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Soft Colloidal Scaffolds Capable of Elastic Recovery after Large Compressive Strains
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posted on 2014-09-09, 00:00 authored by Raja Rajamanickam, Sushma Kumari, Deepak Kumar, Shankar Ghosh, Jong Chul Kim, Giyoong Tae, Sayam Sen Gupta, Guruswamy KumaraswamyAssemblies of inorganic or glassy
particles are typically brittle
and cannot sustain even moderate deformations. This restricts the
use of such materials to applications where they do not experience
significant loading or deformation. Here, we demonstrate a general
strategy to create centimeter-size macroporous monoliths, composed
primarily (>90 wt %) of colloidal particles, that recover elastically
after compression to about one-tenth their original size. We employ
ice templating of an aqueous dispersion of particles, polymer, and
cross-linker such that cross-linking happens in the frozen state.
This method yields elastic composite scaffolds for starting materials
ranging from nanoparticles to micron-sized dispersions of inorganics
or glassy lattices. The mechanical response of the monoliths is also
qualitatively independent of polymer type, molecular weight, and even
cross-linking chemistry. Our results suggest that the monolith mechanical
properties arise from the formation of a unique hybrid microstructure,
generated by cross-linking the polymer during ice templating. Particles
that comprise the scaffold walls are connected by a cross-linked polymeric
mesh. This microstructure results in soft monoliths, with moduli ∼O
(104 Pa), despite the very high particle content in their
walls. A remarkable consequence of this microstructure is that the
monolith mechanical response is entropic in origin: the modulus of
these scaffolds increases with temperature over a range of 140 K.
We show that interparticle connections formed by cross-linking during
ice templating determine the monolith modulus and also allow relative
motion between connected particles, resulting in entropic elasticity.