Abstract: Lignin is the second most abundant plant biopolymer on earth after cellulose. However, lignin is not used extensively due to its complex structures. Lignin micro/nano-particles can provide many opportunities for value-added applications of lignin. Self-assembly method of lignin micro/nano-spheres, which possess regular structure, include solvent and anti-solvent method, aerosol flow reactor and interfacial miniemulsion polymerization.When lignin and its derivatives are dissolved in solvent, such as tetrahydrofuran, dioxane and ethanol, and then dropped disionized water, the micro/nano-spheres can be formed. However, the micro/nano-spheres obtained through solvent and anti-solvent method may agglomerate in the drying process. Lignin precursor solution is directly atomized aerosol through aerosol flow reactor. When the micro/nano-spheres are prepared through interfacial microemulsion polymerization, lignin molecules will be linked by covalent and non-covalent bonded. Currently the micro/nano-spheres are mainly used in the fields of ultraviolet protection, drug carriers and nano-filler. When hydrophobic drugs are loaded by the micro/nano-spheres, the solubility of drugs in aqueous solution will be improved. And the loaded drugs exhibit the controlled release, a longer action time and a lower toxic and side effects. When photosensitive pesticides are loaded by the micro/nano-spheres, they display the characteristics of the controlled release and anti-photodegradation. The micro/nano-spheres are used to encapsulate the enzyme, which exhibit good stability and catalytic activity. Hydrophilic or hydrophobic outside surface of the micro/nano-spheres can be controlled through the change of self-assembly. Therefore, strong intermolecular interaction can be formed between the micro/nano-spheres and corresponding hydrophilic or hydrophobic polymer at the time of blending. In addition, the applications of the micro/nano-spheres have also been reported in the fields of adsorption materials, aggregation-induced emission nanomaterials and li-ion battery electrode materials. At present, studies on the micro/nano-spheres have been still in its infancy, there are much more to do. Because the interfacial miniemulsion polymerization can achieve synergies between non-covalent bond and covalent bond in the self-assembly process of lignin molecules, hollow lignin microspheres can be obtained by this method, which provides a new direction for the preparation of hollow lignin micro/nano-spheres. Moreover, light-emitting nanomaterials based on lignin may be as an important development direction due to the fact that lignin molecules have the characteristic of autofluorescence and aggregation-induced emission through J-aggregates.

Key words: lignin micro/nano-spheres, self-assembly, solvent and anti-solvent, aerosol flow reactor, interfacial miniemulsion polymerization