Four point probe

Films were fabricated
in rectangular
PDMS molds with dimensions of 10 × 10 mm. Film thicknesses were
assessed by imaging using an Ossila contact angle goniometer and comparing
observed thicknesses, averaged across the film, with the thickness
of the glass slide beneath (known to be 1 mm).
Gels were prepared
in the PDMS molds for 24 h using the assembly protocol described above.
These were placed in a sealed container during gelation with a Milli-Q
water reservoir to prevent dehydration. Once unsealed, measurements
were immediately taken using an Ossila four-point probe and thicknesses
estimated. At least 3 measurements were made per sample for at least
3 samples per LMWG. The mean of the resulting conductivities and sheet
resistances was calculated and stated in the main text. The error
given is the standard deviation in each case, with the distribution
here assumed to be normal.

All chemicals were obtained from Sigma (Gillingham, Dorset, UK), were of analytical grade, and were used without any further purification. Paraffin wax pellets (76242) and O,O′-bis(2-aminopropyl) polypropylene glycol–block–polyethylene glycol–block–polypropylene glycol (AP-PEG) were used as phase-change materials to encapsulate the model drugs (chlorophenol red and curcumin). Britton Robinson (BR) buffer solutions were used throughout and were composed of equimolar acetic, boric, and phosphoric acids (each 0.04 M) adjusted to the required pH through the addition of sodium hydroxide. Raman spectroscopy was conducted using a Renishaw Raman Microscope (20× objective lens) with a 532 nm laser operating at 10% power. Conductivity measurements of the lasered polyimide were acquired with an Ossila Four Point Probe. A Thermo Scientific Genesys 150 dual-beam spectrometer (2 nm bandwidth) was used to acquire UV/Vis spectra. Disposable polymethyl methacrylate (PMMA) cuvettes (3 mL volume, 10 mm path length) were used throughout.

Inkjet printing was performed using an industrial flatbed Drop-on-Demand (DoD) printer with an Epson xp600 printhead on glossy photo paper (ORINK, Zhuhai, China), and Novacentrix Novele^TM precoated PET (Austin, TX, USA) and PI (d = 25 μm, Kapton, DuPont, Wilmington, NC, USA) flexible substrates. A conductive ink based on amphiphilic silver nanoparticles formulated in a glass vial was directly connected to the printer cartridge corresponding to black ink. The inkjet printing process was performed under ambient conditions.
Intense pulsed light (IPL) was used to convert the printed nanosilver pattern into a functional metallic conductor. For that purpose, printed squares were set in a Xenon X-1100 IPL system sample chamber and flashed with a Xenon LH-912 lamp source. A series of experiments were conducted at 2500 V to find the optimal flashing energy for various flexible substrates. Electrical properties were characterized by measuring the surface resistivity (sheet resistance) of the printed tracks before and after IPL processing using a Four-Point Probe (Ossila, UK).
Morphological characterization of the printed silver features on the paper and plastic substrates was evaluated using a scanning electron microscope (TESCAN Vega3 Easy Probe, Brno, Czech Republic) equipped with an energy-dispersive detector (EDS) for chemical composition analysis.