ABSTRACT
Optimizing the colloidal state of polyamic acid (PAA) nanoparticles is essential for achieving a uniform and high-performance polyimide coating by electrophoretic deposition (EPD) on metal substrates of various shapes. In this paper, we report two important roles of the counterions in the formation of PAA colloids for EPD, which, to date, have not been recognized. First, when tertiary alkyl amines are used to neutralize PAA, the polarity of neutralizing counterions determines the size and stability of the PAA colloidal particles. The polarity can be finely tuned by using two different tertiary alkyl amines containing polar and nonpolar groups and adjusting the molar ratio. Depending on the polar/nonpolar ratio, various states of PAA colloids were obtained, including dissolved state, stable colloid, and aggregates. Second, we observed that the confined counterions inside PAA nanoparticles can act as an imidization catalyst during the thermal annealing process. It is revealed that some fraction of the counterion species, mostly having nonpolar groups, is not drawn toward the counter electrode and remains inside the PAA nanoparticles during the EPD process. Optimizing the polarity eventually allowed us to form uniform EPD coatings with high dielectric strengths.
ABSTRACT
It is important but remains a challenge to develop solution-processed plasmonic solar thermoelectricity films on various substrates, without strictly considering hierarchical plasmonic-dielectric-metal structures, to harvest a wide range of visible to near-infrared sunlight. We simply fabricate plasmonic silica metastructure sunlight-collecting nanofilms on highly reflective Cu and Si surfaces by introducing spin coating (with an Ag and silica colloidal mixture, a spin coater, and a heating plate) and low-temperature annealing (in an oven at 200 °C for 1 h) processes. The approximately 250 nm thick metastructure consists of a top 60 nm thick silica layer as an antireflective film and a bottom 190 nm thick Ag nanoparticle-silica hybrid film as a sunlight harvester. The metastructure film reduces the reflectivity of Cu (>90%) and Si (25-35%) to less than 5% at visible to near-infrared frequencies. The metastructure film on the Cu sheet has an absorptance of 0.95 and a thermal emittance of 0.06, ideal for high-performance sunlight absorbers. The solar thermoelectric powers of the film-coated Cu and Si are 15.4 and 4.7 times those of the uncoated Cu and Si substrates, respectively. The metastructure film on Cu exhibited a similar or slightly higher performance than that of a top-class vapor-deposited commercialized absorber film on Cu, demonstrating the robustness of the present method.
ABSTRACT
[Purpose] The objective of this study was to compare the effects of flexi-bar training and general lumbar stabilization training on muscle activity and fatigue. [Methods] Twenty normal persons participated in this study. After warm up and a Maximum Voluntary Isomeric Contraction (MVIC) test, participants performed bridging exercise, quadruped lumbar stabilization exercise on quadruped and curl-up, with and without the flexi-bar training, each exercise lasting for 30 seconds. Electromyography was used for the assessment of the muscle activity and fatigue of the rectus abdominis, erector spinae, external oblique and internal oblique muscles. [Results] The bridging and quadruped exercises with the flexi-bar elicited significant increases in the muscle activates of the muscle groups. The curl-up exercise with the flexi-bar showed significant differences in external oblique and internal oblique muscle activities compared to the exercise without the flexi-bar. Muscle fatigue showed different results depending on the exercise. [Conclusion] Generally, flexi-bar exercise induced greater muscle activation and fatigue. However, because there were differences of effect dependent on the posture, we should prescribe the appropriate exercise for the target muscles.
