Mechanisms of repellency

There are different ways that low energy surfaces can be applied to textiles. The first way is mechanical incorporation of the water-repellent prodncts in or on the fibre and fabric surface, in the fibre pores and in the spacing between the fibres and the yams. Examples of these are paraffin emulsions. Another approach is the chemical reaction of the repellent material with the fibre snrface. Examples of these are fatty acid resins. Yet another method is the formation of a repellent fihn on the fibre surface. Examples of these are silicone and flnorocarbon prodncts. The final approach is to use special fabric constructions like stretched polytetrafluoroethylene films (Goretex), films of hydrophilic polyester (Sympatex) and microporous coatings (hydrophilic modified polynrethanes). 

1 Fatty acid metal salts. A, hydrophobic interactions B, polar interactions C, fibre surface. 

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The question might be asked whether the reaction to a toxic material In the food Is any more effective at altering food habits than the other possible mechanism of repellent action, a simple bad-taste effect. Two lines of evidence suggest an answer to this question. First, and most powerful. Is the evidence, discussed above from plant evolution. The plants have emphasized defenses that adversely effect the physiology of their vertebrate predators, they have not frequently used taste stimuli except as cues to toxic events. Second, Is an experiment (30) that directly compared the effectiveness of toxic and non-toxic materials at altering the feeding behavior of red-winged blackbirds. 

Deet is the most widely used mosquito repellent. It was codeveloped by the U.S. military and the USDA as an insect repellent in 1946 and later introduced for public use. Despite several research studies and the wide use of deet for more than five decades, the precise mechanism of repellent action of deet is still being researched, although there are several theories. It seans possible that natural insect repellents act in a similar way, and several hypotheses have recently been reviewed." Curiosity about the mechanism of repellency has resnlted in major advances in nnderstanding how insects perceive odors. This topic has recently been reviewed." Several human-specific kairomones have been hypothesized to attract mosquitoes. Potential kairomones include carbon dioxide, lactic acid, and l-octen-S-ol." The pioneering studies performed by Davis and Sokolove on the mechanism of deet repellency reported that deet blocks the detection of human kairomones. Specifically, Davis and Sokolove showed that carbon dioxide works independently of lactic acid and deet inhibits lactic acid-sensitive neurons. Further studies suggested that there may be several mechanisms of action for deet and other repellents. These studies were supported by behavioral assays that were performed later. 

For simplicity the residence times, r, of 160 and of 180- are assumed to be equal here. With Equations 12 and 13 it is now possible to determine the rate constants kx and k2 at different Vr. The results are shown in Table II and agree fairly well with the rate constants obtained using ordinary oxygen. The ratios of the rate constants for the two mechanisms are constant in the range of repeller potentials from 7 to 12 volts. 

Origin, Chemistry, and Mechanisms of Action of a Repellent, Presynaptic Excitatory, lonophore... 

Although for the moment this model is only partially supported by experimental data it offers the opportunity to design new experiments which will help to understand the mechanisms of pardaxin insertion and pore formation in lipid bilayers and biological membranes which at a molecular level are the events leading to shark repellency and toxicity of this marine toxin. 

The mechanism of action by which silane and siloxanes reduce expansion has been attributed to water repellence and air entrainment. Phosphate addition or coatings may interfere with the dissolution of silica gel and the formation of gel. It is also possible that phosphate reduces the osmotic potential and the swelling pressure in the gel. The manner in which air entrainment reduced expansion was attributed to the accommodation of alkali-silica gel in the air void system. For example, it was found that air-entrained concrete with 4% air voids could reduce AAR expansion by 40% [23]. 

Savage, S. M. (1974). Mechanism of fire-induced water repellency in soil. Soil Sci.Am. Proc. 38, 652-657. 

In summary, natural products have a few known general mechanisms of action. These include toxins, inhibitors of growth, surface-energy modifiers, nervous pathway interference (anesthetics, including nitric oxide synthase inhibitors and neurotransmitter blockers), inhibitors of attachment, inhibitors of metamorphosis, and repellants.46 55117118 It is likely that many compounds have multiple mechanisms of action. 

The rest of the chapter has been devoted to special topics and in materials science there are many possibilities. Those selected include the mechanism of the flotation of minerals in which the addition of a certain organic to the solution causes a specific mineral to become hydrophobic so that it is exposed to air bubbles, the bubbles stick to it and buoy the mineral up to the surface, leaving unwanted minerals on the bottom of the tank. It turns out that the mechanism of this phenomenon involves a mixed-potential concept in which the anodic oxidation of the organic collector, often a xanthate, allows it to form a hydrophobic film upon a semiconducting sulfide or oxide, but only if there is a partner reaction of oxygen reduction. This continues until there is almost full coverage with the dixanthate, and the surface is thereby made water-repelling. 

A unique role is played by chemical communication in the interactions between plants and insects. About half a million insect species feed on plants. The process of reproduction in many plant species is critically dependent upon pollination by insects. It is not surprising, then, to find among the numerous natural products of plants both attractants for useful insects and repellents or even insecticides for plant-eating insects. The remarkable diversity of the these compounds (the list includes acyclic and polycyclic compounds, isoprenoids, aromatic derivatives, heterocyclic compounds, etc.) illustrates the non-selectivity in the structure of the chemical mediators for biological applications. The intimate mechanism of their action is, unfortunately, still insufficiently understood. 

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