CO₂‑Induced Reversible Dispersion of Graphene by a Melamine Derivative

Smart graphene with stimuli-responsive dispersity has great potential for applications in medical and biochemical fields. Nevertheless, reversible dispersion/aggregation of graphene in water with biocompatible and removable trigger still represents a crucial challenge. Here, we report CO₂-induced reversible graphene dispersion by noncovalent functionalization of reduced graphene oxide with <i>N</i>²,<i>N</i>⁴,<i>N</i>⁶-tris­(3-(dimethyl­amino)­propyl)-1,3,5-triazine-2,4,6-triamine (MET). It was demonstrated that MET can be strongly adsorbed on graphene surface through van der Waals interaction to facilitate dispersing graphene in water. Moreover, reversible aggregation/dispersion of graphene can be achieved simply by alternately bubbling CO₂ and N₂ to control the desorption/adsorption of MET on graphene surface

Comparative Studies on Enhanced Oil Recovery: Thermoviscosifying Polymer Versus Polyacrylamide

High-molecular-weight polyacrylamide (PAM) has been widely used in chemically enhanced oil recovery (EOR) processes under mild conditions, but its poor tolerance to high temperature and high salinity impeded the use in severe oil reservoirs. To overcome the inadequacies of PAM, thermoviscosifying polymers (TVPs) whose viscosity increases upon increasing temperature and salinity were developed in recent years. In this work, comparative studies with PAM and TVP, having more similar molecular weights, were performed with regard to their rheological behaviors, thermal stability, and core flooding feasibility. It was found that the TVP aqueous solution exhibited thermothickening ability, even at a polymer concentration of 0.2 wt % with a total dissolved solids ratio (TDS) of 101 000 mg L^–1 upon increasing temperature, while PAM only showed a monotonic decrease in viscosity under identical conditions. Remaining viscosity of TVP was higher than that of PAM after aging at 45 or 85 °C for one month. Core flooding tests demonstrated both polymers show good transportation in porous media, and a higher oil recovery of 16.4% and 15.5% can be attained by TVP at 45 and 85 °C, respectively, while those of PAM are only 12.0% and 9.20%

Effect of SiO₂ Nanoparticles on Wax Crystallization and Flow Behavior of Model Crude Oil

In oil industry, wax deposition is one of the frequently encountered problems that causes severe issues during the production, storage, and transportation of crude oil. Recently, it is found that addition of nanohybrids to crude oil is an effective method to solve this problem. However, the mechanism of how nanoparticles affect the wax crystallization and rheological behavior of crude oil has not been clearly understood. Here we reported the influence of SiO₂ nanoparticles on crystallization and rheological behavior of model oils with and without asphaltene and resin. It was demonstrated that the wax appearance temperature increased upon the addition of SiO₂ nanoparticles of model oil without asphaltenes and resin, while the rheological behavior was less affected. When in the presence of asphaltenes and resin, the amount of wax crystals, wax appearance temperature, and rheological parameter of model oils were found to decrease while SiO₂ nanofluid was added, resulting in the improvement of flowability

Insights into the Relationship between CO₂ Switchability and Basicity: Examples of Melamine and Its Derivatives

Owing to its wide availability, nontoxicity, and low cost, CO₂ working as a trigger to reversibly switch material properties, including polarity, ionic strength, hydrophilicity, viscosity, surface charge, and degree of polymerization or cross-linking, has attracted an increasing attention in recent years. However, a quantitative correlation between basicity of these materials and their CO₂ switchability has been less documented though it is of great importance for fabricating switchable system. In this work, the “switch-on” and “switch-off” abilities of melamine and its amino-substituted derivatives by introducing and removing CO₂ are studied, and then their quantitative relationship with basicity is established, so that performances of other organobases can be quantitatively predicted. These findings are beneficial for forecasting the CO₂ stimuli-responsive behavior of other organobases and the design of CO₂-switchable materials