Surface hydrophobicity, heating effect

To rate the wetting tendency of surfactants for hydrophobic surfaces. A graphitic powder, for example, with its low heat of wetting in water, yields much higher heat effects if immersed in solutions of surface active agents. Heats of dilution and of demicellization can be taken into account, if desired, to arrive directly at energies of interaction. 

Ensembles 600 Enterokinase 480 Enthalpy 55 activation 56, 545-547 protein folding 509 -512 specific heat effects 511, 545 - 547 Enthalpy-entropy compensation 346 Enthalpy versus entropy in protein folding 509-512, 587, 599 Entropy 55, 68-72 activation 56, 545 -547 binding 324, 345 Boltzmann equation 510 chelate effect 345 configurational 510 configurational entropy of loops 535 effective concentration 68-72 equilibria on enzyme surface 118 hydrogen bond 338 hydrophobic bond 332, 510 importance in enzyme catalysis 72 importance in enzyme-substrate binding 72... 

As these cosolvents contain both hydrophilic and hydrophobic groups, the same molecule can induce opposite effects in water. The hydrophilic part can interact with water to form strong HBs, while the hydrophobic part may induce cooperative ordering in the system by a hydrophobic hydration effect. These two effects combine together to regulate the extensive HB network of water in their aqueous binary mixtures that is reflected in strong, often anomalous non-ideal behavior in many physical properties such as viscosity, density, dielectric constant, excess mixing volume, surface tension, heat of formation, etc. 

Butylate probably exhibits a negative heat of solution (and hence a postive heat of adsorption) due to the hydroponic effect described by Tanford ( 4). This effect is caused by the disrupted water molecules rearranging themselves into a lower energy state at the hydrophobic surface of the butylate molecule. In addition, there is probably a negative entropy of solution as the water molecules find themselves in a more ordered state at the hydrophobic surface of the butylate molecule (15). The butylate molecule presents a hydrophobic surface from all directions but metolachlor and alachlor do not (Figure 5). 

Example 7.4. Effect of oil on aquatic birds. Aquatic birds keep their feathers hydrophobic with wax. For them it is essential that the feathers repel water. The air entrapped in and under the feathers provides a good heat insulation. It keeps the birds afloat and light so that they are able to fly. Due to low surface tension, oil has a strong tendency to wet all kinds of solid surfaces. It also wets the surfaces of feathers which then deprives the birds of all the essentials described. In addition, heavy oil is sticky, destroys the feather structure, and prevents the birds from moving freely. 

---