Animal and plant cells are prominent examples of how nature constructs ever-larger units in a targeted, preprogrammed manner using molecules as building blocks. In nanotechnology, scientists mimic this ‘bottom-up’ technique by using the ability of suitably structured nano materials to ‘self-assemble’ into higher order architectures.
The self-assembly process commences with chain-like macromolecules with a size in the range of 10 to 20 nanometers. In chemistry, such macromolecules are called triblock terpolymers. They are composed of three linear sections (blocks) connected to each other in sequence. They are generated using a special synthetic process, i.e., the so-called "living polymerization," and are readily available to researchers. The research team was able to guide the triblock macromolecules into soft nanoparticles with a diameter of roughly 50 nanometers. The choice of solvents played a key role in this macromolecular self-assembly process. The solvents were precisely selected and used so that the varying solubility of the three blocks and the incompatibility of the polymers with one another contributed significantly to the quality of the desired interior structure of the nanoparticles.
The scientists applied this technique to two types of triblock terpolymers. These differed with regard to the chemical properties of the middle blocks. The block sequences of the macromolecules were A-B-C and A-D-C, respectively. The first results in nanoparticles with a single bonding site and tends to form spherical clusters, while the latter creates nanoparticles with two bonding sites and thus tends to form linear superstructures. Importantly, in both cases the structure of the nanoparticles is preprogrammed by the chemical structure of the source macromolecule in the same way as the structure of a protein is determined by its amino acid sequence.
However, the process of self-assembly does not end with the nanoparticles. If the nanoparticles formed by each type of macromolecule were left to their own, spherical superstructures would result on the one hand and linear superstructures on the other. Müller's team has developed and implemented a different approach. The nanoparticles with one and two bonding sites are mixed so that they aggregate together into a completely new superstructure in a process of co-assembly. In the final superstructure, the nanoparticles originating from the A-B-C molecules and nanoparticles formed by the A-D-C molecules alternate in a precisely defined pattern.
When viewed under a transmission electron microscope, the new superstructure bears a strong resemblance to a caterpillar larva, because it also consists of a series of clearly separate, regularly ordered sections. Müller's research team has thus coined the term "caterpillar micelles" for such co-assembled superstructures.
The research findings represent a breakthrough in the field of hierarchical structuring and nano-engineering as it allows creating new materials by self-assemble preprogrammed particles. This could be a game changer, because so far only top-down procedures, i.e., extracting a microstructure from a larger complex, are widely accepted structuring processes.
This story is reprinted from material from Johannes Gutenberg-Universität Mainz, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.