Water Transfer Printing Enhanced by Water‐Induced Pattern Expansion: Toward Large‐Area 3D Electronics

Abstract

flexible electronics have demonstrated extreme bendability. [21,22] Even so, wrinkles and folds are inevitable when wrapping flexible sheets on 3D surfaces with two nonzero principal curvatures. A recently developed curved image array demonstrated that selectively cutting the flexible sheet can effectively reduce folding and wrinkling when conforming it to a 3D surface. [23] On the other hand, stretchable electronics enabled by stretchable serpentine interconnects, [24,25] liquid metal, [26] nanomeshes [27] and nanoscrolls, [28] or intrinsically stretchable conductive and semiconducting polymers [29][30][31][32] are able to not only bend but also expand inplane, hence capable of conforming to 3D surfaces such as spherical domes. But so far, there are limited studies on the conforming process, especially when the target object has a complex 3D surface. Except for conforming planar electronics to 3D surfaces, direct printing of electrical components on 3D surfaces has been demonstrated. [33] However, only limited materials such as conductive inks and devices such as 3D antenna can be printed so far. As a result, simple but versatile transferring techniques are in need for conformable electronics.Water transfer printing (WTP) technology, also known as hydrographic printing, is commonly used to transfer planar graphics to 3D surfaces. [34] The process begins by printing graphics on a water-soluble substrate, which is then placed on water surface. As the substrate gets dissolved by water, the ultrathin graphics layer stays floating on water. A solid Perfectly wrapping planar electronics to complex 3D surfaces represents a major challenge in the manufacture of conformable electronics. Intuitively, thinner electronics are easier to conform to curved surfaces but they usually require a supporting substrate for handling. The water transfer printing (WTP) technology utilizes water surface tension to keep ultrathin electronics floating flat without supporting substrate, enabling their conformal transfer on 3D surfaces through a dipping process. In many cases, however, the size of the microfabricated electronics is much smaller than the target 3D surface. This work proposes that such mismatch in size can be overcome by leveraging stretchable electronics in WTP. Stretchable electronics are compliant to inplane stretch induced by water surface tension, hence can first self-expand in water and then be transferred onto 3D objects. Uniaxial and biaxial expansion ranging from 41% to 166% has been achieved without any externally applied tension. The results demonstrate that expansion-enhanced WTP is a promising fabrication process for conformable electronics on large 3D surfaces.

A Facile Fabrication and Transfer Method of Vertically Aligned Carbon Nanotubes on a Mo/Ni Bilayer for Wearable Energy Devices

“…Once the VACNTs are successfully synthesized, a water soluble tape is applied to the VACNTs. [ 25 ] The entire 3D nanostructure (i.e., VACNTs on the Mo/Ni bilayer) can be easily detached from the substrate using a water‐soluble tape due to the weak adhesion between the Ni layer and the SiO 2 substrate (Figure S1, Supporting Information), the picked‐up 3D nanostructure is transferred onto a selected soft substrate, and the water soluble tape is removed.…”

Wireless Epidermal Electromyogram Sensing System

“…The fabricated metal electrode was transfer-printed on a soft and stretchable PDMS substrate with tens of micrometer thickness to implement stretchable and skin-attachable EMG sensors that Stretchable electronics that are implemented on soft and stretchable elastomeric substrates can be applicable to wearable sensor applications that can be worn or attached to the human body since the mechanical properties of the devices are similar to that of the human skin, allowing long-term use without any side effects such as feeling of irritation or inflammation when used . Manufacturing technologies of these stretchable devices are almost compatible with conventional microfabrication for silicon-based electronics, and for this reason, it has been possible to implement various stretchable and wearable system on soft and stretchable elastomer substrate by using transfer printing method after being processed on a silicon substrate [57][58][59]. These stretchable devices can also operate safely with the elongation of the human skin during deformation .…”

A Cast Net Thrown onto an Interface: Wrapping 3D Objects with an Interfacially Jammed Amphiphilic Sheet

“…Examples include wrapping a gift in daily lives, or wrapping an electrode with a graphene sheet to accommodate volume expansion upon battery cycling . Wrapping has also been developed as a functionalization tool to endow 3D objects with desired properties, such as hydrophobicity, optical properties, or conductive properties . Most recently, the range of wrapped content has expanded to liquids, with the encapsulant being either solid elastic films or solid‐like jammed films of functional particles .…”