Origins of the failure of classical nucleation theory for nanocellular polymer foams
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Date
2011-07-06
Authors
Thompson, Russell B.
Kim, Yeongyoon
Park, Chul B.
Chen, P.
Journal Title
Journal ISSN
Volume Title
Publisher
RSC publishing
Abstract
Relative nucleation rates for fluid bubbles of nanometre dimensions in polymer matrices are calculated
using both classical nucleation theory and self-consistent field theory. An identical model is used for
both calculations showing that classical nucleation theory predictions are off by many orders of
magnitude. The main cause of the failure of classical nucleation theory can be traced to its
representation of a bubble surface as a flat interface. For nanoscopic bubbles, the curvature of the
bubble surface is comparable to the size of the polymer molecules. Polymers on the outside of a curved
bubble surface can explore more conformations than can polymers next to a flat interface. This reduces
the free energy of the curved interface which leads to a significantly smaller barrier energy to nucleation
and thus a much higher nucleation rate. Also, there is a reduction of unfavorable energetic contacts
between polymer and fluid molecules in the vicinity of a curved interface. Polymers on the outside of
a curved interface are less likely to find a portion of themselves in the interior of the unfavorable fluid
bubble. A secondary cause of the failure of classical nucleation theory is due to the collapse of the bulk
region inside the bubble. As the radius of a bubble is reduced, eventually the diffuse walls collide
causing increased mixing of polymer and fluid molecules everywhere. This causes a reduction of
internal energy associated with the interface, leading to smaller nucleation barrier energies and, again,
a reduced barrier energy to nucleation.
Description
DOI: 10.1039/C1SM05575E (Paper) Soft Matter, 2011, 7, 7351-7358
This journal is © The Royal Society of Chemistry 2011
Keywords
self-consistent field theory, nucleation, polymers, Classical nucleation theory