Tuning Cationic Micelle Properties with an Antioxidant Additive: A Molecular Perspective

Strong Synergistic Molecular Interaction in Catanionic Surfactant Mixtures: Unravelling the Role of the Benzene Ring

Noncovalent interactions play a crucial role in driving the formation of diverse self-assembled structures in surfactant systems. Surfactants containing a benzene ring structure are an important subset of surfactants. These surfactants exhibit unique colloid and interfacial properties, which give rise to fascinating transformations in the aggregate structures. These transformations are directly influenced by specific noncovalent interactions facilitated by the benzene ring structure including cation-π and π-π interactions. Investigating catanionic surfactant systems that incorporate benzene ring structures provides valuable insights into the distinct noncovalent interactions observed in mixed surfactant systems. Our approach involved studying the enthalpy change ΔH during the titration process, utilizing isothermal titration calorimetry (ITC). Simultaneously, we employed cryogenic transmission electron microscopy (cryo-TEM) to observe the corresponding self-assembly structures. To gain further insight, we delved into the noncovalent interactions of the mixed systems by analyzing the molecular environments variations through chemical shifts of the aggregates using proton magnetic resonance (1H NMR). The intermolecular interaction was also confirmed by the two-dimensional nuclear Overhauser enhancement spectroscopy (2D NOESY). We conducted a systematic study of the effects of NaCl concentrations, molar ratios, and molecular structures of surfactants on aggregate structures. The existence forms of surfactants are closely linked to the shape of the titration curve and the transition of the aggregate structures. When cationic surfactants were titrated into sodium dodecylbenzenesulfonate (SDBS) micelle solutions, the dominant cation-π interaction leads to the direct formation of vesicle structures. Conversely, when the SDBS system is titrated into benzyldimethyldodecylammonium chloride (DDBAC) micelles, a delicate balance of multiple noncovalent interactions, including cation-π, π-π, hydrophobic, and electrostatic forces, results in a range of aggregate structure transformations such as worm-like micelles and vesicular structures.

Study of wetting and adsorption mechanism of mixed anionic-nonionic nonhomologous surfactants on coal dust based on intermolecular interactions

The research found that mixed anionic-nonionic surfactants have synergistic wetting performance which can be added to the spray solution to greatly enhance the wettability to coal dust. In this study, based on the experiment data and some synergism parameters, and a 1:5 ratio of fatty alcohol polyoxyethylene ether sulphate (AES)-lauryl glucoside (APG) has the best synergism, resulting in a highly wettable dust suppressant. Additionally, the wetting processes of different dust suppressant on coal were comparatively simulated by molecular dynamics. Then, the electrostatic potential on the molecular surface was computed. Following this, the mechanism of surfactant molecule regulation of coal hydrophilicity and the advantage of the interspersed arrangement of AES-APG molecules in the mixed solution were proposed. Also, based on the computation of highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels and binding energy calculations, a synergistic mechanism of the anionic-nonionic surfactant is proposed from the perspective of enhanced hydrogen bonding between the hydrophilic part of the surfactant and the water molecule. Overall, these results present a theoretical basis and development strategy for the preparation of highly wettable mixed anionic and nonionic dust suppressants for different coal types.

Self-Assembly and Micellar Transition in CTAB Solutions Triggered by 1-Octanol

This study exploits higher-order micellar transition ranging from ellipsoidal to rodlike to wormlike induced by 1-octanol (C₈OH) in an aqueous solution of cetyltrimethylammonium bromide (CTAB), characterizing phase behavior, rheology, and small-angle neutron scattering (SANS). The phase diagram for the ternary system CTAB-C₈OH-water was constructed, which depicted the varied solution behavior. Such performance was further inferred from the rheology study (oscillatory-shear frequency sweep (ω) and viscosity (η)) that displayed an interesting solution behavior of CTAB solutions as a function of C₈OH. It was observed that at low C₈OH concentrations, the solutions appeared viscous/viscoelastic fluids that changed to an elastic gel with an infinite relaxation time at higher concentrations of C₈OH, thereby confirming the existence of distinct micelle morphologies. Small-angle neutron scattering (SANS) provided various micellar parameters such as aggregation numbers (N_agg) and micellar size/shape. The experimental results were further validated with a computational simulation approach. The molecular dynamic (MD) study offered an insight into the molecular interactions and aggregation behavior through different analyses, including radial distribution function (RDF), radius of gyration (R_g), and solvent-accessible surface area (SASA).

Adsorption Mechanism of Benzene Alkylation System Catalyzed by an Acid Catalyst: Effect of Pressure

Alkylbenzene is an important chemical intermediate, and its industrial production is mainly through the alkylation reaction of benzene and olefin under the action of an acid catalyst. In this article, the adsorption mechanism of benzene/propylene binary in HY zeolite was first revealed by Monte Carlo molecular simulation. It was found that the adsorption mechanism of benzene and propylene changes at the adsorbate loading of 36 molecules/UC, and benzene plays a dominant role. Below this loading, the adsorption sites of benzene and propylene mainly occupy the "ideal" adsorption sites, and benzene has a "first-hand advantage" toward those sites. Above 36 molecules/UC, benzene and propylene coform "molecular clusters" in the supercage of HY, resulting in the enhanced localization of adsorbates, suggesting that at low and intermediate adsorbate loadings the adsorption property is expected to effectively improve by introducing more superior adsorption sites. However, above 36 molecules/UC, the interaction between adsorbents in the clusters becomes dominant. At this point, it is critical to change the cage-like structure of the micropore and introduce more mesopore to facilitate the disintegration of adsorbates clusters and reduce the steric resistance so that the advantage of adsorption sites can be brought into play. These results lay the foundation for optimizing the operating conditions of alkylation reactions and can be further used to explain the effect of loading on similar adsorption separation or catalytic systems, such as catalytic cracking.

Contrasting effect of 1-butanol and 1,4-butanediol on the triggered micellar self-assemblies of C16-type cationic surfactants

The self-assembly in aqueous solutions of three quaternary salt-based C₁₆-type cationic surfactants with different polar head groups and identical carbon alkyl chain viz., cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number (N_agg) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the three cationic surfactants, the molecular dynamics (MD) simulation was performed for CPB micelles in an aqueous solution of alcohols that highlighted the micelle solvation and structural transition, which is further complemented in terms of critical packing parameter (PP) for the examined systems.