Robust rotation of rotor in a thermally driven nanomotor

Abstract

In the fabrication of a thermally driven rotary nanomotor with the dimension of a few nanometers, fabrication and control precision may have great influence on rotor's stability of rotational frequency (SRF). To investigate effects of uncertainty of some major factors including temperature, tube length, axial distance between tubes, diameter of tubes and the inward radial deviation (IRD) of atoms in stators on the frequency's stability, theoretical analysis integrating with numerical experiments are carried out. From the results obtained via molecular dynamics simulation, some key points are illustrated for future fabrication of the thermal driven rotary nanomotor.

Figure 1. Schematic of symmetrically geometric model of a thermal driven rotary nanomotor ((n_R, m_R)/(n_S, m_S)) formed by two stators (L- and R-Stator with the same chirality) and a rotor.

All tubes are carbon nanotubes. (a) The initial distance between neighbor ends of L-Stator and rotor is a, whose value is ~0.248 nm in this model. The length of each stator is b, which is ~0.495 nm. G_S is the gap between two stators. L_R is the axial length of rotor, which could be different in different models. (b) To drive the rotation of rotor, we adjust the positions of some end carbon atoms on R-stator with “A-type” inward radial deviation, which satisfies Δd = 2e × l_c-c = 0.284 e (nm). Dimensionless parameter “e” is called relative radial deviation of IRD atom. All IRD atoms have the same value of e in (0, 0.6) in simulations. Δr is the radii difference between rotor and stator. N is the number of IRD atoms on each stator.

Figure 2. Dynamic response of motor (9, 9)/(14, 14) with L_R = 8.1164 nm, a = ~0.248 nm, G_S = L_R-2a-2b, N = 1 and e = 0.4 at different temperature.

(a) History curves of rotational frequency of rotor at temperature below 475 K. (b) Stable rotational frequency v.s. temperature. (c) History curves of rotational frequency of rotor at temperature above 475 K. (d) Configurations before and after collapse of the motor at 500 K (blue line in (c), see Movie 1).

Figure 3. Comparison between rotation of motor (9, 9)/(14, 14) with the same stators but different-length of rotors.

(a) Initial models of motor. (b) Rotational frequency history of rotors. (c) Configurations of rotor with λ = 1.8 during rotating (see Movie 2, Movie 3).

Figure 4. Dynamic response of Motor (9, 9)/(14, 14) with L_R = 8.1164 nm, G_S = L_R-2a-2b, N = 1 and e = 0.4 at 300 K.

(a) Initial models of motor. (b) Rotational frequency histories of rotors.

Figure 5. Dynamic response of motor (n_R, m_R)/(14, 14) with L_R = ~8.116 nm, a = ~0.248 nm, G_S = L_R-2a-2b, N = 1 and e = 0.4 at 300 K.

(a) Initial models of motor, the diameter difference between rotor and stator varies from ~0.73 nm of (11, 6) to ~0.61 nm of (10, 9), monotonously. (b) Rotational frequency histories of rotors. The diameter of (14, 14) stator is ~1.898 nm.

Figure 6. Dynamic response of motor (n_R, n_R)/(n_S, n_S) with n_S-n_R = 5; L_R = 8.1164 nm; a = ~0.248 nm; G_S = L_R-2a-2b; N = 1; e = 0.4; at 300 K and the rotor without hydrogenation.

(a) Initial models of the motor. (b) History of rotational frequency of rotors. (c) Fitting function between SRF of the rotor and the chirality parameter of stator, n_S.

Figure 7. Histories of rotational frequency of rotor, which is driven by the stator with different IRD.

(a) e is in [0.15, 0.56]. (b) e is in [0.02, 0.12]. (c) Statistics result of SRF of rotor in [8, 10]ns (e ≥ 0.15) or in [80, 100] ns with respect to e ≤ 0.12.