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The use of an appropriate viscosity reducer is the key during the process of heavy crude oil exploitation. To design a new amphiphilic polymer as an efficient viscosity reducer, we combined the dissipative particle dynamics (DPD) simulation and allatom simulation in this work to reveal the viscosity reduction mechanism. Nine primary polymers were added into the oil−water system, in which the oil−water volume ratio was 4:1, by comparing the mean-square displacement (MSD) of asphaltene, aggregation ratio, the oil−water interfacial tension value, and the effects of nitrogen type, benzene ring morphology, and the alkyl side-chain length of the polymers on the properties of the system. The interaction mechanism was further revealed by analyzing the interaction energy between the asphaltene and the polymer molecules at the atomic scale. Finally, three kinds of polymers, P12, P22, and P31, which used polyacrylamide as a skeleton and were modified by pyrrolidone, a naphthalene ring, and the alkyl side chain without a −CH 2 group, respectively, were selected to design a new amphiphilic polymer as a viscosity reducer. This work combined the advantages of the mesoscopic and atomic simulation methods to design the amphiphilic polymer, shedding light on the development of the novel heavy-oil viscosity reducer.

Imidacloprid (IMI) polymorphs were first found to be sensitive to the content of antisolvent in an antisolvent crystallization process using formic acid (FA) as a solvent and water (W) as an antisolvent. Characterized by XRD, DSC, POM, and Raman, the obtained crystals change from Form II into Form I as the FA/W ratio becomes lower than 1:1. Combined with Hirshfeld surface analysis, it illustrates that IMI molecules have the tail-to-tail and tail-to-head packing modes at a FA/W ratio of 1:1, whereas they adopt the tail-to-tail parallel packing at a FA/W ratio of 2:1. Molecular dynamic simulations disclose that the molecular conformations in the IMI aggregates turn to be approximately the distinct conformations in the corresponding unit cells of crystal Form I and II. The competing parameters were put forward around the active sites of IMI on the basis of the coordination numbers calculated through RDF profiles to understand deeply the competition mechanism of the solute–solvent interactions versus the solute–antisolvent interactions. It is found that as the content of water increases, the solute–antisolvent interactions gradually turn to be dominant around the specific sites, which promotes the conformation change of IMI and then facilitates the nucleation for Form I. These results provide a useful route to study the nucleation pathway of polymorphic products.

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