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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. 

Polymer chain diffusion within a hydrated polyelectrolyte complex, PEC, has been measured using an ultrathin film format prepared by the layer-by-layer method. Isotopically labeled self-exchange of deuterated poly(styrene sulfonate), dPSS, with undeuterated PSS of the same narrow molecular weight distribution permitted reliable estimates of whole-molecule diffusion coefficients, D. Narrow molecular weight distribution poly(diallyldimethylammonium), PDADMA, was used as the polycation for the PEC. Extensive pretreatment of starting films was undertaken to remove residual stress, anisotropy, and layering. PSS/PDADMA “multilayers,” PEMUs, thin enough to provide substantial exchange of polyelectrolyte, even with diffusion coefficients as low as 10–16 cm2 s–1, as a function of salt concentration and temperature were measured for this PEC, which has a glass-transition temperature, Tg, close to room temperature. Two molecular weights of dPSS, about 15 and 100 kDa, presumed to be below and above the entanglement molecular weight, respectively, both diffused faster at higher temperatures with respective activation energies, Ea, of about 21 and 53 kJ mol–1, the latter about the same as Ea for the place exchange between two pairs of PSS:PDADMA. Studies of the linear viscoelastic response of macroscopic PECs showed a difference of about 8 °C in the Tg of the two lengths of PSS complexed with the same PDADMA. Increasing concentrations of NaCl influenced D of 100 kDa PSS but not 15 kDa PSS at room temperature. D was faster in the region of the film near the solution interface, again attributed to a lower Tg caused by greater water content at this interface.