The hydrophobic ink used in this study
was prepared using fumed silica with an average nanoparticle size
of 16 nm, epoxy resin (poly bisphenol A-co-epichlorohydrin,
Sigma-Aldrich, South Korea), reagent (2-butoxyethanol, Sigma-Aldrich,
South Korea), and a curing agent (4,4′-methylene bis (2-chloroaniline),
Sigma-Aldrich, South Korea). Initially, a silica solution was created,
mixing 0.45 g of fumed silica (Aerosoil R 972, Evonik Industry, Germany)
and 9.42 g of 2-butoxyethanol with a magnetic stirrer at room temperature
for 8 h. A separate epoxy resin solution was formed by mixing 0.50
g of epoxy resin pellets, 0.08 g of curing agent, and 9.55 g of 2-butoxyethanol
with a magnetic stirrer at 70 °C for 8 h. Subsequently, the silica
and epoxy resin solutions were combined in an equal volume ratio (50%
by volume) and mixed for an additional 1 h at room temperature. The
resulting solution was then sonicated in an ultrasonic bath for 5
min to ensure a thorough mixture. The formulated solution had a viscosity
of 11 cP and a surface tension of 23.17 mN/m as measured by a viscometer
(DV -III Ultra, Brookfield, USA) at 10 rpm and a surface tension analyzer
(SEO-DST30M, SEO, South Korea), respectively.
was prepared using fumed silica with an average nanoparticle size
of 16 nm, epoxy resin (poly bisphenol A-co-epichlorohydrin,
Sigma-Aldrich, South Korea), reagent (2-butoxyethanol, Sigma-Aldrich,
South Korea), and a curing agent (4,4′-methylene bis (2-chloroaniline),
Sigma-Aldrich, South Korea). Initially, a silica solution was created,
mixing 0.45 g of fumed silica (Aerosoil R 972, Evonik Industry, Germany)
and 9.42 g of 2-butoxyethanol with a magnetic stirrer at room temperature
for 8 h. A separate epoxy resin solution was formed by mixing 0.50
g of epoxy resin pellets, 0.08 g of curing agent, and 9.55 g of 2-butoxyethanol
with a magnetic stirrer at 70 °C for 8 h. Subsequently, the silica
and epoxy resin solutions were combined in an equal volume ratio (50%
by volume) and mixed for an additional 1 h at room temperature. The
resulting solution was then sonicated in an ultrasonic bath for 5
min to ensure a thorough mixture. The formulated solution had a viscosity
of 11 cP and a surface tension of 23.17 mN/m as measured by a viscometer
(DV -III Ultra, Brookfield, USA) at 10 rpm and a surface tension analyzer
(SEO-DST30M, SEO, South Korea), respectively.