Differential scanning calorimetry (dsc) MUHAMMAD AQIL BIN ZULKIFLI MOHAMAD HUZAIFI BIN AHMAD ASRI PRABU A/L GANESON FAZRUL RANOR ASYIKIN BIN MOHD RALPHEAL

DIFFERENTIAL SCANNING CALORIMETRY Thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. Both the sample and reference are maintained at nearly the same temperature throughout the experiment. It is a technique in which the energy necessary to establish a zero temperature, difference between the sample and reference material is measured as a function of temperature.

The main application of DSC is in studying phase transitions, and widely used to determine temperatures and melting enthalpy, glass transitions and the estimation of the crystallization kinetics of polymers The basic principle underlying this technique is that, when the sample undergoes a physical transformation such as phase transitions, more or less heat will need to flow to it than the reference to maintain both at the same temperature. These transitions involve energy changes or heat capacity changes that can be detected by DSC with great sensitivity.

Schematic Principle of DSC Sample and reference material are heated by separate heaters in such way that their temperature are kept equal while these temperature are increased or decreased linearly.

DSC curve

TYPES OF DSC DEVICE Heat Flux DSC Heat flux defined as exchanged of the heat to be measured with the environment takes place via a well defined heat conduction path with given thermal resistance. The primary measurement signal is a temperature difference; it determines the intensity of the exchange and the resulting heat flow rate ɸ is proportional to it. In a heat flux DSC, the sample material, enclosed in a pan, and an empty reference are placed on a thermoelectric disk by a furnace. The furnace is heated at a linear heating rate, and the heat is transferred to the sample and reference pan through the thermoelectric disk.

These are most fundamental types of heat flux DSC: The disk-type measuring system, where the heat exchange takes place via a disk which serves as solid sample support. The turret-type measuring system, where the heat exchange takes place via small hollow cylinders which serve as elevated sample support. The cylinder-type measuring system, where the heat exchange between the (big) cylindrical sample cavities and the furnace takes place via a path with low thermal conductivity (often a thermopile).

Fig.2.1. a Heat flux DSC with disk-type measuring system. 1 disk, 2 furnace, 3 lid, 4 differential thermocouple(s), 5 programmer and controller, S crucible with sample substance, R crucible with reference sample substance, ɸps heat flow rate from furnace to sample crucible, ɸpR heat flow rate from furnace to reference sample crucible, <Pm measured heat flow rate, K calibration factor. b Measured heat flow rate <Pm (schematic curve) (according to Hemminger, 1994)

Fig.2.2. Heat flux DSC with turret-type measuring system (TA Instruments). 1 elevated constantan platform for sample and reference sample, 2 chromel area thermocouple, 3 constantan body, 4 chromel - constantan thermocouple, 5 silver furnace, S sample substance, R reference sample substance,~T platform temperature difference, To body (furnace) temperature

Fig.2.3. Heat flux DSC with cylinder-type measuring system (Calvet, 1948; thermally decoupled sample containers) (according to Hemminger, 1994). 1 containers to take up sample and reference sample, 2 thermopiles, 3 furnace (with programmable temperature controller), 4 lid, S sample substance, R reference sample substance, 1'1 T temperature difference between the containers

Power Compensation DSC The power compensation DSC belongs to the class of heat-compensating calorimeters. The heat to be measured is (almost totally) compensated with electric energy, by increasing or decreasing an adjustable Joule's heat. In a power compensation DSC, the sample and reference pans are placed in separate furnaces heated by separate heaters. The sample and reference are maintained at the same temperature, and the difference in thermal power required to maintain them at the same temperature is measured and plotted as a function of temperature or time.

Fig. 2. S. Power compensation DSC (Perkin-Elmer Instruments) Fig.2.S. Power compensation DSC (Perkin-Elmer Instruments). Set-up of the measuring system (according to Hemminger, 1994). S sample measuring system with sample crucible, microfurnace and lid, R reference sample system (analogous to S), 1 heating wire, 2 resistance thermometer. Both measuring systems - separated from each other - are positioned in a surrounding (block) at constant temperature

Fig. 2. 6. Power compensation DSC (Perkin-Elmer Instruments) Fig.2.6. Power compensation DSC (Perkin-Elmer Instruments). Block diagram showing the function principle (according to Hemminger, 1994). Ts temperature of the sample furnace, TR temperature of the reference sample furnace, IlT = Ts - TR, Pav average heating power, IlP compensation heating power, cf>m measured heat flow rate (measurement signal)

DIFFERENTIAL SCANNING CALORIMETRIC SAMPLE TEST DSC Thermal Analysis is used primarily for : Polymers Plastics Monomers Elastomers Organic materials Chemicals Biological samples

DIFFERENTIAL SCANNING CALORIMETRIC SAMPLE TEST DSC Thermal Analysis Identifies : Thermal Phase Change Thermal Glass Transition Temperature Crystalline Melt Temperature Endothermic Effects Exothermic Effects Thermal Stability Thermal Formulation Stability Oxidative Stability Studies Transition Phenomena Solid State Structure Analysis of a Diverse Range of Materials

DIFFERENTIAL SCANNING CALORIMETRIC SAMPLE TEST Examines the temperature differences between a sample in a small pan and an empty pan when both are heated together. Change in the material states will cause the changes in temperature difference. When a material melts, the temperature differences changes rapidly. Melting point and other changes such as glass transitions and decomposition points can also be determined. Determine the chemical characteristics within the sample relative to its heat capacity. The results can be compared to a DSC curve to further analyses and understand a particular sample.

ADVANTAGES Wide range of temperatures Any material in any form may be tested Small amount of material is needed (1-10mg) Does not take much time (10-30 minutes) Auto sampler and auto analysis

DISADVANTAGES Interpretation of results is often difficult Quantitative analysis of the individual processes is impossible Cannot optimize both sensitivity and resolution in a single experiment Very sensitive to any changes

DSC VS DTA DTA DSC Technique in which the difference is calculated between the temperatures required by the reference and the sample when the heat flow is kept the same for both. A technique in which the difference is calculated between the amount of heat needed (heat flow) to increase the temperature of the sample and the heat required to increase the temperature of the reference Suited for the determination of characteristic temperatures Determination of caloric values such as the heat of fusion or heat of crystallization Same as DTA but the temperature difference can be converted into a heat-flux difference in mw by means of an appropriate calibration