Vandaktivitetsmålinger for et system af poly(styren-co-natriumacrylate)
Translated title
Water activity measurements of a system of poly(styrene-co-sodium acrylate) core-shell particles and water
Author
Christiansen, Katrine Skelbæk
Term
4. term
Education
Publication year
2009
Pages
83
Abstract
This thesis examines how polyelectrolyte core–shell particles of poly(styrene-co-sodium acrylate) (PS-NaPAA) interact with water using water activity measurements, with a focus on concentrated suspensions where this approach has not previously been applied. Water activity was measured as a function of water content and temperature for PS-NaPAA, and for comparison sodium polyacrylate, sodium acrylate, bare polystyrene particles, and protonated poly(styrene-co-acrylic acid) were measured as a function of water content. The work includes particle size characterization and supporting drying experiments. The results show that the water activity of PS-NaPAA is mainly governed by the charges and counterions in the shell, and that there is a threshold water content below which the system is adsorption-dominated and above which it behaves as a suspension. Temperature-dependent measurements enabled determination of the excess enthalpy required to evaporate water from PS-NaPAA samples, and its dependence on water content was supported by a drying experiment. Overall, the study indicates that water activity measurements are a useful tool for describing interactions between polyelectrolyte core–shell particles and water.
Denne afhandling undersøger, hvordan polyelektrolytiske kerneskalpartikler af poly(styren-co-natriumacrylate) (PS-NaPAA) interagerer med vand ved hjælp af vandaktivitetsmålinger, særligt i koncentrerede suspensioner hvor metoden ikke tidligere er anvendt. Vandaktiviteten blev målt som funktion af vandindhold og temperatur for PS-NaPAA, og til sammenligning blev natriumpolyacrylate, natriumacrylate, polystyrenpartikler og protoneret poly(styren-co-acrylsyre) målt som funktion af vandindhold. Arbejdet inkluderer karakterisering af partikelstørrelse samt supplerende tørringsforsøg. Resultaterne viser, at vandaktiviteten for PS-NaPAA primært bestemmes af ladningerne og modionerne i skallen, og at der findes et vandindhold under hvilket systemet kan beskrives ved adsorption, mens det over dette niveau opfører sig som en suspension. Målinger som funktion af temperatur gav en bestemmelse af den ekstra entalpi, der kræves for at fordampe vand fra PS-NaPAA-prøverne, og variationen med vandindholdet blev understøttet af et tørringsforsøg. Samlet peger arbejdet på, at vandaktivitetsmålinger er et anvendeligt værktøj til at beskrive interaktioner mellem polyelektrolytiske kerneskalpartikler og vand.
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