ABSTRACT
Precisely controlling the size and surface chemistry of polymeric nanoparticles (P-NPs) is critical for their versatile engineering and biomedical applications. In this work, various NPs of amphipathic random copolymers were comparatively produced by the flash nanoprecipitation (FNP) method using a tube-in-tube type of micro-mixer up to 330 mg min-1 in production scale in a kinetically controlled manner. The NPs obtained from poly(styrene-co-maleic acid), poly(styrene-co-allyl alcohol), and poly(methyl methacrylate-co-methacrylic acid) were concurrently controlled in the range 51-819 nm in size with narrow polydispersity index (<0.1) and -44 to -16 mV in zeta potential, by depending not only on the polymeric chemistry and the concentration but also the mixing behavior of good solvents (THF, alcohols) and anti-solvent (water) under three flow regimes (laminar, vortex and turbulence, turbulent jet). Moreover, the P(St-MA) derived NPs under turbulent jet flow conditions were post-treated in the initial solution mixture for up to 16 h, resulting in lowering of the zeta potential to -52 mV from the initial -27 mV and decreasing size to 46 nm from 50 nm by further migration of hydrophilic segments with -COOH groups on the outer surface, and the removal of THF trapped in the hydrophobic core.
ABSTRACT
Metallic glass (MG) assists electrical contact of screen-printed silver electrodes and leads to comparable electrode performance to that of electroplated electrodes. For high electrode performance, MG needs to be infiltrated into nanometer-scale cavities between Ag particles and reacts with them. Here, we show that the MG in the supercooled state can fill the gap between Ag particles within a remarkably short time due to capillary effect. The flow behavior of the MG is revealed by computational fluid dynamics and density funtional theory simulation. Also, we suggest the formation mechanism of the Ag electrodes, and demonstrate the criteria of MG for higher electrode performance. Consequently, when Al85Ni5Y8Co2 MG is added in the Ag electrodes, cell efficiency is enhanced up to 20.30% which is the highest efficiency reported so far for screen-printed interdigitated back contact solar cells. These results show the possibility for the replacement of electroplating process to screen-printing process.
ABSTRACT
Bone is an organic-inorganic composite consisting primarily of collagen fibrils and hydroxyapatite crystals intricately interlocked to provide skeletal and metabolic functions. Non-collagenous proteins (NCPs) are also present, and although only a minor component, the NCPs are thought to play an important role in modulating the mineralization process. During secondary bone formation, an interpenetrating structure is created by intrafibrillar mineralization of the collagen matrix. Many researchers have tried to develop bone-like collagen-hydroxyapatite (HA) composites via the conventional crystallization process of nucleation and growth. While those methods have been successful in inducing heterogeneous nucleation of HA on the surface of collagen scaffolds, they have failed to produce a composite with the interpenetrating nanostructured architecture of bone. Our group has shown that intrafibrillar mineralization of type I collagen can be achieved using a polymer-induced liquid-precursor (PILP) process. In this process, acidic polypeptides are included in the mineralization solution to mimic the function of the acidic NCPs, and in vitro studies have found that acidic peptides such as polyaspartate induce a liquid-phase amorphous mineral precursor. Using this PILP process, we have been able to prepare collagen-HA composites with the fundamental nanostructure of bone, wherein HA nanocrystals are embedded within the collagen fibrils. This study shows that through further optimization a very high degree of mineralization can be achieved, with compositions matching that of bone. Synthetic collagen sponges were mineralized with calcium phosphate while analyzing various parameters of the reaction, with the focus of this report on the molecular weight of the polymeric process-directing agent. In order to determine whether intrafibrillar mineralization was achieved, an in-depth characterization of the mineralized composites was performed, including wide-angle X-ray diffraction, electron microscopy and thermogravimetric analyses. The results of this work lead us closer to the development of bone-like collagen-HA composites that could become the next generation of synthetic bone grafts.
