Self-assembled nanomaterials

As part of the wide variety of bottom-up approaches to nanomaterials, self-assembly will necessarily face the challenge of achieving perfect spontaneous ID (onedimensional), 2D, or 3D organization of functional building blocks to produce self-assembled materials. The attractiveness of self-assembled species lies in the expected lower cost of nanomaterials prepared from simple building blocks available on a large scale. Where performances... 

Some important nanostructures include carbon nanotubes, montmorillonite type clays, and biomolecules such as proteins and DNA. Frequently, these nanomaterials self-assemble into highly ordered layers or structures arising from hydrogen bonding, dipolar forces, hydrophilic or hydrophobic interactions, etc. For maximum reinforcement, however, proper dispersal of these nanostructures has become a major research effort. The following sections will emphasize the structure and behavior of carbon nanotube and montmorillonite clay based nanocomposites. 

The types of molecules synthesized by biotechnological techniques are restricted to those biomolecules whose stmctures can be encoded in the DNA of organisms capable of translating them into functional nanomaterials. Other types of molecules and nanomaterials can be synthesized by chemical synthetic approaches, such as covalent syntheses and molecular self-assembly of molecular units. 

The top down approach refers to physically assembling the nanoparticles into desired forms the bottom up approach utilizes specific intermolecular interactions to cause the nanomaterials to self-assemble. 

Tailoring block copolymers with three or more distinct type of blocks creates more exciting possibilities of exquisite self-assembly. The possible combination of block sequence, composition, and block molecular weight provides an enormous space for the creation of new morphologies. In multiblock copolymer with selective solvents, the dramatic expansion of parameter space poses both experimental and theoretical challenges. However, there has been very limited systematic research on the phase behavior of triblock copolymers and triblock copolymer-containing selective solvents. In the future an important aspect in the fabrication of nanomaterials by bottom-up approach would be to understand, control, and manipulate the self-assembly of phase-segregated system and to know how the selective solvent present affects the phase behavior and structure offered by amphiphilic block copolymers. 

Finally, the shape and self-assembly of these particles can also be controlled which gives rise to novel nanomaterials displaying interesting physical properties in the fields of semi-conductors, magnetism, or optics. 

Nadagouda, M.N. and Varma., R.S. (2006) Green and controlled synthesis of gold and platinum nanomaterials using vitamin B2 density-assisted self-assembly of nanospheres, wires and rods. Green Chemistry. 8 516-518. 

Recently, we have also prepared nanosized polymersomes through self-assembly of star-shaped PEG-b-PLLA block copolymers (eight-arm PEG-b-PLLA) using a film hydration technique [233]. The polymersomes can encapsulate FITC-labeled Dex, as model of a water-soluble macromolecular (bug, into the hydrophilic interior space. The eight-arm PEG-b-PLLA polymersomes showed relatively high stability compared to that of polymersomes of linear PEG-b-PLLA copolymers with the equal volume fraction. Furthermore, we have developed a novel type of polymersome of amphiphilic polyrotaxane (PRX) composed of PLLA-b-PEG-b-PLLA triblock copolymer and a-cyclodextrin (a-CD) [234]. These polymersomes possess unique structures the surface is covered by PRX structures with multiple a-CDs threaded onto the PEG chain. Since the a-CDs are not covalently bound to the PEG chain, they can slide and rotate along the PEG chain, which forms the outer shell of the polymersomes [235,236]. Thus, the polymersomes could be a novel functional biomedical nanomaterial having a dynamic surface. 

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems (and are considered as such in fields such as molecular electronics and molecular motors). So can objects that have dimensions of >100 nm, even though such objects can be fabricated—albeit with substantial technical difficulty—by photolithography. We will define (somewhat arbitrarily) nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to 100 nm. Many types of chemical systems, such as self-assembled monolayers (with only one dimension small) or carbon nanotubes (buckytubes) (with two dimensions small), are considered nanosystems. 

The next three chapters (Chapters 9-11) focus on the deposition of nano-structured or microstructured films and entities. Porous oxide thin films are, for example, of great interest due to potential application of these films as low-K dielectrics and in sensors, selective membranes, and photovoltaic applications. One of the key challenges in this area is the problem of controlling, ordering, and combining pore structure over different length scales. Chapter 9 provides an introduction and discussion of evaporation-induced self-assembly (EISA), a method that combines sol-gel synthesis with self-assembly and phase separation to produce films with a tailored pore structure. Chapter 10 describes how nanomaterials can be used as soluble precursors for the preparation of extended... 

Protein is an excellent natural nanomaterial for molecular machines. Protein-based molecular machines, often driven by an energy source such as ATP, are abundant in biology. Surfactant peptide molecules undergo self-assembly in solution to form a variety of supermolecular structures at the nanoscale such as micelles, vesicles, unilamellar membranes, and tubules (Maslov and Sneppen, 2002). These assemblies can be engineered to perform a broad spectrum of functions, including delivery systems for therapeutics and templates for nanoscale wires in the case of tubules, and to create and manipulate different structures from the same peptide for many different nanomaterials and nanoengineering applications. 

The first ever reported molecule to undergo encapsulation was fullerene, which spontaneously and accidentally ended up in the tubes during post-processing of raw tubes prepared via the pulsed laser vaporization method. This could be considered a milestone in the self-assembling of a new class of nanomaterials [78]. 

Yanlian Y, Ulung K, Xiumei W, Horii A, Yokoi H, Zhang S (2009) Designer self-assembling peptide nanomaterials. Nano Today 4 193-210... 

Even newer generations of nanomaterials are based on carbon nanotubes using the bottom-up approach. The materials are still very expensive, but the technology is evolving rapidly. Another type of nanotube has been prepared based on self-assembly of specific molecules such as chitosan-based nanoparticles of polypeptides, DNA or synthetic polymers. Phospholipids or dendrimer-coated particles are suitable for the entrapment of actives in very small vesicles. The current materials are still lacking in selectivity and yield (costs). 

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