Thermally Driven Elastic Micromachines

Abstract

We discuss the directional motion of an elastic three-sphere micromachine in which the spheres are in equilibrium with independent heat baths having different temperatures. Even in the absence of prescribed motion of springs, such a micromachine can gain net motion purely because of thermal fluctuations. A relation connecting the average velocity and the temperatures of the spheres is analytically obtained. This velocity can also be expressed in terms of the average heat flows in the steady state. Our model suggests a new mechanism for the locomotion of micromachines in nonequilibrium biological systems.Comment: 5 pages, 2 figure

Hydrodynamic Interaction between Two Elastic Microswimmers

“…Hence, the mean of v L and v R is again given by Eq. (18) in which V 0 is replaced by v 0 . As mentioned in the previous section, both v L and v R are proportional to Ω.…”

Nonequilibrium probability flux of a thermally driven micromachine

“…For a thermally driven micromachine, however, ℓ is taken to be a constant and characterizes the size of the micromachine [14]. We consider a situation in which the three spheres are in thermal equilibrium with independent heat baths at temperatures T i (i = 1, 2, 3) [14]. When these temperatures are different, the system is inevitably driven out of equilibrium because heat flux from a hotter sphere to a colder one is generated.…”

“…In contrast to Ref. [14], we do not take into account hydrodynamic interactions acting between different spheres in the above equations. Hence, the locomotion of a micromachine is not explicitly considered in this paper, but they are sufficient for the statistical analysis.…”

“…In such a situation, heat transfer occurs inside the micromachine from a hotter sphere to a colder one, driving the whole system out of equilibrium. We have shown that a combination of heat transfer and hydrodynamic interactions among the spheres can lead to directional locomotion in a steady state [14]. Our model has a similarity to a class of ther- * komura@tmu.ac.jp mal ratchet models [15][16][17], and the suggested new mechanism is relevant to non-equilibrium dynamics of proteins and enzymes in biological systems [18,19].…”

“…In this paper, we do not take into account hydrodynamic interactions acting between different spheres. cal mechanics of a thermally driven micromachine consisting of three spheres and two harmonic springs [14]. The main aim of this work is to obtain the steady state conformational distribution function of such a micromachine and calculate its probability flux in the corresponding mode space.…”