es991103o_si_001.pdf (42.99 kB)
Macromolecular Characteristics of Natural Organic Matter. 1. Insights from Glass Transition and Enthalpic Relaxation Behavior
journal contribution
posted on 2000-07-29, 00:00 authored by Eugene J. LeBoeuf, Walter J. WeberThis is the first of a series of papers focusing on an
experimental investigation of mechanisms contributing to
the sequestration of hydrophobic organic compounds (HOCs)
by macromolecular natural organic matter (NOM). It
presents the results of a detailed study by differential
scanning calorimetry (DSC) of NOM-related glass transition
and enthalpic relaxation phenomena. Parallel measurements
for model synthetic organic macromolecules of well
characterized structure provide a basis for interpretation
of the observed behaviors of the structurally heterogeneous
and relatively ill-characterized natural organic materials
investigated. The effects of varied DSC heating rates reveal
transition temperature and enthalpic relaxation responses
consistent with the Gibbs-Dimarzio glass transition
theory, thus providing definitive evidence to support our
earlier reports of the occurrence of glassy/rubbery state
transitions in NOM macromolecules. Quantification of
maximum changes in heat capacity for enthalpic relaxation
phenomena provides insights into the types of physical
and chemical bonds that limit glassy-state macromolecular
mobility. Marked reductions by sorbed water of the
effective temperature at which glass transition phenomena
occur for hydrophilic NOMs are observed, suggesting
that the thermodynamic states of NOM macromolecules
are influenced in natural systems by the presence of large
concentrations of sorbing molecules. The thermodynamic
states of the more hydrophobic components or regions
of NOM macromolecules, for example, are likely influenced
by large amounts of sorbed HOCs in a manner similar to
that affected by sorbed water for hydrophilic macromolecules.
Finally, ramifications of the findings with respect to
alternative remediation end points are discussed.