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The stimuli-sensitive polymeric micelles have huge applications to industrial and technological level, know their behaviour under the influence of a pure stimulus, such as the temperature is an important aspect to control and amplify its application field. In this paper, we investigate the micellar stability zones together with the structural inversion process of thermoresponsive polymeric micelles formed by a diblock copolymer (poly(N-isopropylacrylamide-b-3-[N-(3-methacrylamidopropyl)-N,N-dimethyl]ammoniopropane sulphonate (PNIPA-b-PSPP)) in an aqueous environment employing dissipative particle dynamics simulations. Our outcomes show that the PNIPA-b-PSPP copolymer has the ability to form thermodynamically stable micelles with different core-shell structure (PSPP-core/PNIPA-shell and PNIPA-core/PSPP-shell) depending on the direction of the applied stimulus (low or high temperature), the duality of this micellar behaviour is controlled by temperature effect and by the double hydrophilic character that exhibit the PNIPA and PSPP polymeric segments. Four micellar stability zones and one zone where only exist free unimer chains were detected during the thermal scan. The micellar inversion process is triggered by purely temperature effect, is totally reversible and involves three main stages: (1) micellar dissociation, (2) stabilisation of free unimer chains and (3) formation of inverse micelles, all transitory and metastable stages of micellar inversion process are described and analysed in this paper. [ABSTRACT FROM AUTHOR]

The rheological properties of heavy crude oil have a significant impact on the production, refining and transportation. In this paper, dissipative particle dynamics (DPD) simulations were performed to study the effects of the addition of light crude oil and emulsification on the rheological properties of heavy crude oil. The simulation results reflected that the addition of light crude oil reduced the viscosity effectively. The shear thinning behaviour of crude oil mixtures were becoming less distinct as the increase of the mass fraction of light crude oil. According to the statistics, the shear had an influence on the aggregation and spatial orientation of asphaltene molecules. In addition, the relationship between the viscosity and the oil mass fraction was investigated in the simulations of emulsion systems. The viscosity increased with the oil mass fraction slowly in oil-in-water emulsions. When the oil mass fraction was higher than 50%, the increase became much faster since systems had been converted into water-in-oil emulsions. The equilibrated morphologies of emulsion systems were shown to illustrate the phase inversion. The surfactant-like feature of asphaltenes was also studied in the simulations. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics, a meso–scale particle-based model, was used to study the aggregation of mucins in aqueous solutions. Concentration, strength of the mucin–water interactions, as well as the effects of size, shape, and composition of the model molecules were studied. Model proteins were represented as rod-like objects formed by coarse-grained beads. In the first model, only one type of beads formed the mucin. It was found that all the surfaces were available to form aggregates and the conformation of the aggregates was a function of the strength of the mucin–water interaction. With this model, the number of aggregates was unaffected by the initial position of the mucins in the simulation box, except for the lowest mucin concentration. In a more refined mucin model, two kinds of beads were used in the molecule in order to represent the existence of cysteine-like terminal groups in the actual molecule. With this new scheme, aggregation took place by the interaction of the terminal groups between model molecules. The kinetic analysis of the evolution of the number of aggregates with time was also studied for both mucin models. [ABSTRACT FROM PUBLISHER]

Heavy crude oil consists of thousands of compounds, a significant fraction of which have fairly large molecular weights and complex structures. Our work aims at constructing a meso-scale platform to explore this complex fluid in terms of microstructure, phase behavior, stability and rheology. In the present study, we focus on the treatment of the structures of fused aromatic rings as rigid body fragments in fractions such as asphaltenes and resins. To derive the rotational motion of rigid bodies in a non-conservative force field, we conduct a comparison of three rigid body rotational algorithms integrated into a standard dissipative particle dynamics (DPD) simulation. The simulation results confirm the superiority of the Quaternion method. To ease any doubt concerning the introduction of rigid bodies into DPD, the performance of the Quaternion method was tested carefully. Finally, the aggregation dynamics of asphaltene in very diluted toluene was investigated. The nanoaggregates are found to experience forming, breaking up and reforming. The sizes of the asphaltene monomer and nanoaggregate are identified. The diffusion coefficient of diluted asphaltene in toluene is similar to that found experimentally. All these results verify the rotational algorithm and encourage us to extend this platform to study the rheological and colloidal characteristics of heavy crude oils in the future. [ABSTRACT FROM AUTHOR]