Reorientation and Flow of Liquid Crystal for a Pressure Sensor Using Carbon Nanotube Sheets

Abstract The network formation of carbon nanotubes (CNTs) and the viscoelasticity of liquid crystals (LCs) are synergetic properties that enable the formation of composites very sensitive to external pressure. Using a layered structure with nematic LCs and anisotropic networks formed by highly aligned multiwall CNT sheets, the pressure sensor capability of such structure and its piezoresistive response are demonstrated. The application of pressure on the upper substrate is transmitted via LC elastic deformation and flow onto the underlying CNT sheets, improving the electrical conductance. The fabrication process here is relatively facile and versatile as stretched CNT sheets can be easily transferred to any chosen substrate. The sensor response is linear with decrease of 2.42 Ω kPa⁻¹ as the pressure value increases and it is reversible. The sensitivity depends on the thickness of the overlying LC layer and by its relative change, affected by the spacers during force application, but also on the electrical characteristics of the CNTs. The highest sensitivity is obtained with one single CNT sheet and the responsiveness decreases with the increase of number of layers due to the smaller influence of the LC on the contact resistance of the CNT sheets.