TEM of Fe3O4 CNC

Liquid Colloidal Photonic Crystals

TEM of Fe3O4 CNC

Liquid colloidal photonic crystal (PC) is a special photonic structure that only exist in solution. It can be considered as non-contact close-packed colloidal crystal filled by solvent. The liquid component renders it unique properties, such as fluidity possessed by a solution, and metastable state between colloidal suspension and colloidal crystal. Traditionally, it is prepared by precipitation from colloidal solution after standing for a long time. But now the efficiency has been greatly improved as we have developed a selective evaporation process to prepare supersaturated colloidal solution, which spontaneously precipitate to form highly crystalline liquid PC. The liquid PC can be directly used as responsive materials to fabricate electrically tunable display unit and mesopore detection agent. It can also be converted to solid or gel-like PC via thermal evaporation or photo-polymerization, which will be further used to fabricate PC based fingerprint reader, high-precision molecule sensor, disposable viscosity test-paper and antifraud labels, etc. (JACS, 2013, 18370; Adv. Funct. Mater. 2014, 817; Chem. Commun. 2015, 7382.)

Responsive Photonic Crystals

TEM of Fe3O4 CNC

Responsive photonic crystals usually have changeable crystal structures and structural colors responding to the external stimuli. Our group has successively developed mechanochromatic PC gel with good stability, magnetic responsive PC based on magnetic/non-magnetic colloids, and non-attenuated electric responsive PC based on high refractive-index colloids. These interesting responsive PCs can be utilized to fabricate devices such as display unit and fingerprint reader. (Adv. Funct. Mater. 2014, 3197; Angew. Chem., 2011, 1492; Adv. Funct. Mater. 2017, 1702825)

Photonic Crystal Physical and Chemical Sensors

TEM of Fe3O4 CNC

Photonic crystals with responsive structural colors and reflection signals are intrinsically capable to be used to fabricate various chemical sensors (molecule, ion, pH, VOC, etc.) and physical sensors (temperature, force, etc.) Our group has recently developed high-precision molecule sensor for distinguish homologs and isomers, disposable viscosity test-paper for fast measurement, porosity sensing liquid for detection of mesopore volume and diameter, and magnetic sensing liquid for determination of low field. There are still great challenges to explore the undiscovered photonic sensors or boost the performance of the reported sensors. (Nat. Commun., 2015, 7510; Small, 2017, 1603351; Angew. Chem., 2018, 252)

Photonic Printing and Antifraud Labels

TEM of Fe3O4 CNC

Photonic printing is a significant technique, which patterns the materials in a desired way to realize the specific function of photonic crystals. There are two strategies to print photonic patterns. One is based on the tuning of photonic structures on the selected region of a premade swellable or deformable photonic paper. Another one is based on the on-site assembly of colloidal particles, which directly forms a patterned photonic crystal on a substrate. Our group has developed several printing methods based on these two strategies. Furthermore, we are especially interested in the design of PC based antifraud labels. The printing actually produces two parts of photonic crystals with similar initial structures but extremely different response to the external stimuli. Therefore, the printed patterns are “invisible” at the original state, but show itself after it was stretched, wetted or applied to magnetic and electric field. (Adv. Funct. Mater, 2017, 1702825; Adv. Funct. Mater, 2014, 6430; J. Mater. Chem. C, 2015, 8097; J. Mater. Chem., 2012, 367; ISBN: 978-3-319-24988-9, Chapter 6.)