DSC presentation

Differential ScanningCalorimetry : 

Differential ScanningCalorimetry Stephen Collins

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Technical Group Talk 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.

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Technical Group Talk • 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 involve endothermic or exothermic processes , or changes in heat capacity .

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

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Technical Group Talk 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

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

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Technical Group Talk Technical Group Talk Example DSC - PET

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

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

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Technical Group Talk 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

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Technical Group Talk

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Technical Group Talk 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.

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Technical Group Talk 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

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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 Modulated DSC

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Technical Group Talk Example MDSC

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