Time-resolved light scattering has been used to investigate phase-separation dynamics for off-critical mixtures of polybutadiene (PB) and polyisoprene (PI) with a well defined phase diagram. Percolation-to-cluster transition (PCT) occurs in the course of the phase separation process for an off-critical mixture of the PB and the PI in the shallow quenches covered in this work. Before the onset of PCT occurs, the phase separation dynamics is fast, typically obeying qm∼t−0.9 and Im∼t2.7 (“percolation regime”), where qm is the scattering vector at the maximum scattered intensity Im. After the onset of PCT the time changes in qm and Im become very slow, and the phase separation process might appear to stop, if we observe the dynamics in a short time scale after the onset of PCT. The behavior corresponds to the results which Hashimoto et al. reported for the off-critical mixtures of poly(styrene-ran-butadiene) (SBR) and PB, and SBR and PI (spontaneous pinning of the domain growth) [J. Chem. Phys. 97, 679 (1992)]. However, it is shown in this paper that the droplets formed after PCT eventually grow according to the scaling law of qm∼t−n and Im∼t3n with n=1/4 to 1/3 (“cluster regime”), if we keep observing the phase separation process in the much longer time scale, beyond the time period over which the domain growth appeared to be pinned. To our knowledge, it is for the first time that such crossover of domain-growth behavior from percolation to cluster regime was observed via the intermittent time period over which the growth kinetics are apparently pinned.

Reversible chain association/dissociation phenomenon via CO(2) responsive crosslinking/decrosslinking was detected in aqueous solutions of polyallylamine (PAA). The chain association/dissociation behavior was reversible and useful in the synthesis of porous crosslinked polystyrene, which suggested potential utility in the area of CO(2)-responsive separable adhesives, switches and sensors.

Articles you may be interested inWetting-layer formation mechanisms of surface-directed phase separation under different quench depths with off-critical compositions in polymer binary mixture Crossover of domain-growth behavior from percolation to cluster regime in phase separation of an off-critical polymer mixture Phase separation kinetics of an off-critical polymer mixture involving percolation-to-cluster transition ͑PCT͒ was investigated by time-resolved light scattering and by transmission optical and electron microscopies. The process involving a splitting of a single peak in the light scattering profile into a double peak was observed for the first time after the onset of PCT. Each peak changes with time (t) according to different evolution modes, e.g., the first peak wave number q m,1 evolved according to the power law of percolated structures (q m ϳt Ϫ␣ ; ␣ϭ0.9), while the time evolution of the second peak wave number q m,2 is very slow, which corresponds to the growth of cluster of the droplets after PCT. Furthermore, the real space pictures and the light scattering analysis reveal that a cluster of the small spherical droplets and the locally percolating domains coexist for a very long time. The percolating domains are larger than the small droplets, minor in volume fraction, and formed in bulk and they are developed into sheet-like grains with their surfaces parallel to the glass surface.

Small-angle neutron scattering (SANS) has been used to investigate the thermal concentration fluctuations in a single-phase state of binary polymer mixtures such as deuterated polystyrene (DPS)/poly(vinyl methyl ether) (PVME), deuterated polybutadiene (DPB)/protonated polybutadiene (HPB), and DPB/protonated polyisoprene (HPI) in a wide range of temperatures from far above the glass transition temperature T g of mixtures to below the T g. The DPS/PVME mixture is unique in having a large difference in the T g's for each pure component compared with the mixtures of DPB/HPB and DPB/HPI having a small difference in the T g's. The SANS behavior for the DPS/PVME mixture in the single-phase state can be classified into three temperature regimes. At a temperature far above the T g of the single-phase mixture but below its cloud point, SANS profiles are well described by the scattering formula based upon random phase approximation (RPA) (regime I). As the temperature comes closer to the T g, the scattering intensity in the low-q region was more suppressed than that expected by RPA (regime II), and the Flory−Huggins interaction parameter was q-dependent. At temperatures below the T g, the scattering profiles in the entire q region become independent of temperature, frozen due to vitrification (regime III). On the other hand, for both DPB/HPB and DPB/HPI mixtures in the single-phase state, the scattering behaviors can be classified into only two regimes of regime I and regime III. The abnormal scattering behavior observed for regime II seems to be peculiar to the DPS/PVME mixtures with a large difference in the T g's of pure components.

The time evolution of a phase-separated morphology in a binary polymer mixture involving a percolation-to-cluster transition (PCT) was investigated by a combined use of laser scanning confocal microscopy (LSCM) and light scattering (LS). We constructed three-dimensional images of phase-separating structures in the PCT process by means of the LSCM technique. The three-dimensional image observed by the LSCM was found to be consistent with the result from the LS, revealing that the phase separation process can be classified into four regimes:  (i) percolation regime, (ii) PCT-I regime, (iii) PCT-II regime, and (iv) cluster regime. Details of phase separation dynamics in each regime are described in the text.