Polarizability of Aspirin at Terahertz Frequencies Using Terahertz Time Domain Spectroscopy (THz-TDS)

Zhang, Tianyao; Zhang, Zhaohui; Arnold, Mark A.

doi:10.1177/0003702818815177

Cited by 20 publications

(9 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This estimation is possible when the porosity of the polymer matrix is essentially zero, which enables the sample pellets to be modeled as two components (polymer and analyte) versus the more general ternary model consisting of polymer, analyte, and air. 12 As reported elsewhere, compressed polytetrafluoroethylene (PTFE) offers a matrix essentially free of trapped air. 19 Polytetrafluoroethylene pellets are also physically and chemically stable over time while being nearly transparent over THz frequencies.…”

Section: Introductionmentioning

confidence: 94%

“…The dielectric properties of PTFE were determined previously over the 10-100 cm À1 spectral range from measurements on pellets composed only of PTFE and the dielectric value for air e 0 can be taken as unity across the THz spectrum. 12 Volume fractions for the analyte (amino acid) and polymer (PTFE) require knowledge of the mass of each component within the pellet, the density of each component, and the geometric volume of the pellet. Equations 5 and 6…”

Section: Analytical Solutionmentioning

confidence: 99%

“…7À10 Terahertz (THz) frequencies probe long-range intermolecular interactions within crystalline materials, which makes the measurement of polarizability at THz frequencies uniquely advantageous for characterizing polymorphism of organic crystals as well as long-range intermolecular interactions within organic cocrystals. 11,12 The coherent detection of terahertz time-domain spectroscopy (THz-TDS) provides a straightforward method for directly measuring both refractive index and dielectric properties of materials from which polarizability can be derived. Examples include THz polarizabilities of liquid crystals, branched alkanes, and glasses where the dielectric constants are measured from pure bulk substances.…”

Section: Introductionmentioning

confidence: 99%

“…For crystals only available in small dimensions, such as sub-millimeter crystalline forms, THz polarizability measurements have been demonstrated by embedding a population of crystals within an inert amorphous polymer matrix. 12 The Landau, Lifshitz, and Looyenga (LLL) effective medium model can be used to separate the dielectric properties of the crystals and the polymer matrix, thereby enabling determination of the polarizability properties of the crystalline solutes. An analytical solution is available for such polarizability measurements when the crystal structure is known.…”

Section: Introductionmentioning

confidence: 99%

“…An analytical solution is available for such polarizability measurements when the crystal structure is known. 12 Prior knowledge of the density of the crystal (taken from its crystal structure) coupled with both the LLL effective medium model and the CM relationship widens the breadth of samples for which THz polarizability measurements are possible.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Crystal Structure-Free Method for Dielectric and Polarizability Characterization of Crystalline Materials at Terahertz Frequencies

2021

Self Cite

View full text Add to dashboard Cite

Terahertz (THz) time-domain spectroscopy provides a direct and nondestructive method for measuring the dielectric properties of materials directly from the phase delay of coherent electromagnetic radiation propagating through the sample. In cases when crystals are embedded within an inert polymeric pellet, the Landau, Lifshitz, and Looyenga (LLL) effective medium model can be used to extract the intrinsic dielectric constant of the crystalline sample. Subsequently, polarizability can be obtained from the Clausius–Mossotti (CM) relationship. Knowledge of the crystal structure density is required for an analytical solution to the LLL and CM relationships. A novel crystal structure-free graphical method is presented as a way to estimate both dielectric constants and polarizability values for the situation when the crystal structure density is unknown, and the crystals are embedded within a pellet composed of a non-porous polymer. The utility of this crystal structure-free method is demonstrated by analyzing THz time-domain spectra collected for a set of amino acids (L-alanine, L-threonine, and L-glutamine) embedded within pellets composed of polytetrafluoroethylene. Crystal structures are known for each amino acid, thereby enabling a direct comparison of results using the analytical solution and the proposed crystal structure-free graphical method. For each amino acid, the intrinsic dielectric constant is extracted through the LLL effective medium model without using information of their crystal structure densities. THz polarizabilities are then calculated with the CM relationship by using the determined intrinsic dielectric constant for each amino acid coupled with its crystal density as determined graphically. Comparison between the analytical and graphical solutions reveal relative differences between dielectric constants of 3.7, 5.1, and 13.6% for threonine, alanine, and glutamine, respectively, and relative differences between polarizability of 0.6, 0.9, and 5.4%, respectively. These values were determined over the 10–20 cm−1 THz frequency range. The proposed method requires no prior knowledge of crystal structure information.

show abstract

Section: Introductionmentioning

confidence: 94%

Section: Analytical Solutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations