Self-assembly of nanocrystal checkerboard patterns via non-specific interactions.

Checkerboard lattices-where the resulting structure is open, porous, and highly symmetric-are difficult to create by self-assembly. Synthetic systems that adopt such structures typically rely on shape complementarity and site-specific chemical interactions that are only available to biomolecular systems (e.g., protein, DNA). Here we show the assembly of checkerboard lattices from colloidal nanocrystals that harness the effects of multiple, coupled physical forces at disparate length scales (interfacial, interparticle, and intermolecular) and that do not rely on chemical binding. Colloidal Ag nanocubes were bi-functionalized with mixtures of hydrophilic and hydrophobic surface ligands and subsequently assembled at an air-water interface. Using feedback between molecular dynamics simulations and interfacial assembly experiments, we achieve a periodic checkerboard mesostructure that represents a tiny fraction of the phase space associated with the polymer-grafted nanocrystals used in these experiments. In a broader context, this work expands our knowledge of non-specific nanocrystal interactions and presents a computation-guided strategy for designing self-assembling materials.

Synthesis of PEDOT:PSS Brushes Grafted from Gold Using ATRP for Increased Electrochemical and Mechanical Stability.

We report PEDOT:PSS brushes grafted from gold using surface-initiated atom-transfer radical polymerization (SI-ATRP) which demonstrate significantly enhanced mechanical stability against sonication and electrochemical cycling compared to spin-coated analogues as well as lower impedances than bare gold at frequencies from 0.1 to 105 Hz. These results suggest SI-ATRP PEDOT:PSS to be a promising candidate for use in microelectrodes for neural activity recording. Spin-coated, electrodeposited, and drop-cast PEDOT:PSS have already been shown to reduce impedance and improve biocompatibility of microelectrodes, but the lack of strong chemical bonds of the physisorbed polymer film to the metal leads to disintegration under required operational stresses including cyclic mechanical loads, abrasion, and electrochemical cycling. Rather than modifying the metal electrode or introducing cross-linkers or other additives to improve the stability of the polymer film, this work chemically tethers the polymer to the surface, offering a simple, scalable solution for functional bioelectronic interfaces.

The Modulation of Electrokinetic Streaming Potentials of Silicon-Based Surfaces through Plasma-Based Surface Processing.

A new plasma processing-based methodology for enhancing the streaming potential (Vs) that may be obtained in electrokinetic flows for a given pressure gradient over a silicon surface-based microchannel is indicated. The dependence of the Vs on both the surface zeta potential and the electrolyte slip length was carefully determined through a series of experiments involving the variation of CF4- and Ar-based plasma parameters, incorporating pressure, exposure time, and power. It was determined through analytical estimates that, while the zeta potential is always increased, the slip length may be diminished under certain conditions. A record value of ∼0.1 mV/Pa was obtained using CF4 plasma at 500 W, 10 mTorr, and 300 s of exposure. The implications of the work extend to the investigation of whether smooth surfaces may be effective for generating large Vs's for new modalities of electrical voltage sources in microfluidics-based applications.