We describe a versatile approach for preparing flash memory devices composed of polyelectrolyte/gold nanoparticle multilayer films. Anionic gold nanoparticles were used as the charge storage elements, and poly(allylamine)/poly(styrenesulfonate) multilayers deposited onto hafnium oxide (HfO2)-coated silicon substrates formed the insulating layers. The top contact was formed by depositing HfO2 and platinum. In this study, we investigated the effect of increasing the number of polyelectrolyte and gold nanoparticle layers on memory performance, including the size of the memory window (the critical voltage difference between the 'programmed' and 'erased' states of the devices) and programming speed. We observed a maximum memory window of about 1.8 V, with a stored electron density of 4.2 x 1012 cm-2 in the gold nanoparticle layers, when the devices consist of three polyelectrolyte/gold nanoparticle layers. The reported approach offers new opportunities to prepare nanostructured polyelectrolyte/gold nanoparticle-based memory devices with tailored performance.

Polymer hydrogels are used in diverse biomedical applications including drug delivery and tissue engineering. Among different chemical linkages, the natural and reversible thiol-disulfide interconversion is extensively explored to stabilize hydrogels. The creation of macro-, micro-, and nanoscale disulfide-stabilized hydrogels commonly relies on the use of oxidizing agents that may have a detrimental effect on encapsulated cargo. Herein an oxidization-free approach to create disulfide-stabilized polymer hydrogels via a thiol-disulfide exchange reaction is reported. In particular, thiolated poly(methacrylic acid) is used and the conditions of polymer crosslinking in solution and on colloidal porous and solid microparticles are established. In the latter case, removal of the core particles yields stable, hollow, disulfide-crosslinked hydrogel capsules. Further, a procedure is developed to achieve efficient disulfide crosslinking of multilayered polymer films to obtain stable, liposome-loaded polymer-hydrogel capsules that contain functional enzymatic cargo within the liposomal subcompartments. This approach is envisaged to facilitate the development of biomedical applications of hydrogels, specifically those including fragile cargo.

We introduce a novel and facile approach to improve the desalination performance of pressure-driven layer-by-layer (LbL) assembled membranes. Electrostatic LbL multilayers composed of weak polyelectrolytes (PEs), e.g., cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA), were prepared on commercial polysulfone substrates. In order to measure the ion rejection and permeate flux of these membranes, the ionic concentration of the feed solution and operating pressure were fixed at 2000 ppm NaCl and 20 bar, respectively. It was observed that the crosslinked (PAH pH 7.5/PAA pH 3.5) n¼10,20 multilayers, which were assembled at the pH conditions allowing a low charge density of the respective PEs, show relatively high ion rejection compared to other multilayers. This result suggests that the optimal structures for desalination membranes should contain a large amount of freely charged groups with densely-packed structures via crosslinking. Finally, the recycling process was employed to further improve the desalination performance. In this case the (PAH pH 7.5/PAA pH 3.5) n¼10,20 multilayers exhibited the ion rejection up to 99.8%. This pH-controlled and thermal crosslinking method suggests a new route for the design of well-defined desalination reverse osmosis membranes based on LbL multilayers.

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