Lian-Fang Feng

Membranes of Vertically Aligned Superlong Carbon Nanotubes

In the present work, we have developed a simple but effective method to prepare superlong vertically aligned carbon nanotubes (SLVA-CNT) and epoxy composite membranes, and we have demonstrated that various liquids, including water, hexane, and dodecane, can effectively pass through the SLVA-CNT membranes. These results were confirmed by molecular dynamics simulations. While the mechanical densification was used to further enhance the flow transport through the SLVA-CNT membranes, we developed in this study a magnetic-nanoparticle switching system to turn on and off the flow through the nanotube membrane by simply applying an alternating voltage. The methodologies developed in this study should have a significant implication to the development of various smart membranes for advanced intelligent systems.

Superhydrophobic electrospun POSS-PMMA copolymer fibres with highly ordered nanofibrillar and surface structures

A POSS-PMMA copolymer has been synthesised by conventional free-radical polymerisation reaction. Uniform electrospun fibres from this copolymer showed a water contact angle as high as 165 degrees with a sliding angle as low as 6 degrees . For the first time, we found that the electrospun fibres had a bundled nanofibril secondary structure with an ordered POSS morphology on the fibre surface.

Reversible Self‐Assembly of Terpyridine‐Functionalized Graphene Oxide for Energy Conversion

Terpyridine-functionalized graphene oxides were prepared for self-assembly into 3D architectures with various metal ions (e.g., Fe, Ru). The resulting electrode materials showed significantly improved electroactivities for efficient energy conversion and storage. They showed promise for application in the oxygen reduction reaction (ORR), photocurrent generation, and supercapacitance.

Carbon Nanotube-Coated Macroporous Poly(N-isopropylacrylamide) Hydrogel and Its Electrosensitivity

A facile method of fabricating novel CNT-coated macroporous PNIPAAm hydrogel composite was proposed. The method was based on the deposition of a dense and compact CNT layer on the pore walls of the preformed macroporous PNIPAAm hydrogel scaffold. The resulted hydrogel composite exhibited an electric current sensitivity resulting from electro-thermal conversion. When an external electric current was applied, this hydrogel composite could be electrically heated and then showed a thermally induced shrink.

Fluid mixing in droplet-based microfluidics with a serpentine microchannel

The hydrodynamics and mixing process within droplets travelling along a three dimensional serpentine microchannel are studied using a computational fluid dynamics simulation based on the volume-of-fluid approach. The fluid mixing within the droplet follows symmetric circulations in the straight section, which generates axial mixing. In the winding section, the asymmetric circulations lead to the reorientation of the fluids within the droplet, thus enhancing the mixing efficiency. The mixing performance is controlled by the spatial distribution of the mixing components and the circulation period within the droplet. The best mixing occurs when the droplet size is comparable with the channel width. When the droplet size is less than two times the channel width, the asymmetric circulations make it easy for the fluid to distribute in the axial direction, which leads to a fast mixing process. For larger droplets, the long circulation period becomes more significant, which causes lower mixing efficiency.

Study on Ethylene-α-Olefin Copolymerization Catalyzed by the MgCl2-Supported and Low Ti-Loading Ziegler–Natta Catalyst

Ethylene-α-olefins copolymers were synthesized with MgCl2-supported and low Ti-loading Ziegler-Natta catalyst prepared using the one-pot balling method. The effects of the type of comonomer, the concentration of comonomer, and polymerization temperature on the catalytic activity, kinetic behavior, molecular weight, and its distribution of the resultant copolymer were studied. It was found that the resultant copolymers have a wide molecular weight distribution. The formation mechanism of polymer with broadened molecular-weight distribution was also discussed using the method of fitting the molecular weight distribution (MWD) curves with multiple Flory-Schulz functions.

Crystallization behavior of functional polypropylene grafted graphene oxide nanocomposite

With an aim to understand the role of polymer grafted graphene oxide (GO) in crystallization processes, a functional polypropylene (PP) grafted GO nanocomposite, prepared by isocyanate group-contained polypropylene (PP-g-TMI) reacting with hydroxyl and carboxyl groups on GO, was investigated in terms of isothermal and non-isothermal crystallization by differential scanning calorimetry. Comparing with the PP-g-TMI/natural graphite (NG) nanocomposite, a fully exfoliated and uniformly dispersed GO in the PP-g-TMI matrix for the PP-g-TMI/GO nanocomposite was affirmed by transmission electron microscopy and a large enhancement of its storage modulus. For isothermal crystallization at 140 °C, the addition of GO into PP-g-TMI accelerates the crystallization rate dramatically more than that of NG, indicating the grafted GO can act as a very efficient heterogeneous nucleation agent to increase nucleation dramatically. However, for isothermal crystallization at 126 °C, the crystallization rate of PP-g-TMI accelerated by grafted GO is inferior to that by NG, which can deduce that the grafted GO can restrict migration and diffusion of polymer molecular chains to the surface of the nucleus for spherulitic growth due to strong covalent binding with PP-g-TMI, the formed highly viscous and dense GO layers. These two converse effects of the grafted GO on crystallization can also explain the interesting non-isothermal crystallization behavior that the grafted GO increases the crystallization rate of PP-g-TMI at a low cooling rate, while it decreases the crystallization rate at a high cooling rate.

Synthesis, copolymer composition, and rheological behavior of functionalized polystyrene with isocyanate and amine side groups

Isocyanate and amine functionalized polystyrene (PS) were prepared through the solution copolymerization method with the presence of the intermediate substance 3-isopropenyl-α,α′-dimethylbenzene isocyanate (TMI). The samples with different copolymer composition of functional group were prepared with a range of molecular weights by free radical polymerization, the functional group such as isocyanate, acid amine, and amine group were introduced by appreciate reaction conditions. The isocyanate, acid amine, and amine functionalized polystyrene (PS), denoted as P(St-co-TMI), intermediate product P(St-co-TMITBC) and PS-NH2, respectively. The chemical structure of the samples was characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H NMR spectroscopies. The results indicated that the functional groups successfully formed on the side chain of polystyrene. The molecular weight, its distribution, and copolymer composition of functional group were analyzed by gel permeation chromatography combined with FT-IR. The results showed that the copolymer composition increased with the increasing functional monomer content. Viscoelastic behavior in the melt state was investigated and analyzed with dynamic rheology to determine the influence of the interaction of the polymer chain special groups on the rheological properties.

Computational fluid dynamics simulation of hydrodynamics in an uncovered unbaffled tank agitated by pitched blade turbines

Computational fluid dynamics (CFD) simulations were applied for evaluating the hydrodynamics characteristics in an uncovered unbaffled tank agitated by pitched blade turbines. A volume of fluid (VOF) method along with a Reynolds stress model (RSM) was used to capture the gas-liquid interface and the turbulence flow in the tank. The reliability and accuracy of the simulations are verified. The simulation results show that the vortex can be divided into central zone and peripheral zone, and flow field in the tank can be divided into forced vortex flow region and free vortex flow region. With the increase of impeller speed, the vortex becomes deeper, while the critical radius of the two zones keeps almost unchanged. The impeller clearance and the rotational direction have little effect on the vortex shape. The vortex becomes deeper with increasing of the impeller diameter or the blade angles at the same rotational speed. Power number is little influenced by the impeller speed, and decreases by about 30% when impeller diameter varies from 0.25T to 0.5T. When blade angle varies from 30° to 90°, power number increases by about 2.32-times. Power number in uncovered unbaffled tank is much smaller than that in baffled tank, but is very close to that in a covered unbaffled tank. The discrepancy of power number in uncovered unbaffled tank and that in covered unbaffled tank is less than 10%.

Integration of CFD and polymerization for an industrial scale cis-polybutadiene reactor

ABSTRACT A computational fluid dynamics (CFD) approach, coupled with anionic polymerization kinetics, was used to investigate the solution polymerization in a 12 m3 industrial scale cis-polybutadiene reactor. The kinetic model with double catalytic active sites was integrated with CFD by a user-defined function. The coupled model was successfully validated by the plant data and then used to investigate the key operating variables. Also, predictions of CFD model were compared with those of continuous stirred tank reactor (CSTR) model. Although the reaction mixture is well mixed in the middle and at the top of the reactor, there exists a poor mixing feeding zone at the bottom, which leads to serious deviations from the ideal CSTR. The polymerization process with nonideal mixing is very sensitive to the inlet temperature and the feeding rate. Enhancing the mixing performance in the feeding zone could be an effective way to improve the product quality.