Valerie V. Sheares

Surfactant solvation effects and micelle formation in ionic liquids

The formation of micelles in 1-butyl-3-methyl imidazolium chloride (BMIM-Cl) and hexafluorophosphate (BMIM-PF6) were explored using different surfactants and the solvation behavior of the new micellar-ionic liquid solutions examined using inverse gas chromatography.

Al-Cu-Fe quasicrystal/ultra-high molecular weight polyethylene composites as biomaterials for acetabular cup prosthetics

Polymer composites of Al-Cu-Fe quasicrystals and ultra-high molecular weight polyethylene (UHMWPE) were investigated for use in acetabular cup prosthetics. The wear properties of the Al-Cu-Fe/UHMWPE samples and a 440 steel ball counterface were measured. The mechanical strength of the Al-Cu-Fe/UHMWPE composites was compared to UHMWPE and alumina/UHMWPE. The biocompatibility of the composite material was tested using a direct contact cytotoxicity assay. Al-Cu-Fe/UHMWPE demonstrated lower volume loss after wear and higher mechanical strength than UHMWPE. This composite material also showed no increase in counterface wear or cytotoxicity relative to UHMWPE. These combined results demonstrate that Al-Cu-Fe/UHMWPE composites are promising candidate materials for acetabular cup prosthetics.

Development of novel polymer/quasicrystal composite materials

Abstract We report on a new class of materials, polymer/quasicrystal composites with useful properties for beneficial exploitation in applications, such as dry bearings and composite gears. Our preliminary results indicate that our new composites are a means of enhancing the properties of certain organic polymers while providing a new means of processing quasicrystals. Al–Cu–Fe quasicrystalline materials significantly improved wear resistance to volume loss in polymer-based composites. Furthermore, mechanical testing results showed a two-fold increase in the storage modulus of the reinforced composites compared with the polymer samples. The fabrication in addition to the thermal, mechanical, and wear properties of these unique materials will be described.

Fabrication and wear resistance of Al–Cu–Fe quasicrystal-epoxy composite materials

Abstract Wear resistant polymer composites are prepared using a novel filler material, Al–Cu–Fe quasicrystals (QC). Novolac epoxy filled with Al–Cu–Fe quasicrystalline powder are evaluated by pin-on-disk testing using a 52100 steel counterface. Epoxy samples filled with aluminum, copper, iron, aluminum oxide, and silicon carbide are tested for comparison. The use of Al–Cu–Fe QC powder, as a filler in epoxy, maximizes the composite wear resistance while minimizing abrasion of the 52100 steel counterface. Wear mechanisms of the Al–Cu–Fe composites were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The fabrication and wear properties of these unique materials will be described.

Alkyl-substituted poly(2,5-benzophenone)s synthesized via Ni(0)-catalyzed coupling of aromatic dichlorides and their miscible blends

High molecular weight poly(2,5-benzophenone) derivatives were prepared by Ni(0)-catalyzed coupling of 4-substituted 2,5-dichlorobenzophenones. Monomers were synthesized by the Friedel-Crafts reaction of 2,5-dichlorobenzoyl chloride and alkyl-substituted benzenes in the presence of aluminum chloride. The resulting polymers are soluble and show no evidence of crystallinity by DSC. Number average molecular weights are in the range of 9.2 × 10 3 -11.7 × 10 3 g/mol by multiple angle laser light scattering (MALLS). Molecular weights obtained by MALLS are only slightly lower (∼90%) than those obtained by GPC (polystyrene standards). These polymers exhibit high thermal stability with glass transition temperatures ranging from 173 to 225°C and weight loss occurring above 450°C in nitrogen and 430°C in air. Additionally, the polymers were blended and the resulting polymer films appear to be miscible by DSC results.

Polar, functionalized diene‐based material. III. Free‐radical polymerization of 2‐[(N,N‐dialkylamino)methyl]‐1,3‐butadienes

The bulk free-radical polymerization of 2-[((N,N-dialkylamino)methyl]-1,3-butadiene with methyl, ethyl, and n-propyl substituents was studied. The monomers were synthesized via substitution reactions of 2-bromomethyl-1,3-butadiene with the corresponding dialkylamines. For each monomer the effects of the polymerization initiator, initiator concentration, and reaction temperature on the final polymer structure, molecular weight, and glass-transition temperature (T g ) were examined. Using 2,2-azobisisobutyronitrile as the initiator at 75 °C, the resulting polymers displayed a majority of 1,4 microstructures. As the temperature was increased to 100 and 125 °C using t-butylperacetate and t-butylhydroperoxide, the percentage of the 3,4 microstructure increased. Differential scanning calorimetry indicated that all of the T g values were lower than room temperature. The T g values were higher when the majority of the polymer structure was 1,4 and decreased as the percentage of the 3,4 microstructure increased. The Diels-Alder side products found in the polymer samples were characterized using NMR and gas chromatography-mass spectrometry methods. The polymerization temperature and initiator concentration were identified as the key factors that influenced the Diels-Alder dimer yield.

Bilayer nanocomposite molecular coatings from elastomeric/rigid polymers: fabrication, morphology, and micromechanical properties

We fabricated bilayered nanocomposite coatings composed of a hard polymer layer placed on top of an elastomeric layer. The primary layer of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was attached to the surface by grafting to a chemically reactive silicon surface functionalized with epoxy-terminated SAM. The SEBS layer served as the compliant interlayer in the bilayered polymer coating. The topmost hard layer was a high performance polymer made of epoxy resin (EP) and an amino functionalized poly(paraphenylene) (PPP). We built the bilayered structure by spincoating the EP/PPP mixture on top of the grafted SEBS layer. The solidification of the topmost layer was initiated at low temperatures (40 - 50 °C) to avoid dewetting. The curing of the film was finished at 110 °C (15 hours) and the EP/PPP layer was strongly attached to the SEBS layer. It was found that the EP/PPP layer did not penetrate inside the elastic primary layer during the solidification. The elastic response of the hard polymer layer was affected significantly by the underlying elastomeric layer. The SEBS layer served as a compliant interlayer capable of dissipating the interfacial stresses originating from dissimilarities in the physical properties between the polymer coating and the inorganic substrate.

Thiophene-based poly(arylene ether)s: 5. Imide-arylene ether statistical copolymers

Abstract Imide-aryl ether thiophene copolymers were prepared and their thermal and mechanical properties were investigated. A key feature of these copolymers is the incorporation of the 2,5-thiophene moiety using 5,5′-bis[(3-aminophenoxy)thienyl-2] Ketone or 5,5′-bis[(4-aminophenoxy)thienyl-2] ketone as diamines in polyimide syntheses. The preparation of these thiophene diamines involved the nucleophilic aromatic substitution of bis(5-chlorothienyl-2) ketone with either 3- or 4-aminophenol in N -methyl-2-pyrrolidinone using potassium carbonate. These diamines were reacted with various compositions of pyromellitic dianhydride and 4,4′-oxydianiline to synthesize the desired poly(amic acid)s. Films were cast and cured (300°C) to effect the imide formation, and the resulting films showed tough ductile mechanical properties with high glass transition temperatures that decreased with increasing thiophene diamine content.