以濕式化學法合成PMMA-Ni-Au核殼複合微球與其電阻率特性之研究

Abstract

Listen

Translate article

Poly(methyl methacrylate)-nickel-gold (PMMA-Ni-Au) core-shell composite microspheres have been prepared through chemical routes. By using electrostatic attraction, polyelectrolytes such as cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA) were adsorbed on PMMA surface sequentially in water. The zeta potential of PMMA was changed by adjusting solution pH and concentration of the polyelectrolytes. The zeta potential was at +45 and -35 mV after the adsorption of PAH and PAA at pH of 8 and 4, respectively. Both of the PAH and PAA concentrations were held at 0.022 mM. Ni shell was coated on the PMMA beads via electroless plating. The crystallinity of Ni was tailored by adjusting concentration of dimethylamine borane (DMAB) as the reducing agent. Over the DMAB concentrations examined (0.017 to 0.85 M), increasing the DMAB concentration resulted in a reduced crystallinity while the Ni shell was more complete. Furthermore, bulk electrical resistivity of the PMMA-Ni beads decreased from 8269 to 2.61x10-1 Ω-cm when the DMAB concentration increased from 0.017 to 0.85 M. The PMMA-Ni-Au core-shell composite microspheres were synthesized via redox-transmetalation method in water with the PMMA-Ni beads served as template and hydrogen tetrachloroaurate(III) trihydrate (HAuCl4˙3H2O) as the Au precursor. The interface of the PMMA-Ni-Au composite microspheres was observed by focused ion beam (FIB) microscopy; from which, the thickness of Ni and Au layers were 100 and 200 nm, respectively. Adhesive and continuous interface was found between PMMA and Ni layer, so as that between Ni and Au layer. However, the encapsulation of PMMA-Ni microspheres by the Au layer was found unsuccessful at pH=2. The PMMA spheres were successfully coated by Ni and Au double layers at pHs between 6 to 9. The resistivity from pH of 6, 7, 8, and 9 was 1.96x10-1, 3.12x10-2, 4.78x10-2, and 2.16x10-1 Ω-cm, respectively. This revealed that the resistivity was mostly influence by the solution pH. Au nodule was found when the concentration of HAuCl4 was increased from 13 to 39 mM. The Au surface became rough and porous, and the resistivity accordingly increased from 3.11x10-2 to 8.25x10-1 Ω-cm. Another way to improve the resistivity was attempted by repeating the Au coating process. After repeating the Au process twice, the resistivity decreased from 3.11 x10-2 Ω-cm to 1.46 x10-2 Ω-cm. However, no apparent difference was found when the coating was increased from twice to three times.