Spraying asymmetry into functional membranes layer-by-layer.

As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities. By simply varying the flow rate of charged species passing through an electrospun material during spray-assisted layer-by-layer deposition, individual fibres within the matrix can be conformally functionalized for ultrahigh-surface-area catalysis, or bridged to form a networked sublayer with complimentary properties. Exemplified here by the creation of selectively reactive gas purification membranes, the myriad applications of this technology also include self-cleaning fabrics, water purification and protein functionalization of scaffolds for tissue engineering.

Metal ion reactive thin films using spray electrostatic LbL assembly.

By using the spray-layer-by-layer (Spray-LbL) technique, the number of metal counterions trapped within LbL coatings is significantly increased by kinetically freezing the film short of equilibrium, potentially limiting interchain penetration and forcing chains to remain extrinsically compensated to a much greater degree than observed in the traditional dipped LbL technique. The basis for the enhanced entrapment of metal ions such as Cu2+, Fe2+, and Ag+ is addressed, including the equilibrium driving force for extrinsic compensation by soft versus hard metal ions and the impact of Spray-LbL on the kinetics of polymer-ion complexation. These polymer-bound metal-ion coatings are also demonstrated to be effective treatments for air filtration, functionalizing existing filters with the ability to strongly bind toxic industrial compounds such as ammonia or cyanide gases, as well as chemical warfare agent simulants such as chloroethyl ethyl sulfide. On the basis of results reported here, future work could extend this method to include other toxic soft-base ligands such as carbon monoxide, benzene, or organophosphate nerve agents.

Anti-reflective optical coatings incorporating nanoparticles.

This paper presents a simple approach for forming anti-reflective film stacks on plastic substrates employing aqueous colloidal dispersions of metal oxide nanoparticles. Results demonstrate that it is possible to fabricate a polymeric thin film of continuously tunable refractive index over a wide range by loading the film with varying concentrations of metal oxide nanoparticles. Specifically, the refractive index for the polymer film was tuned from 1.46 to 1.54 using silica nanoparticle loadings from 50 to 0 wt% and from 1.54 to 1.95 using ceria nanoparticle loadings from 0 to 90 wt%, respectively. The low and high refractive index layers are then combined to create an anti-reflective coating which exhibits a reflectance spectrum, abrasion resistance, haze and transmission values that compare well with those produced using state-of-the-art vacuum based techniques. Furthermore, the results show that it is possible to begin with aqueous dispersions and then dilute them with organic solvents for use in a spin coating method to prepare the polymer-metal oxide nanoparticle composite films.