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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.
10
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)
11
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
12
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
13
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
14
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.
16
Chemical reaction
Homogeneous decomposition of dibenzoyl peroxide; peak temperature and peak shape depend on heating rate; peak area is independent of heating rate.
17
MaterialsAdditivesPlasticizersImpuritiesFillers
ProcessingThermal treatment
Mechanical stressingShaping
Storage and use
MaterialProperties
Where to use DSC?
PolymersPharmaceuticalsChemicalsFoodCosmetics
18
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
19
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.
20
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
22
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
23
Noise and sensitivity
24
Resolution
25
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
26
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.
27
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
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Time [min]
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