Law, legislation, and local minima: Solving a problem in Hayek’s theory of common law judging, with historical examples

Friedrich Hayek, Judging, Common law, Local minima, Coverture, B53, D02, J12, K36,

Nanocomposite adhesives: Mechanical behavior with nanoclay

The major objective for this research was to examine the role of epoxy–clay nanocomposites in the area of epoxy bonding to porous stone (granite) substrates. Two bisphenol A epoxy systems were selected based on the prior work that determined optimal adhesive properties from a larger set of epoxy systems to determine the role of viscosity on the intercalation and exfoliation of the clay tactiods in the epoxy resin. The systems were characterized and mechanically tested at varying levels of intercalated and exfoliated organic clay tactiods. In the first stage of the work, epoxy–clay systems were characterized by wide-angle X-ray diffraction (WAXD) to detect inter-laminar distances of clay layers and to determine if the mixing procedures had indeed dispersed and exfoliated the clay layers sufficiently. The second stage of the work involved examining mechanical properties of the epoxy–nanoclay systems. Fracture behavior was studied using granite stone substrates in notched double lap configuration. Compressing a wedge between the cover plates induced the fracture. Fracture toughness was approximated by the load at fracture. Tensile properties were measured using cast dog bone tensile samples. The better layered silicate nanocomposite performance was seen with the lower viscosity resin. The most noticeable improvements in mechanical properties for the lower viscosity resin system were found to be maximum stress, elastic modulus, and yield stress. Increased toughness and stress whitening at 1% by weight nanoclay loading revealed that the clay can act as a shear-yielding toughening agent in this epoxy system

Stress-induced reduction of water uptake in clay-reinforced epoxy nanocomposites

Exfoliated nano-clay/epoxy composites typically contain approximately 1 nm thick layers of clay dispersed in the polymer matrix. Owing to the platy morphology of the silicate layers, exfoliated clay nanocomposites can exhibit dramatically improved barrier and mechanical properties that are not available with conventional composite materials. Since epoxy applications may exist in areas of high moisture content and under mechanically induced stress, the effect of such stressing on water uptake by epoxy-clay nanocomposites is of interest. In this work, low viscosity liquid aromatic diglycidyl ether of bisphenol A (DGEBA) epoxy resin, Epon 815C, was mixed with Montmorillonite nanoclay to produce an exfoliated clay - epoxy resin system containing 0.5% nanoclay by weight. These samples were immersed in water in stressed condition (flexural stress) to assess the effect of stress on the nanocomposite epoxy systems water uptake behavior. Application of the flexural stress affected the water uptake barrier properties for the nanoclay/epoxy nanocomposites, with the stress acting to decrease the rate of absorption as well as to decrease the equilibrium moisture content in the 0.5% loaded nanocomposite. The results revealed up to 33% reduction in water uptake for the stressed samples