Superheating in linear polymers studied by ultrafast nanocalorimetry.

Area of Science:

• Materials Science
• Polymer Science
• Physical Chemistry

Background:

• Understanding phase transition kinetics is crucial for polymer processing and material properties.
• Submillisecond timescale studies require advanced calorimetric techniques.

Purpose of the Study:

• To construct and utilize a sensitive ultrafast nanocalorimeter for studying phase transition kinetics.
• To investigate the superheating phenomenon in linear polymers at high heating rates.

Main Methods:

• Development of a novel ultrafast nanocalorimeter capable of heating and cooling rates up to 10^6 K/s.
• Measurement of superheating in polymers including iPS, PBT, PET, and iPP.
• Analysis of the relationship between superheating and heating rate.

Main Results:

• A power law relationship between superheating and heating rate was observed in the range of 10^-2 to 10^4 K/s.
• A limiting superheating of approximately 10% of the melting temperature was found at heating rates above 10^4 - 10^5 K/s.
• The superheating limit was influenced by pre-sample annealing conditions.

Conclusions:

• The observed superheating limit and power law behavior are explained by internal stresses at the crystalline-amorphous interface in semicrystalline polymers.
• These stresses arise from thermal expansion gradients during rapid heating.
• The findings provide insights into the fundamental behavior of polymers under extreme thermal conditions.