ABSTRACT
Liquid-infused surfaces (LISs) have attracted tremendous attention in recent years owing to their excellent surface properties, such as self-cleaning and anti-fouling. Understanding the effect of lubricant composition on LIS performance is of vital importance, which will help establish the criteria to choose suitable infusing lubricants for specific applications. In this work, the role of chemical composition of lubricant in the properties of LISs was investigated. The apparent water contact angle θapp was dependent on the temperature and beeswax/silicone oil ratio. Nevertheless, the trend of moving velocity of water drop on the tilted LISs did not follow that of θapp at 20 °C and 37 °C, which was attributed to the increased lubricant viscosity with beeswax/silicone oil ratio. At 60 °C, the drop velocity and θapp shared the similar variation trend with beeswax/silicone oil ratio, highlighting the significant role of chemistry of the components in beeswax. The alkanes and fatty acids promoted the drop movement, while the fatty acid esters impeded the movement. The interaction forces between water drop and lubricant surfaces were measured using atomic force microscopy. It was demonstrated that the interaction between water drop and lubricant was not the only factor to control the drop movement, while the interaction between lubricant and substrate as well as of lubricant itself also determined the movement. When the adhesions of water-lubricant and lubricant-substrate were similar for different lubricants, the influence of cohesion of lubricant became significant. This work provides useful insights into the fundamental understanding of the interfacial interactions of test drop, infusing lubricant and solid substrate of LISs, and the effect of infusing lubricant composition on the LIS performance.
ABSTRACT
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.
ABSTRACT
HYPOTHESIS: Imidazolium-based Ionic liquids as new generation cationic surfactants can provide designable alkyl chain length. In the catanionic surfactant systems, the alkyl chain lengths and molar ratios can greatly influence the interactions such as electrostatic and hydrophobic interaction. The variation in these interactions has a significant effect on the molecular environments of the self-assembly structure, and this process is always accompanied by the transition of aggregates and release or consumption of heat. Hence, it is of interest to study the relationship between intermolecular interactions, molecular environments, self-assembly structure and the change in energy of system in the catanionic surfactant mixed systems. EXPERIMENTS: The enthalpy change ΔH of titrations the imidazolium-based into SDS micelle solution was studied to characterize the heat by using isothermal titration calorimetry (ITC) during the transitions of the aggregate structures. The corresponding self-assembly structure was monitored via cryogenic transmission electron microscopy (cryo-TEM). Employing proton magnetic resonance (1H NMR), we focus on the interactions between imidazolium-based ILs and SDS based on the variations in the molecular environments of aggregates. FINDINGS: Of these imidazolium-based ionic liquids/SDS system, the 1-octyl-3-methylimidazolium ([OMIM]Cl)/SDS system shows several features such as intense energy absorption and releasing processes, which indicate the formation of high entanglement wormlike micelles and vesicles. This is related to the formation of self-adjusting state between the SDS and [OMIM]Cl molecules due to the balance between the electrostatic interaction and hydrophobic interaction. Varying the alkyl chain length appears to cause significant differences to the molecular environments. From the molecular environments, three different models about the polarity of the catanionic surfactant molecules are used to explain the balance of the intermolecular interactions.
