Preparation and electrorheology of new mesoporous polypyrrole/MCM-41 suspensions

Abstract

Encapsulation or self-assembly of conducting polymer within the channels of mesoporous silica is one of the ways to prepare new nanostructured materials [1]. The resulting materials may have unique nanostructures and properties controlled by host-guest interactions, as well as new potential applications, such as in nano-scale electronic, optical devices [2] and electrorheological (ER) fluids [3]. For example, stabilization of conducting polyaniline filaments with mobile charge carriers in mesoporous silica (MCM-41) represents a step toward the design of nanometer electronic devices [4]. In this area, Qiu [5] et al. found the impedance of polyaniline/SBA-15 (SBA-15 is another kind of mesoporous silica with larger pore size and thicker pore wall compared to MCM-41) composites more sensitive to humidity than that of bulk polyaniline, and Choi et al. [3] reported a composite material with conducting polyaniline in MCM-41 channels showing interesting ER properties. Of conducting polymers, polypyrrole (PPy) as a promising conducting polymer has been widely studied because of its high polarizability, superior conductivity and electrorheological properties [6, 7]. Accordingly, incorporation of PPy in the pores of mesoporous silica is worth investigating, as it can be beneficial for further exploring electronic characteristics and applications of the resultant composite. On the other hand, ER fluids as one of the most promising smart materials for potential industrial applications have received wide interest. Recently, many studies on dry-based ER fluids have been reported, for example, polyaniline/BaTiO3 [8], polypyrrole/clay [9], polyaniline/clay [10] and polyaniline/MCM-41 [11] particles have been adopted as the dispersed phase of ER fluids. In this work, a new type of anhydrous ER material based on conducting polypyrrole confined in MCM-41 channels was prepared and its ER behavior was also investigated for the first time. The preparation of mesoporous silica (MCM41) followed the method described in literature [12]. To synthesize PPy/MCM-41 nanocomposite, the calcined MCM-41 was vacuumed at 200 C for 4 h to remove air and water from the channels. Then the MCM-41 host was suspended above the pyrrole monomer in a flask under vacuum at room temperature for 24 h. The MCM-41 containing pyrrole was immersed in an aqueous solution of FeCl3 AE 6H2O with continuous stirring in an ice bath for 24 h. The PPy/MCM-41 was washed with de-ionized water and acetone, and dried at 40 C under vacuum. For ER behavior investigation, the PPy/MCM-41 particles were further dried at 120 C and dispersed in silicone oil to form 10 wt.% suspension. Schematic of the synthesis of PPy/MCM-41 nanocomposite and ER tests are shown in Fig. 1. FT-IR spectra were obtained on Nicolet Magna-550 spectrometer. N2 adsorption/desorption isotherms were measured using Micromeritics ASAP 2010 system. High resolution transmission electron micrographs (HRTEM) were taken on a JEM 2100 F electron microscope. Scanning electron microscopy (SEM) was conducted on a JEOL JSM-6360 LV electron microscope. Measurements Q. Cheng AE Y. He AE C. Li Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, 200237 Shanghai, China