A method to improve the quality of silica nanoparticles (SNPs) over increasing storage durations

Zihan Lu,Huw Owens

doi:10.1007/s11051-018-4282-7

Abstract

The solvent varying technique (SVT) provides a simple method for the production of uniform batches of silica nanoparticles (SNPs) of a target average diameter. SNPs synthesized using the SVT have been observed to agglomerate over increasing storage times leading to an increase in average particle diameter. Since the particle diameters of the SNPs produced using the SVT may vary over increasing storage durations, the previous model, suggested by Gao et al., which is based on the diameter of the original SNPs, is unreliable when predicting a target particle diameter using the initial volume of ethanol. A centrifuge and replacement of solvent method has been applied in this investigation to the SNP solutions created using the SV technique. This reduces the amount of unused reactants in the centrifuged colloidal suspensions, which further improves the quality of the SNPs and hence any subsequent photonic crystals. Post centrifuge and replace, the morphology of the centrifuged particles is more uniform than that of the original particles, which has been evaluated using SEM micrographs. The face-centered cubic (FCC) structures observed on the surface of the photonic crystal films have also been imaged using a SEM. A linear equation for the prediction of the SNP diameters for a given initial amount of ethanol is proposed based on the centrifuged SNP diameters. The particle diameter measurements for the new equation were recorded using a DLS instrument. The dispersion of the SNPs was also recorded using DLS. The morphology of the surface of the particles has been confirmed using TEM micrographs.Graphical abstractᅟ

Highlights

Silica nanoparticles (SNPs) are commonly used to coat materials in order to produce structural colors as well as other beneficial surface modification effects (Gaillou et al 2008)
The solvent varying technique provides an easy method for producing uniform batches of silica nanoparticles (SNPs) of a target diameter, the recipes may not be optimum and leave unused reactants, which may influence the SNP diameters over time
Ammonia is used as the catalyst, with the hydrolysis and condensation occurring between the tetraethyl orthosilicate (TEOS) and distilled water (Gao et al 2016a, b; Stöber, Fink and Bohn 1968; Giesche 1994; Gao 2016)

Summary

Introduction

Silica nanoparticles (SNPs) are commonly used to coat materials in order to produce structural colors as well as other beneficial surface modification effects (Gaillou et al 2008). The most popular method uses four chemicals: ammonia, distilled water, ethanol, and tetraethyl orthosilicate (TEOS) to synthesize the SNPs (Stöber, Fink and Bohn 1968; Giesche 1994). In 2016, based on the Stӧber method, Gao et al proposed the solvent varying technique (SVT) and provided a supporting equation that allowed the user to produce a batch of SNPs with a particular target diameter by only varying the initial amount of ethanol in the solution (Gao et al 2016a, b, 2017a, b). Using the SVT, SNPs with target diameters of between 207 and 350 nm have been prepared and these particles can be used to produce tunable structural colors by a process of natural gravity sedimentation (Gao et al 2016a, b). Uniform batches of silica nanoparticles (SNPs) of a target diameter were produced by applying the solvent varying technique (SVT). The particle diameters observed in the micrographs were measured using the ImageJ software package

Results and discussions

Conclusions

Compliance with ethical standards