The overall goal of this patterning procedure is to selectively deposit organic electroactive materials on textiles, which enables the fabrication of wearable organic electronic devices directly on clothing. This method can help to answer a key question in the field of wearable electronics, especially how to seamlessly integrate electronics with clothing to interact efficiently with the human body. The main advantage of this technique stems from elastic capability of textiles, which allows to worn this textiles comfortably in the close contact with the skin.
First an idea of this method. When we look for a nontraditional way of combining organic electronics with textiles platform in a cost-efficient and industry scalable manner. This technique was inspired by old Japanese kimono dying technique, which we adapted for today's micro-fabrication tools and environment.
To begin the procedure, use a laser cutter to cut a pre-designed electrode pattern into a 125-micrometer-thick polyamide sheet to form a mask. Then take a 300-micrometer-thick sheet of 100%interlock knit polyester fabric with a knit direction stretch capability of up to 50%Secure this to a flat, portable surface. In a fume hood, use an automatic tape casting tool to coat the polyamide mask with a polydimethylsiloxane formulation at six meters per minute to a wet film thickness of 200 micrometers.
Gently place the fabric on the PDMS-coated mask and allow the PDMS to be absorbed into the textile structure for 10 minutes. Anneal the PDMS at 100 degrees Celsius for 10 minutes or at 60 degrees Celsius for 20 minutes for heat-sensitive fabrics. In the fume hood, mix together 80 milliliters of PEDOT:PSS dispersion, 20 milliliters of ethylene glycol, 40 microliters of 4-dodecylbenzenesulfonic acid, and one milliliter of 3-propylmethacrylate.
Then place the mixture to stir on a magnetic stirrer. Brush coat the PEDOT:PSS mixture over the masked fabric until the electrode pattern is coated with about one milliliter of the mixture per centimeter squared and appears to be uniform in color. The brush coating step of PEDOT:PSS is the critical step.
The sheet resistance of the pattern needs to be about 230 ohm square. Remove the polyamide mask then cure the electrode pattern at 110 degrees Celsius for one hour or at 60 degrees Celsius for two hours for heat-sensitive fabrics. To fabricate cutaneous electrodes from PEDOT:PSS electrodes on textiles, first prepare a gel mixture composed of 60%by volume ionic liquid, 35%crosslinking agent, and 5%photoinitiator.
In a fume hood, coat the electrodes with 20 microliters per centimeter squared of the ionic liquid, and then add 25 microliters per centimeter squared of the gel mixture by drop casting. Expose the coated electrodes to 365-nanometer UV light for 10 to 15 minutes to solidify the gel and form the cutaneous electrodes. To fabricate capacitive sensors from PEDOT:PSS electrodes on textiles, in a fume hood, apply 10 to one PDMS formulation to the fabric.
Use a squeegee to evenly spread the PDMS formulation over the electrodes to remove any excess. Anneal the insulating layer of the PDMS at up to 100 degrees Celsius for at least 10 minutes, depending on the heat tolerance of the fabric, to form the capacitive sensors. Using this method, PEDOT:PSS electrodes were patterned on knit and woven textiles.
The patterning resolution of knitted polyester is greater than one millimeter. Narrower resolutions can be obtained on tightly knit or woven textiles. The electrodes patterned on knit textiles function as stretch sensors with no further modifications.
When the fabric is stretched, the twisting of the conductive fibers results in a change in the resistivity. An organic electrochemical transistor array was patterned onto a woven nylon ribbon, a wearable sweat sensor, also with no further modifications. The addition of an ionic liquid in gel allowed the electrodes to function as wearable cutaneous electrodes for electro-physiological monitoring.
Alternatively, the addition of an insulating PDMS layer created capacitor sensors. Touching the electrodes causes a capacitance change, allowing fabrication of a wearable keyboard. The combination of close-fitting textiles with organic and soft electrodes offers an improved communication channel with the human body while compared to the traditional solid-state electronic device.
This method allows for the future customization of existing garments with the smart electronic devices. However, one of the critical and in some cases limiting points of this technology is that materials, organic materials'durability and wearable conditions.
