Lecture program

Developing environmentally friendly cleaning processes that use minimal amounts of water and detergents, yet remain effective across a wide range of contaminations, remains a significant challenge. In this context, bubbles and foams have traditionally been regarded as unwanted by-products or, at best, as passive indicators of cleaning efficiency. However, I will argue that—when appropriately designed—bubbles and foams introduce different distinct physical phenomena that actively contribute to the cleaning process. The interplay of these effects can substantially enhance cleaning performance for a broad spectrum of contaminants, ranging from liquids to solids, and from synthetic to biological in nature. I will present the key underlying mechanisms and, through various examples, illustrate how they have been—and could be—harnessed in the development of innovative, sustainable cleaning strategies.

Industrial applications of water-based surfactant systems often require the use of chelating agents to deal with water hardness. Nevertheless, including chelating agents reduces surfactant solubility preventing the formulation of concentrated systems. With current trends aiming to transport less water and develop more efficient cleaning products, understanding how to overcome stability issues in common formulations is of utmost importance.

In this work, specific interactions between chelating agents and surfactants are hypothesized to influence both the self-assembly process and the macroscopic properties of surfactant formulations.

To investigate these interactions and their relationship to the chemical structures of the surfactant and chelating agent, NMR spectroscopy was employed, focusing on 13C chemical shift and line shape analysis. Moreover, the impact of these interactions on the formulation properties was assessed by measuring cloud point, viscosity, surface tension, and contact angle on hydrophobic surfaces.

The study reveals that interactions between the head group of amphoteric surfactants and chelating agents of the aminopolycarboxylate types, such as GLDA and MGDA, lead to the formation of oligomeric surfactant analogues with larger hydrophilic moieties. The interaction between the species results in smaller, more spherical micelles, that can be used to increase the solubility of nonionic ethoxylated surfactants in mixed micellar systems. The interaction offers possibilities for tuning the aggregation behavior of systems containing surfactants and chelating agents, and consequently, the macroscopic properties of the formulation.

References:
Velásquez, J., Evenäs, L., & Bordes, R. (2024). The role of chelating agent in the self-assembly of amphoteric surfactants. Journal of Colloid and Interface Science, 676, 1079-1087.
Velásquez, J., Lundgren, S., Evenäs, L., & Bordes, R. Amphoteric Surfactant-Chelating Agent Interactions: Impact on Bulk and Surface Properties. Available at SSRN 5120630.

The biocide molecules are widely used both in disinfectant formulations and in all-purpose cleaners. The cleaning process should ensure a complete soil removal from the cleaned surface and the long-time biocidal action is controlled by a deposition of the biocidal molecules on the surfaces. The deposited layer must be invisible to the naked eye otherwise, the customers would decide that residues seen on the surfaces are rather soils than something useful. Recently, we have investigated the cleaning properties of biocidal formulations by a new simplified laboratory method for hard surface cleaning [1]. We have paid a special attention to the surface haze as a measure of residues visibility.
The present study aims to investigate the structure of the deposited layers of biocidal molecules composed of di-octyl or di-decyl hydrocarbon chain lengths and different hydrophilic groups. Layers deposited on smooth silicon wafer were characterized by imaging ellipsometry and contact angle measurements. We observed that the evolution of the surface pattern and the hydrophobicity with the biocide concentration follow the stages of surfactant adsorption on solid surfaces from bulk solutions (from hemimicelles at low concentration to dense layers well above the CMC). The obtained results showed less homogeneous layers from octyl chain biocides than from decyl ones. The addition of a nonionic surfactant significantly improve the surface hydrophilicity and does not change the homogeneity of the deposited layer.

[1] Yavrukova, V., Cooban, E., Blanco, I., Pambou, E., Marinova, K., Petkov, J. Investigation of the detergency properties of mixtures of biocides and nonionic surfactants using a new simplified hard surface cleaning method. Journal of Surfactants and Detergents.
The authors are grateful for the financial support from the Project # KP-06-М89/2 – 04.12. 2024, with the National science fund of Bulgaria (abbreviated as BG FNI – MON).

Catanionic surface-active ionic liquids (CASAILs) of the type 1-alkyl-3-methyl-imidazolium alkylcarboxylates ([Cnmim][Cm-1COO]) and 1-alkyl-3-methyl-imidazolium 4-alkoxybenzoate ([Cnmim][ CmOBCOO]) are novel surfactants which self-assemble not only in water but also in ionic liquids. In the ChitinFluid project funded by the Carl Zeiss Foundation, we are using these kinds of complex fluids to transform chitin, which is otherwise difficult to process, into high-quality products. Surface tension isotherms of these CASAILs in water revealed low minimum surface tensions and surface head group areas of the order of 20 mNm-1 and 60 Å2, due to both the electrostatic attraction between the two oppositely charged ionic heads and the van der Waals interaction between anionic and cationic alkyl chains. Freeze-fracture electron microscopy and dynamic light scattering proved the presence of uni- and multilamellar vesicles above the critical aggregation concentration (cac). Systematic surface tension and UV/Vis spectroscopy studies showed a strong linear decrease in log(cac) with increasing anion and cation chain length due to the increasing hydrophobic effect. Based on these excellent properties, the [Cnmim][Cm-1COO]s were then investigated for their ability to efficiently stabilize ionic liquid microemulsions as promising new solvents for chitin. Studies of the phase behavior revealed that indeed only 6 wt.% of [C18mim][C17COO] are actually able to form microemulsions containing equal amounts of EAN and cyclohexane. Electrical conductivity and SANS measurements proved the presence of a bicontinuous structure with a domain size of 20 nm.

Within the Innovation Alliance Biosurfactants, companies and research institutions have joined forces to find sustainable and scalable alternatives to chemically synthesized surfactants, often made from fossil raw materials. Our alliance is researching and developing the production of biosurfactants using biotechnological methods based on local renewable raw and residual materials and systematically investigating their potential applications – for example in detergents, cosmetics, crop protection and lubricant additives.
Initially, the provision of regionally available sugar, fat, and oil-containing raw materials was considered. Various microorganisms for producing different classes of biosurfactants, such as glycolipids and lipopeptides, were examined, promising candidates for subsequent laboratory-scale process development were selected, and the biosurfactants were produced and assessed regarding their possible applications. This work was supported by an academic institution specializing in life cycle assessments (LCA).
Subsequently, fermentation and downstream processes were further developed to ensure robust, controllable processes and simplified downstream processing methods, allowing gradual scaling to a working volume of 40 liters and beyond. In fermentation, feeding concepts were developed to increase biosurfactant concentrations and yields. Technologies like Raman spectroscopy and soft sensors were also employed to better characterize and automate the processes. The complex issue of foam formation in the bioreactor was investigated and sometimes utilized for product separation.
By providing our application partners with larger sample quantities, it was ultimately possible to carry out extensive physico-chemical investigations of the biosurfactants. In a broad screening, the various biosurfactants were tested for suitability in manifold applications. The tests ranged from technical applications (crop protection, fire-fighting foam, etc.) to use in home care products (MGSM, detergents, cleaners, etc.) and testing in personal care formulations (emulsions, foaming products).
In a tandem presentation, we would like to introduce the Innovation Alliance Biosurfactants and highlight the main results of the project.

Glycolipid biosurfactants, especially Rhamnolipids, have gained considerable interest in recent years because of their exceptional combination of excellent solubilization and outstanding mildness against aquatic organisms, skin, proteins, enzymes, (poly)cations and plastics. Because of this unusual combination of properties, it should not be too surprising that they behave differently when formulating as well as during applications, as compared to standard surfactants such as SDS or SLES.
Considering the packing parameter concept, the glycolipid biosurfactants which have been discussed up to now are quite hydrophilic. Therefore, there have been attempts to combine them with rather hydrophobic co-surfactants such as fatty alcohol ethoxylates with a low degree of ethoxylation. The other option to reduce the hydrophilicity of glycolipids is to alter the chemical structure of the sugar headgroup, e.g. removing one or even both of the sugar groups.
Such changes in molecular architecture have important consequences in terms of accessibility of the carboxylate group, which in turn influences not only the interaction with cations, but also the acidity (pKa) of the carboxylate group. As will be shown, also the choice of co-surfactants has an influence on the degree of protonation at formulation pH.
Therefore, supposedly surprising effects encountered when formulating with glycolipids of different chemical structure can all be explained by the laws of physical chemistry. While some consider formulating to be an art, it is mainly science.

The removal of contaminants from surfaces and the prevention of their (re)deposition are key performance criteria of formulations used in the home care sector and various other areas of application. Systematic improvement of cleaning efficiency requires a fundamental understanding of how different active components in the formulation interact with the soil and substrate in question. Along the same lines, the need to replace various established cleaning agents with more sustainable and/or less harmful chemistry can be addressed in a much more targeted way if their mode(s) of action are known. In this presentation, we provide new insights into the complex mechanisms at play during the formation, removal and prevention of unwanted deposits under practically relevant conditions. To that end, case studies from diverse disciplines will be discussed, including but not limited to prominent examples like laundry or dishwashing. In each case, the role and interplay of key formulation ingredients such as surfactants, enzymes, functional polymers, small molecules or builders in the cleaning process will be investigated and linked to the respective types of soil and surface. It will further be shown that deep understanding can only be achieved with the help of advanced in-situ characterization techniques, which allow the relevant processes to be experimentally observed as they occur. For the meaningful use of such methods, simplified model systems have been designed to reduce complexity and separately probe certain steps of the entire process. The potential benefits and predictive power of this approach will be critically assessed and complemented by selected sets of data from real-life application tests. Overall, the results of our work demonstrate the value of interfacial physics for the development of next-generation cleaning formulations.

Non-equilibrium self-assembled nanostructures hold promise for stimulated transitions at otherwise constant conditions. The reliable formation of these structures can be a challenge, especially when considering the delicate balance between kinetic trapping of micelles for long term stability and otherwise implementing the possibility to induce morphological transitions toward the equilibrium structure by applying minute deflections from metastability.

We have introduced a temperature-responsive polymer-based system, allowing considerable changes of the material properties upon triggering the non-equilibrium micelles by various stimuli.[1] Low viscosity dispersions of spherical micelles can be transformed on their way toward equilibrium to gels made of worm-like micelles. This transformation takes place at constant conditions upon application of a temporary trigger. The system remembers the sample`s history, like a past cold wave. Further, the non-equilibrium nature of interpolyelectrolyte complex micelles can be recycled after approaching equilibrium.[2] The interplay between addition/removal of salt as plasticizer and a temperature-responsive polymer gives a handle to modulate the hydrophilic/hydrophobic balance while freezing/melting the micelles. Hence, micellar morphologies obtained at certain conditions can be conserved for other conditions, where the morphology of these micelles is off-equilibrium. Further, we present a micellar system, which memorizes any heat above a certain threshold temperature, as it turns irreversibly turbid upon suffering high temperatures.[3] In addition, we are also interested in transitions of polymeric systems at interfaces. The reorganization of block copolymer micelles at oil-water interfaces was traced by help of interfacial shear rheology and the viscoelastic properties of the resulting monolayer can be adjusted by various means.[4]

[1] F. A. Plamper et al. Adv. Mater. 2017, 29, 1703495.
[2] F. A. Plamper et al. ACS Macro Lett. 2018, 7, 341.
[3] F. A. Plamper et al. ACS Appl. Mater. Interfaces 2023, 15, 57950.
[4] F. A. Plamper et al. Small 2022, 18, e2106956.

Detergents are key ingredients in cosmetic, cleaning, and sanitizer formulations but solubilize hydrophobic matter with low selectivity. This leads to cell damage and side effects, like skin irritation, allergies or antimicrobial resistance. To align detergent chemistry with consumer health, we established ionic/non-ionic hybrid detergents with surprising advantages. Compared to established ionic detergents, like sodium dodecyl sulphate or dodecyltrimethylammonium bromide, related ionic/non-ionic hybrid detergents have low critical micelle concentration values, low cytotoxicity, excellent hard water tolerance and good solubilizing properties. Ionic/non-ionic hybrid detergents will enable the development of cleaning products that demand detergents with scalable cell compatibility, while doing the job of cleaning applications. Furthermore, in context with medical research, we designed non-ionic hybrid detergents to control the stabilization of functional membrane proteins and their interactions with membrane lipids in biochemical assays. Membrane proteins are vital molecular machines in cell membranes and targets for most approved drugs on the market. A detailed analysis of their function and drug binding in context with membrane lipids is crucial for drug discovery but exceptionally challenging. Standard detergents poorly replicate relevant membrane lipid compositions surrounding proteins and limit the transferability of drug binding on purified proteins into patients. To overcome this innovation hurdle, we designed hybrid detergents with scalable solubilization properties. The trick is to fuse headgroups of non-ionic detergents to precisely tune polarity and conical shape of hybrid detergents. Our chemical design led to first detergent micelles that gradually remove or retain protein-lipid interactions during purification from membranes. Surprisingly, our hybrid detergent technology enables new possibilities in membrane protein drug discovery and uncovered a new type of biomolecular interaction between proteins and glycolipids in cell walls of Gram-negative bacteria with relevance for antibiotic research. The chemistry of hybrid detergents delivers exciting avenues for the development of biocompatible consumer products and medical research.

Polyethers constitute a crucially important class of polymers and are suitable for a broad array of applications, ranging from cosmetics, drug delivery and electrochemical devices to lubricants, PU synthesis and rheology modification. In spite of this, the bulk of polyether materials are made via traditional techniques, in particular via conventional anionic polymerization (KOH) or via the so-called Double Metal Cyanide (DMC) catalysis of epoxide monomers.

While largely successful, these techniques also suffer from a number of downsides or inabilities. Work in the Naumann research group focuses on the development of novel, preferentially matel-free polymerization systems which allow a much larger degree of freedom in designing (block) copolyethers.

The latter aspects include:

– an increase of the achievable molar masses, especially for poly(propylene oxide). Here, a novel strategy enabled us to realizes molar masses > 1 Mio. g/mol.

– the suppression of side products/reactions and the realization of narrow molar mass distributions. With modern organocatalysts, transfer-to-monomer can be eliminated (no allylic chain ends) and PDIs of 1.01-1.09 can be routinely achhieved.

– improved functional group tolerance. By “taming” the propagating chain end via coordination, it is possible to, e.g., use polyesters as macrointiators for polyether preparation. No polyester degradation occurs.

– use of polymer tacticity as a novel tool for the fine-tuning of polyether products. To date, polyether tacticity is not considered in commercial products. The Naumann group has developed and patented a specific catalyst family to achieve just that.

The presentation will address some of the above.

Alkoxylation, a cornerstone of industrial surfactant production, has demonstrated its significance for over a century. This presentation explores its journey from a basic chemical process to a modern industrial technology. It highlights how alkoxylation inherently aligned with sustainability principles through its atom economy, energy efficiency, and minimal waste generation. Recent innovations in ethylene oxide insertion and product distribution optimization demonstrate how this century-old technology continues to evolve. As the industry faces new regulatory challenges regarding trace impurities such as 1,4-dioxane, its long history of technological advancement and problem-solving capabilities will pave the way for future solutions.

In 2024 the Nobel Prize for Chemistry was awarded to biology. This presentation will show several examples of how the Nobel Prize winning tool AlphaFold has been adapted to revolutionize enzyme engineering and the development of biosolutions to deliver sustainable innovations in homecare that was unimaginable just a few years ago.

We will also demonstrate examples of how the remarkable advancements in both screening and upscaling have allowed innovations to be commercialized at scale for the first time. We will show how the breakthrough method developments in DNA sequencing have escalated the speed of protein engineering by faster and cheaper analysis of enzyme variants’ genetic sequences, which won the Nobel Prize in Chemistry in 2018. Additionally, a patented method in microfluidics, an ultra-high throughput screening using microdroplets, has allowed a full genomic understanding of the enzyme and production host, enabling sustainable innovations to be commercialized at scale at a speed never seen before.

However, the true value of these tools lies in the application understanding. For example, we will show how AI-driven molecular modelling can predict conformational changes of enzymes in surfactant systems and wash water, aiding in practical applications. High-content screening using microscopy provides mechanistic insights into the wash process at the stain level. And AI-enabled screening of detergent formulations further enhances enzyme performance through predictive modelling. This process has led to the launch of innovative products, including phosphodiesterase, inhibitor-free proteases, and new enzyme classes in new formats like unit dose, which underscore the pivotal role of AI in revolutionizing enzyme engineering for detergents, paving the way for more efficient and sustainable cleaning solutions.

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