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001018701 0247_ $$2datacite_doi$$a10.34734/FZJ-2023-04995
001018701 037__ $$aFZJ-2023-04995
001018701 041__ $$aEnglish
001018701 1001_ $$0P:(DE-HGF)0$$aPrause, Albert$$b0
001018701 245__ $$aStructural Investigation of Hydrophobically Modified Thermoresponsive Polymers andTheir Influence on the Rheology of Microemulsions$$f2000-01-01 - 2002-12-31
001018701 260__ $$c2023
001018701 300__ $$a182p
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001018701 502__ $$aDissertation, TU Berlin, 2023$$bDissertation$$cTU Berlin$$d2023$$o2023-01-09
001018701 520__ $$aA library of nonsymmetrical thermosensitive BAB* block copolymers was investigated in terms of their aggregation behavior and rheological properties as a function of temperature in aqueous solutions. Additionally, these block copolymers were used to study the modification of temperature-dependent rheological properties of microemulsions. The block copolymers comprise a permanently hydrophilic poly(N,N -dimethylacrylamide) (pDMAm) block “A”, a permanently hydrophobic n-dodecyl (C12) chain as end-group “B”, and a ther-moresponsive (TR) block “B*” featuring a lower critical solution temperature (LCST). To vary the chemical nature and LCST behavior, different polyacrylamides, i. e., poly(N -n-propylacrylamide) (pNPAm), poly(N,N -diethylacrylamide) (pDEAm), poly(N -isopropyl-acrylamide) (pNiPAm), and poly(N -acryloylpyrrolidine) (pNAP), were introduced as TR blocks. Additionally, the length of the TR block was varied systematically as well as the architecture of the block copolymer, for which three types were employed, i. e., BAB*, B2AB*, and B(AB*)2.The influence of the length of the TR block on the aggregation behavior and temperature response was studied via light and neutron scattering (SLS, DLS, and SANS). For TR blocks with more than 40 monomer units, a marked hydrophobic interaction occurs above the LCST, leading to ordered, well-structured clusters of micellar aggregates. Thus, the temperature-dependent mesoscopic organization of aggregates can be tuned by the length and type of the TR block.The temperature response of rheological properties was investigated and compared for the various copolymer architectures. Depending on the TR block and the copolymer archi-tecture, their solution’s viscosity can increase significantly with rising temperature. These results are well in line with the observed mesoscopic organization obtained by SLS, DLS, and SANS experiments. Additionally, fluorescence experiments using the solvatochromic probe Prodan revealed a direct relationship between the increased viscosity and the for-mation of additional hydrophobic domains of TR blocks. Consequently, the viscoelastic properties of aqueous solutions can be tuned temperature dependently by carefully designing these copolymers.Following this, the viscoelastic properties of low-viscous oil-in-water (O/W) microemul-sions (MEs) can also be adjusted. For a properly chosen ME concentration, these block copolymers lead to a viscosity increase with rising temperature. At a polymer concentration of about 22 g L−1, the most pronounced enhancement was observed for the pNPAm-based systems, with factors up to about 3, 5, and 8 for BAB*, B2AB*, and B(AB*)2, respectively. The enhancement is caused by the formation of a transient net-work mediated by TR blocks, as evidenced by the direct correlation between the viscosity enhancement and the attraction strength. This kind of tailored temperature-dependent viscosity control of surfactant-based systems could therefore be advantageous for applications requiring a high hydrophobic payload, which is accomplished by the droplet microemulsion.
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001018701 65017 $$0V:(DE-MLZ)GC-1602-2016$$2V:(DE-HGF)$$aPolymers, Soft Nano Particles and  Proteins$$x0
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