Xiaohui Xu

Organic contamination in the greenhouse soils from Beijing suburbs, China.

Selected persistent organic pollutants including HCHs, DDTs and PAHs together with PAEs were determined in the greenhouse soils from Beijing suburbs. The total concentrations were 11.64-29.80 ng g(-1) for HCHs, 18.04-101.33 ng g(-1) for DDTs, 1.34-3.15 microg g(-1) for PAEs and 1.92-7.84 microg g(-1) for PAHs, respectively. Predominance of beta-HCH in all samples was obviously observed, suggesting a lack of new HCHs sources. High concentrations of DDE and DDD in comparison to their parents in the samples indicated that most of the DDT had been transformed into its metabolites. The contamination of PAHs was relatively serious and the most abundant compounds were 4-, 5- and 6-ring unsubstituted PAHs. The profiles reflect the important effect of traffic on the PAHs remaining in greenhouse soils. Three phthalate esters (DIBP, DnBP and DEHP) accounted for more than 97% of the phthalates studied. Analysis of n-alkanes was also performed in order to trace the natural or anthropogenic sources of hydrocarbons. Characterization and identification of these compounds in greenhouse soil may help in development of strategies to be used in monitoring organic pollutants in this region.

Rheologic Properties and Molecular Configuration of Polymers in Salt‐Alkali‐Surfactant Mixed Solutions

With the vacuum sublimation freezing‐drying and rheological techniques, the salt/alkali/surfactant effects on the solution properties and the aggregate conformations of the polymers, synthesized hydrophobically modified poly (acrylamide) (HMPAM), were investigated. The experimental methods included viscosity measurements, the photomicroscopy, scan electron microscopy, and the freeze fracture transmission electron microscopy. The variety of conformations of the ultramolecular aggregates, the hydrophobical region, and the spatial network structures resulted from the hydrophobical interaction were studied. Combined results confirmed that HMPAM could form several of interesting three‐dimensional network structures either in distilled water or NaCl solution. The results have revealed the mechanism of the salt/alkali/surfactant effects on the peculiar rheological properties of the solution.

Synthesis and Emulsification Properties of an Amphiphilic Polymer for Enhanced Oil Recovery

A novel amphiphilic polymer, APAM, for enhanced oil recovery (EOR), was synthesized by radical copolymerization of acrylamide, dodecyl polyoxyethylene acrylate (DPEA), and N-(1,1,3,3-tetramethyl butyl) acrylamide (TBA), using potassium persulfate-sodium bisulfite as initiator–activator. The aggregation morphological observation of APAM in aqueous and NaCl solutions was performed using scanning electron microscope. The ability of APAM to solubilize and emulsify n-heptane and crude oil was investigated by visual methods, microscopy, and particle size analyses. The results show that APAM forms supramolecular aggregates in aqueous and NaCl solutions and has strong emulsification ability. As a result, the emulsion consisting of APAM aqueous solution and n-heptane (or crude oil) is much more stable than that of HPAM (partially hydrolyzed polyacrylamide, widely used in EOR), indicating a important function of APAM to emulsify oil component.

Relationship Between the Polymer Structures and Destabilization of Polymer‐Containing Water‐in‐Oil Emulsions

The viscous properties, scanning electronic microscopy (SEM), and water/oil interfacial tension (IFT) of partially hydrolyzed polyacryamide (HPAM) and hydrophobically associating hydrolyzed polyacryamides modified with N‐dodecylacrylamide were studied with the objective of investigating the influence on destabilization of emulsions. As expected, the copolymers exhibit significant viscosity enhancing capacity and three‐dimensional network structures due to intermolecular hydrophobic associations, and also present high interfacial activities as the IFT decrease with increasing polymer concentration. As a result, the existences of copolymers increased both the viscosity of emulsions and the intensity of interfacial film, in which case slow down the diffusion of demulsifier molecules and enhance the stability of emulsions, finally, the separation of water from oil becomes more difficult.

Study on Rheologic Behavior and Molecular Configuration in the Mixed Systems of Polyacrylamide and Surfactants

Rheologic properties and the conformations of the mixed system of hydrophobically modified polyacrylamide and surfactants in distilled water with or without NaCl were investigated. The vacuum sublimation freezing-drying technique was employed to maintain the aggregation state of the mixed systems. Scan electron microscopy and transmission electron microscopy were used to investigate microstructure of the mixed systems formed, and obtain the system molecular configuration information. The results showed that the rheologic behavior of the mixed solution revealed by viscosity data and microconformation obtained depend on the salt existence and the hydrophobic group content of the polymer. The relationship between polymer microconformation and the macroscopic properties for the mixed systems was analyzed to explore the aggregating mechanism.