## 4 Discussion  
When considering the different amounts of residual gas inside the system, the above phenomenon is proof of understanding the gas behavior under finite circumstances. In general, the gas in a liquid/nanoporous system can be divided into three categories: small bubbles standing in the mixture, the gas dissolved in the liquid, and the gas trapped in pores. For the undegassed condition, although the mixture are stood in atmosphere for 12 h during pretreatment, small bubbles that were introduced in the process of mixing glycerol and zeolite powder would not surface up spontaneously, as well as the gas dissolved and the gas trapped in pores. Therefore, the three categories of gas mentioned above are all included in the undegassed system. For the degassed mixture, as has been placed in vacuum for 12 h, the small bubbles dispersing in the mixture, together with the gas dissolved in the liquid as well, could be excluded. As a consequence, only the gas residual in the nanopores could not be eliminated during degassing pretreatment. To note that after pretreatment and before sealing, when the system is taken out of the vacuum condition, air would dissolved in liquid under atmospheric pressure. Assuming that in both degassed and undegassed cases, the amount of dissolved gas in the liquid are the same and equal to the solubility of air under atmospheric pressure. Therefore, the comparative differences between the above two working conditions are very obvious: there are small bubbles in the undegassed system (referring to Figure 2a), while none in the degassed system (referring to Figure 2b). During intrusion and extrusion, the analyzed three categories of residual gas play different roles, which mainly depend on where the gas is trapped and how easily it dissolves in the liquid phase. According to [PERSON]'s study, gas molecules tend to form clusters in nanochannels less than a few nanometers, which triggers liquid defiltration at a reduced pressure [25]. Since a molecular-sized nanoscale confinement arranges the gas and the water molecules into a single-file chain inside molecular-sized nanochannels [27; 34], the radical confinement therefore provides a high resistance for molecular site exchanges [26]. Thus, the residual gas in nanopores under either undegassed or degassed systems helps to trigger the glycerol outflow. For a system spreading with small bubbles, although the gas solubility would increase with the increasing pressure, nevertheless, the undissolved gaseous phase would inevitably be pressed into the nanochannel during loading process, to form  
Figure 6: Comparison of the infiltration and defiltration percentage of undegassed and degassed glycerol/ zeolite system (loading rate 0.01 mm/s and 0.10 mm/s; system temperature 303 K and 348 K). a long or short section of gas cluster in the nanochannel. As the liquid is abundant in the testing systems, there is always liquid entering the channel. A cartoon depicting the status of gas-liquid in a nanochannel in the current system is given in Figure 7. Firstly, on the inside of the nanochannel, there is always a gas cluster consisting of the gas molecules that exists in nanopores originally. In a degassed system, a liquid column/chain fills the rest of the nanochannel until the open end, as depicted in Figure 7a. In an undegassed system, liquid column and gas cluster or gas molecule exist alternately with each other, as depicted in Figure 7b. In a hydrophobic system, the repelling force of the rigid wall to liquid is one of the most important driving forces for outflow during unloading. For instance, water in the hydrophobic zeolite behaves as a nanodroplet trying to close its hydrogen bonds onto itself, with a few short-lived dangling OH groups [35]. However, there is no such repelling force between the rigid wall and gas molecules. The inserted gas molecule interrupts the continuity of liquid chain, and the attractive intermolecular forces between liquid-liquid molecules is replaced by the repulsive force between the liquid and the gas molecules.