1. Forces Between Particles in Ionic Liquids and Ionic Liquid-Water Mixtures: an Atomic Force Microscopy Study Valentina Valmacco, Michal Borkovec, Plinio Maroni 3 February 2014 ACMM23 & ICONN 2014 Conference, Adelaide, South Australia Valentina.valmacco@unige.ch

2. Geneva Prof. Michal Borkovec

3. Geneva EPFL Lausanne ETH Zurich Sinergia project Ionic liquid/solid interface Ian Wark Institute Adelaide Prof. Michal Borkovec Prof. P. Dyson Prof. N. Spencer Prof. J. Ralston

4. Outline Introduction: Ionic liquids what are Ionic Liquids (ILs) and why are they important? Aim of our research Experimental technique How we do our research Results and discussion Conclusions Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 1

5. Introduction: Ionic liquids Salts with melting point below 100°C Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 2

6. Introduction: Ionic liquids Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 2 Salts with melting point below 100°C

7. Introduction: Ionic liquids Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 2 Salts with melting point below 100°C

8. Introduction: Ionic liquids Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Unique physicochemical properties: Great solvent Low vapor pressure High thermal and chemical stability Wide electrochemical window 2 Salts with melting point below 100°C

9. Introduction: Ionic liquids Organic synthesis and catalysis Batteries and supercapacitors Lubricants Dye Synthesized Solar Cells Fuel cells NP synthesis and suspension stabilization N. V. Plechkova K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123–150. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Unique physicochemical properties: Great solvent Low vapor pressure High thermal and chemical stability Wide electrochemical window 2 Salts with melting point below 100°C

10. Introduction: Ionic liquids Organic synthesis and catalysis Batteries and supercapacitors Lubricants Dye Synthesized Solar Cells Fuel cells NP synthesis and suspension stabilization N. V. Plechkova K. R. Seddon, Chem. Soc. Rev., 2008, 37, 123–150. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia IL-solid interface 2 Salts with melting point below 100°C

11. Introduction: project aim Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Forces between particles in ILs 3

12. Introduction: project aim Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 3 P. Simon, Nature Materials, 2008, 7, 845. Forces between particles in ILs

13. Introduction: project aim Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia K. Ueno et Al., Langmuir, 2011, 27, 9105. 3 X. Yuan et Al., PCCP, 2012, 14, 6026. P. Simon, Nature Materials, 2008, 7, 845. Forces between particles in ILs

14. Introduction: project aim Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 3 IL-water mixtures P. Simon, Nature Materials, 2008, 7, 845. K. Ueno et Al., Langmuir, 2011, 27, 9105. X. Yuan et Al., PCCP, 2012, 14, 6026. Forces between particles in ILs

15. Introduction: project aim Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Diluted solutions ~0.5-5 mM Intermediate-high concentrated solutions Pure IL ~99.8% 3

16. Outline Experimental technique How we do our research Results and discussion Conclusions Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 4 Introduction: Ionic liquid what are ionic liquids (ILs) and why are they important? Aim of our project

17. Experimental: AFM Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Atomic Force Microscopy (AFM) Binnig et al., Physics Review Letters, 56, 1986. Ducker, W. A., Senden, T. J., and Pashley, R. M., Nature, 353, 239-241, (1991). Butt, H. J., Biophysical Journal, 60, 1438-1444, (1991). 5 Asylum MFP3D

18. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

19. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

20. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

21. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

22. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

23. Experimental: Force measurements Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 6 Deflection (nm) Z-displacement (nm)

24. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Experimental: materials Silica 5 μm Sintered (1050°C, 2h) 1-butyl-3-methylimidazolium Thiocyanate SCN Dicyanamide DCA Tetrafluoroborate BF4 BMIM Chloride Cl 7 Fluid cell Glass slide Cl - Optical microscope

25. Outline Experimental technique How we do our research Results and discussion Conclusions Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 8 Introduction: Ionic liquid what are ionic liquids (ILs) and why are they important? Aim of our project

26. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 9 Results: diluted solutions 0.5-5mM Diluted electrolyte solution 1-butyl-3-methylimidazolium Thiocyanate SCN Dicyanamide DCA Tetrafluoroborate BF4 BMIM Chloride Cl pH=4 Cl -

27. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia BMIM SCN 10 Results: diluted solutions 0.5 mM Poisson-Boltzmann equation Force/Effective Radius (N/m) Separation distance (nm)

28. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: diluted solutions Surface potential Ionic strength 0.5 mM Poisson-Boltzmann equation Debye length BMIM SCN Force/Effective Radius (N/m) Separation distance (nm) 10

29. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: diluted solutions 0.5 mM 1 mM BMIM SCN Force/Effective Radius (N/m) Separation distance (nm) 10

30. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 10 Results: diluted solutions 0.5 mM 1 mM 2 mM BMIM SCN Force/Effective Radius (N/m) Separation distance (nm)

31. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 10 Results: diluted solutions 0.5 mM 1 mM 2 mM 3 mM BMIM SCN Force/Effective Radius (N/m) Separation distance (nm)

32. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 10 Results: diluted solutions 0.5 mM 1 mM 2 mM 3 mM 5 mM BMIM SCN Force/Effective Radius (N/m) Separation distance (nm) Ionic strength Surface potential

33. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Surface potentialIonic strenght Diluted IL-water mixtures behave like classical electrolytes 11 Results: diluted solutions

34. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 12 5 wt% - 75 wt% High concentrated electrolyte solution 1-butyl-3-methylimidazolium Thiocyanate SCN Dicyanamide DCA Tetrafluoroborate BF4 BMIM Chloride Cl pH=4 Cl - Results: high-concentrated solutions 5 wt% ~ 0.25 M

35. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 13 Results: high-concentrated solutions 5 wt% BMIM SCN

36. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 13 Results: high-concentrated solutions 5 wt% 10 wt% BMIM SCN

37. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 13 Results: high-concentrated solutions 5 wt% 10 wt% 25 wt% BMIM SCN

38. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 13 Results: high-concentrated solutions 5 wt% 10 wt% 25 wt% 50 wt% BMIM SCN

39. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 13 Results: high-concentrated solutions 5 wt% 10 wt% 25 wt% 50 wt% 75 wt% BMIM SCN

40. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: pure IL Ordered Interfacial layers Bulk R. Atkin, G.G. Warr, J. Phys. Chem. C, 111, 2007, 5162-5168 M. Mezger, et Al., Science, 2008, 332, pp. 424-428. 14

41. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: pure IL 1-butyl-3-methylimidazolium Tiocyanate SCN Dicyanamide DCA Tetrafluoroborate BF4 BMIM chloride Cl 14 Cl - R. Atkin, G.G. Warr, J. Phys. Chem. C, 111, 2007, 5162-5168 M. Mezger, et Al., Science, 2008, 332, pp. 424-428.

42. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: pure IL BMIM SCN 15

43. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: pure IL BMIM SCN Step height Force required to disrupt a layer How strongly the layer is structured Step position Consistent to ion- pair dimension Step number Number of layers formed at the interface 15 Layer thikness 3-4 layers

44. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Results: pure IL BMIM BF4 BMIM DCA BMIM SCN 16 SCNBF4DCA

45. Outline Experimental technique How we do our research Results and discussion Conclusions Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia 17 Introduction: Ionic liquid what are ionic liquids (ILs) and why are they important? Aim of our project

46. Valentina Valmacco 3 February 2014, ACMM23 & ICONN 2014, Adelaide, South Australia Conclusions 18 Diluted (~5mM) IL-water mixtures behave like ‘classical’ electrolyte. Results have been quantitatively interpreted using Poisson-Boltzmann equation At high IL’s content, the force is attractive, beyond a certain concentration,increasing the IL content leads to a decrease in the attraction Forces in pure IL show a step like fashion, meaning layering of molecules on the surface; BMIM SCN shows higher degree of order compared to the other ILs investigated

47. Thanks to.. Swiss National Science Foundation, University of Geneva …and all of you for your attention !!! …questions ??

48. BMIM BF4BMIM DCABMIM SCN

49. BMIM BF4BMIM DCA BMIM SCN Step position