Daming Wu

Improved electrical conductivity of PDMS/SCF composite sheets with bolting cloth prepared by a spatial confining forced network assembly method

A novel method of Spatial Confining Forced Network Assembly (SCFNA) for preparation of high-performance electrically conductive polymeric composites was proposed in this paper. Differing from the self-assembly mechanism, as in traditional compounding processes, the SCFNA process could provide conductive fillers with an effective forced networking assembly action to get a more compacted network. High electro-conductive polydimethylsiloxane (PDMS)/short carbon fiber (SCF) binary composites with a low percolation threshold of 0.15 wt% were prepared by the SCFNA method. A rapid increase in electrical conductivity from 1.71 × 10−12 S m−1 of PDMS to 1.67 × 102 S m−1 was achieved with 4 wt% short carbon fibers. It was shown that a continuous and compact SCF network was built in a PDMS matrix. Furthermore, when the bolting cloth as a sarking was co-compressed with the mixture, a much lower percolation threshold of 0.06 wt% and a higher electrical conductivity of 3.22 × 102 S m−1 with 4 wt% of SCF were obtained due to volume exclusion. Compared with the conventional compounding method, the electro-conductive properties of the composites prepared by the above mentioned method can be enhanced up to several times, or even by orders of magnitudes. Moreover, if the mesh number of the bolting cloth is large enough, the carbon fibers will be impeded from penetrating the bolting cloth together with the polymer when they are co-compressed, thus an electrically conductive film with single or double insulating face could be prepared through this method.

Recent Progress in Metal-Based Nanoparticles Mediated Photodynamic Therapy

Photodynamic therapy (PDT) is able to non-invasively treat and diagnose various cancers and nonmalignant diseases by combining light, oxygen, and photosensitizers (PSs). However, the application of PDT is hindered by poor water solubility and limited light-penetration depth of the currently available photosensitizers (PSs). Water solubility of PSs is crucial for designing pharmaceutical formulation and administration routes. Wavelength of light source at visible range normally has therapeutic depth less than 1 mm. In this review, focus is on the recent research progress of metal-based nanoparticles being applied in PDT. The potential toxicity of these nanoscales and future directions are further discussed.

Effect of surface tension on filling flow of carboxymethyl cellulose solution in microchannel

Abstract The effect of surface tension on filling flow is neglected generally in macroscale flow. However, it may become a significant factor to impact the filling flow in microchannel. In this paper, the effect of surface tension on filling flow was investigated by a visualisation device to facilitate the observation of flow behaviour. Capillaries in the diameter range of 0·1–0·5 mm were chosen as microchannels and 3% solutions of carboxymethyl cellulose polymer were studied. The results indicate that additional pressure accounting for surface tension influences the filling flow in microchannel slightly. The error of theoretical velocity considering the surface tension reaches 8% in capillary of 0·1 mm in diameter. The surface tension can be neglected when feature size of flow channel is >0·1 mm. Meanwhile, wall slip exists during the filling flow into capillaries and slip velocity increases as decreasing feature size. Therefore, some other factors such as wall slip and size effect could impact filling flow together in microchannel if the feature size of channel is <0·1 mm.

Study of the dispersion capability of an in-situ bubble stretching method used for preparing polymer nanocomposites

In-situ Bubble Stretching (ISBS) has been shown to be an effective method for dispersing aggregated nanoparticles in polymer melts. By using the fast expansion of bubbles under certain conditions, a stretching rate as high as 10 5 ∼ 10 6 s -1 and elastic oscillations on the bubble wall can be obtained, and this is effective in the dispersion of the aggregated nanoparticles. In this paper, the dispersion capability of ISBS was simulated using a mathematical model taking into account the foaming conditions and the properties of the polymers. FE-SEM measurements indicate that Mg(OH) 2 nanoparticles in an LDPE located 35 μm away from the bubble surface can be dispersed to a size of 100 nm, which is identical to the simulation. Upon removing the bubbles by grinding, no re-agglomeration of the nanoparticles was observed. The mechanical strength of the LDPE/nano-Mg(OH) 2 composites prepared by ISBS, followed by removal of the bubbles reaches a maximum when 15 phr of nano-Mg(OH) 2 was added. Compared to the pure LDPE, the increase in the tensile strength can be as high as 65%.

Polydimethylsiloxane/aluminum oxide composites prepared by spatial confining forced network assembly for heat conduction and dissipation

Constructing a compacted network in polymer matrices is an important method to improve the thermal conductivity (TC) of polymer composites. In this paper, a compacted network was built using the Spatial Confining Forced Network Assembly (SCFNA) method. The homogeneous compound of polymer and fillers, prepared using a conical twin-screw mixer, was placed in a compression mold with confining space to carry out two-stage compression, free compression and spatial confining compression. Aluminum oxide (Al2O3) was studied as filler in a polydimethylsiloxane (PDMS) matrix to illustrate the applicability of the SCFNA method. The polymer composites with an Al2O3 filler ranging from 10 to 80 wt% were prepared. When the filler content was 80 wt%, the TC of the PDMS/Al2O3 composites prepared using the SCFNA method increased by 16.35 times in comparison to the TC of pure PDMS. Observing the SEM of PDMS/Al2O3 composites with various thicknesses, the gap between fillers decreased with a decrease in thickness. The composite with TC up to 2.566 W (mK)−1 obtained at 80 wt% filler was further employed as a heat spreader, causing a decrease of about 8.23 °C in the set-point compared with the temperature of the heat source.

Microfluidic-Based Single-Cell Study: Current Status and Future Perspective

Investigation of cell behavior under different environments and manual operations can give information in specific cellular processes. Among all cell-based analysis, single-cell study occupies a peculiar position, while it can avoid the interaction effect within cell groups and provide more precise information. Microfluidic devices have played an increasingly important role in the field of single-cell study owing to their advantages: high efficiency, easy operation, and low cost. In this review, the applications of polymer-based microfluidics on cell manipulation, cell treatment, and cell analysis at single-cell level are detailed summarized. Moreover, three mainly types of manufacturing methods, i.e., replication, photodefining, and soft lithography methods for polymer-based microfluidics are also discussed.

The research of soft matter properties by light scattering material adding drop additive

Abstract In the present work, we investigated the effects of the addition of α-hydroxylethyl ferrocene, polymerization initiator and pre-polymer on preparation temperature, microstructure and optical properties of PMMA/PS compound light scattering material. It was found that the haze of the compound material increases significantly from 64% to 84% after introducing styrene (St) pre-polymer. The addition of α-hydroxylethyl ferrocene also leads to several notable properties change of the composite materials including the in situ polymerization temperature decrease to 300 K. The optical property change after the addition of small amount of α-hydroxylethyl ferrocene and prepolymer (St) demonstrates the soft matter characteristic of PMMA.

Visualization experiments on extrudate swell behavior at the microscale

Extrudate swell exerts a significant impact on the shape and dimensional accuracy of extruded products. It is one of the important factors to be considered when designing the extrusion die and controlling the quality of products. The die swell ratio (B) is used to evaluate the degree of extrudate swell. In this article, comparative experiments were performed in order to simulate and observe in a precise fashion the extrudate swell behavior of carboxymethyl cellulose solution at a microscale by means of a visualization device. We chose micro dies capillaries where the inner diameter was in the range of 0.1–0.5 mm. The effects of capillary geometry, entrance velocity, and shear rate (shear stress) on extrudate swell were investigated. The results indicated that shear rate (shear stress) increases and the value of B is enhanced with decreasing capillary diameter under the same capillary entrance velocity. At different entrance velocities, the die swell behavior from 0.3- to 0.5-mm-diameter capillaries was similar to that of conventional ones, and the value of B increased with increasing shear rate. Additionally, the extrudate swell from the 0.2-mm-diameter capillaries revealed a decline, whereas that from the 0.1-mm-diameter capillaries first diminished and then increased concomitantly with rising shear rate. We expect that this was due to wall slip that occurred analytically in our micro channel.

The Polymerization of MMA and ST to Prepare Material with Gradient Refractive Index in Electric Field

Light scattering material with gradient refractive index was prepared under the electrical field by taking methyl methacrylate (MMA) monomer as the matrix with the addition of a little preheated styrene (ST) and peroxidation benzoin formyl (BPO). The material obtained under electrical field presented different transmittance and molecular weight at different parts of the cylindrical sample along the axis of the direction of electric field which led to the layering phenomenon and gradient refractive index. The disparity of molecular weight between different layers can be as much as 230 thousand. There were several peaks in the figure of GPC test of the sample under electric field. This proved that there were polymers with different molecular weights in the sample. Therefore, it can be concluded that electrical field has a significant effect on polymerization.

Fabrication of the polymer diffuser with surface microstructures by using the extrusion roller embossing process

This paper reports a new kind of extrusion roller embossing microstructure process, which enables the fabrication of diffusers with surface microstructures. Established extrusion roller embossing system consists of polymer plate extrusion institution and roller embossing agency. The metal roller microstructure roller for embossing is fabricated by coating the slab mould. During the roller embossing process, the surface temperature of polypropylene (PP) sheet is still close to its melting point, which is suitable for extrusion roller embossing microstructure process. Under the proper processing parameters, the polymer diffusers have been successfully fabricated with uniform distribution micro-lens arrays. The diffuser with surface microstructures can scatter the light uniformly and diffuse the light effectively. The haze of this diffuser increases with its transmittance declining.