Fabrication and testing of bioinspired microstructured alumina composites with sacrificial interpenetrating polymer bonds

Abstract

Bioinspired composites exhibit well-defined microstructures, where anisotropic ceramic particles are assembled and bound by an organic matrix. However, it is difficult to fabricate these composites where both the ceramic particles and organic matrix work together to unlock toughening mechanisms, such as shear dissipation, particle rotation and interlocking, etc., that lead to stiff, strong, and tough composites. Here, we produce composites inspired by seashells, made of alumina microplatelets assembled in complex microstructures and that are physically bonded by a small amount of interpenetrated polymer network (IPN) made of polyacrylamide (PAM) and polyN-isopropylacrylamide (PNIPAM). The fabrication employs magnetically assisted slip casting (MASC) to orient the microplatelets as desired, and in situ gelation of the IPN, followed by drying. The process was successful after carefully tuning the slip casting and gelation kinetics. Samples with horizontal, vertical, and alternating vertical and horizontal microplatelets orientations were then tested under compression. It was found that the IPN threads bonding the microplatelets acted as sacrificial bonds dissipating energy during the compression. Paired with the alternating microstructure, the IPN significantly enhanced the compressive toughness of the composites by 205% as compared to the composites with horizontal or vertical orientation only, with less than 35% reduction on the stiffness. This study demonstrates that microstructure control and design combined with a flexible and tough matrix can effectively enhance the properties of bioinspired ceramic polymer composites.

Multifunctional nacre-like materials

“…81 Magnetic and electrical forces were subsequently employed in addition to these procedures to control the orientation of the platelets. 63,[82][83][84] Post assembly, the metal-and ceramic-coated platelets are joined using either hot compression 85 or spark plasma sintering. 63,86,87 Assemblies made of polymer-coated platelets do not necessarily need to be further processed, as the hydrogen and electrostatic bonds keep the assembly stable.…”

3D printable strong and tough composite organo-hydrogels inspired by natural hierarchical composite design principles

“…While reproducing the exact bottom-up growth and complex hierarchical structures of natural materials can be a tantalizing yet notably challenging endeavor, applying their design principles through practical engineering methods may offer a more feasible route to fabricating bioinspired composite hydrogels. To this end, various structural engineering approaches have been developed to fabricate composite hydrogels with anisotropically aligned microstructures 16 , such as using magnetic 5 , 17 , 18 and electric fields 7 , 19 , mechanical training 20 , 21 , freeze casting 22 , 23 , and self-assembly 24 . Recent advances in direct-ink-write (DIW) 3D printing also showcase its capability to align anisotropic particles along printed filaments by the extrusion shear force 25 – 30 .…”

Nacre-like composites with a soft thermoplastic elastomer matrix

“…Inspired by the outstanding mechanical behavior reached by nacre in comparison to that of its constituents, tentatives to obtain artificial structures that would reproduce nacre morphology were explored by manufacturing particulate composites consisting of platelets (made of brushite [4], glass [5,6] or alumina [7,8]) and of a secondary phase of varying nature (e.g. metal [9,10,11] , glass [8,12], polymer [13,14,15,16,17,18,19,20]). An overview of artificial nacre-like materials was provided by Bouville [21].…”