Real-time label-free monitoring of living crystallization-driven self- assembly in two dimensions Yujie Guo a , Xiatian Lai b , Vivien Walter c , Julia Rho b , Yujie Xie b , Rachel K O’Reilly b *, Mark I. Wallace a *
a Department of Chemistry, King’s College London, London, UK b School of Chemistry, University of Birmingham, Birmingham, UK c Department of Engineering, King’s College London, London, UK
Objectives: Crystallization-driven self-assembly (CDSA) describes a self-assembly process. When block copolymers contain crystallizable core-forming block be exposed to certain solvent conditions, it tends to form morphologies with low interfacial curvature, which provides an easy access to various hierarchical 1,2 . This opens the door to fabrication of monodisperse soft matter-based nanostructures with precisely controlled morphology and size 3–5 . Herein we introduce interferometric scattering (iSCAT) microscopy as a powerful tool for CDSA kinetics study to achieve label-free real-time observation of individual 2D platelets formation, which would bring a positive contribution to a next generation of applications in nanomedicine, catalysis, optoelectronics, and information storages. Procedure: By coupling the light scattered from an individual object to an external reference field provided by the reflection from a surface, iSCAT microscopy is able to achieve fast label-free imaging of a large variety of samples, from biomolecules down to approximate 40 kDa to nanoparticles 6 . With the assistance of iSCAT, the growth process of single platelets and multicompartment platelets is first time monitored with high spatial- temporal resolution. In addition, by altering various self-assembly parameters including concentration and solvent conditions, the growth kinetics of living CDSA system is investigated. Results : The results obtained from iSCAT characterization, which are consistent with those obtained from other microscopy techniques (e.g. transmission electron microscopy, atomic force microscopy and confocal microscopy), support the use of iSCAT as a reliable method for studying self-assembly processes. Our measurements indicate that 2D platelets growth follows the first-order reaction model, and the final platelet size and morphology can be manipulated by adjusting unimer/seeds concentration and addition of selective solvent for crystallizable core-forming block. Multi-block co-platelets growth was also monitored in-situ. Conclusion : The simplicity and versatility of this label-free method has the potential to help accelerate the understanding of self-assembly processes. Nanoobjects such as 1D cylindrical micelles and 2D platelet micelles with refractive index different to the surrounding medium can be efficiently monitored by iSCAT. This paves the road for precision engineering of individual nanoobject properties. References 1. Ganda, S. & Stenzel, M. H. Concepts, fabrication methods and applications of living crystallization-driven self-assembly of block copolymers. Prog. Polym. Sci. 101 , 101195 (2020). 2. MacFarlane, L., Zhao, C., Cai, J., Qiu, H. & Manners, I. Emerging applications for living crystallization-driven self-assembly. Chem. Sci. 12 , 4661–4682 (2021). 3. Gilroy, J. B. et al. Monodisperse cylindrical micelles by crystallization-driven living self-assembly. Nat. Chem. 2 , 566–570 (2010). 4. Finnegan, J. R. et al. Gradient Crystallization-Driven Self-Assembly: Cylindrical Micelles with “Patchy” Segmented Coronas via the Coassembly of Linear and Brush Block Copolymers. J. Am. Chem. Soc. 136 , 13835–13844 (2014). 5. Hudson, Z. M. et al. Tailored hierarchical micelle architectures using living crystallization-driven self-assembly in two dimensions. Nat. Chem. 6 , 893–898 (2014). 6. Young, G. & Kukura, P. Interferometric Scattering Microscopy. Annu. Rev. Phys. Chem. 70 , 301–322 (2019).
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