# Progress on the Application of Nanomaterial Expansion in Oil Displacement
## 3 Nanomaterial Swelling Oil Displacement Mechanism
### Nano-Silica Oil Droplets Enhanced Expansion
formation of water droplets in oil droplets is accelerated, and the volume of droplets increases rapidly, which accelerates the apparent expansion of emulsion droplets. In recent years, ordinary nanoparticles have exposed deficiencies in interfacial activities and maintenance of emulsion stability [75]. In order to overcome this problem, academia and industry have focused their research on Janus nanofluids [76]. Studies have shown that amphiphilic Janus nanosheets have higher interfacial activity and better stability than traditional nanoparticles, which is mainly due to their larger desorption energy and surface area [77]. In addition, the Janus particles exhibit unique characteristics of translational and rotational diffusion at the liquid interface, as shown in Figure 9. These properties enable Janus nanosheets to significantly improve the efficiency of crude oil extraction at very low concentrations. Through their unique asymmetric structure and surface activity, Janus nanomaterials can effectively regulate the physical and chemical properties of the oil-water interface, promote the expansion of emulsion droplets, and thus improve oil recovery. [PERSON] et al. [78] studied the emulsification mechanism of amphiphilic Janus-SiO\({}_{2}\) nanoparticles (Janus-C12) in O/W, O/W/O, and W/O emulsions. They systematically analyzed the effects of nanoparticle concentration, water-oil volume ratio, and NaCl concentration on the emulsification effect. It was observed that the water droplets expanded to different degrees under different conditions. This phenomenon indicates that amphiphilic Janus-SiO\({}_{2}\) nanoparticles can theoretically expand crude oil droplets, thereby improving the exploitation efficiency of unconventional oil and gas fields. The usual preparation of Janus nanosheets is shown in Figure 10. [PERSON] [80] proposed a new strategy for the preparation of amphiphilic Janus nanosheets, using cetyltrimethoxysilane and 3-aminopropyltrimethoxysilane (APTMS) as modifiers and thermally expandable microspheres (TEMS) as templates. Firstly, 3-aminopropyltrimethoxysilane (APTMS) was adsorbed on the surface of thermally expanded microspheres (TEMSs), and Janus spheres (TEMS @ SiO\({}_{2}\)) were obtained by sol-gel treatment. Then, TEMS @ SiO\({}_{2}\) were modified by hexadecyltrimethoxysilane (HDTMS). TEMSs were heated and expanded to break the shell of the Janus spheres; thus, amphiphilic Janus nanosheets were prepared. The amphiphilic Janus nanosheets were analyzed by FT-IR, TG, and TEM. Amphiphilic Janus nanosheets were dispersed into simulated formation water to prepare nanofluids, and their stability, oil-water interfacial tension, emulsification ability, and enhanced oil recovery ability were evaluated. The results showed that the nanofluid (0.1%, mass fraction) did not appear stratified after 10 days of storage, and its Zeta potential was 31.2 mV at pH = 7, showing good stability. The emulsification index of the nanofluid (0.1%) for 10 days was 100%, indicating its excellent emulsification ability. The nanofluid (0.1%) can reduce the oil-water interfacial tension to 3.2 mN/m. Nanofluid flooding (0.1%) can significantly improve the recovery of low-permeability reservoirs. When the permeability is 8.9 \(\times\) 10\({}^{-3}\)\(\upmu\)m\({}^{2}\), the recovery can be increased by 21.5%. This shows that Janus nanosheets have better performance than traditional homogeneous nanoparticles and have great application potential in various fields [19; 45]. Figure 9: In-plane and out-of-plane decomposition diagrams of the translational (**a**) and rotational (**b**) diffusion of Janus particles at the liquid interface [79]. Oil droplets can expand in water under the emulsification state, and the fundamental reason is that there is a chemical potential difference between the surrounding environment and the oil droplets. Due to the relatively high chemical potential of the environment, this potential energy difference drives the increase in oil droplet volume, which in turn leads to the expansion phenomenon.