Design and analysis of a microfluidic colour-changing glasses controlled by shape memory alloy (SMA) actuators

In this work, a microfluidic colour-changing glasses controlled by shape memory alloy (SMA) actuators is designed and presented by circulating colour liquids in the microfluidic channels on the lens. For liquids controlling, a unidirectional NiTi SMA spring is employed to design and fabricate a simple microfluidic actuator, which can provide the maximum restoring force of 5.27 N and the fastest recovering rate of 2.71 mm/s. After the responding characteristics of the SMA controller are tested and calculated under different conditions, the pressure changes at the channel inlet are investigated in liquids circulation process for different channel designs. This liquid colour-changing glasses show fast response, rapid prototyping and high controllability compared with the traditional solid colour-changing way. Meantime, the impacts of different channel designs on response performances are validated, which can provide foundations for further optimization of the channel designs. Soft lithography technology is applied for the fabrication of the colour-changing layer made of transparent silicone PDMS (polydimethylsiloxane) instead of conventional mechanical machining. Organosilicon coating based on methyltrimethoxysilane and phenyltrimethoxysilane (PTMS) is firstly fabricated for modification of PDMS surface to increase the wear resistance of the colour-changing lens.