Configuron
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An amorphous substance is any in which there is no long-range order over the positions of its constituent particles. These particles can be subatomic, atoms, ions, molecules, dust, crystallites, or grains, stones, boulders], or larger debris.
Amorphous substances can fall into the usual categories of solid, liquid, gas, or plasma. But some substances which are amorphous, such as sand are fluids.
In principle, given a sufficiently high cooling rate, any liquid can be made into an amorphous solid. Cooling reduces molecular mobility. If the cooling rate is faster than the rate at which molecules can organize into a more thermodynamically favorable crystalline state, then an amorphous solid will be formed. Because of entropy considerations, many polymers can be made into amorphous solids by cooling even at slow rates. In contrast, if molecules have sufficient time to organize into a structure with two- or three-dimensional order, then a crystalline (or semi-crystalline) solid is formed. Water is one example. Because of its small molecular size and ability to quickly rearrange, it cannot be made amorphous without resorting to specialized hyperquenching techniques. These produce amorphous ice.
Water as a liquid has much of the available kinetic energy expressed through additional degrees of freedom than water vapor. Some of this energy is in the form of intermolecular bonds. These bonds are a resistance to flow. Water has a resistance to flow that is considered relatively "thin", having a lower viscosity than other liquids such as vegetable oil. At 25°C, water has a nominal viscosity of 1.0 × 10-3 Pa∙s and motor oil has a nominal apparent viscosity of 250 × 10-3 Pa∙s.[1]
Viscous flow in amorphous materials such as water is a thermally activated process:[2]
- <math>{\mu} = A \cdot e^{Q_L/RT},</math>
where QL is the activation energy in the liquid state, T is temperature, R is the molar gas constant and A is approximately a constant.
With
- <math>Q_L = H_m\,</math>
where Hm is the enthalpy of motion of the broken hydrogen bonds.
A configuron is an elementary configurational excitation in an amorphous material which is a broken chemical bond and associated strain-releasing local adjustment in centres of vibration.[3]
The higher the temperature of an amorphous material the higher the configuron concentration. The higher the configuron concentration the lower the viscosity. As configurons form percolating clusters, an amorphous solid can transition to a liquid. This clustering facilitates viscous flow. Thermodynamic parameters of configurons can be found from viscosity-temperature relationships[4]
Acknowledgements
The content on this page was first contributed by: Henry A. Hoff.
Initial content for this page in some instances came from Wikipedia.
References
- ↑ Raymond A. Serway (1996). Physics for Scientists & Engineers (4th Edition ed.). Saunders College Publishing. ISBN 0-03-005932-1.
- ↑ Ojovan MI, Lee WE (2004). "Viscosity of network liquids within Doremus approach". J Appl Phys. 95 (7): 3803–10. doi:10.1063/1.1647260. Text "month" ignored (help)
- ↑ Angell CA, Rao KJ (1972). "Configurational excitations in condensed matter, and "bond lattice" model for the liquid-glass transition". J Chem Physics. 57 (1): 470–81. doi:10.1063/1.1677987.
- ↑ Ojovan MI (2008). "Configurons: thermodynamic parameters and symmetry changes at glass transition". Entropy. 10: 334–64. doi:10.3390/e10030334. Text "http://www.mdpi.org/entropy/papers/e10030334.pdf " ignored (help)