Solid monomers, experimental evidence

The whole truth, however, is not nearly as simple as this. The experimental evidence has not been collected systematically, and it is not known, in most cases, whether singlet or triplet states are involved. In the last ten years, at least sixty papers have been published in which reasonably reliable structures have been assigned to the cyclobutane dimers produced by irradiation of a great variety of unsymmetrical olefins in solution. (The stereo- and regioselectivity in solid-state photodimerization reactions have also received a lot of attention, but they are determined by the alignment of the monomers in the crystal lattice, not by frontier orbital effects.) For irradiation in solution, head-to-head dimers are described as major or sole products in forty of these papers, and head-to-tail dimers are described in twenty of them. In addition, almost all photodimerizations of 9-substituted anthracenes (479) give the head-to-head dimer (480),385 whereas the... 

The pseudophase-separation model for surfactant solutions (84, 132, 135) states that a surfactant solution above its critical micelle concentration (CMC) consists of two pseudophases in equilibrium with each other singly dispersed surfactant monomer molecules and micelles. When the surfactant solution is in contact with a solid, the adsorbed phase constitutes a third pseudophase (40). Strong experimental evidence suggests that surfactant adsorption takes place from the surfactant monomer phase but not from the micelles (84), behavior that leads to competition of both the micelles and the adsorbed phase for surfactant molecules from the monomer phase. Adsorption from a surfactant solution above the CMC then depends not only on the affinity of the surfactant for the solid surface but also on its tendency to form micelles. If a mixture can be formulated such that at least one of the surfactants is incorporated into micelles preferentially over the adsorbed phase, then the micelles act as a sink for the surfactant and thus prevent it from being adsorbed. 

Table 5.2 Experimental evidence for solid-state polymerization of certain monomers.

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