Week 9 Differential Scanning Calorimetry

What is glass transition in DSC?

Amorphous sugars undergo a phase change at Tg: rubber or liquid bridge formed between two particles

Important things to get right when using a DSC

Calibration Baseline Sample preparation and pans Type of scan performed Interpretation and analysis of scan

Examples of exothermic heat flows

Crystallisation Decomposition/oxiation Cross linking

What is DSC?

Differential scanning calorimetry The sample and reference maintained at same temperature, even during a thermal event (in the sample) The energy required to maintain zero temperature differential between the sample and the reference, dDq/dt is measured

Examples of endothermic heat flows

Evaporation Melting Protein denaturation Starch gelatinisation

What are DSCs used to measure?

Exothermic Edothermic Heat capacity

Output of a DSC

Exothermic and endothermic processes show up as peaks on a DSC curve, with glass transitions as small negative troughs

Things you can use DSC for

Fat melting Protein denaturation Glass transition Purity

Two principle variants of DSC

Heat flux DSC Power compensated DSC

Commonly used standards for calibration

Indium Water (double distilled)

Difference between heat flux DSC and power compensated DSC?

Same heater used for sample and reference for heat flux DSC

Calibration of a DSC? Baseline?

To match the melting onset temperature indicated by the furnace thermocouple readouts to the known melting points of standards analysed by DSC Should be calibrated as close to desired temperature range as possible Baseline - evaluation of the thermal resistance of the sample and reference sensors

Features of a DSC curve

Ts - onset of temperature of transition Tm - maximum temperature of transition DeltaH - enthalpy of transition DeltaCp - heat capacity

How does a DSC work?

Two sealed pans: reference (blank sample pan) and a sample When a sample undergoes a physical transition, such as phase transitions, more or less heat will need to flow to the sample than the reference to maintain both pans at the same temperature By observing the difference in heat flow between the sample and the reference, they are able to measure the amount of energy absorbed or released during such reactions