Non-covalent self-assembly within microfluidic environments James Nicholas 1,2 , Gemma Llauradó Capdevila 1 , Andrew J. deMello 2 , Alessandro Sorrenti 1 , Josep Puigmartí-Luis 1,3 1 University of Barcelona, Spain, 2 ETH Zürich, Switzerland, 3 ICREA, Spain Self-assembly of materials such as colloidal particles into larger aggregated structures typically arises due to non- covalent interactions occurring between them, and control over this assembly behaviour may be achieved through carefully designed surface-functionalisation, to direct specific interactions such as electrostatic, hydrophobic or H-bonding interactions. 1 The inclusion of supramolecular moieties which are responsive to external triggers can afford further control, for example, colloids bearing an H-bonding moiety have been assembled selectively upon irradiation with UV light which cleaved a photolabile protecting group. 2 Our work aims to use supramolecular host-guest interactions, such as the β-cyclodextrin (β-CD) and ferrocene (Fc) host-guest pair, to control the assembly behaviour of multicomponent systems and achieve new and controllable materials and structures. For example, we have prepared silica nanoparticles functionalised with Fc guest moieties and ditopic linker molecules bearing β-CD host moieties to investigate the potential control we can obtain over the colloidal assembly behaviour in such a system. In particular, the redox-responsive nature of the host-guest pair can be exploited, where reduced Fc will bind inside the β-CD cavity, whilst Fc oxidation to ferrocenium (Fc + ) leads to dissociation. This provides a mechanism to switch the system between the assembled and disassembled states respectively, for example through addition of chemical oxidants (e.g., H 2 O 2 ) and reductants (e.g., sodium ascorbate) to a mixture of the colloids and linkers. By modulating the addition of these chemical fuels using microfluidic devices and techniques, it is possible to gain spatio-temporal control over the assembly, allowing for potential non-equilibrium structures to be achieved. 3 Meanwhile, microfluidic devices also offer the ability to generate an environment in which the transport of reactant species is solely mediated by diffusive processes, which can allow for precise manipulation of concentration gradients and reaction diffusion phenomena, facilitating an improved control over self-assembly kinetics and pathway selection, opening up the possibility of obtaining assembled structures and materials with different properties from the same starting materials. 4 References
1. M. A. Boles, M. Engel, D. V. Talapin, Chem. Rev., 2016 , 116, 11220–11289. 2. N. Vilanova, I. de Feijter, A. J. P. Teunissen, I. K. Voets, Sci. Rep., 2018 , 8, 1271.
3. A. Sorrenti, J. Leira-Iglesias, A. J. Markvoort, T. F. A. de Greef, T. M. Hermans, Chem. Soc. Rev., 2017 , 46, 5476–5490. 4. S. Sevim, A. Sorrenti, C. Franco, S. Furukawa, S. Pané, A. J. deMello, J. Puigmartí-Luis, Chem. Soc. Rev., 2018 , 47, 3788–3803.
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