Unusual Phase Behavior of the Mixture of Poly(acrylic acid) and Poly(diallyldimethylammonium chloride) in Acidic Media

Solid-Liquid-Solution Phases in Poly(diallyldimethylammonium)/Poly(acrylic acid) Polyelectrolyte Complexes at Varying Temperatures

The coacervation and complexation of oppositely charged polyelectrolytes are dependent on numerous environmental and preparatory factors, but temperature is often overlooked. Temperature effects remain unclear because the temperature dependence of both the dielectric constant and polymer-solvent interaction parameter can yield lower and/or upper critical solution phase behaviors for PECs. Further, secondary interactions, such as hydrogen bonding, can affect the temperature response of a PEC. That is, mixtures of oppositely charged polyelectrolytes can exhibit phase separation upon lowering and/or increasing the mixture's temperature. Here, the phase behavior of poly(diallylmethylammonium)/poly(acrylic acid) (PDADMA/PAA) complexes under varying KBr ionic strengths, mixing ratios, and temperatures at a fixed pH (in which PAA hydrogen bonding can occur) is examined. At room temperature, the PDADMA/PAA PECs exhibit four different phase states: precipitate, coexisting precipitate and coacervate, solid-like gel, and coacervate. Variable-temperature optical microscopy reveals the upper critical solution temperature (UCST) at which each phase transitioned to a solution state. Interestingly, the UCST value is highly dependent on the original phase of the PEC, in which solid-like precipitates exhibit higher UCST values. Large-scale all-atom molecular dynamics (MD) simulations support that precipitates exhibit kinetic trapping, which may contribute to the higher UCST values observed in the experiment. Taken together, this study highlights the significance of temperature on the phase behavior of PECs, which may play a larger role in stimuli-responsive materials, membraneless organelles, and separations applications.

New Bio-Based Furanic Materials Effectively Absorb Metals from Water and Exert Antimicrobial Activity

Development of sustainable bio-based materials for removal of toxic contaminants from water is a high priority goal. Novel bio-based binary and ternary copolymers with enhanced ion-exchange, adsorption and antibacterial properties were obtained by using plant biomass-derived diallyl esters of furandicarboxylic acid (FDCA) as crosslinking agents and easily available vinyl monomers. The synthesized copolymer materials showed higher sorption capacities for Ni^II , Co^II and Cu^II compared to the commercial ion-exchange resins, and they maintained their high metal adsorption capacities for over 10 cycles of regeneration. The synthesized copolymer gels containing 1-5 wt % of the crosslinker showed excellent water absorption capacities. The synthesized copolymers with 1 % crosslinker content showed swelling ratios high enough to also act as moisture absorbents. Synthesized copolymers with crosslinker content of 10 wt % performed as contact-active antibacterials by inhibiting the growth of Gram-positive (S. aureus) and Gram-negative bacteria (E. coli, K. pneumonia) in suspension tests.

Interaction Mechanism of Anionic Lignin and Cationic Soft Surface in Saline Systems

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 ζ-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.

Transparent Polyelectrolyte Complex Thin Films with Ultralow Oxygen Transmission Rate

Limiting oxygen permeation through plastic films is important for extending the shelf life of food and flexible electronic devices. Polyelectrolyte complex (PEC) thin films can be used to reduce small molecule diffusion through commodity plastic films. PEC thin films are frequently applied using layer-by-layer assembly, which often requires many processing cycles to deposit a film with desired thickness. An aqueous solution of poly(diallydimethylammonium chloride) and poly(acrylic acid) can be deposited in a single-step to quickly fabricate a high-oxygen barrier thin film. These films have an ionically bonded network that forms after polyelectrolyte deposition and exposure to buffer. Increasing buffer concentration and adding salt increases film cohesion and improves transparency by reducing surface roughness. When deposited onto a 178 μm poly(ethylene terephthalate) film, a ∼1.9 μm thick PEC coating imparts a 2 orders of magnitude reduction in oxygen transmission rate. Achieving this level of gas barrier with a single thin coating layer creates numerous opportunities for the protection of sensitive food, pharmaceuticals, and electronics.

Calcium phosphate hybrid nanoparticles: self-assembly formation, characterization, and application as an anticancer drug nanocarrier

Calcium phosphate hybrid nanoparticles (CaP-HNPs) have been synthesized in aqueous solution through self-assembly by using two oppositely charged polyelectrolytes (poly(diallyldimethylammonium chloride) (PDADMAC) and poly(acrylate sodium) (PAS)) as dual templates. First, the PAS/Ca(2+) and PDADMAC/PO4(3-) complexes form through electrostatic interactions and then two complexes self-assemble into CaP-HNPs after mixing them together. The as-prepared CaP-HNPs exhibit a spherical morphology with a narrow size distribution, good dispersibility, and high colloidal stability in water. The CaP-HNPs are explored as a nanocarrier for the anticancer drug docetaxel (Dtxl). The CaP-HNPs show excellent biocompatibility, high drug-loading capacity, pH-sensitive drug-release behavior, and high anticancer effect after being loaded with Dtxl. Therefore, the as-prepared CaP-HNPs are promising drug nanocarriers for cancer therapy.