High-affinity molecules

Collectors ndFrothers. Collectors play a critical role ia flotation (41). These are heteropolar organic molecules characterized by a polar functional group that has a high affinity for the desired mineral, and a hydrocarbon group, usually a simple 2—18 carbon atom hydrocarbon chain, that imparts hydrophobicity to the minerals surface after the molecule has adsorbed. Most collectors are weak acids or bases or their salts, and are either ionic or neutral. The mode of iateraction between the functional group and the mineral surface may iavolve a chemical reaction, for example, chemisorption, or a physical iateraction such as electrostatic attraction. 

Group 3. These dyes have high affinity under neutral conditions and are large complex molecules. From the previous considerations it is clear that it is difficult to obtain level dyeiags with these dyes, and they are sensitive to physical and chemical variations in the nylon. They do have excellent fastness and therefore it is often worthwhile overcoming these application problems. This is done by using specially developed auxiliary agents that are added to the dyebath. The detailed mechanism has been described in detail elsewhere (26). 

Because of their selectivity, molecular sieves offer advantages over silica gel, alumina or activated charcoal, especially in their very high affinity for water, polar molecules and unsaturated organic compounds. Their relative efficiency is greatest when the impurity to be removed is present at low concentrations. Thus, at 25° and a relative humidity of 2%, type 5A molecular sieves adsorb 18% by weight of water, whereas for silica gel and alumina the figures are 3.5 and 2.5% respectively. Even at 100° and a relative humidity of 1.3% molecular sieves adsorb about 15% by weight of water. 

In spite of the fact that molecular imprinting allows materials to be prepared with high affinity and selectivity for a given target molecule, a number of limitations of the materials prevent their use in real applications. The main limitations are ... 

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