An official website of the United States government
Solution-phase printing of exfoliated graphene flakes is emerging as a low-cost means to create flexible electronics for numerous applications. The electrical conductivity and electrochemical reactivity of printed graphene has been shown to improve with post-print processing methods such as thermal, photonic, and laser annealing. However, to date no reports have shown the manipulation of surface wettability via post-print processing of printed graphene. Herein, we demonstrate how the energy density of a direct-pulsed laser writing (DPLW) technique can be varied to tune the hydrophobicity and electrical conductivity of the inkjet-printed graphene (IPG). Experimental results demonstrate that the DPLW process can convert the IPG surface from one that is initially hydrophilic (contact angle ∼47.7°) and electrically resistive (sheet resistance ∼21 MΩ □ −1 ) to one that is superhydrophobic (CA ∼157.2°) and electrically conductive (sheet resistance ∼1.1 kΩ □ −1 ). Molecular dynamic (MD) simulations reveal that both the nanoscale graphene flake orientation and surface chemistry of the IPG after DPLW processing induce these changes in surface wettability. Moreover, DPLW can be performed with IPG printed on thermally and chemically sensitive substrates such as flexible paper and polymers. Hence, the developed, flexible IPG electrodes treated with DPLW could be useful for a wide range of applications such as self-cleaning, wearable, or washable electronics.
more »
« less
All-graphene-based open fluidics for pumpless, small-scale fluid transport via laser-controlled wettability patterning
Open microfluidics have emerged as a low-cost, pumpless alternative strategy to conventional microfluidics for delivery of fluid for a wide variety of applications including rapid biochemical analysis and medical diagnosis. However, creating open microfluidics by tuning the wettability of surfaces typically requires sophisticated cleanroom processes that are unamenable to scalable manufacturing. Herein, we present a simple approach to develop open microfluidic platforms by manipulating the surface wettability of spin-coated graphene ink films on flexible polyethylene terephthalate via laser-controlled patterning. Wedge-shaped hydrophilic tracks surrounded by superhydrophobic walls are created within the graphene films by scribing micron-sized grooves into the graphene with a CO 2 laser. This scribing process is used to make superhydrophobic walls (water contact angle ∼160°) that delineate hydrophilic tracks (created through an oxygen plasma pretreatment) on the graphene for fluid transport. These all-graphene open microfluidic tracks are capable of transporting liquid droplets with a velocity of 20 mm s −1 on a level surface and uphill at elevation angles of 7° as well as transporting fluid in bifurcating cross and tree branches. The all-graphene open microfluidic manufacturing technique is rapid and amenable to scalable manufacturing, and consequently offers an alternative pumpless strategy to conventional microfluidics and creates possibilities for diverse applications in fluid transport.
more »
« less
- PAR ID:
- 10205849
- Date Published:
- Journal Name:
- Nanoscale Horizons
- ISSN:
- 2055-6756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Although continuous and non‐invasive measurements of sweat biomarkers may provide vital health information, sweat collection often involves intense physical activities or chemical/thermal stimuli. The natural body sweat during endogenous metabolic or stress processes, secreted at much lower rates at rest, may be continuously analyzed using microfluidic devices integrated with hydrophilic rigid fillers; however, the sweat uptake and accumulation in thermoregulatory processes take too long for near‐real‐time measurements. This work provides an innovative body fluid collection strategy using a granular hydrogel scaffold (GHS), facilitating osmotic and capillary effects to uptake and transfer an ultralow amount of sweat into a microfluidic device at rest. Taken together with a spiral microfluidic channel, the GHS‐embedded microfluidics reduce the evaporation of collected sweat and store it in a sensing well for near‐real‐time measurements. Integrating the sweat‐collecting system with an enzymatic gold‐graphene nanocomposite‐modified laser‐induced graphene (LIG) electrode and a LIG‐based pH sensor enables the accurate continuous on‐body detection of sweat lactate during normal daily activities at a low perspiration rate. The novel combination of a GHS‐integrated microfluidic system with a low‐cost, flexible, sensitive, and stable LIG‐based sensing system provides an accessible technology for sweat‐based biosensing during normal daily activities.more » « less
-
Dichtel, William R. (Ed.)The ability of lotus leaves to repel water is desired in numerous applications, such as self-cleaning surfaces, biomedical devices, and naval vessels. Creating materials that mimic the hierarchical structure and surface chemistry of lotus leaves requires multistep processes that are impractical for the mass production of nonwettable products. Superhydrophobic surfaces have been created using graphene. However, graphene sheets obtained through graphite exfoliation or deposition on substrates are not superhydrophobic and require additional processes to achieve lotus-like water repellency. In this work, we show that graphene produced in the gas phase is inherently superhydrophobic. Gas-phase-synthesized graphene (GSG) and lotus leaves have fundamentally different structures, yet water droplets on both materials exhibit comparable contact angles, roll-off angles, and bouncing characteristics. Furthermore, hydrophilic surfaces become superhydrophobic when covered with GSG. The substrate-free synthesis of GSG is straightforward and sustainable, which could enable the manufacturing of a diverse range of water-repellent technologies.more » « less
-
We developed an open microfluidic system to dispense and manipulate discrete droplets on planar plastic sheets. Here, a superhydrophobic material is spray-coated on commercially-available plastic sheets followed by the printing of hydrophilic symbols using an inkjet printer. The patterned plastic sheets are taped to a two-axis tilting platform, powered by stepper motors, that provides mechanical agitation for droplet transport. We demonstrate the following droplet operations: transport of droplets of different sizes, parallel transport of multiple droplets, merging and mixing of multiple droplets, dispensing of smaller droplets from a large droplet or a fluid reservoir, and one-directional transport of droplets. As a proof-of-concept, a colorimetric assay is implemented to measure the glucose concentration in sheep serum. Compared to silicon-based digital microfluidic devices, we believe that the presented system is appealing for various biological experiments because of the ease of altering design layouts of hydrophilic symbols, relatively faster turnaround time in printing plastic sheets, larger area to accommodate more tests, and lower operational costs by using off-the-shelf products.more » « less
-
Laser Induced Deep Etching (LIDE®), developed by LPKF, is a maskless laser processing method capable of patterning glass microstructures similar to microfluidics created by PDMS soft lithography. Here, we demonstrate a self-digitized droplet microfluidics chip with high aspect-ratio features and fine resolution via the LIDE® technology. LIDE® provides the means to translate microfluidic designs into glass in a process suitable for low-cost and high-volume manufacturing.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D0NH00376J
