What is Enthalpic relaxation?
The process of enthalpic relaxation or “physical aging” results in a decrease in the energy content of the material.
What is enthalpy relaxation in DSC?
Glass transition and enthalpy relaxation are commonly investigated by means of DSC. The relaxation enthalpy corresponds to the release upon heating of degrees of freedom after the material had been aged below its glass transition temperature.
How does heating rate affect glass transition temperature?
It takes time for the glass transition to occur – the fast the heating rate, the higher the observed Tg will be due to the thermal lag of the material. Conversely, the higher the cooling rate, the lower the Tg will appear to be if observing on a cooling cycle.
How is glass transition temperature determined?
There are a variety of thermal and mechanical analytical techniques that can be used to measure the glass transition temperature (Tg). Most notably these include: Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermomechanical Analysis (TMA) depending on the sample.
What is modulated DSC?
Modulated DSC is a technique which also measures the difference in heat flow between a sample and an inert. reference as a function of time and temperature. In addition, the same “heat flux” cell design is used. However, in MDSC a different heating profile (temperature regime) is applied to the sample and reference.
How does chain flexibility affect Tg?
Chain Flexibility A polymer with a backbone that exhibits higher flexibility will have a lower Tg. This is because the activation energy for conformational changes is lower. Therefore, conformational changes can take place at lower temperatures.
What is TGA DTA and DSC?
TGA measures weight change of a sample over a temperature range, DSC measures heat flow of a sample over a temperature range, and DTA measures heat differences between a reference sample and a sample of interest over a temperature range.
What is DTA curve?
The DTA curve is a curve of temperature difference between the sample material and the reference material versus temperature or time. Applications of DTA include: DTA is widely used in the pharmaceutical and food industries. DTA may be used in cement chemistry, mineralogical research, and environmental studies.
How does modulated DSC work?
One component is a function of the sample’s heat capacity and rate of temperature change, and the other is a function of absolute temperature and time. Modulated DSC determines the total, as well as these two individual heat flow components, to provide increased understanding of complex transitions in materials.
What are the factors affecting Tg?
Factors Affecting Tg
- Molecular Weight – In straight chain polymers, increase in MW leads to decrease in chain end concentration resulting in decreases free volume at end group region – and increase in Tg.
- Molecular Structure – Insertion of bulky, inflexible side group increases Tg of material due to decrease in mobility,
Which of the following factor affect glass transition temperature?
Molecular weight- GTT (glass transition temperature) is directly proportional to molecular weight of polymer. Flexibility- GTT is inversely proportional to flexibility. Plasticizer – GTT is inversely proportional to plasticization. Inter molecular force – GTT is directly proportional to intermolecular force.
How does chain length affect glass transition temperature?
As the side chain length of poly(3-alkylthiophene) (P3AT) increases, the glass transition temperature of the backbone shifts to a lower temperature while that of the side chain increases.
What is the relaxation enthalpy?
The relaxation enthalpy corresponds to the release upon heating of degrees of freedom after the material had been aged below its glass transition temperature. The amplitude of the relaxation enthalpy depends on aging temperature and time.
What is the onset glass transition temperature enthalpy relaxation time?
This is always higher than the ~mHz frequency that corresponds to the onset glass transition temperature enthalpy relaxation time of 200 s (τ=1/2πf ). The glass transition temperature can, however, be obtained from such measurements if the frequency of the measurement can be varied.
What is enthalpic relaxation of glass?
Enthalpic relaxation leads to an increase in the structural relaxation time of a glassy material. This increases the observed T g and the ER associated with it (Fig. 3b). If the T g increases, it is possible that the end of enthalpic recovery, observed in the DSC, will also be at a higher temperature.
What are the specific heat modes of glass transition region?
The enthalpy/specific heat modes, in principle, couple to all phenomena which occur in the glass transition region. Enthalpy relaxation can be studied by applying a sinusoidal temperature pulse, much like an alternating electric field, which is applied to study dielectric relaxation.