Ph.D Candidate, The University Of Melbourne
Thin polymer films are used in a large variety of applications, from batteries, medical and other electronic devices to gas and water filtration. The properties of these materials can be targeted by engineering the polymers for specific applications. For example, they can change how well the surface repels water, oils, bacteria and other contaminants, or how different chemicals of interest interact with the surface. The Continuous Assembly of Polymers (CAP) method is a robust technique for forming polymer thin films and has a number of advantages over other techniques. Namely, they form virtually pinhole-hole free films and can be built up multiple times to easily create multilayered films. Inclusion of different chemistries in each layer can allow for novel surface compositions not readily available using other techniques. This work describes a method to create patterned multilayered ultrathin films using the CAP process, allowing for the process and advantages that the CAP method has to offer to be used in device manufacture and other applications where patterned polymer films are required.
Abstract: High-density polynorbornene azobenzene liquid-crystalline brushes are synthesized on quartz substrates by surface-initiated ring-opening metathesis polymerization (SI-ROMP) using Grubbs third-generation catalyst. The grafting process is controlled over the thickness of the brush from a solid-supported substrate in a stoichiometric manner. A highly ordered liquid-crystal arrangement was formed for such brushes as revealed by spectroscopic measurements and grazing angle X-ray diffraction analysis. Marked features of this method in the structure and photoalignment behavior are unveiled by comparison with brushes made by surface-initiated atom-transfer radical polymerization (SI-ATRP).
Pub.: 04 Jun '13, Pinned: 31 Jul '17
Abstract: This article reports the enhanced rate of the surface-initiated polymerization (SIP) of 5-(perfluoro-n-alkyl)norbornenes (NBFn) by combining two SIP techniques, namely surface-initiated atom-transfer polymerization (SI-ATRP) to grow a macroinitiator and surface-initiated ring-opening metathesis polymerization (SI-ROMP) to produce the final coating. This polymerization approach promotes the rapid growth of dense partially fluorinated coatings that are highly hydrophobic and oleophobic and yield thicknesses from 4-12 μm. Specifically, the growth rate and the limiting thickness of pNBFn with different side chain lengths (n = 4, 6, 8, and 10) at various monomer concentrations and temperatures are evaluated through two approaches: growing the polymer from an initiator-terminated monolayer (control) or from a modified poly(2-hydroxyethyl methacrylate) (PHEMA) macroinitiator. X-ray photoelectron spectroscopy (XPS) analysis shows that 38% of the hydroxyl termini in the macroinitiator react with a norbornenyl diacid chloride (NBDAC) molecule, and 7% of such anchored norbornenyl groups react with a catalyst molecule. The kinetic data have been modeled to determine the propagation velocity and the termination rate constant. The PHEMA macroinitiator provides thicker films and faster growth as compared to the monolayer, achieving a 12 μm thick coating of pNBF8 in 15 min. Increasing the monomer side chain length, n, from 4 to 10 improves the growth rate and the limiting polymer thickness. Performing the polymerization process at higher temperature increases the growth rate and the limiting thickness as evidenced by an increase in the film growth rate constant. Arrhenius plots show that the reactions involved in the macroinitiation process exhibit lower activation energies than those formed from a monolayer. Electrochemical impedance spectroscopy reveals that the films exhibit resistance against ion transport in excess of 1 × 10(10) Ω·cm(2).
Pub.: 13 Sep '13, Pinned: 31 Jul '17
Abstract: Ultra-thin (∼100 nm) films with uniform thicknesses can facilitate high CO2 permeation and are of potential technological significance for CO2 capture. Among many approaches for obtaining such materials, the recently developed continuous assembly of polymers (CAP) technology provides a robust process, allowing for the production of defect-free, cross-linked and surface-confined thin films with nanometer scale precision. Through utilization of this nanotechnology, we have constructed composite membranes containing cross-linked ultra-thin surface films. The membrane materials formed exhibited significantly high permeances as well as excellent gas separation selectivity.
Pub.: 10 Nov '15, Pinned: 31 Jul '17
Abstract: We report that the continuous assembly of polymers (CAP) approach, mediated by ring-opening metathesis polymerization (ROMP), is a facile and versatile technology to prepare engineered nanocoatings for various biomedical applications. Low-fouling coatings on particles were obtained by the formation of multicompositional, layered films via simple and efficient tandem CAP(ROMP) processes that are analogous to chain extension reactions. In addition, the CAP(ROMP) approach allows for the efficient postfunctionalization of the CAP films with bioactive moieties via cross-metathesis reactions between the surface-immobilized catalysts and symmetrical alkene derivatives. The combined features of the CAP(ROMP) approach (i.e., versatile polymer selection and facile functionalization) allow for the fabrication and surface modification of various types of polymer films, including those with intrinsic protein-repellent properties and selective protein recognition capabilities. This study highlights the various types of advanced coatings and materials that the CAP approach can be used to generate, which may be useful for biomedical applications.
Pub.: 04 Jul '13, Pinned: 31 Jul '17
Abstract: Surface-confined ultra-thin polyrotaxane (PRX)-based films with tunable composition, surface topology and swelling characteristics were prepared by solid-state continuous assembly of polymers (ssCAP). The PRX-based films supported cell attachment, and their degradation in biological media could be tuned. This study provides a versatile nano-coating technology with potential applications in biomedicine, including tissue engineering and medical devices.
Pub.: 10 Dec '14, Pinned: 31 Jul '17
Abstract: This manuscript describes the versatile fabrication and characterization of a novel composite membrane that consists of a porous alumina support, a 100 nm thick nanoporous gold coating, and a selective poly(5-(perfluorohexyl)norbornene) (pNBF6) polymer that can be grown exclusively from the nanoporous gold or throughout the membrane. Integration of the three materials is achieved by means of silane and thiol chemistry, and the use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) to grow the pNBF6. The use of SI-ROMP allows tailoring of the extent of polymerization of pNBF6 throughout the structure by varying polymerization time. Scanning electron microscopy (SEM) images indicate that the thin polymer films cover the structure entirely. Cross-sectional SEM images of the membrane not only corroborate growth of the pNBF6 polymer within both the porous alumina and the nanoporous gold coating but also show the growth of a pNBF6 layer between these porous substrates that lifts the nanoporous gold coating away from the alumina. Advancing contact angle (θ(A)) measurements show that the surfaces of these composite membranes exhibit both hydrophobic (θ(A) = 121-129)° and oleophobic (θ(A) = 69-74)° behavior due to the fluorocarbon side chains of the pNBF6 polymer that dominate the surface. Results from electrochemical impedance spectroscopy (EIS) confirm that the membranes provide effective barriers to aqueous ions, as evidenced by a resistive impedance on the order of 1 × 10(7) Ω cm(2). Sulfonation of the polymer backbone substantially enhances ion transport through the composite membrane, as indicated by a 40-60 fold reduction in resistive impedance. Ion transport and selectivity of the membrane change by regulating the polymerization time. The fluorinated nature of the sulfonated polymer renders the membrane selective toward molecules with similar chemical characteristics.
Pub.: 27 Dec '11, Pinned: 31 Jul '17
Abstract: Ring-opening metathesis polymerization, or ROMP, has been known in the world of polymers as a success story. With its discovery in the middle of the 20th century, the study and understanding of this reaction led to its adoption in a multitude of areas in both academic and industrial domains. However, with the general shift towards hybrid materials and better material integration, surface-initiated polymerization (SIP) has been an area of great interest that ROMP has only tapped into at the very end of the 20th century. With this point in mind, we demonstrate another pathway towards SIP using the si-ROMP approach to form block-copolymers of poly(ethylene-oxide)-poly(norbornene) (PEO-PNB) brushes on particles of titania. In this study, particle modification was first performed and studied, which was then applied towards coating larger, curved tubes to assess their ability for surface modification. In the case of particles, each step was analyzed by XPS to ensure that the expected elements appeared. TGA was then implemented to determine the general grafting density of the PEO chains on the surface, which was found to be 2.7 molecules per nm2. TGA could also determine the degree of polymerization (DP) of the polynorbornene chain, which was 12500. Finally, SEM was used to image the final products, both film formation using particles, and after use of these particles as a surface coating to cover larger surface areas for surface modification. The functionalized titania particles are determined to be an interesting candidate material for a “seed” layer, which can be used for larger surface modification.
Pub.: 14 Mar '16, Pinned: 31 Jul '17
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