纳米晶粒TiO2多孔微球的合成与表征

 钛酸四丁酯经酸性水解得到TiO2溶胶，将溶胶与苯酚混合后加入到正庚烷分散介质中，再滴加甲醛水溶液，通过反相悬浮聚合和溶胶－凝胶过程制备了聚合物与TiO2的复合微球．对复合微球进行焙烧处理，使聚合物分解，从而得到由纳米TiO2晶粒组成的多孔微球．以示差扫描量热法、热重分析、X射线衍射、扫描电子显微镜和氮吸附等方法对TiO2多孔微球的物理性质进行了表征．结果表明，所得TiO2多孔微球主要由锐钛型TiO2纳米晶粒组成，晶粒尺寸为20～30nm；TiO2多孔微球的直径为200～500μm，比表面积为87．40m2／g，平均孔径为8．65nm，孔径的分布具有单分散特征．     

Role of each part of cyanobiphenyl-containing polymers in porous-film preparation by using the breath-figure method

ABSTRACT

The breath-figure method using the condensation of water droplets can easily fabricate regular porous films. Although the method is simple, the phenomenon itself requires the control of many parameters that change throughout the process. Therefore, we require a unified understanding of polymers for the fabrication of ordered porous films. In this study, to clarify the required molecular structures of polymers to form a regular porous structure, we systematically explored poly(methacrylate)s with cyanobiphenyl moieties connected by dodecyl groups in the side chain (P11CB); these could form a hexagonal ordered porous structure on the entire film surface. The comparison of P11CB and P11B, which is a P11CB without cyano groups, showed that the local polar groups in hydrophobic polymers promote the formation of ordered porous films. Furthermore, no holes were formed in films of P0CB which is a P11CB without alkyl spacers due to its hydrophilicity. Long alkyl chains resulted in changed hydrophilic polymers to hydrophobic polymers. The introduction of long alkyl chains as a spacer between the biphenyl moiety and polymer backbone is preferred in the cases of particularly few amounts of biphenyl groups in the polymer. The biphenyl groups showed the ability to improve film formability.     

Electroacoustic and Potentiometric Studies of the Hematite/Water Interface

The basic charging properties of nearly spherical hematite particles were studied by using potentiometric titration and the electroacoustic technique. Both the pH and the ionic strength dependence of the surface charge and the ζ-potential were studied in detail. For calculating the ζ-potential from mobility data a few different theories were used and obtained differences are discussed. At pH values higher than 7 and at high electrolyte concentrations (50 mM and 100 mM NaNO₃), it was difficult to fit the mobility data by using the full mobility spectra including both magnitude and phase angle at several frequencies. In this regime the best fits were obtained by using a theory for aggregated complexes (porous particles). From potentiometric titrations in 0.01, 0.1, and 1.0 M NaNO₃, parameters for a 1-pK Basic Stern Model were determined. The model was used to examine the possibility of correlating the experimentally determined ζ-potentials to the model-calculated potentials at the Stern plane. Qualitatively, the model predicted the correct ionic strength dependence of the ζ-potentials, and there was also a rather good quantitative agreement at high ionic strengths (50 and 100 mM NaNO₃). However, at lower ionic strengths the model predicted values up to 40% higher than those found from the electroacoustic study. Surface conduction behind the slip plane was discussed as a possible cause for this discrepancy.     

Liquid-solid phase transformation of potassium iodide aqueous solutions of different concentrations held inside a porous material

Calorimetric analysis shows a succession of transformations inside and outside the pores, whose characteristics depend on the concentration of the solution and the amount of porous body present.For a given porous body, whatever the initial concentration of the solution, the capillary condensate concentration evolves systematically, during cooling, towards the eutectic concentration even if the initial salt concentration is higher than the eutectic one. It should be noted that this phenomenon indicates migration outside the pores of water or potassium iodide according to the initial concentration.For various samples whose pore size is decreasing, successive solidification of divided water and eutectic occurs at decreasing temperatures. The freezing temperature depression of water in divided KI solutions does not seem to be a function of the salt concentration but is dependent mainly on the division effect. A nearly linear relationship between pore radius and the reciprocal of temperature depression may experimentally be established for divided eutectic.

---

Zusammenfassung Kalorimetrische Analyse zeigt eine Reihe von Umwandlungen inner- und außerhalb von Poren, wobei die Charakteristik der Umformungen von der Konzentration der Lösung sowie von der Menge des anwesenden porösen Körpers abhängt. Bei einem gegebenen porösen Körper verändert sich die Konzentration des Kapillarkondensates unabhängig von der Ausgangskonzentration systematisch immer in Richtung der eutektischen Konzentration, auch wenn die Salzkonzentration zu Beginn über der eutektischen Konzentration liegt. Man muß bemerken, daß diese Erscheinung je nach Ausgangskonzentration auf Migration von Wasser oder Kaliumjodid außerhalb der Poren hinweist.Für verschiedene Proben mit abnehmender Porengröße findet bei sinkender Temperatur ein nacheinanderfolgendes Erstarren von getrenntem Wasser und Eutektikum statt. Die Gefrierpunktserniedrigung von Wasser in derartig getrennten KI-Lösungen scheint nicht eine Funktion der Salzkonzentration zu sein sondern hauptsächlich vom Separierungseffekt abzuhängen. Für unterteilte Eutektika konnte ein annähernd linearer Zusammenhang zwischen dem Porenradius und dem Reziproken der Temperaturerniedrigung festgestellt werden.

     

Preparation of Microporous ORMOSILs by Thermal Degradation of Organically Modified Siloxane Resin

Silicon containing materials have traditionally been used in microelectronic fabrication. Semi-conductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements forming an integrated circuit. These interconnect levels are typically separated by an insulating or dielectric film. Previously, a silicon oxide film was the most commonly used material for such dielectric films having dielectric constants (k) near 4.0. However, as the feature size is continuously scaling down, the relatively high k of such silicon oxide films became inadequate to provide efficient electrical insulation. As such, there has been an increasing market demand for materials with even lower dielectric constant for Interlayer Dielectric (ILD) applications, yet retaining thermal and mechanical integrity. We wish to report here our investigations on the preparation of ultra-low k ILD materials using a sacrificial approach whereby organic groups are burnt out to generate low k porous ORMOSIL films. We have been able to prepare a variety of organically modified silicone resins leading to highly microporous thin films, exhibiting ultra-low k from 1.80 to 2.87, and good to high modulus, 1.5 to 5.5 GPa. Structure property influences on porosity, dielectric constant and modulus will be discussed.     

Structure of natural film on porous silicon surface founded by ellipsometry

Abstract

The multiple-angle-of-incidence ellipsometric studies of the natural film formed on the surface of porous silicon sample after its production and subsequent keeping in isopropyl alcohol have been performed. A new property of porous silicon with the natural film on its surface has been revealed which consists in a drastic change of the polarization characteristics of the reflected light wave after its keeping in alcohol. This property of porous silicon may be the basis for the development of liquid and gas sensors, polarization elements of optical devices etc. It was found that ellipsometric curves are described better by calculations in a two-layer model in comparison with a single-layer one of the investigated film. It was obtained that the outer layer of the film has smaller refractive index than the inner one. As a result of decoration the refractive indices of both layers decrease and further the changes of refractive indices and the redistribution of the thickness of both layers are found. It is suggested that the interaction of the alcohol molecules with silicon and its oxide environment occurs in the walls of the pores during the decoration.     

Constructal Optimization of Rectangular Microchannel Heat Sink with Porous Medium for Entropy Generation Minimization

A model of rectangular microchannel heat sink (MCHS) with porous medium (PM) is developed. Aspect ratio of heat sink (HS) cell and length-width ratio of HS are optimized by numerical simulation method for entropy generation minimization (EGM) according to constructal theory. The effects of inlet Reynolds number (Re) of coolant, heat flux on bottom, porosity and volume proportion of PM on dimensionless entropy generation rate (DEGR) are analyzed. From the results, there are optimal aspect ratios to minimize DEGR. Given the initial condition, DEGR is 33.10% lower than its initial value after the aspect ratio is optimized. With the increase of Re, the optimal aspect ratio declines, and the minimum DEGR drops as well. DEGR gets larger and the optimal aspect ratio remains constant with the increasing of heat flux on bottom. For the different volume proportion of PM, the optimal aspect ratios are diverse, but the minimum DEGR almost stays unchanged. The twice minimized DEGR, which results from aspect ratio and length-width ratio optimized simultaneously, is 10.70% lower than the once minimized DEGR. For a rectangular bottom, a lower DEGR can be reached by choosing the proper direction of fluid flow.     

Recent Advances in Loop Heat Pipes with Flat Evaporator

The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.     

Solid‐state nuclear magnetic resonance relaxation times in crosslinked macroporous polymer particles of divinylbenzene homopolymers

Monodisperse porous particles of poly(divinylbenzene) prepared by the activated swelling method have been investigated by solid‐state ¹³C crosspolarization magic‐angle spinning (CPMAS) nuclear magnetic resonance (NMR) relaxation measurements. Homopolymeric combinations of two porogens (toluene and 2‐ethylhexanoic acid) and two monomers (meta‐ and para‐divinylbenzene) were studied. Residual vinyl groups were systematically reacted with increasing amounts of bromine, producing 20 different polymers samples for which we measured crosspolarization times, T_CH, proton rotating frame spin‐lattice relaxation, T, ¹³C spin‐lattice relaxation, T, and proton spin‐lattice relaxation, T. These parameters were chosen to reflect expected changes in a wide range of frequencies of motion as a function of structure. Relative differences in the molecular mobility of the major functional groups (aromatic, vinyl and aliphatic) is related to initial reactants used, vinyl concentration, relative reactivity of vinyl groups, distribution of vinyl groups, pore structure, and degree of crosslinking. Variable temperature ¹H combined rotation and multiple pulse NMR (CRAMPS) was used to derive activation energies for selected samples via measurement of the proton spin‐lattice relaxation time, T. Irreversible thermal effects were observed in ambient temperature relaxation after heating to temperatures in the range of 393–418 K. Simple univariate statistical analyses failed to reveal consistent correlations among the known variables. However, the application of more sophisticated multivariate and neural network analyses allowed excellent structure–property predictions to be made from the relaxation time data. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1307–1328, 1999     

化学计量比LiNbO3晶体宏观生长缺陷的观察

本文对采用双坩埚提拉法(DCCZ)生长的化学计量比LiNbO3晶体中出现的机械双晶、组分过冷、包裹体等宏观生长缺陷进行了观察和分析.结果表明机械双晶通常以{102}和{104}面族为双晶面,而不是以前文献报道的{102}和{012}面族;化学计量比LiNbO3晶体双坩埚提拉法生长与同成份晶体生长不同,前者是助熔剂生长体系,生长速度稍快或温度较小的波动就会导致组分过冷,而后者属于纯熔体生长体系,不容易产生组分过冷;包裹体是由于组分过冷生长时界面失稳夹入熔体所造成的.由于这些缺陷的存在都会严重影响单晶的获得率和质量,为此,我们通过大量实验研究后提出了可以减少和避免这些生长缺陷提高晶体质量的方法.