2026-10-12T04:49:41Z https://api.figshare.com/v2/oai

oai:figshare.com:article/34024601 2026-09-29T14:41:22Z category_4 category_146 category_7 category_21 category_272 category_873 category_734 portal_63 item_type_6 month_year_09_2026

Rheological Insights: The Role of Divalent Ions on the Stability and Phase Behavior of Oil–Water Emulsions Janett Montaño-Salazar (25137476) A. Paulina Gómora-Figueroa (3862618) Roberto Zenit (568804) Rosa María Mariscal-Romero (25137479) Biochemistry Space Science Medicine Biotechnology Environmental Sciences not elsewhere classified Chemical Sciences not elsewhere classified Biological Sciences not elsewhere classified increased friction due including drilling muds carboxylate family ). day 7 ), commercial anionic surfactant automated image analysis anionic surfactant led identified phase inversion eighteen stable emulsions petroleum industry applications enhanced oil recovery 2 </ sub prepared using cacl </ b >) 2 +</ sup emulsions reached viscosities petroleum industry surfactant dosage higher viscosities experimental analysis eor ), phase behavior multiple emulsions therefore critical study explores statistical characterization specifically calcium rheological insights rheological behavior reducing agents one order magnitude higher larger droplets intermolecular forces higher salinities findings demonstrate emulsion properties emulsion droplets electrostatic interactions divalent ions This study explores the rheological insights into how divalent ions, specifically calcium (Ca²⁺) and magnesium (Mg²⁺), influence the stability and phase behavior of oil-in-water (O/W) emulsions. O/W emulsions are employed for different purposes in the petroleum industry, including drilling muds, viscosity-reducing agents, enhanced oil recovery (EOR), and transportation of crude oil. We investigated the effects of salinity concentration, time, and surfactant dosage on emulsion properties. Eighteen stable emulsions were prepared using CaCl₂ and MgCl₂ brines at 0.5% (group <b>A</b>) and 5.0% v/v (group <b>B</b>) concentrations of a commercial anionic surfactant, Hercoten, (from a carboxylate family). Our findings demonstrate that brine composition significantly affects emulsion phase inversion, rheological behavior, and viscosity; CaCl₂ emulsions reached viscosities of up to 240 cP at 25,000 ppm (day 7), up to one order of magnitude higher than MgCl₂ systems. Furthermore, we identified phase inversion in CaCl₂ systems and evidence of multiple emulsions (O/W/O) in MgCl₂ systems, both at 8000 ppm and 5.0% v/v surfactant. To complement the experimental analysis, we developed a custom Python-based tool, ROJA, for automated image analysis and statistical characterization of emulsion droplets. We suggest that intermolecular forces and increased friction due to electrostatic interactions between Ca²⁺ and the anionic surfactant led to higher viscosities and smaller, more concentrated droplets (as low as 54.27 μm at 25,000 ppm) at higher salinities. In contrast, Mg²⁺ emulsions showed lower viscosities due to larger droplets (up to 127.87 μm at 25,000 ppm), resulting in fewer droplet–droplet interactions. The presence and concentration of divalent ions are therefore critical for the performance of O/W emulsions in petroleum industry applications. 2026-09-29T00:00:00Z Text Journal contribution 10.1021/acsomega.6c01366.s001 https://figshare.com/articles/journal_contribution/Rheological_Insights_The_Role_of_Divalent_Ions_on_the_Stability_and_Phase_Behavior_of_Oil_Water_Emulsions/34024601 CC BY-NC 4.0