Aggregate-containing solutions of poly(n-hexyl isocyanate) (PHIC) and atactic polystyrene
of finite concentrations were studied by static and dynamic light scattering. Their static structure factors
Ŝ(k) and the intensity autocorrelation functions g
(2)(t) exhibited the enhanced low-angle scattering and
bimodal relaxation, respectively. From Ŝ(k) and g
(2)(t) obtained, the fast- and slow-mode components of
the static structure factor (Ŝ
fast(k) and Ŝ
slow(k)) and of the first cumulant (Γfast and Γslow) were estimated
as functions of the magnitude of the scattering vector k. As verified by a theory based on the dynamic
mean-field theory, if the solution contains only a small amount of aggregates with diffusion coefficients
much smaller than that of the nonaggregating component, Ŝ
fast(k) and Γfast give us the osmotic
compressibility ∂c/∂Π and mutual diffusion coefficient D
m of aggregate-free solutions, respectively, and
Ŝ
slow(k) and Γslow provide us the radius of gyration 〈S
2〉
z
,
A
1/2 and hydrodynamic radius R
H,A of aggregates,
respectively, even at a finite polymer concentration, in a good approximation. In fact, the results of ∂c/∂Π
and D
m obtained were favorably compared with theories for binary polymer solutions without aggregates.
For PHIC solutions, aggregates of lower molecular weight samples had larger 〈S
2〉
z
,
A
1/2 and R
H,A, indicating
that the aggregates of lower molecular weight PHIC consist of a larger number of polymer chains.
Furthermore, the ratio of 〈S
2〉
z
,
A
1/2 to R
H,A indicated that aggregates of higher-molecular-weight PHIC are
rigid-chain-like but those of lower-molecular-weight PHIC are spherelike.
The dimensions and intermolecular interactions of a surface-grafted and unbound free polyampholyte, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estimated in aqueous solutions with various ionic strengths. Free linear PMPC was synthesized by atom-transfer radical polymerization (ATRP), and static light scattering (SLS) and dynamic light scattering (DLS) were carried out for the PMPC solutions with various concentrations of NaCl, c s. The hydrodynamic radius R H and the second virial coefficient A 2 of PMPC were independent of c s (0-0.5 M), though both R H and A 2 of polyampholytes usually strongly depend on the ionic strength. PMPC-immobilized silica nanoparticles (PMPC-SiNP) were also synthesized by surface-initiated ATRP, and DLS was carried out as for the solutions of linear PMPC to investigate the dependence of the dimensions of PMPC immobilized on a solid surface on the ionic strength. The molecular weight and surface density of PMPC immobilized on SiNP were estimated from the results obtained by GPC, NMR, and thermogravimetric analysis. The independence of R H of PMPC-SiNP was also observed, but its magnitude was larger than that of linear PMPC, although the molecular weight of PMPC immobilized on SiNP was smaller than that of linear PMPC. The larger dimension of PMPC immobilized on SiNP was explained by the excluded volume effect between the immobilized polymer chains.
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