Nano-material enhanced viscoelastic surfactant (VES) systems have attracted considerable attention as clean fracturing fluids due to their improved rheological properties compared to conventional VES systems. In this study, a pseudo-interpenetrating network VES (PINVES) fracturing fluid, which was composed of sodium oleate (NaOA), potassium chloride (KCl) and surface-modified cellulose nanofibril (SMCNF), was proposed. The rheological behavior of the PINVES fracturing fluid and the interaction mechanism between SMCNF and wormlike micelles (WLMs) were comprehensively studied. The zero-shear viscosity of PINVES increased with appropriate SMCNF addition but decreased with excess SMCNF addition. Meanwhile, the typical viscosity-flat of WLMs gradually disappeared when the concentration of SMCNF exceeded the optimum value. The optimum value was closely related to the functional groups on the surface of SMCNF. The SMCNF physically crosslinked the WLMs through hydrogen bonding but the sulfonic groups and hydrophobic groups on the surface of SMCNF destroyed the network of WLMs at relatively high SMCNF concentration. The network formed by SMCNF dominated the rheological behavior of the PINVES fracturing fluid simultaneously. In addition, due to the competition between the network of WLMs and the network of SMCNF, the PINVES fracturing fluid exhibited higher concentration dependence of surfactant in rheological behavior than conventional VES fracturing fluid. The SMCNF network also endowed the PINVES with better temperature-resistance. Furthermore, the relaxation time and elasticity of PINVES fracturing fluid increased with the increase in SMCNF concentration. The static proppant settling tests demonstrated that the addition of SMCNF improved the sand-carrying capability of PINVES fracturing fluid. The results of the study could provide some enlightenments on the application of SMCNFs in reservoir stimulation.

The strategy of solar-driven steam generation to collect purified water shows great potential in seawater desalination and domestic wastewater treatment. However, there is still a technical gap in achieving high cost-effectiveness and providing sustainable solutions for rapid evaporation to obtain high-quality and safe water. In this study, a natural rich biomass pectin (Nicandra physalodes (Linn.) Gaertn. polysaccharide) and polypyrrole photo-thermal material were introduced into polyvinyl alcohol network to achieve the construction of a low-cost hybrid hydrogel solar evaporator (total material cost of $7.89 /m2). The mixed evaporator works stably in a long-span acid-base range (pH 1 ~ 14) and salinity range (0 ~ 320 g/kg) with a water purification capacity of 2.42 (kg/m2* h) under 1 sun, and its daily water purification capacity can reach 24.4 kg/m2 under natural light. This paper provides a new possibility for a highly efficient and cost-effective water desalination system with guaranteed water quality.