Date/Time: 04-03-2018 - Tuesday - 05:00 PM - 07:00 PM
Yujuan He1 Chih-hung Chang1

1, Oregon State University, Corvallis, Oregon, United States

Hollow silica NPs (HSNPs) have been studied widely as a promising material for various field of applications such as catalysis, drug delivery, cell-labeling, and optical coatings, due to its attractive features like biocompatibility, controllable surface areas and large void volumes, as well as suitable chemical and thermal stability. The template method is a facile and straightforward approach to synthesize HSNPs. Hard templates such as inorganic nanoparticles, polystyrene nanoparticles, and hydroxyapatite nanoparticles, were employed to produce the uniform HSNPs with uniform and tunable void space and shell thickness. High temperature (around 500 °C) post-processing is normally required to remove the hard templates. In contrast, soft templates such as emulsion micelles7, and vesicles could be simply washed away by using a selective solvent at room temperature. However, the preparation of soft templates with a uniform size under 100 nm typically required at least two surfactants and relatively tedious stabilization procedures. Herein, we introduced a microreactor-assisted system with a hydrodynamic focusing micromixer (HFM) to control the conformations of the HSNPs with poly(acrylic acid) (PAA) as soft template. The PAA can self-assemble into globular when meets with the “unfavorable” solvent such as ethanol. Following this self-assembled conformation which is called thermodynamic-locked (TML) conformation, like the other single surfactant/polyelectrolyte, PAA TML in solution has a strong tendency towards aggregation before the growth of silica shells. In the batch reaction, due to the uneven mixing between free PAA chains and “unfavorable” solvent, PAA chains were under the different transition or aggregation stages which finally led to a broad size distribution of the PAA templates. In our system, with the assistance of the HFM in which the transition and aggregation of PAA chains are controlled by varying the mixing time through flow rates, flow rate ratio and PAA concentration, we can obtain the HSNPs only in ~30 nm. By modifying the PAA concentration, the necklace conformation of PAA TML were successfully preserved by the silica shells. COMSOL Multiphysics was performed to investigate the fluidic profile in the microreactor system. The quality of these HSNPs was demonstrated by fabricating anti-reflective coatings on the top of monocrystalline PV cells. Our HSNPs thin film exhibited much higher enhancement of the power conversion efficiency (PCE) than their batch counterparts.

Meeting Program

5:00 PM–7:00 PM Apr 3, 2018

PCC North, 300 Level, Exhibit Hall C-E