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

• 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

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

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

Aqueousorganic solution

Liquid-liquid phase separations in multicomponent mixtures

Summer school 2008

Gabriela Ciobanu

Motivation

hydrophilic hydrophobic

Aqueous salt

solution

Aqueousorganic solution

NaClOxalic acid

HOOC-COOH

Azelaic acidHOOC-(CH2)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

Water cooling

Controlled T°and RH

Small droplet of PEG 400/AS

Z

X Y

objective

spectrometer

N2 +H2O

200C

Temperature regulator

Water cooling

Controlled T°and RH

Small droplet of PEG 400/AS

Z

X Y

Z

X Y

objective

spectrometer

N2 +H2O

200C200C

Temperature regulator

Gabriela Ciobanu

Experimentalsetup

Summer school 2008

Experimental results

• 50:50 wt%• 89:11 wt%

• 33.3:66.6 wt%

• Mechanisms of phase separation - theory• PEG/AS/H2O state diagram

• PEG 400/AS ratios:

Gabriela Ciobanu

Experimentalsetup

Summer school 2008

Experimental results

PEG 400/AS (50:50 wt%)

Summer school 2008

Gabriela Ciobanu

Experimentalresults

1 2&33

2 3 3

2

2 2

2

2

33

3

3

33

4

89.7 %RH 0 s

89.7 %RH 3 s

89.6 %RH 6 s

89.6 %RH 10 s

89.5 %RH 6 s

88.4 %RH 4 min

49 %RH 46 min

35 %RH 106 min

• 1- aqueous solution of PEG 400 and ammonium sulfate

• 2 - aqueous PEG 400

• 3 - aqueous ammonium sulfate

• 4 - effloresced ammonium sulfate

Experimental results

Summer school 2008

Gabriela Ciobanu

Experimentalresults

Summer school 2008

Gabriela Ciobanu

Experimentalresults

Raman spectra from PEG 400/AS (50:50 wt%)

500 1000 1500 2000 2500 3000 3500 4000

Inte

nsity

(a.

u)

Wavenumbers (cm-1)

92% RH

86% RH

28% RH

s(SO42-) (CH2)

Experimental results

PEG 400/AS (89:11 wt%)

Summer school 2008

Gabriela Ciobanu

Experimentalresults

88.8 %RH 0 s

88.7 %RH 5 s

86.6 %RH 4 min

85.6 %RH 5 min

72.6 %RH 28 min

23 %RH 58 min

11

3

2

3

2

3

22

3 4

•1- aqueous solution of PEG 400 and ammonium sulfate

•2 - aqueous PEG 400

•3 - aqueous ammonium sulfate

•4 - effloresced ammonium sulfate

Experimental results

Summer school 2008

Gabriela Ciobanu

Experimentalresults

PEG 400/AS (33.3:66.6 wt%)

Experimental results

Summer school 2008

Gabriela Ciobanu

Experimentalresults

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

1 32 2

2 2 2&3

3

3 3

90.4%RH 0 s

•1- aqueous solution of PEG 400 and ammonium sulfate

•2 - aqueous PEG 400

•3 - aqueous ammonium sulfate

•4 - effloresced ammonium sulfate

Experimental results

Summer school 2008

Gabriela Ciobanu

Experimentalresults

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 decomposit

ion

Phase separation mechanisms

Spinodal decomposition

Nucleation and growth

Growth at the surface

1 2&33

2 3 3

2

2 2

2

2

33

3

3

33

4

89.7 %RH 0 s 89.7 %RH 3 s 89.6 %RH 6 s 89.6 %RH 10 s

89.5 %RH 16 s 88.4 %RH 4 min 49 %RH 46 min 35 %RH 106 min

1 2&33

2 3 3

2

2 2

2

2

33

3

3

33

4

89.7 %RH 0 s 89.7 %RH 3 s 89.6 %RH 6 s 89.6 %RH 10 s

89.5 %RH 16 s 88.4 %RH 4 min 49 %RH 46 min 35 %RH 106 min

88.8 %RH 0 s 88.7 %RH 5 s 86.6 %RH 4 min

85.6 %RH 5 min 72.6 %RH 28 min 23 %RH 58 min

1 1 32

3

2

3

22

3 4

88.8 %RH 0 s 88.7 %RH 5 s 86.6 %RH 4 min

85.6 %RH 5 min 72.6 %RH 28 min 23 %RH 58 min

1 1 32

3

2

3

22

3 4

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

1 32 2

2 2 2&3

3

3 3

90.4%RH 0 s 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

1 32 2

2 2 2&3

3

3 3

90.4%RH 0 s 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

1 32 2

2 2 2&3

3

3 3

90.4%RH 0 s

50:50 wt%PEG/AS

89:11 wt%PEG/AS

33.3:66.6 wt%PEG/AS

Summer school 2008

8

Gabriela Ciobanu

Effect of particle size on morphology

Summer school 2008

8

Gabriela Ciobanu

PEG 400/AS 50:50 wt%RH=53%

PEG 400/AS 89:11 wt%RH=53%

State diagram of PEG 400-AS-H2O system

Experimentalresults

Summer school 2008

Gabriela Ciobanu

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

2 liquid phases

%R

H

wt% AS of dry mass

Bulk measurements:

1 liquid phase/2 liquid phases boundary AS deliquescence/2 liquid phases boundary

1 liquid phase

State diagram of PEG 400-AS-H2O system

Experimentalresults

Summer school 2008

Gabriela Ciobanu

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

2 liquid phases

%R

H

wt% AS of dry mass

Bulk measurements:

1 liquid phase/2 liquid phases boundary AS deliquescence/2 liquid phases boundary

Particle measurements:

Upon drying

1 phase 2 phases by nucleation&growth 1 phase 2 phases by spinodal decomposition 1 phase 2 phases by growht of 2nd phase from the surface AS efflorescenced

upon drying: 2 liquid phases

1 liquid, 1 solid phase

1 liquid phase

State diagram for PEG 400-AS-H2O system

Experimentalresults

Summer school 2008

Gabriela Ciobanu

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

2 liquid phases

%R

H

wt% AS of dry mass

Bulk measurements:

1 liquid phase/2 liquid phases boundary AS deliquescence/2 liquid phases boundary

Particle measurements:

Upon moistening

beginning of AS deliquescence AS totally deliquesced 2 liquid phases 2 phases 1 phase

Upon drying

1 phase 2 phases by nucleation&growth 1 phase 2 phases by spinodal decomposition 1 phase 2 phases by growht of 2nd phase from the surface AS efflorescenced

upon moistening: 1 liquid, 1 solid phaseupon drying: 2 liquid phases

1 liquid, 1 solid phase

1 liquid phase

Summaryo 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 ClaudiaUli Krieger Uwe Weers

Financial support:Swiss National Foundation

Thank you for attention!

Summer school 2008

Gabriela Ciobanu