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Differential Scanning Calorimetry

Differential Scanning Calorimetry. Stephen Collins. Definitions. •. A. calorimeter. measures the heat into or out of a. sample. •. A. differential calorimete. r measures the heat of a. sample relative to a reference. •. A. differential scanning calorimeter. does all of the.

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Differential Scanning Calorimetry

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  1. Differential ScanningCalorimetry Stephen Collins

  2. Definitions • A calorimeter measures the heat into or out of a sample. • A differential calorimete r 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. • Endothermic heat flows into the sample. • Exothermic heat flows out of the sample. Technical Group Talk

  3. DSC: The Technique • 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 endothermic exothermic processes changes involve or , or in heat capacity . Technical Group Talk

  4. Conventional DSC Empty Sample Metal 1 Metal 2 Metal 1 Metal 2 Sample Temperature Reference Temperature Temperature Difference = Heat Flow • A “linear” heating profile even for isothermal methods Technical Group Talk

  5. 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 Technical Group Talk

  6. DSC Thermogram Oxidation Cross - Linking Crystallisation (Cure) > exothermic - Glass Transition Heat Flow Melting Temperature 6 Technical Group Talk

  7. Sample : PET 80 PC 20 _ MM 1 1 min File : C :... \ DSC \ Melt Mixed 1 \ PET 80 PC 20 _ MM 1 . 001 DSC Size : 23 . 4300 mg Operator : SAC Method : standard dsc heat - cool - heat Run Date : 05 - Apr - 2006 15 : 34 Comment : 5 / 4 / 06 Instrument : DSC Q 1000 V 9 . 4 Build 287 1 . 5 245 . 24 °C 1 . 0 ) g 137 . 58 °C / Tc Tm Tg W 20 . 30 J / g 228 . 80 °C ( 22 . 48 J / g 79 . 70 °C ( I ) 81 . 80 °C 0 . 5 75 . 41 °C Heat Flow Cycle 1 144 . 72 °C 0 . 0 - 0 . 5 0 50 100 150 200 250 300 Exo Down Temperature ( °C ) Universal V 4 . 2 E TA Instruments Example DSC - PET Technical Group Talk Technical Group Talk

  8. Influence of Sample Mass 0 Onset not Indium at influenced 10°C/minute -2 by mass Normalized Data 15mg 10mg 4.0mg -4 1.7mg 1.0mg 0.6mg DSC Heat Flow (W/g) -6 150 152 154 156 158 160 162 164 166 Temperature (°C) 6 70 Technical Group Talk

  9. Effect of Heating Rate on Indium Melting Temperature 1 0 - 1 - 2 Heat Flow (W/g) heating rates = 2, 5, 10, 20 ° C/min - 3 - 4 - 5 154 156 158 160 162 164 166 168 170 Temperature ( ° C) 6 Technical Group Talk

  10. 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 Technical Group Talk

  11. Technical Group Talk

  12. 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. Technical Group Talk

  13. Other DSC Techniques • Modulated DSC • Composite heating profile: • Determines heat capacity and separates heat flow into that due to reversible and non-reversible events. Typicaly: Heating rates: 0 - 50C Modulation: Period: 60 second Amplitude: +/-10C Technical Group Talk

  14. Modulated DSC 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 Into Their Heat Capacity and Kinetic Components • Ability to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions Downside • Slow data collection Technical Group Talk

  15. Example MDSC Technical Group Talk

  16. Modulated DSC • Reversible Transitions • Glass Transition • Melting • Non-reversible • Crystallisation • Curing • Oxidation/degradation • Evaporation Technical Group Talk

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