The characterization, properties and applications of the novel nanostructured microgel (nanoparticle network and microgel crystal) composed of poly-N-isopropylacrylanmide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid(AA) have been investigated. For the novel nanostructured hydrogels with the two levels of structure: the primary network inside each individual particle and the secondary network of the crosslinked nanoparticles, the new shear modulus, drug release law from hydrogel with heterogeneous structure have been studied. The successful method for calculating the volume fraction related the phase transition of colloid have been obtained. The kinetics of crystallization in an aqueous dispersion of PNIPAM particles has been explored using UV-visible transmission spectroscopy. This dissertation also includes the initial research on the melting behavior of colloidal crystals composed of PNIPAM microgels. Many new findings in this study area have never been reported before. The theoretical model for the columnar crystal growth from the top to bottom of PNIPAM microgel has been built, which explains the growth mechanism of the novel columnar hydrogel colloidal crystals. Since the unique structure of the novel nanostructured hydrogels, their properties are different with the conventional hydrogels and the hard-sphere-like system. The studies and results in this dissertation have the important significant for theoretical study and valuable application of these novel nanostructured hydrogels.

Monodispersed nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) and PNIPAM-co-acrylic acid (AA) have been synthesized and used as building blocks for creating three-dimensional networks. The close-packed PNIPAM-co-allylamine and PNIPAM-co-AA nanoparticles were stabilized by covalently bonding neighboring particles at room temperature and at neutral pH; factors which make these networks amicable for drug loading and release. Controlled release studies have been performed on the networks using dextran markers of various molecular weights as model macromolecular drugs. Drug release was quantified under various physical conditions including a range of temperature and molecular weight. These nanoparticle networks have several advantages over the conventional bulk gels for controlling the release of biomolecules with large molecular weights. Monodispersed nanoparticles of poly-N-isopropylacrylamide-co-allylamine (PNIPAM-co-allylamine) can self-assemble into crystals with a lattice spacing on the order of the wavelength of visible light. By initiating the crystallization process near the colloidal crystal melting temperature, while subsequently bonding the PNIPAM-co-allylamine particles below the glass transition temperature, a nanostructured hydrogel has been created. The crystalline hydrogels exhibit iridescent patterns that are tunable by the change of temperature, pH value or even protein concentration. This kind of soft and wet hydrogel with periodic structures may lead to new sensors, devices, and displays operating in aqueous solutions, where most biological and biomedical systems reside. The volume-transition equilibrium and the interaction potential between neutral PINPAM particles dispersed in pure water were investigated by using static and dynamic light-scattering experiments. From the temperature-dependent size and energy parameters, the Sutherland-like potential provides a reasonable representation of the inter-particle potential for PNIPAM particles in swollen and in collapsed phases. An aqueous dispersion of PNIPAM particles can freeze at both high and low temperatures. At low temperatures, the freezing occurs at a large particle volume fraction, similar to that in a hard-sphere system; while at high temperature, the freezing occurs at low particle concentrations, driven by the strong van der Waals attraction due to the collapsed microgel particles. The calculated phase diagram has been confirmed semi-quantitatively by experiments.

Polímeros termossensíveis apresentam grandes alterações em suas propriedades quando submetidos a pequenas mudanças de temperatura (T) próximas à temperatura de solução crítica inferior (LCST) ou superior (UCST). Um dos polímeros termossensíveis mais estudados é o Poli(N-isopropilacrilamida) (PNIPAm) porque ele apresenta a LCST, aproximadamente, 32 oC ( 305 K), próxima à temperatura do corpo humano. Em temperatura abaixo da LCST o polímero apresenta-se solúvel devido um grande número de interações hidrofílicas (ligações de hidrogênio polímero-água), entretanto quando a temperatura é elevada acima da LCST ocorre a precipitação do polímero devido a um aumento de interações polímero-polímero e uma diminuição brusca nas interações polímero-água. Com essas características o PNIPAm tem despertado o interesse para aplicações em um vasto campo de pesquisas, como por exemplo na liberação controladas de fármacos. Nesse trabalho, utilizando simulações de dinâmica molecular (DM), foi proposta uma imagem microscópica do fenômeno de transição de fases apresentado por esse polímero em solução aquosa influenciado por alterações na estereoquímica do backbone (taticidade), bem como o efeito da copolimerização com Acrilamida (Am). Com base nas análises estruturais e termodinâmicas, os resultados sugerem que as diferentes estereoquímicas (isotático, atático e sindiotático) possibilitam diferentes conformações dificultando ou possibilitado um maior número de interações polímero-polímero e polímero água modificando a LCST. Já o aumento da concentração de Am (xAm) na copolimerização aumenta o número de interações polímero-água dificultando o colapso da cadeia. / Thermosensitive polymers exhibit large changes in their properties when submitted to small changes in temperature T, near the lower (LCST) or upper critical solution temperature( UCST). The most extensively studied thermosensitive polymer is PNIPAm because it has a LCST of approximately 32 oC (305 K), near human body temperature. For temperatures below the LCST the polymer is soluble due to strong hydrophilic interactions (polymer-water hydrogen bonds). However, when the temperature is raised above the LCST, the precipitation of the polymer occurs due to increased polymer-polymer interactions and a sharp decrease in polymer-water interactions. That feature makes the PNIPAm a compound widely studied and with a wide range of applications, such as for drug delivery. In this work, using molecular dynamics simulations, it was proposed a microscopic picture of the phase transition phenomenon presented by this polymer in aqueous solution influenced by changes in stereochemistry of the backbone (tacticity), as well as the effect of copolymerization with acrylamide (Am). Based on the thermodynamic and structural analysis, the results suggest that different stereochemistries (isotactic, atactic and syndiotactic) enable different conformations allowing different scenarios of polymer-polymer and polymer-water interactions, therefore modifying the LCST. The presence of the strongly polar copolymer acrylamide as the effect of maintain the high hydration even at higher temperatures, shifting in this way the LCST to higher values.

Sedimentation is one of many characterization tools used to test materials in nanotechnology. Characterization of settling behavior is complex as there are many variables which can affect sedimentation. In our research, we focused on sedimentation in colloidal systems with the aid of an optical turbidometer. Nanoparticles of CeO2 (Ceria Oxide) and TiO2 (Titanium Dioxide) are embedded onto a polymeric matrix of a thermally responsive microgel of poly(N-isopropylacrylamide) (PNIPAM) and interpenetrating chains of poly(acrylic acid) to create novel composites. The composites are loaded with the inorganic oxide nanoparticles at different weight percent from a low value of 10 weight % to 75 weight %. The loading of the colloidal particles affects the sedimentation rate. In this thesis a turbidomenter is used to characterize the settling rate, which is an important characteristic for application of these new composites. TiO2 is a key constituent in many industrial products; cosmetics, paints, ceramics and used in waste water remediation. It is a potent photocatalyst which breaks down almost any organic compound when exposed to ultraviolet light. By combining nanoparticles of TiO2 with microgels of a polymer, the composites can facilitate use and recovery of the catalyst. Gravity settling of these loaded composites provides an easy separation of TiO2 nanoparticles. In this context, characterization of settling plays an important role. CeO2 composites are used to polish oxide coatings in the semiconductor industry and sedimentation of the composite particles is important as it can affect the efficiency of the planarization process. Therefore, measuring sedimentation of these composites is necessary. In this study, the settling behavior is measured optically for a variety of conditions that differ in loading of inorganic nanoparticles within the microgels, temperature of the solution, and concentration of particles in solution. The overall goal is to understand the sedimentation behavior of these novel composites and facilitate their use in industrial processes.

Magnetic nanoparticles (MNPs) have found use in a wide variety of biomedical applications including hyperthermia, imaging and drug delivery. Certain physical properties, such as the ability to generate heat in response to an alternating magnetic field, make these structures ideal for such purposes. This study's objective was to elucidate the mechanisms primarily responsible for RF MNP heating and determine how such processes affect polymer solutions that might be useful in drug delivery. 15-20 nm magnetite (Fe3O4) nanoparticles at 0.2% and 0.5% concentrations were heated with RF fields of different strengths (200 Oe, 400 Oe and 600 Oe) in water and in 0.5% gellan gum solution. Mixing and fan cooling were used in an attempt to improve accuracy of data collection. Specific absorption rate (SAR) values were determined experimentally for each combination of solvent, concentration and field strength. Theoretical calculation of SAR was performed using a model based on linear response theory. Mixing yielded greater precision in experimental determination of SAR while the effects of cooling on this parameter were negligible. Solutions with gellan gum displayed smoother heating over time but no significant changes in SAR values. This was attributed to low polymer concentration and lack of structural phase transition. The LRT model was found to be adequate for calculating SAR at low polymer concentration and was useful in identifying Neel relaxation as the dominant heating process. Heating trials with MNPs in 2% agar confirmed Neel relaxation to be primarily responsible for heat generation in the particles studied.

This dissertation investigates the self assembly and automatic oscillation of intelligent poly (N-isopropylacrylamide) [PNIPAM] microgel particles. The equilibrium phase diagram as a function of temperature and concentration was constructed for the charged PNIPAM spheres. The PNIPAM microgel particles display rhythmic size oscillations when covalently coupled to a nonlinear chemical reaction, the Belousov-Zhabotinsky (BZ) reaction. The nonequilibrium dynamics of PNIPAM microgels in the presence of BZ reaction was studied by the systematic variation of substrate concentrations and temperature. In addition, the BZ chemical reaction was modeled to reveal the existence of upper temperature limits for nonlinear chemical systems. The experiments employ environment sensitive PNIPAM particles that are sensitive to temperature, pH, and ionic strength. The PNIPAM particles have been demonstrated here to behave as hard spheres at low pH values and soft spheres at high pH. This is done by measuring the freezing and melting boundary of fluid-crystal coexistence region with a new technique which is simpler and quicker compared to the traditional sedimentation method. A novel method was developed to achieve size uniformity of PNIPAM gel particles with covalently-bound tris(bipyridyl)ruthenium(II) via the coordination chemistry between a ruthenium complex and the monodispersed PNIPAM gel particles bearing bipyridine ligands. The correlation between the dynamic behavior of BZ reaction induced mechanical oscillations of PNIPAM particles and substrate concentrations was presented in a ternary phase diagram. In particular, the dependence of oscillation frequency and induction time on the substrate concentrations was studied. The temperature dependency of the induction time and oscillatory frequency of the BZ reaction in this polymerimmobilized catalyst system were compared to the bulk BZ reaction with the catalyst in the solution phase. Prolonged induction times were observed for the immobilized catalyst, compared with free catalyst, while little difference was observed on the oscillation frequency. A theoretical improvement has been achieved by incorporating the temperature dependence in the BZ Oregonator model. Bifurcation has been calculated in the phase space spanned by initial reagents concentration ratio, stoichiometric factor and temperature. The existence of upper temperature limits has been demonstrated.

This dissertation focuses on the study of inverse temperature transition processes of the poly(N-isopropylacrylamide) (PNIPAM) and the elastin-like polypeptides (ELPs). A novel temperature jump microfluidic system is introduced and this system shows the ability to measure the kinetics of the PNIPAM and the ELPs collapse without a heat transfer problem. The conformational change of the ELPs during the phase transition process is utilized as a nanoscale protein filter to modulate ligandreceptor binding events on supported lipid bilayers (SLBs). This research study is divided into three main parts. The first part is the development of the temperature jump microfluidics. The kinetics of PNIPAM collapse is used as a model system to show the capability of this new device to measure millisecond time scale phase transition processes. The effects of salts on the kinetics of PNIPAM collapse are also shown in this part. To our knowledge, this is the first study which shows the effects of salts on PNIPAM collapse kinetics. The second part of this research is the application of the novel temperature jump microfluidics. The hydrophobic collapse of ELPs composed of identical sequence but different chain length is investigated. By controlling the molecular weight of the ELPs, the thermodynamic contributions from intermolecular hydrophobic interactions, and intramolecular hydrophobic interactions could be calculated individually for this unique system. The third part is the application of the phase transition property of ELPs. The ELPs are conjugated on the surface of the SLBs as a nanoscale protein filter. The conformation of the ELPs can be modulated by ionic strength of the buffer solution or ambient temperature. The ELPs conjugated SLBs platform showed the ability to block IgG binding to biotin conjugated on the SLBs when the ELPs were in the extended coil state and open the access for protein to bind to biotin in compact globule conformation.

Poly(N-isopropylacrylamide) (PNIPAM), a temperature responsive polymer, undergoes a phase change at a lower critical solution temperature (LCST) in aqueous solutions. For PNIPAM this temperature is 32 °C in water. Below the LCST, the polymer is readily solvated by water. As the temperature of the solution increases, the polymer undergoes a phase transition so that above the LCST it is no longer water soluble. The LCST of PNIPAM may be changed by the addition of salt solutions from the Hofmeister series which will follow the Hofmeister effect for salting-in and salting-out the polymer. Temperature responsive polymers may be grafted to a surface in a variety of methods to create responsive thin films that exhibit a change in wettability. The surface wettability is directly related to the polymers ability to be solvated in its coil conformation. When PNIPAM is grafted to a surface, the surface becomes alternatively hydrophobic and hydrophilic in response to both temperature and the anions in the Hofmeister series which take the surface either above or below the LCST of PNIPAM. The synthesis of responsive nanocomposite grafts was successfully applied to glass slides and three-dimensional surfaces, porous glass frits which were capable of controlling the passive flow rate. The nanocomposite graft was assembled in a covalent layer-by-layer approach to create more chemically robust surfaces, and also to incorporate nanoparticles into the graft for increased surface roughness and therefore improve wettability response. Because of a much greater inherent roughness to a glass frit, characterization of the polymers and nanoparticles was performed before they were covalently bound to the surface. The final product, a functionalized frit with a PNIPAM/SiO2 nanocomposite graft, was analyzed by observing changes in the passive permeation rate of the frit between water and salt solutions. These changes in flow were indicative of the surface bound PNIPAM changing between its hydrophilic and hydrophobic conformation in response to water and concentrations of kosmotropic salts such as sodium sulfate and sodium citrate. In addition to the solute response, the frit was also determined to be responsive to temperature and concentration. Water exhibited a passive flow rate 1000 times faster than a kosmotropic salt but had a similar flow rate to that a chaotropic salt. By measuring the flow rate of 0.5 M Na2SO4 at ~7 °C in a cold room and at room temperature it was observed that sodium sulfate in the cold room passed through the frit at a rate 100 times faster than at room temperature. Because of the hysteresis of PNIPAM documented in literature, washing procedures were kept consistent between experiments to achieve more reproducible results. It was concluded that the frits were temperature responsive and had relative standard deviations below 25 percent for flow rates on a single frit. However, standard deviations of flow rates between frits were higher. This was likely due to a combination of factors, such as the frits’ pore size range of 10 μm resulting in the possibility of varied degrees of functionalization of each frit.

Surface Laser Light Scattering (SLLS) is a heterodyne detection technique used to probe the surface properties of fluid interfaces. These interfaces are either liquid/liquid or vapor/liquid, and they may include insoluble monolayers or polymer films deposited on liquid surfaces as well as microemulsions in solution at low concentration. This technique provides one with a nonperturbative way to obtain surface tension and viscosity. A diffraction grating is employed to provide a stable local oscillatior, hence selecting an accurate ripplon wave vector . This thesis deals with the investigation of the interface between air and solution consisting of the methanol and water mixture and poly(N-isopropylacrylamide) or PNIPAM which is one of the fascinating polymeric materials. The polymer PNIPAM shows distinct responses to variations in the surrounding environment (such as thermal gradient, change in pH, etc.). The surface tension extracted from the SLLS data using the Kelvin equation is found to agree well with that obtained by using the Wilhelmy plate method. For the range of wave vectors cm-1, the power spectrum detected in frequency domain can be fit to a Lorentzian profile. Our experiments show that when the volume percentage of methanol increases, the interfacial property becomes insensitive to the presence of PNIPAM.

Tunable nanostructures have many important uses in thin film applications. Tunability can be achieved by creating a film that has features that respond to external stimuli, such as temperature, humidity, or pH. However, the response can vary greatly between a confined and unconfined case. In the case of confined materials, this response can be greatly reduced, even completely suppressed, which indicates that separate studies must be conducted on confined states in order to better understand their use for real applications. Microgels have been previously shown to have exceptional responsive properties that depend on their chemical structure and synthesis. Unlike solid thin hydrogel films that respond on the order of hours, microgels arrange on a surface with no external force and create a highly porous layer which responds rapidly, on the order of minutes, to outside stimuli. These properties make microgels a promising candidate for use in tunable thin films. Although the responsive properties of microgels have been extensively studied in solution and unconfined films, this is not indicative of conditions that would most likely have the microgels placed between two stiffer layers of material. Microgels have been shown to respond to glucose concentration, temperature, pH, and light. One well-studied microgel is poly-N-isopropylacrylamide copolymerized with Acrylic Acid (pNIPAM-co-AAC). These microgels use the thermal response of pNIPAM combined with the pH sensitivity of pAAC to create a dually-responsive material. To study the effects of confinement on pNIPAM-co-AAC microgels, we encapsulated these particles within bi-layers of poly(allylamine hydrochloride)-poly(sodium 4-styrenesulfonate) (PAH-PSS) in order to simulate their response within a polyelectrolyte material. Our samples were prepared with a method called tilt-drying, which creates a microgel concentration gradient. This allowed us to study both the confinement caused by the multi-layered film as well as the effects of microgels on each other. Our results have shown that the change in particle height is unaffected by the concentration of the film, but the thermal response of pNIPAM-co-AAC microgels is significantly suppressed by the encapsulation of microgels into nanoscale layers.