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Polyelectrolyte complexes, PECs, are glassy and brittle when dry but may be plasticized with water. Though hydrated PECs contain a high proportion of water, many still exhibit a glass transition in the 0 to 100 oC range. The apparently unique effectiveness of water as a plasticizer of PECs has been an obstacle to further developments in applications and in fundamental studies of PEC properties. In this work it is shown that formamide is an excellent and even superior solvent for plasticizing PECs, substantially decreasing glass transition temperatures relative to those of hydrated PECs when formamide is used as a solvent instead. The affinities of PECs for water and formamide, indicated by the (exothermic) enthalpies of solvent swelling of dry PECs, are comparable. Ion transport dynamics revealed similar lifetimes, about 1 ns, of charge pairs within a PEC solvated with water compared to formamide, despite the differences in their dielectric constants. Ion transport dynamics, which depend on the mobility of pendant groups, have lower cooperativity than those of the polymer backbone. The use of formamide is a significant experimental variable for reducing the glass transition temperature/viscosity of complexed polyelectrolytes and can turn a solidlike hydrated complex into a fluidlike coacervate. 

The linear viscoelastic response, LVR, of a hydrated polyelectrolyte complex coacervate, PEC, was evaluated over a range of frequencies, temperatures, and salt concentrations. The PEC was a nearly-stoichiometric blend of a quaternary ammonium poly([3-(methacrylamido)propyl]trimethylammonium chloride), PMAPTAC, and poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt), PAMPS, an aliphatic sulfonate, selected because they remain fully charged over the conditions of use. Narrow molecular weight distribution polyelectrolytes were prepared using fractionation techniques. A partially deuterated version of PMAPTAC was incorporated to determine the coil radius of gyration, Rg, within PECs using small angle neutron scattering. Chain dimensions were determined to be Gaussian with a Kuhn length of 2.37 nm, which remained constant from 25 to 65 0C. The LVR for a series of matched molecular weight PECs, mostly above the entanglement threshold, exhibited crossovers of modulus versus frequency classically attributed to the reptation time, relaxation between entanglements, and the relaxation of a Kuhn length of units (the “monomer” time). The scaling for zero shear viscosity, η0, versus chain length N, was η0 ~ N3.1, in agreement with “sticky reptation” theory. The lifetime and activation energy, Ep, of a pair between polyanion and polycation repeat units, Pol+Pol-, were determined from diffusion coefficients of salt ions within the PEC. The activation energy for LVR of salt-free PECs was 2Ep, showing that the key mechanism limiting the dynamics of undoped PECs is pair exchange. An FTIR technique was used to distinguish whether SCN- acts as a counterion or a co-ion within PECs. Doping of PECs with NaSCN breaks Pol+Pol- pairing efficiently, which decreases effective crosslinking and decreases viscosity. An equation was derived that quantitatively predicts this effect. 

Coatings that prevent or decrease fouling are sought for many applications, including those that inhibit the attachment of organisms in aquatic environments. To date, antifouling coatings have mostly followed design criteria assembled over decades: surfaces should be well/strongly hydrated, possess low net charge and maintain a hydrophilic character when exposed to the location of use. Thus, polymers based on ethylene glycol or zwitterionic repeat units have been shown to be highly effective. Unfortunately, hydrated materials can be quite soft, limiting their use in some environments. In a major paradigm shift, this work describes glassy antifouling films made from certain complexes of positive and negative polyelectrolytes. The dense network of electrostatic interactions yields tough materials below the glass transition temperature, Tg, in normal use, while the highly ionic character of these polyelectrolyte complexes ensures strong hydration. The close proximity of equal numbers of opposite charges within these complexes mimics zwitterionic structures. Films, assembled layer-by-layer from aqueous solutions, contained sulfonated poly(ether ether ketone), SPEEK, a rigid polyelectrolyte which binds strongly to a selection of quaternary ammonium polycations. Layer-by-layer buildup of SPEEK and polycations was linear, indicating strong complexes between polyelectrolytes. Calorimetry also showed complex formation was exothermic. Surfaces coated with these films in the 100 nm thickness range completely resisted adhesion of the common flagellate green algae, Chlamydomonas reinhardtii which were removed from surfaces at the minimum applied flow rate of 0.8 cm s-1. The total surface charge density of adsorbed cations, determined with a sensitive radioisotopic label, was very low, around 10% of a monolayer, which minimized adsorption driven by counterion release from the surface. The viscoelastic properties of the complexes, which were stable even in concentrated salt solutions, were explored using rheology of bulk samples. When fully hydrated, their Tgs were observed to be above 75 oC. 

The modulus of coacervates made from charged (bio)polymers and small molecules jumps when valency increases from three to four.