Forg, Sandra (2024)
Mussel-inspired microgels with improved mechanical and adhesive properties.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00026492
Ph.D. Thesis, Primary publication, Publisher's Version
Abstract
This thesis aims to develop microgels with improved adhesive and mechanical properties by drawing inspiration from the remarkable under-water adhesion of mussels. The synthesised microgels are based on poly(N-isopropylacrylamide) (PNIPAM), known for its temperature-responsive behaviour. Dopamine methacrylamide (DMA) can be used as a co-monomer to mimic the mussel’s properties. Due to its catechol group, it is capable of cross-linking microgel structures. However, its scavenging ability demands a precise synthesis control.
In the first part of this thesis, the microgel synthesis is analysed and controlled through kinetic studies. Time-samples, taken during the synthesis, are evaluated by using mass spectrometry (MS) to determine the individual monomer consumption rates. The incorporation of DMA is quantified using UV-vis and nuclear magnetic resonance (NMR) spectroscopy. An optimised synthesis protocol is developed: A DMA injection after 15 min ensures the full NIPAM and cross-linker N,N’-methylene-bisacrylamide (BIS) consumption, while an overall synthesis reaction time of 60 min guarantees the DMA incorporation. The synthesis is reproducible and independent of UV light. DMA exhibits second-order reaction kinetics. In the second part, the temperature-dependent swelling behaviour of P(NIPAM-co-DMA) microgels with varying DMA incorporations is analysed: DMA lowers the volume phase transition temperature (VPTT) due to its higher hydrophobicity when compared to NIPAM and sharpens the transition itself. Force spectroscopy measurements on single adsorbed microgel particles reveal that the incorporation of DMA stiffens PNIPAM microgels over their entire cross-section. The swelling behaviour and mechanical properties are linearly correlated as predicted by the affine network model for both types of microgels. Nonetheless, when a large amount of DMA is incorporated, catechol interactions within the network inhibit the shrinking of the microgel, while maintaining its high mechanical stiffness. In the final part of this thesis, the adhesive properties of the microgels are characterised by colloidal probe atomic force microscopy (AFM) on monolayers of microgels prepared by the Langmuir-Blodgett technique. P(NIPAM-co-DMA) microgels exhibit superior adhesion when compared to pure PNIPAM microgels. Adhesive forces reach their maximum at 10 mol% DMA content. However, higher DMA amounts lead to reduced adhesive but increased mechanical properties - this highlights the delicate balance between the material’s cohesive and adhesive properties. When further increasing the packing densities of microgel particles, the adhesion of P(NIPAM-co-DMA) microgels decreases, possibly due to catechol interactions within the densely compressed microgels.
Item Type: | Ph.D. Thesis | ||||
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Erschienen: | 2024 | ||||
Creators: | Forg, Sandra | ||||
Type of entry: | Primary publication | ||||
Title: | Mussel-inspired microgels with improved mechanical and adhesive properties | ||||
Language: | English | ||||
Referees: | Klitzing, Prof. Dr. Regine von ; Karg, Prof. Dr. Matthias | ||||
Date: | 8 January 2024 | ||||
Place of Publication: | Darmstadt | ||||
Collation: | vii, 156 Seiten | ||||
Refereed: | 20 December 2023 | ||||
DOI: | 10.26083/tuprints-00026492 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/26492 | ||||
Abstract: | This thesis aims to develop microgels with improved adhesive and mechanical properties by drawing inspiration from the remarkable under-water adhesion of mussels. The synthesised microgels are based on poly(N-isopropylacrylamide) (PNIPAM), known for its temperature-responsive behaviour. Dopamine methacrylamide (DMA) can be used as a co-monomer to mimic the mussel’s properties. Due to its catechol group, it is capable of cross-linking microgel structures. However, its scavenging ability demands a precise synthesis control. In the first part of this thesis, the microgel synthesis is analysed and controlled through kinetic studies. Time-samples, taken during the synthesis, are evaluated by using mass spectrometry (MS) to determine the individual monomer consumption rates. The incorporation of DMA is quantified using UV-vis and nuclear magnetic resonance (NMR) spectroscopy. An optimised synthesis protocol is developed: A DMA injection after 15 min ensures the full NIPAM and cross-linker N,N’-methylene-bisacrylamide (BIS) consumption, while an overall synthesis reaction time of 60 min guarantees the DMA incorporation. The synthesis is reproducible and independent of UV light. DMA exhibits second-order reaction kinetics. In the second part, the temperature-dependent swelling behaviour of P(NIPAM-co-DMA) microgels with varying DMA incorporations is analysed: DMA lowers the volume phase transition temperature (VPTT) due to its higher hydrophobicity when compared to NIPAM and sharpens the transition itself. Force spectroscopy measurements on single adsorbed microgel particles reveal that the incorporation of DMA stiffens PNIPAM microgels over their entire cross-section. The swelling behaviour and mechanical properties are linearly correlated as predicted by the affine network model for both types of microgels. Nonetheless, when a large amount of DMA is incorporated, catechol interactions within the network inhibit the shrinking of the microgel, while maintaining its high mechanical stiffness. In the final part of this thesis, the adhesive properties of the microgels are characterised by colloidal probe atomic force microscopy (AFM) on monolayers of microgels prepared by the Langmuir-Blodgett technique. P(NIPAM-co-DMA) microgels exhibit superior adhesion when compared to pure PNIPAM microgels. Adhesive forces reach their maximum at 10 mol% DMA content. However, higher DMA amounts lead to reduced adhesive but increased mechanical properties - this highlights the delicate balance between the material’s cohesive and adhesive properties. When further increasing the packing densities of microgel particles, the adhesion of P(NIPAM-co-DMA) microgels decreases, possibly due to catechol interactions within the densely compressed microgels. |
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Status: | Publisher's Version | ||||
URN: | urn:nbn:de:tuda-tuprints-264920 | ||||
Classification DDC: | 500 Science and mathematics > 530 Physics | ||||
Divisions: | 05 Department of Physics 05 Department of Physics > Institute for Condensed Matter Physics 05 Department of Physics > Institute for Condensed Matter Physics > Soft Matter at Interfaces (SMI) |
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Date Deposited: | 08 Jan 2024 13:05 | ||||
Last Modified: | 18 Jan 2024 12:07 | ||||
PPN: | |||||
Referees: | Klitzing, Prof. Dr. Regine von ; Karg, Prof. Dr. Matthias | ||||
Refereed / Verteidigung / mdl. Prüfung: | 20 December 2023 | ||||
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