Research

The self-assembly of colloidal particles differing in size, shape and chemistry at a range of interfaces presents currently a very important impact in both academia and industry. On the fundamental side, particles trapped at oil/water or air/water interfaces offer researcher a quasi-two-dimensional system to directly investigate many fundamental problems in condensed matter physics such as low-dimensional phase transitions, jamming transitions and crystal melting, in which the particles can be viewed as large atoms and their trajectories can be used to elucidate the interactions, thermodynamics, and dynamics in those distinctive phases. On the practical side, particle-laden interfaces open many opportunities for modulating the assembly of particles and for the chemical modification of particles, which in turn allows its exploitation to the fabrication of novel materials, such as Pickering emulsions, foams, liquid marbles and colloidosomes. Currently our group is interesting in:

Non-covalent intermolecular forces, such as van der Waals, electrostatic, steric, and hydrophobic interactions, have played essential roles in determining the association, aggregation, adhesion and sedimentation processes of colloidal particles, surfactant micelles, and macromolecules, in solutions and biological systems. These interaction forces, however, are normally weak (<pN) and are challenging and difficult to be directly measured by common force techniques. In recent years, our group has successfully developed a Total Internal Reflection Microscope (TIRM), which has no commercially available equivalent, and employed it in a series of experiments to study how particle-surface interactions are affected by factors such as chemical surface modification, adsorbed nanoparticle and polymer layers, and surface morphology.

We have established a setup that enables the study of the micro-rheological properties and structure of materials near a flat surface. The basic idea is to combine the spatial resolution of total internal reflection microscopy (TIRM) with a magnetic tweezers. In a standard TIRM measurement, an evanescent wave is generated by the total internal reflection of an incident laser light at a solid (glass slide)/liquid interface. The light intensity of such a wave decays exponentially with the distance away from the interface. When a micrometer scale magnetic particle probe is placed within 100 nm of the interface, it probes all the particle-surface separations that TIRM can resolve. As a result, TIRM is a highly sensitive spatial detector for tracking the vertical motion of the embedded probe particle, and viscoelastic moduli can be quantitatively determined from the effect of confinement. The motion of the embedded probe particle can be controlled by a magnetic driving force, produced by two sets of four electromagnetic pole pieces symmetrically arranged in the upper and lower planes of the sample cell so as to achieve a three-dimensional position control. High precision of the magnetic force, at pN scale, can be achieved by real-time control of the electric current. We are therefore able to oscillate the embedded magnetic particle and monitor the response to infer network viscoelasticity by a combination of the magnetic tweezers and the evanescent wave-scattered particle tracking near a surface. We expect that this technique will have great potential for non-invasive and spatially resolved characterization of the micro-rheological properties of soft materials and living cells.

Biocompatible and biodegradable magnesium (Mg) and its alloys possess excellent potential as orthopaedic implant biomaterials because they have similar mechanical properties to natural bones and magnesium ions (Mg++) are known to promote the growth of new bone. However, because Mg/Mg alloys corrode inside the human body, their mechanical properties deteriorate too quickly and lose their support functions if they are used for bone fracture fixation. Additionally, when the rate of corrosion-induced hydrogen generation is higher than the body’s natural hydrogen adsorption rate, hydrogen bubbles and alkalization can occur. As such, it is important to develop new biocompatible and corrosion-controlled bio-implants made of Mg and its alloys. Currently our group is interesting in:

Plastics, as most people refer to common polymers, are made from fossil fuels and have brought great convenience to our lives. We use plastic-based products in various fileds, such as food packaging, electronics, construction, and many other fileds, among which about 16 billion disposable coffee cups are consumed every year and half a billion plastic straws are discarded every day worldwide. However, most plastics are not degradable and common schemes including reducing, reusing, and recycling have been largely ineffecive. Most single-use plastics go directly into waste and then are dumped to landfill and into oceans, which has casued significant harm to environment and marine life. In the past decades, biodegradable plastics have been intensely investigated in academic environments with the perpetual optimism to remedy plastic pollution problem. Unfortunately, the commercial impact has been demonstrated to be minimal. Therefore, developing environmentally friendly and biodegradable alternatives to current plastics represents an emerging need for a sustainable future.