Phase transitions of an ionic liquid self-assembled monolayer on Au

Abstract

The properties of a surface modified with an ionic liquid self-assembled monolayer (IL-SAM) can be tuned by simply changing the deposition temperature. Mid-IR, SERS, and molecular modelling demonstrated that 1-(12-mercaptododecyl)-3-methylimidazolium bromide (MDMIBr) exhibited a crystalline monolayer for deposition temperatures below 25 °C. Above 25 °C, the aliphatic chain collapsed into a disordered conformation. At 40 °C, another phase transition occurs due to the imidazolium group tilting parallel to the surface. Consequently, the wettability of IL-SAM was tuned over a broad range of contact angle (from 20° to nearly 40°) by varying the deposition temperature. Permeation of redox mediators to a Au electrode coated with MDMIBr strongly depends on the net charge of the redox mediator. Electron transfer was excellent for neutral and negatively charged redox mediators on electrodes coated with IL-SAM regardless of deposition temperature.

Interface Controls Spontaneous Crystallization in Thin Films of the Ionic Liquid [C2C1Im][OTf] on Atomically Clean Pd(111)

“…Time-resolved infrared reflection–absorption spectroscopy (TR-IRAS) was used to investigate the film during deposition and temperature ramps. While a number of studies deal with the thermal behavior of ILs in the bulk and their crystal structure in the frozen state, − only a few publications address the thermal behavior of thin IL films on solid substrates − and even a lower number of studies deal with films prepared under UHV conditions. , The properties of the thin IL films depend upon the structure and phase of the IL at the surface, and we concentrate on their identification in this study.…”

Properties of ionic liquids on Au surfaces: non-conventional anion exchange reactions with carbonate

“…2 In order to exploit the benefits of ILs in biochips, while analyzing actual biological samples, there is interest in developing biochips with IL immobilized to the surface in a SAM format. The properties of IL-SAM based on MDMI are still relatively unknown, but the influence of the counter-anion on wettability 3 and of the deposition temperature on the conformation 4 has been reported in the literature. The length of the alkyl chain may also be influencing the properties of IL-SAM, as solutions of 1-alkyl-3-methylimidazolium of different chain lengths do not organize similarly near mica surfaces.…”

Electroformation of Peptide Self-Assembled Monolayers on Gold

“…Although SPR provides a good measure of the surface concentration, it is also influenced by the orientation of the molecules at the surface. For example, phase transitions where the self-assembled molecules of an alkylthiol chain melts by becoming disorganized with gauche defects creates a thinner monolayer, which results in larger SPR shifts . This increase in the SPR shift at high potential may be indicative of the monolayer collapsing to the surface, increasing the local refractive index close to the SPR sensor.…”

“…For example, phase transitions where the self-assembled molecules of an alkylthiol chain melts by becoming disorganized with gauche defects creates a thinner monolayer, which results in larger SPR shifts. 20 This increase in the SPR shift at high potential may be indicative of the monolayer collapsing to the surface, increasing the local refractive index close to the SPR sensor. However, complementary methods are necessary to elucidate the mechanism of monolayer formation at potentials greater than 200 mV.…”