Optimization of the catalyst layer structure is necessary to realize high performance and low cost of a polymer electrolyte fuel cell (PEFC). The catalyst layer is normally composed of Pt/C powder and an ionomer. The adhesion state of ionomer to Pt/C powder not only changes the proton transport route but also influences the microstructure of the electrode, which is an important factor in controlling cell performance. In this study, in order to investigate the adhesion state of ionomer, we developed the new measurement technique of the specific surface area of catalyst layer. The measurement method was based on the gas adsorption method (N2), and the adhesion ratio of the ionomer was determined from the ratio of the specific surface area before and after removal of the ionomer in the catalyst layer. In addition, the electrode characteristics of the catalyst layer were also measured, and the relationship between the ionomer adhesion ratio and the cell performance was discussed. As a result, it was found that the adhesion ratio of ionomer was correlated with electrode characteristics, meaning that the adhesion ratio of ionomer should be an important parameter for improving cell performance.
A scale-up method of a low drug content mixing process in a V-type blender was proposed. Acetaminophen was used for the model drug, and the low drug mixing experiment was conducted using three scales of V-type blenders under the same fill level and Froude (Fr) number. However, the uniformity of mixtures could not correspond with the mixing time or the total revolution number. To find the optimum scale-up factor, discrete element method (DEM) simulations of three different scales of V-type blender mixing were conducted, and the total travel distance of particles under the different scales was calculated. The uniformity of drug content obtained from the scale-up experiments was well correlated with the mixing time determined by the total travel distance. It was found that the scale-up DEM simulation based on the travel distance of particle was valid for the low drug content mixing scale-up processes.
Our recent study on design of partial complex of polyethyleneimine and fatty acids/anionic surfactants toward dispersion stability control of non-aqueous, dense, and multicomponent slurries were reviewed. A series of polyethyleneimine complex were successfully designed by simple mixing process and found to effectively adsorb on many species of particles which lead to stability improvement of non-aqueous, dense, multicomponent slurries. A simple elaboration in the mixing orders of powders, solvents, and polyethyleneimine complex also found to compatibly realize the particle assembling and dispersion improvements. An example for applying these dispersion/particle assembling techniques to microstructure design of ceramic green parts will also introduced.
In biomedical technologies that use nanoparticles, the nanoparticles are often required to translocate across a cell membrane. Application of an external electric field has been used to increase the cell membrane permeability; however, damage to the cell is of great concern. In this review, our recent molecular dynamics simulation study of the nanoparticle translocation across cell membrane under external electric field is presented. Firstly, a finding, where a cationic nanoparticle directly translocates across a model cell membrane without membrane disruption even under a weak external electric field that is lower than the membrane breakdown intensity, is presented. The physical mechanism of this nanoparticle translocation is then explained in terms of the interfacial electric potential between the nanoparticle and the cell membrane. Our finding can provide an insight into the cellular delivery of nanoparticles via a non-endocytic and non-disruptive pathway.