52351416 DSC Presentation

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Differential Scanning

Calorimetry

Stephen Collins



Technical Group Talk

Definitions

• A calorimeter measures the heat into or out of a

sample.

• A differential calorimeter measures the heat of a

sample relative to a reference.• A differential scanning calorimeter does all of the

above and heats the sample with a linear temperature

ramp.

• Endothermicheat flows into the sample.• Exothermicheat flows out of the sample.




• Differential Scanning Calorimetry (DSC) measures the

temperatures and heat flows associated with transitions in

materials as a function of time and temperature in a

controlled atmosphere.

• These measurements provide quantitative and qualitative

information about physical and chemical changes that

involve endothermic or exothermic processes, or changes

in heat capacity.

DSC: The Technique




Conventional DSC

Metal

1

Metal

2

Metal

1Metal

2

Sample Empty

Sample

TemperatureReference

Temperature

Temperature

Difference =

Heat Flow

•A “linear” heating profile even for isothermal methods




What can DSC measure?

•Glass transitions

•Melting and boiling points

•Crystallisation time and temperature

•Percent crystallinity•Heats of fusion and reactions

•Specific heat capacity

•Oxidative/thermal stability

•Rate and degree of cure

•Reaction kinetics

•Purity




6

DSC Thermogram

Temperature

H

eatFlow

->exot

hermic

Glass

Transition

Crystallisation

Melting

Cross-Linking

(Cure)

Oxidation



79.70°C(I)

75.41°C81.80°C

144.72°C

137.58°C20.30J/g

245.24°C

228.80°C22.48J/g

Cycle 1

-0.5

0.0

0.5

1.0

1.5

HeatFlow(W

/ g

)

0 50 100 150 200 250 300

Temperature(°C)

Sample: PET80PC20_MM1 1minSize: 23.4300 mgMethod: standard dsc heat-cool-heatComment: 5/4/06

DSCFile: C:...\DSC\Melt Mixed1\PET80PC20_MM1.001Operator: SACRun Date: 05-Apr-2006 15:34Instrument: DSC Q1000 V9.4 Build 287

Exo Down Universal V4.2E TA Instruments

Technical Group TalkTechnical Group Talk

Example DSC - PET

Tg

Tc

Tm




670

Influence of Sample Mass

Temperature (°C)

150 152 154 156

0

-2

-4

-6

DSCHeatFlow

(W

/g)

10mg

4.0mg

15mg

1.7mg

1.0mg

0.6mg

Indium at10°C/minuteNormalized Data

158 160 162 164 166

Onset notinfluenced

by mass




6

Effect of Heating Rateon Indium Melting Temperature

154 156 158 160 162 164 166 168 170

- 5

- 4

- 3

- 2

- 1

0

1

Temperature ( °C)

H

e a t

F l

o w

( W / g )

heating rates = 2, 5, 10, 20°C/min




DSC: Main Sources of Errors

•Calibration

•Contamination

•Sample preparation – how sample is loaded into a pan

•Residual solvents and moisture.

•Thermal lag

•Heating/Cooling rates

•Sample mass

•Processing errors




99

Sample Preparation : Shape

• Keep sample as thin as possible (to minimise thermalgradients)

• Cover as much of the pan bottom as possible

• Samples should be cut rather than crushed to obtain a

thin sample (better and more uniform thermal contactwith pan)




Other DSC Techniques

Hyper-DSC

Based on principle that high heating rates give large broad

transitions.

•Heating rates typically 400-500oC/min

•Need very small sample sizes (~nanograms)

Good for:

•A quick overview of new sample

•Picking out minute transition

Poor for:

•Accuracy: transitions can be shifted by as much as 40oC

•Repeatabiliy: Very sensitive to thermal lag.




Other DSC Techniques

Modulated DSC

•Composite heating profile:•Determines heat capacity and separates heat flow into that due

to reversible and non-reversible events.

Note that temperature is not decreasing duringModulation i.e. no cooling

Modulate +/- 0.42 °C every 40 secondsRamp 4.00 °C/min to 290.00 °C

52

54

56

58

60

62

M o d u l a t e d T e m p e r a t u r e ( ° C )

52

54

56

58

60

62

T e m p e r a t u r e ( ° C )

13.0 13.5 14.0 14.5 15.0

Time (min)

Typicaly:

Heating rates: 0 - 50C

Modulation:

Period: 60 second

Amplitude: +/-10C



Benefits• Increased Sensitivity for Detecting Weak (Glass) Transitions

– Eliminates baseline curvature and drift

• Increased Resolution Without Loss of Sensitivity

– Two heating rates (average and instantaneous)

• Ability to Separate Complex Thermal Events and Transitions IntoTheir Heat Capacity and Kinetic Components

• Ability to Measure Heat Capacity (Structure) Changes DuringReactions and Under Isothermal Conditions

Downside

• Slow data collection


Modulated DSC




Example MDSC

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

N o n r e v H e a t F l o w ( W / g )

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

R e v H e a t F l o w ( W / g )

-0.14

-0.12

-0.10

-0.08

-0.06

-0.04

-0.02

0.00

H e a t F l o w ( W / g )

-50 0 50 100 150 200 250

Temperature (°C)Exo Up Universal V4.2E TA Instruments




Modulated DSC

Reversible Transitions

•Glass Transition

•Melting

Non-reversible

•Crystallisation

•Curing•Oxidation/degradation

•Evaporation

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