Measurement of THF clathrate hydrate nucleation

The THF clathrate hydrate nucleation temperature (T) and delay time (t_D) were measured in a sealed sample cell consisting of a glass O-ring (height 1.5 mm, inner diameter changed from 2.5 to 5 mm) sandwiched between one glass substrate with anchored GO nanosheets (metal nanocubes) and one optical microscope cover glasses by the UV fast cure glue. Inside the closed cell, 3.5 μL THF/water mixture was dropped atop the modified glass substrate anchored with GO nanosheets (metal nanocubes) of different lateral sizes. The entire preparation of the sample cell was carried out in a Class II Type A2 biosafety cabinet to avoid contamination. Then the closed cell was placed atop a cryo-stage (Linkam LTS420) and the cryo-stage was calibrated as outlined in Ref. ⁶³. The formation of THF clathrate hydrate and ice was observed through an optical microscopy. On the one hand, the temperature of the crystal morphology^44,45 first appearing, was identified as the hydrate nucleation temperature (shown in Supplementary Movie ¹); on the other hand, the temperature at which a sudden change in the opacity⁴⁶ of samples after the formation of hydrate was regarded as ice nucleation temperature. In this method, the number of nucleation sites was tuned by the GO (metal nanocube) graft density and the contact area of the THF/water sample with the substrate. Moreover, for the used nanoparticles (including melt nanocube with size large than 45 nm, and GO nanosheets with size larger than 30 nm) in this study, the calculated temperature difference between the top and bottom surfaces of the nanoparticles is within 0.03 °C. This marginal temperature difference has no impact on the statistical analysis of nucleation temperatures, consequently, does not influence the conclusions drawn from the study. The data of THF hydrate nucleation temperature are the mean with the standard error of the mean (SEM). For each mean nucleation temperature, the total number of measurements is more than 80. We follow the mentioned method to estimate the mean delay time of THF hydrate nucleation²⁹. In brief, the delay time at a certain temperature was measured as the time period elapsed from the time when the samples were cooled to a target temperature to the time when the THF clathrate hydrate nucleation occurred. We independently measured the clathrate hydrate nucleation delay time with more than 35 valid nucleation events.