Browsing by Author "Laibinis, Paul E."
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Item Assembling nanoparticle-assembled capsules on a planar substrate(2006) Yoo, Regina Mi-Kyung; Wong, Michael S.; Laibinis, Paul E.In this thesis, a technique to assemble nanoparticle-assembled capsules (NACs) onto a planar substrate has been demonstrated. NACs are micron-sized spherical capsules produced from organic and inorganic materials. New sensing materials of various length scales are needed for numerous sensing needs of today, and NACs on substrate are interesting to investigate. Several parameters were optimized to achieve maximum surface density of capsules (0.09 NACs/mum 2). NACs are best adsorbed onto negatively charged surface. The NaCl concentration in the poly(diallyldimethylammonium chloride) and poly(styrene sulfonic acid) solutions used to coat the glass coverslip substrate should be at least 1 M. In addition, a minimum of one bilayer of PDADMAC/PSS is required. The deposition time required to achieve the maximum density was at least 10 minutes. Finally, aging NACs before assembling them on the substrate decreased NAC coverage on the surface which could be attributed to change in NACs' surface charge.Item Development of surface-initiated atom transfer radical polymerization for the synthesis of functional biomaterials(2007) Khapli, Sachin; Laibinis, Paul E.The research presented in this thesis is focused towards applying Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) for the synthesis of functional biomaterials. ATRP is a method of living radical polymerization which gives control over the polymer chain length and the end group. SI-ATRP is carried out after immobilization of the molecules that initiate ATRP on surfaces (Gold, Glass, and Silicon). When a surface modified with the initiator molecules is exposed to polymerization solution, the resulting polymer chains are covalently bound; yielding a densely grafted polymer brush. I have developed the SI-ATRP of commercially available oligo(ethylene glycol) methacrylate (OEGMA) monomers to prepare nanoscale poly(OEGMA) coatings that expose PEG chains in high surface density. Protein adsorption for plasma proteins (lysozyme, fibrinogen, and albumin) as measured by XPS shows that, these coatings exhibit remarkable resistance against protein adsorption that depends on the attributes of the monomer. Polymer films thicker than 3 nm are effective in retarding protein adsorption with the level of proteins adsorbed on these films being 99.4% less than that on a bare Silicon surface. I have also evaluated the effects of chain length and end group of the monomers on the kinetics of their polymerization and the wettabilities of the resulting films. Poly(NiPAAm) gels that exhibit a thermal phase transition at 32°C have been widely studied for possible applications in drug delivery systems. I have applied SI-ATRP to synthesize diblock, random, and gradient copolymer brushes of NiPAAm and OEGMA with a goal to obtain polymeric films with an outer biocompatible surface and an inner bulk capable of swelling-deswelling transition. XPS and wetting studies are employed to characterize these coatings. Reactivity ratios in the copolymerization of NiPAArn and OEGMA through SI-ATRP are determined by application of the Mayo-Lewis terminal model of copolymerization. Observed monomer reactivity ratios---r1 (for NiPAAm) and r 2 (for PEGMA, MW 300)---are 0.07 and 3.85, respectively. Finally, the techniques developed above are applied to create a nanoscale device capable of photothermally triggered drug release. Nanoshell-PNiPAAm hybrids are synthesized by SI-ATRP of NiPAAm on gold nanoshells and characterized by XPS and TEM.Item Nanoscale polymeric coatings that inhibit adsorption of proteins(2005) Khapli, Sachin; Laibinis, Paul E.The ability of an artificial surface to resist the non-specific adsorption of proteins in biological solutions greatly improves its biocompatibility---a desirable property to overcome many problems across the biomedical and biochemical processing areas. This thesis demonstrates the effectiveness of surface-initiated atom transfer radical polymerization for the synthesis of hydrophilic, protein resistant coatings with controlled thicknesses in the nanoscale regime (1--100 nm). The strategy uses the surface initiated atom transfer radical polymerization of commercially available oligo(ethylene glycol) methacrylate monomers with different chain lengths and either hydroxyl or methoxy group terminations. This thesis evaluated the effects of chain length and end group of the monomers on the kinetics of their polymerization and the protein resistance of the resulting films. Protein adsorption for plasma proteins (lysozyme, fibrinogen, and albumin) as measured by XPS shows that, these coatings show remarkable resistance against protein adsorption that depends on the attributes of the monomer.Item Protein adsorption on tailored oligo(ethylene glycol) surfaces(2006) Griffin, Vesta Leigh; Laibinis, Paul E.Unwanted protein adsorption is a problem in many areas of biotechnology and medicine where biological samples contact the surface of a material. This thesis has employed self-assembled monolayers (SAMs) of controlled composition to examine the influence that specific chemical interactions have on the protein adsorption characteristics of a surface. Specifically, the effects of surface hydrophilicity and of conformational mobility were examined using a series of mixed SAMs formed on gold, where one component included a terminating oligo(ethylene glycol) (OEG) tail group and the other was a simple unsubstituted n-alkyl chain used to modulate the surface energy of the mixed SAM and the free space available to the OEG tail group. The composition of the surface was easily varied by changing the ratio of alkanethiols in a solution used to form the SAM. The resulting mixed SAMs were characterized by wetting measurements using water, ellipsometry to determine film thickness, and x-ray photoelectron spectroscopy (XPS) to determine composition. (Abstract shortened by UMI.)Item Structure, wettability, and barrier properties of self-assembled monolayers on metallic surfaces(2007) Srivastava, Piyush; Chapman, Walter G.; Laibinis, Paul E.Self-assembled monolayers (SAMs) offer a convenient approach for fabricating molecularly tailored interfaces with well-defined compositions, structures, and thicknesses. SAMs have been suggested for use as corrosion barriers, antifouling coatings, and as components of molecular electronics and lithography. Still, researchers lack the molecular description of the interfacial properties, structural features, and barrier properties of SAMs that would be useful for optimizing and tailoring the behavior of SAMs. This dissertation makes connections between the molecular level structural features of SAMs and macroscopic properties such as wettability and barrier properties using molecular dynamics (MD) simulations and experimental techniques. MD simulations were performed to explain the unexpected experimental observation that the wetting properties of some liquids on SAMs prepared using alkanethiols (CnSH) depend on whether the chain length (n) is odd or even. The difference in near-surface structure of the liquid (and not that of reorganization events by the monolayer) appears responsible for the high sensitivity of hexadecane and the general insensitivity of water to the structural differences expressed by odd- and even-chained monolayer surfaces. MD simulations were also performed to investigate the influences of molecular structure on the ability of n-alkanethiolate SAMs on gold and copper to act as barrier films against through-film oxygen transport as relevant to the uses of these films in corrosion inhibition. The barrier resistances offered by these films towards oxygen transport, as calculated by the MD simulations, were a function of the crystallinity of the center region of the SAMs. Upon the introduction of an ether linkage within the SAM, the results from MD simulations show that when the ether linkage is too close to the metal surface or to the chain ends, the free energy barrier of SAMs towards oxygen diffusion was almost 10 kJ/mole less than that for an n-alkanethiolate SAM having the same chain length. Phytanylthiol (3, 7, 11, 15-tetramethyl-hexadecanethiol) SAM on gold was characterized by ellipsometry, wetting measurements, X-ray photoelectron spectroscopy, and MD simulations to gain insights into the effect of a branched chain on the thickness, chain packing and orientation, wettability, and barrier properties of a SAM. These experimental and computational studies indicate that phytanylthiolate SAM on gold contains a fully extended 16-carbon backbone which is more disordered as compared to n-hexadecanethiolate monolayer on gold, with the sulfur head group possibly occupying four-fold hollow sites on gold.