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Unformatted text preview: DOI: 10.1021/la1030747 A Langmuir XXXX, XXX(XX), XXX–XXX pubs.acs.org/Langmuir © XXXX American Chemical Society Layer-by-Layer Surface Modification of Functional Nanoparticles for Dispersion in Organic Solvents Motoyuki Iijima* and Hidehiro Kamiya Institute of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan Received August 2, 2010. Revised Manuscript Received October 8, 2010 In order to prepare SiO 2 nanoparticles that are dispersible in various organic solvents, an anionic surfactant 1 , which branches into a hydrophobic chain and a hydrophilic chain, was adsorbed on to SiO 2 nanoparticles through a layer-by-layer surface modification route using polyethyleneimine (PEI). First, the relationship among the additive content of PEI, adsorbed content of PEI, and the redispersion stability of the SiO 2 nanoparticles in water was investigated. While almost the entire PEI was adsorbed when the additive PEI content was lower than 67 mg/g of SiO 2 , the adsorbed content of PEI became saturated when the additive content was increased above 90 mg/g of SiO 2 . SiO 2 nanoparticles that were saturated with PEI could be redispersed into water at sizes close to their primary particle size without the large-scale formation of aggregates. Next, the anionic surfactant 1 was adsorbed on the SiO 2 nanoparticles by using a SiO 2 aqueous suspension saturated with adsorbed PEI. It was found that the adsorbed content of 1 increased almost linearly as the additive content was increased when the additive condition was below 1400 mg/g of SiO 2 . Furthermore, SiO 2 nanoparticles adsorbedwith 80 mg/g of SiO 2 of PEI and 810 mg/g of SiO 2 of 1 could bedispersed into various organic solvents with different polarities. This layer-by-layer modification technique can also be applied to Ag nanoparticles in order to prepare Ag nanoparticles that can be dispersed in various organic solvents. 1. Introduction The use of nanoparticles has became indispensable in industrial applicationsbecauseoftheiruniquesize-dependentpropertiessuch as their electrical, magnetic, mechanical, optical, and chemical properties,whichdifferconsiderablyfrom thoseofthe correspond- ingbulkmaterials. 1- 4 Manystudieshavebeenconductedtoenable the use these functional nanoparticles in the fabrication of nano- structured devices such as polymer composites, ceramic compo- sites, composited particulates, and assembled structures because of their wide range of important applications. 5- 10 In order to design nanostructured devices with good properties, techniques that can completely disperse nanoparticles into a particular solvent must be developed. Furthermore, the ability to control the dispersion stability of nanoparticles during the processing procedures is quite essential....
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