Numerical study of dynamic thermal conductivity of nanofluid in the forced convective heat transfer

In this work, forced convective heat transfer of nanofluid in the developing laminar flow (entrance region) in a circular tube is considered. The nanofluid thermal conductivity, as an important parameter, is considered as two parts: static and dynamic part. Simulated results show that the dynamic part of nanofluid thermal conductivity due to the Brownian motion has a minor effect on the heat transfer coefficients, on the other hand, static part of thermal conductivity including nanolayer around nanoparticle has an important role in heat transfer.     

Surface modification of a silicate substrate by a “grafting from” methodology utilizing a perester initiator

The perester silane t-butyl peroxy-11-trichlorosilylundecanoate was synthesized by hydrosilylation of t-butyl peroxy-10-undecanoate with trichlorosilane. These radical initiators were covalently bound to the surface of silicate substrates by self-assembled monolayer (SAM) techniques. Several hydrophilic and hydrophobic acrylate monomers were successfully grafted onto the silicate substrate by in situ polymerization from the surface bound perester initiators. The polymer brushes were characterized by the ATR-IR, XPS, AFM and water contact angles. The results of the study indicate this “grafting from” technique can be used for the preparation of polymer layers with high graft density. While these surface-bound initiators function similarly to surface-bound azo initiators, the preparation of the surface-active perester is a simple, two-step synthesis.     

Evolution of domain walls and reversal mechanism in exchange-coupled nanolayers

The demagnetization process for an exchange-coupled double-nanolayer system with perpendicular easy axes has been investigated within a micromagnetic model. The nucleation field, coercivity and angular distribution of the magnetization, have been obtained as functions of the thickness L of the misaligned layer, the layer with the easy axis perpendicular to the applied field. It is found that the coercivity is identical to the nucleation field only for very small L. For larger L (larger than a quarter of its Bloch wall width), the nucleation field is negative while the coercivity saturates at 0.414H_K, where H_K is the anisotropy field. Thus for larger L, the coercivity mechanism is self-pinning rather than pure nucleation. This self-pinning has both attributes of traditional nucleation and pinning.     

Growth and characteristics of ZnO nano-aggregates electrodeposited onto p-Si(1 1 1)

In this paper we study nanocrystalline zinc oxide thin films produced by oxidation of electrodeposited zinc nanolayers on a monocrystalline p-Si(1 1 1) substrate.The electrolyte used is ZnCl₂, an aqueous solution of 4 × 10⁻² mol/l concentration. Several deposits were made for various current densities, ranging from 13 mA/cm² to 44 mA/cm², flowing through the solution at room temperature. A parametric study enabled us to assess the effect of the current density on nucleation potential and time as well as zinc films structure. The grazing incidence X-ray diffraction (GIXD) revealed that both Zn and ZnO films are polycrystalline and nanometric. After 1-h oxidation of zinc films at 450 °C in the open air, the structural analyses showed that the obtained ZnO films remained polycrystalline with an average crystal size of about 47 nm and with (1 0 0), (0 0 2) and (1 0 1) as preferential crystallographic orientations.     

Synthesis of crosslinked polymer nanoparticles suitable for the formation of nanolayer organic films

Free radical crosslinking copolymerization of styrene and ethylene glycol dimethacrylate (n_ST/n_EGDM in feed = 5/5) has been investigated in toluene. Variation of the reaction conditions allows the formation of macromolecules with low molecular weight (21.6 kDa and 12 nm in diameter), perfectly soluble branched particles in the early stage of the polymerization. Elongation of the reaction time leads to the formation of soluble/swelling microgels with medium molecular weight (156 kDa and 41–120 nm) and, finally, swelling/particularly soluble colloidal polymer particles with very high molecular weight (3.6 MDa and 59–324 nm). Conversion, molecular weight [by gel permeation chromatography (GPC)], ratio of pendant vinyl groups [by nuclear magnetic resonance (NMR)], size of nanoparticles in swollen [by dynamic light scattering (DLS)] and dried state [by transmission electron microscopy (TEM)], morphology [by scanning electron microscopy (SEM)], and nanolayer film formation (by SEM) were measured. The role of reaction conditions in producing different polymer structures and morphologies was demonstrated.     

Properties of nanometric and submicrometric multilayered films of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole)

Multilayered films formed by 3, 5 and 7 alternated layers of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole) have been prepared by chronoamperometry under a constant potential of 1.4 V using a layer-by-layer electrodeposition technique. In order to examine influence of the interface:bulk dimensional ratio, the thickness of the yielded films was reduced from the submicrometric to the nanometric scale by decreasing the polymerization time of each layer from 100 s to 10 s. The electroactivity, electrochemical characteristics and morphologies of the resulting multilayered films have been compared with those obtained for both single-component poly(3,4-ethylenedioxythiophene) films prepared using identical experimental conditions and previously reported multilayered films with thickness within the micrometric scale [Estrany F, Aradilla D, Oliver R, Alemán C. Eur Polym J 2007;43:1876].     

Nanoscale potentiometry

Potentiometric sensors share unique characteristics that set them apart from other electrochemical sensors. Potentiometric nanoelectrodes have been reported and successfully used for many decades, and we review these developments. Current research chiefly focuses on nanoscale films at the outer or the inner side of the membrane, with outer layers for increasing biocompatibility, expanding the sensor response, or improving the limit of detection (LOD). Inner layers are mainly used for stabilizing the response and eliminating inner aqueous contacts or undesired nanoscale layers of water. We also discuss the ultimate detectability of ions with such sensors and the power of coupling the ultra-low LODs of ion-selective electrodes with nanoparticle labels to give attractive bioassays that can compete with state-of-the-art electrochemical detection.