© 2004 Robert A. Freitas Jr. and Ralph C. Merkle. All Rights Reserved.

Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.

4.1.2 Self-Assembling Crystalline Solids

Self-assembled crystalline solids such as zeolites [1471-1473] incompletely fill space, leaving substantial voids that may be occupied by solvent molecules or other guest molecules. Such occupation produces solid-state host-guest complexes known as clathrates (from the Latin clathratus, meaning “enclosed by the bars of a grating”). MacNicol and co-workers [1468] reported the first rationally designed clathrate host in 1978, but the first true de novo design of an organic clathrate was in 1991 [1469]. This involved the formation of an extensive three-dimensional diamond-like porous lattice built from a single Tinkertoy-type subunit containing four tetrahedrally arrayed pyridone groups that acted as connectors to assemble the units together in a well-defined geometry. However, the crystal was held together only by weak hydrogen bonds and the links had a rotational degree of freedom, rendering the exact crystal molecular arrangement unpredictable [1470]. Engineered nanoporous molecular crystals can provide molecular-scale voids with controlled sizes, shapes, and embedded chemical environments at resolutions of 0.3-4.0 nm [1473-1479].

Other self-assembling crystal structures have been described [1480-1482] including the crystal engineering of diamondoid networks [1483], template-directed colloidal crystallization or colloidal epitaxy [1484], organic templating to form crystalline zeolite-type structures with ordering lengths <3 nm [1485], 3-D polymer channels with chemically functionalizable channel linings [1486], silver nanowire arrays [1487], and micromolding combined with templating and cooperative self-assembly of block copolymers to produce hierarchical ordering over discrete and tunable characteristic length scales of ~10 nm, ~100 nm, and ~1000 nm in a single body [1488]. Redl et al [1489] at IBM have created a self-assembling 3-D metamaterial with a repeating pattern made up of 11-nm diameter (~60,000-atom) magnetic iron oxide particles and 6-nm diameter (~3000-atom) semiconductor lead selenide particles. This demonstrates “a modular assembly method that will let us bring almost any materials together...[and] the ability to bring together complementary materials with an eye to creating materials with interesting custom properties.” Of course, the simple process of crystallization can be viewed as an example of templated self-assembly.

Non-crystallographic polyhedral nano-clusters that are not able to grow but nevertheless have the potential to bifurcate, regroup, and even “self-replicate” have also been proposed [1490].

Last updated on 1 August 2005