Institute of Fundamental Technological Research

A simple and inexpensive method for the controlled loading of silica particles with dyes and nanocrystals is presented. Polydiallyldimethylammonium chloride is used as a positively charged bridge to facilitate electrostatic adsorption of negatively charged dyes onto negatively charged silica microspheres. The particles are subsequently coated with a further silica shell to protect the dyes against chemical degradation and leakage and this shell affords a unform particle surface independent of its doping. This encapsulation method is highly versatile and can be extended to doping with semiconductor nanocrystals, which we demonstrate using CdSe/ZnS core/shell quantum dots. The synthesis steps and end products are characterized with electron microscopy, optical spectroscopy and the electrokinetic potential of the colloidal suspensions. We show that the particles adapt the optical properties of their dopants and are resistant to degradation, dopant leakage and show reasonable emission even at acidic pH values due to the protective shell.

Silica particles, Dye, Quantum dot, Polydiallyldimethylammonium chloride, Doping

We propose a simple and inexpensive SiO2 submicron particle synthesis method based on a PTFE helical capillary microreactor. The device is based on Dean flow mediated, ultrafast mixing of two liquid phases in a microfluidic spiral pipe. Excellent control of particle size between 100 nm and 600 nm and narrow polydispersity can be achieved by controlling the device and process parameters. Numerical simulations are performed to determine the optimal device dimensions. In the mother liquor the silica particles exhibit zeta potentials < -60 mV, rendering them very stable even at high particle volume fractions. The current device typically produces around 0.234 g/h of the silica particles.

SiO2 particle synthesis, continuous flow synthesis, helical capillary microreactor

Gold colloids have been homogeneously coated with silica using the silane coupling agent (3-aminopropyl)- trimethoxysilane as a primer to render the gold surface vitreophilic. After the formation of a thin silica layer in aqueous solution, the particles can be transferred into ethanol for further growth using the Stöber method. The thickness of the silica layer can be completely controlled, and (after surface modification) the particles can be transferred into practically any solvent. Varying the silica shell thickness and the refractive index of the solvent allows control over the optical properties of the dispersions. The optical spectra of the coated particles are in good agreement with calculations using Mie's theory for core-shell particles.

Citrate- and alkanethiol-stabilized gold colloids have been electrophoretically deposited onto carboncoated copper grids. The colloid particles form ordered monolayers, and the core-to-core interparticle spacing is determined by the size of the alkane chains on the stabilizers used in the preparation of the sols. In the case of longer alkane chains, some interpenetration of the chains occurs when the gold particles form monolayers. When the gold sols are stabilized by sodium 3-thiopropionate, they can be reversibly coagulated and peptized by cycling the pH between 3 and 7. The method has also been used to form ordered monolayers and bilayers of latex particles.