ATP synthase represents a machine at the molecular level which couples the rotation of an axle in a wheel with the endergonic production of ATP, the general source of chemical energy in the cell. The natural system prototypically bears all features of a macroscopic motor: a rotor within a stator held by a membrane and fueled by a difference in chemical potential in the form of a proton gradient combined with a machine for ATP production. The assembly of axle and wheel to a rotor device reminds one very much of a rotaxane. In this Account, we discuss some important features of motors and their (potential) realization in simpler artificial model systems, that is, the molecular mobility of mechanically bound molecules, the importance of chirality for unidirectional motion, the sources of energy for driving the rotation, and the potential of using membranes and surfaces for ordering a large number of devices to achieve macroscopic effects.

The phase behavior of ternary water−alkyl methacrylate−alkyl polyglycol ether (C i E j ) systems has been examined. Specifically, using seven different alkyl methacrylates ranging from methyl to hexadecyl methacrylate and C10E6 as surfactant, vertical sections through the phase prism were determined, from which the phase inversion temperature, the upper and lower critical temperature of the three-phase body, and the efficiency of the surfactant and its monomeric solubility in the oil were obtained. Keeping hexyl methacrylate as oil-fixed, 18 different surfactants were applied including short- and long-chain surfactants such as C4E3 and C14E8. The microemulsion systems examined here show the same general patterns as the well-known nonionic microemulsions with alkanes as oil. Notably, the phase inversion temperature is highly dependent on the alkyl chain length of the oil, a fact that is often left out of consideration when choosing a surfactant in emulsion polymerization. For a given oil the phase inversion temperature can be adjusted by appropriate choice of the number of ethylene glycol units of the surfactant. The efficiency of the surfactant systematically depends on the alkyl chain length of both the surfactant and the oil. Interestingly, there is a striking parallel between efficiency of a surfactant and its monomeric solubility in the oil. Finally, in preparation for applying these systems to the synthesis of nanoscaled latexes in microemulsion polymerization the water-rich part of the phase prism was examined. Both the expected shape of the emulsification failure phase boundary and the near-critical phase boundary with its nonmonotonic decay characteristic of branched network structures are delineated. The results of some preliminary polymerizations are briefly discussed.

The y-ray-induced post-polymerization of mesogenic 4-methoxy-4'-(6-methacryloyloxyhexy1oxy)biphenyl (1) was investigated. Reaction kinetics and molecular weight distribution of the polymer were studied. Molecular weights and weight distributions were analyzed using size exclusion chromatography. Especially, effects of radiation dose, polymerization time and temperature were investigated. Post-polymerization was found in the crystalline, liquid crystalline and melt phase. Rate of polymerization and limiting conversion to polymer increase with radiation dose, polymerization time and temperature. Samples exposed to a low y-ray dose of 5 kGy and subsequently polymerized in the crystalline state at 20°C, for example, only reach a limiting conversion of about 7% within 100 h, while samples exposed to a high dose of 20 kGy and polymerized in the melt at 79 "C reach a limiting conversion of 85.1 % within 90 s. Molecular weights increase with polymerization temperature and reach values comparable with in-source polymerization. Different from in-source polymerization, they are additionally affected by the parameters radiation dose and polymerization time. High molecular weights are obtained, if samples are exposed to a low radiation dose and isothermally polymerized at high temperature for a long time, while low molecular weights result from high radiation dose and short time of polymerization at low temperature, e. g., at 20°C. By carefully adjusting the reaction parameters, molecular weights can be reliably tailored in the range from 2 x lo4 to 6 x lo5. Polymerization at room temperature leads to a normal molecular weight distribution, while distributions are broader when the polymerization is carried out in the liquid crystalline or melt phase. The origin of the different reaction rates and molecular weights obtained under the various conditions is discussed in terms of the mobility of growing chain ends and residual monomer, which influences chain growth and termination and thus the kinetic chain length.