(44f) Surface Tension Analysis of Lignin Nanoparticles and Cellulose Nanocrystals with Magnetic Properties in Water-Ethanol Mixtures Under Varying Experimental Conditions

The surface tension of ethanol-water mixtures varies significantly as a function of concentration; however, the ethanol concentration in certain processes, such as broth fermentations, is limited to low alcohol percentages. In an effort to find a practical and alternative approach to surfactants use to decrease surface tension, this work analyzes the use of lignin nanoparticles (LNPs) and cellulose-nanocrystals (CNCs) combined with magnetic nanoparticles for controlling surface tension in water-ethanol mixtures. The addition of iron oxide (Fe₃O₄) to LNPs and CNCs allowed the generation of hybrid bio-based nanocomposites which are able to be manipulated under the presence of an external magnetic field.

The synthesis of hybrid LNPs and CNCs with iron oxide nanoparticles was performed using co-precipitation techniques, and these efforts are currently being reported by the authors elsewhere. Briefly, LNPs/Fe₃O₄ were synthesized using a modified co-precipitation procedure with two steps. The first step used iron chloride (II) and iron chloride (III) salts in the presence of a base to produce Fe₃O₄ nanoparticles. After several washes with ultra-pure type I water, a second step in the preparation was done by adding lignin solubilized in basic solution at low concentration via a self-assembly method using a syringe pump at a fast addition rate of 30 mL/min. The second bio-based hybrid nanoparticles, CNC/Fe₃O₄, were synthesized using the same iron salts but in a one-step co-precipitation method with the CNCs already dispersed in the solution. Vibrating Sampling Magnetometer (VSM) and Raman spectroscopy techniques were used to obtain the magnetic and structural properties of both nanocomposites.

In this study, the specific aim is to evaluate the structure-property relationships on the surface tension of water-ethanol mixtures caused by the addition of LNPs/Fe₃O₄ and CNC/Fe₃O₄ at varying concentrations, temperature, and magnetic fields. A goniometer instrument was used to collect surface tension measurements, and a custom 3-D printed holder was used to manipulating the magnetic field by adding cylindrical-shaped earth magnets while the measurements were recorded. Various studies were performed to analyze the effects on surface tension caused by the nanocomposites. The first experiment analyzed the impact of at least six different water-ethanol mixtures with each hybrid nanocomposite, LNPs/Fe₃O₄ and CNC/Fe₃O₄, dispersed in a concentration varying from 0 – 2.5 wt%. There was little to no change in surface tension (~2 mN/m) at low nanoparticles concentrations (< 1 wt%) for both bio-based nanocomposites. However, for the LNPs/Fe₃O₄ at concentrations above 1 wt%, there was a significant decrease in surface tension at low ethanol concentrations in water-ethanol mixtures (10 % or less). To analyze the effect of temperature conditions, the LNP/ Fe₃O₄ concentration was kept constant at 1 wt% in a pure water solution between 20 °C - 35°C. The surface tension decreased with increased temperature for all samples. Results revealed a maximum reduction of ~8.5 mN/m for the LNP/ Fe₃O₄ at 35 °C. Lastly, the magnetic field effects on surface tension were analyzed at various LNP/ Fe₃O₄ concentration in water at 5.22, 7.05, and 9.24 Gauss, respectively. On the contrary to the effects of increasing temperature, the surface tension increased as a function of the applied magnetic field and LNP/ Fe₃O₄ concentration. The change in surface tension was greater for higher magnetic fields. Overall, this study shows that the surface tension of water-ethanol mixtures can be increased or decreased by using LNP/ Fe₃O₄ or CNC/Fe₃O₄ under different experimental conditions, including nanoparticle concentration, temperature and applied magnetic field. These findings using bio-based magnetic nanocomposites to control surface tension could result in enhancements for ethanol extraction from aqueous-based solutions using currently-available chemical separation techniques.