Monodispersed Lignin Colloidal Spheres with Tailorable Sizes for Bio‐Photonic Materials

Abstract

Lignin colloidal spheres (LCSs) are promising biomaterials for application in drug storage and delivery, pollutant adsorption, and ultraviolet protection due to their biocompatibility, amphiphilicity, and conjugated structure. However, wide size distribution of LCSs greatly limits their performances, especially in many precise and advanced applications. Herein, the fabrication of monodispersed LCSs with tailorable sizes ranging from the nanoscale to microscale is reported. Lignin raw materials are first fractionated by solvent extraction, and then the lignin fraction is used to fabricate monodispersed LCSs by solvent/antisolvent self‐assembly. The underlying mechanism for the formation of monodispersed LCS is primarily ascribed to the improved homogeneity of long‐range intermolecular forces, especially the electrostatic forces and hydrophobic forces, between lignin molecules. Moreover, by manipulating the short‐range order of LCSs, an innovative application of lignin as bio‐photonic materials with tunable structural colorations (e.g., red, green, or blue) is demonstrated. This work not only provides deep insight and an effective strategy to eliminate the serious inhomogeneity of LCSs, but also makes lignin resources have great potential as biodegradable and biocompatible photonic materials in diverse advanced optical application fields such as photonic devices, anti‐counterfeiting labels, and structural color pigments.

Photonic Lignin with Tunable and Stimuli-Responsive Structural Color

“…To produce monodisperse LCSs, EHL should be separated into different fractions to improve the homogeneity of longrange intermolecular forces during self-assembly, which is described in detail in our previous work. 25 Briefly, as shown in Figure S1, 40 g of EHL was mixed with 200 mL of ethanol with constant stirring for 2 h. The soluble and insoluble fractions were separated by centrifugation. The soluble part was dried to obtain EHL fraction 1, denoted as F1.…”

“…Our recent work has developed a promising strategy to prepare monodisperse lignin colloidal spheres (LCSs) by improving the homogeneity of long-range intermolecular forces during self-assembly, which provided the uniform lignin units to fabricate lignin-based advanced materials with ordered structures. 25 In this work, we present an approach that transforms disordered lignin into ordered structural color materials. Asreceived ordered lignin bulk possesses the photonic structure, and thus we define it as "photonic lignin".…”

“…The primary bottleneck lies in the disordered structure of lignin and thus lacking extremely uniform lignin units to construct the periodically ordered structure. Our recent work has developed a promising strategy to prepare monodisperse lignin colloidal spheres (LCSs) by improving the homogeneity of long-range intermolecular forces during self-assembly, which provided the uniform lignin units to fabricate lignin-based advanced materials with ordered structures …”

Fabrication Mechanisms of Lignin Nanoparticles and Their Ultraviolet Protection Ability in PVA Composite Film

“…This has attracted much attention as these materials can be used as drug carriers, antibacterial agents, anti-UV materials, emulsion stabilizers, and electrocatalytic carbon materials [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ]. To date, LNPs have been primarily obtained following self-assembly (anti-solvent) [ 27 , 28 , 29 , 30 , 31 ], emulsion solvent evaporation [ 32 , 33 ], pH conversion [ 34 , 35 , 36 ], electrostatic spinning [ 37 , 38 ], physical grinding [ 39 ] and other processing methods [ 40 , 41 , 42 , 43 , 44 ]. Jiang et al [ 27 ] used 90%, 70%, and 40% ethanol to fractionate the sulfated lignin into three fractions, labelled as LS90, LS70, and LS40.…”

“…Among them, lignin nanorods were prepared from LS40, and nanospheres were prepared from LS70 following the anti-solvent method. Wang et al [ 28 ] first fractionated the lignin systems following the solvent extraction process. Subsequently, the optimal components were prepared to form homogeneous, monodispersed LNPs exploiting solvent/anti-solvent self-assembly properties to improve the homogeneity of the intermolecular forces in lignin during the self-assembly process.…”