Masashi Osa

Is a Cloud-Point Curve in Aqueous Poly(N-isopropylacrylamide) Solution Binodal?

Transmittance of light passing through an aqueous solution of a linear poly(N-isopropylacrylamide) (PNIPA) sample synthesized by living anionic polymerization was examined in detail in the vicinity of its cloud point. It is found that the transmittance approaches a constant value between 0 and 100% even at a temperature slightly higher than the cloud point, indicating that macroscopic phase separation does not take place at the cloud point in the solution and therefore the cloud-point curve dose not correspond to the binodal. Static and dynamic light scattering measurements were then carried out for aqueous solutions of the linear sample and also of another one synthesized by radical polymerization, which has random-branched structure, at some temperatures considerably lower than the cloud point. It was found that both the PNIPA samples in aqueous solutions form aggregates even at such temperatures, and the number, size, and density profile of the aggregates depend on the kind of chain end group and also on the primary structure.

Dynamics of coarse-grained helical wormlike chains. III. First cumulant of the dynamic structure factor

The dynamic structure factor S(k,t) as a function of the magnitude k of the scattering vector and time t and its first cumulant Ω(k) are evaluated in the Gaussian approximation on the basis of the coarse-grained helical wormlike chain model. In this approximation, S(k,t) and therefore Ω(k) may be expressed in terms of the solutions of the 1(1) eigenvalue problem previously obtained. It is then found that the eigenvalues in the j=0 branch of the 1(1) eigenvalue spectrum at small wave numbers make main contribution to Ω(k). The numerical results for typical flexible polymers show that the so-called “universal” plot of η0Ω(k)/kBTk3 against 〈S2〉1/2k depends on the kind of polymer, where η0 is the solvent viscosity, kB the Boltzmann constant, T the absolute temperature, and 〈S2〉 the mean-square radius of gyration. It is also shown that for semiflexible chains, the plot depends appreciably on the reduced total contour length. A comparison of theory with experiment is made with respect to Ω(k) and also the coefficient C introduced by Stockmayer and co-workers. It is then found that the theory may give a rather satisfactory explanation of experimental results for both flexible and semiflexible polymers despite the fact that the preaveraged Oseen tensor is used along with the Gaussian approximation.The dynamic structure factor S(k,t) as a function of the magnitude k of the scattering vector and time t and its first cumulant Ω(k) are evaluated in the Gaussian approximation on the basis of the coarse-grained helical wormlike chain model. In this approximation, S(k,t) and therefore Ω(k) may be expressed in terms of the solutions of the 1(1) eigenvalue problem previously obtained. It is then found that the eigenvalues in the j=0 branch of the 1(1) eigenvalue spectrum at small wave numbers make main contribution to Ω(k). The numerical results for typical flexible polymers show that the so-called “universal” plot of η0Ω(k)/kBTk3 against 〈S2〉1/2k depends on the kind of polymer, where η0 is the solvent viscosity, kB the Boltzmann constant, T the absolute temperature, and 〈S2〉 the mean-square radius of gyration. It is also shown that for semiflexible chains, the plot depends appreciably on the reduced total contour length. A comparison of theory with experiment is made with respect to Ω(k) and also the coeff...

Dynamics of coarse‐grained helical wormlike chains. II. Eigenvalue problems

The eigenvalue problem for the matrix representation of the diffusion operator appearing in the diffusion equation previously derived for the coarse‐grained helical wormlike (HW) chain model is considered. Following the procedure already established in the study of the original diffusion equation for the discrete HW chain, the problem is solved in the subspace and block‐diagonal approximations in the subspace L(1), where L is the ‘‘total angular momentum quantum number’’ and (1) indicates the one‐body excitation basis set. The 1(1) eigenvalues λ1,kj thus obtained form three branches of the eigenvalue spectrum specified by the index j as before, and it is shown that λ1,k0 in the j=0 (lowest) branch at small wave number k is approximately proportional to the corresponding Rouse–Zimm eigenvalue in the Hearst version. The behavior of the eigenvalue spectra is also numerically examined taking atactic polystyrene with the fraction of racemic diads fr=0.59 and atactic poly(methyl methacrylate) with fr=0.79 as ty...

Difference in dilute aqueous solution behavior between poly(ethylene glycol) and poly(ethylene oxide)

AbstractStatic light scattering behavior was examined for poly(ethylene glycol) (PEG) and poly(ethylene oxide) (PEO) of small weight-average molecular weight Mw (3 × 103−2 × 104), in methanol and water at 25.0 °C, the former polymer having hydroxy groups at both ends and the latter having a methoxy group at one end and a hydroxy group at the other. It was found that some aggregates of large size are formed in aqueous solutions of the PEO samples with Mw = 3.81 × 103 and 7.00 × 103, while all PEG and PEO samples are isolated in methanol solutions, and the PEG samples and the PEO sample of the largest Mw (=1.60 × 104) are also isolated even in the aqueous solutions. From the results of dynamic light scattering measurements for the aqueous solution of the PEO sample with Mw = 3.81 × 103 at 25.0 °C, there were detected two classes of scatterers having different sizes, i.e., the isolated chains and aggregates, the apparent hydrodynamic radius of the latter being ca. twenty times as large as that of the former.Static light scattering measurements are carried out for poly(ethylene glycol) and poly(ethylene oxide) (PEO) of the weight-average molecular weight Mw ranging from 3×103 to 2×104 in methanol and water at 25.0 °C. Some aggregates of large size are found to be formed only in the cases of PEO of Mw∼O(103) in aqueous solutions, although for other cases polymer chains are isolated in solutions.

Fine characterization of oligomers and polymers in dilute solution

Abstract A fine characterization was made of atactic poly(a-methylstyrene) and atactic polystyrene on the basis of the helical wormlike chain model. It is found that there is a remarkable difference in chain stiffness and local chain conformation between the two polymers. Such a difference is shown to be reflected clearly in behavior of equilibrium, transport, and dynamical properties and also in the excluded-volume effects.