How does the chain extension of poly (acrylic acid) scale in aqueous solution? A combined study with light scattering and computer simulation

Abstract

This work addresses the question of the scaling behavior of polyelectrolytes in solution for a realistic prototype. We show results of a combined experimental (light scattering) and theoretical (computer simulations) investigation of structural properties of the sodium salt of poly (acrylic acid) (Na-PAA). Experimentally, we determined the molecular weight (MW) and the hydrodynamic radius (RH) by static and dynamic light scattering for six different Na-PAA samples in aqueous NaCl-containing solution (0.1–1 mol/l) of polydispersity DP between 1.5 and 1.8. On the computational side, three different variants of a newly developed mesoscopic force field for Na-PAA were employed to determine RH for monodisperse systems of the same MW as in the experiments. The force field effectively incorporates atomistic information and one coarse-grained bead corresponds to one PAA monomer. We find that RH matches with the experimental data for all investigated samples. The effective scaling exponent for RH is found to be around 0.55, which is well below its asymptotic value for good solvents. Additionally, data for the radius of gyration (RG) are presented.

Coarse-Graining in Polymer Simulation: From the Atomistic to the Mesoscopic Scale and Back

“…The hydrodynamic radius of poly(acrylic acid) (sodium salt in dilute aqueous solution, 3.2 wt. %, 333 K, 1 bar) as a function of chain length from dynamic light (*) measurements and simulation (&) [77] . The simulations have been performed using a coarse-grained model parameterised for a 23-mer.…”

“…Reproduced with permission from ref. [77], copyright 2002 American Institute of Physics. a few days, once the atomistic reference data are available.…”

Poly(vinyl phosphonic acid): Hydrodynamic Properties and SEC‐Calibration in Aqueous Solution

“…For PAA-Na with M w of 100 000 a dn/dc of 0.141 mL Á g À1 has been determined, and a difference in dn/dc between 0.136 and 0.147 for different M w has been reported. [21] The apparent increase in the dn/dc with the molar mass may be explained by the influence of the end-groups on the magnitude of dn/dc, and by a possible difference in the microstructure of the PVPA samples as far as they have been prepared at different temperatures. The ratio of head-head to head-tail linkages may be temperature dependent in the Poly(vinyl phosphonic acid): .…”

“…For PAA-Na of different M w , a r about 1.5 for less polydisperse samples has been determined, [21] indicative of the surmise that the PAA chains exhibit a random coil structure in dilute solution for which the r-value normally is between 1.3 and 2.1.…”

“…[1,3,4] R g and R h values are of similar magnitude as observed for pure PAA-sodium salt solutions. [21] The r-parameter (the ratio r ¼ R G /R h ) varies from 1.8 to 2.6 for the PVPA samples. This is unexpectedly high and cannot be easily accounted for by structural differences due to polymerization at different temperatures.…”