Selective Adsorption and Patterning of Halloysite Nanotubes

Abstract

Halloysite nanotubes (HNTs), a type of natural clay with nanotubular structures, are promising candidates for various applications such as controlled release, nanotemplating and catalyst carrier. In this study, we examined the effects of concentration, dipping time, sonication time and pH on the selective adsorption and pattern formation of HNTs. Selective adsorption of HNT was achieved by dipping in the HNT solution of the polymer-patterned substrate. HNTs also can be used as anionic materials in basic pH condition than neutral pH condition. To provide the selective adsorption region for HNTs, we modified silicon surface using poly ethyleneimine (PEI) due to its each strong positively. It was found that HNTs were selectively adsorbed on PEI layer due to electrostatic interaction with PEI layer. μ-patterns of HNTs with a high aspect ratio were fabricated at the following experimental conditions; pH 9, 1 mg/mL of HNTs concentration, selective adsortption for 3min and sonication for 3min. In addition, (3-aminopropyl)triethoxysilane (APTES) and octadecylphosphonic acid (ODPA) modified HNTs could be adsorbed selectively onto Si substrate. APTES was modified on the inner and outer surface of HNTs, but ODPA was only modified on the inner surface of HNTs. We also demonstrated that modified HNTs were selectively sdsorbed on the patterned PEI surfaces at specific experimental conditions. The HNTs and modified HNTs is confirmed by infrared (IR) spectroscopy, tunneling electron microscope (TEM), Zeta-potential. The selective adsorption of HNTs was confirmed by atomic force microscopy (AFM), scanning electron microscope (SEM).