The process of molecular self-assembly has attracted tremendous attention due to its novel structural organizations and applications. The self-organization of amphiphilic molecules provides unique opportunities for designing novel materials for advanced nanotechnology. The development of molecular self-assembly involves the precise tailoring of chemical structures and the effective use of non-covalent forces. We are interested in the molecular design and synthesis of amphiphilic macromolecules that exhibit various self-assembled nanostructures. We modify the amphiphilic building blocks during their synthesis, investigate the structure-property relations of these amphiphilic molecules and explore their applications. Amphiphilic dendrimers are obtained when these building blocks are grown in a perfectly branched fashion, whereas amphiphlic homopolymers are produced from the linearly grown building blocks. We show that facially amphiphilic dendrimers exhibit significant difference in surface wettability due to subtle changes in structure. These amphiphilic dendrimers respond to the surface polarity and modify the polar surfaces from hydrophilic to hydrophobic. The monodendrons are capable of providing hydrophobic surfaces, while the didendrons provide superhydrophobic surfaces. This provides an example of how a molecular level change could result in dramatic changes in surface property. Amphiphilic homopolymer films have been immobilized onto substrates and shown to reduce protein adsorption, despite the high affinity of the hydrophobic or hydrophilic groups by themselves toward proteins. This protein-resistant property seems to arise from the unique molecular-scale alternation of incompatible functionalities. The combination of incompatible functionalities with a predefined alternating pattern within a monomer could provide a potential design for nonfouling materials. We also designed and synthesized proton conducting systems that derived from facially amphiphilic polymers. We show that our novel molecular design leads to organized supramolecular assemblies that dramatically enhance the anhydrous conductivity. We describe the design, synthesis, and characterization of these materials, which suggest that nanoscopic organization of proton conducting functionalities should be a key consideration in obtaining efficient anhydrous proton transport.

Nanoimprinting with anodized aluminum membranes was performed to produce nanoposts with controlled diameter and aspect ratio. The polymer nanoposts were found to remain upright and preserve the post-packing structure at low aspect ratios, but succumbed to elastocapillary coalescence at higher aspect ratios, with the morphology of the aggregates directly related to the aspect ratio of the polymer nanoposts. Replication of the replicated nanoposts at low aspect ratio was achieved to reproduce the pore packing structure of the original alumina membrane. Teflon microparticles were found to be effective stabilizers for inverse foams, producing dry water with excellent flow properties and contact stability and consisting of non-spherical liquid marbles 90-500 microns in diameter. The chemical inertness of the PTFE particles allowed for use of not only water, but also aqueous solutions of acids and bases and organic molecules including ionic liquids and water-soluble polymers. The teflon particle shell stabilized the liquid drop such that two particles containing two solutions which would ordinarily mix and/or react would remain separate. The wettability studies focused on demonstrating that entrapped gases are not responsible for Cassie superhydrophobic wetting behavior, that the removal of the pockets of air would not lead to Wenzel wetting behavior with an increase in contact angle hysteresis. The measurement of advancing and receding contact angles on surfaces with controlled topography consisting of square posts holes showed that the contact angles remained unchanged despite removal of over 90% of the air. It showed that water was not intruding into the hydrophobic topography because the Laplace pressure was thermodynamically preventing water from increasing its interaction with the topographically-patterned surface. Wettability studies were also aimed at extending our understanding of wettability as a one-dimensional phenomenon from the three-phase contact line perspective, by investigating the ability of hydrophilic arcs, short and long wedges, and the outlines of the wedges, to pin water drops on hydrophobic, low hysteresis surfaces. They were additionally aimed at studying the ability of hydrophilic lines to deform the three-phase contact line of a water drop and kinetically trap a water drop in a distorted shape on a hydrophobic surface.

Fabrication and characterization of different nanomaterials by using porous anodic aluminum oxide (AAO) templates were studied. Amorphous carbon nanotubes were prepared by casting thin films of polyacrylonitrile (PAN) and polystyrene-block-polyacrylonitrile (PS-b-PAN) within a AAO membrane followed by pyrolysis. Raman and wide angle X-ray diffraction (WAXD) measurements indicate that the carbon nanotubes are of low crystallinity. When diblock copolymers of PS-b-PAN were used, it was found that, nanopores were created within the nanotube walls after pyrolysis. Nanotubes of the cylinder-forming polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer nanotubes were generated. Because of the water solubility of the cylindrical PEO microdomains and the orientation of the cylindrical PEO microdomains with respect to the nanotube walls, the nanotubes were permeable to aqueous media. Rayleigh instabilities in thin polymer films confined within AAO membranes were studied. Thin films of PMMA were prepared by filling cylindrical nanopores in an AAO membrane with a PMMA solution in chloroform followed by solvent evaporation. When the PMMA nanotubes were annealed above the glass transition temperature (Tg), undulations in the film thickness were observed that were induced by a Rayleigh instability. The amplitude of the undulations increased with time and eventually bridged across the cylindrical nanopore in the AAO membrane, resulting in the formation of polymer nanorods with periodically encapsulated holes. A facile route to prepare hierarchical structures by wetting polymer microspheres into the nanopores of AAO templates was presented. In this approach, polystyrene (PS) microspheres were first spread and self-assembled into well-ordered monolayers on a silicon wafer. By contacting the porous AAO template, polymer chains wet the porous template and form short nanorods on top of the micrsopheres after thermal annealing. These hierarchical structures show ordering at two length scales which can be controlled by the size of the polystyrene microspheres and the pore sizes of the template. The generation of one-dimensional mesoporous silica and titania nanomaterials by using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) as precursors was described. The porous structures were fabricated by evaporation induced self-assembly followed by pyrolysis. The orientation of the mesopores is parallel to the channels of the AAO membrane.

Nanoparticles were functionalized in order to incorporate their unique properties into functional materials. Gold nanoparticles were functionalized to direct their assembly at the oil-water interface, and further modified to achieve cross-linking at the interface, incorporation of charged groups or targeting groups, and extrusion to resize the capsules for potential delivery applications. Capsules were characterized by fluorescence microscopy by encapsulation of a fluorescent dye, and after drying on substrates by scanning force microscopy (SFM) and transmission electron microscopy (TEM). Gold nanoparticles were functionalized for their assembly into a microphase separated block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-PVP) and the nanoparticles were directed within the domains by modification of the ligand periphery. Varying the ratio of hydrophobic to hydrophilic ligands allowed for the controlled assembly of the nanoparticles within the PVP domain of the diblock copolymer or at the interface between the two blocks. Thermal annealing resulted in ripening of the particles and migration of all particles to the center of the PVP domain. Location of the nanoparticles was determined by TEM and SFM. Gold nanoparticles were modified with acid-labile groups for potential use in photolithography applications, and with amine groups for incorporation in water purification membranes. Silica particles were modified with a dithiocarbonate chain transfer agent to achieve controlled polymerization by reversible addition fragmentation chain transfer polymerization (RAFT) of vinyl acetate from the particle surface. The poly(vinyl acetate) was hydrolyzed to poly(vinyl alcohol) to achieve particles dispersible in water with potential gas barrier properties. Functionalized silica particles were characterized by thermogravimetric analysis, TEM, and polymer was characterized by size exclusion chromatography.

The autonomous organization of components into patterns or structures without human intervention is known as self-assembly. This process is common throughout nature and technology and may involve many different kinds of interactions. This thesis treats the self assembly of block copolymers (BCPs) confined within cylindrical nanopores and generation of novel structures resulting from the constraints of size and forced curvature. Lamella-, cylinder-, and sphere-forming BCPs were drawn into the pores of anodized aluminum oxide (AAO) membranes in the melt phase by capillary forces. After thermal annealing, BCP nanorods were isolated by dissolution of the AAO with a weak acid and transmission electron microscopy (TEM) was used to investigate the resultant morphologies of the confined BCPs. The diameter and surface chemistry of AAO nanopores and molecular weight of BCP were varied to investigate the effect of confinement on the microphase separation of BCP. Concentric cylinders were observed for the lamella-forming BCPs under 2D confinement and deviations of the lamella repeat period were measured as a function of AAO pore diameter. For the bulk cylinder-forming BCP, a rich variety of morphologies, not seen in bulk, were observed that included stacked discs, toruses, single, double and triple helices and helices with a cylinder in the core. The specific morphology observed depended on D/Lo, where D is the pore diameter and Lo is the period of the BCP in the bulk. Electron tomography was performed on the cylinder-forming BCP to obtain 3D image of the confined morphology. For bulk sphere-forming BCP, novel structures, such as core-shell cylinders and spiraling rows of single, double and triple paired spherical microdomains were observed. The bulk cylinder-, and sphere-forming BCP were also placed in silane modified AAO and a rich variety of novel structures were observed. Inside silane modified AAOs, the preference of the blocks towards the pore wall was also altered. The results of cylinder-forming BCP were consistent with the results from the simulations. This method offers and exciting opportunity to manipulate the phase separation of BCPs and discover the novel periodic structures that are significantly different from those observed in bulk.

Polymers are interesting macromolecules that have gained great interest in a wide variety of applications. In this thesis, polymers have been utilized for gene and drug delivery, and to modulate enzyme activity. Simply, the idea of gene therapy is to deliver a therapeutic gene into defective cells. This field of medicine has enormous potential to cure many genetic diseases such as cancer, Alzheimer’s, and Huntington’s disease. A major obstacle in gene therapy is in safely and efficiently delivering the exogenous DNA into the nucleus of a cell. After the tragic failures in virus based gene therapy in clinical trials, there is a necessary search for a non-viral material. Polymers have been shown to interact and facilitate the entry of therapeutic DNA into the nucleus. Several types of polymers, including polyethyleneimine and poly-lysine, have had initial success in gene delivery. The first part of this thesis discusses about interesting approaches to further enhance the level of transfection and decrease toxicity. In one approach, an inspiration is taken from HIV-TAT protein that translocate exogenous materials into the nucleus. The basic domain of HIV-TAT protein, TAT peptide has been utilized in the polymeric design. A method has been developed to effectively display the TAT peptide on the polyplex surface. This significantly enhances the transfection efficiency of polyethylenimine polymers. In the search for a successful polymeric design for gene delivery, several naturally occurring amino acids are placed on a biocompatible polymer backbone. These polymers have high transfection and low toxicity when compared to the polymeric gold standards for gene delivery PEI and PLL. The design of these polymers also provided an opportunity to understand the structure-property relationships of different amino acid based polymers. Polymeric materials are also an interesting candidate for drug delivery. Polymeric micelles are designed to incorporate the cytotoxic anti-cancer drug, doxorubicin, and target it to cancer cells. These amphiphilic polymers have redox sensitive disulfide bonds and their cleavage causes the micelle to fall apart. This helps the polymeric micelles to selectively release the drug in high redox environment of cancer cells. Proteins regulate most of the cellular functions in our bodies and the alteration of their activities can lead to life threatening diseases. In the final part of this thesis, polymeric scaffolds are designed and developed to tune enzyme activity. The cationic polymers have the ability to electrostatically interact with proteins, namely serine protease chymotrypsin. At the physiological pH, these polymers can regulate chymotrypsin activity from 20% to 200% at nanomolar concentration without denaturing the protein.

Modern polymer research is uncovering new materials for biomedical applications. This thesis centers on novel polymer syntheses towards anti-cancer therapeutics termed polymer “pro-drugs”. In particular, aliphatic polyesters are potentially useful for drug delivery due to their biocompatibility and biodegradability. However, conventional aliphatic polyesters lack functionality. Incorporating functionality into aliphatic polyesters carries the potential to tailor their properties, and provides a method to attach drugs covalently. There are significant challenges associated with aliphatic polyester functionalization due to side-reactions including degradation of the polymer backbone. To overcome this challenge, alkyne functionalized lactones were synthesized, and click cycloaddition chemistry was employed to covalently attach novel azides to these alkyne containing aliphatic polyesters. A novel trimethylsilane protected alkyne d-valerolactone was synthesized and used in the preparation of block copolymers allowing for orthogonal functionalization strategies. Tin (II) mediated ring-opening polymerization of the lactones led to aliphatic polyesters with a narrow molecular weight distribution that had pendent alkynes available for post-polymerization chemistry. Click cycloaddition chemistry afforded water-soluble aliphatic polyesters by attaching PEGylated and zwitterionic azides to the polymer backbone. Novel phosphorylcholine and phosphobetaine-azides were prepared and grafted to the polyester chain. Camptothecin (CPT), an anti-cancer drug, was covalently attached to the aliphatic polyesters through a variety of covalent linkers. High pressure liquid chromatography (HPLC) was used to examine the release of CPT from the pro-drugs. With some of the linkers, CPT was seen to release from the aliphatic polyester with half-lives of 2–4 hours in human plasma. Physicochemical characterization techniques, including light scattering and atomic force microscopy (AFM), were used to investigate the properties of the polymeric pro-drug micelles. These micelles were approximately 60-120 nm in hydrodynamic radius. In vitro assays with MCF7 (breast cancer) and COLO205 (colorectal cancer) cells were used to evaluate the cytotoxicity of the polymers pro-drugs. IC50 values as low as 4 µM in COLO205 cells indicated the release of CPT in its cytotoxic form, and the potential of these aliphatic polyesters to function as a drug delivery platform.

Quantitative analyses of configurational defects and chain distribution in the semi-crystalline random copolymers have been established in order to understand the structure-property relationship of these polymeric materials. Poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)), Ethylene-vinyl acetate (EVA) and poly(methyl methacrylate-co-nbutyl methacrylate) ((P(MMA-nBMA) copolymers have been studied. Structural analyses of P(VDF-HFP) copolymer is motivated by its application in drug-eluting stent as a coating material. The copolymerization of bulky HFP unit into the VDF chains influences the crystallizable segments of PVDF. These configurational defects can be correlated to the structure evolution as the function of storage time and temperature. Using the spectroscopic techniques such as infrared (IR), Raman and nuclear magnetic resonances (NMR), the configuration and conformation of P(VDF-HFP) copolymers have been analyzed. The thermal fractionation called Successive Self-nucleation/Annealing (SSA) method is adopted in order to investigate the configurational defects on the crystallizable chain sequences of P(VDF-HFP) copolymers. From the results, the configurational defects introduced by HFP units have been correlated to the multiple thermal transitions. In addition, it is interesting to find that the thermal fractionation can induce a different crystalline conformation in P(VDF-HFP) copolymers. Analysis of chain configuration and crystallizable segmental distribution in ethylene-vinyl acetate (EVA) copolymers is motivated by development of hot-melt adhesives composed mainly of EVA-Wax-tackifier multicomponents blend. In this study, the main focus is on understanding co-crystallization between ethylene segments with paraffins. Using the same thermal fractionation technique used for the characterization of P(VDF-HFP) copolymers, EVA copolymers are also studied. Due to the wide distribution of ethylene segments in EVA, it is expected that the n-alkanes of matching length can cocrystallize with EVA. The presence of co-crystallization is observed by the enhancement in crystallization and faster crystallization kinetics in the binary blends. It has been determined by Infrared spectroscopy by observing changes in the crystalline form and intermolecular interaction in the crystalline unit cell. From the results, the mechanism of co-crystallization has been proposed. Influence of copolymer configuration on the crystallization and phase behavior of ternary blends is also of great interest in order to develop polyurethane-based hot melt adhesives. The phase behavior of various ternary polymer blends containing crystallizable polyester, a non-crystallizable polyether, and an acrylic random copolymer of different chain configuration is investigated. The mean-field Flory-Huggins theory for the free energy of mixing, extended to ternary polymer blends, is adopted for predicting phase diagrams. The differences observed in the rheological processes of various ternary blends with different acrylic copolymers are directly related to changes in miscibility, associated phase behavior and chain configuration.

No description available.

Rheology modifiers are used in paints and coatings to ease their application to a surface, prevent sagging once applied, and allow the leveling of brushstrokes, among other benefits. The early rheology modifiers were hydroxyethyl celluloses (HECs), a type of non-associative thickener that is relatively inexpensive and synthesized from cellulose, which is abundant. However, coatings that are modified with HECs tend to suffer from poor leveling and syneresis (phase separation). HECs have since been replaced with associative thickeners (ATs). These thickeners, when properly formulated, produce stable dispersions that have improved rheological properties, yet, unlike HECs, are sensitive to changes to the coating formulation. This drawback has encouraged research that attempts to predict the phase behavior and rheology of systems that are modified with ATs. This work is concerned with the phase behavior and rheology of waterborne latex / hydrophobically-modified ethoxylated urethane (HEUR) AT systems. When latex volume fraction is held constant, the amount of HEUR (and surfactant) in the mixture determines whether the system experiences syneresis. Dispersion phase diagrams (DPDs) of such systems have been previously studied, but the rheology of the mixtures used to prepare the DPDs have not been studied in any detail. A study on the rheology of phase separated latex / HEUR mixtures that were prepared with commercial materials was done at Cal Poly and showed a correlation between syneresis and complex rheology. However, a proper analysis was limited because the compositions and chemical structures of the commercial materials were not well known. To better understand the relationships between phase behavior and rheology, waterborne latex / HEUR mixtures were prepared from latex and HEURs that were made at Cal Poly. Three series of mixtures were studied: commercial latex / commercial HEUR (I), commercial latex / Cal Poly HEUR (II), and Cal Poly latex / Cal Poly HEUR (III). The latex volume fraction was held constant at 0.25 and the concentration of HEUR was varied from 0–2.0 wt%. Mixtures were allowed to equilibrate for 7 days, syneresis was measured on day 7, and steady-state viscosities over a shear rate range of 0.01–1000 s-1 were determined on days 7–9 with a DHR-2 rheometer (TA Instruments) that was outfitted with 40 mm, 2o cone. The mixtures were also studied by microscopy and dynamic oscillatory testing. The chemical structures of the Cal Poly HEURs were determined by proton nuclear magnetic resonance spectroscopy (1H NMR) and the molecular weight by gel permeation chromatography (GPC). From this study, a correlation between syneresis and complex rheology was observed in I. Similar trends were observed in phase-separated II and dispersed (not phase-separated) III, though II with over 0.4 wt% HEUR were ejected from the cone / plate geometry at 1–100 s-1 and III did not demonstrate syneresis. Further investigation of dispersed II and phase-separated III is recommended to confirm the presence of the syneresis–rheology correlation of I in both II and III. In addition to these trends, only 2.1–4.2 wt% II were able to be analyzed by the single-mode Maxwell model. Also the transition from phase-separated to stable dispersion was observed with a polarized microscopy at 5x magnification. In conclusion this study represents progress in the ongoing study at Cal Poly to better understanding the mechanisms behind the syneresis and rheology of these latex / HEUR AT dispersions.