Aseem Pandey1, Maziar Derakhshandeh2, Stephanie A Kedzior3, Brandy Pilapil4, Neta Shomrat5, Tamar Segal-Peretz6, Steven L Bryant7, Milana Trifkovic8. 1. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: aseem.pandey2@ucalgary.ca. 2. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: maziar.derakhshandeh@ucalgary.ca. 3. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: stephanie.kedzior@ucalgary.ca. 4. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: bpilapil@ucalgary.ca. 5. Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel. Electronic address: sneta@technion.ac.il. 6. Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel. Electronic address: tamarps@technion.ac.il. 7. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: steven.bryant@ucalgary.ca. 8. Department of Chemical and Petroleum Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada. Electronic address: mtrifkov@ucalgary.ca.
Abstract
HYPOTHESIS: Microstructural and rheological properties of particle-stabilized emulsions are highly influenced by the nanoparticle properties such as size and surface charge. Surface charge of colloidal particles not only influences the interfacial adsorption but also the interparticle network formed by the non-adsorbed particles in the continuous phase. EXPERIMENTS: We have studied oil-in-water emulsions stabilized by cellulose nanocrystals (CNCs) with two different degrees of surface charge. Surface charge was varied by means of acidic or basic desulfation. Confocal microscopy coupled with rheology as well as cryogenic scanning electron microscopy were employed to establish a precise link between the microstructure and rheological behavior of the emulsions. FINDINGS: CNCs desulfated with hydrochloric acid (a-CNCs) were highly aggregated in water and shown to adsorb faster to the oil-water interface, yielding emulsions with smaller droplet sizes and a thicker CNC interfacial layer. CNCs desulfated using sodium hydroxide (b-CNCs) stabilized larger emulsion droplets and had a higher amount of non-adsorbed CNCs in the water phase. Rheological measurements showed that emulsions stabilized by a-CNCs formed a stronger network than for b-CNC stabilized emulsions due to increased van der Waals and H-bonding interactions that were not impeded by electrostatic repulsion.
HYPOTHESIS: Microstructural and rheological properties of particle-stabilized emulsions are highly influenced by the nanoparticle properties such as size and surface charge. Surface charge of colloidal particles not only influences the interfacial adsorption but also the interparticle network formed by the non-adsorbed particles in the continuous phase. EXPERIMENTS: We have studied oil-in-water emulsions stabilized by cellulose nanocrystals (CNCs) with two different degrees of surface charge. Surface charge was varied by means of acidic or basic desulfation. Confocal microscopy coupled with rheology as well as cryogenic scanning electron microscopy were employed to establish a precise link between the microstructure and rheological behavior of the emulsions. FINDINGS: CNCs desulfated with hydrochloric acid (a-CNCs) were highly aggregated in water and shown to adsorb faster to the oil-water interface, yielding emulsions with smaller droplet sizes and a thicker CNC interfacial layer. CNCs desulfated using sodium hydroxide (b-CNCs) stabilized larger emulsion droplets and had a higher amount of non-adsorbed CNCs in the water phase. Rheological measurements showed that emulsions stabilized by a-CNCs formed a stronger network than for b-CNC stabilized emulsions due to increased van der Waals and H-bonding interactions that were not impeded by electrostatic repulsion.