Electrochemistry in supercritical fluids

A wide range of supercritical fluids (SCFs) have been studied as solvents for electrochemistry with carbon dioxide and hydrofluorocarbons (HFCs) being the most extensively studied. Recent advances have shown that it is possible to get well-resolved voltammetry in SCFs by suitable choice of the conditions and the electrolyte. In this review, we discuss the voltammetry obtained in these systems, studies of the double-layer capacitance, work on the electrodeposition of metals into high aspect ratio nanopores and the use of metallocenes as redox probes and standards in both supercritical carbon dioxide–acetonitrile and supercritical HFCs

Orientation and symmetry control of inverse sphere magnetic nanoarrays by guided self-assembly

Inverse sphere shaped Ni arrays were fabricated by electrodeposition on Si through the guided self-assembly of polystyrene latex spheres in Si/SiO2 patterns. It is shown that the size commensurability of the etched tracks is critical for the long range ordering of the spheres. Moreover, noncommensurate guiding results in the reproducible periodic triangular distortion of the close packed self-assembly. Magnetoresistance measurements on the Ni arrays were performed showing room temperature anisotropic magnetoresistance of 0.85%. These results are promising for self-assembled patterned storage media and magnetoresistance devices

Comportamento elettrochimico di polimeri compositi poli(anilina)/poli(stirensolfonato) a pH neutri: influenza dello spessore del film

A differenza della maggior parte dei polimeri conduttori, per i quali si osserva una sola transizione conduttore/isolante, la poli(anilina) (PANI) passa, per ossidazione elettrochimica in soluzione acquosa acida, dallo stato isolante (leucoemeraldina) allo stato conduttore (emeraldina) e nuovamente ad uno stato isolante (pernigranilina). In più le sue proprietà conduttrici dipendono anche dalla protonazione del polimero cosicché è possibile osservare anche una transizione conduttore/isolante a seguito della deprotonazione dell'emeraldina. E' evidente che quest'ultimo comportamento limita significativamente l'impiego del PANI in un ristretto intervallo di pH acidi. Tale limitazione è in parte superabile con la realizzazione di film compositi di PANI, ottenuti per polimerizzazione elettrochimica in presenza di polianioni quali il poli(vinilsolfonato) o il poli(stirensolfonato) (PSS). L'anione polimerico infatti, essendo intrappolato all'interno della matrice polimerica, non può essere scambiato con gli anioni presenti in soluzione il che assicura quindi un apprezzabile grado di protonazione del PANI anche in soluzioni con bassa concentrazione protonica. Incidentalmente, tali polimeri compositi rivestono grande importanza nel campo della bioelettrochimica in quanto sono in grado di promuovere il trasferimento elettronico diretto di taluni enzimi [1] in condizioni tali da non precludere la stabilità di questi ultimi. Essi pertanto sono utilizzabili per la realizzazione di dispositivi innovativi quali ad esempio i "transistor elettrochimici" [2]. La presente comunicazione intende illustrare uno studio sul comportamento elettrochimico a pH neutri di un film composito PANI/PSS, elettrosintetizzato potenziostaticamente in presenza di un monomero para sostituito, quale l'1,4-diamminobenzene, in grado di promuovere la formazione di gruppi fenazinici (mediatori efficaci per una vasta serie di enzimi) in seguito ad accoppiamenti di tipo orto all'interno del polimero e successiva ciclizzazione [3]. Questo studio ha evidenziato la capacità dell'1,4-diamminobenzene di modulare il grado di cross-linking del polimero risultante, la sua struttura e quindi la sua elettroattività. In particolare il comportamento elettrochimico del polimero è risultato fortemente influenzato dal suo spessore. Infatti si è osservato un grado di elettroattività apprezzabile solo per film polimerici sottili: ciò suggerisce che gli accoppiamenti orto sembrano prevalere all'inizio del processo di elettrosintesi garantendo così una struttura compatta con alto grado di cross-linking. Questa indagine ha permesso la realizzazione di film compositi PANI/PSS elettroattivi e stabili a pH neutri, ad elevato carattere fenazinico e quindi di sicuro interesse in campo bioelettrochimico. [1] Bartlett, P. N.; Wang, J. H. J. Chem. Soc., Faraday Trans. 1996, 92, 4137 [2] Bartlett, P. N.; Birkin, P. R. Anal. Chem. 1994, 66, 1552 [3] Mailhe, C.; Desilvestro, J. J. Electroanal. Chem. 1989, 262, 28

The Oxidation of Hydrogen Peroxide on Nanostructured Rhodium Microelectrodes

在含有C12EO8(Octaethyleneglycol Monododecyl Ether)的H1溶致液晶相中Pt微电极上电沉积Rh介孔膜. 该电极在中性、低浓度（CH2O2 <10 mmol•L-1）条件下，对H2O2有较好的氧化还原响应及稳定性. 由于电流磁滞效应，H2O2在Rh介孔膜微电极上的氧化与电位相关，且遵循与Rh(OH)3有关的CEE（Chemical Reaction-Electron Transfer Reaction- Electron Transfer Reaction）反应机制. H2O2浓度较大时，孔电极表面其结合点位趋于饱和或在孔内溶液酸化的反应限制，电流可呈现一个平台. Rh介孔膜厚度小于200 nm的电极，H2O2浓度校正曲线符合膜孔反应一维扩散模型.Mesoporous Rh films were deposited onto platinum microelectrodes from the H1 lyotropic liquid crystalline phase of C12EO8 (octaethyleneglycol monododecyl ether). The electrodes show well defined voltammetry for the oxidation and the reduction of hydrogen peroxide at low concentrations (<10 mmol•L-1) with excellent stability for operation at neutral pH. Based on the hysteresis in the current and the potential dependence the oxidation of hydrogen peroxide occurs through a CEE mechanism involving Rh(OH)3 on the mesoporous Rh electrode surface. At higher hydrogen peroxide concentrations the current reaches a plateau that is due to either saturation of the binding sites for hydrogen peroxide or limitation of the reaction due to acidification of the solution within the pores. For the thin films (below 200 nm) the hydrogen peroxide calibration curves we fitted to a one dimensional model for diffusion and reaction within the pores.This work was supported by the EPSRC Grant EP/E0473X/1This work was supported by the EPSRC Grant EP/E0473X/1作者联系地址：南安普顿大学化学系, 英国 南安普顿 SO17 1BJ 1Now at: Department d’Enginyeria Quimica, Universitat Rovira i Virgili, Avinguda Pa?sos Catalans 26, 43007 Tarragona, SpainAuthor's Address: Chemistry, University of Southampton, Southampton, SO17 1BJ, UK通讯作者E-mail：[email protected]

Компьютерное моделирование удара упругой сферы с упругим полупространством

В последнее время физика взаимодействия твердых частиц представляет интерес для большинства технологических процессов, связанных с динамикой сыпучих сред. Однако до сих пор не было разработано единой теории взаимодействия частиц при их соударении из-за сложности описания контакта взаимодействующих частиц. Аналитическое решение существует только для простейшего случая, когда при ударе наблюдается полное скольжение без трения

AC-assisted deposition of aggregate free silica films with vertical pore structure

Silica thin films with vertical nanopores are useful to control access to electrode surfaces and may act as templates for growth of nanomaterials. The most effective method to produce these films, electrochemically assisted surfactant assembly, also produces aggregates of silica particles. This paper shows that growth with an AC signal superimposed onto the potential avoids the aggregates and only very small numbers of single particles are found. This finding is linked to better control of the diffusion field of hydroxide ions that are responsible for particle growth. The resultant films are smooth, with very well-ordered hexagonal pore structures

Hard Spheres in Vesicles: Curvature-Induced Forces and Particle-Induced Curvature

We explore the interplay of membrane curvature and nonspecific binding due to excluded-volume effects among colloidal particles inside lipid bilayer vesicles. We trapped submicron spheres of two different sizes inside a pear-shaped, multilamellar vesicle and found the larger spheres to be pinned to the vesicle's surface and pushed in the direction of increasing curvature. A simple model predicts that hard spheres can induce shape changes in flexible vesicles. The results demonstrate an important relationship between the shape of a vesicle or pore and the arrangement of particles within it.Comment: LaTeX with epsfig; ps available at http://dept.physics.upenn.edu/~nelson/index.shtml Phys Rev Lett in press (1997

3D-structured mesoporous silica memristors for neuromorphic switching and reservoir computing

Memristors are emerging as promising candidates for practical application in reservoir computing systems that are capable of temporal information processing. Here, we experimentally implement a physical reservoir computing system using resistive memristors based on three-dimensional (3D)-structured mesoporous silica (mSiO2) thin films fabricated by a low cost, fast and vacuum-free sol–gel technique. The in situ learning capability and a classification accuracy of 100% on a standard machine learning dataset are experimentally demonstrated. The volatile (temporal) resistive switching in diffusive memristors arises from the formation and subsequent spontaneous rupture of conductive filaments via diffusion of Ag species within the 3D-structured nanopores of the mSiO2 thin film. Besides volatile switching, the devices also exhibit a bipolar non-volatile resistive switching behavior when the devices are operated at a higher compliance current level. The implementation of mSiO2 thin films opens the route to fabricate a simple and low cost dynamic memristor with a temporal information process functionality, which is essential for neuromorphic computing applications