The aggregation and phase behavior in water of several triblockcopolymers of poly(oxyethy1ene)-poly(oxypropy1ene)-poly(oxyethy1ene) [(EO),(PO),(EO),I has been studied. The y-values of the compounds ranged from 16 to 70 and the x y ratios from 0.1 to 2.5. All studied compounds form micelles and lyotropic liquid crystalline phases. For a constant temperature the critical micelle concentrations (crnc) of the compounds decrease exponentially with y . The energy increment for the transfer of a PO group from the aqueous to the micellar state is about (0.25 f 0.05) kT. The cmc values for all compounds decrease strongly with increasing temperature. As a consequence the solutions undergo a monomer-micelle transition for constant concentration and increasing temperature. This micellization process is associated with a large endothermic heat which is linearly dependent on the size of the PO block. It is concluded that this heat is due to the dehydration of the PO groups, and it is called the heat of micellization AH, . For most of the studied cornpounds AH, = 3.0 f 0.5 kJ/mol for one PO group. The large change of the cmc values with temperature can quantitatively be explained by the large AH,,, values. The sequence of the lyotropic mesophases is mainly determined by the r : y ratio. Systems with x:y > = 0.5 form spherical micelles for c > cmc. The size of the micellea is independent of the concentration and temperature, if the temperature is about 20 "C above the micellization temperature T,; in a transition region around T, the micellar size increases strongly with temperature. Below T, or the cmc only monomeric block copolymer molecules are present in the solution.At higher concentrations and temperatures solutions with spherical micelles form in a fiist-order transition a transparent, optically isotropic, highly viscous, and elastic cubic phase. The formation of this cubic phase can be understood by hard-sphere interaction between the aggregates. With further increasing concentrations transitions to hexagonal and to lamellar phases are observed. Samples with a smaller hydrophilic EO block, Le., with x:y = 0.25, usually form a hexagonal phase as the fiist liquid crystalline mesophase, while for systems with ratios x:y = 0.15 a lamellar phase is found as the first mesophase; samples with x:y << 0.1 are no longer soluble in water. The lyotropic mesophases show also a thermotropic behavior; Le., reversible transitions cubic -hexagonal -lamellar or from isotropic Solutions to mesophases occur at constant block copolymer concentration with increasing temperatures. The mesophases usually melt at temperatures below 100 O C to systems consisting of one or more isotropic liquid phase.

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Publication costs assisted by Universitat Bayreuth New developments of the theory of micellar kinetics are reported together with new experimental results obtained in the course of chemical relaxations (T-jump, p-jump, and shock tube) studies of micellar solutions of ionic surfactants. These results as well as those obtained in previous studies are quantitatively interpreted in terms of this theory. Several pieces of information thus far not available on micellar solutions have been obtained: (1) the rate constants k+ and k~for the association/dissociation reactions of one amphiphilic ion to/from micelles. The association reaction is very close to being diffusion controlled. The variation of the dissociation rate constant with the alkyl chain length is in quantitative agreement with what is expected from theory; (2) the width of the distribution curve of stable micelles is found to increase with chain length but the micelle polydispersity is small and decreases for increasing chain length; (3) an approximate value of the average number of amphiphilic ions in the micellar species at the minimum of the distribution curve; (4) the enthalpy and entropy changes associated with the incorporation of one amphiphilic ion into the most stable micelle and into the aggregate at the minimum of the distribution curve. The enthalpy changes for these two processes are of opposite signs. This explains why the overall heat of micellization is very small.

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The first part of the work presents an overview of the physical chemistry of surfactants which in aqueous solutions reduce the frictional loss in turbulent pipe flow. It is shown that these surfactants form rodlike micelles above a characteristic concentraion c t. The experimental evidence for rodlike micelles are reviewed and the prerequisites that the surfactant system must fulfill in order to form rodlike micelles are given. It is demonstrated by electrical conductivity measurements that the critical concentration for the formation of spherical micelles shows little temperature dependence, whereas ct increases very rapidly with temperature. The length of the rodlike micelles, as determined by electric birefringence, decreases with rising temperature and increases with rising surfactant concentration. The dynamic processes in these micellar systems at rest and the influence of additives such as electrolytes and short chain alcohols are discussed.In the second part, the rheological behaviour of these surfactant solutions under laminar and turbulent flow conditions are investigated. Viscosity measurements in laminar pipe and Couette flow show the build-up of a shear induced viscoelastic state, SIS, from normal Newtonian fluid flow. A complete alignment of the rodlike micelles in the flow direction in the SIS was verified by flow birefringence. In turbulent pipe flow, drag reduction occurs in these surfactant systems as soon as rodlike micelles are present in the solution. The extent and type of drag reduction, i.e. the shape of the friction factor versus Reynolds number curve, depends directly on the size, number and surface charge of the rodlike micelles. The friction factor curve of each surfactant investigated changes in the same characteristic way as a function of temperature. For each surfactant, independent of concentration, an upper absolute temperature limit, TL, for drag reduction exists which is caused by the micellar dynamics. T L is influenced by the hydrophobic chain length and the counter-ion of the surfactant system. A first attempt is made to explain the drag reduction of surfactants by combining the results of these rheological measurements with the physico-chemical properties of the micellar systems.