Hairy Particles: Polymer Brush-Supported Organocatalysts and Asymmetric Mixed Homopolymer Brushes

This dissertation presents the synthesis and studies of polymer brush-supported organocatalysts and asymmetric mixed homopolymer brushes grafted on particles. The brushes were synthesized from initiator-functionalized particles by surface-initiated “living” radical polymerizations. Polymer brush-supported organocatalysts were designed to combine the advantages of both soluble polymer- (high activity) and crosslinked insoluble polymer-supported catalysts (recyclability). Chapter 1 describes the synthesis of a polymer brush-supported 4-N,N-dialkylaminopyridine (DAAP) catalyst from initiator-functionalized latex particles by surface-initiated nitroxide-mediated radical polymerization (NMRP). The hairy particles efficiently catalyzed the acylation of secondary alcohols and Baylis-Hillman reaction and were recycled six times with no or negligible decrease in the reaction yield. Chapter 2 presents the synthesis of a thermosensitive polymer brush-supported DAAP by surface-initiated atom transfer radical polymerization (ATRP) from silica particles with addition of a free initiator. Both hairy particles and the free copolymer formed from the free initiator were used as catalysts for hydrolysis of nitrophenyl acetate at various temperatures. Below the lower critical solution temperature (LCST), the activity of hairy particles was very close to that of the free copolymer. LCST transitions exerted different effects on the reactions catalyzed by hairy particles and the free copolymer. Chapters 3 and 4 present the studies of the effects of chain length disparity and grafting density on phase morphology of mixed brushes grafted on silica particles. A series of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes with a fixed PtBA molecular weight and various PS molecular weights were grown from silica particles functionalized with a monochlorosilane-terminated asymmetric difunctional initiator (Y-initiator) by sequential ATRP and NMRP. The total grafting densities of these brushes were 0.6 – 0.7 chains/nm2. The morphology of mixed brushes evolved from isolated PS nanodomains, to short PS cylinders, to a nearly bicontinuous nanostructure, and a two-layered nanostructure with the change of chain length disparity of two homopolymers. To study the grafting density effect, a set of high density asymmetric mixed brushes with total grafting densities of 0.9 – 1.2 chains/nm2 was prepared from triethoxysilane- terminated Y-initiator-functionalized silica particles. The feature sizes of the patterns formed from high density mixed brushes were much smaller than those of lower density mixed brushes

Synthesis and Application of Oil-Soluble Polymer Brush-Grafted Silica Nanoparticles as Lubricant Additives for Friction and Wear Reduction

Although inorganic and metallic nanoparticles are potentially effective oil lubricant additives for friction and wear reduction, their high tendency to undergo aggregation and precipitation in base oils has been an obstacle for real-world applications. This dissertation research aims to develop oil-soluble, polymer brush-grafted nanoparticles (hairy NPs) for use as additives for base oils such as polyalphaolefin (PAO). Well-defined hairy NPs were synthesized by surface-initiated reversible addition-fragmentation chain transfer polymerization from chain transfer agent-functionalized, 23 nm silica NPs, and their lubrication properties were investigated in PAO by high-contact-stress ball-on-flat reciprocating sliding tribological tests.The effects of alkyl pendant groups of poly(alkyl methacrylate) brushes on oil dispersibility, stability, and tribological properties of hairy NPs were studied. It was found that hairy NPs with sufficiently long alkyl pendants ( \u3e 8 carbon atoms, such as 12, 13, and 16) were readily dispersed in PAO and formed homogeneous, clear dispersions with long-term stability over a wide temperature range. Significant friction and wear reductions were achieved by using 1 wt% homogenous dispersions of hairy NPs in PAO. In an effort to increase the function of polymer brushes through the introduction of triboactive phosphorus into the grafted polymers, three phosphonate-containing monomers were synthesized and copolymerized with a long alkyl methacrylate. A significant amount of phosphonate can be incorporated into the brushes without comprising the dispersibility of hairy NPs in PAO. A synergistic effect of combining hairy NPs with a phosphonium-phosphate ionic liquid as PAO additives was discovered. The lubricating performance was improved significantly when the two additives were mixed at certain ratios. Analysis showed that both silica NPs and the ionic liquid participated in the tribo-chemical reaction. These research efforts have shown that hairy NPs have promise for use as lubricant additives. Lastly, as a side project, a series of isotactic and atactic polyethers with monosulfone-containing pendants were synthesized by the reaction of corresponding poly(epichlorohydrin) with various n-alkanethiols and subsequent oxidation of thioether groups with a goal of seeking ferroelectric liquid crystalline polymers for use in solid state cooling. The isotactic poly((R)-epichlorohydrin) was synthesized by ring-opening polymerization of (R)-(-)-epichlorohydrin using a commercial methylaluminoxane as the catalyst

Brushing the hairs of transcendental entire functions

Let f be a hyperbolic transcendental entire function of finite order in the Eremenko-Lyubich class (or a finite composition of such maps), and suppose that f has a unique Fatou component. We show that the Julia set of $f$ is a Cantor bouquet; i.e. is ambiently homeomorphic to a straight brush in the sense of Aarts and Oversteegen. In particular, we show that any two such Julia sets are ambiently homeomorphic. We also show that if f\in\B has finite order (or is a finite composition of such maps), but is not necessarily hyperbolic, then the Julia set of f contains a Cantor bouquet. As part of our proof, we describe, for an arbitrary function f\in\B, a natural compactification of the dynamical plane by adding a "circle of addresses" at infinity.Comment: 19 pages. V2: Small number of minor corrections made from V

Adsorption and grafting on colloidal interfaces studied by scattering techniques

The adsorption of polymer and surfactant molecules onto colloidal particles or droplets in solution can be characterized non-destructively by scattering techniques. In a first part, the general framework of Dynamic Light Scattering, Small Angle Neutron and X-ray Scattering for the determination of the structure of adsorbed layers, and namely of the density profile, is presented. We then review recent studies of layers of the model polymer poly(ethylene oxide), as homopolymer or part of a block copolymer. In this field, scattering with contrast variation has been shown to be a powerful tool to obtain a detailed description of the layer structure. Adsorption of chemically more complex systems, including polyelectrolytes, polymer complexes, grafted chains and biomacromolecules are also discussed in this review, as well as surfactant adsorption

Hairy Tongue

Hairy tongue (lingua villosa) is a commonly observed condition of defective desquamation of the filiform papillae that results from a variety of precipitating factors. [1] The condition is most frequently referred to as black hairy tongue (lingua villosa nigra); however, hairy tongue may also appear brown, white, green, pink, or any of a variety of hues depending on the specific etiology and secondary factors (eg, use of colored mouthwashes, breath mints, candies). [2, 3] See the images below

Experimental rheology of model colloidal dispersions

Experimental rheological aspects of colloidal dispersions are now being investigated with improved skills and with better defined model systems. New methods allow more detailed investigations. The relationship between the rheological macroproperties, microproperties and processes is the focus of the most recent investigations. Better insight has been gained concerning this relationship

Synthesis and Application of Polymer Brush-Grafted Nanoparticles as Hydrogel Gelators and Lubricant Additives

This dissertation describes the synthesis of polymer brush-grafted nanoparticles (hairy NPs) and an analysis of their behavior or utility in multiple areas. The hairy NPs were synthesized from silica NPs functionalized with initiating moieties by surface-initiated atom transfer radical polymerization. A brief introduction to hairy NPs, with a focus on the synthesis and behavior of stimuli-responsive polymer brush-grafted particles, is given in Chapter 1 to provide context for this work. Chapters 2 and 3 present the synthesis of thermosensitive diblock copolymer brush-grafted nanoparticles designed as hairy NP analogues in place of thermosensitive block copolymers micelles for the construction of hybrid, physical hydrogels. Chapter 2 details a series of hairy NPs with a thermosensitive poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA) inner block and a charge-bearing, poly(DEGMMA-co-2-(methacryloyloxy)ethyltrimethylammonium iodide) (PDEGMMA-co-TMAEMA-I) outer block. These hairy particles underwent a reversible, cooling-induced gelation at moderate concentrations in water, based on the packing of hairy NPs due to the LCST-driven increase in brush volume fraction upon cooling. Another series of thermosensitive hairy NPs was made with brushes composed of P(TMAEMA-I)-b-PDEGMMA, which exhibited a heating-induced reversible gelation at concentrations as low as 3 wt % in water, due to the association of PDEGMMA outer blocks at temperatures above their LCST. The inner hydrophilic polyelectrolyte block served to bridge these domains and NPs to form a three-dimensional gel network. Chapter 4 details the use of NPs grafted with oil-soluble poly(lauryl mathacrylate) as lubricant additives. These hairy NPs showed superior stability in a poly(alphaolefin) (PAO) base lubricating oil, and the addition of 1.0 wt % hairy NPs to PAO yielded significant reductions in both friction and material wear. These gains were attributed to the formation of a load-bearing tribofilm at the rubbing interface. Chapter 5 explores the brush microphase separation of poly(n-butyl acrylate)-b-polystyrene (PnBA-b-PS) brush-grafted particles with PnBA as inner block. From TEM analysis, there appeared an evolution of phase morphology from a stripe-like nanostructure to a more uniform layered structure with increasing PS molecular weight, in qualitative agreement with simulation studies. Chapter 6 includes a look back on this dissertation work in its entirety and possible future work