Shenwen Fang

Real-time monitoring the adsorption of sodium dodecyl sulfate on a hydrophobic surface using dual polarization interferometry

The adsorption process of sodium dodecyl sulfate (SDS) at a hydrophobic layer was investigated by dual polarization interferometry (DPI), which provided the real-time information at solid/liquid interface. In dilute solution, the molecules adsorb at the surface as isotropic layer. With the increase in concentration, the molecules aggregate to form hemimicelles and the critical hemimicelles concentration (HMC) is 1 mM. The adsorption of SDS at C18 surface obeys two-step process. The competitive formations of micelles in solution and hemimicelles on C18 surface lead to particular adsorption behavior in higher concentration. We also proposed a four-stage adsorption model of SDS at C18 surface according to bulk concentration.

Treatment of Produced Liquid from Polymer Flooding by using Cationic Surfactant

The treatment of produced liquid from polymer flooding is a significant problem in the oil field industry. Produced liquid from polymer flooding studied in this paper was composed of W/O emulsion and wastewater containing the residual polymer. Alkyltrimethylammonium halides (C12TAB, C14TAB, C16TAB, and C18TAB) and dialkyl-dimethylammonium halides (DC12TAB, DC16TAB, DC18TAB) were used both as the demulsifier for the W/O emulsion and as the flocculant for the wastewater. The demulsification tests showed that C16TAB is the best performing demulsifier for the W/O emulsion of these cationic surfactants and its water removal can reach 91% at the dosage of 150 ppm. The results of interfacial tension and interfacial dilational modulus showed that C16TAB had a rapid migration of surface-active agents to the water/oil interface and can lower the film strength significantly at the same time. Therefore, the C16TAB can have the best demulsification performance. In addition, C14TAB and C16TAB exhibited much better flocculation performance than the other surfactants. After the treatment with C14TAB and C16TAB, the oil content in wastewater decreased significantly to the 30 ppm because C14TAB and C16TAB can move to the oil/water interface and destroy the stability of the oil droplet in wastewater easily, which can be confirmed by the results of zeta potential.

Synthesis of Star Hydrophobically Modified Acrylamide Copolymer and its Dilute Solution Behavior in Water

The primary objective of this work was to prepare star copolymers of acrylamide and N,N-dimethyl-N-vinylnonadecan-1-aminium chloride(C18DMAAC) and to investigate the dilute solution behavior of these star hydrophobically modified acrylamide (SHMPAM) copolymers with different C18DMAAC content. The SHMPAMs were prepared using photopolymerization. For the different polymer solutions, the relationship between specific viscosity and polymer concentration obeyed the Rabins relation well, which means that the conformations of these polymer chains were nearly spherical in dilute solution. The data of these dilute solutions were fitted by four different equations. The results showed that Schulz–Blaschke(S–B) and Fedors equations more accuratly described the dilute solution properties of these kinds of copolymers. The intrinsic viscosities calculated by different equations were different from each other, which is different from the results found for linear HMPAM. The equivalent hydrodynamic volume (voluminosity VE ) of these star copolymer solutions can not calculated by the regular method because the relationship between Y (Y = (ηr 0.5−1)/C (1.35ηr 0.5−0.1), ηr is relative viscosity and C is polymer concentration) and polymer concentration was abnormal.

Synthesis and Characterization of Star Polyacrylamides Using Poly(ethylene imine) as a Core via Photopolymerization in Water

Water-soluble thioxanthone-terminated poly(ethylene imine) (PEI 600, PEI 1800, PEI 3000 and PEI 10000; 600, 1800, 3000 and 10000 are the weight-average molecular weights of the above PEIs, respectively). Macrophotoinitiators were synthesized by introducing a certain amount of thioxanthone (TX) moieties into the periphery of PEI, and the products were confirmed by 1H-NMR, FT-IR, and elemental analysis. Star polyacrylamides (PAMs) were prepared using the obtained macrophotoinitiator as a core via photopolymerization. The effect of the molecular weight of the macrophotoinitiator on photoinitiation efficiency of the resulting polymers was investigated. The result shows that the choice of the macrophotoimitator has no influence on the rate of polymerization. In addition, three plots of characteristic properties with the star polymer were studied to confirm the existence of arms in the resulting star PAM.

Optical sensor for fluoride determination in tea sample based on evanescent-wave interaction and fiber-optic integration

In this work, a miniaturized optical sensor was developed for fluoride determination in tea samples to evaluate their specific risks of fluorosis for public health based on evanescent-wave interaction. The sensor design was integrated on the optical fiber by utilizing the evanescent wave produced on the fiber surface to react with sensing reagents. According to the absorption change at 575nm, fluoride could be determined by colorimetric method and evaluated by Beers law. With improved performances of small detection volume (1.2μL), fast analysis (0.41min), wide linear range (0.01-1.4mgL-1), low detection limit (3.5μgL-1, 3σ) and excellent repeatability (2.34%), the sensor has been applied to fluoride determination in six different tea samples. Conventional spectrophotometry and ion chromatography were employed to validate the sensors accuracy and potential application. Furthermore, this sensor fabrication provided a miniaturized colorimetric detection platform for other hazardous species monitoring based on evanescent wave interaction.

A LED-based fiber-optic sensor integrated with lab-on-valve manifold for colorimetric determination of free chlorine in water

In this work, a colorimetric methodology was developed for free chlorine determination by constructing a fiber-optic sensor (FOS) which was designed by using a small LED as light source and two silica fibers as light transmission elements. Then the FOS was integrated with the sequential injection lab-on-valve (SI-LOV) manifold to fabricate a FOS-SI-LOV system for free chlorine detection. The colorimetric determination was based on the reaction between N,N-diethyl-p-phenylenediamine (DPD) reagent and free chlorine, which would produce a chromophore showing maximum absorbance at 511 and 551nm and detected by a micro spectrometer detector. By choosing a green LED with emission wavelength at 520nm as light source, the chlorine concentration could be simply evaluated according to Beers law. The developed FOS-SI-LOV system showed improved performances of wide linear range (10-400μgL-1), low detection limit (3.5μgL-1, 3σ), fast analysis (6.85s) and excellent repeatability (0.0083 RSD, n=8) for chlorine determination. The proposed FOS-SI-LOV system has been applied to on-line and real-time chlorine determination in different water samples with excellent selectivity. Furthermore, this FOS-SI-LOV methodology provided a colorimetric and fluorescence detection platform for other hazardous species monitoring in water environment based on Beers law and Stern-Volmer relationship, respectively.

The Phase Inversion Properties of a Non-ionic Surfactant and its Performance for Treatment of Oily Wastewater Produced from Polymer Flooding

The treatment of oily wastewater produced from polymer flooding (OWPF) is a big problem for offshore oilfields. A non-ionic surfactant named poloxyproylenated-poloxyethyleneated hydrogenated tallow alkyl secondary amine (PPHTA) was prepared. The relationship between its interfacial tension and temperature and the result of conductivity measurement showed that its phase inversion temperature (PIT) was about 60°C and it had good interfacial activity. Then, OWPF was treated by PPHTA. It was interesting that the PPHTA had a good performance for treatment of OWPF at the temperature which was higher than its PIT. At 63°C, after the treatment by PPHTA at dosage of 800 mg/L, the oil content in OWPF changed from 4724 mg/L to 72 mg/L. The reason was discussed and it was proposed that the PPHTA can displace the natural active agents in OWPF and form a new oil-PPHTA-water emulsion. When the temperature increased, the hydrophilic- lipophilic deviation (HLD) of oil-PPHTA-water moved to zero and the emulsion stability decreased. At the PIT, the most unstable emulsion was formed and it was destroyed after stirring. In addition, it is important to note that the floc of PPHTA was composed of oil drops and was not viscous. The result was different from the viscous floc caused by the cationic polymer.

Synthesis of Copolymer of Acrylamide and a Cationic-Nonionic Bifunctional Polymerizable Surfactant and Its Micellar Behavior in Water

A novel cationic-nonionic bifunctional polymerizable surfactant (PEP) was prepared by the quaternarization of poly (ethylene oxide-propylene oxide) block polymers (PEO-PPO) having terminal tertiary amine group with chloropropene. Polymeric surfactant (PAM-g-PEP) was prepared by the copolymerization of acrylamide and PEP in water and the product was confirmed by FTIR. PAM-g-PEP has exhibit excellent surface and interfacial activity and its surface tension and interfacial tension at cmc are 40.13 mN/m and 11.69 mN/m, respectively. The influence of temperature on the micellar behavior of the PAM-g-PEP in water was studied by the dynamic laser scatting (DLS) and ultraviolet spectroscope. The results showed that PAM-g-PEP in water is thermo-associative. In diluted PAM-g-PEP solution, the Rh of the polymeric surfactant increases with the temperature due to the interpolymeric aggregations are formed. In the case of concentrated PAM-g-PEP solution, the light transmittance of PAM-g-PEP aqueous solution decreases with the increasing temperature, which is may be caused by the increase of the number of the interpolymeric PEP chain aggregates.

Shear degradation resistance of star poly(ethyleneimine) - polyacrylamides during elongational flow

Abstract An experimental study of the flow-induced scission behaviour of four star hydrolyzed polyacrylamides (HPMA) with different arms during planar elongational flow in a cross-slot flow cell is described. The results showed that the shear stability of linear HPAM in distilled water was not essentially different from star HPAM. Polymer scission was not observed in either system in a shear rate range from 20,000 to 100,000s-1, which can be attributed to the strong polyelectrolyte behaviour of HPAM in distilled water. However, at the same shear rate, the star HPAMs exhibited superior shear stability in comparison to the linear HPAMs in aqueous solutions containing NaCl (CNaCl=0.2-1.0%wt) and, in particular, the initial reduction rate of relative viscosity (R) decreased with the degree of branching of the HPAMs. In addition, it was found that the R of five HPAMs in NaCl aqueous solutions exhibited an exponential dependence on shear rate, in which the coefficient C1 can be used to quantitatively evaluate shear stability. In star HPAM NaCl aqueous solutions, the increase of R with shear rate is very likely due to the decrease of the hydrodynamic radius (Rh) of these HPAMs, while the increase of R with NaCl concentrations can be attributed to the relatively low viscosity of these polymers at high NaCl concentrations.

Viscometric Studies of Interactions between Hydrophobically Modified Acrylamide Copolymer and Poly(N-isopropylacrylamide) in Dilute Solutions

The viscosity behavior of the dilute aqueous solutions of hydrophobically modified acrylamide copolymer (HMPAM) and poly(N-isopropylacrylamide) (PNIPAM) was investigated. A negative deviation of reduced viscosity of HMPAM + PNIPAM from the theoretical values was observed. Both a conventional viscometry method and a method using an aqueous solution of one polymer as the solvent for the other polymer were used to clarify the mechanism behind the observed viscosity behavior. With the conventional method, the theoretical predictions obtained by the Δb (or α) criterion are contradictory to the experimental results and cannot be applied to describe the interaction between HMPAM and PNIPAM, where Δb is the difference of experimental interspecific interaction coefficient bm and theoretical bm,i and α is the difference of experimental Huggins coefficient km and theoretical km,i. The change of Δ[η]/[η]i suggests that there is only an attractive interaction between HMPAM and PNIPAM, where Δ[η] is the difference of experimental intrinsic viscosity [η]m and theoretical [η]i. Results from the method using an aqueous solution of one polymer as the solvent for the other polymer confirmed the attractive interaction between HMPAM and PNIPAM and indicated that the attachment of the PNIPAM molecules to the hydrophobic groups in HMPAM can disrupt both the initial intra- and intermolecular associations between HMPAM chains simultaneously. The disruption of the original intramolecular association of HMPAM leads to an increase in the intrinsic viscosity [η], while the disruption of the original intermolecular association of HMPAM yields a negative deviation of the reduced viscosity.