Self-Assembly Of Nanoparticles Monolayer For The Application Of Strain Sensor

A flexible strain gauge is an essential component in advanced human-machine interfacing, especially when it comes to many important mobile and biomedical appliances that require the detection of finger touches. To promote the strain sensitivity, extend the strain regime, metal nanoparticle arrays assembled onto flexible substrates have recently been utilized as high sensitivity strain gauges. In this work, one assembly technique is initialized to fabricate parallel nanoparticle strips by precisely tailoring the contact angle of a gold colloid on a substrate. Nanoparticle monolayer with close-packed arrangement is fabricated through the method of convective assembly, which is used as the active units of the flexible strain sensor. We systematically study the relationship between the assembly procedure of nanoparticle strip and the contact angle as well as the sensing properties of the strain gauge based on a single strip of nanoparticle monolayer. The main content of this paper is divided into the following aspects:(1) The gold nanoparticles with uniform particle size, regular shape were successfully synthesized by conventional liquid phase reduction method. Meanwhile, the processes for preparing strain gauge and its performance measurement technique are introducted briefly.(2) The assembly of a nanoparticle monolayer with a close-packed pattern by convective assembly was detailly researched. It has been conviced that the contact angle of a gold colloid on a substrate could be precisely tailored, which can be characterized by wedge interference. Besides, it has also been proved that self-assembly of a NP monolayer can be switched on and off by precisely tailoring the contact angle of gold colloid on the substrates across a critical value of 4.2°. Finally, by SEM morphology characterization, we can see that the assembled monolayer gold nanoparticle arrays have almost the same gap and the gap size is distributed in the nanoscale.(3) The sensing properties of flexible strain sensor based on monolayer gold nanoparticle array are illuminated in detail. The important finding during the research is that there is a linear relationship between electrical conduction and mechanical displacement in compressive state. Meanwhile, the study confirms that the gauge could accurately track various mechanical stimuli running at the frequencies of interest, which is firstly reported although many kinds of strain gauges have been investigated in the references. In addition, experiments have confirmed that the proposed strain gauge has a strain detection limit as low as 9.4 × 10-5, and its gauge factor can be as large as 70, making this device particularly suitable for sensitive finger touch sensing. Furthermore, negligible degradation in the gauge's output electrical signal is observed even after 9000 loading/unloading cycles.