In this study, the kinetics of vesicle formation of ABA amphiphilic triblock copolymers from an initially homogeneous state was theoretically and experimentally investigated by adding a selective solvent into the system. The pathway of spontaneous vesicle formation depended greatly on the selective solvent addition rate. At a slow addition rate, the pathway followed three stages: (1) the amphiphilic triblock copolymer combined into a large irregular aggregation; (2) the large irregular aggregation broke into big irregular spheres; and (3) some hydrophilic molecules in the big irregular spheres diffused toward the surface, and some hydrophilic molecules diffused toward the center, forming vesicles. However, at a fast addition rate, the pathway was as follows: (1) the amphiphilic triblock copolymer aggregated into many small spheres; (2) the small spheres merged to form rod-like micelles first and then oblate membranes; and (3) the oblate membranes closed up to form vesicles. This pathway difference for vesicle formation can be attributed to the existence of many metastable states in the system. This finding not only provides new insight into the origins of vesicles but also provides further understanding on the self-assembly kinetics of amphiphilic block copolymers in a selective solvent.

The tunable-laser flash-absorption technique has been used to study the high-temperature behavior of the reaction H+O2→OH+O by monitoring the absorption of the hydroxyl radical. Sensitivity analysis of a detailed reaction mechanism shows that for fuel rich mixtures only two reactions are sensitive when hydroxyl is monitored: H2+M→2H+M and H+O2→OH+O. Rate coefficients for these reactions have been determined by least-squares analysis of measured absorption profiles. For the rate of dissociation of H2 in krypton we obtain k1(T)=(8.86±0.88)×10−10 exp[−48321/T(K)] cm3 s−1 from 3450 to 5300 K. For the H+O2 reaction we combined our results with previous low temperature measurements and recommend k2(T)=(1.62±0.12)×10−10 exp[−(7474±122)/T(K)] cm3 s−1 from 960 to 5300 K. The uncertainties are at the 95% confidence level. Measured cross sections for rotational and vibrational energy transfer in O2 and OH have been used to show that relaxation effects do not influence the results. We compare our results to recent trajectory calculations. In addition, we calculate the rate of the reverse reaction, OH+O→H+O2, and compare it to trajectory and statistical adiabatic channel calculations. Finally, we point out that the first excited surface of the hydroperoxyl radical, 2A′, which correlates with H(2S)+O2(1Δg), may be needed to explain very high temperature results.