Polysulfone ultrafiltration membranes were fabricated using various sizes (20, 40, and 90–210 nm) of silver nanoparticles (nAg) blended in a dope solution. To characterize the performance and properties of the prepared membranes, scanning electron microscopy (SEM), water contact angle, protein separation, water flux, and antibacterial tests were conducted. The characterization results revealed that when nAg particles (20 nm) were blended into the base polymer PSF, the PSF/nAg blended membrane had the lowest contact angle (58.5°) and surface energy (110.7 mN/m). When experimenting with ultrafiltration using protein solutions, bare PSF and PSF/nAg-20 blended membranes gave similar values of protein rejection: 93% of bovine serum albumin (BSA) and 70% of lysozyme rejection. Furthermore, SEM studies showed that the surface pore size was reduced by adding 20 nm nAg particles in the casting solution. Most importantly, the introduction of 40 nm nAg particles reduced the growth of bacterial colonies on the membrane surface by up to 72%. These findings revealed that nAg particles are expected to be a potential modifier for the fabrication of an ultrafiltration membrane.
Micromachining in the micro-electric discharge machining (μ-EDM) process requires high material-removal rate with good surface quality. Power-mixed μ-EDM, a modified machining process by introducing specific powder into the dielectric fluid, is among the key inventions to achieving these requirements. This article presents a review of the implementation of powder-mixed micro-EDM processes for microfabrication. Special attention was given to the influence of the powder characteristics, such as the concentration, electrical conductivity, shape and size of the powder. Subsequently, when describing the use of powder for obtaining a high material-removal rate and surface quality, other major applications in μ-EDM for surface modification and geometrical accuracy were also discussed. Finally, some of the varied methods that are used in powder-mixed μ-EDM and industrialization challenges are extensively elaborated.
Orbiting EDM has the advantages of superior machining quality over static EDM due to advanced flushing. However, improper tool correction to the relative motion in orbiting EDM will result in dimension errors of the product. As features vary in morphology, tool design for orbiting EDM is a challenging task, particularly for mould comprises assorted features. A strategy for correcting the orbital motion to the tool shape is proposed in this study. Effect of different orbital types to the feature's shapes is discussed from its geometrical point of view. This method also applies for orbiting automation by utilizing feature recognition to identify features inside a CAD model and recommends the corresponding orbiting pattern for all detected features. The shaped tool created with this method is capable of fabricating a complex mould precisely. More than 20 different features with different orientations to the machining axis have been tested to accommodate real designs in mould industries.
Nanoporous polyethersulfone (PES) membrane is widely used as a filtration membrane in hemodialysis systems. Unfortunately, it has low blood compatibility, and induces blood clots that adhere to the membrane's surface during dialysis treatment. This paper reports on a review of surface modification that is used to improve the PES membrane's blood compatibility. The method consists of applying two coating materials, in the form of parylene and fluorinated diamond-like carbon (F-DLC) films, onto the membrane's surface. The parylene film is deposited on the diffusion layer of the membrane surface using glycerin liquid, while the F-DLC film is specially coated on the supporting layer of the membrane. The unique property of parylene, which has the characteristics of conformal coating, prevents the parylene from being coated on the supporting layer of the membrane. Conversely, F-DLC film, which is hard, fragile and has a less conformal coating than parylene, is only meant to be coated on the supporting layer. Finally, the coated membranes, along with the bare PES membrane, are compared and investigated under a long-term diffusion test to assess their permeability and blood compatibility. The experiment results show that both coating materials have the capacity to improve the membrane's blood compatibility in different ways.
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