Predicting Stability Predicting Stability of of

Emulsions and Dispersions Emulsions and Dispersions byby

Conductivity Conductivity

ByBy

Gerd Gerd H. H. DahmsDahms*Institute for Applied *Institute for Applied Colloidtechnology Colloidtechnology

Duisburg, GermanyDuisburg, Germany

CorrelationCorrelation

betweenbetween

Rheology Rheology and Conductivity and Conductivity

in in

Emulsions and DispersionsEmulsions and Dispersions

Background Information Background Information

During storage emulsions and dispersions During storage emulsions and dispersions often change their structure and stability.often change their structure and stability.

Consequently changes can be observed inConsequently changes can be observed in

ApplicationApplication

Flow characteristicsFlow characteristics

StabilityStability

2 * r² * g *2 * r² * g *DDρρ99ηη

V = V =

Instabilities of emulsions and dispersions are Instabilities of emulsions and dispersions are described best by Stokes law.described best by Stokes law.

The higher the velocity V of the particles caused by The higher the velocity V of the particles caused by gravity the more instable is the emulsions or dispersiongravity the more instable is the emulsions or dispersion

The velocity (V) of the particle to the top (creaming) or to The velocity (V) of the particle to the top (creaming) or to the bottom (sedimentation) depends on the particle size the bottom (sedimentation) depends on the particle size

radius (r) and the viscosity.radius (r) and the viscosity.

Instability described by Stokes Law

According Stokes law the driving forces in According Stokes law the driving forces in emulsions and dispersions are the particle emulsions and dispersions are the particle

size and the viscosity.size and the viscosity.

Any change in those parameter during the Any change in those parameter during the storage leads to structural changes, which storage leads to structural changes, which

are very often followed by visible instabilitiesare very often followed by visible instabilities

2 * r² * g *2 * r² * g *DDρρ99ηη

V = V =

Instability described by Stokes Law

Impact of Structure ChangesImpact of Structure Changes

Structural changes are caused byStructural changes are caused by

AggregationAggregation

CoalescenceCoalescence

Assessments of Structure Change by Assessments of Structure Change by RheologyRheology

Structural changes in emulsions and dispersions are Structural changes in emulsions and dispersions are analyzed today mainly by rheological assessmentanalyzed today mainly by rheological assessment

Most important information in rheological assessment Most important information in rheological assessment can be obtained by oscillation performancecan be obtained by oscillation performance

Flow characteristics reveal only limited information Flow characteristics reveal only limited information on structural changes on structural changes

Structure changes in low viscous systems are Structure changes in low viscous systems are extremely difficult to observe by rheological extremely difficult to observe by rheological

measurementsmeasurements

Ion Mobility and Flow Ability in EmulsionsIon Mobility and Flow Ability in Emulsions

In emulsions and dispersions the reason of changes in conductiviIn emulsions and dispersions the reason of changes in conductivity ty and viscosity fall back on structural changes in the aqueous phaand viscosity fall back on structural changes in the aqueous phase.se.

Structural changes in the aqueous phase lead to a change of the Structural changes in the aqueous phase lead to a change of the fluid mobility measured byfluid mobility measured by rheologyrheology and a change of the ion and a change of the ion

mobility determined by conductivitymobility determined by conductivity

Decreasing ion mobility and flow ability due to Decreasing ion mobility and flow ability due to structure built up structure built up

Relation between viscosity and conductivityRelation between viscosity and conductivity

Direct mathematical relationship between Direct mathematical relationship between

conductivity and viscosityconductivity and viscosity

κκ = F * C ( = F * C ( νν++ ** zz++ * * µµ++ + + νν−− ** z z -- * * µµ-- ))

ννii == zzii * e * E / 6 * * e * E / 6 * ππ ** rrii **ηη

µµii = = zzii * e / 6 * * e / 6 * ππ * * rrii **ηη

F = accelerated force acting on an ionF = accelerated force acting on an ion C = ion concentrationC = ion concentrationE = electrical fieldE = electrical field

z = charge numberz = charge number r = ion radiusr = ion radiusγγ = = ion velocityion velocity µµ = = ion mobilityion mobility

ηη = = viscosityviscosity

κκ11

κκ22

∆∆κκ

Measurement Measurement Technique Technique

Two parallel electrode pairs Two parallel electrode pairs -- one pair on top, one pair one pair on top, one pair at the bottom at the bottom –– detect droplet / particle migrationdetect droplet / particle migration

Electrode Electrode PairPair

II

RR

R = Resistance R = Resistance I = Current I = Current

( ( U = Voltage ) U = Voltage )

OhmOhm‘‘s Law: R = s Law: R = UUI I

κκ = = 1 1 RR

Correlation between Viscosity Correlation between Viscosity and Phase Volume Fractionand Phase Volume Fraction

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0Internal Phase Volume [ % ]

Visc

osity

@ 1

/s [

Pas

]

MeasurementY = A * e^(B*X)

Correlation between Conductivity Correlation between Conductivity and Phase Volume Fractionand Phase Volume Fraction

0

20

40

60

80

100

120

0.0 20.0 40.0 60.0 80.0Internal Phase Volume [ % ]

Con

duct

ivity

[ 킪

/cm

]

MeasurementY = A * e^(B*X)

Correlation between conductivity and viscosityCorrelation between conductivity and viscosity

Einstein equationEinstein equation

ηη= A * e= A * e B * B * ΦΦ

Conductivity correlationConductivity correlation

κκ= A * e= A * e -- B * B * ΦΦ

The Einstein and conductivity equations differ only with respecThe Einstein and conductivity equations differ only with respect to the sign t to the sign in front of the exponent and can be correlated. in front of the exponent and can be correlated.

Conductivity Conductivity ––Viscosity correlationViscosity correlation

k = k = A * A * hh-- BB

Correlation between Viscosity and ConductivityCorrelation between Viscosity and Conductivity

0

5

10

15

20

25

30

35

40

0 50 100 150Conductivity [ 킪 /cm ]

Visc

osity

@ 1

/s [m

Pas]

measurementY = A * X^B

Application of Conductivity in Stokes LawApplication of Conductivity in Stokes Law

We can conclude that the viscosity of the dispersion is indirectWe can conclude that the viscosity of the dispersion is indirectly ly proportional to the conductivity.proportional to the conductivity.

2 * r² * g *2 * r² * g *DDρρ99

ddV = V = ((dkdkAA ))**1/ B1/ B

Consequently conductivity can be applied in Stokes law by Consequently conductivity can be applied in Stokes law by exchanging the viscosity termexchanging the viscosity term

Determination of Changes in Stability by ConductivityDetermination of Changes in Stability by Conductivity

Con

duct

ivity

[µS/

cm]

Time

No structural changeNo structural change

Con

duct

ivity

[µS/

cm]

TimeTime

AggregationAggregationCoalescenceCoalescence

TimeTime

Con

duct

ivity

[µS/

cm]

Sedimentation can be determined by conductivity top to bottom Sedimentation can be determined by conductivity top to bottom

κκ11

κκ22

∆∆κκ

Determination of Sedimentation / CreamingDetermination of Sedimentation / Creamingby Conductivityby Conductivity

Determination of Temperature depending Structure Determination of Temperature depending Structure Changes by Oscillation Performance MeasurementChanges by Oscillation Performance Measurement

Determination of Temperature depending Structure Determination of Temperature depending Structure Changes by Conductivity MeasurementChanges by Conductivity Measurement

Determination of Temperature depending Structure Determination of Temperature depending Structure Changes by Conductivity Measurement Changes by Conductivity Measurement

Similar to temperature sweeps conducted by oscillation performanSimilar to temperature sweeps conducted by oscillation performance ce structural changes can be determined also by conductivity measurstructural changes can be determined also by conductivity measurementsements

Stability PredictionStability Prediction

andand

Structural AnalysisStructural Analysis

ofof

Emulsions and DispersionsEmulsions and Dispersions

κκ11

κκ22

∆∆κκ

Measurement Measurement Technique Technique

By means of two parallel electrode pairs, one pair on By means of two parallel electrode pairs, one pair on top, one pair at the bottom top, one pair at the bottom –– droplet / particle droplet / particle

migration is detected:migration is detected:

Electrode Electrode PairPair

II

RR

R = Resistance R = Resistance I = Current I = Current

( ( U = Voltage ) U = Voltage )

OhmOhm‘‘s Law: R = s Law: R = UUI I κκ = = 1 1

RR

DualCon DualCon Measurement during Measurement during Creaming ProcessCreaming Process

RR

%UU

RR

RR

%UU

RR

UU

RR

RR

%UU

RR

UU

RR

Are

a of

A

rea

of

““ No

Det

ectio

nN

o D

etec

tion ””

DualConDualCon Measurement during Measurement during Creaming ProcessCreaming Process

Creaming PhenomenaCreaming Phenomena

Bottom Bottom -- ElectrodesElectrodes

Top Top -- ElectrodesElectrodes

Creaming PhenomenaCreaming Phenomena

Flocculation PhenomenaFlocculation Phenomena

Top Top -- ElectrodesElectrodes

Bottom Bottom -- ElectrodesElectrodes

Flocculation PhenomenaFlocculation Phenomena

During the flocculation, an During the flocculation, an „„internal internal structurestructure““ is built up. Within that structure, is built up. Within that structure,

water is entrapped.water is entrapped.

As a result, viscosity increases and the ionAs a result, viscosity increases and the ion--mobility decreases. mobility decreases.

Logically, conductivity decreases parallel at Logically, conductivity decreases parallel at top and bottom.top and bottom.

Entrapped Entrapped WaterWater

Flocculation PhenomenaFlocculation Phenomena

Flocculation PhenomenaFlocculation Phenomena

Coalescence PhenomenaCoalescence Phenomena

Constant climb, uniform slopeConstant climb, uniform slope

As a result of droplets in the internal phase flowing together, As a result of droplets in the internal phase flowing together, more more water becomes available from the external phase.water becomes available from the external phase.

Logically, the conductivity increases.Logically, the conductivity increases.

Coalescence PhenomenaCoalescence Phenomena

Coalescence PhenomenaCoalescence Phenomena

DualConDualCon FeaturesFeatures Temperature dependent measurements, adaptable to Temperature dependent measurements, adaptable to standardized measurements in YOUR company.standardized measurements in YOUR company.

Temperature Range: Temperature Range: -- 2020°°C / + 100C / + 100°°CC

Automatic Automatic Thermostat ControlThermostat Control

Independent Independent Heating and Cooling Rate Heating and Cooling Rate

Variable Variable Measurement TimeMeasurement Time

Number of Cycles Number of Cycles variable (1variable (1--15)15)

DualConDualCon FeaturesFeatures TheThe DualConDualCon is compatible with the following is compatible with the following Thermostats:Thermostats:

ThermoThermo--HaakeHaake DC30/K10DC30/K10 JulaboJulabo F12/MV and F25/MVF12/MV and F25/MV

DualConDualCon FeaturesFeatures Up to Up to 8 Samples8 Samples can be examined at the same time can be examined at the same time under equal conditions!under equal conditions!

DualConDualCon FeaturesFeatures EasyEasy to understand Analysis Softwareto understand Analysis Software

DualConDualCon FeaturesFeatures Each sample has a Each sample has a detailed Sampledetailed Sample reportreport, containing , containing all measurement data and describing data.all measurement data and describing data.

DualConDualCon FeaturesFeaturesThe The comprehensive comprehensive „„EASY STABEASY STAB““ databasedatabase is is

available to assist you in the interpretation of obtained available to assist you in the interpretation of obtained results, containing lots of hints and information. results, containing lots of hints and information.

The database is The database is updated frequentlyupdated frequently and works with any and works with any internet browser. Updates can be downloaded internet browser. Updates can be downloaded free of chargefree of charge!!

Choose your Choose your result.result.

Get detailed Get detailed InformationInformation

Hyperlinks Hyperlinks bring up a bring up a complete complete

encyclopediaencyclopedia

Conductivity reacts just as sensitively as Conductivity reacts just as sensitively as viscosity to changes in emulsion structure. viscosity to changes in emulsion structure.

SummarySummary

Consequently, conductivity measurement offers a fairly Consequently, conductivity measurement offers a fairly uncomplicated method of determining the stability of emulsions uncomplicated method of determining the stability of emulsions

and dispersions over a short period of time. and dispersions over a short period of time.

2 * r² * g *2 * r² * g *DDρρ99

ddV = V = ((dkdkAA ))**1/ B1/ B

Consequently conductivity can be applied in Stokes law by Consequently conductivity can be applied in Stokes law by exchanging the viscosity termexchanging the viscosity term