Glass Transitions in Peat:  Their Relevance and the Impact of Water

Abstract

This contribution aims to expand the macromolecular view of fractionated natural organic matter (NOM)to organic matter in whole soils. It focuses on glass transition behavior of whole soil organic matter (SOM) and its interrelation with water through use of differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Three processes of structural relaxation related to macromolecular mobility were distinguished. Process I occurs in thermally pretreated and very low water-content samples and corresponds to classic glass transition behavior. Process II occurs in water-containing samples, where water is believed to act as an antiplasticizing agent in the peat at water contents below 12%, causing decreased macromolecular mobility and increased glass transition temperature. We suggestthe formation of hydrogen bond-based cross-links being responsible for this antiplasticizing effect. Process III represents a slow swelling process induced by water uptake with a time constant of swelling in the order of days, with water acting as a plasticizing agent. Results from this work are of particular importance for environmental systems as changes in environmental conditions (e.g., water content, temperature) may induce slow structural relaxation processes in NOM over periods of time ranging from days to weeks. These influences on NOM macromolecular mobility lead to continuous changes in physicochemical properties that may greatly influence sorbate-sorbent interactions in surface and subsurface environments.

Effect of microbial activity, soil water content and added copper on the temporal distribution patterns of HCB and DDT among different soil organic matter fractions

“…A significant difference was found between rapid mass transfer rates (k r ) values, whereas slow mass transfer rate (k s ) values of non-sterilized soil were higher than that of sterilized soil. Both FA and HA fractions are believed to consist of two distinct regions for HOC sorption: the expanded (rubbery) region which is responsible for rapid mass transfer and the condensed (glassy) region which is responsible for slow mass transfer (Pignatello and Xing, 1996;Schaumann and Leboeuf, 2005). The unchanged k r and increased k s values suggest that the microbial activity could enhance HCB and DDT mass transfer by encouraging HCB and DDT to move into the condensed organic matrix.…”

Restructuring of polygalacturonate on alumina upon hydration—Effect on phosphate sorption kinetics

“…Under field and laboratory conditions, organic matter is subjected to moisture fluctuations that may change its physico-chemical properties due to interaction with water molecules (LeBoeuf and Weber, 2000;Schaumann, 2005;Schaumann and LeBoeuf, 2005). Hydration-induced changes in the macromolecules' mobility (Schaumann and LeBoeuf, 2005) may affect the retention of nutrients and pollutants by minerals coated with organic matter.…”

“…Under field and laboratory conditions, organic matter is subjected to moisture fluctuations that may change its physico-chemical properties due to interaction with water molecules (LeBoeuf and Weber, 2000;Schaumann, 2005;Schaumann and LeBoeuf, 2005). Hydration-induced changes in the macromolecules' mobility (Schaumann and LeBoeuf, 2005) may affect the retention of nutrients and pollutants by minerals coated with organic matter. The ability of soils and soil organic matter to sorb or release organic pollutants has been shown to depend on the state of hydration, hydration time, wetting and drying cycles, and the water content of the samples (Gaillardon, 1996;Altfelder et al, 1999;Johnson et al, 1999;Schaumann et al, 2004).…”

The role of attached phase soil and sediment organic matter physicochemical properties on fullerene (nC60) attachment

“…At higher temperatures the AP-SOM layers expand or swell due to increased thermal motions and apparent increased hydration, much like the matrix relaxation observed in previous studies (Schaumann, 2005;Schaumann and LeBoeuf, 2005). Swelling will increase the volume of the layers, allowing them to take a more extended conformation from the surface of the sensor and also provide an increasingly cross-linked or bridged mesh of organic matter for the C 60 particles to become entangled in.…”