Shiling Yuan

An experimental study on alkaline/surfactant/polymer flooding systems using nature mixed carboxylate

Abstract The orthogonal-test-design method was used to determine the optimal formula by phase behavior and transient interfacial tension (IFT) studies, respectively. The results indicate the major components are cheap, naturally mixed carboxylate SDC (0.5%), alkaline NaHCO 3 /Na 2 CO 3 weight ratio of 1 (1.0%), and HAPM (1000 mg dm −3 ). In the coreflood experiment, their oil recovery will be increased by a factor of 25.2 and 26.8% the original oil in place (OOIP).

Molecular Dynamics Study of Alkyl Benzene Sulfonate at Air/Water Interface: Effect of Inorganic Salts

Molecular dynamics simulations have been performed to investigate the effect of inorganic salts on the structural and dynamic properties of alkyl benzene sulfonate monolayer formed at the air/water interface. The alkyl benzene sulfonates are two surfactant isomers in the family of sodium hexadecane benzene sulfonates defined by 1C16 and 5C16, indicating a benzene sulfonate group attached to the first and fifth carbon atom in hexadecane backbone. It has been observed that both benzene ring groups and headgroups (-SO(3)(-)) are hydrated due to their polar nature. Water molecules can form stable hydrogen bonds with headgroups of surfactants, and the counterions (Na(+), Mg(2+), or Ca(2+)) are distributed close to the air/water interface. The stronger electrostatic repulsion drives the 1C16 monolayer arranged in disorder in comparison with 5C16, and the presence of inorganic salts may screen electrostatic repulsions between headgroups and decrease the thickness of the interfacial water layer, which follows the series Ca(2+) > Mg(2+) > Na(+). The order of inorganic salt tolerance of two surfactants is 5C16 > 1C16. The counterions may penetrate into the hydration shell of the surfactant headgroups and restrict the mobility of the water molecules situated in this area.

The adsorption of hydrophobically modified polyacrylates at interfaces of quartz/liquid and gas/liquid

The properties of hydrophobically modified polyacrylates (HMPAs) at the interfaces of quartz/liquid and gas/liquid (g/l) are studied. From the determination of contact angle, adsorption isotherm and atomic force microscopy (AFM) images, the adsorption mechanism of HMPAs on the quartz surface is discussed. The hydrophilicity of quartz increases with the adsorption of HMPAs, which shows that they are adsorbed to the surface by hydrogen bond between carboxyl and quartz and the hydrophilic groups direct toward the bulk solution. In addition, there appear the island-like aggregates at lower concentration and with the concentration increasing above critical micelle concentration (cmc) large micelle-like clusters of HMPAs are observed on the quartz surface from the AFM images. The results of surface tension and surface pressure measurements show the HMPAs are easy to pack tightly at the g/l interface, which leads to the remarkable decrease of surface tension of water. Moreover the capability of HMPAs to form film is good.

Self-assembly of dipeptide sodium salts derived from alanine: a molecular dynamics study

Dipeptide sodium salts derived from alanine can readily self-assemble into helical nanostructures as observed in experiments. But what are the primary driving forces of the organizing process at the molecular level is still worthwhile discussing. In this study, molecular dynamics simulation was employed to investigate the nanostructure at the molecular level, and different driving forces were deduced for the self-assembled process of dipeptide sodium salts. The simulated results showed that van der Waals forces are in favour of the aggregation of alkyl chains in the solution, resulting in one hydrophobic core of condensed fibril. Hydrogen bonds and electrostatic interactions represented by the water-bridge and salt-bridge structure between dipeptide molecules are major driving forces for the hydrophilic amide groups to form the nanostructure shell. In the self-assembly, the bilayer structure of the dipeptide was the basic unit of helical fibril. The structures of the salt bridge and water bridge are distributed over the surface of the fibril, weakening the electrostatic interaction between the dipeptide molecules. The results show that water molecules penetrating into the self-assembled structure should be considered as one part of the peptide self-assembly. Analysis of the self-assembled conformation showed that the hydrophilic amide groups aggregated as small clusters in the hydrophilic shell. Terminal amide groups, forming hydrogen bonds with water molecules around the chiral carbon atom, decide the handedness of the self-assembly.

Effect of Polyvinylpyrrolidone on the States of Water in Water-in-Oil Microemulsions with Betaine Surfactant

A water-in-oil (w/o) microemulsion was prepared with the zwitterionic surfactant dodecyl betaine (C12BE), n-pentanol (C5OH), n-heptane (C7H16) and water. Effects of polyvinylpyrrolidone (PVP) with different molecular weight on the state of water in w/o microemulsions at a given water/C12BE molar ratio were investigated by FT-IR and differential scanning calorimetry (DSC). The experimental results showed that addition of PVP resulted in an increase of the content of the bound water in water pool of a w/o microemulsion, but a decrease of the amount of the bulky water. The higher the molecular weight of PVP, the more bound water; and the less bulk water. The change of the trapped water was not obvious due to the interference of C5OH.

Aggregation behavior of betaine-amphiphiles in the presence of polyvinylpyrrolidone

The aggregation behavior of zwitterionic surfactant dodecylbetaine (C12BE) with and without polyvinylpyrrolidone (PVP) has been investigated by means of surface tension and steady-state fluorescence techniques. It shows that addition of PVP results in a decrease in the aggregation number of C12BE micelle and “hydrophobic index” (I1/I3) of the probe (pyrene and pyrene-1-carboxaldehyde). PVP molecules are responsible for the phenomena: they bind to the surface of the micelle and prevent the rapid exchange of amphiphiles between micelles and water phase. There are two transition points in the plot of surface tension vs. concentration of C12BE in the presence of PVP. The results indicate that the association takes place between PVP and C12BE when the C12BE concentration is above a critical aggregation concentration (CAC).

Influence of self-assembled monolayers on the growth and crystallization of rubrene films: a molecular dynamics study

At present, rubrene, which exhibits a high charge mobility, has become one of the most promising organic semiconductors because of its potential applications in organic thin-film transistors (OTFTs). The performance of organic molecule crystalline films is governed by both their molecular packing state phase and their molecular structures, which are greatly influenced by the growth process and inducing layer. In this paper, molecular dynamics (MD) simulations were performed to study the deposition behavior and crystallization of rubrene films. Four systems with different self-assembled monolayers (SAMs) were constructed to investigate the microscopic configuration of rubrene deposition, their interfacial reactions, and to further discuss how the template structures affect the crystallization of rubrene molecules. Our results suggest that the phase states of the inducing layer exhibit a significant effect on the rubrene growth. The theoretical results are consistent with the experimental findings and provide theoretical assistance on the further design of appropriate inducing layers for the crystallization of organic molecules.

Adsorption of sodium oleate on kaolinite

In this paper the effect of additives on adsorption of sodium oleate on kaolinite in aqueous solution is examined. Kaolinite with specific surface area 20.2 m2/g and zero point of charge 2.0 is used as adsorbent. Adsorption of sodium oleate on kaolinite has been investigated with or without additives such as NaCl, n-butanol, n-penanol, PHPAM (partially hydrolyzed polyacrylamide) and AEO (a nonionic polyoxyethylene surfactant). The adsorption isotherm of sodium oleate, which is different from that of other anionic surfactants on kaolinite, showed two plateaus (i.e. LS type). But it is interesting that an adsorption maximum is found in the isotherms when these additives are added in the liquid/solid adsorption system. Basically, three different adsorption behaviors have been found when the additives are added. The adsorbed amount of sodium oleate decreases considerably when alcohols are added to the solution, while the amount increases when NaCl or PHPAM is added; only a slight alteration is observed when AEO is added to the solution. The adsorption process on kaolinite is found to follow a two-step first-order kinetic rate equation with two different (k1 and k2) rates constants. Values of the energy of activation Ea1 and Ea2 are calculated from the slope of the linear plot of –lnk against 1/T for different systems. The enthalpies of activation (ΔH), entropies of activation (ΔS) and free energies of activation (ΔG) are calculated by using thermodynamic equations. It is found that there is an entropy-enthalpy compensation effect in the adsorption process from the values of ΔH and ΔS. These results are useful in controlling the surfactants adsorbent loss in tertiary oil recovery.

Theoretical calculation on the reaction of alkene molecules on H-terminated Si(100)-3×1 surface

A study on mechanisms of radical initiated surface chain reaction of ethylene molecule on H-terminated Si(100)-3 × 1 has been carried out in a supercell approach by using density functional theory and ab initio molecular dynamic method. On the H-terminated Si(100)-3 × 1 surface, one of the crucial steps of the surface chain reaction, namely, the abstraction of a H atom from a nearby surface hydride unit, is found to have a somewhat smaller activation energy from the nearest silicon site than from the next-nearest silicon site. From the intermediate state to the final state, the transition state has bigger activation energy. Ab initio molecular dynamics (MD) shows that the H-abstraction on Si(100)-3 × 1 surface bound organic group with a carbon-centered radical is very easy to be obtained from the transition state, and it also shows that the C…H bond at methyl group is formed in a very short MD time, and the Si…C bond between the Si surface and the alkyl chain oscillates with time evolution on Si(100)-3 × 1 surface.