Shinn-Jen Chang

An efficient approach to derive hydroxyl groups on the surface of barium titanate nanoparticles to improve its chemical modification ability.

Highly hydroxylated barium titanate (BaTiO(3)) nanoparticles have been prepared via an easy and gentle approach which oxidizes BaTiO(3) nanoparticles using an aqueous solution of hydrogen peroxide (H(2)O(2)). The hydroxylated BaTiO(3) surface reacts with sodium oleate (SOA) to form oleophilic layers that greatly enhance the dispersion of BaTiO(3) nanoparticles in organic solvents such as tetrahydrofuran, toluene, and n-octane. The results of Fourier transform infrared spectroscopy confirmed that the major functional groups on the surface of H(2)O(2)-treated BaTiO(3) nanoparticles are hydroxyl groups which are chemically active, favoring chemical bonding with SOA. The results of transmission electron microscopy of SOA-modified BaTiO(3) nanoparticles suggested that the oleate molecules were bonded to the surfaces of nanoparticles and formed a homogeneous layer having a thickness of about 2 nm. Furthermore, the improved dispersion capability of the modified BaTiO(3) nanoparticles in organic solvents was verified through analytic results of its settling and rheological behaviors.

Synthesis of non-oxidative copper nanoparticles

A novel aqueous reduction method for the efficient synthesis of non-oxidative copper (Cu) nanopowders without using a protecting agent or introducing of an inert gas is presented. By this new method, high purity Cu nanopowders can be produced that exhibit good electrical conductivity with an electrical resistivity on the order of 10−4 Ω cm.

Conductive microcapsules for self-healing electric circuits

Conductive microcapsules that are compatible with inorganic-based materials such as Ag conductive paste for casting electric circuits are prepared. These conductive microcapsules show high efficiency, more than 80% within 30 s, for the restoration of an interrupted circuit that presented a cracking width of about 150 μm.

Newly designed diblock dispersant for powder stabilization in water-based suspensions

A newly designed dispersant for water-based suspensions, ammonium poly(methacrylate)-block-poly(2-phenoxyethyl acrylate) (PMA-b-PBEA), is proposed in this study. According to the results of rheological analysis, the dispersion efficiency of this new dispersant is superior to that of the commercially available ammonium polyacrylate (PAA-NH4). The diblock structure of PMA-b-PBEA, which simultaneously contains a low-polar anchoring head group and a water-dissociable stabilizing moiety, is the main cause for its extremely high efficiency for powder dispersion. The unique structure not only results in effective adsorption approximately double that of PAA-NH4, but also produces a low number of counter-ions that compress the electrical double layer and ruin powder stabilization. Based on Derjaquin-Landau-Verwey-Overbeek calculations, the large adsorbance of PMA-b-PBEA gives the powder, titania (TiO2) in this study, a high steric stabilization energy. In addition, PMA-b-PBEA provides TiO2 with a remarkably high electrostatic energy because it generates fewer counter-ions. This energy provides excellent dispersity of powder in the suspensions with a high solid content of 60wt% without showing any rheological hysteresis.

Preparation of highly dispersed and concentrated aqueous suspensions of nanodiamonds using novel diblock dispersants

HYPOTHESIS Finding an efficient dispersant for obtaining a good dispersion of 5-nm detonation nanodiamond (DND) is always a challenge. Two newly designed diblock copolymers, both poly(ammonium methacrylate)-block-poly(2-phenoxyethyl acrylate) (PMA-b-PBEA) but with different molar ratios of PMA to PBEA, were proposed to be efficient dispersants in stabilizing the concentrated aqueous suspensions of DND. EXPERIMENTS The dispersion efficiency of dispersants for DND in aqueous suspensions was studied by the measurements of particle size, sedimentation property, and rheological behavior. The interactions between the added dispersants and DND were identified by the zeta potential and adsorption analyses. Calculations based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were conducted for clarifying the dominant parameters relating to the dispersion efficiency of dispersants. FINDINGS Compared with the commercially popular dispersant ammonium polyacrylate, these two diblock dispersants exhibited superior efficiency in the stabilization of DND suspensions. Using the diblock copolymers as dispersants, good dispersion stability in a DND suspension with an extremely high solid content of 30 wt% was achieved. According to experimental analyses and based on DLVO calculations, a low number of accompanied counter-ions, high adsorption capability, and thick PMA-b-PBEA adsorption layer are the main reasons for the extremely high dispersion efficiency of the two new dispersants.

Effects of sp 2 - and sp 3 -carbon coatings on dissolution and electrochemistry of water-based LiFePO 4 cathodes

Lithium iron phosphate (LiFePO4) is recognized as being less stable and easily dissolvable in aqueous suspensions, particularly when the suspension pH is adjusted to be more alkaline or acidic. In this investigation, an unexpected and interesting finding is revealed, which contradicts the conventional understanding of the dissolution of LiFePO4. As most of the surface of commercial LiFePO4 is coated with carbon, the key factor determining its dissolution behavior is the chemical quality of the surface carbon. With more sp2-bonded carbon on the surface, both the dissolution and electrochemistry of LiFePO4 are independent of pH variations in aqueous suspensions. When the surface carbon is mainly sp3-bonded, LiFePO4 exhibits distinct dissolution and electrochemical properties at different pH levels and, under alkaline conditions, shows greater dissolution and poorer cell performance than that characterized mainly by sp2-bonded carbon.Graphical Abstract

Synthesis of conductive microcapsules for fabricating restorable circuits

Three types of conductive microcapsules are proposed; they all contain the same phase change material, eicosane, as the core and have different conductive shells with various types of nano silver (Ag) coatings. Due to the Ag coating, these microcapsules are highly compatible with commercial Ag pastes and nano Ag ink and show an improvement of almost 500% in mechanical strength. When an electrical circuit is incorporated with these conductive microcapsules, it exhibits at least 70% lower electrical resistivity than when incorporated with insulated microcapsules. In addition, a restoration efficiency of higher than 90% in the electrical current of a damaged circuit is achieved when 20 vol% conductive microcapsules are incorporated. Based on their excellent mechanical and electrical properties, the proposed conductive microcapsules are capable of being directly mixed with inorganic Ag particles, and show the capacity for being used as self-restorable ink for conductive inkjet printing.