Taking advantage of the aromatic and cross-linking tendency of lignin macromolecules extracted from plants, we present a novel method for their assembly into supracolloidal structures. Specifically, spherical particles with controllable size (∼90 nm to 1 μm) were obtained from water-in-oil (W/O) microemulsions formulated with a mixture of nonionic surfactants and a colloidal dispersion of a low molecular weight alkali lignin. After spontaneous emulsification, the internal lignin-rich phase was cross-linked to produce the solid particles that could be easily separated by removal of the organic, continuous phase. The efficiency of the fractionated lignin particles to stabilize hexadecane-in-water Pickering emulsions was demonstrated and their properties were compared against those obtained by using traditional inorganic particles. The effect of the particle size of lignin on the emulsion structure is discussed. As a proof of concept we further introduce the use of related emulsions to enable in situ reduction of silver and loading of silver nanoparticles in lignin carriers.
Cellulose nanocrystals
(CNCs) self-assemble and can be flow-assembled
to liquid crystalline orders in a water suspension. The orders range
from nano- to macroscale with the contributions of individual crystals,
their micron clusters, and macroscopic assemblies. The resulting hierarchies
are optically active materials that exhibit iridescence, reflectance,
and light transmission. Although these assemblies have the potential
for future renewable materials, details about structures on different
hierarchical levels that span from the nano- to the macroscale are
still not unraveled. Rheological characterization is essential for
investigating flow properties; however, bulk material properties make
it difficult to capture the various length-scales during assembly
of the suspensions, for example, in simple shear flow. Rheometry is
combined with other characterization methods to allow direct analysis
of the structure development in the individual hierarchical levels.
While optical techniques, scattering, and spectroscopy are often used
to complement rheological observations, coupling them in situ to allow simultaneous observation is paramount to fully understand
the details of CNC assembly from liquid to solid. This Review provides
an overview of achievements in the coupled analytics, as well as our
current opinion about opportunities to unravel the structural distinctiveness
of cellulose nanomaterials.
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