Liquid-Liquid Phase Separation In Mixed Organic-Inorganic Aerosols Institute For Atmosphere And Climate Science

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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
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Outline

• Introduction
• Motivation
• PEG 400/AS model system
• Experimental setup
• Experimental results
• Summary
• 3 take home messages

Outline
Summer school 2008
Gabriela Ciobanu
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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
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Motivation

• Physical state of mixed organic/inorganic
  aerosols -atmospheric implications

Motivation
Summer school 2008
Ravishankara, A.R. , Science,1997
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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
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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
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Liquid-liquid phase separations in multicomponent
mixtures
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Liquid-liquid phase separations in multicomponent
mixtures
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Liquid-liquid phase separations in multicomponent
mixtures
Expected morphology of aerosol particle with
liquid-liquid phase separation
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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
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PEG 400/AS model system
EDB measurements
Ref. Colberg et al, J.Phys.Chem.,2004
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Experimental setup
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Experimental results

• PEG 400/AS ratios

• 5050 wt

• 8911 wt

• 33.366.6 wt

• Mechanisms of phase separation - theory

• PEG/AS/H2O state diagram

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Experimental results

• PEG 400/AS (5050 wt)

• 1- aqueous solution of PEG 400 and ammonium
  sulfate
• 2 - aqueous PEG 400
• 3 - aqueous ammonium sulfate
• 4 - effloresced ammonium sulfate

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Experimental results
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Raman spectra from PEG 400/AS (5050 wt)
n(CH2)
ns(SO42-)
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Experimental results

• PEG 400/AS (8911 wt)

• 1- aqueous solution of PEG 400 and ammonium
  sulfate
• 2 - aqueous PEG 400
• 3 - aqueous ammonium sulfate
• 4 - effloresced ammonium sulfate

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Experimental results
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Experimental results

• PEG 400/AS (33.366.6 wt)

• 1- aqueous solution of PEG 400 and ammonium
  sulfate
• 2 - aqueous PEG 400
• 3 - aqueous ammonium sulfate
• 4 - effloresced ammonium sulfate

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Experimental results
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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

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Nucleation and growth vs. spinodal decomposition
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Phase separation mechanisms
Nucleation and growth
8911 wt PEG/AS
Spinodal decomposition
5050 wt PEG/AS
Growth at the surface
33.366.6 wt PEG/AS
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Effect of particle size on morphology
PEG 400/AS 5050 wt RH53
PEG 400/AS 8911 wt RH53
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State diagram of PEG 400-AS-H2O system
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State diagram of PEG 400-AS-H2O system
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State diagram for PEG 400-AS-H2O system
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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
• 
  

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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
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• Thanks to
• Thomas Peter
• Marcolli Claudia
• Uli Krieger
• Uwe Weers
• Financial support
• Swiss National Foundation
• Thank you for attention!

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Systems presenting phase separation
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