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Phase Transitions02:31

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Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to...
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A phase transition is the process in which a substance changes from one state of matter to another, like from a solid to a liquid, liquid to gas, or vice versa, at a specific temperature and under given pressure conditions. This change is spontaneous and is affected by alterations in temperature and pressure. These parameters impact the strength of the forces between molecules (intermolecular forces) in the substance.During a phase transition, both the initial and final phases of the substance...
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Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
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The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize (convert into vapor). The process is called vaporization—a surface phenomenon. Vaporization occurs when the thermal motion of the molecules overcome the intermolecular forces, and the molecules (at the surface) escape into the gaseous state. When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules...
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The internal energy of a substance—the total kinetic energy of all its molecules and the potential energy of their associated forces—depends on the strength of the intermolecular forces in the condensed phases and the pressure exerted on the substance. The internal energy of a substance is the highest in the gaseous state, the lowest in the solid state, and intermediate in the liquid state. Phase transitions are caused by changes in physical conditions, such as temperature and...
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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
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Phase transitions at high energy vindicate negative microcanonical temperature.

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Negative absolute temperature is validated by Boltzmann entropy, enabling the study of phase transitions in systems with bounded energy. This contrasts with Gibbs entropy, offering new insights into nonlinear lattice models and ultracold gases.

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Area of Science:

  • Thermodynamics
  • Statistical Mechanics
  • Condensed Matter Physics

Background:

  • The concept of negative absolute temperature arises from Boltzmann's microcanonical entropy definition for systems with bounded energy.
  • Recent challenges questioned the validity of Boltzmann entropy, favoring Gibbs entropy for consistent thermodynamics.

Purpose of the Study:

  • To provide evidence for the consistency of Boltzmann microcanonical entropy for both positive and negative temperatures.
  • To demonstrate the capability of Boltzmann temperature in describing phase transitions at high energy densities.

Main Methods:

  • Analytical derivations.
  • Numerical simulations.
  • Application to nonlinear lattice models.

Main Results:

  • Boltzmann microcanonical entropy consistently describes systems with both positive and negative temperatures.
  • Negative Boltzmann temperature successfully describes phase transitions at high energy densities, unlike Gibbs temperature.
  • The findings are applicable to nonlinear lattice models, including photonic lattices and ultracold gases.

Conclusions:

  • Boltzmann entropy offers a consistent thermodynamic framework for negative temperatures.
  • This framework is crucial for understanding phase transitions in specific physical systems like optical lattices.