ABSTRACT sPBI is a heterocyclic aromatic polymer assuming a para- catenated backbone yielding a rod-like configuration. Because of its rigidity, this rod-like molecule displays superior mechanical tenacity, thermo-oxidative stability, and solvent resistance. It is also the precursor of rigid-rod solid polyelectrolyte exhibiting high solubility and superior ionic conductivity. Isotropic solution were prepared by dissolving sPBI in distilled methanesulfonic acid containing 0.0, 0.989, 4.76, 9.09, 15.0, 20.0, 23.1 wt. % lithium ion of dopants of LiCF3SO3 or LiN(CF3SO2)2. The room-temperature DC conductivity of sPBI cast film doped with 15.0 wt. % LiN(CF3SO2)2 parallel (

Layer-by-layer assembly of polyelectrolytes is a simple technique based on the self-assembly of polycations and polyanions mainly by electrostatic interactions, which has gained considerable scientific interest for its versatility of applications. Ease of fabrication process, inexpensive approach and use to coat surfaces with various geometries prompts the researchers to select this technique not only for the surface modification applications but also to study the processes which exploit the 3D matrix properties of polyelectrolyte multilayer films (PEMs). Recent advances have been made where PEMs coatings have been utilized for their bio-applications like drug delivery and in tissue engineering for modifying the biomaterial's surfaces. In the field of drug delivery and tissue engineering the location and availability of the constituent molecules is very important, which is defined by their ability to diffuse through the encapsulating material or reservoir. So the main objective of this thesis is to understand the transport of molecules in ultrathin Polyelectrolyte Multilayer Films in lateral as well as transverse direction to the substrate. To study this transport behaviour in PEMs, we have employed various strategies which can enhance or suppress the diffusivity across PEMs. Thus, understanding the diffusion at nanoscale resolution will lead us to design better host materials for loading of drugs and growth factors for various biomedical applications.

Phenylene-based conjugated polymers are of interest for their fascinating electronic and optical properties. The introduction of bound ions into these materials adds great versatility because it can affect solubility, aggregation properties, doping chemistry, luminescence, and response to electrical stimuli. Despite ionic density being a central materials parameter in ionically functionalized conjugated polymers (IFCPs), it has been explored only in limited ranges. The primary advance reported in this dissertation is the development of three complementary synthetic routes to anionic and cationic poly(fluorene)s where the density of ionic functional groups was systematically varied between 0.05 and 0.5 per phenylene unit. There have been very few reports of IFCPs in this range. The three routes all use the Suzuki polycondensation reaction (SPR) to form poly[(R-fluorene)-co-alt-(R'-fluorene)] (PFF) IFCPs, and they differ from one another in when ionic functionality is introduced to the polymer. The development of these approaches grew out of studies on the SPR as it applies to ionically functionalized monomers, specifically, complications created by the two-phase nature of typical Suzuki couplings. In the first route, ions are added to the monomer and directly polymerized into the polymer using a single-phase SPR made possible by using oligoether functionality and a judiciously chosen solvent system. This route was used in the synthesis of a family of sulfonate and oligoether containing PFFs. In the second and third routes, ionic functionality is added after the polymer is formed either in solution or in solid films, respectively. The use of all nonionic monomers during the SPR avoided the complications encountered with two-phase reactions involving ionic monomers. The precursor polymers synthesized for these routes included a family of hexyl and bromohexyl containing PFFs and a family of oligoether and bromohexyl containing PFFs. The former were used to demonstrate post-polymerization quaternization to form cationic PFFs in solid films, and the later were quaternized in solution to yield soluble cationic PFFs. All of the polymers had very similar optical properties with the wavelengths of maximum absorption and emission in the range of 370-385 and 416-425 nm, respectively, and molecular weights greater than 10kDa and exhibited both positive and negative solvatofluorchromism due to aggregation phenomena.

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Polymers having many ionizable groups in their molecular structure are called Polyelectrolytes. They are extensively used in industries like papermaking, food processing, medicine and pharmaceuticals, water purification, oil field exploration, cosmetic formulation etc. In spite of wide applicability its current status of knowledge is precursory due complexity of their behavior in solution as well as at interface. Solution properties of polyelectrolytes are extensively studied in last 40 years to understand their behavior. The activity is important thermodynamic property. From activity we can get most of thermodynamic properties like interaction parameter, free energy of dilution of the polyelectrolyte, degree of dissociation of polyelectrolytes etc.Several models of Polyelectrolytes thermodynamics have been proposed. Two general approaches have been used to model Polyelectrolytes thermodynamics, spherical and cylindrical (chain) models. Two of the successful models to explain and predict commonly measured properties of polyelectrolytes such as osmotic coefficient and counterion activity coefficients have been proposed by Manning and Oosawa. Most of these models are applicable at infinite dilution only may be due to weak inter chain interactions. An Excess Gibb’s free energy model can predict properties at finite concentrations of polyelectrolytes, which is combination of Manning model and Local composition model.Vapor pressure osmometry and isothermal Titration Microcalorimetry are experimental methods to determine the thermodynamic properties of polymer solvent system. Osmometry helps to understand the thermodynamics of polymer solutions as it determines the value of osmotic pressure, which in turn gives the value of thermodynamic parameters. Isothermal Titration Microcalorimetry gives the heat of dilution directly from which we can calculate activity of the solution.The osmotic coefficient and activity of water in aqueous NaPSS solution are found out using Vapor pressure osmometry and Isothermal titration calorimeter at different temperatures. The results are compared with result obtained by an excess Gibb’s free energy model. Measured data show good agreement with available literature data at that temperature.

The electrical double layer (EDL) is formed due to the accumulation of charge at the interface of a metal surface in contact with an electrolyte. The total charge in the EDL compensates the charge on the metal surface. As EDL is the layer that "connects" the electrode to the "bulk", all electrode mediated transport and redox reaction depends on the structure and dynamics of the ions in the EDL. Thus the ion dynamics in the EDL are critical to a wide range of physical and biological phenomena such as electrochemical reaction, flow in channels of nanofluidic devices, wetting of fluids; to biology, for example, folding and function of proteins, conformation change of DNA and ionic flow through cell membranes. EDL polarization is the ion accumulation or depletion in the EDL due to the potential of the metal surface. The conventional method of measuring the EDL polarization is by monitoring the current flowing through the electrochemical system. Thus, the electrical characteristics of the EDL are inferred indirectly from the total current that is implicitly related to effects such as the impedance of the bulk solution. We have developed a sensitive optical interferometric technique to directly measure the polarization of the metal-electrolyte interface. The key advantage of our method is high sensitivity, and the measurement is specific only to the changes at the metal-electrolyte interface. The ion accumulation in the EDL of a simple salt like NaCl is studied as a function of the frequency and the amplitude of the applied potential on the metal electrode. The amplitude of modulation of the ions is linearly proportional to the amplitude of the applied AC potential. The linearity is observed up to high amplitude (up to 2V) and salt concentration as high as 0.5M. Furthermore, the local segmental dynamics of polyelectrolytes such as polystyrene sulfonate have been measured. Next we extend this novel technique to study electrochemical redox reactions. The oxidation of the widely used redox ion [Fe(CN)6]4- is followed by measuring the response to an AC potential (amplitude ~100mV) as a function of a superimposed saw-tooth potential ramp, at a time period 106 fold slower and amplitude 5-10 fold larger than the AC potential. The sensitivity of the optical method is significantly better than the measurement of the AC current. For a redox process on the electrode, the change in the optical signal is over two orders of magnitude larger than the electrical signal. Using the optical technique, we can separate the kinetic events in redox processes: transport of charged species to the electrode surface and charge transfer across the electrode-electrolyte interface. Because we measure the local electrochemical process, the method can be used to probe redox reaction at multiple spots on the same electrode (i.e., combinatorial electrochemistry). / Ph. D.

We report the design and assembly of three-dimensional (3D) multi-cellular liver models comprised of primary rat hepatocytes, liver sinusoidal endothelial cells (LSECs), and Kupffer cells (KCs). LSECs and KCs in the liver model were separated from hepatocytes by a nanoscale, detachable, optically transparent chitosan and hyaluronic acid (HA) polyelectrolyte multilayer (PEM) film. The properties of the PEM were tuned to mimic the Space of Disse found in liver. The thickness of the detachable PEM was 650 to 1000 nm under hydrated conditions. The Young's modulus of the PEM was approximately 42 kPa, well within the range of modulus values reported for bulk liver. The 3D liver models comprised of all three cell types and a detachable PEM exhibited stable urea production and increased albumin secretion over a 12 day culture period. Additionally, the 3D liver model maintained the phenotype of both LSECs and KCs over the 12 day culture period, verified by CD32b and CD163 staining, respectively. Additionally, CYP1A1 enzyme activity increased significantly in the 3D liver models. The number of hepatocytes in the 3D liver model increased by approximately 60% on day 16 of culture compared to day 4 indicating. Furthermore, only the 3D hepatic model maintained cellular compositions virtually identical to those found in vivo. DNA microarray measurements were conducted on the hepatocyte fractions of the 3D liver mimic to obtain insights into hepatic processes. Gene sets up-regulated in the 3D liver model were related to proliferation, migration, and deposition of extracellular matrix, all functions observed in regenerating hepatocytes. Taken together, these results suggest that inter-cellular signaling between the different cell types in the 3D liver model led to increased hepatic functions. To the best of our knowledge, this is the first study where three of the major hepatic cell types have been incorporated into a model that closely mimics the structure of the sinusoid. These studies demonstrate that the multi-cellular liver models are physiologically relevant. Such models are very promising to conduct detailed investigations into hepatic inter-cellular signaling. / Ph. D.

Polyelectrolyte capsules fabricated by layer-by-layer (LbL) technique are introduced as a simple and efficient carrier system for spontaneous deposition of proteins and low molecular water soluble drug. The objective of the work was to investigate the applicability of polyelectrolyte capsules as vehicles for sustained or controlled delivery of drugs. Two different polymeric systems composed of weak and strong polyelectrolytes were chosen to study the loading and release behavior in order to meet the requirements of biomedical applications. In the first system, the wall permeability of weak polyelectrolyte (PAH/PMA) capsules could be readily manipulated from open to closed state by simply varying the pH. The open and closed state of the capsules could be attributed to the charge density variation of weak polyelectrolytes, which induces the capsule wall to undergo a transition from continuous to nanoporous morphology due to phase segregation. Bovine Serum Albumin (BSA) was spontaneously deposited in the hollow capsules and deposition was investigated by CLSM, SEM and AFM techniques. The driving force for spontaneous deposition was electrostatic interaction between the preloaded polystyrene sulfonate (PSS) and BSA. The deposition was uniform and concentration of BSA in the capsule interior reached a few hundred times greater than that of bulk. The amount of loading was significantly influenced by the loading pH, loading concentration and charge density of substance to be loaded at the corresponding pH. The deposition was successful up to the isoelectric point of BSA (pH = 4.8) and there was no loading observed above that, since the deposition is based on electrostatic attraction between PSS and BSA. During the release at physiological pH of 7.4, charge reversal of BSA occurred which induced electrostatic repulsion between PSS and BSA thereby triggering the movement of BSA from the interior to the bulk. Release continued up to 5 h in water and a total release of 63 % was observed which increased to 72 % when release was performed in PBS. Spontaneous deposition of low molecular weight, water soluble drug, ciprofloxacin hydrochloride was performed in the same manner and its release profile was studied. Controlling diffusion of smaller drug molecules is extremely difficult in drug delivery applications. Cross linking of capsule wall components could be used to control the release rates of smaller drug molecules. Cross linking density is dependent on the cross linking time and increases the stiffness of the capsule wall. Release of ciprofloxacin hydrochloride was possible even up to 6 h after cross linking. Antibacterial studies showed that the drug released even after 25 h has a significant effect on the bacterial pathogen E.coli. The second system included weak and strong polyelectrolytes (PAH & DS) and a novel route was employed to fabricate optically addressable capsules that could be laser activated for delivery of drugs. This approach involved a combination of LbL assembly and polyol reduction method wherein PEG was used to reduce AgNO3 to Ag nanoparticles (NPs). The capsules were prepared via LbL assembly of PAH and DS on silica template followed by synthesis of silver NPs in the layers and subsequent dissolution of the silica core. The sulfonate groups of DS present in the polyelectrolyte film act as binding sites for the adsorption of silver ions which are then reduced to silver NPs in the presence of PEG. The size of the silver NPs formed was influenced by the AgNO3 concentration used. At lower concentration, smaller particles of uniform distribution were observed which turned into larger particles of random distribution when the concentration of AgNO3 is increased. Silver NPs embedded capsules ruptured when exposed to laser and was significantly influenced by silver NPs size, their distribution, laser intensity and time of exposure. The synthesis of silver NPs increased the permeability of the capsules to higher molecular weight substances like dextran caused by the defects, discontinuities and pores created on the polymeric network due to the newly formed silver NPs. Encapsulation of FITC-dextran was performed using thermal encapsulation method by exploiting temperature induced shrinking of the capsules at elevated temperatures. During heat treatment the porous morphology transformed into smooth pore free structure which prevented the movement of dextran into the bulk and hence enrichment inside the capsules. The loaded dextran was readily released when exposed to laser and the release could be controlled from linear to burst release in order to meet practical requirements in biomedical applications.

<p>In recent years, antibacterial surfaces have been a subject of increased interest. Especiallyinteresting are non-leaching, contact-active surfaces that physically disrupts the bacterialcell using immobilised cationic polymers. Thus the risks of bacterial resistance and discharge of hazardous biocides is minimised. The assembly of such surfaces is elaborate andusually involves organic solvents. Here, polyelectrolyte multilayers (PEM) are proposed as an effective surface modification method, with an overall goal of producing antibacterial cellulose fibres. The PEM process is based on physical adsorption of oppositely charged polymers in aqueous solutions. Multilayers were formed with the bactericidal polymer polyvinylamine (PVAm) and polyacrylic acid. PVAm compounds with hydrophobic modificationswere applied as well, as they possess increased antibacterial activity in solution.</p><p>In this work, the multilayer formation was studied on model surfaces of silicone oxide and glass in order to obtain fundamental knowledge of the polymer system. QCM-D and reflectometry, which detect total mass including bound water and polymer mass only, respectively, were used to analyse the layer formation. Salt-concentrations were varied at 1, 10 or 100 mM NaCl. A stepwise multilayer formation with exponential-like polymer adsorption but with decreasing water content for each layer was seen at all salt concentrations.A higher salt concentration resulted in an increased adsorbed mass. No significant differences in adsorption between the modified and unmodified PVAm could be detected. AFM imaging applied to multilayers having nine layers showed large surface aggregates under high salt conditions for the C6-modified PVAm. Dynamic light scattering showed that the polymer occurred as single molecules in solution; hence it was concluded that theaggregation is surface-associated.</p><p>The multilayers were then tested for bacterial growth inhibition. The relative bacterial inhibition was time-dependent, as the surface was saturated with bacteria over time. After two hours, a maximal inhibition of 99 % could be observed for the multilayers. After eight hours, a moderate inhibition of less than 40 % was detected. Using multilayers affected the results positively compared to single layers. After three layers, though, no further reductionwas seen. Viability staining of the surface-adhered bacteria revealed that the adhered bacteria had intact membranes. Therefore, the microbiological properties of the multilayers can at this point be described more as growth-inhibiting by bacterial adhesion effectsthan as biocidal. However, this work has shown the importance of combining surface characterisation and microbial testing to understand the bacteria-surface interaction.</p> / Biointeractive fibres