Abstract
Electronic Textiles (e-textiles) should ideally be handled and cleaned like traditional textiles. Therefore, we can expect e-textiles to be machine washed or hand washed. As e-textiles enhance traditional fabrics with electronic functionality, any embedded microsystem i.e., flexible electronic circuits, will be expected to survive and show functionality after the e-textile has been washed multiple times to ensure the garment is practical. Therefore, the choice of encapsulation material for microsystems in a textile must be hydrophobic and offer minimal expansion when washed and ensure the electronics are undetectable when the textile is handled or cleaned. This paper evaluates five different base/curing agent mixing ratios—5:1, 7:1, 10:1, 15:1, and 20:1—of commercial polydimethylsiloxane (PDMS) as an electronic packaging encapsulation. Contact angle and aqueous permeability experiments were conducted to tailor the PDMS mixture specifically for washable e-textile applications. The experimental results show that 20:1 PDMS is the most suitable as it is sufficiently hydrophobic with minimal swelling in commercial washing machine trials. Following this, a 40.3 µm-thick 20:1 conformal encapsulation of PDMS upon an touch and proximity flexible circuit that can be integrated into textiles via knitting and/or weaving, was examined. Results show the washing spin speed is a crucial factor with washing cycle duration having minimal impact when determining circuit functionality survival. Overall, the e-textiles in this work survived between 10 and 15 washes with microscopic inspection of the circuits revealing failure of the external wires but not the PDMS encapsulation—suggesting its sufficient robustness and durability as a suitable encapsulation material for washable electronic textiles.
Highlights
Polydimethylsiloxane (PDMS) is an organic polymer commonly used in the bioscience field for microfluidics (Fujii 2002) and in situ microelectronics (Mark and Pan 1982)
Literature reports microsystems integrated into textiles but not packaging the entire system for hydrophobic purposes to protect it from water, detergent, and fabric conditioner solutions
This paper explored the relationship between PDMS crosslinking and its hydrophobicity and permeability to aqueous solvent solutions specific to textile washing
Summary
Polydimethylsiloxane (PDMS) is an organic polymer commonly used in the bioscience field for microfluidics (Fujii 2002) and in situ microelectronics (Mark and Pan 1982). If electronic textiles (e-textiles,) formed by electronic circuits integrated into textiles at yarn-level are to be considered functional, safe, and durable for use they need to survive a sufficient number of washing cycles to be considered robust (Wainwright 2016). It would be added maintenance for consumers to remove all electronic components from an e-textile before washing. The intention of the washing test is to investigate PDMS as an e-textile circuit encapsulation—for example, when cleaned using a washing machine and/or handwashing with detergent and fabric conditioner. This paper includes the initial PDMS mixing ratio experimental investigation on how a capacitive proximity and touch sensory circuit—with the experimentally-verified PDMS mixing ratio—was embedded into a textile to take part in a washing test
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