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Simultaneous measurements of small-angle light scattering/shear stress (Rheo-SALS) and small-angle X-ray scattering/shear stress (Rheo-SAXS) have been performed in the lamellar phase of the C(16)E(7)/D(2)O system. As the temperature is increased and exceeds 67 degrees C at constant shear rates (at 1 and 3 s(-1)), the shear stress increases abruptly and a four-lobe pattern is observed in the depolarized SALS. These results suggest that the lamellar-to-onion transition occurs with increasing temperature, which has not yet been reported. The diameter of onions obtained from the depolarized SALS pattern at 3 s(-1) increases with increasing temperature. The transition is reversible against the change in temperature. The Rheo-SALS measurements have also been made with a stepwise increase in shear rate at constant temperature. The results are consistent with the above temperature-scan experiments at constant shear rate, suggesting that the transition does not depend on the path. The variation of the SAXS pattern at 3 s(-1) indicates that the orientation of lamellae becomes isotropic as the temperature is increased from 67 to 69 degrees C, which also supports the lamellar-to-onion transition. The transition temperature at constant shear rate (at 3 s(-1)) increases rapidly with a slight increase in surfactant concentration. From this, together with the SAXS results at rest in our previous study, we deduce that an increase in the water-layer thickness is necessary for the lamellar-to-onion transition with increasing temperature.

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The structure of the lamellar phase formed in the heptaethylene glycol n-hexadecyl ether (C16E7)-water system has been studied using small-angle X-ray scattering (SAXS). The concentration dependence of the repeat distance d follows the power law d ∝ φhc -s where φhc is the volume fraction of hydrophobic layer. The exponent s obtained is unity as expected at 75 °C where the "LR" phase extends to the lower concentration range. As the temperature decreases below about 70 °C, however, s decreases rapidly. Below about 55 °C, s becomes constant again and takes values of about 2/3. From the line shape analysis of SAXS in the "LR" phase, half-thickness of the hydrophobic layer δhc and the thickness of the hydrophilic layer have been obtained. It has been shown that the anomalous behaviors of the exponent s cannot be explained by the variation of δhc with concentration and temperature. In other words, the structure of the "LR" phase varies with concentration and temperature. Assuming that the bilayer sheets have water-filled defects, we have made a "map" showing how the fraction of the defects fw depends on concentration and temperature. Strong correlation has been found among the fw value, the appearance of the broad component superimposed on the first-order reflection, and the quadrupolar splitting of 2 H2O. Relations between the phase behaviors and the structures of the L1, "LR", and V1 phases have been discussed based on these results.

conduction of heat on this time scale is a minor factor and the heavier tantalum atoms will conduct heat at a slower rate than carbon atoms at the same temperature. Summary and ConclusionsThe significant results with thin gold deposits on carbon support films may be summarized as follows. Crater or void dimensions in the gold layer are relatively insensitive to projectile cluster size but are directly related to the total cluster energy. This is in contrast to results obtained with pure carbon films. The presence of thin gold layers serves to reduce the energy density deposited in the supporting carbon films to the point that only with the small 25or 50-water-molecule clusters at the highest energy per constituent atom can damage be observed in the carbon layer. With the relatively nonvolatile and heavy target material tantalum, the holes and craters formed are much more sensitive to cluster size and energy in analogy to the carbon results.Crude estimates of stopping power of cluster atoms in both the gold and tantalum experiments support the conclusion that cluster atoms lose energy more rapidly than atomic projectiles would at the same energy per atom. In addition the morphology of the holes and craters formed indicates the importance of wide angle scattering processes.The magnitude of target removed to form the largest craters or hole in our experiments is on the order of 105 atoms per incident ion. These values are much larger than one would observe for the same total energy deposited by laser sputtering, isolated atomic sputtering processes, or sputtering with polyatomic ions containing up to three atoms.Acknowledgment. The help of A. P. Irsa in the performance of these bombardment experiments is gratefully acknowledged, and we thank Neal Tempel for help in film preparation and photography. This research was carried out at Brookhaven National Laboratory under contract DE-AC02-76CH00016 with the