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This paper describes the consequences of pair interactions in dilute suspensions of rigid rods of length 2l and radius a subjected to weak, steady shear flows. The combination of hydrodynamic and Brownian forces increases alignment with the flow, thereby enhancing the shear thinning and strain thickening expected from dilute theories. The theory is asymptotic in Pe [Lt ] 1 and ε = (ln 2l/a)−1 [Lt ] 1 but requires an ad hoc approximation to simplify the form of the hydrodynamic interactions and the rod-rod excluded volume. The theoretical predictions of the Huggins coefficient in simple shear flow are compared with data in the literature for Xanthan gum, a semi-rigid biopolymer. Comparison with semi-dilute theories emphasizes the fundamentally different nature of the interactions in the two regimes and indicates that the transition between the two lies in the range 1.5 [les ][η]0 n [les ] 6.

The strengths of epoxy/aluminum joints reinforced with a zirconium-silicon based sol-gel adhesion promoter were investigated using an ADCB (Asymmetric Double Cantilever Beam) wedge test. The fracture energies and loci of failure of these joints were shown to depend upon the mixity of the normal and shear modes of stress acting at the crack. The ADCB geometry enabled the crack to propagate along the epoxy/aluminum interfaces so that the effect of surface pretreatment and the processing conditions of the adhesion promoter on adhesion strength could be directly evaluated. The dry strength of these joints depends on the thickness of the sol-gel film derived from different concentrations of the precursors. Thinner films are more fully crosslinked and thus give higher adhesion strengths than those obtained with thicker films. The differences in the wet strengths of the sol-gel reinforced joints for various surface pretreatments suggest that the sol-gel films are subject to moisture degradation with certain surface pretreatments. The loci of failure of many of these joints alternate between the sol-gel/aluminum and epoxy/sol-gel interfaces. This behavior is similar to that observed more generally in adhesively-bonded joints tested in DCB (Double Cantilever Beam) geometry. The brittle versus ductile behavior associated with the failure process reveals important information about how the sol-gel films affect the adhesion strength.

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Insect residue adhesion to moving surfaces such as turbine blades and aircraft not only causes surface contamination problems but also increases drag on these surfaces. Insect fouling during takeoff, climb and landing can result in increased drag and fuel consumption for aircraft with laminar-flow surfaces. Hence, certain topographical and chemical features of non-wettable surfaces need to be designed properly for preventing insect residue accumulation on surfaces. In this work, we developed a superhydrophobic coating that is able to maintain negligible levels of insect residue after 100 high speed (50 m/s) insect impact events produced in a wind tunnel. The coating comprises alternating layers of a hydrophobic, perfluorinated acrylic copolymer and hydrophobic surface functional silicon dioxide nanoparticles that are infused into one another by successive thermal treatments. The design of this coating was achieved as a result of various experiments conducted in the wind tunnel by using a series of superhydrophobic surfaces made by the combination of the same polymer and nanoparticles in the form of nanocomposites with varying surface texture and self-cleaning hydrophobicity properties. Moreover, the coating demonstrated acceptable levels of wear abrasion and substrate adhesion resistance against pencil hardness, dry/wet scribed tape peel adhesion and 17.5 kPa Taber linear abraser tests.

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