Characterization of self-assembled monolayers from lithium dialkyldithiocarbamate salts.
We report the formation of self-assembled monolayers (SAMs) onto gold substrates by exposure to lithium dialkyldithiocarbamate salts [(Li+(R2DTC-), where R = n-propyl, n-butyl, n-octyl, n-decyl, n-dodecyl, or n-octadecyl] in ethanol or methylene chloride. The crystallinity and composition of the monolayers were assessed by polarized modulation infrared reflection absorption spectroscopy (PM-IRRAS), wettability was characterized by contact angles of water and hexadecane, thickness was measured by spectroscopic ellipsometry, and barrier properties determined by electrochemical impedance spectroscopy. While the shorter R2DTC-s formed monolayers with liquid-like packing, monolayers prepared from the longest R2DTC- (where R = n-octadecyl) exhibit similar thickness, crystallinity, wettability, and capacitance as monolayers prepared from n-octadecanethiol. The hydrocarbon chains within the monolayers prepared from (C18)2DTC- are less canted on average than those prepared from n-octadecanethiol. Nonetheless, the (C18)2DTC- SAM exhibits an order of magnitude lower resistance against the penetration of redox probes, which is attributed to a higher density of pinhole defect sites.
Weinstein
Randy D
RD
Department of Chemical Engineering, Villanova University, Villanova, PA 19085, USA. randy.weinstein@villanova.edu
Richards
Joshua
J
Thai
Susan D
SD
Omiatek
Donna M
DM
Bessel
Carol A
CA
Faulkner
Christopher J
CJ
Othman
Siti
S
Jennings
G Kane
GK
D000327:Adsorption; D002219:Carbamates / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D017097:Electric Impedance; D004563:Electrochemistry; D000431:Ethanol / Q000737:chemistry; D006838:Hydrocarbons / Q000737:chemistry; D008094:Lithium / Q000737:chemistry*; D008752:Methylene Chloride / Q000737:chemistry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012492:Salts / Q000737:chemistry*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013859:Thiocarbamates / Q000737:chemistry*
D002219:Carbamates; D006838:Hydrocarbons; D012492:Salts; D013859:Thiocarbamates; D000431:Ethanol; D008752:Methylene Chloride; D008094:Lithium