Asphaltenes exhibit an amphiphlic behavior and tend to form colloidal i-mers, because of their chemical structure. The formation of colloidal aggregates can generate formation damage for the precipitation and/or deposition of asphaltenes, because of the degree of self-association, altering the wettability of rock surface and significantly affect crude oil viscosity and specific gravity. This study aims at introducing a novel model for describing, at the macroscopic level, the adsorption equilibria of self-associating molecules such as asphaltenes in solution onto solid surfaces based on the "chemical theory". The model describes the adsorption isotherms temperature-dependent using three parameters, namely, maximum amount adsorbed, constant of i-mer reactions, and Henry's law constant. Furthermore, a temperature-independent model of five parameters, based on the modifications of the constants of reaction and Henry's law using an Arrhenius-type equation was proposed for estimating the thermodynamics parameters, such as ΔG ads °, ΔH ads °, and ΔS ads °of the adsorption process. This model improves the understanding of interactions asphaltene−asphaltene and asphaltene−solid surface on the adsorption−equilibrium process. The theoretical predictions of isotherms were validated successfully by determining the root mean-square errors (RSM%) between data obtained from published literature and values predicted for asphaltenes and surfaces with differing chemical natures. More than 40 experimental data taken from literature have been used for validating the solid−liquid equilibrium (SLE) model for describing the adsorption isotherm of asphaltenes from different origins on surfaces with different chemical nature, which shows the model robustness due to the complexity of the liquid phase adsorption for those complex molecules.

Biomedical magnetic colloids commonly used in magnetic hyperthermia experiments often display a bidisperse structure, i.e., are composed of stable nanoclusters coexisting with well-dispersed nanoparticles. However, the influence of nanoclusters in the optimization of colloids for heat dissipation is usually excluded. In this work, bidisperse colloids are used to analyze the effect of nanoclustering and long-range magnetic dipolar interaction on the magnetic hyperthermia efficiency. Two kinds of colloids, composed of magnetite cores with mean sizes of around 10 and 18 nm, coated with oleic acid and dispersed in hexane, and coated with meso-2,3-dimercaptosuccinic acid and dispersed in water, were analyzed. Small-angle X-ray scattering was applied to thoroughly characterize nanoparticle structuring. We proved that the magnetic hyperthermia performances of nanoclusters and single nanoparticles are distinctive. Nanoclustering acts to reduce the specific heating efficiency whereas a peak against concentration appears for the well-dispersed component. Our experiments show that the heating efficiency of a magnetic colloid can increase or decrease when dipolar interactions increase and that the colloid concentration, i.e., dipolar interaction, can be used to improve magnetic hyperthermia. We have proven that the power dissipated by an ensemble of dispersed magnetic nanoparticles becomes a nonextensive property as a direct consequence of the long-range nature of dipolar interactions. This knowledge is a key point in selecting the correct dose that has to be injected to achieve the desired outcome in intracellular magnetic hyperthermia therapy.

Several examples of nanosized therapeutic and imaging agents have been proposed to date, yet for most of them there is a low chance of clinical translation due to long-term in vivo retention and toxicity risks. The realization of nanoagents that can be removed from the body after use remains thus a great challenge. Here, we demonstrate that nonequilibrium gold–iron alloys behave as shape-morphing nanocrystals with the properties of self-degradable multifunctional nanomedicines. DFT calculations combined with mixing enthalpy-weighted alloying simulations predict that Au–Fe solid solutions can exhibit self-degradation in an aqueous environment if the Fe content exceeds a threshold that depends upon element topology in the nanocrystals. Exploiting a laser-assisted synthesis route, we experimentally confirm that nonequilibrium Au–Fe nanoalloys have a 4D behavior, that is, the ability to change shape, size, and structure over time, becoming ultrasmall Au-rich nanocrystals. In vivo tests show the potential of these transformable Au–Fe nanoalloys as efficient multimodal contrast agents for magnetic resonance imaging and computed X-ray absorption tomography and further demonstrate their self-degradation over time, with a significant reduction of long-term accumulation in the body, when compared to benchmark gold or iron oxide contrast agents. Hence, Au–Fe alloy nanoparticles exhibiting 4D behavior can respond to the need for safe and degradable inorganic multifunctional nanomedicines required in clinical translation.

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