2004 Training Seminars
DSC
MDSC®
What it’s all about & how to
get better results
5
What Does MDSC® Measure?
• MDSC separates the Total heat flow of DSC into two
parts based on the heat flow that does and does not
respond to a changing heating rate
• MDSC applies a changing heating rate on top of a
linear heating rate in order measure the heat flow that
responds to the changing heating rate
• In general, only heat capacity and melting respond to
the changing heating rate.
• The Reversing and Nonreversing signals of MDSC
should never be interpreted as the measurement of
reversible and nonreversible properties
Modulated
®
DSC
Theory
• MDSC® uses two simultaneous heating rates
– Average Heating Rate
•
This gives Total Heat Flow data which is equivalent
to standard DSC @ same average heating rate
– Modulated Heating Rate
•
Purpose is to obtain heat capacity information at the
same time as heat flow
Average & Modulated Temperature
(Heat-Iso)
62
62
Temperature (°C)
60
60
58
58
56
56
Average Temperature
54
54
Note that temperature is not decreasing during
Modulation i.e. no cooling
52
13.0
13.5
14.0
Time (min)
14.5
52
15.0
Modulated Temperature (°C)
Modulated Temperature
Modulate +/- 0.42 °C every 40 seconds
Ramp 4.00 °C/min to 290.00 °C
Average & Modulated Temperature
62
62
Modulate +/- 0.42 °C every 40 seconds (Heat-Iso)
Ramp 4.00 °C/min to 290.00 °C
Modulated Temperature
57.0
56.5
56.5
56.0
56.0
55.5
55.5
55.0
55.0
54.5
13.70
13.75
13.80
13.85
13.90
13.95
14.00
58
54.5
14.05
Time (min)
56
56
Average Temperature
54
54
Note that temperature is not decreasing during
Modulation i.e. no cooling
52
13.0
13.5
14.0
Time (min)
14.5
52
15.0
Modulated Temperature (°C)
57.0
Modulated Temperature (°C)
58
60
Amplitude
Temperature (°C)
Temperature (°C)
60
Average & Modulated Heating Rate
10
10
Period
Note That Heating Rate is
Never Negative (no cooling)
8
6
6
Average
Heating Rate
4
4
2
2
Modulated
Heating Rate
0
13.0
13.5
14.0
Time (min)
14.5
0
15.0
Deriv. Modulated Temperature (°C/min)
Deriv. Temperature (°C/min)
8
MDSC® Raw Signals
24
Cold Crystallization
Modulated Heat Flow
(Response)
Crystal Perfection
20
Modulated Heat Flow (mW)
16
Glass Transition
12
-4
MDSC Raw Data Signals for 13.54mg Quenched PET;
+/-0.48;60sec;3°C/min
Note that all transitions are visible in MHF signal
Melting
8
-8
4
0
Modulated Heating Rate (Stimulus)
-12
0
Exo Up
50
100
150
Temperature (°C)
200
250
300
Deriv. Modulated Temperature (°C/min)
0
Modulated
®
DSC
Theory
• MDSC® Heat Flow & Signals
dH
dt

Total =
dT
Cp
dt
Reversing

+
f (T, t)
Nonreversing
Modulated
®
DSC
Theory
• MDSC® Data Signals
dH
dt

Total =
Reversing
Transitions
dT
Cp
dt

Reversing
+
•Heat Capacity
•Glass Transition
•Most Melting
f (T, t)
Nonreversing
Modulated
®
DSC
Theory
• MDSC® Data Signals
dH
dt

Total =
Nonreversing
Transitions
dT
Cp
dt

Reversing
+
f (T, t)
Nonreversing
•Enthalpic Recovery
•Evaporation
•Crystallization
•Thermoset Cure
•Protein Denaturation
•Starch Gelatinization
•Decomposition
•Some Melting
MDSC® of Quench-Cooled PET
0.4
0.2
0.0
Heat Flow (W/g)
Total
-0.2
Reversing
0.0
0.2
-0.2
0.0
-0.4
-0.2
-0.4
-0.4
0
Exo Up
50
100
150
Temperature (°C)
200
250
300
Rev Heat Flow (W/g)
Nonrev Heat Flow (W/g)
Nonreversing
When & Why to Run MDSC®
• Always run a standard DSC @ 10°C/min
first
• If you’re looking for a glass transition -– If the glass transition is detectable and can be routinely
analyzed, then you don’t need to use MDSC
– However, if the Tg is hard to detect, or has an enthalpic
recovery, then run MDSC
When & Why to Run MDSC®
• If looking at melting and crystallization –
– If the melting process looks normal (single
endothermic peak) and there is no apparent
crystallization of the sample as it is heated, then
there is no need to use MDSC
– However, if melt is not straightforward, or it is
difficult to determine if crystallization is
occurring as the sample is heated, use MDSC
When & Why to Run MDSC®
• If you want heat capacity (Cp) – run MDSC
– To get Cp by normal DSC (Q1000 is an
exception due to Direct Cp)
• Use High heating rates, >10°C/min
• Three experiments required
– Baseline
– Reference (sapphire)
– Sample
The Natural Limitations of DSC
• The next several slides discuss some of the
natural limitations of DSC & how they are
solved by MDSC®. This is by no means a
complete list, just some of the more
significant limitations.
The Natural Limitations of DSC
1. It is not possible to optimize both sensitivity and
resolution
in a single DSC experiment.
•
•
•
Sensitivity is increased by increasing weight or heating rate
dH
dT
 Cp
 f (T, t)
dt
dt
Although increased sample size or heating rate improves
sensitivity, they decrease resolution by causing a larger
temperature gradient within the sample
MDSC® solves this problem because it has two heating rates:
the average heating rate can be slow to improve resolution,
while the modulated heating rate can be high to improve
sensitivity
Sensitivity & Resolution
PC-PEE Blend
16.13mg
MDSC® .424/40/1
Natural Limitations of DSC (cont.)
2. Baseline curvature and drift limit the sensitivity
of DSC for detecting weak transitions
•
MDSC® eliminates baseline curvature and drift in the
Heat Capacity and Reversing signals by using the
ratio of two measured signals rather than the absolute
heat flow signal as measured by DSC.
Cp 
AmplitudeMod Heat Flow
xK
AmplitudeMod HeatingRate
Reversing Cp x Avg HeatingRate
Where’s the Tg?
Tablet Binder, 44%RH
3.08mg
MDSC® 1/60/5
Vented pan
Here’s the Tg!
Natural Limitations of DSC
(cont.)
3. Transitions are often difficult to interpret
because DSC can only measure the Sum of
Heat Flow within the Calorimeter
• MDSC® minimizes this problem by providing
not only the Total Heat Flow signal but also
the heat capacity and kinetic components of it
Complicated Example
Quenched Xenoy
14.79mg
10°C/min
®
MDSC Aids
Xenoy 13.44 mg
MDSC .318602
Interpretation
Natural Limitations of DSC (cont.)
4. It is often difficult to accurately measure the
crystallinity of polymers by DSC because the
crystallinity increases as the sample is being
heated in the DSC cell.
– To measure the correct crystallinity requires the
ability to:
• determine the true heat capacity (no transitions) baseline
• quantitatively measure how much crystallinity developed
during the heating process
DSC of Amorphous PET/PC
DSC
Mixture…Where is the PC Tg ?
Sample: Quenched PET and PC
Size: 13.6000 mg
Method: DSC@10
Comment: DSC@10; PET13.60/PC 10.40/Al film 0.96mg
-2
File: C:...\Len\Crystallinity\qPET-PCdsc.001
Standard DSC @ 10°C/min
57% PET; 43% PC
4
30.74J/g
0
170.00°C
215.00°C
Heat Flow (mW)
270.00°C
42.95J/g
-10
-4
270.00°C
120.00°C
-14
-8
13.31J/g
-18
-12
DSC Heat Flow Analyzed
Two Different Ways
-22
-16
50
Exo Up
[ ––––– · ] Heat Flow (mW)
120.00°C
-6
100
150
Temperature (°C)
200
250
Universal V3.8A TA Instruments
MDSC® Shows Two Tgs in Polymer Mixture
Sample: Quenched PET and PC
Size: 13.6000 mg
DSC
Method: MDSC .318/40@3
Comment: MDSC 0.318/40@3; PET13.60/PC 10.40/Al film 0.96mg
File: C:\TA\Data\Len\Crystallinity\qPET-PC.002
-2.0
-2.0
Cold Crystallization Peak
Seen Only in Total Signal
-2.2
Total
Heat Flow
Glass Transition
of Polycarbonate
Heat Flow (mW)
-2.4
-2.4
True Onset
of Melting
-2.6
-2.8
-3.0
-2.6
Reversing
Heat Flow
-2.8
Decrease in Heat Capacity
Due to Cold Crystallization
-3.0
MDSC® .318/40/3
-3.2
-3.2
50
Exo Up
[ ––––– · ] Rev Heat Flow (mW)
-2.2
100
150
Temperature (°C)
200
250
Universal V3.8A TA Instruments
MDSC® Gives Correct Crystallinity of Zero
Optimization of MDSC®
Conditions
• Proper selection of the three experimental
parameters is important in order to maximize
the quality of the results.
– In general, temperature is controlled to either
provide or not provide cooling during the
temperature modulation
– Cooling is desirable for heat capacity transitions
– Cooling is undesirable for melting &
crystallization
Select Modulated Mode
Select signals to store
Select Test
(Template)
MDSC® Heat-Cool Modulation
Heating &
Cooling
Heating Rate goes below 0°C/min
MDSC® Heat-Iso Modulation
No Cooling
Heating Rate never goes below 0°C/min
MDSC® Heat-Iso Amplitudes
No Cooling
H
e
a
t
i
n
g
0.1
0.2
0.5
1.0
2.0
5.0
40
0.011
0.021
0.053
0.106
0.212
0.531
Period (sec)
50
0.013
0.027
0.066
0.133
0.265
0.663
60
0.016
0.032
0.080
0.159
0.318
0.796
70
0.019
0.037
0.093
0.186
0.371
0.928
80
0.021
0.042
0.106
0.212
0.424
1.061
90
0.024
0.048
0.119
0.239
0.477
1.194
100
0.027
0.053
0.133
0.265
0.531
1.326
R
a
t
e
This table is additive, i.e. the heat only amplitude for a period of 40 sec & a
heating rate of 2.5°C/min is the sum of the values for 2.0°C/min & 0.5°C/min
Amplitude (40s,2.5°C/min)=0.212+0.053=0.265°C
MDSC® Conditions for Q Series
DSC
Glass Transitions (Tg)
• For “standard Tg”:
Sample Size: 10 – 15 mg
Amplitude*:
2X Table
Period: 40 seconds
Heating Rate: 3°C/min
• If Tg is Hard to Detect
Sample Size: 10 – 20 mg
Period: 60 seconds
Amplitude*: 4X Table
Heating Rate: 2°C/min
• If Tg has Large Enthalpic Relaxation
Sample Size: 5 – 10 mg
Period: 40 seconds
Amplitude*: 1.5X Table
Heating Rate: 1°C/min
*Use a minimum of 0.5°C amplitude
MDSC® Conditions for Q Series
DSC
Heat Capacity (Cp)
• Heating Rate; isothermal up to 5ºC/min
• Modulation Period
– 100 seconds with crimped pans
– 120 seconds with hermetic pans
• Modulation Amplitude; 1.5X Table Value
with a minimum of 0.5ºC
• Sample Size; 10-15mg
MDSC® Conditions for Q Series
DSC
Melting and crystallinity:
• Sample Size; 10-15mg
• Period
– 40 sec. with crimped pans
– 60 sec. With hermetic pans
• Heating Rate
– Slow enough to get a minimum of 4-5 cycles at half-height
of the melting peaks
• Amplitude
– Use “Heat-Iso” amplitude which provides no cooling
during temperature modulation (see Table)