Xulong Cao

Responsive wetting transition on superhydrophobic surfaces with sparsely grafted polymer brushes

We demonstrate here that surface wetting transitions and contact angle hysteresis can be significantly altered by manipulating the droplet–surface interaction, which has never been reported before. The dynamic wetting behavior of a pressed water droplet on responsive polymer brushes-modified anodized alumina with pre-modified dilute initiator is shown. The wetting transition between superhydrophobicity and hydrophilicity can or cannot be achieved depending on the responsiveness between droplets of different pH, the concentrations of electrolytes and the environmental temperature and surface grafted stimuli-responsive polymer brushes. The contact angle changes are rather apparent, giving the surface double-faced wetting characteristics. The responsive surface composition regulated wetting will be very useful in understanding wetting theory, and will be helpful experimentally in designing smart surfaces in, for example, microfluidic devices.

Tribological properties of self-assembled monolayers of catecholic imidazolium and the spin-coated films of ionic liquids.

A novel compound of an imidazolium type of ionic liquid (IL) containing a biomimetic catecholic functional group normally seen in mussel adhesive proteins was synthesized. The IL can be immobilized on a silicon surface and a variety of other engineering material surfaces via the catecholic anchor, allowing the tribological protection of these substrates for engineering applications. The surface wetting and adhesive properties and the tribological property of the synthesized self-assembled monolayers (SAMs) are successfully modulated by altering the counteranions. The chemical composition and wettability of the IL SAMs were characterized by means of X-ray photoelectron spectroscopy (XPS) and contact angle (CA) measurements. The adhesive and friction forces were measured with an atomic force microscope (AFM) on the nanometer scale. IL composite films were prepared by spin coating thin IL films on top of the SAMs. The macrotribological properties of these IL composite films were investigated with a pin-on-disk tribometer. The results indicate that the presence of IL SAMs on a surface can improve the wettability of spin-coated ionic liquids and thus the film quality and the tribological properties. These films registered a reduced friction coefficient and a significantly enhanced durability and load-carrying capacity. The tribological properties of the composite films are better than those of pure IL films because the presence of the monolayers improves the adhesion and compatibility of spin-coated IL films with substrates.

Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions. GRAPHICAL ABSTRACT

Dilational Rheological Properties of P-(n-alkyl)-benzyl Polyoxyethylene Ether Carboxybetaine at Water–Decane Interface

The dilational rheological behaviors of absorbed films of p-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine CxBE2CB (x = 8, 10, 12) at the water–decane interface have been investigated by the drop-shape analysis method. The influences of time, oscillation frequency, and bulk concentration on dilational modulus and phase angle have been expounded. The experimental results show that the phase angle of CxBE2CB (x = 10, 12) decreases with the increase of time, the slope of the log ϵ − log ω curve and phase angle of CxBE2CB (x = 10, 12) decrease in a wide concentration range. These phenomena become more and more apparent with the increase of hydrocarbon chain length and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. Therefore, the compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sublayer play a more important role for CxBE2CB (x = 10, 12) adsorption film. The dependence of dilational modulus on interfacial pressure can support our provided mechanism strongly.

Effect of Demulsifier Structures on the Interfacial Dilational Properties of Oil–Water Films

The dilational properties of a branch-shaped polyether-type nonionic demulsifier (PEB), a comb-shaped polyether-type nonionic demulsifier (PEC), and a star-shaped polyether-type nonionic demulsifier (PES) at the decane–water interfaces were investigated by Langmuir trough method through oscillating barrier and interfacial tension relaxation methods, which are mainly in the influences of oscillating frequency and bulk concentration on dilational properties. Meanwhile, the effect of demulsifiers on interfacial dilational modulus of diluted crude oil was also explored. The experimental results indicate that all demulsifiers can decrease the dilational modulus of diluted crude oil at the experimental concentration. The addition of PEB causes the dilational modulus of crude oil to be lower than that at the water–decane interface. The demulsifier PEC has a similar effect with PES to influence the interfacial film of crude oil: at low concentration, the dilational modulus of mixed interfacial film is lower than that of demulsifier alone, while at high concentration, the dilational modulus of mixed interfacial film is slightly higher than that of demulsifier alone. The dependence of static modulus on the bulk concentration is consistent with the trend of interfacial dilational modulus with concentration for demulsifiers PEB, PEC, and PES. The studies about the structure modulus show that the new demulsifiers PEC and PES have a stronger ability than branch-shaped demulsifier PEB to destroy the interfacial film. GRAPHICAL ABSTRACT

One Factor Influencing the Oil-displacement Ability of Polymer Flooding: Apparent Viscosity or Effective Viscosity in Porous Media?

Abstract Polymer flooding has been an important process to enhance oil recovery (EOR) worldwide. In practice, partially hydrolyzed polyacrylamides (HPAMs) have many defects including shear degradation and sensitivity to salt. For these reasons, hydrophobically associating polyacrylamides (HAPAMs) have been developed for harsh oil reservoirs. In this work, the properties of two classes of polymers (HPAMs and HAPAMs), including apparent viscosities, effective viscosities in porous media, and oil-displacement efficiencies, are studied. As expected, HAPAM exhibits apparent viscosity enhancement properties due to intermolecular hydrophobic association while HPAM cannot. However, the effective viscosity of HAPAM is always lower than HPAM possibly because of adsorption loss and the reduction in strength of the hydrophobic association through porous media. The tertiary oil recovery increases with the increment of the effective viscosity of polymer. Oil-displacement efficiency of HAPAM is also lower than HPAM at the same concentration of 2,000 mg/L.

Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

ABSTRACT Various experimental methods were used to investigate interaction between polymer and anionic/nonionic surfactants and mechanisms of enhanced oil recovery by anionic/nonionic surfactants in the present paper. The complex surfactant molecules are adsorbed in the mixed micelles or aggregates formed by the hydrophobic association of hydrophobic groups of polymers, making the surfactant molecules at oil-water interface reduce and the value of interfacial tension between oil and water increase. A dense spatial network structure is formed by the interaction between the mixed aggregates and hydrophobic groups of the polymer molecular chains, making the hydrodynamic volume of the aggregates and the viscosity of the polymer solution increase. Because of the formation of the mixed adsorption layer at oil and water interface by synergistic effect, ultra-low interfacial tension (∼2.0 × 10−3 mN/m) can be achieved between the novel surfactant system and the oil samples in this paper. Because of hydrophobic interaction, wettability alteration of oil-wet surface was induced by the adsorption of the surfactant system on the solid surface. Moreover, the studied surfactant system had a certain degree of spontaneous emulsification ability (D50 = 25.04 µm) and was well emulsified with crude oil after the mechanical oscillation (D50 = 4.27 µm). GRAPHICAL ABSTRACT

Synthesis and Interfacial Activity of Nonyl Phenol Polyoxyethylene Ether Carboxylate

In order to study the interfacial activity of the anionic-nonionic surfactant, five nonyl phenol polyoxyethylene ether carboxylates were synthesized and mass spectra were used to characterize their structures. The tensions of the anionic–nonionic surfactant aqueous solutions against crude oil were measured and the effects of the surfactant structure, concentration, and salinity on the interfacial activities were discussed. It was shown that nonyl phenol polyoxyethylene (6) ether carboxylate can produce ultralow interfacial tension when the concentrations are not lower than 0.10%, exhibiting a high interfacial activity and a good anti-dilution resistance. Moreover, it was proved that there exists synergism between NaCl and MgCl2 (or CaCl2), which is crucial to achieve the ultralow interfacial tension.

Fly Ash Particles Modified with Various Surface Coupling Densities and Its Thermal Stability Mechanism of Oil-in-Water Emulsion

The fly ash particle was modified with various surface coupling densities and IR testified that γ-glycidoxy propyl trimethoxy silane (GPMS) is located on the surface of it Vis chemical bond. The surface GPMS-coupling density could influence the hydrophilic–lipophilic properties of the particles. The contact angles increase with the increase of additive amounts of modifiers. It indicates the surface of fly ash changed from water wetting to oil gradually. Using DLS, the dispersion state of fly ash with different GPMS-coupling densities was studied. A suitable modification of fly ash with GPMS did not change the dispersion state significantly. To achieve good dispersibility in HPAM solution, the surface GPMS-coupling density should be controlled within the range of 1.4–3 μmol (m2 FA)−1. Using fly ash particle–surfactant–polymer system, the O/W emulsion stabilized is investigated to stable Pickering emulsion. The particle in surfactant and polymer solution synergistically interacted at the oil/water interface. The emulsion system of GPMS (2.98)-FA particles in PAM and SDS solution shows higher thermal stability as compared to other particles as it was dispersed very well on the emulsion interface.

Chemical Enhanced Oil Recovery Technology in Shengli Oilfield

The original oil in place suitable for chemical flooding in Shengli oilfield is 1.6 billion ton. Though the resource is abundant, the oil recovery is poor due to rigorous reservoir conditions, including high temperature, high salinity, high divalent-cation content, high oil viscosity and severe heterogeneity. In an effort to counteract the rigorous reservoir conditions, polymer flooding technologies for class I and II reservoirs has been improved, and surfactant/polymer flooding has been implemented industrially. Heterogeneous combination flooding technology has made great breakthroughs. A unique series of chemical flooding technologies has been developed and played a significant role in maintaining oil production in mature fields.