The Preparation Of Nanoscaled Particles And Their Assembly With Ordered Thin Films

The building of nanoscaled subassembly is interrelated with the coming nanoelectronics and biomolecular recognition devices nearly. In the process of nanomaterial converting to devices, the nanoparticles must be immobiled or deposited onto some substrate slice to fabricate composite nano-films with prearranged two-dimensional (2D) structures. Having a knowledge of how to prepare nano-film using molecular assembly technique such as Langmuir-Blodgett (LB) film technique and self-assembly (SA) technique, and what is the relation between the properties and the structures in the obtained composite thin film contribute to provide novel approach to prepare nanoelectronics devices and micro-optical and electronic materials etc and is still the focus of the modern research of nanotechnology.The aim in this paper is to prepare ordered assembled composite thin film and the emphasis of the research is to prepare well-arrayed two-dimensional thin film or nanopattern, then assembly them with nanoscaled particles to build ordered composite nano-film. Fe₃O₄ nanoparticles were first synthesized from cotrolled chemical coprecipitation of aqueous Fe³⁺ and Fe²⁺ ions and then they were dispersed into the high purity water to obtain Fe₃O₄ hydrosol. The resulted Fe₃O₄ hydrosols were assembled with arachidic acid (AA) to obtain ordered Fe₃O₄-AA composite monolayer using LB film technique. Also in this way we assembled Gemini surfactant monolayer with magnetite nanoparticles which were modified by sodium dodecyl benzene sulfonate (SDBS) at the air/liquid interface. Dynamic domains morphology of monolayer of arachidic acid and Gemini at the air/liquid interface of magnetite hydrosol have been studied by Brewster angle microscopy (BAM) .The CdSe nanocrystal was synthesized in aqueous phase, and then multilayers of cationic polyelectrolyte Poly (diallyldimethylammonium chloride) (PDDA) and CdSe nanocrystal were deposited onto glass substrate using electrostatic self-assembly method (ESAM). The properties of the self-assembly PDDA/CdSe multilayer thin film was investigated by the means of UV-VIS spectra and photoluminescence spectra. The results in this paper are shown as follow:The prepared nanoscaled Fe₃O₄ particles is of about 10 nm, and the concentration of the obtained magnetite hydrosol is 0.96×10^-5 mol·L^-1 and its isoelectric point is pH=6.9. The surface pressure-area per molecule isotherm (π-A isotherm) of AA chloroformic solution at the air/liquid interface of high purity water and Fe₃O₄ hydrosol (pH=4) were measured respectively. The results indicates that the mean molecular area of AA is about 0.22nm², and the collapse pressure of the monolayer is 62 mN·m^-1 with the subphase of puried water. While the two value are 0.28 nm² and 67 mN·m^-1 respectively at the air/liquid of magnetite hydrosol due to the significant interaction between the positively charged Fe₃O₄ nanoparticles and the negatively charged AA molecules on the surface, which results in the magnetite nanoparticles moving into AA monolayer through the electrostatic interaction.Dynamic domains morphology of arachidic acid monolayer at the air/liquid interface of magnetite hydrosol have been researched by BAM. The results shows that AA molecules distribute randomly just as insular domain originally during the formation process of the monolayer, then they are shaped into a whole condensed monolayer at a surface pressure of 30mN·m^-1. The monolayer cracks with the increased pressure, and then they overlap and form multilayer. Finally we assembled Fe₃O₄ in the whole condensed and ordered AA monolayer at a pressure of 30 mN·m^-1 through the interaction of AA and magnetite molecules.Magnetite nanoparticles of about 10 nm were synthesized by cotrolled chemical co- precipitations method in the presence of SDBS. As-surface modified magnetite nanoparticles were dispersed into the pure water and the resulted SDBS-Fe₃O₄ hydrosols whose surface are taking positive charge at pH=4 has a concentration of 1.30×10^-5 mol·L^-1. Theπ-A isotherm of Gemini surfactant chloroformic solution at the air/liquid interface of puried water and Fe₃O₄ hydrosol were measured respectively. The results indicates that the collapse pressure of the monolayer and the aera per molecule of Gemini are increased to 1.28 nm² and 40 mN·m^-1 in contrast to the results of pure water as subphase which are 1.00 nm² and 34 mN·m^-1 respectively because there is a significant interaction between the positively charged Fe₃O₄ nanoparticles and the negatively charged cationic ammonium groups of Gemini molecules on the surface, which result in the magnetite nanoparticles moving into Gemini monolayer through the electrostatic interaction. However, the shape of theπ-A isotherm of Gemini dislikes the results of AA in a degree because of the special structure of Gemini molecules.Using magnetite hydrosols as subphase, we assembled Gemini surfactant monolayer with magnetite nanoparticles at the air/liquid interface. At the beginning, a low concentration of the Fe₃O₄ nanoparticles, randomly distributed on the Gemini monolayer. Aggregates of nanoparticles are apparent on the film, leading to larger irregular shapes. As the surface pressure increases, the surface concentration of the Gemini repeat unit increases, which leads to a higher negative surface charge and a stronger electrostatic interactions between the Fe₃O₄ nanoparticles and the monolayer, causing more of the positively charged nanoparticles to adhere to the monolayer at higher surface pressures. The attachment of the nanoparticles at the surface of the monolayer should make the collapse of the monolayer more difficult. Extraordinarily between the surface pressure of 12mN·m^-1 and 15mN·m^-1, Gemini molecules are likely to have a specific hexagonal configuration which attracted the magnetite nanoparticles into the aera forming a composite monolayer. While the Fe₃O₄ nanoparticles arrange well in the Gemini monolayer when the surface pressure is more than 15mN·m^-1.The nanocrystal CdSe quanta dots were synthesized in aqueous phase with the materials of CdCl₂·2H₂O, NaBH4 and selenium powder using 3-mercaptopropionic acid(MPA)as stabilization reagent. As-prepared CdSe particles has a narrow size distribution and an average sizes of about 5nm. With PDDA and the resulted nanocrystal CdSe hydrosol, we deposited multilayers of PDDA and CdSe nanocrystal onto pre-treated glass substrate using layer-by-layer electrostatic self-assembly method. The self-assembly PDDA/CdSe multilayer thin film was characterized by the means of UV-VIS spectra and photoluminescence spectra. The results indicates that the PDDA/CdSe multilayer has a good quality and shows very strong luminescence intensity.