Title Thermoreversible Polymers Adsorbed to Colloidal Silica: A 1H NMR and DSC Study of the Phase Transition in Confined Geometry
Date 03.12.2002
Number 10126
Abstract The phase transition of the thermoreversible polymer PNIPAM, which shows a coil-to-globule transition dueto the lower critical solution temperature (LCST) behavior in aqueous solution, is investigated in the restrictedgeometry of an adsorption layer. Furthermore, a charged copolymer is studied to investigate the influence ofcharges on the phase transition. Both polymers are adsorbed to colloidal silica and studied by <SUP>1</SUP>H NMR anddifferential scanning calorimetric (DSC) experiments. In solid state <SUP>1</SUP>H NMR relaxation experiments the signalsof solid spins in trains and of liquid spins in tails and loops can be identified. <SUP>1</SUP>H liquid state spectra detectthe phase transition of the loops and tails into immobile segments with increasing temperature. The transitionis broadened as compared to the polymer in solution, especially at low surface coverage. For the copolymer,the transition is incomplete, since mobile segments remain even at high temperature. They are attributed toelectrostatic repulsion from the surface, leading to a mobile arrangement of the copolymer layer. Micro-DSCexperiments confirm the finding of an increased width of the transition at the interface, which depends on thesurface coverage. Furthermore, an increase of the transition temperature with decreasing polymer amount isobserved, which is most pronounced for the copolymer, and is a further indication of an electrostaticallyhindered phase tra<br />nsition. In conclusion, despite a negligible influence of a low fraction of charges on thephase transition in solution, the phase transition in adsorption layers is very sensitive to charged segments.Combining NMR and DSC methods, local information on the transition behavior of different polymer segmentsat the interface, such as loops and tails, or charged monomers, can be obtained.
Publisher Journal of Physical Chemistry / B
Citation Journal of Physical Chemistry / B 106 (2002) 7800-7808
Authors Schönhoff, M. ; Larsson, A. ; Welzel, P. ; Kuckling, D.

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