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The process of surrounding a solute with solvent is called solvation. It involves evenly distributing the solute within the solvent. The rule of thumb for determining a solvent for a given compound is that like dissolves like. A good solvent has molecular characteristics similar to those of the compound to be dissolved. For example, polar solutions dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent is a solvent that has a high dielectric constant (ϵ...
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Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
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The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy.
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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
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Gold Nanoparticle Synthesis
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Negative Casimir entropies in nanoparticle interactions.

Kimball A Milton1, Romain Guérout, Gert-Ludwig Ingold

  • 1H. L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA. Laboratoire Kastler-Brossel, CNRS, ENS, UPMC, Case 74, F-75252 Paris, France.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|May 13, 2015
PubMed
Summary
This summary is machine-generated.

Negative entropy, a counterintuitive phenomenon, can arise from the geometry of interactions between small objects and conducting surfaces. This study explores novel scenarios where geometric configurations drive negative entropy in Casimir systems.

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Area of Science:

  • Quantum Field Theory
  • Nanophysics
  • Thermodynamics

Background:

  • Negative entropy in Casimir systems is established, particularly between parallel metallic plates with Drude permittivity.
  • Geometric origins of negative entropy, such as between a sphere and a plate, are less understood but significant.
  • The dipole approximation highlights the importance of size and separation in geometric negative entropy effects.

Purpose of the Study:

  • To investigate the occurrence of negative entropy in systems involving electrically and magnetically polarizable nanoparticles or atoms.
  • To explore negative entropy generation between small, potentially anisotropic objects and conducting surfaces.
  • To examine novel configurations beyond parallel plates, including sphere-plate and nanoparticle-nanoparticle interactions.

Main Methods:

  • Analysis of Casimir forces and associated thermodynamic properties.
  • Consideration of realistic material properties (Drude permittivity) and perfect conductors.
  • Examination of electrostatic and magnetostatic polarizability, including anisotropy.

Main Results:

  • Negative entropy can occur between two perfectly conducting spheres.
  • Sufficient anisotropy in electrically polarizable nanoparticles can lead to negative entropy.
  • Negative entropy is observed between a perfectly conducting sphere and a Drude sphere.
  • Anisotropic nanoparticles interacting with a transverse magnetic conducting plate also exhibit negative entropy.

Conclusions:

  • Geometric factors play a crucial role in generating negative entropy in Casimir systems.
  • The study expands the understanding of negative entropy to diverse nanoparticle and sphere configurations.
  • Anisotropy in polarizable objects is a key factor enabling negative entropy in novel setups.