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- All Subjects: Chemistry, Physical and theoretical
- All Subjects: Dielectric relaxation
- Creators: Richert, Ranko
Description
The objective of the present investigations is to experimentally determine the fundamental molecular properties of the transient metal containing pieces. The transient molecules have been generated using laser ablation production technique and detected by using laser induced fluorescence technique. Ultra-high resolution spectra of the diatomic molecules, 87SrF, 135&137BaF, YbF, HfF, and IrSi were recorded at a resolution of approximately 30 Mhz. The fine and hyperfine structure of these molecules were determined for the ground and the excited state. The optical Stark splittings of 180HfF and IrSi were recorded and analyzed to determine the permanent electric dipole moments of the ground and the excited state. An effective Hamiltonian operator, including the rotational, centrifugal distortion, spin-orbit, spin-spin, spin-rotation, Λ-doubling, magnetic hyperfine and quadrupole interactions, and Stark effect, was employed to model and analyze the recorded spectra. The electronic spectra of the triatomic molecules, TiO2 and ZrO2, were recorded using pulsed dye laser, LIF, spectrometer at a resolution of 300MHz. These molecules have C2v symmetry. The harmonic frequencies, lifetime measurements were determined. These spectra of ZrO2 and TiO2 were modeled using a normal coordinate analysis and Franck-Condon factor predictions. High resolution field-free and Stark effect spectra of ZrO2 were recorded and for future investigation.
ContributorsLe, Anh Thun (Author) / Steimle, Timothy C (Thesis advisor) / Richert, Ranko (Committee member) / Chizmeshya, Andrew (Committee member) / Arizona State University (Publisher)
Created2013
Description
A driving force for studies of water, alcohols, and amides is the determination of the role of hydrogen bonding. Hydrogen bonds can break and reform, consequently creating supramolecular structures. Understanding the role supramolecular structures play in the dynamics of monohydroxyl alcohols is important to understanding hydrogen bonding in more complex systems such as proteins. Since many monohydroxyl alcohols are good glass formers, dielectric spectroscopy in the supercooled regime is used to gather information about the dynamics of these liquids. Application of high external fields will reversibly alter the polarization responses of the material from the linear response. This results in nonlinear dielectric effects (NDE) such as field induced suppression (saturation) and enhancement of amplitudes (chemical effects) as well as shifts in the time constants toward slower (entropy) and faster (energy absorption) dynamics.
The first part of this thesis describes the nonlinear dielectric experiments on monohydroxyl alcohols, with an emphasis on the time dependence of NDEs. For the first time, time-dependent experiments on monoalcohols were done, the results showed that NDEs occur on the Debye time scale. Furthermore, physical vapor deposition (PVD) is used to modify the supramolecular structure of 4-methyl-3-heptanol. Upon deposition the film cannot form the ring like structures, which are preferred in the bulk material. The as deposited film shows an enhancement of the dielectric peak by a factor of approximately 11 when compared to the bulk material. The conversion from the as deposited material back to the near bulk material was found to occur on the Debye timescale.
The second part of this thesis focuses on the question of what is governing the field induced changes seen in the liquids studied. Here a complete set of high field experiments on highly polar propylene carbonate derivatives were performed. It was demonstrated that these materials exhibit a Debye-like peak and using a combination of Adam-Gibbs and Fröhlich’s definition of entropy, proposed by Johari [G.P. Johari, J. Chem. Phys 138, 154503 (2013)], cannot solely be used to describe a frustration of dynamics. It is important to note that although these material exhibit a Debye like peak, the behavior is much different than monoalcohols.
The first part of this thesis describes the nonlinear dielectric experiments on monohydroxyl alcohols, with an emphasis on the time dependence of NDEs. For the first time, time-dependent experiments on monoalcohols were done, the results showed that NDEs occur on the Debye time scale. Furthermore, physical vapor deposition (PVD) is used to modify the supramolecular structure of 4-methyl-3-heptanol. Upon deposition the film cannot form the ring like structures, which are preferred in the bulk material. The as deposited film shows an enhancement of the dielectric peak by a factor of approximately 11 when compared to the bulk material. The conversion from the as deposited material back to the near bulk material was found to occur on the Debye timescale.
The second part of this thesis focuses on the question of what is governing the field induced changes seen in the liquids studied. Here a complete set of high field experiments on highly polar propylene carbonate derivatives were performed. It was demonstrated that these materials exhibit a Debye-like peak and using a combination of Adam-Gibbs and Fröhlich’s definition of entropy, proposed by Johari [G.P. Johari, J. Chem. Phys 138, 154503 (2013)], cannot solely be used to describe a frustration of dynamics. It is important to note that although these material exhibit a Debye like peak, the behavior is much different than monoalcohols.
ContributorsYoung-Gonzales, Amanda R (Author) / Richert, Ranko (Thesis advisor) / Angell, Charles (Committee member) / Wolf, George (Committee member) / Arizona State University (Publisher)
Created2019
Description
How water behaves at interfaces is relevant to many scientific and technological applications; however, many subtle phenomena are unknown in aqueous solutions. In this work, interfacial structural transition in hydration shells of a polarizable solute at critical polarizabilities is discovered. The transition is manifested in maximum water response, the reorientation of the water dipoles at the interface, and an increase in the density of dangling OH bonds. This work also addresses the role of polarizability of the active site of proteins in biological catalytic reactions. For proteins, the hydration shell becomes very heterogeneous and involves a relatively large number of water molecules. The molecular dynamics simulations show that the polarizability, along with the atomic charge distribution, needs to be a part of the picture describing how enzymes work. Non Gaussian dynamics in time-resolved linear and nonlinear (correlation) 2D spectra are also analyzed.
Additionally, a theoretical formalism is presented to show that when preferential orientations of water dipoles exist at the interface, electrophoretic charges can be produced without free charge carriers, i.e., neutral solutes can move in a constant electric field due to the divergence of polarization at the interface. Furthermore, the concept of interface susceptibility is introduced. It involves the fluctuations of the surface charge density caused by thermal motion and its correlation over the characteristic correlation length with the fluctuations of the solvent charge density. Solvation free energy and interface dielectric constant are formulated accordingly. Unlike previous approaches, the solvation free energy scales quite well in a broad range of ion sizes, namely in the range of 2-14 A° . Interface dielectric constant is defined such that the boundary conditions in the Laplace equation describing a micro- or mesoscopic interface are satisfied. The effective dielectric constant of interfacial water is found to be significantly lower than its bulk value. Molecular dynamics simulation results show that the interface dielectric constant for a TIP3P water model changes from nine to four when the effective solute radius is increased from 5 A° to 18 A° . The small value of the interface dielectric constant of water has potentially dramatic consequences for hydration.
Additionally, a theoretical formalism is presented to show that when preferential orientations of water dipoles exist at the interface, electrophoretic charges can be produced without free charge carriers, i.e., neutral solutes can move in a constant electric field due to the divergence of polarization at the interface. Furthermore, the concept of interface susceptibility is introduced. It involves the fluctuations of the surface charge density caused by thermal motion and its correlation over the characteristic correlation length with the fluctuations of the solvent charge density. Solvation free energy and interface dielectric constant are formulated accordingly. Unlike previous approaches, the solvation free energy scales quite well in a broad range of ion sizes, namely in the range of 2-14 A° . Interface dielectric constant is defined such that the boundary conditions in the Laplace equation describing a micro- or mesoscopic interface are satisfied. The effective dielectric constant of interfacial water is found to be significantly lower than its bulk value. Molecular dynamics simulation results show that the interface dielectric constant for a TIP3P water model changes from nine to four when the effective solute radius is increased from 5 A° to 18 A° . The small value of the interface dielectric constant of water has potentially dramatic consequences for hydration.
ContributorsDinpajooh, Mohammadhasan (Author) / Matyushov, Dmitry V (Thesis advisor) / Richert, Ranko (Committee member) / Beckstein, Oliver (Committee member) / Arizona State University (Publisher)
Created2016
Description
Broadband dielectric spectroscopy is a powerful technique for understanding the dynamics in supercooled liquids. It generates information about the timescale of the orientational motions of molecular dipoles within the liquid. However, dynamics of liquids measured in the non-linear response regime has recently become an area of significant interest, because additional information can be obtained compared with linear response measurements.
The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be ‘slaved’ to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein β-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins.
The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the electro-optical Kerr effect. A model was discussed which quantitatively captures the observed magnitudes and time dependencies of the NDE. Asymmetry in these rise and decay times was demonstrated as a consequence of the quadratic field dependence of the entropy change. It was demonstrated that the high bias field modifies the polarization response to the field, even including the zero field limit.
The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be ‘slaved’ to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein β-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins.
The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the electro-optical Kerr effect. A model was discussed which quantitatively captures the observed magnitudes and time dependencies of the NDE. Asymmetry in these rise and decay times was demonstrated as a consequence of the quadratic field dependence of the entropy change. It was demonstrated that the high bias field modifies the polarization response to the field, even including the zero field limit.
ContributorsSamanta, Subarna (Author) / Richert, Ranko (Thesis advisor) / Steimle, Timothy (Committee member) / Wolf, George H. (Committee member) / Arizona State University (Publisher)
Created2016