Optimising yield stress fluids for 3D printing applications via branched copolymer surfactant design

Dr Sean Flynn

Hierarchal colloidal self-assembly offers an elegant and effective method for the preparation of yield stress fluids containing a range of functional materials.¹ This approach has enabled advanced processing of colloidal formulations containing oils, aluminium oxide, graphene oxide and ceramics, using several techniques including direct-ink-writing (DIW) three-dimensional (3D) printing.^2-4 Branched copolymer surfactant (BCS) binders play a critical role in colloid stabilisation and underpinning the hierarchal microstructures which govern yield stress behaviour. However, the use of BCS binders in the preparation of such complex fluids remains limited and the roles of BCS structure and chemical functionality on the rheology of hierarchal self-assemblies remains unclear.

Here, we explore the synthetic versatility of the BCS platform to understand the contributions of polymer design to the rheology of colloidal self-assemblies. A series of next-generation BCS binders have been synthesised, containing variations in chemical functionality and macromolecular architecture. The generation of bespoke chain transfer agents (CTA) has facilitated the introduction of aromatic moieties at BCS chain ends; this has allowed the role of π-stacking interactions in the surface functionalisation of graphene oxide and activated carbons to be determined. Optimisation of polymer syntheses has also provided influence over BCS architecture. This has facilitated the preparation of BCS containing systematic variations in molecular weight (M_w 10⁴-10⁶ g mol^-1), primary chain length and degree of branching.

Bespoke BCS have been used to generate a series of hierarchal graphene oxide and activated charcoal self-assemblies which exhibit varied rheological behaviours (G’_(LVR) 10³-10⁵ Pa). Rheological analyses have revealed the influence of colloids and BCS binders on the rheology of such complex fluids. The role of BCS binder design in the development of yield stress fluids suitable for DIW 3D printing applications will be discussed.

References:

1. Angew. Chem., 2009, 121, 2165–2168.

2. Angew. Chem., Int.Ed., 2013, 52, 7805–7808.

3. Soft Matter, 2019, 15, 1444-1456.

4. J. Eur. Ceram. Soc., 2017, 37, 199–211.