Differential Scanning Calorimetry

1What is a DSC?

Differential: measurement of the difference in heat flow from sample and reference side

Scanning: the common operation mode is to run temperature or time scans

Calorimeter: instrument to measure heat or heat flow.

Heat flow: a transmitted power measured in mW

What is DSC?

2Ice

Ts Tr

Hot Plate

Heat the hot plate from -20 C to 30 C,

What will happen to the ice?How do Ts and Tr react?How do the Ts and Tr relate to each other?

Air

DSC working principle

3Timeor Tr

TemperatureTrTs

Tf

TimeT =Ts-Tr

0

-0.5

Tf

DSC raw signal

DSC working principle

4DSC working principle

DSC raw signal,

Timeor Tr

T =Ts-Tr

0

-0.5

Tf

Timeor Tr

Heat flow (mW)

0

-10DSC signal,

Peak integral H

=T/RthRth, thermal resistence of thesystem

H

5Baseline slope

Where,

m is the sample masscp is the specific heat capacity

of the sample is the heating rate

Timeor Tr

Heat flow (mW)

0

-10

Initial deflection

A normal DSC curve is not horizontal, its baseline shows a slope.

= pcm

6ICTA and Anti-ICTAICTAC (International Confederation for Thermal Analysis and Calorimetry)

Direction of DSC signal

mW

-20

-10

0

C120 130 140 150 160 170

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ICTA (T=Ts-Tr)endothermic downwards,

exothermic upwards.

Anti-ICTA (T=Tr-Ts)endothermic upwards,

exothermic downwards.

7Endothermic and exothermic effects

Endothermic:

When the sample absorbs energy, the enthalpy change is said to beendothermic. Processes such as melting and vaporization are endothermic.

Exothermic:

When the sample releases energy, the process is said to be exothermic. Processes such as crystallization and oxidation are exothermic.

8Exothermic effect

DSC raw signal

Timeor Tr

TemperatureTrTs

Time

0

T =Ts-Tr

9Schematic DSC curve of a polymer

1 23 4 5

6

Temperature

H

e

a

t

f

l

o

w

exo

endo

1. initial startup deflection; 2. glass transition; 3. crystallization; 4. melting; 5. vaporization; 6. decomposition.

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What is melting and crystallization?

amorphouscrystalline

Melting of Indium: 156.6 C, -28.6 J/g (endothermic)

Crystallization of Indium: 153.5 C, +28.6 J/g (exothermic)

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In: 6.18 mg10 K/min

Integral -193.95 mJ normalized -28.52 Jg -^1Onset 156.58 C

Integral 194.27 mJ normalized 28.57 Jg -^1Onset 153.43 C

mW

-10

0

10

20

C140 145 150 155 160 165

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Melting and Crystallization with DSC

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How to evaluate melting peaks

Pure materials:- onset (independent of heating rate)- Hf baseline: line, integral tangential

Impure materials:- peak temperature (depends on )- Hf baseline: line, tangential right - purity analysis for eutectic systems

(based on curve shape analysis)

Polymers- peak temperature (depends on and m)- Hf baseline: line, spline, integral tangential

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amorphous solid,rigid, brittle

liquid (non polymers)rubber like (polymers)

What is glass transition?

Glass transition is cooperative molecular movement.

Glassy state Rubbery stateGlass transition

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The glass transition with DSC

dTdH

mcp =

1

= pcm

Temperature

cp

Temperature

e

x

o

t

h

e

r

m

15

Chemical reaction

A chemical reaction is a process that one or more substances (reactants) are converted to one or more new chemical substances(products) with different properties. e.g. oxidation, decomposition, polymerization etc.

Chemical reactions always involve a change in energy. Depending on whether the energy is absorbed or released during the process, theycan be endothermic or exothermic.

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Chemical reaction

Homogeneous decomposition of dibenzoyl peroxide; peak temperature and peak shape depend on heating rate; peak area is independent of heating rate.

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MaterialsAdditivesPlasticizersImpuritiesFillers

ProcessingThermal treatment

Mechanical stressingShaping

Storage and use

MaterialProperties

Where to use DSC?

PolymersPharmaceuticalsChemicalsFoodCosmetics

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DSC

Multiple Thermocouples increase sensitivity and reduce noise

For Best Resolution: Low signal time constant e.g1.7 s (20-L Al crucible, N2 gas)

High baseline stability using chemically resistant ceramic substrate and relatively inert silver furnace

Resolution and Sensitivity

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Sensor technology

TSR

S R Temperature gradients on the sensor lead to baseline deviation from zero

TR0 TS0

S RT0 A single sensor temperature (T0) is measured.

Inhomogeneous temperature distribution of the sensor is not considered.

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Inner ring of thermocouples measure TR and TS Outer ring measures sensor temperatures at reference and

samples sides, TS0 and TR0 Thermocouples act as thermal resistence, R.

TSS R

TS TR

TS0 TR0

Sensor technology

21

Heat flow on the sample and reference sides are separately measured

N is the number of thermocouples (TC) per ring.FRS5 sensor (56 TC): N = 14HSS7 sensor (120 TC): N = 30

TSS R

TS TR

TS0 TR000 RSdt

dq =

=

=N

i i

iSiSS R

TT

1

,0,0

=

=N

i i

iRiRR R

TT

1

,0,0

Sensor technology

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Noise and sensitivity

Peak Height 137 uW

Lysozyme dissolved in 0.1 M HCl/glycinebuffer at pH = 3Heating rate 3 K/minSample Mass around 105 mg

1.7 % Lysozyme

uW100

C50 60 70 80 90

Peak Height 6.5 uW

Step 0.69 uW

0.1 % Lysozyme

uW5

min

C60 65 70 75 80

18 20 22 24

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Noise and sensitivity

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Resolution

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How long does the system take to equilibrate? How fast does the signal come back to the baseline? Small Signal better resolution

Signal = RthCs, Cs = Cpan+ Csample+ Csensor

FRS5 sensor (Rth 0.04 K/mW) & Al40 l (50 mg)Cpan 50 mJ/KCsample (10 mg, 1.5 J/gK) 15 mJ/K => Signal 3 sCsensor 10 mJ/K

FRS5 sensor (Rth 0.04 K/mW) & Al20 l (20 mg)Cpan 20 mJ/K => Signal 1.8 s

Signal time constant

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Signal time constant

How to improve Signal?

Cs can be strongly influenced by the choice of the pan.

Recommendations for better resolution: -> Al20 ul pan instead of Al40 ul pan-> Al pans instead of alumina pans

Cs can be reduced by using smaller sample size

Signal can be further decreased by using He as purge gas.

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Cooling behavior

0 5 10 15 20 25

-150

-100

-50

0

50

100

150

200

250

Air cooled Intracooler Liquid nitrogen

T

e

m

p

e

r

a

t

u

r

e

[

C

]

Time [min]

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