Near surface dynamics of layers of non-cross-linked and cross-linked polymer architectures at solid planar surfaces
Final Report Abstract
In this project, we investigated the interplay of the inner structure and dynamics of differently cross-linked model-type soft matter systems, namely PNIPAM microgels and PNIPAM polymer brushes in the vicinity of a confining solid substrate. Two different types of microgels were investigated, the classical system, prepared in a batch approach and a more homogeneously crosslinked microgel system obtained from a continuous monomer feeding approach. In both cases, the influence of the cross-linker content on the swelling was studied with dynamic light scattering. Moreover, adsorbed microgel particles were imaged with atomic force microscopy (AFM) to identify and characterize suitable systems for further surface sensitive neutron scattering experiments. Hence, the inner structure of lowly (0.5 mol%, 2 mol%), medium (5 mol%) and highly cross-linked PNIPAM microgels (10 mol% cross-linker) were investigated with small angle neutron scattering (SANS). The inner dynamics was investigated with neutron spin echo spectroscopy (NSE) in transmission mode and the collective and Zimm-type diffusion constants were determined on different lengths and compared as a function of composition and inner structure. The inner dynamics of adsorbed microgel particles (10 mol%) was investigated with NSE under grazing incidence (GINSES). This method generates an evanescent field and probes the near surface region of the adsorbed sample. By variation of the angle of incidence the investigated depth can be varied and hence, a depth profile of the inner dynamics could be measured. We found, that the inner dynamics of feeding-microgels was highly suppressed in proximity to the solid-liquid interface. Additional nanoindentation measurements showed the relation of this fact to the soft nature of those particles. In contrast, the inner dynamics of the conventional batch microgel was not influenced by the interface. Furthermore, PNIPAM-based polymer brushes were synthesized by surface-initiated atom transfer radical polymerization (SI ATRP). The polymer volume profile was determined with neutron reflectometry (NR) and resulted in a parabolic brush profie. GINSES measurements showed a variation of the fluctuation dynamics over the brush height and agreed with the existing theoretical considerations for the dynamics in polydisperse polymer brushes. Additionally, virtual experiments on the BornAgain software platform were done to improve the data analysis of grazing incidence scattering data and to understand the influence of the experimental background on the data analysis and to extract additional information from it. Realistic modeling of the sale geometry and structure and of the experimental conditions was possible. Hence, contributions from sample scattering have been separated from the instrumental background. In grazing incidence, this is hardly possible with additional measurements since the standard background determination known from transmission methods is impossible here.
Publications
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"Simpler neutron resonator enhances the wave-field for grazing incidence scattering experiments with lower parasitic scattering“, Physica B, 551, 405-406, 2018
Kyrey, T., Witte, J., Gavaramia, M., Kotsioubas, A., Mattausch, S., Wellert, S., Holderer, O., Frielinghaus, H.
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Grazing Incidence SANS and Reflectometry Combined with Simulation of Adsorbed Microgel Particles“, Physica B, 551, 172-178, 2018
Kyrey,T., Ganeva, M., Gawlitza, K., Witte, J., von Klitzing, R., Soltwedel, O., Di, Z., Wellert, S., Holderer, O.
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„A grazing incidence neutron spin echo study of near surface dynamics in p(MEO2MA-co-OEGMA) copolymer brushes“, Colloid Polym. Sci., 296, 2005-2014, 2018
Wellert, S., Hübner, J., Boyciyan, D., Ivanova, O., von Klitzing, R., Soltwedel, O., Holderer, O.
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„A comparison of the network structure and inner dynamics of homogeneously and heterogeneously crosslinked PNIPAM microgels with high crosslinker content", Soft Matter, 15, 1053-1064, 2019
Witte, J., Kyrey, T., Lutzki, J., Dahl, A. M., Houston, J., Radulescu, A., Pipich, V., Stingaciu, L., Kühnhammer, M., Witt, M. U., von Klitzing, R., Holderer, O., Wellert, S.
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„Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach“, Soft Matter, 15, 6536-6546, 2019
Kyrey, T. , Witte, J., Feoktystov, A., Pipich, V., Wu, B. H., Pasini, S., Radulescu, A., Witt, M.U., Kruteva, M., von Klitzing, R., Wellert, S., Holderer, O.
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„Influence of the cross-linker content on adsorbed functionalised microgel coatings“, Polymer, 169, 29-35, 2019
Kyrey, T., Witte J., Pipich, V., Feoktystov, A., Koutsioubas, A., Vezhlev, E., Frielinghaus, H., von Klitzing, R., Wellert, S., Holderer, O.
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„Grazing Incidence Neutron Spin Echo Study of Poly(N- isopropylacrylamide) Brushes“, Macromolecules, 53, 1819-1830, 2020
Witte, J., Krause, P., Kyrey, T., Dahl, A. M., Lutzki, J., Schmidt, B.V.K.J., Ganeva, M., Koutsioubas, A., Holderer, O., Wellert, S.
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„Grazing Incidence Small- Angle Neutron Scattering: Background Determination and Optimization for Soft Matter Samples“, Appl. Sci., 11, 2021
Kyrey, T., Ganeva, M., Witte, J., Feoktystov, A., Wellert, S., Holderer, O.
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„Looking inside Poly(N-isopropylacrylamide) Microgels: Nanomechanics and Dynamics at Solid- Liquid Interfaces“, ACS Appl. Polym. Sci., 3, 976-985, 2021
Witte, J., Kyrey, T., Lutzki, J., Dahl, A. M., Kühnhammer, M., von Klitzing, R., Holderer, O., Wellert, S.
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„Mobility of bound water in PNIPAM microgels“, Phys. Chem. Chem. Phys.,23, 14252-14259, 2021
Kyrey, T., Witte, J., Lutzki, J., Zamponi, M., Wellert, S., Holderer, O.
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„Understanding nearsurface polymer dynamics by a combination of grazing-incidence neutron scattering and virtual experiments“, J. Appl. Cryst., 54, 72-79, 2021
Kyrey, T., Ganeva, M., Witte, J., von Klitzing, R., Wellert, S., Holderer, O.
