Differential Scanning Calorimetry

Queens University Belfast 16/02/12

2

What 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?

3

Ice

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

4

Timeor Tr

TemperatureTr

Ts

Tf

Time∆T =Ts-Tr

0

-0.5

Tf

DSC raw signal

DSC working principle

5

DSC 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/Rth

Rth, thermal resistence of the system

∆H

6

Baseline 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.

β pcm

7

ICTA and Anti-ICTA

ICTAC (International Confederation for Thermal Analysis and Calorimetry)

Direction of DSC signal

melting

In, 6.0000 mg

mW

-20

-10

0

°C120 130 140 150 160 170

exo

STARe SW 9.10MSG Lab: NJ

melting

In, 6.0000 mg

mW

0

5

10

15

20

°C120 130 140 150 160 170

endo

STARe SW 9.10MSG Lab: NJ

ICTA (∆T=Ts-Tr) endothermic downwards,

exothermic upwards.

Anti-ICTA (∆T=Tr-Ts) endothermic upwards, exothermic downwards.

8

Endothermic and exothermic effects

Endothermic:

When the sample absorbs energy, the enthalpy change is said to be endothermic. 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.

9

Exothermic effect

DSC raw signal

Timeor Tr

TemperatureTr

Ts

Time

0

∆T =Ts-Tr

10

Schematic DSC curve of a polymer

1 23 4 5

6

Tem perature

He

at f

low

e xo

endo

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

11

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)

12

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

exo prod 1 13.03.2006 13:58:29

STARe SW 9.01MSG2006: Marco

Melting and Crystallization with DSC

13

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

14

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

15

The glass transition with DSC

dT

dH

mcp

1

pcm

Temperature

cp

Temperature

ex

othe

rm

16

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, they can be endothermic or exothermic.

17

Chemical reaction

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

18

Materials

Additives

Plasticizers

Impurities

Fillers

Processing

Thermal treatment Mechanical stressing

Shaping Storage and use

MaterialProperties

Where to use DSC?

Polymers

Pharmaceuticals

Chemicals

Food

Cosmetics

19

DSC

Multiple Thermocouples increase sensitivity and reduce noise

For Best Resolution: Low signal time constant e.g 1.7 s (20-μL Al crucible, N2 gas)

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

Resolution and Sensitivity

20

Sensor technology

TSR

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

TR0 TS0

S R T0

A single sensor temperature (T0) is measured.

Inhomogeneous temperature distribution of the sensor is not considered.

21

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.

TS

S R

TSTR

TS0 TR0

Sensor technology

22

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 = 14

HSS7 sensor (120 TC): N = 30

TS

S R

TSTR

TS0 TR0

00 RSdt

dq

N

i i

iSiSS R

TT

1

,0,0

N

i i

iRiRR R

TT

1

,0,0

Sensor technology

23

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

exo Lysozyme 1.7% and 0.1% 29.01.2008 16:41:22

STARe SW 9.10MSG Lab: NJ

24

Noise and sensitivity

25

Resolution

26

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/K

Csample (10 mg, 1.5 J/gK) 15 mJ/K => Signal 3 s

Csensor 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

27

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.

28

Cooling behavior

For More Information Visit:www.mt.com/ta