Editorial for the special issue commemorating the impact of <scp>Dr. Jean‐Louis Salager</scp> on academy and on industrial surfactant research and development

Professor Jean-Louis Salager has significantly advanced surfactant science over more than five decades, guiding researchers with his foundational work on emulsions, microemulsions, and the hydrophilic–lipophilic deviation (HLD) concept. His approach integrates theoretical insights with practical applications, benefiting a wide range of industries from petroleum and cosmetics to pharmaceuticals and personal care products. In recognition of his remarkable legacy, the Journal of Surfactants and Detergents (JSD) presents this special issue featuring 23 articles that highlight his ongoing influence and the expansive scope of contemporary surfactant research. Contributors from several countries, including the USA, Canada, Venezuela, Brazil, France, the United Kingdom, Spain, Italy, Germany, and China, as well as from both academia and industry (notably Dow Chemical, TotalEnergies, and Henkel) reflect the far-reaching impact of Salager's work on surfactant science. The special issue opens with the review article by Rojas et al. (2025) titled “Jean Louis Salager: A Life of Service to Applied Surfactant Science”, which celebrates the remarkable career of Prof. Salager. His illustrious legacy includes serving as Editor-in-Chief of JSD from 2008 to 2014, followed by his ongoing role as Editor-in-Chief Emeritus, and receiving prestigious honors such as the Samuel Rosen Memorial Award from the American Oil Chemists' Society (AOCS) in April 2020 (Figure 1). This tribute highlights over 50 years of his pioneering contributions to surfactant science and his profound impact on generations of researchers worldwide. A particular emphasis of the review is his “useful science” approach, which focuses on translating fundamental research (know-how) into practical solutions that bridge the gap between academia and industrial applications. Following the bibliographical review article on Dr. Salager, the Special Issue also includes “Surfactants Produced from Carbohydrate Derivatives: Part 2. A Review on the Value Chain, Synthesis, and the Potential Role of Artificial Intelligence within the Biorefinery Concept” (Marquez et al., 2025). This comprehensive review explores the synthesis and applications of carbohydrate-based surfactants within the biorefinery concept, detailing the production of sorbitan esters, sucrose esters, alkyl polyglycosides, and fatty acid glucamines. It critically assesses the surfactant contribution parameter (SCP) within the HLD framework and discusses the value chain of biobased surfactants and biosurfactants from feedstock to product. Additionally, it highlights the potential of generative artificial intelligence (AI) in developing customized surfactant molecules with optimized properties for targeted applications. The focus on applied solutions is exemplified in “Experimental Study on the Effect of Formulation and Hydrodynamic Variables on Non-Aqueous Foams Stability” (Cova-Bonillo et al., 2024). This study explores the factors influencing foamability and stability by systematically varying surfactant and alcohol concentration, viscosity, and gas flow rates, providing critical insights into the stabilization of non-aqueous foam formulations for industrial applications. Similarly, López et al. (2024) in “Application of Surfactants for the Resolution of Emulsions and Suspensions in Slop Oil Storage Tanks, Cleaning and Final Disposal” present the effectiveness of surfactant formulations in treating oily residues from refineries. Oil separation efficiencies ranging from 47% to 100%, depending on the tank, were achieved in field tests, and concluded that combining heat treatment with demulsifiers significantly enhances crude oil recovery. do Nascimento et al. (2024) in “Properties of Liquid Foams Stabilized by Sugar-Based Surfactants and Prepared Under Different Conditions” examined foam stability using nonionic sugar-based surfactants by varying concentration, gas flow rate, and disk porosity. Results revealed that longer surfactant chains and larger head groups increased foam stability, with longer-chain surfactants maintaining stable structures over time. Advancements in material formulation are further showcased in “Effect of Emulsification Step on Calcium Carbonate Encapsulated Eicosane and Incorporation into Geopolymer” (Boland et al., 2024). This study explored how different emulsification techniques impact the encapsulation efficiency of n-eicosane within calcium carbonate shells. The research achieved a 55% n-eicosane core in CaCO₃ shells and successfully incorporated 33 wt.% CaCO₃ microcapsules into geopolymer paste without altering the hardening conditions. These microcapsules demonstrated effective thermal energy storage, enhancing the functionality of geopolymer-based materials. Rokni et al. (2024) in “Lamellar Liquid Crystals in Commercial Polyether-Modified Polydimethylsiloxanes for Coating Applications: Structure, Rheology and Cross-Linking” present the phase behavior and rheological properties of polyether-modified polydimethylsiloxanes. The study identified lamellar liquid crystal mesophases at concentrations above 60 wt.%, characterized by temperature-dependent viscoelasticity. Additionally, the feasibility of cross-linking these structures to create gelled liquid crystals was demonstrated, offering a pathway to advanced coating applications with improved durability and performance. The fundamental aspects of interfacial science are addressed in “Surfactant Monolayers at Oil-Water Interfaces. Behavior upon Compression and Relation to Emulsion Stability” (Wallon et al., 2024). This research investigated the response of surfactant monolayers to compression and its impact on emulsion stability. The study utilized surface tension measurements and Gibbs adsorption equations to calculate high-frequency elastic moduli, revealing that oil–water interfaces exhibit lower moduli compared to air–water interfaces. Optatzi et al. (2024) in “Addressing the Non-Ideality of Surfactant Mixtures within the Hydrophilic-Lipophilic-Deviation Concept” advances the HLD model by incorporating interaction terms for mixtures of ionic and non-ionic surfactants. By leveraging the dynamic salinity phase inversion method (DSPI), the study rapidly obtained experimental data to determine interaction parameters, validating them with the net-average-curvature concept. The findings demonstrate that DSPI is an effective tool for predicting the behavior of mixed-surfactant systems. Zhang et al. (2024) in “Effect of Droplet Charge Density on Stabilization of Oil-in-Dispersion Emulsions co-stabilized by binary mixed surfactants and nanoparticles” examine the role of electrostatic interactions in emulsion stability. This research investigated how varying droplet charge densities, achieved through different surfactant mixtures, influence the stability of oil-in-dispersion emulsions. The study found that alumina nanoparticles concentration effectively compensated for higher droplet charges, preventing flocculation and coalescence. Enhanced oil recovery (EOR), a foundational theme in Prof. Salager's research since his PhD studies at the University of Texas, is featured in “Study of Worm-Like Micelles of Extended-Anionic/Nonionic Ethoxylated Surfactants Mixtures for Crude Oil Recovery” (Guevara et al., 2024). This study examined the viscoelastic properties and interfacial tension of worm-like micelles formed by varying the carbon chain length and propylene oxide units in surfactant mixtures. The findings revealed that longer carbon chains and increased propylene oxide units enhanced micelle formation and reduced interfacial tension to the order of 10−3 mN/m, making these systems highly effective for mobilizing residual oil in complex reservoirs. Advanced surfactant system designs are explored in “Modulation of Cationic Surfactant Micellization by Imidazolium-Based Ionic Liquids: A Thermodynamic Study” (Patiño-Agudelo et al., 2024) and “Silver Nanoparticle Synthesis Assisted by Micelles for the Development of a Colorimetric Nanobiosensor Capable of Detecting Contaminants in Water” (Guasamucare et al., 2024). The former investigates the impact of imidazolium-based ionic liquids on the micellization behavior of cationic surfactants, revealing that hydrophobic interactions play a crucial role in affecting micelle formation and stability. The latter presents a novel approach to silver nanoparticles synthesis using surfactant templates, yielding nanoparticles with an average size of 8.25 nm and stable dispersions with a positive surface charge. These nanoparticles effectively detect contaminants such as Hg2+, Pb2+, Cr6+, and As3+ through colorimetric changes. Lemahieu et al. (2024) in “Rheology as a Tool for Identifying and Characterizing Optimal Microemulsions Formulations” utilizes rheological measurements to identify the phase inversion point in surfactant–oil–water systems. The viscosity minimum is correlated with phase inversion temperature, providing a rapid method for identifying the optimum formulation, significantly reducing the time required compared to traditional equilibrium scans. Two articles, “Macroscopic Thermodynamic Properties of Ionic Micellar Solutions Depending on the Physicochemical Formulation for the sodium dodecyl sulfate/sodium sulfate/water/n-heptane/1-pentanol system” (Marfisi-Valladares et al., 2025) and “Microstructure of Sulfosuccinates Based Microemulsions” (Tartaro et al., 2024), continue providing deep insights into how formulation variables affect macroscopic properties. The former examines the thermodynamic behavior of ionic micellar solutions, demonstrating how salinity and oil–water ratios influence micellar solubilization and phase behavior. The latter investigates the microstructural characteristics of sulfosuccinate-based microemulsions, revealing a linear correlation between reciprocal characteristic length and HLD values, thereby enhancing the predictive capabilities, and additionally, clarifying the concept of surfactant parameter in the HLD equation. Renewable and fundamental research themes are further explored in “Interfacial Properties of Cellulose Derivatives from Guinea Grass (Megathyrsus maximus)” (Silva et al., 2025) and “Appointing the Optimal Surfactant Concentration for Efficient 2D-Laminar O/W Emulsion Flow” (O'Neil et al., 2025). The former investigates cellulose-derived surfactants, highlighting their interfacial properties and potential as sustainable alternatives to traditional surfactants. Synthesized from methylated cellulose fibers extracted from Guinea grass, the double-methylated derivatives exhibited enhanced foaming activity and emulsion stability comparable to synthetic counterparts. The latter examines the relationship between surfactant concentration and laminar flow efficiency in oil-in-water emulsions, providing guidelines for optimizing flow processes in various industrial applications. Utilizing the population balance equation and integrating hydrodynamic and surface coverage models, the study predicts the minimum surfactant concentration needed to stabilize emulsions during droplet transport in two-dimensional laminar flow, aligning findings with experimental reports and hydrodynamic theory. Challenges in cleaning and antimicrobial applications are addressed by Falk (2025) in “Sodium Hypochlorite in Cleaning Products: Effects on Anionic Surfactant/Oil/Water Formulations using the Hydrophilic-Lipophilic Difference (HLD) Model” and by Hayes et al. (2025) in “Gramicidin and Chlorhexidine Encapsulated in Bicontinuous Microemulsions: Antimicrobial Activity Performance and Their Impact on Self-Assembly”. The former demonstrates the role of sodium hypochlorite as a salt in surfactant-oil–water systems is analyzed using the HLD model. The study evaluates the impact of hypochlorite salt on formulations containing anionic surfactants—sodium linear alkylbenzene sulfonate, sodium lauryl sulfate, and sodium cocoate—as well as a zwitterionic surfactant, cocoamidopropyl betaine. The latter investigates the encapsulation of antimicrobial peptides (AMPs) within bicontinuous microemulsions (BMEs) to assess their stability and bioactivity. The work highlights the interactions between AMPs and microemulsion components, identifying potential inhibitory effects arising from surfactant-AMP interactions, particularly when anionic surfactants like AOT are present. Mata-Zabala et al. (2025) in “Influence of Sodium Benzoate on Key Colloid Properties of Sodium Lauryl Ether Sulfate: Identification of A Possible Interfacial Structure Decoupler” study the influence of sodium benzoate on fundamental interfacial properties of the surfactant lauryl ether sulfate, particularly when packaged in metal containers, which require chemical reagents with preservative and anticorrosive properties. The results suggest that sodium benzoate acts as an interfacial structure decoupler, disrupting interactions within the surfactant system and preventing aggregation. Mazabel-Rios et al. (2025) in “Statistical Simplex Centroid Experimental Design and Formulation Maps to Predict the Stability in Cosmetic Emulsions Containing Commercial Emulsifiers” conducts a systematic evaluation of emulsion stability with three commercial emulsifiers used in cosmetics in combination with three emollients. The study integrates multivariate regression modeling to quantify the influence of composition on stability, droplet size, rheology, and texture. Emulsions containing potassium cetyl phosphate exhibited higher separation velocities (above 60 μm/s), while those stabilized with the other emulsifiers maintained larger lifetimes with separation rates below 40 μm/s. Signorelli et al. (2025) in “Pyridinium Surfactants Can Modulate the UV Response of Methyl Green Dye-Doped Polymeric Films for Sensor Development” explore the influence of surfactants on the stability and photosensitizing behavior of a polymeric colorimetric sensor. The study investigates polymeric films doped with methyl green dye, synthesized using carboxylated or hydroxylated polyvinyl alcohol, and exposed to ultraviolet radiation (UV-R). By incorporating dodecylpyridinium chloride, hexadecylpyridinium chloride, or sodium dodecyl sulfate (SDS), the research evaluates how surfactant structure and concentration affected the film's color response, monitored through the CIELab system. Pyridinium surfactants induce a color shift from blue to pale yellow, attributed to radical-driven photodegradation processes modulated by hydrophobic interactions. Miller et al. (2025) in “A High-Throughput Method for Screening Surfactant Additives for the Removal of Water from Bitumen” conduct an extensive screening of 67 model and commercial surfactants to identify effective dewatering agents for solvent-diluted bitumen. The study highlights that (ethylene oxide)-(propylene oxide)-(ethylene oxide) (EOx-POy-EOx) triblock copolymers with hydrophilic–lipophilic balance (HLB) values below 16 are the most effective surfactants for destabilizing water-in-bitumen emulsions. These surfactants promote the adsorption of amphiphilic molecules at the droplet interface, weakening asphaltene-rich elastic films and facilitating coalescence through interfacial film drainage. These 23 articles, authored by leading scientists in the field, serve as a single surfactant molecule at the interface linking the vast body of research that represents the ongoing relevance of Professor Salager's work. His groundbreaking contributions seamlessly integrate theoretical principles, such as the HLD model as a predictive tool, with practical innovations across diverse industries, including petroleum, cosmetics, pharmaceuticals, cleaning, and personal care. Professor Salager's remarkable achievements in surfactant science have fostered collaborations across continents and disciplines, leaving a lasting impact on academic research and industrial applications. This Special Issue stands as a fitting tribute to his dedication and influence. By celebrating Jean-Louis Salager's lifetime of scientific impact, this special edition also wants to inspire the next generation of researchers to pursue excellence, push the boundaries of surfactant-based knowledge and technologies, and progress in this dynamic field. All the authors contributed to the Editorial in writing, review and editing. The Editorial Board for this Special Issue extends sincere appreciation to all authors, reviewers, and readers who contributed to this issue. The authors declare that they have no conflict of interest. Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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