A Versatile Approach for Direct Patterning of Liquid Metal Using Magnetic Field

Abstract

Patterning of liquid metal (LM) is usually an integral step toward its practical applications. However, the high surface tension along with surface oxide makes direct patterning of LM very challenging. Existing LM patterning techniques are designed for limited types of planar substrates, which require multiple-step operation, delicate molds and masks, and expensive equipment. In this work, a simple, versatile, and equipment-free approach for direct patterning of LM on various substrates using magnetic field is reported. To achieve this, magnetic microparticles are dispersed into LM by stirring. When a moving magnetic field is applied to the LM droplet, the aggregated magnetic microparticles deform the droplet to a continuous line. In addition, this approach is also applicable to supermetallophobic substrates since the applied magnetic field significantly enhances the contact between LM and substrate. Moreover, remote manipulation of the magnetic microparticles allows direct patterning of LM on nonplanar surfaces, even in a narrow and near closed space, which is impossible for the existing techniques. A few applications are also demonstrated using the proposed technique for flexible electronics and wearable sensors.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201901370. used for the other liquids. Therefore, it is challenging to directly pattern LM using some well-established printing strategies such as inkjet or screen printing.Various LM patterning techniques have been developed in the past few years based on microfluidic injection, [11] selective wetting, [2d,12] LM suspensions printing, [13] stencil lithography, [14] reductive printing, [15] imprint lithography, [16] selective mechanical sintering, [17] laser patterning, [18] microcontact printing, [19] and three-dimensional (3D) printing. [20] However, the reported techniques involved multiple-step operation, additional pretreatment of substrate, post sintering, delicate molds and masks, tedious microfabrication process, as well as sophisticated equipment. These not only complicated the fabrication but also increased the cost. Besides, each of these reported techniques was designed for a specific substrate, which limited the widespread applications of LM. Due to low adhesion, it is rather difficult to directly pattern LM or transfer the existing LM patterns onto supermetallophobic substrates, on which the contact angle of an LM droplet exceed 150°. In addition, most existing patterning techniques were limited to planar substrates. 3D patterning of LM remains rather challenging, which involved sophisticated facilities (e.g., pressure pump, translation stage) and additional encapsulation and fixation steps for practical applications. [20a] Thus, developing a simple, versatile, and equipment-free LM patterning technique for various planar and nonplanar substrates is highly desired to broaden the applications of LM.It has been reported that magnetic actuation can be used for LM manipu...

Liquid Metal–Based Soft Microfluidics

“…Directly writing [36,77,79] Injection [40] Selective plating [90,91] Magnetic field patterning [92] Electric field patterning [95] Laser patterning [68] Resolution…”

“…Then, the LM pattern is directly drawn using magnetic field from a magnet on various substrates, as shown in Figure 13a. [92] This method is also effective for supermetallophobic substrates because the magnetic field enhances the adhesion of the pattern. The magnetic field patterning method does not require modification of the substrate, and can be performed on the surface of a curved, thin (e.g., egg shell, glass bottle, see Figure 13b), hard and soft substrates alike, solving the drawbacks of conventional LM patterning methods, which are mostly limited to planar elastomer substrates.…”

“…b) Optical images of the LM patterns on different substrates, including hydrogel, egg shell, and curved glass bottle. Reproduced with permission [92]. Copyright 2019, John Wiley and Sons.…”

Wearable and Stretchable Strain Sensors: Materials, Sensing Mechanisms, and Applications

“…The dominant working principle of the liquid metal-based stretchable strain sensors is the geometrical effect. [167][168][169][170][171] In the following sections, it will be shown that the contribution of this mechanism to the overall sensing performance of nanomaterials-based stretchable sensors may not be significant.…”

Liquid Metal Direct Write and 3D Printing: A Review

“…Loading nickel particles also enables modulation of liquid metals by a magnetic field shown in the schematic of Figure 5d. [78] This image also shows a resulting patterned circuit from this process lighting up LEDs. This can be used to enable patterning of liquid metal on unique surface that ordinarily would not be wet by direct write.…”