INDEX thermal energy

The transition between crystalline and amorphous polymers is characterized by the so-called glass transition temperature, Tg. This important quantity is defined as the temperature above which the polymer chains have acquired sufficient thermal energy for rotational or torsional oscillations to occur about the majority of bonds in the chain. Below 7"g, the polymer chain has a more or less fixed conformation. On heating through the temperature Tg, there is an abrupt change of the coefficient of thermal expansion (or), compressibility, specific heat, diffusion coefficient, solubility of gases, refractive index, and many other properties including the chemical reactivity. 

The components in a mixture separate in the column and exit from the column at different times (retention times). As they exit, the detector registers the event and causes the event to be recorded as a peak on the chromatogram. A wide range of detector types are available and include ultraviolet adsorption, refractive index, thermal conductivity, flame ionization, fluorescence, electrochemical, electron capture, thermal energy analyzer, nitrogen-phosphorus. Other less common detectors include infrared, mass spectrometry, nuclear magnetic resonance, atomic absorption, plasma emission. 

The number of unrelaxed modes per chain at time t is equal to the mode index p. Each unrelaxed mode contributes energy of order kT to the stress relaxation modulus. The stress relaxation modulus at time t is proportional to the thermal energy kT and the number density of sections with Njp monomers, 4>/(b N/p) ... 

In terms of intermolecular interactions, the boiling point represents the temperature at which molecules possess enough thermal energy to overcome the various intermolecular attractions binding the molecules into the liquid (e.g. hydrogen bonds, dipole-dipole attraction, instantaneous-dipole induced-dipole attractions). Therefore the boiling point is also an index of the strength of intermolecular attractive forces. 

Physical and thermodynamic properties density and refractive index, thermal and electrical conductivity, hygroscopicity, melting points, free energy and chemical potential, heat capacity, vapor pressure, solubility, thermal stability... 

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