Master of Science in Polymer Engineering, University of Akron, 2019, Polymer Engineering

Complex coacervation and precipitation are two different types of phase separation in a polyelectrolyte complex system composed of two oppositely charged polyelectrolytes. Complex coacervate and precipitate refer to a dense soluble and insoluble polymer-rich phase respectively. Many experimental studies have investigated the effect of solution and environmental conditions on the formation of polyelectrolyte complexes (PECs), including pH values, the added salts and temperature, etc. The formation of PECs is believed to be entropically driven, resulting from the release of small counter ions from the polymer backbone chains. The addition of salts is expected to influence the ionic strength of the polyelectrolyte system, which further influences the complexation process and the physicochemical properties of the complexes, including phase boundaries of coacervation and precipitation, hydrophobicity and water content within complexes. To better understand the polyelectrolyte complexation process and the difference between strong polyelectrolyte vs. weak polyelectrolyte complexation, phase behavior of polyelectrolyte complex systems containing oppositely charged polyelectrolytes, including poly(diallyldimethylammonium chloride) (PDAC), poly(sodium 4-styrene sulfonate) (SPS), poly(allylamine hydrochloride) (PAH), poly (acrylic acid) (PAA), poly(methacrylic acid) (PMAA) were investigated in the presence of four different salts (KCl, KNO3, KBr, KI) based on Hofmeister series to study the effect of salts on water content of different salt-added PEC systems. The additional methyl groups on PMAA backbones can offer a structural difference between PMAA-PAH and PAA-PAH complex systems. In addition, the hydrophobicity and water content of the salt-free or salt-added complexes on the phase boundaries were also studied to help us conversely understand phase behavior. Turbidity was carried out to qualitatively show the phase boundaries of coacervation and precipitation and th (open full item for complete abstract)

Committee: Nicole Zacharia (Advisor); Kevin Cavicchi (Committee Member); Bryan Vogt (Committee Member); Yu Zhu (Committee Member) Subjects: Polymers

Master of Science, University of Toledo, 2021, Chemical Engineering

Polyelectrolytes are polymers with ionizable groups on their chains, which (like regular electrolytes) become charged when dissolved in solution. Polyelectrolytes are widely used in areas including drug delivery, water treatment, and underwater adhesives. The polyelectrolyte examined here is polyallylamine (PAH), which can be crosslinked by multivalent counterions, such as sodium tripolyphosphate (TPP), to form adhesive viscoelastic materials known as coacervates. PAH-based adhesives have previously been shown to be able to adhere to both hydrophobic and hydrophilic surfaces under water. The adhesive properties of these coacervates can also be reversed by raising or lowering the pH. This thesis further explores the rheological and adhesion properties of underwater adhesive coacervates formed via the coacervation of PAH and TPP. The adhesive properties of the material are examined on various substrates, including stainless steel, copper, polyvinyl chloride, polyethylene, and polypropylene under varying pH and ionic strength conditions. The adhesion strengths achieved with PAH/TPP coacervates are also examined in various water types, such as tap water, lake water, and artificial seawater. iv Finally, the shelf-life of the adhesive coacervates is studied over a 9-month storage period while varying the solution pH and ionic strength used during their preparation and their storage temperature. The PAH/TPP coacervates, when prepared from neutral-pH parent PAH and TPP solutions, deliver the highest adhesion strength (with tensile bond strengths on stainless steel surfaces reaching 0.6 MPa), which remains undiminished when the deionized water medium is replaced with tap, lake, or artificial seawater. The coacervates can also bond low-energy surfaces, such as high-density polyethylene, consistently delivering tensile adhesion strengths above 0.1 MPa with all examined substrates. Finally, the rheological and adhesion properties of PAH/TPP coacervates c (open full item for complete abstract)

Committee: Yakov Lapitsky Dr. (Committee Chair); Matthew Liberatore Dr. (Committee Member); Maria Coleman Dr. (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

This research aims to study the dynamics of charged ions moving through a charged system, and the interactions they have on each other. The underlying principles that govern the movement through a polyelectrolyte system can give insight into biological fibers such as actin, muscles and neurons. This investigation seeks to: developing an electrolyte-based system that exhibits movement, understanding the driving forces of movement from a macromolecular perspective, and developing an actuating system based on the parameters developed therefrom. Understanding fundamental polyelectrolyte behavior is the key to inducing physiological movement mimicking muscles and neurons. Previously, we have verified that poly(acrylate) gels exhibit electrical potentials in the range normally afforded by living cells. However, we have unexpectedly found that poly(acrylate) gels in aqueous solutions of monovalent salts such as KH2PO4 in a narrow concentration range (ca. 8-16 mM) leads to a softening of gels without measurable volume changes. The electrical potentials of the gels, using standard electrophysiological methods, show an abrupt increase in gel potential (to ca. -100 mV) with no appreciable macromolecular size change or mechanical transition, seen by elastic and compressive modulus. Magnetic resonance imaging experiments reveal a change in water mobility in the same transition region. Small angle neutron scattering also does not demonstrate a structural change in mesh size at this transition, suggesting a change is due to the cation and anion type and association with the chain. Through this, we predict the counterions have a larger factor in polyelectrolyte theory than previously known. By utilizing this transition region, we can induce facile movement through a polyelectrolyte gel with salt solutions and active movement with electrical current. Generating movement of the whole gel solely due to ion concentrations of mono- and divalent salt, ion interactions with the poly (open full item for complete abstract)

Committee: Gary Wnek (Advisor); Michael Hore (Committee Member); Horst von Recum (Committee Member); LaShanda Korley (Committee Member); Svetlana Morozova (Committee Member) Subjects: Polymers

Master of Science in Polymer Engineering, University of Akron, 2020, Polymer Engineering

Association of two oppositely charged polyelectrolytes via electrostatic interaction can lead to soluble complex formation, or phase separation, including liquid-liquid (coacervation) and liquid-solid (precipitation) phase separation. Coacervation exhibits promising applications in various fields due to its unique properties. Proteins, a common polyelectrolyte, are known to form coacervate phases. As protein are complex macromolecules with multiple different hydrophobic and hydrophilic repeat units, it was hypothesized that the hydrophobic units may broaden the composition window for coacervation as at non-stoichiometric charge ratios hydrophobic groups can associate to stabilize phase separated structures similar to ion-pair interactions. Therefore, a simple synthetic system was investigated to isolate the influence of hydrophobic groups on the phase behavior of an aqueous polyelectrolyte blend. The objective of this work was to investigate if hydrophobically modify poly (methacrylic acid), a synthetic polyelectrolyte, was able to expand the composition window of the coacervate phase. In this work, a series of hydrophobically modified poly (methacrylic acid) and poly (allylamine hydrochloride) were investigated as negatively and positive charged polyelectrolytes, respectively. Poly (methacrylic acid), poly (methacrylic acid)-co-poly (methyl acrylate) and poly (methacrylic acid)-co-poly (ethyl acrylate) and poly (methacrylic acid)-co-poly (isopropyl acrylate) were synthesized by free radical polymerization. The target molar ratio was 9:1, where the hydrophobic acrylate part accounts for 10 mol% of the backbone repeat units. Nuclear magnetic resonance (NMR) was used to characterize the composition of the synthesized polymer. Gel permeation chromatography (GPC) was utilized to determine the molecular weight of the synthesized polymer. The phase separation and coacervate complex formation of poly (methacrylic acid) (PMAA) or its copolymers with poly (allylamine hydro (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Bryan Vogt (Committee Member); Nicole Zacharia (Committee Member) Subjects: Polymer Chemistry; Polymers

Doctor of Philosophy, University of Toledo, 2019, Chemical Engineering

More than 70% of the Earth's surface is covered by water, which is the basic substance and essential requirement for all forms of life on earth. However, only 2.5% of world's water is freshwater. Due to lack of physical water resources and/or overuse of water in industrial and agricultural applications, physical and/or economic water scarcity is affecting more than 1.2 billion people all around the globe, respectively. Half of the world's population is living in 88 developing countries, which can be severely influenced by water scarcity. Indeed, poor water quality causes 80-90% of all diseases and 30% of all deaths in such countries. Due to population growth and increased demands of industrialization, the number of people affected by serious water shortages is increasing. Therefore, all over the world, governments are beginning to pay special attention to the looming crisis. Membrane-based desalination has been extensively developed during the last 50 years as a promising solution for the growing concern of clean water scarcity in many parts of the world. In the same period, ion exchange membranes (IEM) have evolved from laboratory stage to industrial products with remarkable technical and commercial impacts. The evolution of ion exchange membranes has enabled their use in a variety of separation processes including electrodialysis for desalination. In contrast IEMs which possess either positive or negative fixed charges, a charge mosaic (CM) membrane consists of arrays of anion and cation exchange elements with fixed and mobile ions of both charges. Adjacent ionic channels of opposing charge provide a continuous pathway from one side of the membrane to the other. Negative osmosis and salt permeability occur in CM membranes much greater than non-electrolyte permeability. This work describes a new formation technique to develop CM membranes, which offers the potential to increase the density of contact regions and thereby is expected to greatly enhance performanc (open full item for complete abstract)

Committee: Glenn Lipscomb (Advisor); Yakov Lapitsky (Committee Member); Maria Coleman (Committee Member); Ana Alba-Rubio (Committee Member); Youngwoo Seo (Committee Member) Subjects: Chemical Engineering

Master of Science, University of Akron, 2018, Polymer Engineering

This work examines two distinct cases where the mechanical properties are controlled by additives or structure. First, the viscoelastic properties of polymer complexes are examined as a function of salt content as salt provides a route to tune the rheological properties through disruption of the associations of the complex. These salt effects have been proposed to collapse to a master curves for the rheological properties of ionic systems through time-salt superposition (TSS) as an analog to time-temperature superposition. Here we demonstrate differences in the salt (sodium chloride and choline chloride) dependence of branched polyethylenimine-poly(acrylic acid) (BPEI-PAA) containing approximately 50 wt % water using the frequency dependence of G' and G'' and extensional measurements for complexes. The shape of the time average modulus ([E(t)]) obtained from constant strain rate extension experiments is applied to study the relaxation behavior in long timescales. However, inconsistent hydration (partially from dehydration during extension) leads to inconsistences in [E(t)], which hinders the ability to firmly draw conclusions about the applicability of TSS in these systems. Three-dimensional (3D) printing has been commonly used for rapid prototyping manufacturing. However, application of 3D printed parts to products has been limited by their inferior mechanical properties due to the printing process. Core-shell structured filaments can overcome the drawback of the weak interfaces in 3D printing, where the shell material enhance the interfacial strength due to their lower solidification temperature than the core materials. In this work, we demonstrate that PC-ABS-polyethylene core-shell filaments can improve the mechanical properties of 3D printed parts as compared to those printed from pure PC-ABS. We compare the influence of HDPE vs LDPE on the properties of the printed part. The impact resistance can be approximately increased to 3 times as that of pure PC-ABS.

Committee: Nicole Zacharia (Advisor); Bryan Vogt (Advisor); Kevin Cavicchi (Committee Member) Subjects: Plastics; Polymers

Doctor of Philosophy, University of Akron, 2018, Polymer Science

Nanotechnology revolves around the creation of functional materials at the molecular scale. Both top-down and bottom-up approaches have been developed during the last few decades to design nanomaterials for a wide range of applications. Due to the limitations of the top-down methods in reaching nanoscale, bottom-up approaches have enjoyed more attention. Consequently, growing attention has been devoted to the concept of self-assembly as an effective tool for designing well-ordered structures from their basic building blocks. Self-assembly uses different molecular interactions such as electrostatic, hydrogen bonding, hydrophobic, p- p stacking, van der Waals, and coulomb forces to design the materials of interest with desired lengths, shapes and functions. The bourgeoning field of nanotechnology demands more advance materials with more precise structures and functions. This has motivated scientists to advance the concept of self-assembly in two direction: First, to propose new approaches in self-assembly of nano- and microstructures towards faster, more precise and cost-effective methods; and second, to design self-assembled systems with dynamic nature and responsiveness to external stimuli which are pivotal to the construction of the so called “smart” materials. In addition to the need for the development of new methods for the construction of smart nanostructures, judicious choice of molecular tiles is also very important. Dendritic polymers are unique and known for their wide range of applications especially as unimolecular micelles due to the availability of multiple charges, presence of cavity and lack of CMC limitations compared to micellar and vesicular systems. However, their role as an effective building block in designing self-assembled systems require more investigations. This dissertation will focus on the application of dendrimers in both development of novel supramolecular assembly methods to design hierarchical and stimuli responsive nanostructur (open full item for complete abstract)

Committee: Tianbo Liu (Advisor); Mesfin Tsige (Committee Chair); Toshikazu Miyoshi (Committee Member); Yu Zhu (Committee Member); Chrys Wesdemiotis (Committee Member) Subjects: Nanoscience; Nanotechnology; Polymer Chemistry; Polymers

Master of Science, University of Toledo, 2014, Chemical Engineering

Underwater adhesives have several potential applications in industry as well as in medicine. Much of the recent research in this area has focused on adhesive preparation from biological or custom-designed biomimetic polymers. As a simpler alternative, we have recently shown that ionically crosslinked, gel-like underwater adhesive complexes can be prepared by the mixing of the readily-available and inexpensive polyelectrolyte, poly(allylamine hydrochloride) (PAH), with commonly-used multivalent anions, pyrophosphate (PPi) and tripolyphosphate (TPP). Remarkably, these gel-like complexes adhere to both hydrophilic and hydrophobic substrates under water with tensile adhesive strength considerably greater than that of Scotch Permanent Double Sided Tape (up to ~400 kPa vs. ~85 kPa when used as a pressure-sensitive adhesives) and due to the reversible nature of the ionic crosslinks, self-heal when torn. These complexes also exhibit very high storage moduli (greater than 100 kPa), indicative of a very high crosslink density. The high crosslink density allow these gel-like complexes to also entrap and deliver small molecule payloads over multiple-month timescales. Moreover, their formation and rheological/adhesion properties can be controlled using external stimuli (pH and ionic strength). In this thesis we characterize formation and rheological/adhesion properties of gel-like PAH/PPi and PAH/TPP complexes the through the use of dynamic and electrophoretic light scattering, rheology and tensile adhesion tests. We also describe their sensitivity to pH and ionic strength, and explain how the complexes can be dissolved on demand by raising or lowering the ambient pH, and can form spontaneously by increasing the NaCl concentration (which can be used for developing injectable underwater adhesive formulations). Finally, we demonstrate the ability of these adhesives to release small molecule payloads over multiple-month timescales by characterizing their ability to take up and (open full item for complete abstract)

Committee: Yakov Lapitsky PhD (Committee Chair); Isabel Escobar PhD (Committee Member); Youngwoo Seo PhD (Committee Member) Subjects: Chemical Engineering; Chemistry; Materials Science; Polymer Chemistry; Polymers

MS, University of Cincinnati, 2014, Arts and Sciences: Chemistry

Upconversion is the process in which two or more low-energy photons are absorbed and emitted as one high-energy photon. This research reports on the effect of layer-by-layer polyelectrolytes and silver coating on hexagonal NaYF4:Yb3+,Tm3+ in an attempt to enhance the upconversion intensity. The synthesized upconversion nanoparticles were separated into two, ~140 nm and a mixture of two populations, ~250 nm and ~25 nm. The former case observed enhancement, when silver coated on the upconversion nanoparticles using hydroquinone as the reducing agent, with no layers and with several layers (three, four and five) of polyelectrolytes. The size (140 nm) and morphology of the hexagonal NaYF4:Yb3+,Tm3+ were similar. The enhancement was confirmed when sodium cyanide was added to remove the silver coating from the sample resulting in a decrease in the upconversion intensity. Quenching was observed in the latter case, when silver coating was unsuccessful and that there are two populations of upconversion nanoparticles (large ~250 nm and small ~25 nm).

Committee: Laura Sagle Ph.D. (Committee Chair); Peng Zhang Ph.D. (Committee Chair); Allan Pinhas Ph.D. (Committee Member) Subjects: Chemistry

Master of Science in Bioengineering, University of Toledo, 2005, Bioengineering

Studies have shown that the mechanical properties of bone, as a composite material, depnd on the mineralization, crystallinity, molecular structure, and arrangement of the mineral crystals with the collagen matrix. [1,2] Knowing that the strength of any ocmposite material is intimately affected by the size and shape of reinforcing inclusions, it can be proposed thar the material level mechanical function of bone tissue can be altered by modifying the size and/or shape of carbonated hydroxyapatite crystals. [3,4] Polyelectrolytes (negatively and positively charged macromolecules) have been shown to alter the nucleation, growth, and the resulting morphology of mineral crystals in solution by limiting growth on specific crystal faces. [5-8] Some of these polyelectrolytes are in peptide form and possess biocompatible properties. Therefore, polyelectrolytes carry the potential of being administered in vivo with the intention of modulating bone's mechanical function by way of tailoring crystal geometry and size. This study assessed biocompatibility of polyelectrolytic agents on osteoblast-like cells as well as the capability of polyelectrolytic agent to alter crystal properties in bone nodules formed in vitro. It was hypothesized that collagen production would not be altered, but the viability and genetic expression will differ with polyelectrolytic treatment. Furthermore, it is hypothesized that the size and shape of crystals will also differ with polyelectrolyte treatment.

Committee: Ozan Akkus (Advisor) Subjects:

Doctor of Philosophy, Case Western Reserve University, 2010, Macromolecular Science and Engineering

A novel two-dimensional poly(1,3,5-phenylene-4,4'-biphenylene-2,2'-disulfonic acid) (CPPSA) was synthesized using palladium-catalyzed Suzuki coupling in water. The postulated architecture is comprised of hexagonal, macrocyclic, 2-dimensional polymer sheets resembling a honeycomb. Such structures should exhibit a high driving force for 3-dimensional packing thereby creating materials with incompressible nano-channels which can retain water at very low relative humidity. Motivation for the design of such polymers is for use as significantly improved polymer electrolyte membranes for fuel cells. A series of model compound studies based on monomer 4,4'-dibromobiphenyl-2,2'-disulfonic acid were performed to determine the optimal reaction conditions for cyclopolymerization. Emphasis was placed on evaluating water-soluble boronate compounds, bases, and ligands/catalyst systems in order to obtain quantitative yield of model compound quaterphenyl-2',2”-disulfonic acid. A kinetics model based off of the standard Suzuki coupling catalytic cycle was constructed to evaluate the rate of reaction based on the results of sampled model compound reactions. Cyclopolymerization reactions were run under pseudo high-dilution conditions with slow monomer addition. The resulting polymers showed usual physical properties including insolubility in water after condensing to the solid state. Subsequent ultrasonication with heating was shown to disperse the intractable solid polymers into “solutions” which could be used for film casting suggesting that their insolubility was due to aggregation and not from 3-dimensional crosslinking. Further supporting the postulated structural picture was the slow diffusion of water from CPPSA films into D2O in proton NMR experiments. Imaging of the CPPSA polymers by scanning electron microscopy (SEM) indicated evidence of layered structures formed by extensive aggregation. Atomic force microscopy (AFM) showed further evidence of stacking of planar structu (open full item for complete abstract)

Committee: Morton H. Litt PhD (Advisor); Stuart J. Rowan PhD (Committee Member); Alexander M. Jamieson PhD (Committee Member); Anthony J. Pearson PhD (Committee Member) Subjects: Polymer Chemistry

Master of Science, University of Akron, 2006, Civil Engineering

In a recent study, we have performed first-order analysis and proof-of-concept experiments for a novel application of nanoporous materials in developing high-performance pressure controllable nanoporous energy absorption system. When nanoporous particles are immersed in a non-wetting liquid, the liquid cannot enter the nanopores spontaneously. With the increase in external pressure, however, as the capillary effect is overcome, the liquid can be forced to infiltrate into the nanoporous material. Because of the factors that are still under investigation, as the pressure is reduced, in a certain types of nanoporous materials the confined liquid would remain in the nominally energetically unfavorable nanopores, and thus the excess solid-liquid interfacial energy can be considered as being "absorbed". Due to the large specific surface area (100-1000 m2/gm), the energy absorption effectiveness of this system can be in the range of 10-100 J/g. We experimentally demonstrated full control on system parameters like infiltration pressure (pin), recoverability and accessible infiltration pore volume (Vp) using admixtures and promoters. And we have successfully developed a solid like composite nanoporous energy absorption system which can largely simplify the design of protection devices and mechanical dampers.

Committee: Yu Qiao (Advisor) Subjects: