Self-assembly is a new technology for material design, which breaks the traditional "top-down" principle of material preparation and adopts a "bottom-up" molecular preconstruction model to obtain new materials with multi-level structures by making rational use of the various interactions contained in the special molecular structures. Specifically, the materials formed by self-assembly are molecular aggregates or supramolecular structures with clear, stable structures and specific functions, which are formed by spontaneous combination of non-covalent bonding interactions between molecules, and the self-assembled materials have unique optical, electrical and catalytic functions, which possess great applications in the fields of molecular devices and molecular regulation. Self-assembly materials include the following three main categories.
Small molecule assembly technology includes LB technology and self-assembly technology, and the current research mainly focuses on ultra-thin film system. LB membrane and self-assembly membrane are both ultra-thin film assembly of molecules, the difference is that LB membrane and substrate rely on van der Waals force bonding; while self-assembly membrane and substrate are bonded by covalent or ionic bonding, so the latter has higher stability.
Self-assembly of macromolecules refers to the process by which molecules of polymeric materials are spontaneously constructed into aggregates with specific structures and shapes driven by electrostatic interactions, hydrogen bonding, hydrophobic and esterophilic interactions, van der Waals and other weak interaction forces. For example, the self-assembly between poly(endo-alkenoic acid) and poly(vinyl acetal), polyaniline and poly(ethylene glycol) (or poly(vinyl acetal) and poly(vinyl alcohol)), diazo resin and phenolic resin, poly(p-vinyl phenol) and diazo resin, etc. are based on the adsorption or cyclic adsorption of intermolecular hydrogen bonds on the substrate to form monolayer or multilayer super thin films. In addition, side chain liquid crystal polymers can also be self-assembled by special intermolecular interactions such as hydrogen bonding and ionic bonding, which can improve the thermal stability and orderliness of liquid crystals.
The self-assembly of nanomaterials is mainly driven by the electrostatic interaction of positive and negative ions to assemble a variety of inorganic nanomaterials into multilayer membranes. Various polymeric nanocomposite membranes have been successfully synthesized, including polyelectrolyte-polyelectrolyte, polyelectrolyte-clay-based sheet materials, polyelectrolyte-inorganic nanoparticles, polyelectrolyte-biomolecules, and other inorganic/polymer hybrid nanolayer structures.
With the development of self-assembling materials, the principle of self-assembly has long been utilized in the manufacture of some common products. For example, cell membranes are mainly composed of molecules called phospholipids, which are dual in nature: one end of the phospholipid is hydrophilic, while the other end is hydrophobic. The researchers used these phospholipids to make liposomes, allowing the liposomes to act as carriers for in vivo drug delivery. In addition, self-assembly allows the production of tiny graphite tubes, comparable to the finest wires that have been made, which are called Bucky tubes, because they have a similar structure to the Bucky sphere of carbon. Breakthroughs in the technology of synthesizing or assembling practical functional molecular assemblies will certainly lead to industrial technological revolutions in the fields of information, materials and biology in the coming period.