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Liquid-Liquid Phase Separation In Mixed Organic-Inorganic Aerosols Institute For Atmosphere And Climate Science – ETH Zurich . Gabriela Ciobanu Göteborg, Summer school 23-29 June 2008. Outline.

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Outline

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  1. Liquid-Liquid Phase Separation In Mixed Organic-Inorganic AerosolsInstitute For Atmosphere And Climate Science – ETH Zurich Gabriela Ciobanu Göteborg, Summer school 23-29 June 2008

  2. Outline • Introduction • Motivation • PEG 400/AS model system • Experimental setup • Experimental results • Summary • 3 take home messages Outline Summer school 2008 Gabriela Ciobanu

  3. Gabriela Ciobanu Introduction Mixed organic-inorganic aerosols • Organics: ~50% of the aerosol mass Several reasons to account for the organic fraction : • influence on DRH, ERH of inorganic components • contribution of WSOC to CCN formation • uptake of gases on a surface active organic coating • humic-like substances - absorption of solar radiation Introduction Summer school 2008

  4. Gabriela Ciobanu Motivation Physical state of mixed organic/inorganic aerosols -atmospheric implications Motivation Summer school 2008 [Ravishankara, A.R. , Science,1997]

  5. Gabriela Ciobanu Motivation Multi-component aerosol particle two or more condensed phases • Possibilities: • two liquid phases • one liquid, one solid phase • two solid phases • two liquid phases and one solid phase • … Motivation Summer school 2008

  6. Gabriela Ciobanu Motivation Multi-component aerosol particle two or more condensed phases • Possibilities: • two liquid phases • one liquid, one solid phase • two solid phases • two liquid phases and one solid phase • … Motivation Summer school 2008

  7. Aqueous salt solution Aqueous organic solution Motivation Summer school 2008 hydrophilic hydrophobic Gabriela Ciobanu Liquid-liquid phase separations in multicomponent mixtures

  8. Aqueous salt solution Aqueous organic solution Motivation Azelaic acid HOOC-(CH2)7-COOH Oxalic acid HOOC-COOH NaCl Summer school 2008 hydrophilic hydrophobic Gabriela Ciobanu Liquid-liquid phase separations in multicomponent mixtures

  9. Motivation Summer school 2008 Gabriela Ciobanu Liquid-liquid phase separations in multicomponent mixtures Expected morphology of aerosol particle with liquid-liquid phase separation:

  10. Motivation Summer school 2008 Gabriela Ciobanu PEG 400/AS model system • Polyethylene glycol (M= 400) - PEG 400 • Water soluble organic • Chosen to represent oligomeric or polymeric nonvolatile fraction • Liquid at the room temperature • Antisolvent for ammonium sulfate • Ammonium sulfate – AS • -common salt of aerosol particles • PEG 400/AS - liquid-liquid phase separation in bulk solutions

  11. Motivation Summer school 2008 Gabriela Ciobanu [Ref. Marcolli et al, J.Phys.Chem.,2006] PEG 400/AS model system EDB measurements [Ref. Colberg et al, J.Phys.Chem.,2004]

  12. Experimental setup Gabriela Ciobanu Experimental setup Summer school 2008

  13. Experimental setup Gabriela Ciobanu Experimental results • PEG 400/AS ratios: • 50:50 wt% • 89:11 wt% • 33.3:66.6 wt% • Mechanisms of phase separation - theory • PEG/AS/H2O state diagram Summer school 2008

  14. Experimental results Summer school 2008 Gabriela Ciobanu Experimental results PEG 400/AS (50:50 wt%) 89.7 %RH 0 s 89.7 %RH 3 s 89.6 %RH 6 s 89.6 %RH 10 s 3 2&3 3 1 2 3 2 89.5 %RH 6 s 49 %RH 46 min 35 %RH 106 min 88.4 %RH 4 min 2 2 2 3 3 3 4 3 3 2 3 • 1- aqueous solution of PEG 400 and ammonium sulfate • 2 - aqueous PEG 400 • 3 - aqueous ammonium sulfate • 4 - effloresced ammonium sulfate

  15. Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

  16. Experimental results Summer school 2008 Gabriela Ciobanu Raman spectra from PEG 400/AS (50:50 wt%) n(CH2) ns(SO42-)

  17. 86.6 %RH 4 min 88.8 %RH 0 s 88.7 %RH 5 s 1 3 1 3 2 85.6 %RH 5 min 72.6 %RH 28 min 23 %RH 58 min Experimental results 4 3 3 Summer school 2008 2 2 2 Gabriela Ciobanu Experimental results PEG 400/AS (89:11 wt%) • 1- aqueous solution of PEG 400 and ammonium sulfate • 2 - aqueous PEG 400 • 3 - aqueous ammonium sulfate • 4 - effloresced ammonium sulfate

  18. Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

  19. 88.4%RH 7 min 89.1%RH 5 min 90.4%RH 0 s 2 3 2 1 3 30.3%RH 258 min 74.8%RH 62 min 44.2%RH 200 min 2 3 2 3 2&3 Experimental results Summer school 2008 Gabriela Ciobanu Experimental results PEG 400/AS (33.3:66.6 wt%) • 1- aqueous solution of PEG 400 and ammonium sulfate • 2 - aqueous PEG 400 • 3 - aqueous ammonium sulfate • 4 - effloresced ammonium sulfate

  20. Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

  21. Summer school 2008 Gabriela Ciobanu Phase separation mechanisms Nucleation and growth • large fluctuations in concentration • an energy barrier has to be overcome for the formation of a nucleus • isolated droplets of the minor phase in the major phase Spinodal decomposition • small fluctuations in concentration • energy barrier is absent • high interconnectivity between phases in the early stages of phase separation

  22. Nucleation and growth Spinodal decomposition Summer school 2008 Gabriela Ciobanu Nucleation and growth vs. spinodal decomposition

  23. Summer school 2008 8 Gabriela Ciobanu Phase separation mechanisms Nucleation and growth 89:11 wt% PEG/AS Spinodal decomposition 50:50 wt% PEG/AS Growth at the surface 33.3:66.6 wt% PEG/AS

  24. Summer school 2008 8 Gabriela Ciobanu Effect of particle size on morphology PEG 400/AS 50:50 wt% RH=53% PEG 400/AS 89:11 wt% RH=53%

  25. Experimental results Summer school 2008 Gabriela Ciobanu State diagram of PEG 400-AS-H2O system

  26. State diagram of PEG 400-AS-H2O system Experimental results Summer school 2008 Gabriela Ciobanu

  27. Experimental results Summer school 2008 Gabriela Ciobanu State diagram for PEG 400-AS-H2O system

  28. Summary Summer school 2008 Gabriela Ciobanu Summary • Combined optical microscopy and micro- Raman spectroscopy – useful tools to characterize the phases of aerosol particles as a function of relative humidity • Different mechanisms for liquid-liquid phase separation – for different ratios of PEG/AS • Agreement between bulk and particle measurements Atmospheric implications Organic coating – hygroscopicity of inorganic components - heterogeneous chemistry

  29. Summer school 2008 Gabriela Ciobanu 3 Take home messages • In presence of miscibility gap between water soluble organics and inorganic aerosol constituents, liquid-liquid phase separation is likely to occur under varying relative humidity conditions. • The ratio of immiscible organic/inorganic aerosol constituents determines the phase separation mechanism into two liquid phases. • When two liquid phases are present within an aerosol particle the most likely morphology is sphere-in-a-sphere, with the organic phase at the surface. Conclusions

  30. Summer school 2008 Gabriela Ciobanu Thanks to: Thomas Peter Marcolli Claudia Uli Krieger Uwe Weers Financial support: Swiss National Foundation Thank you for attention!

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