| Jul 25, 2023 |
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(Nanowerk News) From internal combustion engines to household refrigerators, heat engines are a ubiquitous component of daily life. These machines convert heat into usable energy which can then be used to do work. Heat engines can be as small as a single molecule whose random movements exchange energy with the environment. But determining the efficiency of a molecular heat engine is no simple task.
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In a study published in EPJ B (“Time-dependent solutions for efficiency and velocity of a Brownian heat engine that operates in a two-dimensional lattice coupled with a nonuniform thermal background”), Mesfin Asfaw Taye, of West Los Angeles College, California, USA now calculates the performance of a molecular heat engine in terms of a series of molecular ratchets that transfer energy, step-wise, in one direction. He shows and discusses how to manipulate such a system for transporting a particle along a complex path.
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| Ratchets transfer energy in a lattice arrangement. (Image: M. A. Taye)
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Taye and his colleagues have previously invoked the concept of a “Brownian ratchet” to calculate the velocity, efficiency, and overall performance of a molecular heat engine. Here, a particle (the motor) changes position through thermal motion according to a mechanism that forces an otherwise randomly moving object to travel in one direction only.
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Now Taye and his group provide a complete analytical solution to their model equations, that allows them to calculate the system’s performance at every time along the way. Doing so provides a way to examine how the ratchet arrangement impacts the motor’s efficiency and velocity. They also show that a motor operating in a heat bath with gradually decreasing temperature can lead to higher velocity but lower efficiency compared to a system with fixed hot and cold baths—another tool for manipulating the motor’s movement.
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This finding provides a framework for studying the thermodynamic features of protein-based molecular motors and other micro- and nano-scale systems known to convert chemical energy into mechanical motion. It offers a way of transporting a particle to a desired location in a network at a speed that depends on the arrangement of the ratchets.
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