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Author: Ariel Michelman-Ribeiro
Publisher:
ISBN:
Category :
Languages : en
Pages : 232
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Abstract: This dissertation investigates the transport of ions and particles and dynamics in polymer systems. The first study is of structural changes in agarose gels as ions migrate through them under applied electric fields (E-fields). The second is on the translational diffusion of probes in polymer solutions and gels, using poly(vinyl alcohol) (PVA) as a model system. Understanding the transport of particles and ionic migration is important for applications such as biomedical devices and gel electrophoresis. In the first study, I performed small-angle light scattering (SALS) on agarose gels in E-fields, and observed anisotropic SALS patterns, which developed more quickly at higher E-fields and were more anisotropic at higher polymer concentration. Analysis of the data using a model of oriented rods suggested that these patterns arose from rod-like domains 10-15 microns in length oriented perpendicular to the applied field. Microscope imaging revealed rod-like domains on the same length scale, also aligned perpendicular to the E-field. Profiles of pH variation across the gel, measured by video photography, indicated that the anisotropic patterns appeared when the H + and OH - ions, migrating in opposite directions, met. Calculations of pH profiles using a model based on electro-diffusion reproduced several features of the measured pH profiles. This study showed that electrolysis and the resulting ion migration produce pH changes that are correlated with macroscopic shrinking and orientation of the gel. In the second study, I used fluorescence correlation spectroscopy (FCS) to study probe diffusion in PVA solutions and cross-linked gels to obtain diffusion coefficients, D, of nanosized particles as a function of PVA concentration, c, and cross-link density. For probes smaller than the correlation length, x, of the polymer solution, diffusion followed D/D 0 = [Special characters omitted.], as suggested by various models, with n depending on solvent quality Diffusion of small particles (R
Author: Ariel Michelman-Ribeiro
Publisher:
ISBN:
Category :
Languages : en
Pages : 232
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Book Description
Abstract: This dissertation investigates the transport of ions and particles and dynamics in polymer systems. The first study is of structural changes in agarose gels as ions migrate through them under applied electric fields (E-fields). The second is on the translational diffusion of probes in polymer solutions and gels, using poly(vinyl alcohol) (PVA) as a model system. Understanding the transport of particles and ionic migration is important for applications such as biomedical devices and gel electrophoresis. In the first study, I performed small-angle light scattering (SALS) on agarose gels in E-fields, and observed anisotropic SALS patterns, which developed more quickly at higher E-fields and were more anisotropic at higher polymer concentration. Analysis of the data using a model of oriented rods suggested that these patterns arose from rod-like domains 10-15 microns in length oriented perpendicular to the applied field. Microscope imaging revealed rod-like domains on the same length scale, also aligned perpendicular to the E-field. Profiles of pH variation across the gel, measured by video photography, indicated that the anisotropic patterns appeared when the H + and OH - ions, migrating in opposite directions, met. Calculations of pH profiles using a model based on electro-diffusion reproduced several features of the measured pH profiles. This study showed that electrolysis and the resulting ion migration produce pH changes that are correlated with macroscopic shrinking and orientation of the gel. In the second study, I used fluorescence correlation spectroscopy (FCS) to study probe diffusion in PVA solutions and cross-linked gels to obtain diffusion coefficients, D, of nanosized particles as a function of PVA concentration, c, and cross-link density. For probes smaller than the correlation length, x, of the polymer solution, diffusion followed D/D 0 = [Special characters omitted.], as suggested by various models, with n depending on solvent quality Diffusion of small particles (R
Author:
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ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 846
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Author: John J. Kasianowicz
Publisher: Springer Science & Business Media
ISBN: 9781402006975
Category : Science
Languages : en
Pages : 46
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Book Description
Polymers are essential to biology because they can have enough stable degrees of freedom to store the molecular code of heredity and to express the sequences needed to manufacture new molecules. Through these they perform or control virtually every function in life. Although some biopolymers are created and spend their entire career in the relatively large free space inside cells or organelles, many biopolymers must migrate through a narrow passageway to get to their targeted destination. This suggests the questions: How does confining a polymer affect its behavior and function? What does that tell us about the interactions between the monomers that comprise the polymer and the molecules that confine it? Can we design and build devices that mimic the functions of these nanoscale systems? The NATO Advanced Research Workshop brought together for four days in Bikal, Hungary over forty experts in experimental and theoretical biophysics, molecular biology, biophysical chemistry, and biochemistry interested in these questions. Their papers collected in this book provide insight on biological processes involving confinement and form a basis for new biotechnological applications using polymers. In his paper Edmund DiMarzio asks: What is so special about polymers? Why are polymers so prevalent in living things? The chemist says the reason is that a protein made of N amino acids can have any of 20 different kinds at each position along the chain, resulting in 20 N different polymers, and that the complexity of life lies in this variety.
Author: Norio Ise
Publisher: Springer Science & Business Media
ISBN: 3540277153
Category : Technology & Engineering
Languages : en
Pages : 351
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Book Description
This book is designed to critically review experimental findings on ionic polymers and colloidal particles and to prove a theoretical framework based on the Poisson-Boltzmann approach. Structure formation in ionic polymer solutions has attracted attention since the days of H. Staudinger and J. D. Bernal. An independent study on ionic colloidal dispersions with microscopy provided a compelling evidence of structure formation. Recent technical developments have made it possible to accumulate relevant information for both ionic polymers and colloidal particles in dilute systems. The outstanding phenomenon experimentally found is microscopic inhomogeneity in the solute distribution in macroscopically homogeneous systems.To account for the observation, the present authors have invoked the existence of the counterion-mediated attraction between similarly charged solute species, in addition to the widely accepted electrostatic repulsion.
Author: Iwao Teraoka
Publisher: John Wiley & Sons
ISBN: 0471460761
Category : Science
Languages : en
Pages : 355
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Book Description
Polymer Solutions: An Introduction to Physical Properties offers a fresh, inclusive approach to teaching the fundamentals of physical polymer science. Students, instructors, and professionals in polymer chemistry, analytical chemistry, organic chemistry, engineering, materials, and textiles will find Iwao Teraoka’s text at once accessible and highly detailed in its treatment of the properties of polymers in the solution phase. Teraoka’s purpose in writing Polymer Solutions is twofold: to familiarize the advanced undergraduate and beginning graduate student with basic concepts, theories, models, and experimental techniques for polymer solutions; and to provide a reference for researchers working in the area of polymer solutions as well as those in charge of chromatographic characterization of polymers. The author’s incorporation of recent advances in the instrumentation of size-exclusion chromatography, the method by which polymers are analyzed, renders the text particularly topical. Subjects discussed include: Real, ideal, Gaussian, semirigid, and branched polymer chains Polymer solutions and thermodynamics Static light scattering of a polymer solution Dynamic light scattering and diffusion of polymers Dynamics of dilute and semidilute polymer solutions Study questions at the end of each chapter not only provide students with the opportunity to test their understanding, but also introduce topics relevant to polymer solutions not included in the main text. With over 250 geometrical model diagrams, Polymer Solutions is a necessary reference for students and for scientists pursuing a broader understanding of polymers.
Author: Joshua Everett Bostwick
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Gel polymer electrolytes (GPEs) are ion-conducting polymers where the polymer matrix is swollen with a certain amount of solvent. While GPEs are able to take advantage of both the mechanical properties of the polymer matrix and the conductive properties of the solvent, they are limited due to the inverse relationship between the ionic conductivity ([sigma]o) and the modulus, diminishing their potential as next generation lithium-ion battery electrolytes. In this dissertation, we studied the fundamental properties of three different GPEs, molecular ionic composites (MICs) where the solvent is an ionic liquid (IL), single-ion-based MICs where the 'solvent' is poly(ethylene glycol), and cellulose-ionic liquid solutions, for their potential use as battery electrolytes. MICs utilize the mechanical and thermal stability of a rigid-rod sulfonated polyelectrolyte, poly(2,2')-disulfonyl-4,4'benzidine terephthalamide (PBDT), and the high conductivity, electrochemical stability, and low volatility of ILs. This allows the MICs to produce a simultaneous high modulus (from the PBDT) and a high conductivity (from the IL). The first half of this dissertation explores how the change in either the PBDT concentration with a constant IL or the IL molecular volume (Vm) and chemistry with a constant PBDT concentration affects both the mechanical and charge transport properties of the MICs. The varying PBDT concentration MICs were produced via an ion exchange method to form 3 mm diameter cylinders (ingots) while the varying IL Vm MICs were produced via solvent casting to form six free-standing films. The single-ion PBDT membranes were also formed via the solvent casting method. The mechanical properties were measured using a combination of oscillatory shear rheology and uniaxial tensile tests (only for the films), while the dielectric properties and morphology of the films were determined through dielectric relaxation spectroscopy (DRS) and atomic force microscopy (AFM) respectively. Increasing the MIC PBDT concentration with a constant IL, 1-butyl- 3-methylimidazolium tetrafluoroborate (BMIm-BF4), showed a minimal change in dynamic glass transition temperature (Tg) of roughly 2 °C through rheology with its respective IL. This allowed for the MIC ionic conductivity ([sigma]o) at elevated PBDT concentrations to be within a factor of two of the neat IL at room temperature while also producing a shear modulus (G') in the MPa range up to 200 °C. This is due to the MICs producing a two-phase environment corresponding to an IL-rich "puddle" phase and a PBDT-rich "bundle" phase, shown through the phase contrast in atomic force microscopy (AFM), where IL ions form alternating sheaths of cations and anions around each PBDT rod. As the PBDT concentration increases, these puddles shrink and produce a near single bundle phase. This potentially increases the polarizability of the MIC, shown by an increasing static dielectric constant, as well as allowing for more IL ions to contribute to [sigma]o shown by a decrease in the Haven ratio (HR), the ratio between the total number of charge carriers observed through NMR and the number conductive charge carriers that can be analyzed through the ionic conductivity. Incorporating ILs with different molecular volumes (Vm) and chemistries in the MICs with a constant PBDT concentration showed that all MICs maintain low Tgs, ranging between 0 -- 8 °C above their respective neat IL. This was confirmed through analyzing the derivative spectra from DRS to determine the dynamic Tg as well as measuring the thermal Tg through differential scanning calorimetry (DSC). The agreement in Tg between these two methods suggests that the glassy dynamics of MICs is dictated by the rearrangement of IL ions during charge transport. All MICs are able to produce high [sigma]o, ranging from 1 -- 6 mS cm-1 at 30 °C with smaller imidazolium-based cations producing higher [sigma]o than MICs with larger imidazolium cations and similar anions due to their larger molar conductivity. Tensile measurements showed that all MICs produce IL-dependent Young's modulus (E), ranging from 50 -- 500 MPa at 30 °C, up to 60 x higher when compared to the G' of the same MICs. We propose this is due the difference in the distribution of PBDT chains between the shear and tensile planes as well as the competing interactions between the IL ions and the PBDT rods. This hypothesis is supported by the AFM phase contrast images, where the 1-ethyl- 3-methylimidazolium (EMIm+) based MICs show the largest formation of the bundle phase (with very small puddles) while the BMIm+ based MICs produce a larger puddle phases as the anion Vm decreases, thus lowering E. Relating the [sigma]o to their corresponding diffusive coefficients through the Nernst-Einstein shows that all MIC have an ionicity (inverse Haven ratio, HR--1) range between 0.54 -- 0.63, suggesting that a fraction of the diffusive ions do not contribute to charge transport. Along with the IL-based MICs, we analyzed the dielectric and mechanical dynamics of single-ion conducting PBDT-based membranes by incorporating poly(ethylene glycol) with a molecular weight of 400 g mol-1 (PEG400) and either Na+ or Li+ counterions are studied in detail. Varying the PBDT and PEG400 wt% allowed for the preparation of varying PBDT concentrated membranes. All membranes have low DSC Tgs, regardless of counterion attached to the PBDT and the Tg increases with elevated PBDT concentration. The ionic conductivity of the membranes systematically decreases with increasing PBDT concentration, ranging from 0.1 -- 7 [mu]S cm-1` at 30 °C and reaching 100 [mu]S cm-1 at 120 °C in the lowest NaPBDT concentration film. Normalizing the temperature-dependent ionic conductivities divided by their respective Coulombic dielectric constant by the dynamic DRS Tg show that all data roughly collapse onto a single curve, suggesting that the glassy dynamics are dictated the speed of the diffusive motion and the dissociation of ion-pairs produced from strong ionic interactions in the membrane. Tensile stress-strain analysis on the membranes reveal that the E is dominated by the counterion used with the Na+-based membranes producing an E ranging from approximately 100 -- 400 MPa while the Li+-based membranes produced an E ranging from approximately 300 -- 2100 MPa. We suggest that Li+ counterions forms a stronger network with the PBDT sulfonate groups off of the PBDT than the Na+ counterions. The smaller Li+ binds to the sulfonates on the PBDT chain more strongly, confirming that the modulus of this class of materials has ionic origins. We investigated the dielectric dynamics of cellulose in ILs through DRS to understand the fundamental properties of cellulose-IL solutions with varying cellulose concentration and IL. Like the MICs, the cellulose-IL solutions showed relatively high ionic conductivity compared to their respective neat IL, all within a factor of 4 at 30 °C at the highest cellulose concentration, as well as minimal increase in the dynamic DRS Tg (up to 10 °C). The ionic conductivity normalized by the DRS Tg show all data collapsing on a single curve with each IL suggesting that the glassy dynamics in these solutions is dictated by the ion arrangement produced on charge transport. Additionally, increasing the cellulose concentration increases the static dielectric constant relative to the neat ILs suggesting the association between the cellulose and IL ions enhances the polarizability of the solution over the neat IL.
Author: D. DeRossi
Publisher: Springer Science & Business Media
ISBN: 1468458922
Category : Science
Languages : en
Pages : 336
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Book Description
This volume contains a series of papers originally presented at the Symposium on Polymer Gels organized and sponsored by the Research Group on Polymer Gels,The Society of Polymer Science of Japan and co-sponsored by the Science and Technology Agency (ST A) and MIT!, Japan. The Symposium took place at Tsukuba Science City on 18th and 19th September, 1989. Recognized experts in their fields were invited to speak and there was a strong attendance from government, academic and industrial research centers. The purpose of the Symposium was to review the state of the art and to present and discuss recent progress in the understanding of the behavioral properties of polymer gels and their application to biomedical, environmental and robotic fields. Most of the papers and related discussions concentrated on the swelling behavior of hydrogels and chemomechanical systems, both artificial and naturally occurring, in which external stimuli of a physical or chemical nature control energy transformation or signal transduction. The recent great interest in chemomechanical systems based on polymer gels has stimulated considerable effort towards the development of new sensors and actuators, controllable membrane separation processes, and delivery systems in which the functions of sensing, processing and actuation are all built into the polymeric network device. Artificial chemomechanical systems, through the use of environmentally sensitive polymer gels, are emerging as interesting materials for mimicking basic processes previously only confined to the biological world, and commercially viable applications are also foreseen in the not-too-distant future.
Author: Ali Eftekhari
Publisher: Royal Society of Chemistry
ISBN: 1782629602
Category : Science
Languages : en
Pages : 564
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Book Description
The series covers the fundamentals and applications of different smart material systems from renowned international experts.
Author: William S. Price
Publisher: Cambridge University Press
ISBN: 0521806968
Category : Medical
Languages : en
Pages : 417
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Book Description
Overview of NMR theory and applications in fluid systems, fully referenced for research use.
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Languages : en
Pages :
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