Acrylamide [KLH]

As a first step toward understanding the electroacoustic response of polyelectrolyte hydrogel nanocomposites, we systematically vary the linear charge density of acrylic acid-co-acrylamide polymer networks (at a fixed total polymer concentration) to ascertain how the charge and mobility affect the electrokinetic sonic amplitude (ESA) spectra. A weakly charged polymer registers a negative ESA (real part), which we attribute to dynamics of the elastic network and its charge, whereas a highly charged polymer registers a positive ESA, attributed to sodium counterions. A mechanistic theoretical model is proposed that attributes the transition to the subtle manner in which the hydrodynamic friction of the network strands scale with their linear charge density. Further insights are gained from the electrical conductivity and dynamic shear moduli (in the linear viscoelastic regime). The electrical conductivity is dominated by the mobility of the sodium counterions and is diminished by network hindrance and counterion condensation, and the storage modulus decreases systematically with the linear charge density, suggesting a dominant role of interchain electrostatics, and possibly electro-steric influence on the polymerization and cross-linking.

Lignin has a complicated three-dimensional structure that is different from other synthetic and bio-based materials. In this work, we first examined the physicochemical behavior, i.e., apparent hydrodynamic radius (R-h) and zeta-potential, of carboxymethylated lignin (CM) in a saline system. Then, the detailed interaction and adsorption behavior of CM on a cationic poly(diallyldimethylammonium chloride) (PDADMAC)-coated surface were investigated in a saline system by a quartz crystal microbalance with dissipation. The theoretical and experimental adsorption data revealed that CM made limited surface coverage at a low salt concentration via charge neutralization following an intrinsic compensation mechanism. At a higher salt concentration, the adsorption of CM was improved significantly following the extrinsic compensation mechanism and nonionic interaction (e.g., hydrophobic interaction). The adsorption affinity of CM in the urea environment revealed the contribution (10-30%) of hydrogen bonding in the adsorption of CM on the PDADMAC surface. Contrary to what was found for the CM, the adsorption of a linear poly(acrylic acid-acrylamide) (PAM) on the PDADMAC surface exhibited a dramatic decrease at higher salinity, possibly due to the absence of nonionic and hydrophobic interactions between PAM and the surface. The findings of this study showed the superior adsorption performance of the lignin-based polyelectrolytes to the synthetic ones in salt-containing systems.