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

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

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 Gabriela Ciobanu Introduction Summer school 2008

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

Motivation Gabriela Ciobanu Summer school 2008 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 Gabriela Ciobanu Summer school 2008 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 …

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

Liquid-liquid phase separations in multicomponent mixtures Summer school 2008 Gabriela Ciobanu Motivation hydrophilic hydrophobic Aqueous salt solution Aqueous organic solution NaCl Oxalic acid HOOC-COOH Azelaic acid HOOC-(CH 2 ) 7 -COOH

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

PEG 400/AS model system Summer school 2008 Gabriela Ciobanu Motivation - liquid-liquid phase separation in bulk solutions 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

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

Experimental setup Gabriela Ciobanu Experimental setup Summer school 2008

Experimental results 50:50 wt% 89:11 wt% 33.3:66.6 wt% Mechanisms of phase separation - theory PEG/AS/H 2 O state diagram PEG 400/AS ratios: Gabriela Ciobanu Experimental setup Summer school 2008

Experimental results PEG 400/AS (50:50 wt%) Summer school 2008 Gabriela Ciobanu Experimental results 1 2&32& %RH 0 s 89.7 %RH 3 s 89.6 %RH 6 s89.6 %RH 10 s 89.5 %RH 6 s 88.4 %RH 4 min 49 %RH 46 min35 %RH 106 min 1- aqueous solution of PEG 400 and ammonium sulfate 2 - aqueous PEG aqueous ammonium sulfate 4 - effloresced ammonium sulfate

Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

Summer school 2008 Gabriela Ciobanu Experimental results Raman spectra from PEG 400/AS (50:50 wt%) s (SO 4 2- ) (CH 2 )

Experimental results PEG 400/AS (89:11 wt%) Summer school 2008 Gabriela Ciobanu Experimental results 88.8 %RH 0 s88.7 %RH 5 s 86.6 %RH 4 min 85.6 %RH 5 min 72.6 %RH 28 min 23 %RH 58 min aqueous solution of PEG 400 and ammonium sulfate 2 - aqueous PEG aqueous ammonium sulfate 4 - effloresced ammonium sulfate

Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

PEG 400/AS (33.3:66.6 wt%) Experimental results Summer school 2008 Gabriela Ciobanu Experimental results 89.1%RH 5 min 88.4%RH 7 min 74.8%RH 62 min 44.2%RH 200 min 30.3%RH 258 min &32& %RH 0 s 1- aqueous solution of PEG 400 and ammonium sulfate 2 - aqueous PEG aqueous ammonium sulfate 4 - effloresced ammonium sulfate

Experimental results Summer school 2008 Gabriela Ciobanu Experimental results

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 Summer school 2008 Gabriela Ciobanu

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

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

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

State diagram of PEG 400-AS-H 2 O system Experimental results Summer school 2008 Gabriela Ciobanu

State diagram of PEG 400-AS-H 2 O system Experimental results Summer school 2008 Gabriela Ciobanu

State diagram for PEG 400-AS-H 2 O system Experimental results Summer school 2008 Gabriela Ciobanu

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

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 Summer school 2008 Gabriela Ciobanu

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

Systems presenting phase separation Summer school 2008 Gabriela Ciobanu