Heng Zhang

Understanding the microstructural self-assembly and mechanical response of unaged and oxygen-aged asphaltenes within oil droplets is essential for elucidating the stabilization mechanisms of weathered crude oil emulsions generated during oil-spill weathering and remediation. Herein, quantum chemical calculations and multiscale molecular dynamics simulations were employed to systematically evaluate the impact of oxidative molecular evolution on multibody aggregation and droplet surface properties. Results revealed that aging drove asphaltenes from a bulk-dispersed state to pronounced interfacial enrichment, narrowing the radial distribution width by 51% (from 43 Å to 21 Å) and enhancing local structural ordering (radial distribution functions peak) by 10-fold via face-to-face aromatic stacking. This interfacial orientation exposed edge heteroatoms, causing the droplet hydrophilic surface area to surge by 175% (from 16 to 44 nm2) at a 20 wt % mass fraction, while the single-molecule hydration energy intensified by 84% from −2.09 to −3.85 kcal/mol. Conversely, under dynamic nonequilibrium perturbations, polar functionalization compromised the skeletal compatibility with nonpolar light oil fractions, reducing the bulk framework-solvent coupling energy to 56% of the unaged asphaltene system. Consequently, the aged droplet deformation increment (63 nm2) reached 3.9 times that of the unaged counterpart (16 nm2). This study unravels a competitive mechanism between aging-induced 2D interfacial rigidity and 3D bulk cohesion degradation, providing a critical molecular framework for designing targeted demulsifiers to accelerate phase separation in weathered crude oils.

Disruption of the stratum corneum (SC) lipid matrix compromises the skin barrier function; however, the molecular mechanisms by which exogenous lipids promote its repair remain unclear. Here, all-atom molecular dynamics (MD) simulations were employed to investigate how initially dispersed lipid molecules and preassembled nanoparticles influence the direct rearrangement behavior of exogenous lipids at a localized defect in ceramide (CER)/cholesterol (Chol)/free fatty acid (FFA) ternary lipid bilayers. The results show that barrier repair efficiency depends strongly on both delivery format and lipid species. Initially dispersed lipids, limited by inefficient random diffusion, exhibit effective local repair but constrained overall efficiency. In contrast, preassembled lipid nanoparticles follow an “adsorption-spreading-reassembly” pathway, where localized high-concentration delivery overcomes diffusional barriers and significantly enhances repair efficiency. The three lipid species exhibit different molecular repair mechanisms at the damage site, governed by their unique molecular structures: CER shows stronger enrichment, FFA displays greater diffusion and dynamic reorganization, and Chol forms a denser and more stable bilayer. This study provides a molecular-level reconstruction associated with barrier repair and offers guidance for developing more effective topical lipid repair formulations.

The application of an electric field to demulsification of oil-in-water (O/W) emulsions has received extensive attention. However, microcosmic information about the effect of surfactant type on the demulsification of an O/W emulsion under an electric field is still rare. In this work, the effects of cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS) on oil droplet demulsification in an emulsion under a pulsed-DC electric field were studied by molecular dynamics (MD) simulation. The MD simulation results show that oil droplets underwent directional movement under the action of an electric field. The larger the electric field strength, the shorter the time required for the oil droplets to coalesce. However, the movement direction of the oil droplets in the electric field was different depending on the type of surfactant. Compared to oil droplets containing SDS, oil droplets containing CTAB molecules exhibited faster deformation and easier migration coalescence under low electric field strength. It was mainly attributed to the fact that the deformation of oil droplets will be accelerated when oil droplets contain asphaltene molecules and surfactant molecules with different electronegativities under an electric field. During the demulsification of oil droplets containing CTAB molecules, CTAB molecules generated electrostatic attraction with asphaltene molecules in adjacent oil droplets, strengthened the interaction between oil droplets, and promoted the demulsification of oil droplets. In the process of oil droplet demulsification containing SDS molecules, the potential energy of the electrostatic interaction between oil droplets did not change, and the demulsification mainly depended on the van der Waals force between oil droplets.

The destruction of plasma membrane integrity is closely related to immune response, neuronal injury, cell apoptosis, and other pathological events. However, the construction of ratiometric fluorescent probes capable of detecting plasma membrane integrity remains a significant challenge, hindering in-depth studies on related biomedical areas. Herein, a polarity-responsive fluorescent probe was constructed for the ratiometric detection of cell membrane integrity for the first time. The probe targeted intact plasma membranes in healthy cells and relocated into the cytoplasm to give significantly red-shifted fluorescence after plasma membrane damage. Molecular simulations revealed that the high transmembrane barrier and amphipathic nature of the probe were responsible for its targeting ability. With the probe, the ratiometric detection of late apoptosis stage was realized for the first time, and the membrane damage of tumor cells induced by UV irradiation, toxins, and antitumor drugs was visualized. The effect of formaldehyde on membrane integrity was evaluated using a probe, and cysteine was proved to be a potential detoxifier to counteract the toxicity of formaldehyde.

Polysaccharide foulants play a key role in the adhesion of many fouling organisms, which may cause severe marine biofouling. However, the detailed interaction mechanism between polysaccharides and antifouling membranes is still indistinct compared with that between the fouling protein and antifouling surfaces. In this paper, a model oligosaccharide built based on the monosaccharide composition found in diatom extracellular polymeric substances (EPS) was used as a model foulant to investigate its adsorption and desorption above three T4 antifouling membranes. It was found that the anionic poly(3-(methacryloyloxy)propane-1-sulfonate) (T4-SP) antifouling membrane had excellent antifouling ability with respect to the model oligosaccharide, while the oligosaccharide can be easily adsorbed on the poly(2-(dimethylamino)ethyl methacrylate) (T4-DM) membrane with vdW attraction and on the zwitterionic poly(sulfobetaine methacrylate) (T4-SB) membrane with electrostatic attraction. As little is known about the details of polysaccharides' adsorption above antifouling membranes at the molecular level, we hope this work will serve as a theoretical basis for finding more effective materials to prevent or control marine biofouling.

The combination of Al nanoparticles (ANPs) as fuel and H₂O₂ as oxidizer is a potential green space propellant. In this research, reactive force field molecular dynamics (ReaxFF-MD) simulations were used to study the influence of water addition on the combustion of Al/H₂O₂. The MD results showed that as the percentage of H₂O increased from 0 to 30%, the number of Al-O bonds on the ANPs decreased, the number of Al-H bonds increased, and the adiabatic flame temperature of the system decreased from 4612 K to 4380 K. Since the Al-O bond is more stable, as the simulation proceeds, the number of Al-O bonds will be significantly higher than that of Al-H and Al-OH bonds, and the Al oxides (Al[O]_x) will be transformed from low to high coordination. Subsequently, the combustion mechanism of the Al/H₂O₂/H₂O system was elaborated from an atomic perspective. Both H₂O₂ and H₂O were adsorbed and chemically activated on the surface of ANPs, resulting in molecular decomposition into free radicals, which were then captured by ANPs. H₂ molecules could be released from the ANPs, while O₂ could not be released through this pathway. Finally, it was found that the coverage of the oxide layer reduced the rate of H₂O₂ consumption and H₂ production significantly, simultaneously preventing the deformation of the Al clusters’ morphology.