Poly(vinyl Alcohol) Based Hydrogen-bonded Multilayers

Poly(vinyl Alcohol) Based Hydrogen-bonded Multilayers
Author: Hyomin Lee (Ph. D.)
Publisher:
Total Pages: 184
Release: 2014
Genre:
ISBN:

Understanding the mechanisms that govern the structure and function of synthetic polymer thin films is of fundamental and practical significance for developing a diverse range of functional surfaces including antifogging coatings, switchable surfaces and stimuli-responsive hydrogels. The first part of this thesis is focused on extending hydrogen-bonding driven polymer thin film assembly by developing a novel systematic framework in which poly(vinyl alcohol) (PVA) can be incorporated into LbL assembled multilayer thin films. Incorporation of PVA into multilayer thin films is advantageous due to its biocompatibility and ease of chemical functionalization and cross-linking. The optimal assembly conditions of PVA multilayer films were discovered through extensive investigation on the degree of PVA hydrolysis, molecular weight and the type of weak polyacids. Subtle variations due to the prevalence of PVA acetate moieties, characterized by the degree of hydrolysis, were shown to cause drastic differences both in self-assembly with its hydrogen-bonding partners as well as its overall pH-stability. The library of materials that can be hydrogen-bonded with PVA was further extended by assembling films with biologically relevant molecules such as tannic acid. This leads to enhanced pH-stability as a result of the high pKa value of tannic acid. Multiple stacks of hydrogen-bonded LbL structures with differing composition and properties were also assembled resulting in complex heterostructured architectures that sequentially dissolve with an increase in local pH conditions. The abundance of free hydroxyl and carboxylic acid groups in the PVA/PAA multilayer allows for enhanced pH stability up to physiological conditions using thermal and chemical methods which offer numerous opportunities for post-assembly functionalization. This was demonstrated by functionalizing PVA/PAA multilayers with poly(ethylene glycol methyl ether) (PEG) to generate a novel antifogging coating with switchable surface properties. To facilitate the characterization of the antifogging coatings a new protocol was developed that enables quantitative analysis of antifogging performance via real-time monitoring of transmission levels as well as image distortion. The antifogging PVA/PAA multilayers were shown to exhibit "zwitter-wettable" behavior, whereby the multilayer film exhibited a facile, rapid absorption of molecular-level water into a film from the gas phase while simultaneously exhibiting very high contact angles for macroscopic liquid drops of water placed on the surface of the same film. An additional step of functionalizing this nano-blended PVA/PAA multilayer with PEG segments produced significantly enhanced antifog and even frost-resistant behavior which was due to the increase in the nonfreezing water capacity of the multilayer film. The PEG-functionalized PVA/PAA multilayers exhibited transient and reversible water contact angle behavior which was studied by both goniometry and dynamic tensiometry. The time-dependent wetting behavior of these coatings was attributed to the transient surface rearrangement of hydrophilic functional groups towards the surface in response to exposure to a liquid water environment. Using a simple first-order thermally-activated model, the kinetics of surface rearrangement was explored in detail. Finally, a model system was designed to study the zwitter-wettable phenomenon in more detail. The complex network of hydrophilic and hydrophobic moieties was decoupled into a heterostructured film consisting of a hydrophilic reservoir and a hydrophobic capping layer. Surface chemistry and roughness were previously believed to be the main factors controlling condensation of water on the film, however, the capacity of the film to transport water molecules was also found to be important for designing functional zwitter-wettable films.

Hydrogen-bonded Capsules

Hydrogen-bonded Capsules
Author: Julius Rebek, Jr.
Publisher: World Scientific Publishing Company
Total Pages: 219
Release: 2015-09-23
Genre: Science
ISBN: 9789814678353

This monograph describes the behavior of molecules confined to small spaces. The small spaces are created by the self-assembly of modules into hollow capsular structures through hydrogen bonding; capsules assembled by metal/ligand binding or other forces are not included. Topics discussed include how assembly of capsules occurs, how molecules get in and out of the capsules, new spatial arrangements (stereochemistry) created in the capsules, and the altered shapes, interactions and reactivities of molecules held inside the small spaces. The descriptions emphasize molecular recognition phenomena and the perspective is that of physical organic chemistry.The book is the first monograph to treat reversible molecular encapsulation. More than 20 university and institute groups worldwide engage in this research, which represents the leading edge of activity in molecular recognition and the physical organic chemistry of confined molecules.

Polymer Capsules

Polymer Capsules
Author: Ye Liu
Publisher: CRC Press
Total Pages: 359
Release: 2019-05-10
Genre: Science
ISBN: 0429767870

Polymers are one of the most versatile and important materials used for capsule preparation despite various others available. Suitably formulated capsules can securely protect ingredients, deliver them to targeted sites, and release them expeditiously, improving functions and minimizing adverse effects. New polymers are constantly being explored to develop more efficient capsules as they are routinely used in pharmaceuticals, consumer healthcare products, nutrients, and food. This book focuses on the current state of the art of polymer-based capsules and delivery systems. It describes the formulation processes of capsules developed from redox-responsive polymers and polymer-functionalized carbon nanotubes, in addition to shedding light on coacervation of polymers for encapsulation. It reviews different active ingredients that can be used with polymer capsules in various products, encapsulation of essential oils using such capsules, and development of polymer capsules of cells and bacteriophages.

Stimuli-Responsive Gels

Stimuli-Responsive Gels
Author: Dirk Kuckling
Publisher: MDPI
Total Pages: 289
Release: 2018-10-11
Genre: Science
ISBN: 303897210X

This book is a printed edition of the Special Issue "Stimuli-Responsive Gels" that was published in Gels

Bio-inspired Polymers

Bio-inspired Polymers
Author: Nico Bruns
Publisher: Royal Society of Chemistry
Total Pages: 613
Release: 2016-10-14
Genre: Science
ISBN: 1782626662

Many key aspects of life are based on naturally occurring polymers, such as polysaccharides, proteins and DNA. Unsurprisingly, their molecular functionalities, macromolecular structures and material properties are providing inspiration for designing new polymeric materials with specific functions, for example, responsive, adaptive and self-healing materials. Bio-inspired Polymers covers all aspects of the subject, ranging from the synthesis of novel polymers, to structure-property relationships, materials with advanced properties and applications of bio-inspired polymers in such diverse fields as drug delivery, tissue engineering, optical materials and lightweight structural materials. Written and edited by leading experts on the topic, the book provides a comprehensive review and essential graduate level text on bio-inspired polymers for biochemists, materials scientists and chemists working in both industry and academia.