Nanocelluloses and Related Materials Applicable in Thermal Management of Electronic Devices: A Review.

Owing to formidable advances in the electronics industry, efficient heat removal in electronic devices has been an urgent issue. For thermal management, electrically insulating materials that have higher thermal conductivities are desired. Recently, nanocelluloses (NCs) and related materials have been intensely studied because they possess outstanding properties and can be produced from renewable resources. This article gives an overview of NCs and related materials potentially applicable in thermal management. Thermal conduction in dielectric materials arises from phonons propagation. We discuss the behavior of phonons in NCs as well.

TiO2 synthesis inspired by biomineralization: control of morphology, crystal phase, and light-use efficiency in a single process.

Hydroxyapatite is mineralized along the long axis of collagen fiber during osteogenesis. Mimicking such biomineralization has great potential to control inorganic structures and is fast becoming an important next-generation inorganic synthesis method. Inorganic matter synthesized by biomineralization can have beautiful and functional structures that cannot be created artificially. In this study, we applied biomineralization to the synthesis of the only photocatalyst in practical use today, titanium dioxide (TiO(2)). The photocatalytic activity of TiO(2) mainly relates to three properties: morphology, crystal phase, and light-use efficiency. To optimize TiO(2) morphology, we used a simple sequential peptide as an organic template. TiO(2) mineralized by a ß-sheet peptide nanofiber template forms fiber-like shapes that are not observed for mineralization by peptides in the shape of random coils. To optimize TiO(2) crystal phase, we mineralized TiO(2) with the template at 400 °C to transform it into the rutile phase and at 700 °C to transform it into a mixed phase of anatase and rutile. To optimize light-use efficiency, we introduced nitrogen atoms of the peptide into the TiO(2) structure as doped elemental material during sintering. Thus, this biomineralization method enables control of inorganic morphology, crystal phase, and light-use efficiency in a single process.

Multistep growth mechanism of calcium phosphate in the earliest stage of morphology-controlled biomineralization.

We studied the effect of surface-functional-group position on precipitate morphology in the earliest stage of calcium phosphate biomineralization and determined the detailed mechanism of precipitation starting from nucleation to precipitate growth. The biomineralization template was a ß-sheet peptide scaffold prepared by adsorption with carboxyl groups arranged at strict 7 Å intervals. Phosphate was then introduced. Within 10 s, highly ordered embryos of calcium phosphate were formed and confined by a peptide nanofiber pattern. They repeatedly nucleated and dissolved, with the larger embryos absorbing the smaller ones in a clear demonstration of an Ostwald-ripening-like phenomenon, then aggregated in a line pattern, and finally formed highly ordered nanofibers of amorphous calcium phosphate. This multistep growth process constitutes the earliest stage of biomineralization.

Morphology control of calcium phosphate by mineralization on the beta-sheet peptide template.

To investigate the influence of the spatial placement of the organic functional groups in mineralization, an amphiphilic peptide assembled monolayer with strictly arrayed carboxyl groups was applied to a mineralization system of calcium phosphate.

[Effects of intravenous vasopressor on spread of spinal anesthesia with 0.5% hyperbaric bupivacaine for caesarean delivery].

BACKGROUND: It is known that when isobaric bupivacaine is applied for Caesarean delivery, phenylephrine is superior to ephedrine in preventing rostral spread of spinal anesthesia. In this study, we prospectively investigated whether phenylephrine can prevent rostral spread of spinal hyperbaric bupivacaine. METHODS: We randomly divided 32 patients undergoing Caesarean delivery into two groups: phenylephrine group and ephedrine group. In both groups, after the spinal injection of 2.0 ml of hyperbaric 0.5% bupivacaine, we started continuous intravenous infusion of phenylephrine or ephedrine. Blood pressure and heart rate were recorded every minute. Block height of cold sensation was assessed at 5, 10 and 15 minutes after the spinal injection. We measured umbilical artery pH after birth. Data were analyzed using a statistical software package. RESULTS: Block height was significantly lower with phenylephrine than with ephedrine at 10 and 15 minutes. Umbilical artery pH was significantly higher with phenylephrine than with ephedrine. Haemodynamic changes were significantly different between the two groups. There were no significant differences in age, BMI and spinal-delivery intervals. CONCLUSIONS: 1. Phenylephrine prevented rostral spread of spinal hyperbaric bupivacaine. 2. Haemodynamic changes were significantly different between the two groups. 3. Umbilical artery pH was significantly higher with phenylephrine than with ephedrine.

[Clinical utility of epidural anesthesia during and after major spine surgery].

BACKGROUND: Spine surgery causes severe postoperative pain, but epidural anesthesia is not commonly used. The main reason is that it might cause some complications, such as motor block and infection. We compared the efficacy of epidural infusion with hypodermic infusion. METHODS: Thirty-two patients scheduled for spine surgery were included in the study. Patients were randomly assigned to receive either continuous epidural infusion (ropivacaine 0.18% and fentanyl 45.5 microg x ml(-1) at 2 ml x hr(-1)) or continuous hypodermic infusion via a patient-controlled analgesia system (morphine 0.04 mg x kg(-1) x ml(-1) at 0.5 ml x hr(-1); bolus: 0.5 ml x hr(-1)). We investigated pain and nausea by using visual analogue scale after surgery. RESULTS: Patient data did not differ between groups. Pain and nausea scores were significantly lower in the epidural infusion group than in the hypodermic infusion group. Epidural infusion did not cause any complications. The incidence of nausea in the hypodermic infusion group was 13 times as high as that in the epidural infusion group. Similarly, the incidence of nausea in female patients was 13 times as high as that in male patients. CONCLUSIONS: Continuous epidural infusion provides superior analgesia even if high-dose local anesthetics are not used. Besides, it decreases the incidence of nausea because systemic administration of opioids can be avoided.

Fluidity of methyl cellulose-contained suspensions and pastes prepared from differently milled Al2O3 powder.

The boundary factors of transition from a methyl cellulose (MC)-contained Al(2)O(3) suspension to a paste were investigated from the view points of adsorption affinity and correlation between average surface to surface separation distance between particles (SDP) and polymer size. Non-damaged and damaged particle surfaces were prepared by wet-jet milling and ball milling, respectively. The amount of MC adsorbed on the wet-jet milled Al(2)O(3) particle surface was decreased by half compared to the ball-milled one. By increasing the solids loading from 10.0 to 12.8 vol%, the MC-contained Al(2)O(3) suspension prepared from ball milling was turned into a paste. On the other hand, it prepared from wet-jet milling was not turned into a paste even if the solid loading was increased from 10.0 to 12.8 vol%. From the creep-recovery measurements, the fluidity of the wet-jet milled sample with 12.8 vol% of solids loading was estimated to be 4 times as large as that of ball-milled one. Therefore, it was found that the state of particle surface had a strong effect on the fluidity of a suspension. The polymer size estimated from the molecular weight and Flory exponent relationship was calculated to be 266 nm. The SDP of suspensions with 10.0 and 12.8 vol% solids loading was calculated to be 215 and 165 nm, respectively. With the decreasing of SDP, the effect of adsorption affinity between the particle surface and the polymer became more striking because the contact area between them was increased. Hence, there are two factors that control the transition between a suspension and a paste; one is the relationship between SDP and polymer size, and the other is the adsorption affinity between the particle surface and the polymer.

AFM interaction study of alpha-alumina particle and c-sapphire surfaces at high-ionic-strength electrolyte solutions.

Ionic strength dependence of interaction and friction forces between hydrophilic alpha-alumina particles and c-sapphire surfaces (0001) were investigated under basic pH conditions using the colloidal probe method. The compression of the double layer could be seen from force-distance curves as the ionic strength of the solution increased. The forces were repulsive at all ionic strengths measured, even though the interaction distance changed drastically. No jump to contact occurred. The interaction distance decreased from about 20 nm in 10(-3) M KCl solution to about 7 nm in the 1 M KCl case. The lubricating effect of hydrated cations on the lateral friction force was demonstrated at high electrolyte concentrations. This was attributed to more hydrated cations being present in the solution. The friction behavior was closely related to the short-range repulsive forces between the alpha-alumina surfaces at pH 11.

Macroporous ZrO2 ceramics prepared from colloidally stable nanoparticles building blocks and organic templates.

ZrO2 macroporous materials with well-ordered structures were prepared using nano-ZrO2 particles as the building materials and polystyrene spheres as the organic templates. A well-dispersed nano-ZrO2 suspension with a narrow particle size distribution was prepared by deagglomeration of as-received nano-ZrO2 powders via ultrasonication, and then centrifugation was performed to remove agglomerated bigger particles. Negatively charged polystyrene spheres were uniformly coated with positively charged nano-ZrO2 particles by means of electrostatic attraction at pH 4. Green samples were prepared by slip casting from colloidally stable suspension of nano-ZrO2 coated polystyrene spheres. ZrO2 macroporous materials with well-ordered microstructure derived from the nano-ZrO2 coated polystyrene spheres.

Crystal Orientation of Hydroxyapatite Induced by Ordered Carboxyl Groups.

Hydroxyapatite (HAp) crystals were grown from simulated body fluid (SBF) onto the arachidic acid monolayers with carboxyl groups, which were prepared by the Langmuir-Blodgett (LB) method on substrates. From X-ray diffraction patterns, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectra, it was concluded that the crystalline phase nucleated on the LB monolayers was HAp, which was induced by the monolayer because no crystalline materials were grown on substrates without a monolayer. According to SEM and TEM observations, HAp precipitates were hemispherical aggregates consisting of the plate-like crystallites whose specific {100} surfaces were well developed. The HAp crystallites were preferentially oriented with their c-axes in a specific direction parallel to the substrate near the inorganic/organic interface, which suggests the control of the crystallographic orientation in HAp by the aligned carboxyl groups in the LB monolayer. Copyright 2001 Academic Press.