Layer by layer

Abstract: Unilamellar colloids of graphite oxide (GO) were prepared from natural graphite and were grown as monolayer and multilayer thin films on cationic surfaces by electrostatic self-assembly. The multilayer films were grown by alternate adsorption of anionic GO sheets and cationic poly(allylamine hydrochloride) (PAH). The monolayer films consisted of 11−14 A thick GO sheets, with lateral dimensions between 150 nm and 9 μm. Silicon substrates primed with amine monolayers gave partial GO monolayers, but surfaces primed with Al13O4(OH)24(H2O)127+ ions gave densely tiled films that covered approximately 90% of the surface. When alkaline GO colloids were used, the monolayer assembly process selected the largest sheets (from 900 nm to 9 μm) from the suspension. In this case, many of the flexible sheets appeared folded in AFM images. Multilayer (GO/PAH)n films were invariably thicker than expected from the individual thicknesses of the sheets and the polymer monolayers, and this behavior is also attributed to folding...

Abstract: Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

Abstract: Multilayer films which contain ordered layers of more than one protein species were assembled by means of altemate electrostatic adsorption mostly with positively charged poly(ethy1enimine) (PEI) or with negatively charged poly(styrenesu1fonate) (PSS). Water-soluble proteins used are cytochrome c (Cyt), myoglobin (Mb), lysozyme (Lys), histone f3, hemoglobin (Hb), glucoamylase (GA), and glucose oxidase (GOD). Charged protein layers formed multilayers with linear polymers acting as glue or filler. The assembly was monitored by a quartz crystal microbalance and W spectroscopy. Linear film growth was observed up to at least 25 molecular layers. The assembly of Mb and Lys, both positively-charged, was realized in altemation with PSS in the form of {PEI/PSS + (Mb/PSS)2 + (MbPSS/Lys/PSS)d}. The assembly of oppositely-charged (at pH 6.5) Lys and GOD consists from Lys and GOD layers separated by a polycatiodpolyanion bilayer: {PEYPSSPEI f (PSS/Lys)2 + PSSPEI f (GOD/PEI)6}. Hb was assembled as “positive” unit at pH 4.5 (in alternation with PSS) and as “negative” unit at pH 9.2 (in altemation with PEI). A multilayer consisting of alternating montmorillonite, PEI, and GOD layers was also assembled. These biomolecular architecture open a way to construct artificially orchestrated protein systems that can carry out complex enzymic reactions.