CHEN, Shing-Bor

Associate Professor

PhD (Chem. Eng.) Cornell, 1996
MSc (Chem. Eng.) Natn'l Taiwan, 1988
BSc (Chem. Eng.) Tsing-Hua, 1986

Contact information
Blk E5, 4 Engineering Drive 4, #02-30, Singapore 117576
Tel: (65) 6516 5237    Fax: (65) 6779 1936
Email: checsb@nus.edu.sg

Research Group Page

RESEARCH

Microstructure and dynamics of polyelectrolyte and gel

Polyelectrolytes are polymers carrying charge due to dissociation of ionizable groups in a polar solvent, and show very different behaviors from their neutral counterpart. For aqueous systems, they are widely used as a viscosity modifier in many industries. The charge effect plays a dominant role in the behavior of these polymers. In aqueous nondilute solutions of low ionic strength, clusters form, each consisting of a number of polymer chains. This phenomenon has been attributed to the attractive interaction arising from the distribution of condensed counterions. Also, intra- and interchain bridging may take place in the presence of multivalent counterions. When crosslinked, these polymers form a hydrogel, whose properties are strongly affected by the presence of small ions. We use Brownian dynamics simulations to study dynamics of polyelectrolyte in dilute solutions, and tracer diffusion with hydrodynamics interaction taken into account. For polyelectrolyte gels, a similar simulation technique is employed to examine the dynamics via probe diffusion.

Phase behavior and rheology of surfactant-polymer solutions

Surfactant-polymer mixtures are widely used in cosmetics, daily care product and pharmaceuticals industries. The former species is used to remove dirt and grease, while the latter acts as thickener. The molecular interactions and microstructure play a critical role in the properties of the materials. Currently, we are experimentally investigatingthe mixture of hydrophobically modified polymer and surfactant regarding a sol-gel transition, clouding phenomenon, shear enhanced association, rheology, etc. For clouding behavior and phase separation, we examine the influence of the presence of polymer on the clouding point temperature, micellar growth and phase compositions. For rheology, we seek a better understanding of the interplay between the microstructure and macroscopic properties via rheometry and light scattering

Deliquescence and efflorescence of nanoparticles

Most of aerosol is hygroscopic and grows dramatically in size when the relative humidity exceeds a critical value. This phenomenon known as deliquescence due to water absorption is important for the formation of cloud droplets in the atmosphere. The reverse process, where the aerosol droplets become dry at a sufficiently low humidity, is named efflorescence. The two processes show an interesting hysteresis behavior. The critical relative humidities depend on the particle species and size. When particles are deposited on a substrate, the surface properties will also affect the critical relative humidities, and is an important issue for microelectronic industry and material corrosion. We are carrying out theoretical study to predict how the critical relative humidities are affected by the hydrophilicity and hydrophobicity of the substrate. AFM is also used to monitor the particle growth and reduction to determine the deliquescence and efflorescence points.

SELECTED PUBLICATIONS

T. Zhou, and S. B. Chen "Computer simulations of diffusion and dynamics of short-chain polyelectrolytes," J. Chem. Phys., 124, 034904 (2006).

G. Q. Zhao, C. C. Khin., S. B. Chen, and B. H. Chen "Nonionic surfactant and temperature effects on the viscosity behavior of hydrophobically modified hydroxyethyl cellulose solutions," J. Phys. Chem. B, 109, 14198 (2005).

T. Zhou, and S. B. Chen "A Brownian dynamics study on the self-diffusion oc charged tracers in dilute polyelectrolyte solutions," J. Chem. Phys., 122, 124905 (2005).

S. B. Chen "Monte Carlo simulations of conformations of chain molecules in a cylindrical pore," J. Chem. Phys., 123, 074702 (2005).

T. Zhou, and S. B. Chen "Monte Carlo simulations of dendrimer-polymer conjugates," Macromolecules, 38, 8554 (2005).