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The phase separation mechanism in semidilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions is investigated with small-angle neutron scattering (SANS). The nature of the phase transition is probed in static SANS measurements and with time-dependent SANS measurements after a temperature jump. The observed critical exponents of the phase transition describing the temperature dependence of the Ornstein-Zernike amplitude and correlation length are smaller than values from mean-field theory. Time-dependent SANS measurements show that the specific surface decreases with increasing time after a temperature jump above the phase transition. Thus, the formation of additional hydrogen bonds in the collapsed state is a kinetic effect: A certain fraction of water remains as bound water in the system. Moreover, H-D exchange reactions observed in PNIPAM have to be taken into account.

We have studied the structural rearrangements in a lamellae-forming poly(styrene-b-butadiene) film during exposure to toluene vapor. Real-time, in situ grazing-incidence small-angle X-ray scattering allowed us to identify distinct kinetic regimes: First, the lamellae swell linearly, and the blocks stretch uniaxially. Then, the blocks relax to a more globular molecular conformation, and the lamellar thickness abruptly shrinks again. The increased interfacial area culminates in a dramatic instability causing a major rearrangement of the lamellar stack and the formation of new lamellae. Finally, the lamellar thickness levels off, and the interfaces flatten again.