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Effect of sub-micrometer structural features on rheology of polymer nanocomposites
Lepcio, Petr ; Chodák,, Ivan (oponent) ; doc.Ing.Marián Lehocký, Ph.D. (oponent) ; Jančář, Josef (vedoucí práce)
Polymer nanocomposites (PNCs) hold a great promise as future lightweight functional materials processable by additive manufacturing technologies. However, their rapid deployment is hindered by their performance depending strongly on the nanoparticle (NP) spatial organization. Therefore, the ability to control the nanoparticle dispersion in the process of PNCs preparation is a crucial prerequisite for utilizing their potential in functional composites. This work investigates solution blending of PNCs in a model glass forming polymer matrix, a bulk processing technique of a tailored NP spatial organization controlled by structural and kinetic variables of the preparation protocol. The presented results describe the differences between nanoparticle induced changes on the rheological behavior of a polystyrene solution under large amplitude oscillation shear (LAOS). High-affinity OP-POSS NPs seem to interact with the PS at low filler loadings and form stiffened aggregates, whereas low-affinity OM-POSS NPs remained rather uninvolved in the polymer deformation at these conditions. Furthermore, an interest was focused on the impact of the blending solvent on the NP spatial arrangement in silica/PMMA and silica/PS nanocomposites, which has already been suggested as the controlling parameter of the solid-state structure. An emphasis was put on the qualitative differences between “poorly dispersed” NP arrays which, by combination of rheological assessment and structural analysis (TEM, USAXS), were identified as chain bound clusters and two types of aggregates, one of thermodynamic and the other of a kinetic origin, which are characterized by substantially distinct formation kinetics and mismatched properties compared to individually dispersed NPs and each other. The currently observed types of NP dispersion were quantitatively linked with their rheological properties during the solution blending step and the amount of polymer adsorption and depletion attraction. The results were compared to the PRISM theory. Finally, the importance of NP spatial organization was demonstrated on the comparison of glass transition temperatures of various structures at constant chemical composition.
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Vliv huminových kyselin na půdní strukturu
KLENOTOVÁ, Eva
Půdní struktura je jedním z ukazatelů kvality půdy. Za strukturní typ s nejlepšími vlastnostmi je považován drobtovitý. Jeho vznik je ovlivněn řadou fyzikálních, chemických a biologických faktorů. V bakalářské práci byl zkoumán vliv huminových kyselin jakožto tmelicích agens na agregaci půdy. Ze třech získaných roztoků huminových kyselin pocházejících z různých zdrojů byl k následným experimentům vybrán nejkvalitnější. Ke stanovení vlivu roztoku na agregaci půdy bylo využito srovnání dvou metod, prosévání za sucha a za mokra. Výsledkem bylo průkazné zjištění vlivu huminových kyselin na tvorbu vodostálých makroagregátů, které jsou z hlediska agregace půd nejvýznamnějším ukazatelem. Dále byl potvrzen vliv koncentrace roztoku huminových kyselin na agregaci půdy. Vyšší koncentrace umožnila větší tvorbu makroagregátů. Vliv aplikační dávky roztoku na půdní strukturu nebyl prokázán.
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Effect of sub-micrometer structural features on rheology of polymer nanocomposites
Lepcio, Petr ; Chodák,, Ivan (oponent) ; doc.Ing.Marián Lehocký, Ph.D. (oponent) ; Jančář, Josef (vedoucí práce)
Polymer nanocomposites (PNCs) hold a great promise as future lightweight functional materials processable by additive manufacturing technologies. However, their rapid deployment is hindered by their performance depending strongly on the nanoparticle (NP) spatial organization. Therefore, the ability to control the nanoparticle dispersion in the process of PNCs preparation is a crucial prerequisite for utilizing their potential in functional composites. This work investigates solution blending of PNCs in a model glass forming polymer matrix, a bulk processing technique of a tailored NP spatial organization controlled by structural and kinetic variables of the preparation protocol. The presented results describe the differences between nanoparticle induced changes on the rheological behavior of a polystyrene solution under large amplitude oscillation shear (LAOS). High-affinity OP-POSS NPs seem to interact with the PS at low filler loadings and form stiffened aggregates, whereas low-affinity OM-POSS NPs remained rather uninvolved in the polymer deformation at these conditions. Furthermore, an interest was focused on the impact of the blending solvent on the NP spatial arrangement in silica/PMMA and silica/PS nanocomposites, which has already been suggested as the controlling parameter of the solid-state structure. An emphasis was put on the qualitative differences between “poorly dispersed” NP arrays which, by combination of rheological assessment and structural analysis (TEM, USAXS), were identified as chain bound clusters and two types of aggregates, one of thermodynamic and the other of a kinetic origin, which are characterized by substantially distinct formation kinetics and mismatched properties compared to individually dispersed NPs and each other. The currently observed types of NP dispersion were quantitatively linked with their rheological properties during the solution blending step and the amount of polymer adsorption and depletion attraction. The results were compared to the PRISM theory. Finally, the importance of NP spatial organization was demonstrated on the comparison of glass transition temperatures of various structures at constant chemical composition.
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