Yuan Shi-Ling

Properties of a water layer on hydrophilic and hydrophobic self-assembled monolayer surfaces：A molecular dynamics study

The microscopic behaviors of a water layer on different hydrophilic and hydrophobic surfaces of well ordered self-assembled monolayers (SAMs) are studied by molecular dynamics simulations. The SAMs consist of 18-carbon alkyl chains bound to a silicon(111) substrate, and the characteristic of its surface is tuned from hydrophobic to hydrophilic by using different terminal functional groups (-CH3, -COOH). In the simulation, the properties of water membranes adjacent to the surfaces of SAMs were reported by comparing pure water in mobility, structure, and orientational ordering of water molecules. The results suggest that the mobility of water molecules adjacent to hydrophilic surface becomes weaker and the molecules have a better ordering. The distribution of hydrogen bonds indicates that the number of water-water hydrogen bonds per water molecule tends to be lower. However, the mobility of water molecules and distribution of hydrogen bonds of a water membrane in hydrophobic system are nearly the same as those in pure water system. In addition, hydrogen bonds are mainly formed between the hydroxyl of the COOH group and water molecules in a hydrophilic system, which is helpful in understanding the structure of interfacial water.

Mesoscopic Simulations on the Aggregation Behavior of Polymeric Surfactants in Aqueous Solutions

Polymeric surfactants are widely used in many fields.Their aggregation behavior is different from that of small molecule surfactants because of complex configurations and large molecular weights.The studies of aggregation behavior at the micro-level can guide applications and therefore,many researchers have focused on theoretical investigations.With the recent advances in computer simulations,the study of surfactant aggregation behavior in aqueous solutions at the micro-or meso-level has been successfully undertaken.Based on our recent work,we review the aggregation behavior of polymeric surfactants by dissipative particle dynamics (DPD) and mesoscopic dynamics (MesoDyn).This paper especially introduces research about the phase behavior of polymeric surfactants as well as their interactions with low molecular weight surfactants.This method can directly provide the process of phase separations and changes in the conformation of the aggregates,which are not observable in macro-experiments.This method has the potential to complement and guide experimental methods.

C and N stable isotope analysis of human and animal bones at the Beiqian site

The Beiqian site, located in Jimo city, Qingdao, went through three archaeological excavations, and a large number of human and animal bones in the Dawenkou culture and the Zhou Dynasty period were unearthed. By carbon and nitrogen stable isotope analysis, the diet of ancestors is expected to be recovered, and the domesticated plants and animals will be discussed. The investigated results showed that the food structure of ancestors in both periods included food crops, mainly C4 foods, and meat, mainly marine shellfish and livestock. For domestic pigs, they mainly eat C3 plants, and were affected by the lifestyle of ancestors. This study also showed that the diet of ancestors is the shellfish rather than marine fish despite the Beiqian site is located near the shoreline. We can conclude that the diet of ancestors in Dawenkou culture period included millet crops (C4 plants), shellfish, marine food, and livestock, representing the lifestyle of farming, domestication, and fishing, supplemented by hunting. In the Zhou dynasty period the meat resource was enriched by domesticated animals and marine fisheries, and the living conditions were significantly improved.

Molecular dynamics simulation of pyrene solubilization in a sulfobetaine micelle

The structural and dynamical properties of the solubilization process of pyrene within a zwitterionic surfactant sulfobetaine micelle were studied using molecular dynamics simulations. Our results showed that free pyrene as the fluorescence probe can be solubilized spontaneously into the micelle and prefers to be located in the hydrophobic core region. When the local concentration of pyrene increased, two probes could both enter into the core region and the excited dimmer of pyrene was formed, which presented a stacking mode of π-π conjugation. Since the π-π stacking interaction was very week, the formation of the excimer was a dynamic process with the two pyrene molecules alternately separating and associating with each other. The simulation showed that the method of molecular dynamics can investigate the location of probe molecules in the micelle in the molecular level, and interpret the dynamic behavior of the probes.