Abstract
In this study, a novel method based on the transfer of graphene patterns from a rigid or flexible substrate onto a polymeric film surface via solvent casting was developed. The method involves the creation of predetermined graphene patterns on the substrate, casting a polymer solution, and directly transferring the graphene patterns from the substrate to the surface of the target polymer film via a peeling-off method. The feature sizes of the graphene patterns on the final film can vary from a few micrometers (as low as 5 µm) to few millimeters range. This process, applied at room temperature, eliminates the need for harsh post-processing techniques and enables creation of conductive graphene circuits (sheet resistance: ~0.2 kΩ/sq) with high stability (stable after 100 bending and 24 h washing cycles) on various polymeric flexible substrates. Moreover, this approach allows precise control of the substrate properties such as composition, biodegradability, 3D microstructure, pore size, porosity and mechanical properties using different film formation techniques. This approach can also be used to fabricate flexible biointerfaces to control stem cell behavior, such as differentiation and alignment. Overall, this promising approach provides a facile and low-cost method for the fabrication of flexible and stretchable electronic circuits.
Highlights
Conventional methods such as chemical vapor deposition (CVD) can fabricate low-cost and large-scale graphene films on metal substrates at high growth temperatures (300–1000 °C), and the graphene is subsequently transferred to the substrate of interest[23,24,25,26,27]
Most polymer-based transfer methods are an intermediate step between the donor and receiver substrates and use sacrificial polymer carrier layers mostly limited by poly(methyl methacrylate) (PMMA) or PDMS stamping[46,47,48], etching[48,49], hot lamination/delamination[38,49,50], or electrochemical bubbling[51] to transfer the graphene patterns to the target substrate
The method consists of three main steps; (i) Preparation of graphene-based patterns/films via channel filling, ink-jet printing or CVD on rigid or flexible substrates/molds; (ii) Casting of the target substrate polymer solution on the graphene-based patterns/films formed on substrates/ molds; (iii) Drying of the solvent and formation of films followed by peeling off the films from the substrate/ mold, transferring the graphene pattern from substrate/mold surface to the target polymeric film surface
Summary
Conventional methods such as chemical vapor deposition (CVD) can fabricate low-cost and large-scale graphene films on metal substrates at high growth temperatures (300–1000 °C), and the graphene is subsequently transferred to the substrate of interest[23,24,25,26,27]. Our method consists of two main steps; (i) the formation of graphene patterns/films on substrates/molds via conventional methods such as CVD, channel filling or ink-jet printing and (ii) direct casting of target substrate polymer solution on the graphene patterned substrates/molds and direct transfer of graphene patterns to the target substrate via peeling off upon drying and film formation This makes our method versatile allowing the use of different polymers including natural/synthetic, biodegradable/non-biodegradable polymers (such as Poly-L-Lactic Acid (PLLA), Cellulose Acetate (CA), Gelatin (GEL), Poly Lactic-co-Glycolic Acid (PLGA) or Whey Protein Isolate (WPI)) with well-defined characteristics and provides precise control of 3D microstructural and mechanical properties (such as film porosity, pore size, elasticity etc.) of the target substrate material with high resolution graphene patterns (feature dimensions of ~5 μm width/depth). The use of this new room-temperature facile method to fabricate biodegradable, biocompatible, flexible, and electrically-conductive graphene circuits could pave the way for various applications including tissue engineering, robotics, implantable heart sensors, brain-computer interfaces, or low-cost wearable sensors[56,57,58]
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