To the resulting suspension, 1000 mg of octadecane (Sigma Aldrich) was added and melted in a 40 °C water bath and sonicated using the same probe for 3 minutes continuously at an amplitude of 30%. A dark emulsion was formed which is stable (i.e., no visual phase separation) for ~6 months. Emulsion droplets were sized using laser diffraction (Malvern MasterSizer 3000). For further analysis, the resulting emulsion was freeze-dried for 24 h forming a black powder. The energy storage properties and melting temperatures were determined using differential scanning calorimetry (DSC, TA Instruments Discovery DSC), scanning from 10 °C → 60 °C at a rate of 1 °C min -1 in a sealed alumina pan under nitrogen flow. The thermal stability of the capsules was determined by thermogravimetric analysis (TGA, TA Instruments) from 20 °C → 300 °C at a rate of 10 °C min -1 under a nitrogen flow. For scanning electron microscopy (SEM, JSM-7001F JEOL) capsules were suspended in ethanol and dried directly onto an SEM stub. Raman spectroscopy (InVia Renishaw) was performed using a 532 nm laser to assess the formation of products.