Differential ScanningCalorimetryStephen Collins

Technical Group TalkDefinitionsA calorimetermeasures the heat into or out of a sample.A differential calorimeter measures the heat of a sample relative to a reference.A differential scanning calorimeterdoes all of the above and heats the sample with a linear temperature ramp.Endothermicheat flows into the sample.Exothermicheat flows out of the sample.

Technical Group TalkDifferential Scanning Calorimetry(DSC) measuresthe temperatures and heat flowsassociated with transitions in materials as a function of time and temperature in a controlled atmosphere.These measurements provide quantitative and qualitativeinformation about physical and chemical changes that involve endothermicor exothermicprocesses, or changes in heat capacity.DSC: The Technique

Technical Group TalkConventional DSCMetal 1Metal 2Metal 1Metal 2SampleEmptySample TemperatureReference TemperatureTemperature Difference = Heat FlowA linear heating profile even for isothermal methods

Technical Group TalkWhat can DSC measure?Glass transitionsMelting and boiling pointsCrystallisation time and temperaturePercent crystallinityHeats of fusion and reactionsSpecific heat capacityOxidative/thermal stabilityRate and degree of cureReaction kineticsPurity

Technical Group Talk6DSC ThermogramTemperatureHeat Flow -> exothermicGlassTransitionCrystallisationMeltingCross-Linking(Cure)Oxidation

Technical Group TalkTechnical Group TalkExample DSC - PET

Technical Group Talk670Influence of Sample MassTemperature (C)1501521541560 -2 -4 -6DSC Heat Flow (W/g)10mg4.0mg15mg1.7mg1.0mg0.6mgIndium at10C/minute Normalized Data158160162164166Onset not influenced by mass

Technical Group Talk6Effect of Heating Rateon Indium Melting Temperature154156158160162164166168170-5-4-3-2-101Temperature (C)Heat Flow (W/g)heating rates = 2, 5, 10, 20C/min

Technical Group TalkDSC: Main Sources of ErrorsCalibrationContaminationSample preparation how sample is loaded into a panResidual solvents and moisture.Thermal lagHeating/Cooling ratesSample massProcessing errors

Technical Group Talk

Technical Group TalkOther DSC TechniquesHyper-DSCBased on principle that high heating rates give large broad transitions.Heating rates typically 400-500oC/minNeed very small sample sizes (~nanograms)

Good for: A quick overview of new samplePicking out minute transition

Poor for:Accuracy: transitions can be shifted by as much as 40oCRepeatabiliy: Very sensitive to thermal lag.

Technical Group TalkOther DSC TechniquesModulated 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

BenefitsIncreased Sensitivity for Detecting Weak (Glass) TransitionsEliminates baseline curvature and driftIncreased Resolution Without Loss of SensitivityTwo heating rates (average and instantaneous)Ability to Separate Complex Thermal Events and Transitions Into Their Heat Capacity and Kinetic ComponentsAbility to Measure Heat Capacity (Structure) Changes During Reactions and Under Isothermal Conditions

DownsideSlow data collectionTechnical Group TalkModulated DSC

Technical Group TalkExample MDSC

Technical Group TalkModulated DSCReversible TransitionsGlass TransitionMelting

Non-reversibleCrystallisationCuringOxidation/degradationEvaporation