Spatiotemporally controllable acoustothermal heating and its application to disposable thermochromic displays

Polydimethylsiloxane, the most common microchannel material, effectively absorbs acoustic waves and converts the acoustic energy into thermal energy. Here, we quantitatively characterize this phenomenon and develop a heating platform that offers spatiotemporal temperature control in two dimensions. We demonstrate the use of this heating platform to innovate thermochromic displays (TCDs). A TCD comprises a display layer covered with a thermochromic substance and a heater attached to the bottom of the display layer. The thermochromic substance is opaque at room temperature and becomes translucent when heated beyond a transition temperature. Consequently, the TCDs deliver visual information concealed beneath the thermochromic substance by controlling the temperature of the display layer. The previously reported TCDs have limitations including restricted flexibility in display information and cumbersome spatiotemporal temperature control. We address these limitations by developing a disposable TCD system using our spatiotemporally controllable heating platform. The utility of the proposed system is demonstrated in shutter-type TCDs for coloured, intricate picture displays, as well as in segment-type TCDs for on-demand information displays of alphanumeric characters. Finally, we propose a new type of TCD that can represent colour gradients based on the ability of the heating technique to generate free-form, continuous temperature gradients.