Abstract
Angle-independent structural colors obtained from colloidal nanoparticles (NPs) are of interest for potential applications in displays, color printing, 3D printing, and direct writing. However, it remains challenging to prepare uniform structural colors that can be directly written from colloidal inks that not only have no coffee-ring effect, but also have ultrasmooth film thickness, which will be important for layer-by-layer stacking. Herein, we synthesize polypyrrole (PPy) black coated silica NPs that have a low coverage (∼10.7 wt%) of bumpy PPy nanogranules (10-30 nm in diameter). When the PPy@silica NPs are drop-cast on a substrate, the surface roughness of the PPy@silica NPs effectively suppresses the coffee-ring effect and center aggregation during the drying of the colloidal ink, leading to ultrasmooth surfaces with sub-micron thickness and uniform structural colors with wide viewing angles. The color can be fine-tuned by the size of silica NPs, and the presence of PPy black significantly enhances the color contrast by suppressing incoherent and multiple light scattering. Moreover, we show that the bumpy colloidal ink is very versatile: the ink can be formulated from both low and high surface tension liquids as solvents and applied to a hydrophilic or hydrophobic substrate. We demonstrate direct writing of uniformly colored lines and three different color drops stacked on top of each other.
| Original language | English |
|---|---|
| Pages (from-to) | 17357-17363 |
| Number of pages | 7 |
| Journal | Nanoscale |
| Volume | 9 |
| Issue number | 44 |
| Early online date | 2 Nov 2017 |
| DOIs | |
| Publication status | Published - 28 Nov 2017 |
| Externally published | Yes |
Bibliographical note
Publisher Copyright:© 2017 The Royal Society of Chemistry.
Funding
The project is supported in part by the University Research Foundation grant at University of Pennsylvania (S. Y.). The authors also acknowledge partial support from the Fundamental Research Funds for the Central Universities, the Natural Science Foundation of China 11604045, the Shanghai Pujiang Program 16PJ1400100, the Natural Science Foundation of Shanghai 17ZR1440000, the Jiangsu Overseas Research and Training Program for University Prominent Young and Mid-aged Teachers and Presidents, China Postdoctoral Science Foundation (2013 M541715 and 2014 T70541), and the Priority Academic Program Development of Jiangsu Higher Education Institutions. The Singh Center for Nanotechnology is acknowledged for the use of SEM.