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Epoxies are commonly used in art conservation as adhesives for artifact reconstruction and repair. However, with the development of colorless epoxies, it has become more difficult to detect repair work. Fluorescent epoxies would allow for easy detection of the epoxy joints by simple visual inspection under UV light while remaining unnoticeable under normal display lighting. Coumarins are natural dyes that can be added in very small amounts to make thermosets fluoresce. Depending on the functionality of the coumarin used, the dye may be physically encapsulated in the cross-linked polymer or it may be bound to the polymer through covalent bonds. In this paper, we examine the efficacy of coumarin (1) and coumarin 480 (2) as physically encapsulated dyes and 7-hydroxycoumarin (3) and 7-glycidyloxycoumarin (4) as covalently bound dyes in a commercial epoxy thermoset, Epo-Tek 301. All four dyes could be used to make the epoxy fluorescent, but coumarins 1 and 2 slightly reduced the lap shear strength of the thermoset and could be extracted with solvent. In contrast, coumarins 3 and 4 had little effect on the mechanical properties of the epoxy and only minute amounts could be extracted.

Silica aerogels were silated with coumarin functionalities to allow for strengthening through the photochemical dimerization of the coumarin groups. Coumarin modified silica gels were prepared by either co-polymerizing tetramethoxysilane (TMOS) with small amounts of 7-(3-triethoxysilylpropoxy)coumarin (TEPC) or by surface modifying the silica gel with 7-(3-trimethoxysilylpropoxy)coumarin (TMPC). Aerogels, prepared by supercritical carbon dioxide drying, were irradiated with ultraviolet light (365 nm) for varying lengths of time and the flexural strength of cylindrical samples was measured. Copolymerization of TEPC with TMOS resulted in aerogels that, while initially weaker than pure silica aerogels, showed a 41% increase in flexural strength with 20 min exposure to UV. In contrast, the surface modified aerogels, while stronger than pure silica aerogels, showed no influence on flexural strength with exposure to UV.

Laboratory experiments to detect chloride in a cement matrix using pulse nuclear magnetic resonance (NMR) were conducted. The coils were in the centimeter scale and the magnetic field was 2.35 T. NMR signals were obtained from both aqueous chloride solution and samples of both regular and white Portland cement (WPC). A concrete sample from a sidewalk that had been in the field for 20 years was also tested. The experiments demonstrated that the signal-to-noise ratio (SNR) for a centimeter-scale cement sample volume is so small, even after averaging, that sample volumes much lower than that are unlikely to produce measurable signals at fields of 1 T or below. The consequence is that the potential for realizing an embedded NMR-based sensor including the magnet is low. Parametric studies identify feasible alternative coil diameters and magnetic field strengths for detecting chloride ion concentrations in hardened concrete.

Monitoring chloride concentration and transport in concrete structures susceptible to corrosion of embedded steel reinforcement is a challenge as difficult as it is important. An embedded sensor based on nuclear magnetic resonance (NMR) would be a good solution to the problem because it would make a non-destructive atom-specific measurement of the presence and concentration of chloride. The important question is the scale of the device required to detect the chloride. Laboratory experiments to detect chloride in a cement matrix using pulse-NMR were conducted to assess the potential of this application; they provided a basis for projecting the scale of a device that would have a good chance of success. The coils were cm-scale and the magnetic field was 2.35 T. NMR signals were obtained from both aqueous chloride solution and samples of both regular and white portland cement. The experiments demonstrated that the signal-to-noise ratio (SNR) for a cm-scale cement sample volume is so small, even after averaging, that sample volumes much lower than that are unlikely to produce measurable signals at fields of 1 T or below. Thus the potential for realizing an embedded NMR-based sensor including the magnet is low. Parametric studies identify feasible alternative coil diameters and magnetic field strengths for detecting chloride ion concentrations in hardened concrete.

CMOS MEMS devices, fabricated from up to 13 layers of materials to create independent conducting paths, are subject to incremental fracture at high stress and to charging effects. This paper expands on preliminary reserach, which has revealed several stages of change in CMOS MEMS physical properties as they are exposed to resonant motion. Cracks are the first induced inside the stiffest lasyers, often silicon dioxide, in laterally resonant test structures with cyclic stress of 620 Mpa. Prior to cracking, the aluminum top layer of the structure can also deform, which affects the electrical integrity of the conductor. Measured frequency reponses of folded-flexure resonators demonstrate a nonlinear Duffling effect, producing mushroom-shaped resonant peak. Cyclic stress of 70 Mpa at the maximal stress points was insufficient to induce significant mechanical fracture in foled flexure resonators after 5 billion cycles, however an onset of change in stiffness was detected. Devices with a fixed dc actuation voltage experienced a change in electrostatic force attributed to charge accumulation in polymer and oxide layers. The force decayed with an approximate one-hour time constant while resonant frequency and quality factor remained constant.