# Intrinsic energy conversion mechanism via telescopic extension and retraction of concentric carbon nanotubes

## TL;DR

This study reveals an intrinsic, thermodynamically reversible energy conversion mechanism in double-walled carbon nanotubes, where thermal energy can be converted into mechanical work through telescopic motion, with potential nanodevice applications.

## Contribution

The paper uncovers a new reversible energy conversion process in DWCNTs driven by entropy changes, advancing understanding of nanotube mechanics and energy transduction.

## Key findings

- DWCNTs can convert heat into mechanical work during extension.
- The process is thermodynamically reversible.
- Entropy effects influence telescopic motion and can induce extrusion at high temperatures.

## Abstract

The conversion of other forms of energy into mechanical work through the geometrical extension and retraction of nanomaterials has a wide variety of potential applications, including for mimicking biomotors. Here, using molecular dynamic simulations, we demonstrate that there exists an intrinsic energy conversion mechanism between thermal energy and mechanical work in the telescopic motions of double-walled carbon nanotubes (DWCNTs). A DWCNT can inherently convert heat into mechanical work in its telescopic extension process, while convert mechanical energy into heat in its telescopic retraction process. These two processes are thermodynamically reversible. The underlying mechanism for this reversibility is that the entropy changes with the telescopic overlapping length of concentric individual tubes. We find also that the entropy effect enlarges with the decreasing intertube space of DWCNTs. As a result, the spontaneously telescopic motion of a condensed DWCNT can be switched to extrusion by rising the system temperature above a critical value. These findings are important for fundamentally understanding the mechanical behavior of concentric nanotubes, and may have general implications in the application of DWCNTs as linear motors in nanodevices.