Molecular dynamics dielectric spectroscopy

Vchirawongkwin V, Kritayakornupong C, Rode BM (2010) Structural and dynamical properties and vibrational spectra of bisulfate ion in water a study by ab initio quantum mechanical charge field molecular dynamics. J PhysChemB 114 11561-11569 Vchirawongkwin V, PribU AB, Rode BM (2010a) Ab initio quantum mechanical charge field study of hydrated bicarbonate ion structural and dynamical properties. J Comput Chem 31 249-257 Wachter W, Kunz W, Buchner R, Hefter G (2005) Is there an anionic Hofmeister effect on water dynamics dielectric spectroscopy of aqueous solutions of NtiBr, Nal, NaNOs, NaQOa, and NaSCN. J Phys Chem A 109 8675-8683... 

Roudaut et al. (1999a) used low-frequency pulsed-proton NMR and dielectric dynamic mechanical spectroscopies to study molecular mobility in glassy bread (<9%) as a function of temperature. Based on NMR results, they reported that some (if not all) of the water molecules were much more mobile than the polymer matrix whose relaxation time could not be measured within the 20-p,s dead time of the RF probe. 

Braun et al. [341] investigated the molecular dynamics of the rigid polypeptide brush by means of dielectric spectroscopy and prepared patterned brushes by SIP from pCP SAM initiators [342]. 

During the last two decades, studies on ion solvation and electrolyte solutions have made remarkable progress by the interplay of experiments and theories. Experimentally, X-ray and neutron diffraction methods and sophisticated EXAFS, IR, Raman, NMR and dielectric relaxation spectroscopies have been used successfully to obtain structural and/or dynamic information about ion-solvent and ion-ion interactions. Theoretically, microscopic or molecular approaches to the study of ion solvation and electrolyte solutions were made by Monte Carlo and molecular dynamics calculations/simulations, as well as by improved statistical mechanics treatments. Some topics that are essential to this book, are included in this chapter. For more details of recent progress, see Ref. [1]. 

Dielectric spectroscopy was also used by the same group in order to study the local and global dynamics of the PI arm of the same miktoarm star samples [89]. Measurements were confined to the ordered state, where the dynamics of the PI chain tethered on PS cylinders were observed in different environments since in the SIB case the faster moving PB chains are tethered in the same point as the PI arm. The distribution of segmental relaxation times were broader for SI2 than SIB. The effect was less pronounced at higher temperatures. The PI normal mode time was found to be slower in SIB, when compared to SI2 although both arms had the same molecular weight. Additionally, the normal mode relaxation time distributions of the PI chains tethered to PS cylinders in the miktoarm samples were narrower than in P(S-h-I) systems of lamellar structure. 

An innovative approach due to Haider et al. [113] may help to sidestep the challenges involved in explicit molecular dynamics simulation and obtain information on these slow dynamics. The authors use the results of dielectric reflectance spectroscopy to model the IL as a dielectric continuum, and study the solvation response of the IL in this framework. The calculated response is not a good description of the subpicosecond dynamics, a problem the authors ascribe to limited data on the high frequency dielectric response, but may be qualitatively correct at longer times. We have already expressed concern regarding the use of the dielectric continuum model for ILs in Section IV. A, but believe that if the wavelength dependence of the dielectric constant can be adequately modeled, this approach may be the most productive theoretical analysis of these slow dynamics. 

Since the late nineteenth century, dielectric spectroscopy has been used to monitor dynamical properties of solid and liquid materials. At that time, dielectric measurements were performed either at a single frequency or in a very limited frequency range now, however, measurement technique and instrumentation have developed to such an extent that dielectric spectroscopy is today a well-established method to probe molecular dynamics over a broad range in frequency or time (cf. reviews by Johari [1], Bottcher and Bordewijk [34], Williams [35,36], and Kremer and Schonhals [37]), even with commercially available equipment. Including the latest developments, one can even say that nowadays dielectric spectroscopy is the only method that is fully able to realize the idea of 0- to 1-THz spectroscopy. In data sets that cover the range of up to 10 6—1013 Hz—that is, from ultra-low frequencies up to the far infrared—the full range of reorientational dynamics in... 

The characterization of the elastomer-filler interactions at a molecular level may be cairied out by spectroscopic techniques such as IR and NMR spectroscopy. X-ray and neutron scattering, dynamic mechanical and dielectric spectroscopy, and molecular dynamics simulations [6]. Up to now, the most comprehensive studies of silica filled PDMS [4, 7-22] and carbon black filled conventional rubbers [23] have been carried out by H [4, 7—20, 23], [21], and C NMR relaxation experiments [22],... 

The dielectric spectroscopy is an essential probe for nondestructive studies required for biomolecule analysis. The study of internal motion/dynamics related to the dielectric relaxation in biomolcules require the coverage of periodic vibration along with other mechanisms, such as diffusion, molecular orientations, and relaxation processes. 

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