Ichiro Noda

Experimental tests of the scaling relation for textured materials in mixtures of two immiscible fluids

To examine the scaling relation proposed for textured materials, viscoelastic properties of binary mixtures of immiscible Newtonian fluids were measured in steady shear flows and in the transient states after step changes of the shear rate. The sample was a mixture of silicone oil and resin oil, which have almost equal density and viscosity. It was observed that (i) the shear stress and the first normal stress difference, under the steady shear flows, are almost proportional to the shear rate, and that (ii) the plots of the scaled transient stresses after a step change of shear rate, against the scaled strain, compose a single curve. These results can be well explained by the scaling relation. However, the shape of the transient stress curves after step changes of shear rate do not agree with that predicted by the constitutive equation proposed by Doi and Ohta.

Rheological properties and domain structures of immiscible polymer blends under steady and oscillatory shear flows

Rheological properties of three immiscible polyisoprene (PI)/polydimethylsiloxane (PDMS) blends (PI:PDMS=1:9 by weight) having viscosity ratios ηd/ηm=0.155, 0.826, and 4.02, where ηd and ηm are the viscosities of the droplet and matrix, were investigated by directly measuring the droplet size distributions with a video microscope. Steady state measurements were performed by sequentially stepping up the shear rate γ (step-up) and step decrease (step-down) of the shear rate. Dynamic frequency sweep measurements were also performed immediately following cessation of steady shear flow. In the step-up measurements for blends with ηd/ηm=0.155 and 0.826, stresses were proportional to γ and the droplet sizes were well regulated by the flow and inversely proportional to γ for γ⩾0.553 s−1, in good agreement with the Doi–Ohta model [J. Chem. Phys. 95, 1242–1248 (1991)]. The results of step-down measurements were consistent with dynamic moduli measurements, because the droplet sizes were almost unchanged during t...

Preparation and morphology of multiblock copolymers of the (AB)n type

Abstract Styrene(S)-isoprene(I) multiblock copolymers of the (SI)n type (n = 1, 2, 3, 4) were prepared by a multistep monomer addition technique of anionic polymerization. Molecular weights of SI diblock units are almost the same and the total polystyrene volume fractions are about 0.5. All the film specimens cast from toluene solutions were found to have alternating lamellar structures. The lamellar domain spacing monotonically decreases and approaches an asymptotic value with increasing the number of blocks.

Shear-rate dependence of first normal stress difference of poly(isoprene-b-styrene) in solution near the order—disorder transition temperature

Abstract Viscoelastic properties of poly(isoprene-b-styrene) in dioctylphthalate under steady shear flow were measured near the order—disorder transition temperature. In ordered states, first normal stress difference N1 is proportional to shear rate γ at low γ region, but becomes proportional to γ 2 at the high γ region, similar to the N1 behaviour of polymer blends undergoing shear-induced homogenization. Because the existence of microdomains was confirmed at the high γ region by the flow birefringence method, it is concluded that the above N1 behaviour is not caused by shear-induced homogenization, but is probably caused by the shear-induced alignment of the microdomain structure.

Preparation and morphologies of 4- and 12-armed styrene-isoprene star-shaped block copolymers

Abstract Styrene(S)-isoprene (I) star-shaped block copolymers of the (SI)4 and (SI)12 types were prepared by an anionic polymerization technique. Linear SI arm molecules were prepared with sec-butyllithium as an initiator in benzene, followed by a coupling reaction with the 4-functional linking agent 1,2-bis(methyl-dichlorosilyl)ethane and the 12-functional 1,1,2,2-tetrakis(2-(trichlorosilyl)ethyl)silane, respectively, under vacuum. The star-shaped block copolymers were isolated by precipitational fractionation from aspolymerized crude products using benzene-methanol mixtures. They were confirmed to have the designed molecular structures by careful characterization. Using a transmission electron microscope it was observed that the microphase-separated structures of solvent-cast films of the samples are polystyrene (PS) cylinders in a polyisoprene (PI) matrix, alternating lamellar structures and PI cylinders in a PS matrix for 4-armed star-shaped block copolymers when the values of the volume fraction of PS, ф s , are 0.23, 0.47 and 0.78, respectively, and lamellar structures for the 12-armed star-shaped block copolymers when the ф s values are ∼0.5. Small-angle X-ray scattering studies revealed that lamellar domain spacings of the star-shaped block copolymers are essentially the same as those of the arm molecules, that is, linear diblock copolymers, irrespective of the number of arms.

Preparation and characterization of ABB graft copolymers

Abstract Poly(2-vinylpyridine- g -styrene)s were prepared by successive coupling reactions of polystyryl anion and poly-2-vinylpyridinyl anion prepared by anionic polymerizations, with trifunctional coupling agent, tris-bromomethylbenzene. Five samples were prepared and characterized. Their volume fractions of polystyrene graft,o s , were determined to be 0.24, 0.34, 0.45, 0.58 and 0.67, respectively. Morphologies of the solvent-cast films of the samples were observed by transmission electron microscopy and small-angle X-ray scattering. It was revealed that two samples, with o s of 0.24 and 0.34, show cylindrical structures, while the other three samples have alternating lamellar structures.

Flow effects on microdomain structure of poly(styrene-b-2-vinylpyridine) solutions studied by flow-SANS

Abstract Flow effects on lamellar structures of symmetric poly(styrene-d 8 -b-2-vinylpyridine) (DP) in a common good solvent were studied at two different concentrations by flow-SANS (small angle neutron scattering) measurements. The anisotropic scattering observed under the flow implies that the lamellar normals are preferentially oriented to the vorticity direction of shear flow. At lower concentrations, however, the anisotropy was significantly weaker than that at higher concentrations even at the highest shear rate.

Lamellar domain spacing of the ABB graft copolymers

Abstract The molecular weight dependence of lamellar domain spacing of poly(2-vinylpyridine-g-styrene) was measured by small angle X-ray scattering (SAXS). The samples used are six three-arm star-shaped polymers having one polystyrene arm connected at the centre of a poly(2-vinylpyridine) chain. The volume fractions of grafted polystyrene chains, ƒ s , of the samples range from 0.45 to 0.78, though all the samples were confirmed to have alternating lamellar structure by SAXS and transmission electron microscopy. It was found that the relationship between lamellar domain spading, D, and the molecular weight, M, of the graft copolymers is given by D = 0.0153 M0.69 (nm) over the molecular weight range from 49 to 283 k irrespective of the difference in composition. The exponent 0.69 is quite close to 2 3 , which is predicted for AB diblock copolymers by several different theories. However, the magnitude of the prefactor in the above relationship is apparently smaller than that for styrene-2-vinylpyridine diblock copolymers. This difference can be explained by considering the difference in structure between AB diblock copolymers and ABB graft copolymers.

Viscoelastic properties of polyelectrolyte solutions in non-entangled concentrated regions

Viscoelastic properties of non-entangled concentrated aqueous solutions of three sodium polystyrenesulfonates with low molecular weights were measured in oscillation flows. Master curves of dynamic moduli were obtained by shifting the moduli data measured at different concentrations along the frequency (ω) axis for each molecular weight. The concentration shift factor used in making the master curves composes a single line irrespective of molecular weight. Storage and loss moduli are proportional to ω 2 and ω, respectively, in the terminal region, while they are proportional to ω 1/2 in the transition region. All the master curves can be well represented by the modified Rouse theory using the experimental values of concentration, molecular weight and viscosity in a reference state.

Studies on the interfaces of microphase-separated structures of block copolymers by neutron reflectivity

Abstract Segment distributions in lamellar microphase-separated structures of three partially deuterium-labeled poly(styrene-b2-vinylpyridine)s were investigated by neutron reflectivity measurement. By fitting the calculated reflectivity profiles to the experimental one, it was clarified that the lamellar microdomains preferentially oriented parallel to the film surface and that the thickness of the lamellar interface was about 35 A. Also, it was found that the segments in the vicinity of the chemical junction points between two blocks were localized strongly near the lamellar interface, while the segments on the free ends were localized at the center of the lamellar microdomains with fairly wide distribution.