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Title: Extraordinary Slowing of Structural Dynamics in Thin Films of a Room Temperature Ionic Liquid

Journal Article · · ACS Central Science

The role that interfaces play in the dynamics of liquids is a fundamental scientific problem with vast importance in technological applications. From material science to biology, e.g., batteries to cell membranes, liquid properties at interfaces are frequently determinant in the nature of chemical processes. For most liquids, like water, the influence of an interface falls off on a ~1 nm distance scale. Room temperature ionic liquids (RTILs) are a vast class of unusual liquids composed of complex cations and anions that are liquid salts at room temperature. They are unusual liquids with properties that can be finely tuned by selecting the structure of the cation and anion. RTILs are being used or developed in applications such as batteries, CO2 capture, and liquids for biological processes. Here, it is demonstrated quantitatively that the influence of an interface on RTIL properties is profoundly different from that observed in other classes of liquids. The dynamics of planar thin films of the room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2), were investigated using two-dimensional infrared spectroscopy (2D IR) with the CN stretch of SeCN as the vibrational probe. The structural dynamics (spectral diffusion) of the thin films with controlled nanometer thicknesses were measured and compared to the dynamics of the bulk liquid. The samples were prepared by spin coating the RTIL, together with the vibrational probe, onto a surface functionalized with an ionic monolayer that mimics the structure of the BmimNTf2. Near-Brewster’s angle reflection pump–probe geometry 2D IR facilitated the detection of the exceedingly small signals from the films, some of which were only 14 nm thick. Even in quarter micron (250 nm) thick films, the observed dynamics were much slower than those of the bulk liquid. Using a new theoretical description, the correlation length (exponential falloff of the influence of the interfaces) was found to be 28 ± 5 nm. This very long correlation length, ~30 times greater than that of water, has major implications for the use of RTILs in devices and other applications.

Research Organization:
Stanford Univ., CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES); US Air Force Office of Scientific Research (AFOSR); National Science Foundation (NSF)
Grant/Contract Number:
FG03-84ER13251; FA9550-16-1-0104; ECCS-1542152; FG02-84ER13251
OSTI ID:
1462131
Alternate ID(s):
OSTI ID: 1498667; OSTI ID: 1788260
Journal Information:
ACS Central Science, Vol. 4, Issue 8; ISSN 2374-7943
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 29 works
Citation information provided by
Web of Science

References (85)

Ultrafast vibrational dynamics of water at a charged interface revealed by two-dimensional heterodyne-detected vibrational sum frequency generation journal September 2012
Aqueous Heterogeneity at the Air/Water Interface Revealed by 2D-HD-SFG Spectroscopy journal June 2014
Ultrafast to Ultraslow Dynamics of a Langmuir Monolayer at the Air/Water Interface Observed with Reflection Enhanced 2D IR Spectroscopy journal November 2017
Water dynamics in large and small reverse micelles: From two ensembles to collective behavior journal July 2009
Structure and Dynamics of Benzene Confined in Silica Nanopores journal July 2011
Ultrafast Orientational Dynamics of Nanoconfined Benzene journal July 2005
Ionic Liquids: Structure and Photochemical Reactions journal May 2011
Structure and Nanostructure in Ionic Liquids journal June 2015
Applications of ionic liquids in the chemical industry journal January 2008
Ionic Liquid Redox Catholyte for High Energy Efficiency, Low-Cost Energy Storage journal April 2015
An ultrafast rechargeable aluminium-ion battery journal April 2015
Recent advances in supported ionic liquid membrane technology journal July 2011
Combination of ionic liquids with membrane technology: A new approach for CO2 separation journal January 2016
Protein solubilising and stabilising ionic liquids journal January 2005
Influence of the ionic liquid 1-butyl-3-methylimidazolium bromide on amyloid fibrillogenesis in lysozyme: Evidence from photophysical and imaging studies journal February 2018
Structure and Dynamics at Ionic Liquid/Electrode Interfaces journal July 2015
Irreversible structural change of a dry ionic liquid under nanoconfinement journal January 2015
Long-Range Ordering of Ionic Liquid Fluid Films journal May 2016
Nanoconfined ionic liquids: effect of surface charges on flow and molecular layering journal January 2010
A Multiscale Coarse-Graining Study of the Liquid/Vacuum Interface of Room-Temperature Ionic Liquids with Alkyl Substituents of Different Lengths journal January 2008
Structures of Ionic Liquids Having Both Anionic and Cationic Octyl Tails: Lamellar Vacuum Interface vs Sponge-Like Bulk Order journal September 2016
Dynamics of a Room Temperature Ionic Liquid in Supported Ionic Liquid Membranes vs the Bulk Liquid: 2D IR and Polarized IR Pump–Probe Experiments journal December 2016
Carbon Dioxide in a Supported Ionic Liquid Membrane: Structural and Rotational Dynamics Measured with 2D IR and Pump–Probe Experiments journal August 2017
Latex composite membranes: structure and properties of the discriminating layer journal March 2004
The influence of mesoscopic confinement on the dynamics of imidazolium-based room temperature ionic liquids in polyether sulfone membranes journal November 2017
Ionic Liquid Dynamics Measured with 2D IR and IR Pump–Probe Experiments on a Linear Anion and the Influence of Potassium Cations journal February 2016
Enhanced nonlinear spectroscopy for monolayers and thin films in near-Brewster’s angle reflection pump-probe geometry journal March 2017
Molecular layering and local order in thin films of 1-alkyl-3-methylimidazolium ionic liquids using X-ray reflectivity journal May 2001
Physical Vapor Deposition of [EMIM][Tf 2 N]: A New Approach to the Modification of Surface Properties with Ultrathin Ionic Liquid Films journal October 2008
Coexistence of Liquid and Solid Phases of Bmim-PF 6 Ionic Liquid on Mica Surfaces at Room Temperature journal June 2006
Evidence of Extended Solidlike Layering in [Bmim][NTf2] Ionic Liquid Thin Films at Room-Temperature journal May 2009
Toward Ionic-Liquid-Based Model Catalysis: Growth, Orientation, Conformation, and Interaction Mechanism of the [Tf 2 N] Anion in [BMIM][Tf 2 N] Thin Films on a Well-Ordered Alumina Surface journal May 2010
Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum journal September 2010
Ionic liquid ultrathin films at the surface of Cu(100) and Au(111) journal February 2017
Superhydrophobic self-assembled monolayers of long-chain fluorinated imidazolium ionic liquids journal January 2012
Molecular Structure and Interactions in the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(Trifluoromethylsulfonyl)imide journal March 2014
Concepts and Methods of 2D Infrared Spectroscopy book January 2011
2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces journal June 2015
Site-Specific Coupling of Hydration Water and Protein Flexibility Studied in Solution with Ultrafast 2D-IR Spectroscopy journal November 2012
Water Dynamics in Gyroid Phases of Self-Assembled Gemini Surfactants journal February 2016
Frequency-frequency correlation functions and apodization in two-dimensional infrared vibrational echo spectroscopy: A new approach journal September 2007
Taking apart the two-dimensional infrared vibrational echo spectra: More information and elimination of distortions journal May 2008
A Stochastic Theory of Line Shape book January 2007
On the Structure and Dynamics of Ionic Liquids journal February 2004
Heterogeneity at the glass transition: a review journal February 1999
S PATIALLY H ETEROGENEOUS D YNAMICS IN S UPERCOOLED L IQUIDS journal October 2000
Direct Experimental Evidence of a Growing Length Scale Accompanying the Glass Transition journal December 2005
Direct observation of dynamic crossover in fragile molecular glass formers with 2D IR vibrational echo spectroscopy journal March 2017
Colloidal Glass Transition Observed in Confinement journal July 2007
Dynamics of Nanoconfined Supercooled Liquids journal May 2011
Ionic Liquid Redox Catholyte for High Energy Efficiency, Low-Cost Energy Storage journal April 2015
Aqueous Heterogeneity at the Air/Water Interface Revealed by 2D-HD-SFG Spectroscopy journal June 2014
Physical Vapor Deposition of [EMIM][Tf 2 N]: A New Approach to the Modification of Surface Properties with Ultrathin Ionic Liquid Films journal October 2008
Influence of the ionic liquid 1-butyl-3-methylimidazolium bromide on amyloid fibrillogenesis in lysozyme: Evidence from photophysical and imaging studies journal February 2018
Latex composite membranes: structure and properties of the discriminating layer journal March 2004
Recent advances in supported ionic liquid membrane technology journal July 2011
Combination of ionic liquids with membrane technology: A new approach for CO2 separation journal January 2016
Ionic Liquid Dynamics Measured with 2D IR and IR Pump–Probe Experiments on a Linear Anion and the Influence of Potassium Cations journal February 2016
Structures of Ionic Liquids Having Both Anionic and Cationic Octyl Tails: Lamellar Vacuum Interface vs Sponge-Like Bulk Order journal September 2016
Long-Range Ordering of Ionic Liquid Fluid Films journal May 2016
Structure and Nanostructure in Ionic Liquids journal June 2015
Coexistence of Liquid and Solid Phases of Bmim-PF 6 Ionic Liquid on Mica Surfaces at Room Temperature journal June 2006
Site-Specific Coupling of Hydration Water and Protein Flexibility Studied in Solution with Ultrafast 2D-IR Spectroscopy journal November 2012
Water Dynamics in Gyroid Phases of Self-Assembled Gemini Surfactants journal February 2016
Dynamics of a Room Temperature Ionic Liquid in Supported Ionic Liquid Membranes vs the Bulk Liquid: 2D IR and Polarized IR Pump–Probe Experiments journal December 2016
Carbon Dioxide in a Supported Ionic Liquid Membrane: Structural and Rotational Dynamics Measured with 2D IR and Pump–Probe Experiments journal August 2017
Ultrafast to Ultraslow Dynamics of a Langmuir Monolayer at the Air/Water Interface Observed with Reflection Enhanced 2D IR Spectroscopy journal November 2017
On the Structure and Dynamics of Ionic Liquids journal February 2004
Molecular Structure and Interactions in the Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(Trifluoromethylsulfonyl)imide journal March 2014
Evidence of Extended Solidlike Layering in [Bmim][NTf2] Ionic Liquid Thin Films at Room-Temperature journal May 2009
Toward Ionic-Liquid-Based Model Catalysis: Growth, Orientation, Conformation, and Interaction Mechanism of the [Tf 2 N] Anion in [BMIM][Tf 2 N] Thin Films on a Well-Ordered Alumina Surface journal May 2010
Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum journal September 2010
An ultrafast rechargeable aluminium-ion battery journal April 2015
Protein solubilising and stabilising ionic liquids journal January 2005
Nanoconfined ionic liquids: effect of surface charges on flow and molecular layering journal January 2010
Superhydrophobic self-assembled monolayers of long-chain fluorinated imidazolium ionic liquids journal January 2012
Frequency-frequency correlation functions and apodization in two-dimensional infrared vibrational echo spectroscopy: A new approach journal September 2007
Taking apart the two-dimensional infrared vibrational echo spectra: More information and elimination of distortions journal May 2008
2D attenuated total reflectance infrared spectroscopy reveals ultrafast vibrational dynamics of organic monolayers at metal-liquid interfaces journal June 2015
Ionic liquid ultrathin films at the surface of Cu(100) and Au(111) journal February 2017
Enhanced nonlinear spectroscopy for monolayers and thin films in near-Brewster’s angle reflection pump-probe geometry journal March 2017
Ultrafast α -Like Relaxation of a Fragile Glass-Forming Liquid Measured Using Two-Dimensional Infrared Spectroscopy journal April 2012
Ionic Liquids: Structure and Photochemical Reactions journal May 2011
S PATIALLY H ETEROGENEOUS D YNAMICS IN S UPERCOOLED L IQUIDS journal October 2000
Structure and Dynamics at Ionic Liquid/Electrode Interfaces journal July 2015

Cited By (1)


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