- Titel
- Surface Forces & Colloidal Interactions of Microplastic Particles
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-1060863
- Erstveröffentlichung
- 2026
- Datum der Einreichung
- 30.09.2025
- Datum der Verteidigung
- 24.02.2026
- Abstract (EN)
- Plastics have become indispensable due to their versatility, durability, and low cost, with applications ranging from healthcare and aerospace to construction and textiles. However, this same durability contributes to severe environmental challenges. Millions of tons of plastic enter the environment each year, part of which appears as microplastics (MPs), defined as particles between 100 nm and 5 mm. MPs are found globally—from the Mariana Trench to Mount Everest, in polar regions, in plants, animals, and even human tissues. While MPs are not considered acutely toxic, they may induce chronic stress in organisms and act as vectors for hazardous substances such as plastic additives, pesticides, or heavy metals. The aim of this dissertation was to investigate how microplastic surface properties influence their interaction with cells and with natural environmental particles, focusing particularly on the role of the eco-corona—a soft, hydrated layer of adsorbed natural organic and inorganic matter that forms on MPs in aquatic systems. The eco-corona modifies particle surface characteristics and thereby affects cellular interactions as well as transport and sedimentation processes. A combination of analytical techniques was employed, including ζ-potential measurements, dynamic light scattering (DLS), scanning electron microscopy (SEM), and colloidal probe atomic force microscopy (CP-AFM). CP-AFM provided unique insights into single particle–particle interactions at a resolution unattainable with conventional methods, making it a key tool in this work. The results show that MPs of identical size, shape, and polymer type can nevertheless exhibit distinct surface properties depending on their manufacturer. This finding explains many contradictory results in the literature regarding polystyrene MP–cell interactions and emphasizes the necessity of thorough particle characterization in ecotoxicological studies. Notably, the ζ-potential was identified as a reliable proxy for MP–cell interaction and internalization. This relationship held true not only for pristine polystyrene particles but also for those incubated in fresh- and saltwater and thus covered with an eco-corona. This demonstrates that a single, relatively simple parameter can be used to approximate the likelihood of MP uptake into cells, reducing the need for more complex cellular assays. In addition, it was shown that the eco-corona substantially alters the mechanical properties of MPs. CP-AFM experiments, interpreted using polymer brush models, revealed that the eco-corona behaves mechanically like a polymer brush, conferring steric stabilization when surfaces are fully covered. However, when coverage is incomplete, attractive interactions dominate, enabling eco-corona-mediated heteroaggregation between MPs and mineral particles such as SiO₂ or bentonite. Raman spectroscopy confirmed the formation of these aggregates, and hydrodynamic simulations indicated that the attractive forces are sufficient to overcome drag forces in flowing waters. This explains why MPs, even those less dense than water, are commonly found in sediments: through heteroaggregation with natural particles, their density increases and they are incorporated into sediment beds. In conclusion, this dissertation demonstrates that surface properties—and in particular ζ-potential and eco-corona effects—are critical in determining the interactions of MPs with cells and natural particles. These mechanistic insights improve our understanding of MP uptake, aggregation, and sedimentation and provide tools for better environmental risk assessment. Future work should focus on disentangling the specific contributions of eco-corona properties such as stiffness, charge, and chemistry to cellular interactions. Polyelectrolyte multilayer systems offer a promising model to mimic individual eco-corona characteristics in a controlled way. Furthermore, combining laboratory aggregation studies with field data will be essential for building predictive models of MP transport and fate in aquatic environments. Such models could form the basis for improved risk assessment and regulation of plastic pollution. This thesis highlights the importance of surface characterization in MP research and demonstrates the need for interdisciplinary approaches to tackle the complexity of the microplastic problem. Only through collaborative efforts across physics, chemistry, biology, environmental science, and engineering can meaningful progress be made towards understanding and mitigating the impacts of MPs in the environment.
- Verweis
- Repulsive Interactions of Eco-corona-Covered Microplastic Particles Quantitatively Follow Modeling of Polymer Brushes
DOI: 10.1021/acs.langmuir.1c03204 - Supposedly identical microplastic particles substantially differ in their material properties influencing particle-cell interactions and cellular responses
DOI: 10.1016/j.jhazmat.2021.127961 - Nominally identical microplastic models differ greatly in their particle-cell interactions
DOI: 10.1038/s41467-024-45281-4 - How Microplastics cross the Buoyancy Barrier: A multi-scale Study
DOI: 10.48550/arXiv.2509.14371 - Freie Schlagwörter (EN)
- surface forces, colloidal interaction, microplastic
- Klassifikation (DDC)
- 530
- Klassifikation (RVK)
- UP 7500
- GutachterIn
- Prof. Dr. Andreas Fery
- Prof. Dr. Hans-Jürgen Butt
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-1060863
- Veröffentlichungsdatum Qucosa
- 04.08.2026
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY-NC-SA 4.0- Nutzungshinweis
- Inhalte mit unterschiedlichem Rechtestatus
- Inhaltsverzeichnis
Zusammenfassung 3 Abstract 5 I. List of Abbreviations 7 II. List of symbols 11 III. List of Publications and Contributions 17 1. Introduction 31 1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.2. Objective of the Thesis . . . . . . . . . . . . . . . . . . . . . . . 34 2. Theoretical Background - Particle-Particle Interactions and Surface Forces in Aqueous Solutions 39 2.1. Electric Double Layer . . . . . . . . . . . . . . . . . . . . . . . . 39 2.2. Interaction Potential of Two Overlapping Double Layers . . . 41 2.3. ζ-Potential Measurements via Electrophoretic Light Scattering 43 2.4. Van-der-Waals and DLVO Force . . . . . . . . . . . . . . . . . 48 2.5. Polymers at the Interface . . . . . . . . . . . . . . . . . . . . . 50 2.5.1. Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . 50 2.5.2. Polyelectrolytes . . . . . . . . . . . . . . . . . . . . . . . 53 2.5.3. Polymer adsorption . . . . . . . . . . . . . . . . . . . . 54 2.5.4. Steric Repulsion of Polymer Saturated Surfaces like Grafted Polymers . . . . . . . . . . . . . . . . . . . . . 56 2.5.5. Polymer Bridging . . . . . . . . . . . . . . . . . . . . . . 58 2.6. DLVO Theory and Presence of Non-DLVO Forces Between Microplastic Particles . . . . . . . . . . . . . . . . . . . . . . . . 62 2.7. Formation and Influence of the Eco-corona on Microplastic Particles Interaction . . . . . . . . . . . . . . . . . . . . . . . . 63 2.8. Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . 65 2.8.1. Conversion of AFM Raw Data into Force-Separation Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 2.8.2. Calibration of Cantilevers . . . . . . . . . . . . . . . . . 68 2.8.3. Advances in CP-AFM . . . . . . . . . . . . . . . . . . . . 70 3. Detailed Practical Description on Performing CP-AFM on Microplastic particles 73 3.1. Cantilever Preparation and Calibration . . . . . . . . . . . . . 73 3.2. Glueing Colloidal Probes to Cantilevers . . . . . . . . . . . . . 75 3.3. Substrate Preparation . . . . . . . . . . . . . . . . . . . . . . . 76 3.4. Colloidal Probe AFM Direct Force Measurements of (Ecocorona Covered) Polystyrene Microplastic Particles . . . . . . 76 4. Supposedly identical microplastic particles substantially differ in their material properties influencing particle-cell interactions and cellular responses 81 4.1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 4.2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.3. Materials and Methods . . . . . . . . . . . . . . . . . . . . . . 84 4.3.1. Materials . . . . . . . . . . . . . . . . . . . . . . . . . . 84 4.3.2. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.4.1. Surface structures and size distributions of P-MPP and M-MPP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.4.2. Differences in particles’ ζ-potentials . . . . . . . . . . 92 4.4.3. Particles’ chemical composition and surface charge distribution . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.4.4. Particle-cell interactions and subsequent internalisation 96 4.4.5. Cellular responses MTT results . . . . . . . . . . . . . 100 4.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 4.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 5. Nominally identical microplastic models differ greatly in their particle-cell interactions 107 5.1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.3. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.3.1. Microplastic particles . . . . . . . . . . . . . . . . . . . 111 5.3.2. Environmental Exposure . . . . . . . . . . . . . . . . . 111 5.3.3. Microplastic particle characterization . . . . . . . . . . 111 5.3.4. Derivation of the hydrodynamic drag force on the microparticles 116 5.3.5. Internalization experiment . . . . . . . . . . . . . . . . 125 5.3.6. Internalization mechanisms . . . . . . . . . . . . . . . 127 5.3.7. Statistical Analysis . . . . . . . . . . . . . . . . . . . . . 129 5.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 5.4.1. The ζ-potential of nominally identical microplastics differ129 5.4.2. Eco-coronas affect the ζ-potential of microplastic particles 132 5.4.3. Particle-cell adhesion depends on the ζ-potential . . 133 5.4.4. Absolute internalization probability depends on ζ-potential137 5.4.5. Microplastics internalized via actin-dependent pathways139 5.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 6. Repulsive Interactions of Eco-corona-Covered Microplastic Particles Quantitatively Follow Modeling of Polymer Brushes 145 6.1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 6.2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 6.3. Methods and materials . . . . . . . . . . . . . . . . . . . . . . 148 6.3.1. Microplastic particles and pre-treatment conditions . 148 6.3.2. Colloidal probe-atomic force microscopy (CP-AFM) . . 149 6.3.3. Estimating the irrelevance of electrostatic interactions 151 6.3.4. Scanning electron microscopy (SEM) . . . . . . . . . . 152 6.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 6.4.1. Scanning electron microscopy (SEM) . . . . . . . . . . 152 6.4.2. Direct force measurements with colloidal probe . . . 153 6.4.3. Repulsive interactions of eco-corona particles: Quantitative description . . . . . . . . . . . . . . . . . . . . . 155 6.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 6.6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 7. How Microplastics cross the Buoyancy Barrier: A multi-scale Study163 7.1. Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 7.3. Eco-corona mediated attraction on different length scales . 166 7.4. Detailed understanding of eco-corona mediated attraction . 174 7.4.1. Eco-corona coverage influences bridging forces between MP and sediment particles . . . . . . . . . . . . 175 7.4.2. Ionic strength influences eco-corona bridging between MP and sediment particles . . . . . . . . . . . . . . . . 176 7.5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 7.6. Materials and Methods . . . . . . . . . . . . . . . . . . . . . . 180 7.6.1. Microplastic particle incubation . . . . . . . . . . . . . 180 7.6.2. Colloidal Probe-Atomic Force Microscopy (CP-AFM) . 181 7.6.3. Data evaluation of CP-AFM experiments . . . . . . . . 182 7.6.4. Numerical simulation of environmental separation force182 7.6.5. Aggregation experiments of PS and model sediment particles . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 7.6.6. Raman imaging of MP-model sediment aggregates . 183 7.6.7. Aggregation-Sedimentation Experiments with LDPE MP Particles . . . . . . . . . . . . . . . . . . . . . . . . . 184 7.6.8. Comparative Column Transport Experiments of Plain and Eco-corona covered MP . . . . . . . . . . . . . . . 185 8. Conclusion 189 9. Outlook 191 10.Appendix 193 10.1.S1 - Supposedly identical microplastic particles substantially differ in their material properties influencing particle-cell interactions and cellular responses . . . . . . . . . . . . . . . . 193 10.2.S2 - Nominally identical microplastic models differ greatly in their particle-cell interactions . . . . . . . . . . . . . . . . . . . 193 10.3.S3 - Repulsive Interactions of Eco-corona-Covered Microplastic Particles Quantitatively Follow Modeling of Polymer Brushes219 10.3.1. Description of marine aquarium facility . . . . . . . . . 219 10.3.2. Attractive forces of pristine and eco-corona particles 219 10.3.3. Repulsive interactions of freshwater eco-corona particles223 10.4.S4 - How Microplastics cross the Buoyancy Barrier: A multiscale Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 10.4.1. Comparison of Debye-length and bridging range of eco-corona . . . . . . . . . . . . . . . . . . . . . . . . . 226 10.4.2. Numerical simulation of river flow . . . . . . . . . . . . 227 10.4.3. Raman imaging and optical microscopy of sediment- MP heteroaggregates . . . . . . . . . . . . . . . . . . . 227 10.4.4. Plain and eco-corona covered MP buoyancy behaviour 230 10.4.5. Comparison of LDPE-particles in the presence and absence of a biofilm with SEM . . . . . . . . . . . . . . 230 10.4.6. Simulated influence of the pore geometry on the drag force exerted on MP . . . . . . . . . . . . . . . . . . . . 230 10.4.7. Results of Fluorescence Microscopy Drainage Analysis 230 10.4.8. DABEST Bootstrap Estimation Analysis of Microplastic Retention . . . . . . . . . . . . . . . . . . . . . . . . . . 234 10.4.9. Influence of relative particle velocity on eco-corona bridging forces on approach and retraction . . . . . . 235 10.4.10. Force-separation curves obtained via CP-AFM . . . . 236 10.4.11.Influence of the eco-corona coverage on bridging energy237 10.4.12. Repulsive interaction ranges at different ionic strengths237 10.4.13. Microplastic Particle information used in the Column Transport Experiments . . . . . . . . . . . . . . . . . . 238 10.4.14. Particle size determination of Bentonite Clay . . . . . 239 10.4.15. Physicochemical properties of Quartz Sands used in the Column Transport Experiments . . . . . . . . . . . 247 10.4.16. Dispersant-free Transport Column Experiment Design 247