Author: David ŠustrPublisher:
ISBN:
Category : Diffusion
Languages : en
Pages :
Book Description
Molecular Diffusion in Polyelectrolyte Multilayers
Author: David ŠustrMolecular Diffusion in Polyelectrolyte Multilayers
Author: David SustrPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Research on novel and advanced biomaterials is an indispensable step towards their applications in desirable fields such as tissue engineering, regenerative medicine, cell culture, or biotechnology. The work presented here focuses on such a promising material: polyelectrolyte multilayer (PEM) composed of hyaluronic acid (HA) and poly(L-lysine) (PLL). This gel-like polymer surface coating is able to accumulate (bio-)molecules such as proteins or drugs and release them in a controlled manner. It serves as a mimic of the extracellular matrix (ECM) in composition and intrinsic properties. These qualities make the HA/PLL multilayers a promising candidate for multiple bio-applications such as those mentioned above. The work presented aims at the development of a straightforward approach for assessment of multi-fractional diffusion in multilayers (first part) and at control of local molecular transport into or from the multilayers by laser light trigger (second part). The mechanism of the loading and release is governed by the interaction ...
Diffusion, Doping, and Stability of Polyelectrolyte Multilayers
Author: Rachel Lynn AbbettPublisher:
ISBN:
Category : Analytical chemistry
Languages : en
Pages : 131
Book Description
Polyelectrolytes are polymers consisting of charged repeat units resulting in a netcharge for the macromolecules. Mixing oppositely charged polyelectrolytes creates polyelectrolyte complexes (PEC). Different types of complexes can be obtained by modifying the preparation technique. This dissertation focuses primarily on one kind of PEC known as a polyelectrolyte multilayer (PEMU). These systems are formed by depositing alternating "layers" of oppositely charged polymers onto a substrate. PEMUs have been proposed for various applications, from electronic devices to antibacterial coatings and drug delivery. These applications rely on the composition and integrity of these films to withstand dynamic changes in the external environment, such as temperature and environmental composition. They also rely on doping the films with additives called "dopants" to modify the properties of these films. This dissertation focuses on the stability of PEMUs and the motion of various analytes through the films. This first aspect centers initially around the water content. The PEMUs in this work are plasticized by water, becoming brittle when dry. This plasticization led to the theory that the change in modulus close to room temperature for these systems was not a glass transition but instead a dehydration/rehydration event. Fully hydrated films were monitored using ATR-FTIR to assess the water content through the glass transition at various salt concentrations. There was no discernible change in water content that would indicate hydration or dehydration, supporting the theory that this change in modulus results from a glass transition. The commonly used polyelectrolyte pairs in this work are hydrophilic. This affinity for water combined with added salts bringing in additional water and breaking up Pol+Polinteractions causes concern for the stability of the film. PEMUs were built again on the ATR-FTIR and monitored in-situ as a solution of changing salt concentration flowed over the film. The salt concentrations ranged from 0 to 1.0 M NaCl for 1, 2, and 4 hours and then were brought back to 0 M NaCl over the same time period. The rapid change in salt concentration was expected to stress the film, potentially causing it to swell to the point of degradation. All three rates resulted in intact films, with the fastest change in concentration resulting in the water not having sufficient time to equilibrate in the film, 14 shown by a difference in response to increasing and decreasing NaCl concentration. Long-term exposure to NaCl, especially high concentration salt, was also monitored. Films were constructed on quartz slides and placed parallel to the beam in the cuvette. Solutions of NaCl ranging from 0 to 2.5 M were added to the cuvette and monitored for 10 hours. The spectra indicate minimal leaching from the films into the solution at all but the highest salt concentrations. Ferrocyanide and ferricyanide diffusion through PEMUs was tested to determine if their movement through the film would be sufficient to impact the rate of electrons transferring from the redox centers through the film to an electrode. Films were built on silicon wafers and monitored using transmission FTIR by taking spectra of the dried film at specific time points during the exposure to the ferri- or ferrocyanide solutions. The diffusion coefficients were determined, indicating ferricyanide diffuses significantly faster than ferrocyanide. From the diffusion and the IR spectra, the concentration and spacing of the redox centers were determined, indicating that the motion of the redox species is not sufficient to alter the rate of electron motion. Ligated lanthanide complexes are efficient emitters but often have issues with the substrate quenching emission. PEMUs were tested to see if they could be used as scaffolding to prevent this quenching. Hydrophilic and hydrophobic systems were compared based on quantum yield and fluorescence lifetime. Hydrophilic films had faster and higher uptake of the emissive sites, needing only five minutes for full incorporation, but the hydrophobic films outperformed the hydrophilic films in emission under various environmental humidity levels by better maintaining the quantum yield. Diffusion of PSS through films was monitored with varying molecular weight, temperature, and solution salt concentrations. Shorter chains diffused faster at the same temperatures and were not impacted by changes in salt concentration. This could be because the short-chain systems are above the Tg in those salt concentrations. Both long and short-chain films were slower below Tg. Long-chain systems had a dependence on salt concentration and a two-part diffusion regime at room temperature. This is because the polymers closer to the surface of the film were more hydrated, and therefore above the Tg, while the chains at the substrate were below Tg at room temperature. This resulted in a two-part diffusion
Proceedings of 3rd Annual Conference and Expo on Biomaterials 2018
Author: ConferenceSeriesPublisher: ConferenceSeries
ISBN:
Category :
Languages : en
Pages : 124
Book Description
March 05-06, 2018 Berlin, Germany Key Topics: Dental Biomaterials, Advanced Materials, Tissue Engineering and Regenerative Medicine, Biomaterials Applications, Biomaterials Companies and Market Analysis, Polymer Biomaterials, Biomaterials and Nanotechnology, Properties of Biomaterials, 3D printing of Biomaterials, Biomaterials in Delivery Systems, Biodegradable Biomaterials, Entrepreneurs Investment Meet, Bio-based Materials and Sustainability, Biophotonics and Biomedical Optics,
Vertical Diffusion of Polyelectrolytes in Polyelectrolyte Multilayers During Film Preparation and Post Preparation Treatment
Author: Annekatrin SillHandbook of Polyelectrolytes and Their Applications: Applications of polyelectrolytes and theoretical models
Author: Sukant K. TripathyPublisher:
ISBN:
Category : Polyelectrolytes
Languages : en
Pages : 378
Book Description
Ion and Electron Transport in Polyelectrolyte Multilayers
Author: Samir Abou ShaheenPublisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 0
Book Description
Polyelectrolytes are charged polymers, widely spread in nature and industry. The spontaneous association between two oppositely charged polyelectrolytes in solution yields a compact and versatile material called a polyelectrolyte complex. Polycations and polyanions can also form thin films or polyelectrolyte multilayers when they are alternately deposited on a substrate. These interesting macromolecules have been integrated into a long list of applications including fuel cells, electronics and membranes for separation. Information on the interactions and dynamics of species across polyelectrolyte composites is highly desirable to understand the performance of these materials and enhance the aspects of their applications. This dissertation focuses on probing ion, water and electron transport across a polyelectrolyte complex and investigating the interaction between a polyelectrolyte and metal surfaces. The work can be divided into three main parts: In the first part, the response of water and ions in a hydrated polyelectrolyte complex made of poly(diallyldimethylammonium), PDADMA, and poly(styrene sulfonate), PSS, were evaluated as a function of temperature. The glass transition temperature, Tg, at which the material softens was determined using rheology. The behavior of water diffusion coefficient versus temperature was monitored using pulse field gradient NMR. No change in the diffusion response was detected as the material went through Tg. Similar observation was found for the transport of small monovalent ions, such as Na+ and Cl-, which was measured using variable temperature ionic conductivity. In contrast, flux measurements on a rotating disk electrode revealed a transition point for the diffusion versus temperature of triple-charged ions, ferricyanide and ruthenium hexamine. These responses were interpreted to show the cooperative segmental mobility near the glass transition temperature. In the second part, the polyelectrolyte multilayer system made of PDADMA and PSS was also employed to produce pinhole-free ultrathin films and a radiolabeling approach was developed to determine their exact thicknesses. Electrochemical methods were used to assess electron transport from ferrocyanide redox ion to a platinum rotating disk electrode across the polymeric barriers. It was shown that even the thinnest film made of one bilayer (about 1 nm thick) provides significant blocking of electron transfer from ferrocyanide in solution to the electrode and a complete insulating film could be formed from six additional layers (9 nm). Over the 1-9 nm range, a weak current-distance dependence suggested a hopping electron transport mechanism. The classical Butler-Volmer description, which shows the current-voltage dependence, for charge transfer kinetics was modified to produce a consistent model for multi-step hopping transport through the multilayer films. Studies of polyelectrolyte interactions and the transport rate of species in polyelectrolyte complexes are fundamental to understand the often-perplexing behavior of these materials and improve their performance in the wide array of energy and separation applications. In the final part, the pairing strength between a polyelectrolyte and metal surfaces was examined. Fractional precipitation of poly(4-vinylpyridine) was used to obtain narrow molecular weight fractions. The fractions were methylated using iodomethane and characterized using NMR, FTIR and size-exclusion chromatography. One fraction was labeled with 14C radionuclide and the interaction between methylated poly(4-vinylpyridine) and metal oxide powders was monitored as a function of ionic strength using radiocounting. Metal oxides interacted differently and were divided into 3 categories: classical desorbing, peak-less desorbing and non-adsorbing. An interaction scale was set based on the cut-off salt concentration.
Polyelectrolytes
Author: Visakh P. M.Publisher: Springer
ISBN: 3319016806
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
This book offers a valuable reference source to graduate and post graduate students, engineering students, research scholars polymer engineers from industry. The book provides the reader with current developments of theoretical models describing the thermodynamics polyelectrolytes as well as experimental findings. A particular emphasis is put on the rheological description of polyelectrolyte solutions and hydrogels.
The Theory of Polymer Dynamics
Author: Masao DoiPublisher: Oxford University Press
ISBN: 9780198520337
Category : Science
Languages : en
Pages : 420
Book Description
This book provides a comprehensive account of the modern theory for the dynamical properties of polymer solutions. The theory has undergone dramatic evolution over the last two decades due to the introduction of new methods and concepts that have extended the frontier of theory from dilute solutions in which polymers move independently to concentrated solutions where many polymers converge. Among the properties examined are viscoelasticity, diffusion, dynamic light scattering, and electric birefringence. Nonlinear viscoelasticity is discussed in detail on the basis of molecular dynamical models. The book bridges the gap between classical theory and new developments, creating a consistent picture of polymer solution dynamics over the entire concentration range.
Multilayer Thin Films
Author: Gero DecherPublisher: John Wiley & Sons
ISBN: 3527316485
Category : Technology & Engineering
Languages : en
Pages : 1157
Book Description
This second, comprehensive edition of the pioneering book in this fi eld has been completely revised and extended, now stretching to two volumes. The result is a comprehensive summary of layer-by-layer assembled, truly hybrid nanomaterials and thin fi lms, covering organic, inorganic, colloidal, macromolecular, and biological components, as well as the assembly of nanoscale fi lms derived from them on surfaces. These two volumes are essential for anyone working in the field, as well as scientists and researchers active in materials development, who needs the key knowledge provided herein for linking the field of molecular self-assembly with the bio- and materials sciences.