MemorySil™ is a remarkable line of shape-memory materials, products of Adaptive Rubber LLC. These materials are viscoelastic silicone rubbers (VSR), dynamic thermoset elastomers invented by physicist Lou Bloomfield at the University of Virginia.
Like ordinary silicone rubber, a VSR contains silicone polymer chains that have been permanently crosslinked into a vast molecular network. Although the silicone chains remain locally mobile at ambient temperatures, their permanent crosslinks limit their motions and give the material a permanent equilibrium shape. Because the macromolecular network formed by the chains and permanent crosslinks cannot flow, it is a solid network and the material containing it is a network solid. Ordinary silicone rubbers and VSR are network solids, otherwise known as thermosets.
Unlike an ordinary silicone rubber, however, a VSR is also a network liquid. That’s because, in addition to its permanent crosslinks, a VSR also has temporary crosslinks. Discovered by Bloomfield in silicones, temporary crosslinks are rare and revolutionary: they form strong covalent attachments between polymer chains but those attachments are brief. While permanent crosslinks bind the same polymer chains forever, temporary crosslinks swap polymer chains rapidly in an endless series of exchanges.
The temporary crosslinks add to a VSR’s vast molecular network, but their contribution can evolve with time and shape. In the absence of any permanent crosslinks, the temporary crosslinks would assemble the silicone chains into a macromolecular network that can flow, a liquid network, and the material containing it would be a network liquid. In a VSR, the temporary crosslinks build on the solid network formed by the permanent crosslinks, so the VSR consists of a liquid network piggybacking on a solid network. A VSR is thus a dual-network rubber: it contains one network with dual character: solid and liquid.
For more details, see the complete scientific manuscript at: http://arxiv.org/abs/1801.09253