Aerosol assisted self-assembly as a route to synthesize solid and hollow spherical lignin colloids and its utilization in layer by layer deposition

Lignin, a major constituent of plant cell-wall and by-product of paper based industries is traditionally used for low value applications (heat or electricity generation), but its potential in high value utilization has also been widely reported. In this work, we synthesized lignin colloidal particles using ultrasonic spray-freezing route without any chemical functionalization of material, and stabilized it by electrostatic route. As per our knowledge, this technique is the first reported method which yields hollow/solid lignin colloids having good particle size control without any chemical functionalization of material. Dioxane soluble fraction of Alkali lignin (d-lignin) was used without any further chemical functionalization. d-lignin dissolved in DMSO was sprayed upon liquid nitrogen cooled copper plate using an ultrasonic nebulizer. The resulting frozen droplets were collected and found to possess hollow and solid morphology. Particles thus obtained were characterized for their size distribution and morphology, and compared to theoretically anticipated values. Size tunability of particles in relation to concentration of sprayed lignin solution was also studied. In addition to that, six layers of lignin colloids were deposited on quartz slide with the aid of negligible UV absorbing polyelectrolyte aqueous solution PDADMAC [Poly (diallyldimethylammonium chloride)]. Gradation in UV absorbing ability of lignin with increase in number of layers could be clearly observed. Hollow and solid lignin colloids, apart from their application in sunscreen cosmetics owing to their UV absorbing ability, show potential applications in drug delivery also.