Tokihiro Hashimoto

Order–disorder transition of polystyrene-block-polyisoprene Part II. Characteristic length as a function of polymer concentration, molecular weight, copolymer composition, and χ parameter

Abstract A series of polystyrene-block-polyisoprene diblock copolymers having various degrees of polymerization Nn and composition fPS were studied as a function of temperature T and polymer concentration φp by means of in situ small-angle X-ray scattering methods. The results indicated that the characteristic length D as evaluated from D=2π/qm with qm being the wave number of the first-order scattering maximum was found to obey the following scaling law: D∼(φp/T)1/3Nn2/3 for φp/T≥(φp/T)MF∼Nn−1/2, and D∼(φp/T)0Nn1/2 for φp/T≤(φp/T)MF for the copolymer systems covered in this work. Here (φp/T)MF is a crossover value of φp/T from the mean-field disordered state to the non-mean-field disordered state. These results are consistent with our previous experimental observations [Hashimoto et al., Macromolecules 16 (1983) 1093]. The results obtained here together with our previous results of χeff∼(φp/T)Nn−1/2 and D0∼Nn1/2 (Mori et al., J Chem Phys, 104 (1996) 7765) give the following scaling law: D/D 0 ∼(χ eff N n ) 1/3 for (χ eff N n )≥(χ eff N n ) MF and D/D 0 ∼(χ eff N n ) 0 for (χ eff N n )≤(χ eff N n ) MF where χeff is an effective segmental interaction parameter between polystyrene and polyisoprene segments at a given φp and T for a given copolymer, and D0 is the wavelength of the dominant mode of the concentration fluctuations of the copolymer systems in the mean-field disordered state. (χeffNn)MF is the crossover value of χeffNn at the mean-field disordered state to the non-mean-field disordered state, which depends on fPS.

The effect of added polymers on n-butylammonium vermiculite swelling

A 4-component clay-polymer-salt-water system was studied by neutron scattering. The clay-salt-water system consisted of n-butylammonium vermiculite, n-butylammonium chloride and heavy water, and the volume fraction of clay in the system was held constant, at r = 0.01. Three polymers in the molecular weight range 10,000 to 30,000 were studied, poly( vinyl methyl ether) (PVME), poly (ethylene oxide) (PEO) and poly(acrylic acid) (PAA), at a polymer volume fraction of v = 0.01. The addition of PAA suppressed the clay swelling, irrespective of the salt concentration, c. The addition of the neutral polymers had no effect on the phase transition temperature, Tc, between the gel and tactoid phases of the system, its value remaining at 14 °C for c = 0.1 M and 30 °C for c = 0.01 M. At c = 0.01 M, the neutral polymers also had a negligible effect on the lattice constant d along the swelling axis of the clay colloid, but at c = 0.1 M, the d-value was significantly lower than in the system without added polymer. For a PVME sample of molecular weight 18,000, both d and Tc were measured as a function of ν, for volume fractions between 0 and 0.04. The addition of polymer, up to v = 0.04, had no effect on Tc. However, even for v values as low as 0.001, the vermiculite layers in the gel phase were more parallel and more regularly spaced than in the system without added polymer. In the gel phase, d decreased exponentially as a function of v, from 12 nm at v = 0 to 8 nm at v = 0.04. In the tactoid phase, at T < 14 °C, the d-value in the crystalline regions was equal to 1.94 nm at v = 0 and v = 0.04, showing that the spacing between the vermiculite layers is not affected by the added polymer when they are collapsed by an increase in temperature. The addition of a PVME sample of molecular weight 110,000, at v = 0.001, had no noticeable effect on either d or Tc.

Transient interfacial instability in bilayer polymer films as observed by neutron reflectivity studies

Fundamental processes associated with reactive blending were explored for a system composed of polyamide (PA) and deuterated polysulfone having a reactive phthalic anhydride end group (R) (dPSU-R) diluted with a low molecular weight hydrogenous polysulfone (low-hPSU) by neutron reflectivity (NR). By preparing bilayer films composed of a mixed film of dPSU-R/low-hPSU and a PA film, an intriguing phenomenon was observed in NR studies during the thermal annealing of the sample. This phenomenon can be described as a transient instability of the interface between the PA layer and the dPSU-R/low-hPSU layer during annealing at temperatures high enough to allow chemical reactions to occur between the dPSU-R end groups and the terminal amino groups of PA. The signature for the interfacial instability was a transient disappearance of the NR fringes followed by a subsequent recovery of the fringes during additional annealing at high temperatures. The driving force for this phenomenon is rapid interdiffusion of a small, low molecular weight fraction of low-hPSU into the PA layer. A consequence of the rapid interdiffusion is an attendant Kirkendall shift of the interfacial position as the PSU layer shrinks. The magnitude of this special Kirdendall effect accompanying the interfacial instability is directly controlled by the amount of the miscible low molecular weight fraction of low-hPSU present in the normally immiscible PSU/PA pair.

SANS Studies of Early Stage Spinodal Decomposition

Time-resolved small-angle neutron scattering (SANS) experiments were performed on the self-assembling process of a binary mixture of deuterated polybutadiene and protonated polybutadiene at the critical composition. Specimens held in the single-phase state at an initial temperature (Ti) were quenched to a point inside the spinodal phase boundary at a final temperature (Tf) to induce phase separation via spinodal decomposition (SD). The effect of the thermal concentration fluctuations on the SD was examined by changing Ti for a fixed Tf. The wave number and temperature dependence of Onsager kinetic coefficient were also investigated as a function of Ti and Tf.