Snapping Together

Gady found that, depending on the charge of the particle, van der Waals forces dominated over the forces associated with electrostatically charged patches when the particle-to-substrate separation was between 3 and 10 nm, depending on the particle charge. In addition, he found that the distance at which the snap-together occurred required that van der Waals forces dominate over electrostatic. In all his measurements, however, a component of the total attractive force, even at close separations, was observed to be electrostatic in nature. 

Hydrocarbon Isomers Suppose you had ten blocks that could be snapped together in different arrangements. Each arrangement of the same ten blocks is different. The atoms in an organic molecule also can have different arrangements but still have the same molecular formula. Compounds that have the same molecular formula but different arrangements, or structures, are called isomers (I suh murz). Two isomers, butane and isobutane, are shown in Figure 7. They have different chemical and physical properties because of their different structures. As the size of a hydrocarbon molecule increases, the number of possible isomers also increases. 

When one-third of the initial gap has been closed, the plates snap together or pull in. This pull-in instability limits the useful range of parallel plate electrostatic actuators with linear springs. For parallel plate electrostatic actuators formed in surface micromachining processes, the initial gap is defined by the sacrificial layer thickness, which is practically limited to a few microns, so that the useful actuation range is typically less than a micron. To find the pull-in voltage, the gap at pull-in, go/3, can be substituted into equation (3.22) and solved for the voltage ... 

H- atom, and converts the victim molecule into a radical. That radical attacks another molecule, so producing yet another radical, and so on. The chain of reactions continues until it terminates in some way, such as by the encounter of two radicals, which snap together without forming a new radical and bring the chain of links to an end. 

Like most radicals, this newly formed one is highly reactive, and almost immediately forms a bond to the oxygen molecules that surround and pepper it with collisions (Figure 24.4). The outcome is yet another radical. Lurking nearby we see an NO2 molecule, which is itself a radical. We see them collide and snap together to form the compound known as PAN, 4 (peroxy-acetyl nitrate). The chain of reactions ceases. PAN is highly soluble in water and moisture and is one of the principal eye irritants of photochemical smog. 

Perhaps you can design a system made out of plastic parts that can be snapped together instead of bunch of metal parts that need to be welded in place (and then painted or otherwise coated to prevent corrosion). 

Using a small strip of extrusion with two slots, approximately 108° apart, twelve parts were snapped together. The student was required to use all twelve parts from the group that he had molded. He then could visually examine the assemble dodecahedron, and visual evaluate the consistency of his process. Finally, each student contributed one pentagon to a community pool of twelve parts, which were subsequently assembled into a different dodecahedron. The entire class and the four instructors then examined it. 

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