Jun-Ying Xiong

Determination of agarose gel pore size: Absorbance measurements vis a vis other techniques

The absorbance measurements in the wavelength range 700 nm to 800 nm were used to probe the agarose gel topology evolution and extract the pore size of the trapped solvent. By following the changes in absorbance and pore size, the gelation process could be clearly divided into three stages - induction stage, gelation stage and pseudo-equilibrium stage. The gelation mechanism is explained as a nucleation and growth process. Following the kinetics of gelation using dynamic light scattering is complicated by multiple scattering (for high concentrations) and large fluctuations in intensity and relaxation time. Comparatively, scanning the absorption spectrum is fast and the method is suitable for a wide range of concentrations and setting temperatures. Pore size determination using absorbance is a fast and non-invasive method when compared to the DNA electrophoresis measurements, which extend over several hours and use probe diffusion.

Surfactant free fabrication of polyimide nanoparticles

Polyimide nanoparticles are fabricated using a combined liquid–liquid phase separation and solvent/nonsolvent mixing technology. This technology allows us to produce stable polyimide nanoparticles with tunable size without any surfactants. Selective solvation and electron pair donor/electron pair acceptor interaction are employed to stabilize nanoparticles. The formation of polyimide nanoparticles is governed by a nucleation-dominated process and therefore the particle size is controlled by the nucleation rate. A very high level of supersaturation can be attained under the intensive local motions induced by ultrasound, resulting in a very high nucleation rate. This effect is found extremely useful in the fabrication of sub-50-nm polyimide nanoparticles.

Understanding of hydrogel network formation and its application in the architecture of significantly enhanced hydrogel

An understanding of the physical hydrogel network formation has been obtained by dynamic rheological experiments. The evidence shows that the network formation turns out to be a nucleation-controlled process. It was found that there exists a critical temperature Tc; fiber branching is greatly enhanced when the network formation is performed in the regime of T<Tc (T, the final setting temperature). This finding enables the authors to build significantly enhanced gel networks. So far G′ (elastic modulus) of the hydrogel network has been enhanced by 187% while the formation period can be greatly shortened to only 1∕20 of the previous process.An understanding of the physical hydrogel network formation has been obtained by dynamic rheological experiments. The evidence shows that the network formation turns out to be a nucleation-controlled process. It was found that there exists a critical temperature Tc; fiber branching is greatly enhanced when the network formation is performed in the regime of T<Tc (T, the final setting temperature). This finding enables the authors to build significantly enhanced gel networks. So far G′ (elastic modulus) of the hydrogel network has been enhanced by 187% while the formation period can be greatly shortened to only 1∕20 of the previous process.