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Published March 21, 2000 | public
Journal Article

Dynamic Inhibition of Constrained Crystallization by Mesoscopic Morphology Modifiers


We investigate the mechanisms by which two chemically diverse polymer additives affect crystal separation from hexacosane/decane solutions under various conditions. The additives are dissimilarly effective for delaying the onset of crystallization in supercooled solutions, although none, of course, ultimately prevents their reaching equilibrium. Remarkably, one polymer significantly raises the dissolution temperature of the crystal aggregates grown in its presence, even at sub-parts-per-million additive levels. More interesting is the finding that sufficiently large concentrations of either additive are able to cap at a common minimum thickness the porous layers formed on a cold surface swept by undersaturated solutions. The thin layers formed in the presence of crystallization inhibitors are mesoscopically more compact (i.e., have pore sizes about 10-fold smaller) than those produced in their absence, although all meltwhen rid of solventas neat hexacosane at 329.5 ± 0.5 K. We infer that inhibitors permanently limit the extent of crystal separation from undersaturated solutions subjected to fixed temperature constraints by blocking solute transfer across the boundary layer. This lasting action is mediated by the subtle modification of mesoscopic crystal morphology and is remotely related to the kinetics of isothermal crystal nucleation or the thermodynamics of phase separation.

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© 2000 American Chemical Society. Received August 10, 1999. In Final Form: January 25, 2000.

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