We report direct evidence for charge-induced long-range (ca. 100 μm) order in the room-temperature ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM(+)BF4(-)), supported on a silica surface. We have measured the rotational diffusion dynamics of anionic, cationic, and neutral chromophores as a function of distance from a silica surface. The results reflect the excess charge density gradient induced in the IL by the (negative) charge present on the silica surface. Identical measurements in ethylene glycol reveal spatially invariant reorientation dynamics for all chromophores. Capping the silica support with Me2SiCl2 results in spatially invariant reorientation dynamics in the IL. We understand these data in the context of the IL exhibiting a spatially damped piezoelectric response mediated by IL fluidity and disorder.
The morphology, microstructure, chemistry, electronic properties, and electrochemical behavior of a boron-doped nanocrystalline diamond (BDD) thin film grown on quartz were evaluated. Diamond optically transparent electrodes (OTEs) are useful for transmission spectroelectrochemical measurements, offering excellent stability during anodic and cathodic polarization and exposure to a variety of chemical environments. We report on the characterization of a BDD OTE by atomic force microscopy, optical spectroscopy, Raman spectroscopic mapping, alternating-current Hall effect measurements, X-ray photoelectron spectroscopy, and electrochemical methods. The results reported herein provide the first comprehensive study of the relationship between the physical and chemical structure and electronic properties of a diamond OTE and the electrode's electrochemical activity.
We have reported previously on the existence of charge-induced long-range organization in the room-temperature ionic liquid (RTIL), BMIM + BF 4 − . The induced organization is in the form of a free charge density gradient (ρ f ) that exists over ca. 100 μm into the RTIL in contact with a charged surface. The fluorescence anisotropy decay of a trace-level charged chromophore in the RTIL is measured as a function of distance from the indium-doped tin oxide support surface to probe this free charge density gradient. We report here on the characterization of the free charge density gradient in five different imidazolium RTILs and use these data to evaluate the magnitude of the induced free charge density gradient. Both the extent and magnitude of this gradient depend on the chemical structures of the cationic and anionic constituents of the RTIL used. Control over the magnitude of ρ f has implications for the utility of RTILs for a host of applications that remain to be explored fully.
In
an earlier article (Langmuir
2016, 32, 9507–9512), we reported the existence
of an induced charge density gradient, ρf, in a room-temperature
ionic liquid (RTIL, BMIM+BF4
–) normal to a charged planar silica surface. In this work, we demonstrate
experimental control over the sign and magnitude of the gradient.
The spatial extent of ρf can exceed 100 μm
from the charged surface. We characterized ρf through
the rotational diffusion time constant gradient of a cationic chromophore
in the room-temperature ionic liquid (RTIL). The sign and magnitude
of ρf in BMIM+BF4
– is linked directly to the surface charge density of the electrode,
which can be controlled. We used transparent conductive electrodes
(FTO and ITO coated on glass) as supports and demonstrated that control
over the electrode surface charge carrier density can influence the
magnitude and sign of ρf. There are limitations to
this approach based on the FTO and ITO properties, and we demonstrate
these limits experimentally.
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