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Physical Chemistry at
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Dr. Williams is interested in…
The ability to detect
explosives and explosive materials follows naturally from this
expertise. Additionally, detection of the
degradation products that result from long-term material
incompatibilities is also a goal. Topics in this area include
the following. Materials Compatibility
The integrity and safety of
military munitions in long-term storage depends upon the compatibility
of the explosive formulation materials, the packing material, and in
some cases the storage containers. Artificial
aging and accelerated aging studies are used to reveal physical and
chemical changes associated with material incompatibilities. An artificial aging study
evaluates material mixtures containing artificially large amounts of
degradation products. An accelerated aging
study uses high temperature to accelerate the aging process. The reactivity of the system may be further
tested by the addition of humid air, oxygen, or other gases.
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Useful Links . |
Spectroscopic Signatures of Degradation and
Environmental Damage
The stability of high
explosives depends upon the molecular properties of the explosive,
binder, stabilizer, and plasticizer. Micro-infrared
(IR) spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR)
spectroscopy, ion mobility spectrometry (IMS), and gas / liquid
chromatography – mass spectrometry (LC-MS-MS, GC-MS) are all
available to investigate changes to the molecular species present in an
explosive formulation. These various techniques
are combined to determine the spectroscopic signatures that indicate
compatibility issues and aging mechanisms.
The structure of a
poly(ester urethane) block co-polymer that is used in some explosive
formulations. The spectral signatures of
the nitrated polyurethane segment have been determined by synthesizing
nitrated model compound fragments of the aromatic region of the polymer. The model compound spectra (IR and Raman) were fully assigned
using ab initio calculations (Gaussian Inc).
The quantitative method for analyzing the extent of
nitration was determined with solvent-cast films and micro and
macro-ATR-FTIR. The micro-ATR-FTIR was
able to see segregation and crystallization of the solvent cast films,
and the macro-ATR-FTIR was insensitive to segregation and
crystallization in the quantitation. The
image below shows the depressions made by the germanium ATR crystal. The crystalline nitrated material is seen on
the top-left half of the image, and the poly(ester urethane) matrix is
seen on the lower-right half of the image. Likewise,
the FTIR spectrum of the crystalline region is shown on top and the
spectrum of the polymer matrix is shown on bottom.
Color ChangesAnother signal of chemical
change is the color of the material. Many
colorless polymers become yellow over time as they are The study of color changes
requires a specific definition of color, such as the CIE tristimulus
values, the chromaticity coordinates, and the standard red-green-blue
(sRGB) values. For example, the
chromaticity coordinates of potassium permanganate, nickel (II)
chloride, cobalt (II) chloride, and copper sulfate are shown in the
figure to the right. Color changes in a
material will create a measureable shift of the chromaticity
coordinates. The precise method has been
published for transforming visible spectra to the CIE tristimuli,
chromaticity coordinates and sRGB values. A
standard technique for simulating the specific color values for a
molecule using semi-empirical modeling methods has also been submitted
for publication.
A temperature-controlled
digital hydrometer / Du Nouy ring tensiometer was constructed in the
Williams lab to measure the surface and interfacial tension of solvents
and solvent blends used in the filled-polymer formulation process. It has also been used to measure the surface
tension during the curing process of Sylgard elastomeric polymer. A paper has been submitted detailing the
performance characteristics of this instrument and giving the necessary
details for construction of a similar instrument. The comparison of the
experimental results of surface tension compared to NIST surface
tension values for toluene and water at 13 different temperatures is
shown in the image to the left. |
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Some publications related to these topics
include:
· Flaherty T. J., Timmons
J.C., Wrobleski D. A., Orler E. B., Langlois D. A., Wurden, K. J.,
Williams, D. L.*,Infrared and Raman Spectral Signatures of Aromatic
Nitration in Thermoplastic Urethanes, Applied
Spectroscopy, 61(6), (2007) · Williams, D. L.*, Jupe C.
L., Kuklenz K. D., Flaherty T. J., An Inexpensive, Digital Instrument
for Surface Tension, Interfacial Tension, and Density Determination, The Chem. Ed., submitted (MS#T0709081). · Williams, D. L.*, Flaherty,
T. J., Al-Naslah, B. Beyond Lambda-Max Part 2: Predicting Molecular
Color, Journal of
Chemical Education, MS#2007-0645, to be published in 2008. · Williams, D. L.*, Flaherty,
T. J., Jupe, C. L., Coleman, S. A., Marquez K. A., Stanton J. J.,
Beyond Lambda-Max: Transforming Visible Spectra into 24-bit Color
Values, Journal
of Chemical Education, 84, 1873-1877, (2007) · Lopez, E. P.*, Moddeman, W.
E., Birkbeck, J. Williams, D.L., Benkovich
M.G., Solvent Substitution – PART 2: The Elimination of
Flammable, RCRA and ODC Solvents for Wipe Application, CleanTech
Magazine, 4(10); 14-16 (2004) · Lopez, E. P.*, Moddeman, W.
E., Birkbeck, J. Williams, D.L., Benkovich
M.G., Solvent Substitution – PART 1: The Elimination of
Flammable, RCRA and ODC Solvents for Wipe Application, CleanTech
Magazine, 4(9); 16-19 (2004)
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Contact
Information for Web: http://www.shsu.edu/~chm_dlw/;
Email: dlwilliams@shsu.edu;
Phone: (936)294-1529; FAX: (936)294-4996 Chemistry
Department ( |
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