Yangwen Zhu

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.

Studies of Synergism/Antagonism for Lowering Interfacial Tensions in Alkyl Benzene Sulfonate Mixtures

Synergistic effect for lowering interfacial tension in alkyl benzene sulfonates mixtures-alkane systems was studied by spinning drop tensiometer. The results show that surfactant mixtures of similar structure tend to give the same γmin for the same nmin, while the alkane preference curve of the surfactant mixtures with different structures take on the shape of that of surfactant with higher interfacial activity. In the case of surfactant mixtures with different interfacial activities, the one with lower activity will modify the hydrophilic-lipophilic balance of surfactant with higher activity and result in synergism/antagonism.

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.