hydration water molecules.
Department of Chemical Engineering, University of Washington, Washington 98195, USA.
Yi
Y
He
Qing
Q
Shao
Shengfu
S
Chen
Shaoyi
S
Jiang
D001622:Betaine / Q000737:chemistry*; D017276:Friction; D007477:Ions / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry
D007477:Ions; D014867:Water; D001622:Betaine