Laser-light-scattering study of structure and dynamics of waxy corn amylopectin in dilute aqueous solution

Abstract

The average molecular weight ( M ¯ w ) , gyration radius (< R g>), second virial coefficient ( A 2) and fractal dimension ( d f) of waxy corn amylopectin in aqueous solution were characterized by static light scattering. The results indicated that the single waxy corn amylopectin molecule had a compact structure compared with the linear polymer and was like a swollen branched cluster. The associated waxy corn amylopectin molecule was like a non-swollen branched cluster. The dynamics of waxy corn amylopectin in dilute aqueous solution were investigated by dynamic light scattering. When qR g≤2 (where q is the scattering vector and R g is the gyration radius of amylopectin), the single line-width distribution was found, which was caused by the translational diffusion of waxy corn amylopectin in dilute aqueous solution. The average hydrodynamic radius < R h> could be obtained through Stokes-Einstein equation. When qR g>2, the dynamics of waxy corn amylopectin were dominated by the internal motion of waxy corn amylopectin branching sections, and the first cumulant line-width (< Γ>) could be scaled to the scattering vector ( q) as < Γ>∼ q n ( n=2.73±0.06). It was found that some internal motions were not found at certain observation length by dynamic laser light scattering and some internal motions were suppressed due to the hyperbranched structure of amylopectin. The reduced cumulant Γ*=< Γ>/( q 3 k B T/η 0) could not approach a plateau value with increase of the qR g, and the < Γ>/( q 3 k B T/η 0) value of waxy corn amylopectin was much lower than the value of the linear polymer due to the branched structure and rigid chain of waxy corn amylopectin.