MANIPULATING SINGLE POLYMER MOLECULES FOR APPLICATIONS IN NANOMATERIALS

Polymeric nanoparticles have been utilized in an increasing number of fields over the past two decades due to their unique properties such as design flexibility and good biocompatibility. Despite various techniques available to produce polymer nanoparticles, the preparation of small nanoparticles with customized functions in the sub 20 nm dimension remains challenging. Inspired by the self-organizing behavior of natural biomacromolecules, a class of single-chain nanoparticles (SCNP) are synthesized featuring biomimicry and ultrafine size. These nanoparticles are prepared from self-folding of polymer precursors bearing reactive pendant groups by intramolecular cross-linking reactions. A variety of cross-linking chemistries are available including covalent, dynamic covalent and non-covalent chemistries. Among these methods intramolecular polymerization is of particular importance as it allows for easy control of an SCNP’s degree of cross-linking, and lead to SCNP with tunable level of compaction. The aim of this dissertation is to 1) provide a comprehensive overview of recent advances in the field of single-chain folding; 2) investigate the synthesis of SCNP by intramolecular polymerizations, and 3) study the synthetic variations relating to the efficiency of a polymer’s self-folding by intramolecular polymerization. Chapter 2 of this work discusses the synthesis of poly(oxanorbornene imide) single-chain nanoparticles by intrachain radical polymerization of pendant methacryloyl units. Structure/ property relationships related to methacryloyl pendant length and percent incorporation were studied. Chapter 3 investigates the synthesis of an epoxide-maleimide bifunctional monomer, and its ring-opening polymerization to afford polyethyleneglycol based polymer precursor. The polymer precursor could undergo intramolecular radical polymerization to afford SCNP, and the cross-linked moiety could potentially be isolated for the study of degree of intrachain polymerization. Chapter 4 expands the scope of intrachain polymerization and explores the synthesis of SCNP by intramolecular ring-opening metathesis polymerization (ROMP). A series of poly(pentafluoro-methacrylate)s containing pendant norbornene imide groups was synthesized and subjected to intrachain ROMP. The efficiency of chain folding was explored relating to norbornene content on the polymer precursor, species and feed ratio of Grubbs catalysts, as well as doping effects of fluorinated aromatic comonomer

Plasmonic atoms and molecules for imaging and sensing

Nanoscale structures play a fundamental role in diverse scientific areas, including biology and information technology. It is necessary to develop methods that can observe nanoscale structures and dynamic processes that involve them. Colloidal plasmonic nanoparticles (plasmonic “atoms”) and their clusters (plasmonic “molecules”) are nanoscale objects with remarkable optical properties that provide new opportunities for sensing and imaging on the relevant length and time scales. Many biology questions require optically monitoring of the dynamic behavior of biological systems on single molecule level. In contrast to the commonly used fluorescent probes which have the problem of bleaching, blinking and relatively weak signals, plasmonic probes display superb brightness, persistency and photostability, thus enable long observation time and high temporal and spacial resolutions. When plasmonic atoms are clustered together, their resonances redshift while the intensities increase as a result of plasmon coupling. These optical responses are dependent on the interparticle gaps and the overall geometry, which makes plasmonic molecules capable of detecting biomolecule clustering and measuring nanometer scale distance fluctuations. In this dissertation, individual plasmonic atoms are firstly evaluated as imaging probe and their interactions with lipid membrane are tested on a newly developed on-chip black lipid membrane system. Subsequently, plasmonic dimers (plasmon rulers) prepared through DNA-programmed self-assembly are monitored to detect the mechanical properties of single biopolymers. Measurement of the spring constant of short (tens of nucleotides or base pairs) DNAs is demonstrated through plasmon coupling microscopy. Colloidal plasmonic atoms of various materials, sizes and shapes scatter vivid colors in the full-visible range. Assembling them into plasmonic molecules provides additional degrees of freedom for color manipulation. More importantly, the electric field in the gaps of plasmonic molecules can be enhanced by several orders of magnitude, which is highly desirable in single molecule sensing applications. In this dissertation, the fundamentals of plasmonic coupling are investigated through one-dimensional gold nanosphere chains. Using the directed self-assembly approach, multichromatic color-switchable plasmonic nanopixels composed of plasmonic atoms and molecules of various materials, sizes, shapes and geometries are integrated in one image with nanometer precision, which facilitates the encoding of complex spectral features with high relevance in security tagging and high density optical data storage.2017-01-01T00:00:00

Development of a titanium sheet manufacturing process via direct powder rolling and spark plasma sintering.

Masters Degree. University of KwaZulu-Natal, Durban.The intention of this research was the improvement of titanium processing in South African industry. South Africa currently has limited ability to efficiently process its titanium reserves and the results of this research, combined with other work in the associated research consortium, has the potential to lead to significant positive economic impact. A novel method of titanium processing, combining the processes of direct powder rolling (DPR) and spark plasma sintering (SPS), was explored in the course of this research. A rolling mill was designed using modelling and simulation techniques, manufactured based on the resulting design, and the DPR-SPS process parametrically tested on the rolling mill using commercially pure titanium powder. The mechanical aspects of this project included experimental testing on a range of titanium powder samples to determine the properties of the powder, modelling of the rolling mill behaviour using MATLAB, 3D modelling of the proposed and iterated rolling mill frame design and its components using Siemens NX and OnShape, finite element analysis of the rolling mill frame and auxiliary components using Siemens NX, and manufacture and parametric testing of the mill for titanium powder compaction. The electrical aspects of this project included connecting and programming a variable speed drive and AC motor to control the speed of the mill rolls, simulating the behaviour of the integrated SPS-type sintering circuit using Simulink, designing a suitable method for safely and effectively transmitting the large SPS current to the rotating rolls, and building and testing the circuit for titanium compact spark plasma sintering. The manufactured direct powder rolling mill compacts titanium powder into strip through a pair of rolls, measuring 350mm diameter and 50mm width. Each of the rolls is mounted on the same shaft as a worm-driven gear. A 5.5kW three phase AC motor drives the worm shafts, which have opposing threads to ensure the rolls rotate in opposing directions. The worm and gear arrangement serves to both evenly transmit the drive power to both rolls, and to increase the torque from the motor to the rolls. The motor is controlled using a variable speed drive – this allows the roll speed to be adjusted as necessary, to optimise the consolidation process. The bearings used on the roll and worm shafts were designed and manufactured using an insulating bearing material to ensure the current used for sintering is not instead transmitted through the steel rolling mill frame. Flexible couplings with polymeric inserts isolate this current from the motor and between each worm gear. The minimum density of the green compact required for further handling was determined empirically as being greater than 65 % of the theoretical density of titanium. The mill was designed for an optimal density of 81%. The density range achieved by varying the parameters of roll speed, number of passes through the mill, and roll gap, was 55 – 84%. It is expected that the strip density may be greatly increased with implementation of the improvements and parameter changes identified. The spark plasma sintering circuit sinters the titanium either during the direct powder compaction process (simultaneous DPR-SPS), or following it (sequential DPR-SPS) during re-rolling through the same set of rolls used for compaction. A number of electrical circuits with different output types were designed for the SPS process; one of these was built and tested towards proof of concept of the DPR-SPS process. The tested circuit uses a DC source to apply a sintering current through the titanium sample. Application of the SPS current to the titanium resulted in a theoretical density increase of 11 –14% compared to DPR only, depending on whether the processes were performed sequentially orsimultaneously This multidisciplinary project employed a broad range of combined materials, mechanical and electrical design and analysis methods. The resulting mill can be used as is for further parametric testing, improved as will be discussed for the same process, or adapted to a range of different applications

Modular and Dynamic Approaches to the Formation of Single-chain Polymer Nanoparticles

The methodology towards the creation of nanoscale polymeric objects by way of the folding of single polymer chains has been enjoying success in the field of polymer chemistry and materials science. By synthesizing polymer chains with built in functionality either through functional side groups, or direct incorporation into the polymer backbone, polymer chemists are able to fold single polymer chains onto themselves through a broad range of covalent and non-covalent interactions in dilute solution. These compact, nano-sized objects can now be used in a wide arrange of functions and applications. The aim of this dissertation is to provide first, a comprehensive overview of the recent advances and success enjoyed by this field and second, to showcase some of the various routes towards the dynamic and modular creation of these single-chain polymer nanoparticles (SCNPs). Chapter 2 of this work discusses the use of dynamic covalent cross-linking chemistry via reversible disulfide bridges in the folding and unfolding of SCNPs. Through the use of triple detection size-exclusion chromatography (SEC) it was shown through changes in retention time, a phenomena indicative of hydrodynamic volume, a polymer was being folded into compact SCNPs and then unfolded and refolded via redox chemistry. Chapter 3 explores the design of polymers that had various different cross-linkable moieties incorporated into the monomer side units. By having cross-linkable moieties that can undergo different chemical cross-linking reactions (i.e thiol-yne click reactions, epoxide ring-opening reactions, activated esters), a modular approach towards the folding and subsequent functionalization of SCNPs is created. Looking to design a system with a greater degree of control over the modular functionality, chapter 4 investigates the use of norbornene imide monomers containing pentafluorophenyl activated esters with varying methylene spacer unites between the polymerizable olefin and the activated ester. It was here that an unexpected phenomena was observed; the doping effects of fluorinated aromatic hydrocarbons (FAHs) on second and third generation Grubbs’ catalysts. This chapter aims to shed some light on this subject. Finally in chapter 5 an additional click-chemistry reaction is observed to take place with pentafluorophenyl methacrylate. Thiol-para fluoro click reactions are used to react with the pentafluorophenyl activated esters, while still leaving the ester moiety reactive towards primary alkyl amines

Reverse Osmosis and Ultrafiltration Membrane Surface Nano-Structuring with Tethered Hydrophilic Polymer Layers for Seawater Desalination

A systematic investigation of membrane surface nano-structuring (SNS) with surface tethered hydrophilic polymer layers was conducted in order to mitigate fouling of reverse osmosis (RO) and ultrafiltration (UF) membranes and tune membrane performance in seawater desalination. Surface tethered hydrophilic polymer (i.e., polyacrylic acid (PAA)) layers were synthesized onto base polysulfone (PSf) UF and polyamide (PA) thin film composite (TFC) RO membranes via membrane surface activation with an atmospheric pressure plasma (APP), followed by graft polymerization (GP) of acrylic acid. Both APP surface activation and GP conditions impacted the structure of the synthesized tethered PAA layers and RO membrane desalination performance. Detailed characterization of tethered PAA chain extension length via atomic force microscopy (AFM) based force spectroscopy (FS) revealed that the number average molecular weight of the synthesized tethered PAA chains was estimated to be in the range of ∼13,000–35,000 with chain-chain separation of 1.5–2.4 nm. Extension of the tethered PAA chains in DI water was significantly greater in DI water than in high salinity aqueous environment. UF fouling stress tests with alginic acid in high salinity water and post-cleaning with non-saline water demonstrated permeability restoration of up to 90–100% for a surface nano-structured (SNS)-PAA-PSf membrane relative to 50–70% for the native PSf membrane. Synthesized SNS-PAA-PA BWRO and SWRO membranes having water and salt permeability coefficient in the range of 2.3 – 3.4 L�m-2�h-1�bar-1 and 0.15 – 0.54 L�m-2�h-1 revealed that membrane surface structuring with a tethered PAA layer enabled tuning membrane performance (in terms of Lp and B) to achieve water/salt selectivity (evaluated as Lp:B ratio) that was significantly higher (by up to 56%) relative to the base PA membranes. It was demonstrated that, depending on APP surface activation and GP conditions, PA TFC membranes could be tuned to have essentially the same salt rejection over a wide permeability range or a given permeability over a range of salt rejection. It was also shown that membrane performance could be achieved that overcomes the permeability-selectivity trade-off. Lastly, the present study developed an approach to scale up the APP surface activation and GP process by performing membrane surface nano-structuring for large PA TFC flat sheet membranes that are suitable for fabricating 2.5” x 21” spiral wound RO elements

Evaluation of U.S. and European Concrete Pavement Noise Reduction Methods, July 2006

Highway noise is one of the most pressing of the surface characteristics issues facing the concrete paving industry. This is particularly true in urban areas, where not only is there a higher population density near major thoroughfares, but also a greater volume of commuter traffic (Sandberg and Ejsmont 2002; van Keulen 2004). To help address this issue, the National Concrete Pavement Technology Center (CP Tech Center) at Iowa State University (ISU), Federal Highway Administration (FHWA), American Concrete Pavement Association (ACPA), and other organizations have partnered to conduct a multi-part, seven-year Concrete Pavement Surface Characteristics Project. This document contains the results of Part 1, Task 2, of the ISU-FHWA project, addressing the noise issue by evaluating conventional and innovative concrete pavement noise reduction methods. The first objective of this task was to determine what if any concrete surface textures currently constructed in the United States or Europe were considered quiet, had long-term friction characteristics, could be consistently built, and were cost effective. Any specifications of such concrete textures would be included in this report. The second objective was to determine whether any promising new concrete pavement surfaces to control tire-pavement noise and friction were in the development stage and, if so, what further research was necessary. The final objective was to identify measurement techniques used in the evaluation

The Journal of ERW and Mine Action Issue 15.2 (2011)

Victim Assistance | Deminers on the Frontline | Information Systems and GIS Mapping | Notes from the Field | Research and Developmen