Shape- and Activity-Controlled Assembly of Amphiphilic Colloidal Motors under Light

Professor Wang, Yufeng   (Principal Investigator (PI))

24

2022-01-01

2023-12-31

436015

Shape- and Activity-Controlled Assembly of Amphiphilic Colloidal Motors under Light

Active colloids, Anisotropic particles, Colloidal assembly, Light-driven, Micromotors

Chemical SciencesMaterials Sciences

Physical Sciences (P)

17307221

General Research Fund (GRF)

2021

Completed

1 Objective 1. To design and synthesize light-activated amphiphiles colloidal motors (ACMs) with tunable shapes. The self-assembly of active, self-propelled colloidal particles (or micromotors) is an emerging approach for making materials that are dynamic and reconfigurable. Powered by external energy, the assembly process is also likely to overcome entropic limit and leads to new structures unfavored in materials at equilibrium state. Yet, the pathway to control and regulate the dynamic interactions is elusive and the types of dynamic structures that have been obtained remain very limited. One promising strategy to regulate the dynamics of active colloidal system is to tune the particle shapes, but how to relate shapes and dynamics to achieve extended assemblies is largely unexplored. The aim of this project is to explore how shapes and activity of micromotors can enable dynamic assemblies. Inspired by the extremely diverse assembly structures of amphiphilic molecules when varying the size ratio of the hydrophilic and hydrophobic part, we will design and synthesize ""amphiphilic colloidal motors, ACMs"". ACMs have one photo-active component and one passive component, both tunable in size. When those interesting shapes are coupled with various particle activity controlled by light, a huge parameter space becomes available for expanding possible dynamic assemblies. Objective 1 tackles the challenges in the design and synthesis of the proposed ACMs. 2 Objective 2. To study the shape effect on the self-propulsion of ACMs. One feature that makes active colloids distinct is their ability to autonomously propel. The propulsion can be powered by various external stimuli, which convert the energy of light, electric field and chemical reactions to the mechanical movements of the particles. The direction and magnitude of such autonomous movements are determined by the asymmetric flows generated by chemical gradients. Changing the particle shapes alter such chemical distribution and therefore their propulsion dynamics. The situation gets more complex when a substrate is involved, which is often the case as micromotor likes to surf on surface. In Objective 2, by numerical calculation and experiments, we will study how shapes of ACMs will be an effective handle to regulate the particle propulsions. This will prepare us ready for exploring their dynamic assembly. 3 Objective 3. To explore the shape effect on the dynamic assembly of ACMs. The dynamic assembly of colloidal motor particles emerge when they bump into each other to form cluster (nuclei), creating collective local flows that may (may not) stabilize the cluster. Particles can also escape the clusters as they tend to propel. A stable cluster may further grow and develop to larger structures. It is unclear when and how a structure (and what type) will be formed. With ACMs, we will explore how to manipulate the complex dynamics via changing particle shapes, sizes, and activities as an effort to facilitate stable nuclei of assemblies. The shapes can also influence how particles pack in the assembly, while their activity may be transferred to the assembled structures. Preliminary tests show promising results that a variety of collective, extended structures can establish according to ACM shapes and activities, and more to be discovered. In Objective 3, a shape (or other parameters)-structure phase diagram will be constructed experimentally. 4 Objective 4. To derive principles that govern the self-assembly of active particles. Unlike materials in equilibrium, active colloids with the ability to propel and interact dynamically produces structures that are otherwise possible. The principles governing such assembly is worth exploring. In this project, based on the structure formed and the various parameters we can tune, we will derive factors and pathways leading to such assemblies. We will try to elucidate the mechanisms of, for example, ""orientation-enabled"" crystal nucleation, and ""activity-directed"" structure propagation, etc., preliminary phenomena observed in our ACM systems that are directly or indirectly influenced by particles shapes. These new concepts and fundamental understanding shall guide the design of active materials that are truly unique and potential functional. Objective 4 aims to uses experimental and simulation approaches to derive and generalize such principles.