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The Arrhenius equation relates the activation energy and the rate constant, k, for chemical reactions. In the Arrhenius equation, k = Ae−Ea/RT, R is the ideal gas constant, which has a value of 8.314 J/mol·K, T is the temperature on the kelvin scale, Ea is the activation energy in J/mole, e is the constant 2.7183, and A is a constant called the frequency factor, which is related to the frequency of collisions and the orientation of the reacting molecules.
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Chemical reactions often occur in a stepwise fashion involving two or more distinct reactions taking place in a sequence. A balanced equation indicates the reacting species and the product species, but it reveals no details about how the reaction occurs at the molecular level. The reaction mechanism (or reaction path) provides details regarding the precise, step-by-step process by which a reaction occurs. Each of the steps in a reaction mechanism is called an elementary reaction. These...
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The slow Arrhenius process in small organic molecules.

Federico Caporaletti1, Simone Napolitano1

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The Slow Arrhenius Process (SAP) was found in molecular glassformers, offering a new pathway for equilibration beyond structural relaxation. This study confirms SAP as a universal feature in liquid and glassy dynamics.

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Area of Science:

  • Physical Chemistry
  • Materials Science
  • Condensed Matter Physics

Background:

  • Equilibration in materials involves molecular rearrangements to reach stable states, typically dominated by structural (α-)relaxation.
  • The timescale of α-relaxation increases significantly with cooling, posing challenges for studying material dynamics.

Purpose of the Study:

  • To investigate the presence and universality of the Slow Arrhenius Process (SAP) as an alternative equilibration pathway in molecular glassformers.
  • To explore the experimental challenges in observing SAP in small molecules compared to polymers.

Main Methods:

  • Utilizing dielectric spectroscopy to study the dynamics of three different molecular glassformers.
  • Investigating these systems in a thin film geometry to overcome experimental difficulties.

Main Results:

  • The Slow Arrhenius Process (SAP) was successfully identified in three distinct molecular glassformers.
  • This marks the first reported observation of SAP in small molecule systems.

Conclusions:

  • The findings reinforce the hypothesis that the Slow Arrhenius Process (SAP) is a universal characteristic of both liquid and glassy dynamics.
  • This discovery expands the understanding of molecular mobility and equilibration mechanisms in materials.