Morphology-Controlled Synthesis of Colloidal Polyphenol Particles from Aqueous Solutions of Tannic Acid

Abstract

The properties and application of particulate systems can be tailored by gaining control on their morphology. Here, a facile method is described for the bottom-up synthesis of biobased colloidal particles with varied morphologies by simple aqueous oxidation of tannic acid used as a precursor in alkaline solutions. Initial tannic acid concentrations of 1−2 wt % produce the largest crystalline yields, while total precipitate yields (up to 64%) are achieved at 2 wt %. Structural and thermochemical evaluations are reported from measurements based on X-ray diffraction and thermogravimetry, as well as infrared, mass, nuclear magnetic resonance, and X-ray photoelectron spectroscopies. The analyses suggest a galloyl-rich composition of the particles with thermal stability up to 450−500 °C. We show that the selection of the base species and pH affords control of the particle morphologies that include rods, platelets, rhomboids, cuboids, and quasi-spherical shapes. The main cause−effect relations are elucidated from principal component analysis of process conditions and particle morphogenetic parameters, which are derived from their physical dimensions and yield. The results indicate an anticorrelation between base countercation ionic radius and particle volume, whereas base strength and initial solution pH correlate with the total precipitate yield and elongated morphologies, respectively.

Machine Learning as a Tool to Engineer Microstructures: Morphological Prediction of Tannin-Based Colloids Using Bayesian Surrogate Models

“…Oxidized tannic acid (OTA) particle synthesis. Oxidized tannic acid particles were synthesized using the protocol reported previously [4]. Briefly, aqueous tannic acid solution (2% w/v) was prepared by adding tannic acid powder (1701.20 g/mol, Sigma-Aldrich) into Milli-Q water and rigorously stirring (magnetic bar) until completely dissolved.…”

“…Abundant hydroxyl groups make TA highly soluble and stable in aqueous solutions. In alkaline conditions, TA undergoes oxidation [3,4] and produces oxidized tannic acid (OTA) followed by oligomerization. Concomitant oligomerization of OTA leads to the formation of compounds with higher molecular weight and thereby decreases the solubility of the substance [4].…”

“…They obtained OTA particles of different size and shape by simply varying ultrasonic parameters. Kämäräinen et al [4] further presented a facile and scalable protocol to prepare OTA of varying morphologies by altering the TA oxidation conditions. The dimensions, shapes and the yield of these crystalline particles were highly sensitive to initial TA concentration, reaction time, initial pH and pKa of the base.…”

Electromagnetic Transparency of Composites of Unsaturated Polyester and Nanolignin: Morphological and Surface Energy Considerations

“…The synthesis of spherical particle of lignin has been discussed in our previous reports. (Ago et al 2016b) , (Kämäräinen et al 2019) , (Abbati de Assis et al 2018) Briefly, Kraft lignin was dissolved in DMF at a concentration of 5 % and above. The experimental set up used to synthesize the particles included a nebulizer, a heated reactor, and a cyclone collector.…”

Machine Learning as a Tool to Engineer Microstructures: Morphological Prediction of Tannin-Based Colloids Using Bayesian Surrogate Models

“…In alkaline conditions, TA undergoes oxidation [3,4] and produces oxidized tannic acid (OTA) followed by oligomerization. Concomitant oligomerization of OTA leads to the formation of compounds with higher molecular weight and thereby decreases the solubility of the substance [4]. In this form, OTA can interact with different molecules and serve as coatings [3,5], surface modifiers [1,6] and emulsion stabilizers [1,3,6,7], or act as stabilizing and reducing agents to aid in inorganic nanoparticle growth [8][9][10], all the while imparting beneficial biological functionality [11,12].…”