Applications of Aggregation-Induced Emission Luminogens in Multicomponent Fluid Systems and Smart Surfaces

Speaker :
Ms Xin CAI
Department of Mechanical and Aerospace Engineering, HKUST
Date : 12 Feb 2019 (Tue)
Time : 10:00 am
Venue : Room 2548+2549, HKUST (2/F., Lift #27/28)


Fluorescent materials with aggregation-induced emission (AIE) characteristics is attracting more attentions due to the fascinating optical properties, high sensitivity, and fast response of AIE luminogens (AIEgens). With the development of new AIE systems and the underlying mechanism are increasingly perfect, exploration of their high technological applications has become our pursuit. AIE materials have been developed in the applications of efficient light-emitting devices, chemo-bio sensors and stimulus-response materials during the past two decades. However, these explorations are just a small part of a big picture. As AIE luminogens show advantages like superior photostability and high quantum efficiency, as well as the AIEgens aggregates are born in the various binary systems, there are many possible applications attracting us to explore.

AIE systems were investigated and validated for the applications in multicomponent fluid systems. In this work, we mainly focus on the binary sessile droplets. We propose to track the fluorescence intensity profile from AIEgens for probing the local concentration gradient of the evaporating binary (tetrahydrofuran) THF/water droplets on the homogenous substrate. In this study, the concentration gradient inside
evaporating THF/water droplets with different initial concentrations was investigated. The 5 µL binary droplets were evaporated on a transparent hydrophobic substrate. The pre-established function of fluorescence intensity versus water volume fraction in THF/water mixtures gives us the ability to depict the local THF concentration inside the binary droplet during its evaporation process. During the droplet evaporation, the local concentration can be directly visualized by the change of fluorescence emission intensity. This method of using AIEgens to visualize the concentration distribution can be used for different binary water/solvent systems by utilizing different AIE systems.

AIEgens applications in a very typical and popular ethanol/water system have been explored in this study. First, an ethanol soluble AIEgen has been verified that the intensity is monotonically increased upon water fraction increased. We then studied the evaporation of sessile ethanol/water droplets on heterogeneous surfaces. The non-uniform concentration distribution along the contact line can be directly visualized by using the selected AIEgens.

A new AIE system with an imidazole ring has been design and synthesized in this work. The fluorescence of nano-aggregates of this AIEgen can be easily modulated by taking advantage of anion- interactions and intramolecular hydrogen bonding. The fluorescent response of this nano-aggregates shows a super high sensitivity upon acid stimuli, where the acid concentration can be as low as 10-20 M. This AIEgen can be further developed to functionalize the silicon substrate through a simple self-assemble approach. The AIEgen-functionalized surface possess a reversible modulation of fluorescence signal with an ultra-fast response upon acid vapor stimuli. Meanwhile, the obtained surface also possesses a tunable wettability. By alternating the surface polarity, different wetting status can be realized on the smart surface. Meanwhile, the change in wettability can be self-recovered. Multiple wetting states can be precisely and reversibly controlled on this surface. Moreover, the smart surface has been demonstrated as a reusable platform for creating different wettability gradients and patterns, and for wetting-dependent and bio-adhesion applications.

(Supervisor: Prof. Kai Tang [MAE] & Prof. Ben Zhong Tang [CHEM])