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Title: Surface structure evolution in a homologous series of ionic liquids

Abstract

Interfaces of room temperature ionic liquids (RTILs) are important for both applications and basic science and are therefore intensely studied. However, the evolution of their interface structure with the cation’s alkyl chain length n from Coulomb to van der Waals interaction domination has not yet been studied for even a single broad homologous RTIL series. We present in this paper such a study of the liquid–air interface for n = 2 to 22, using angstrom-resolution X-ray methods. For n < 6, a typical “simple liquid” monotonic surface-normal electron density profile ρ e ( z ) is obtained, like those of water and organic solvents. For n > 6, increasingly more pronounced nanoscale self-segregation of the molecules’ charged moieties and apolar chains yields surface layering with alternating regions of headgroups and chains. The layering decays into the bulk over a few, to a few tens, of nanometers. The layering periods and decay lengths, their linear n dependence, and slopes are discussed within two models, one with partial-chain interdigitation and the other with liquid-like chains. No surface-parallel long-range order is found within the surfacemore » layer. For n = 22, a different surface phase is observed above melting. Finally, our results also impact general liquid-phase issues like supramolecular self-aggregation and bulk–surface structure relations.« less

Authors:
 [1]; ORCiD logo [2];  [3];  [4];  [4];  [3];  [5];  [6];  [7]; ORCiD logo [1]
  1. Bar-Ilan Univ., Ramat Gan (Israel). Physics Dept. Inst. of Nanotechnology and Advanced Materials
  2. European Synchrotron Radiation Facility (ESRF), Grenoble (France). The European Synchrotron and Partnership for Soft Condensed Matter (PSCM)
  3. Kiel Univ. (Germany). Inst. for Experimental and Applied Physics. Ruprecht Haensel Lab.
  4. Kiel Univ. (Germany). Inst. for Experimental and Applied Physics
  5. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lab. (SSRL). Materials Science Division
  6. European Synchrotron Radiation Facility (ESRF), Grenoble (France)
  7. Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States); Kiel Univ. (Germany); Bar-Ilan Univ., Ramat Gan (Israel)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); German Federal Ministry of Education and Research (BMBF); US-Israel Binational Science Foundation (BSF)
OSTI Identifier:
1433970
Report Number(s):
BNL-203505-2018-JAAM
Journal ID: ISSN 0027-8424
Grant/Contract Number:  
SC0012704; 05k13fk2; 05k16fk1
Resource Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 115; Journal Issue: 6; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ionic liquids; X-ray reflectivity; surface layering; liquid-like; interdigitated chains

Citation Formats

Haddad, Julia, Pontoni, Diego, Murphy, Bridget M., Festersen, Sven, Runge, Benjamin, Magnussen, Olaf M., Steinruck, Hans-Georg, Reichert, Harald, Ocko, Benjamin M., and Deutsch, Moshe. Surface structure evolution in a homologous series of ionic liquids. United States: N. p., 2018. Web. doi:10.1073/pnas.1716418115.
Haddad, Julia, Pontoni, Diego, Murphy, Bridget M., Festersen, Sven, Runge, Benjamin, Magnussen, Olaf M., Steinruck, Hans-Georg, Reichert, Harald, Ocko, Benjamin M., & Deutsch, Moshe. Surface structure evolution in a homologous series of ionic liquids. United States. doi:10.1073/pnas.1716418115.
Haddad, Julia, Pontoni, Diego, Murphy, Bridget M., Festersen, Sven, Runge, Benjamin, Magnussen, Olaf M., Steinruck, Hans-Georg, Reichert, Harald, Ocko, Benjamin M., and Deutsch, Moshe. Mon . "Surface structure evolution in a homologous series of ionic liquids". United States. doi:10.1073/pnas.1716418115. https://www.osti.gov/servlets/purl/1433970.
@article{osti_1433970,
title = {Surface structure evolution in a homologous series of ionic liquids},
author = {Haddad, Julia and Pontoni, Diego and Murphy, Bridget M. and Festersen, Sven and Runge, Benjamin and Magnussen, Olaf M. and Steinruck, Hans-Georg and Reichert, Harald and Ocko, Benjamin M. and Deutsch, Moshe},
abstractNote = {Interfaces of room temperature ionic liquids (RTILs) are important for both applications and basic science and are therefore intensely studied. However, the evolution of their interface structure with the cation’s alkyl chain length n from Coulomb to van der Waals interaction domination has not yet been studied for even a single broad homologous RTIL series. We present in this paper such a study of the liquid–air interface for n = 2 to 22, using angstrom-resolution X-ray methods. For n < 6, a typical “simple liquid” monotonic surface-normal electron density profile ρe(z) is obtained, like those of water and organic solvents. For n > 6, increasingly more pronounced nanoscale self-segregation of the molecules’ charged moieties and apolar chains yields surface layering with alternating regions of headgroups and chains. The layering decays into the bulk over a few, to a few tens, of nanometers. The layering periods and decay lengths, their linear n dependence, and slopes are discussed within two models, one with partial-chain interdigitation and the other with liquid-like chains. No surface-parallel long-range order is found within the surface layer. For n = 22, a different surface phase is observed above melting. Finally, our results also impact general liquid-phase issues like supramolecular self-aggregation and bulk–surface structure relations.},
doi = {10.1073/pnas.1716418115},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 6,
volume = 115,
place = {United States},
year = {2018},
month = {1}
}

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Figures / Tables:

Figure 1 Figure 1: Figure 1: (a) Fresnel-normalized, measured (symbols) and model-fitted (lines) XR curves of the liquid/air interface of the RTILs studied at temperatures given in parenthesis (in °C). Note the higher temperatures for $n$ ≥ 14 which melt above room temperature (see Supplementary Information for melting temperatures). Curves are shiftedmore » for clarity from each other by a decade for $n$ ≥ 14, and by multiplication by 4 × 10−2 ($n$ = 16), 3 × 10−3 ($n$ = 18), 3×10−4 ($n$ = 20), and 3×10−7 and 5×10−9 ($n$ = 22). The different colours indicate different surface phases. Curves in two colours denote transitions between surface phases. Note the lower-temperature surface phase of $n$ = 22, tentatively identified as a liquid-crystal surface phase. (b) The EDPs (normalized to the bulk electron density) obtained from the model ts in (a). The brown Gaussian represents the density enrichment at the air side of the surface. EDPs are shifted from each other for clarity, with black horizontal lines denoting ρ/ρb = 0 for each. See text for discussion.« less

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    Structural characteristics of alkylimidazolium-based salts containing fluoroanions
    journal, April 2007


    Structure of protic (HCnImNTf2, n=0–12) and aprotic (C1CnImNTf2, n=1–12) imidazolium ionic liquids: A vibrational spectroscopic study
    journal, October 2015


    Multiscale Studies on Ionic Liquids
    journal, February 2017


    Modern Room Temperature Ionic Liquids, a Simple Guide to Understanding Their Structure and How It May Relate to Dynamics
    journal, August 2015

    • Araque, Juan C.; Hettige, Jeevapani J.; Margulis, Claudio J.
    • The Journal of Physical Chemistry B, Vol. 119, Issue 40
    • DOI: 10.1021/acs.jpcb.5b05506

    Mesoscopic Correlation Functions in Heterogeneous Ionic Liquids
    journal, January 2017

    • Weiss, Henning; Mars, Julian; Li, Hailong
    • The Journal of Physical Chemistry B, Vol. 121, Issue 3
    • DOI: 10.1021/acs.jpcb.6b11220

    Accounting for the Unique, Doubly Dual Nature of Ionic Liquids from a Molecular Thermodynamic and Modeling Standpoint
    journal, November 2007

    • Rebelo, Luís Paulo N.; Lopes, José N. Canongia; Esperança, José M. S. S.
    • Accounts of Chemical Research, Vol. 40, Issue 11
    • DOI: 10.1021/ar7000556

    Small-Angle X-ray Scattering Studies of Liquid Crystalline 1-Alkyl-3-methylimidazolium Salts
    journal, February 2002

    • Bradley, A. E.; Hardacre, C.; Holbrey, J. D.
    • Chemistry of Materials, Vol. 14, Issue 2
    • DOI: 10.1021/cm010542v

    Photoelectron Spectroscopy of Ionic Liquid-Based Interfaces
    journal, September 2010

    • Lovelock, Kevin R. J.; Villar-Garcia, Ignacio J.; Maier, Florian
    • Chemical Reviews, Vol. 110, Issue 9
    • DOI: 10.1021/cr100114t

    Ionic Liquids at Electrified Interfaces
    journal, March 2014

    • Fedorov, Maxim V.; Kornyshev, Alexei A.
    • Chemical Reviews, Vol. 114, Issue 5
    • DOI: 10.1021/cr400374x

    Structure and Nanostructure in Ionic Liquids
    journal, June 2015

    • Hayes, Robert; Warr, Gregory G.; Atkin, Rob
    • Chemical Reviews, Vol. 115, Issue 13
    • DOI: 10.1021/cr500411q

    Surface Layering in Ionic Liquids:  An X-ray Reflectivity Study
    journal, June 2005

    • Sloutskin, Eli; Ocko, Benjamin M.; Tamam, Lilach
    • Journal of the American Chemical Society, Vol. 127, Issue 21
    • DOI: 10.1021/ja0509679

    Unique Spatial Heterogeneity in Ionic Liquids
    journal, September 2005

    • Wang, Yanting; Voth, Gregory A.
    • Journal of the American Chemical Society, Vol. 127, Issue 35
    • DOI: 10.1021/ja053796g

    Densities and Derived Thermodynamic Properties of Ionic Liquids. 3. Phosphonium-Based Ionic Liquids over an Extended Pressure Range
    journal, January 2006

    • Esperança, José M. S. S.; Guedes, Henrique J. R.; Blesic, Marijana
    • Journal of Chemical & Engineering Data, Vol. 51, Issue 1
    • DOI: 10.1021/je050358g

    Surface Tensions for the 1-Alkyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids
    journal, June 2008

    • Carvalho, Pedro J.; Freire, Mara G.; Marrucho, Isabel M.
    • Journal of Chemical & Engineering Data, Vol. 53, Issue 6
    • DOI: 10.1021/je800069z

    Double-Layer in Ionic Liquids:  Paradigm Change?
    journal, May 2007

    • Kornyshev, Alexei A.
    • The Journal of Physical Chemistry B, Vol. 111, Issue 20
    • DOI: 10.1021/jp067857o

    Assessing the Dispersive and Electrostatic Components of the Cohesive Energy of Ionic Liquids Using Molecular Dynamics Simulations and Molar Refraction Data
    journal, May 2010

    • Shimizu, Karina; Tariq, Mohammad; Gomes, Margarida F. Costa
    • The Journal of Physical Chemistry B, Vol. 114, Issue 17
    • DOI: 10.1021/jp101910c

    What is the Origin of the Prepeak in the X-ray Scattering of Imidazolium-Based Room-Temperature Ionic Liquids?
    journal, December 2010

    • Annapureddy, Harsha V. R.; Kashyap, Hemant K.; De Biase, Pablo M.
    • The Journal of Physical Chemistry B, Vol. 114, Issue 50
    • DOI: 10.1021/jp108545z

    High-Accuracy Vapor Pressure Data of the Extended [C n C 1 im][Ntf 2 ] Ionic Liquid Series: Trend Changes and Structural Shifts
    journal, September 2011

    • Rocha, Marisa A. A.; Lima, Carlos F. R. A. C.; Gomes, Lígia R.
    • The Journal of Physical Chemistry B, Vol. 115, Issue 37
    • DOI: 10.1021/jp2049316

    Effect of the Chain Length on the Structure of Ionic Liquids: from Spatial Heterogeneity to Ionic Liquid Crystals
    journal, January 2013

    • Ji, Yumeng; Shi, Rui; Wang, Yanting
    • The Journal of Physical Chemistry B, Vol. 117, Issue 4
    • DOI: 10.1021/jp310231f

    Making Sense of Enthalpy of Vaporization Trends for Ionic Liquids: New Experimental and Simulation Data Show a Simple Linear Relationship and Help Reconcile Previous Data
    journal, May 2013

    • Verevkin, Sergey P.; Zaitsau, Dzmitry H.; Emel’yanenko, Vladimir N.
    • The Journal of Physical Chemistry B, Vol. 117, Issue 21
    • DOI: 10.1021/jp311429r

    Alkylimidazolium Based Ionic Liquids: Impact of Cation Symmetry on Their Nanoscale Structural Organization
    journal, September 2013

    • Rocha, Marisa A. A.; Neves, Catarina M. S. S.; Freire, Mara G.
    • The Journal of Physical Chemistry B, Vol. 117, Issue 37
    • DOI: 10.1021/jp406374a

    Bulk and Liquid–Vapor Interface of Pyrrolidinium-Based Ionic Liquids: A Molecular Simulation Study
    journal, January 2014

    • Paredes, Xavier; Fernández, Josefa; Pádua, Agílio A. H.
    • The Journal of Physical Chemistry B, Vol. 118, Issue 3
    • DOI: 10.1021/jp406651f

    Structure and Aggregation in the 1-Alkyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid Homologous Series
    journal, January 2014

    • Shimizu, Karina; Bernardes, Carlos E. S.; Canongia Lopes, José N.
    • The Journal of Physical Chemistry B, Vol. 118, Issue 2
    • DOI: 10.1021/jp409987d

    Ionic Liquid–Vacuum Interfaces Probed by Reactive Atom Scattering: Influence of Alkyl Chain Length and Anion Volume
    journal, February 2015

    • Tesa-Serrate, Maria A.; Marshall, Brooks C.; Smoll, Eric J.
    • The Journal of Physical Chemistry C, Vol. 119, Issue 10
    • DOI: 10.1021/jp5126238

    Interfacial Restructuring of Ionic Liquids Determined by Sum-Frequency Generation Spectroscopy and X-Ray Reflectivity
    journal, November 2008

    • Jeon, Yoonnam; Sung, Jaeho; Bu, Wei
    • The Journal of Physical Chemistry C, Vol. 112, Issue 49
    • DOI: 10.1021/jp807873j

    IR and X-ray Study of Polymorphism in 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides
    journal, July 2009

    • Paulechka, Y. U.; Kabo, G. J.; Blokhin, A. V.
    • The Journal of Physical Chemistry B, Vol. 113, Issue 28
    • DOI: 10.1021/jp903702c

    Alkyl Chain Length and Temperature Effects on Structural Properties of Pyrrolidinium-Based Ionic Liquids: A Combined Atomistic Simulation and Small-Angle X-ray Scattering Study
    journal, December 2011

    • Li, Song; Bañuelos, José Leobardo; Guo, Jianchang
    • The Journal of Physical Chemistry Letters, Vol. 3, Issue 1
    • DOI: 10.1021/jz2013209

    Mesoscopic Structural Heterogeneities in Room-Temperature Ionic Liquids
    journal, December 2011

    • Russina, Olga; Triolo, Alessandro; Gontrani, Lorenzo
    • The Journal of Physical Chemistry Letters, Vol. 3, Issue 1
    • DOI: 10.1021/jz201349z

    O( 3 P) Atoms as a Probe of Surface Ordering in 1-Alkyl-3-methylimidazolium-Based Ionic Liquids
    journal, November 2009

    • Waring, Carla; Bagot, Paul A. J.; Slattery, John M.
    • The Journal of Physical Chemistry Letters, Vol. 1, Issue 1
    • DOI: 10.1021/jz900247y

    Temperature Dependence of Multilayering at the Free Surface of Ionic Liquids Probed by X-ray Reflectivity Measurements
    journal, June 2011

    • Nishi, Naoya; Uruga, Tomoya; Tanida, Hajime
    • Langmuir, Vol. 27, Issue 12
    • DOI: 10.1021/la200252z

    Cation Alkyl Side Chain Length and Symmetry Effects on the Surface Tension of Ionic Liquids
    journal, May 2014

    • Almeida, Hugo F. D.; Freire, Mara G.; Fernandes, Ana M.
    • Langmuir, Vol. 30, Issue 22
    • DOI: 10.1021/la501308q

    Structure of the Ethylammonium Nitrate Surface: An X-ray Reflectivity and Vibrational Sum Frequency Spectroscopy Study
    journal, June 2010

    • Niga, Petru; Wakeham, Deborah; Nelson, Andrew
    • Langmuir, Vol. 26, Issue 11
    • DOI: 10.1021/la904697g

    Local Order in Liquid n -Alkanes:  Evidence from Raman Spectroscopic Study
    journal, April 2005

    • Brambilla, Luigi; Zerbi, Giuseppe
    • Macromolecules, Vol. 38, Issue 8
    • DOI: 10.1021/ma047390k

    Bilayer order in a polycarbazole-conjugated polymer
    journal, January 2012

    • Lu, Xinhui; Hlaing, Htay; Germack, David S.
    • Nature Communications, Vol. 3, Issue 1
    • DOI: 10.1038/ncomms1790

    First example of interdigitated U-shape benzimidazolium ionic liquid crystals
    journal, January 1997

    • Lee, Kwang Ming; Lee, Ching Kuan; Lin, Ivan J. B.
    • Chemical Communications, Issue 9
    • DOI: 10.1039/a608517b

    X-Ray reflectometry studies on the effect of water on the surface structure of [C4mpyr][NTf2] ionic liquid
    journal, January 2009

    • Lauw, Y.; Horne, M. D.; Rodopoulos, T.
    • Physical Chemistry Chemical Physics, Vol. 11, Issue 48
    • DOI: 10.1039/b916046a

    Probing the protic ionic liquid surface using X-ray reflectivity
    journal, January 2011

    • Wakeham, Deborah; Nelson, Andrew; Warr, Gregory G.
    • Physical Chemistry Chemical Physics, Vol. 13, Issue 46
    • DOI: 10.1039/c1cp22351h

    Influence of the ionic liquid/gas surface on ionic liquid chemistry
    journal, January 2012

    • Lovelock, Kevin R. J.
    • Physical Chemistry Chemical Physics, Vol. 14, Issue 15
    • DOI: 10.1039/c2cp23851a

    Mixtures of ionic liquids
    journal, January 2012

    • Niedermeyer, Heiko; Hallett, Jason P.; Villar-Garcia, Ignacio J.
    • Chemical Society Reviews, Vol. 41, Issue 23
    • DOI: 10.1039/c2cs35177c

    Insights into the interplay between molecular structure and diffusional motion in 1-alkyl-3-methylimidazolium ionic liquids: a combined PFG NMR and X-ray scattering study
    journal, January 2013

    • Martinelli, A.; Maréchal, M.; Östlund, Å.
    • Physical Chemistry Chemical Physics, Vol. 15, Issue 15
    • DOI: 10.1039/c3cp00097d

    Mixing ionic liquids – “simple mixtures” or “double salts”?
    journal, January 2014

    • Chatel, Gregory; Pereira, Jorge F. B.; Debbeti, Varun
    • Green Chemistry, Vol. 16, Issue 4
    • DOI: 10.1039/c3gc41389f

    The effect of lithium salt doping on the nanostructure of ionic liquids
    journal, January 2015

    • Aguilera, Luis; Völkner, Johannes; Labrador, Ana
    • Physical Chemistry Chemical Physics, Vol. 17, Issue 40
    • DOI: 10.1039/c5cp03825a

    Structure of ionic liquids of 1-alkyl-3-methylimidazolium cations: A systematic computer simulation study
    journal, January 2004

    • Urahata, Sérgio M.; Ribeiro, Mauro C. C.
    • The Journal of Chemical Physics, Vol. 120, Issue 4
    • DOI: 10.1063/1.1635356

    Small angle neutron scattering from 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids ([Cnmim][PF6], n=4, 6, and 8)
    journal, August 2010

    • Hardacre, Christopher; Holbrey, John D.; Mullan, Claire L.
    • The Journal of Chemical Physics, Vol. 133, Issue 7
    • DOI: 10.1063/1.3473825

    Nanoscale heterogeneity in alkyl-methylimidazolium bromide ionic liquids
    journal, March 2011

    • Aoun, Bachir; Goldbach, Andreas; González, Miguel A.
    • The Journal of Chemical Physics, Vol. 134, Issue 10
    • DOI: 10.1063/1.3563540

    Experimental evidences for molecular origin of low- Q peak in neutron/x-ray scattering of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids
    journal, December 2011

    • Fujii, Kenta; Kanzaki, Ryo; Takamuku, Toshiyuki
    • The Journal of Chemical Physics, Vol. 135, Issue 24
    • DOI: 10.1063/1.3672097

    Surface structures of binary mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy and time of flight secondary ion mass spectroscopy
    journal, December 2013

    • Nakajima, Kaoru; Miyashita, Motoki; Suzuki, Motofumi
    • The Journal of Chemical Physics, Vol. 139, Issue 22
    • DOI: 10.1063/1.4838376

    Vapor pressures of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with long alkyl chains
    journal, October 2014

    • Rocha, Marisa A. A.; Coutinho, João A. P.; Santos, Luís M. N. B. F.
    • The Journal of Chemical Physics, Vol. 141, Issue 13
    • DOI: 10.1063/1.4896704

    Solid-liquid interfaces of ionic liquid solutions—Interfacial layering and bulk correlations
    journal, April 2015

    • Mezger, Markus; Roth, Roland; Schröder, Heiko
    • The Journal of Chemical Physics, Vol. 142, Issue 16
    • DOI: 10.1063/1.4918742

    Surface structure of imidazolium-based ionic liquids: Quantitative comparison between simulations and high-resolution RBS measurements
    journal, March 2016

    • Nakajima, Kaoru; Nakanishi, Shunto; Lísal, Martin
    • The Journal of Chemical Physics, Vol. 144, Issue 11
    • DOI: 10.1063/1.4943887

    Surface layering and melting in an ionic liquid studied by resonant soft X-ray reflectivity
    journal, February 2013

    • Mezger, M.; Ocko, B. M.; Reichert, H.
    • Proceedings of the National Academy of Sciences, Vol. 110, Issue 10
    • DOI: 10.1073/pnas.1211749110

    Long-range electrostatic screening in ionic liquids
    journal, May 2015

    • Gebbie, Matthew A.; Dobbs, Howard A.; Valtiner, Markus
    • Proceedings of the National Academy of Sciences, Vol. 112, Issue 24
    • DOI: 10.1073/pnas.1508366112

    Thermally excited capillary waves at vapor/liquid interfaces of water–alcohol mixtures
    journal, February 2009


    Morphology and intermolecular dynamics of 1-alkyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ionic liquids: structural and dynamic evidence of nanoscale segregation
    journal, September 2009


    Intrinsic profiles and the structure of liquid surfaces
    journal, June 2012


    Molecular Layering of Fluorinated Ionic Liquids at a Charged Sapphire (0001) Surface
    journal, October 2008


    Anomalous and Not-So-Common Behavior in Common Ionic Liquids and Ionic Liquid-Containing Systems
    journal, June 2019

    • Esperança, José M. S. S.; Tariq, Mohammad; Pereiro, Ana B.
    • Frontiers in Chemistry, Vol. 7
    • DOI: 10.3389/fchem.2019.00450

    Anomalous and Not-So-Common Behavior in Common Ionic Liquids and Ionic Liquid-Containing Systems
    journal, June 2019

    • Esperança, José M. S. S.; Tariq, Mohammad; Pereiro, Ana B.
    • Frontiers in Chemistry, Vol. 7
    • DOI: 10.3389/fchem.2019.00450

      Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.