Related Experiment Video
Updated: May 25, 2026
11:03
An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
Langevin dynamics, entropic crowding, and stochastic cloaking.
1Department of Technology Management, Holon Institute of Technology, PO Box 305, Holon 58102, Israel. eliazar@post.tau.ac.il
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|February 7, 2012
Summary
We explore "entropic crowding," a state where probe and particle distributions match in a thermal bath. This phenomenon, achieved through specific bath or force conditions, optimizes probe cloaking within the system.
Area of Science:
- Statistical Mechanics
- Soft Matter Physics
- Physical Chemistry
Background:
- Independent probes in a spatially inhomogeneous thermal bath experience stochastic dynamics governed by Langevin's equation.
- Probes typically reach a steady-state distribution distinct from the surrounding particle concentration.
Purpose of the Study:
- To investigate the phenomenon of
- entropic crowding,
- where probe and particle distributions coincide.
- To analyze the conditions leading to maximal relative entropies between probes and particles.
Main Methods:
- Analysis of probe dynamics governed by Langevin's equation.
- Exploration of two distinct scenarios for achieving entropic crowding: crowding thermal baths and crowding Langevin forces.
Main Results:
- Entropic crowding occurs when probe distribution matches particle concentration, maximizing relative entropy.
- Two scenarios identified: uniform particle crowding around probes and uniform probe crowding among particles.
- Entropic crowding is demonstrated to be equivalent to optimal stochastic cloaking.
Conclusions:
- Entropic crowding represents a unique state of probe-particle interaction in inhomogeneous thermal baths.
- The study elucidates mechanisms for achieving this state and its implication for probe visibility.
Related Concept Videos
01:10Entropy Change in Reversible Processes
In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
02:05Entropy and Solvation
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 ≥ 15); an...
02:39Entropy
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...
01:21Entropy Changes Accompanying Specific Processes
Entropy, a measure of disorder in a system, changes during phase transitions like freezing or boiling. At the transition temperature Ttrs, where two phases are in equilibrium, the phase transition is a reversible process. The entropy change can be calculated from a substance's enthalpy of transition using the equation ΔStrs = ΔtrsH /Ttrs.When a perfect gas expands isothermally from one volume to another, entropy increases logarithmically with volume. Conversely, isothermal compression results...
01:20Entropy and the Second Law of Thermodynamics
The second law of thermodynamics can be stated quantitatively using the concept of entropy. Entropy is the measure of disorder of the system.
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
The relation between entropy and disorder can be illustrated with the example of the phase change of ice to water. In ice, the molecules are located at specific sites giving a solid state, whereas, in a liquid form, these molecules are much freer to move. The molecular arrangement has therefore become more randomized. Although the change in average...
01:26Entropy and the Second Law of Thermodynamics
Consider an isolated system in which a hot object is placed in contact with a cold one. This is an irreversible process that eventually leads both objects to reach the same equilibrium temperature. It is crucial to note that the constituents of any substance exhibit increased disorder at higher temperatures. As a cold substance absorbs heat, its constituents become more disordered. The energy transfer from a hotter object to a cooler one increases the system's disorder or randomness. This...