Boron nitride

Iron(III)
chloride hexahydrate (reagent grade,
≥98%), iron(II) chloride tetrahydrate (p.a. ACS reagent), cobalt(II)
chloride hexahydrate (reagent grade, ≥98%), ethylene glycol
(anhydrous 98%), HMTA (reagent grade, 99%), methylene blue (reagent
grade), ethanol (HPLC grade), and boron nitride (reagent grade) were
supplied by Sigma-Aldrich. Sodium acetate (extra pure >99%) and
Durapore
0.45 μm PVDF membrane were supplied by Merck. Ethylenediamine
(>99%) was supplied by Merck-Schuchardt. Sodium hydroxide (reagent
grade) was supplied by Fisher Scientific. MP H₂O (Millipore
water) was obtained using a Synergy 185 Millipore filtration system
equipped with a 0.22 μM filter that was filtering distilled
water. Technical grade solvents (>99%; ethanol, methanol, and acetone)
supplied by Lennox were used for washing and storage.

Iron(lll) chloride hexahydrate,
reagent grade ≥98%; manganese(ll) chloride tetrahydrate, reagent
grade ≥98%; ethylene glycol, anhydrous 98%; methylene blue,
reagent grade; ethanol, HPLC grade; and boron nitride, reagent grade
were supplied by Sigma-Aldrich. The Durapore 0.45 μm PVDF membrane
was supplied by Merck. Ethylenediamine, >99% was supplied by Merck-Schuchardt.
Sodium hydroxide, reagent grade was supplied by Fisher Scientific.
MP H₂O (Millipore water) was acquired through a Synergy
185 Millipore filtration system employing a 0.22 μM filter designed
for purifying distilled water. Technical-grade solvents, >99% pure
(ethanol, Methanol, and Acetone), provided by Lennox, were utilized
for washing and storage purposes.

β-Nickel hydroxide powder (>95% 283622), magnesium hydroxide (95% 310093), copper hydroxide (289787), talc (243604), boron nitride (255475) and sodium cholate were purchased from Sigma Aldrich. gallium sulphide was purchased from American Elements (99.999% GaS-05-P). De-ionized water was prepared in house and all solvents used were purchased with the highest available purity.

Boron nitride (BN) and an ionic liquid ([EMIM][BF₄]) were purchased from Sigma Aldrich (USA). A ~3 wt % CNF aqueous dispersion was purchased from the University of Maine (Orono, ME, USA). The width and length of the CNF were ~50 nm and several μm, respectively.

The fabrication steps for the formulations employed and the rationale for their use can be found elsewhere [8 (link)]. The PCM (n-Nonadecane, Sigma-Aldrich, St. Louis, MO, United States) was melted using a water bath and then mixed with Part A (resin) of EpoFix (Struers Inc., Cleveland, OH, United States) using a dual asymmetric speed mixer (Flacktek, Landrum, SC, United States). The thickening agent (Carbopol, Sigma-Aldrich, St. Louis, MO, United States) was then added, followed by the thermally conducting fillers, carbon nanofibers (CNF, 2 wt.%) and boron nitride (BN, 10 wt.%) particles, both of which were procured from Sigma Aldrich. Part B (hardener) of the EpoFix was finally added to the mixture, and the formulation was left to cure at room temperature in flexiform molds for 24 h (Struers, Inc. Cleveland, OH, United States). The samples containing CNF and BN powders were designated as EC-PCM40-CNF2 and EC-PCM40-BN10, respectively. The sample preparation steps for the specimen without thermally conductive fillers, designated as EC-PCM40, were identical than for the other formulations except the filler addition. Detailed sample formulations are presented in Table 1.