(448p) Microfluid-Aassisted Hollow Silica Nanoparticle Synthesis for Inkjet-Printed Antireflective Coating

Hollow spherical silica nanoparticles (HSNPs) are a promising material for anti-reflective coating (ARC) due to their void space and cage-structured shells. Tuning the void space, diameter and wall thickness of HSNPs could reach various refractive indices (RI) to produce an optimal ARC for different substrates. To prepare the HSNPs, template method is a facile and straightforward approach. Hard templates such as polystyrene particles [1] and hydroxyapatite nanoparticles [2], were successfully applied to produce the uniform HSNPs in tunable void space and shell thickness. Nevertheless, the high temperature (around 500â??) was required to calcinate out these hard templates thoroughly after the formation of silica shell. Oppositely, soft templates made from emulsion micelles [3] and vesicles [4] can be easily washed away by a selective solvent at room temperature. However, to prepare the soft templates in a uniform shape usually involved at least two surfactants and tedious procedures, especially to obtain and control the uniform HSNPs under 100 nm which have higher surface area is still a challenge. The groups of Du et al. [6] and Wan et al. [7] proposed a simplified and environment-friendly approach by applying a single polyelectrolyte - poly(acrylic acid) (PAA) as the soft-template. However, the rapid aggregation of the PAA templates in the batch reaction only can produce the HSNPs in a broad size distribution which results in an uneven ARC thin film and finally diminishes its anti-reflective capability.

By our microfluidic system with the hydrodynamic focusing micromixer (HFM), the uniform HSNPs in 50 nm were successfully synthesized in a short-time scale. The fast and homogeneous mixing of the microfluidic system enable the PAA globules monomers protected instantly by evenly dispersed silica precursor. Along the further attachment of silica precursor and the rapid growth of silica shell, the aggregation of PAA monomers are efficiently avoided due to the hydroxide bond on the particle surface. A micro-channel following the HFM was applied to accomplish the growth of silica shell. By controlling the residence time of the microfluidic flow, different thickness and density of the silica shell can be obtained. In this study, a numerical model was established by using COMSOL Multiphysics to investigate the mixing profile under different flow condition. Incorporated with this computational model, we describe the experimental operation of the microfluidic chemical reactor to control the continuous synthesis of HSNPs. The effects of the mixer geometry and the operating variables on the particle structure and size distribution are discussed.

As coating the uniform HSNPs in 50 nm on glass substrates by the inkjet printer, the enhanced smoothness and transmittance has been detected. Compare to the thin film of the HSNPs in broad size distribution, the thin film of uniform HSNPs raised the increment of the transmittance from 3.6% to 3.8%. It successfully helped to increase the efficiency of the monocrystalline solar panels by 1.82%. Reference

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