Zeming Li

Bio: Zeming Li is an academic researcher from Beihang University. The author has contributed to research in topics: Lubrication & Materials science. The author has an hindex of 3, co-authored 3 publications receiving 11 citations.

A Bioinspired Flexible Film Fabricated by Surface-Tension-Assisted Replica Molding for Dynamic Control of Unidirectional Liquid Spreading.

Abstract: The unidirectional liquid spreading without external energy input has presently aroused widespread concern. Recently, on the peristome of Nepenthes alata, a novel 2D unidirectional liquid spreading has been reported. It has been revealed that its exquisite superhydrophilic multistage microstructure, overlapping microcavities with arc-shaped edges and wedge-shaped corners, is the main reason for this phenomenon. To fabricate a peristome-inspired surface, a replica molding method is highly efficient and provides an ideal structure. However, the curved shape of the finally formed surface cannot be adjusted, and a specific surface shows only one type of liquid spreading state, greatly limiting its potential application. Here, we aimed to develop a novel surface-tension-assisted replica molding method to fabricate an artificial peristome film. The artificial peristome film was fabricated by pouring styrenic block copolymers (SBS) dissolved in organic solvents into a negative replica prepared in polydimethylsiloxane (PDMS), based on the natural peristome. With volatilizing the organic solvent, the SBS agglomerates formed an artificial peristome film via surface tension effects. More importantly, the PDMS-negative replica swelled in the organic solvent and then returned to the original size, which is conducive for replicating microstructures. The liquid spreading speed could be dynamically controlled by stretching the artificial peristome film. We demonstrated that the microcavity wedge angle decreases with an increasing stretching ratio. A smaller wedge angle can result in a much stronger unidirectional liquid spreading ability. This study provides insight into the dynamic control of unidirectional liquid spreading for novel pump-free medical microfluidic devices.

Mechanical and swelling properties of PDMS interpenetrating polymer networks

Abstract: Abstract Poly(dimethylsiloxane) (PDMS) interpenetrating networks (IPNs) of two different molecular weight PDMS were prepared. Six series of IPNs were obtained by first tetra-functionally end-linking long vinyl-terminated PDMS (molar mass 23 × 10 3 or 21 × 10 3 g mol −1 ) neat or in a 50% solution with unreactive PDMS chains. These networks were then dried and swollen with short reactive telechelic PDMSs (molar mass 800, 2.3 × 10 3 or 5.7 × 10 3 g mol −1 ) that were subsequently end-linked. The mechanical, toughness and swelling properties of these IPNs were investigated. We found that the correlation between modulus ( E ) and equilibrium swelling ( Q ) in toluene of the PDMS IPNs obeys a scaling relation identical to that of a normal unimodal PDMS network. This result strongly suggests effective load transfer between the networks. The results of the elastic modulus and of the toughness of the networks represented by the energy required to rupture them were analyzed in terms of a recent model by Okumura [Europhys Lett 2004;67:470.]. Although the modulus results are in reasonable agreement with the equal-stress model of Okumura, the toughness results are not. In addition, our measured toughness decreases instead of increases with composition in an opposite trend to that predicted by the equal-strain model. An empirical model based on fracture mechanics gives a good representation of the toughness data.

Capillary rise of a liquid between two vertical plates making a small angle

Abstract: The penetration of a wetting liquid in the narrow gap between two vertical plates making a small angle is analyzed in the framework of the lubrication approximation. At the beginning of the process, the liquid rises independently at different distances from the line of intersection of the plates except in a small region around this line where the effect of the gravity is negligible. The maximum height of the liquid initially increases as the cubic root of time and is attained at a point that reaches the line of intersection only after a certain time. At later times, the motion of the liquid is confined to a thin layer around the line of intersection whose height increases as the cubic root of time and whose thickness decreases as the inverse of the cubic root of time. The evolution of the liquid surface is computed numerically and compared with the results of a simple experiment.