Material Highlights: Liquid Crystal Polymers

Abstract

A key issue in the area of side chain liquid crystal polymers concerns the conformation of the backbone within the mesophase. In order to resolve this matter, Noirez and co-workers (Liquid Crystals, 1995, 18 129) have studied a wide range of polymers exhibiting both nematic and smectic behaviour using small angle neutron scattering. Their results combined with a survey of those in the literature reveal that if the polymer is solely nematogenic, then the backbone adopts a prolate conformation in which on average it lies along the director. By contrast, in a smectic phase the backbone adopts an oblate shape and on average lies perpendicularly with respect to the director. This arises from a microphase separation in which the backbones are distributed between the mesogenic layers. However, the backbones can cross the mesogenic layers although their ability t o do so depends on, amongst other factors, the degree of polymerization. If the polymer exhibits both nematic and smectic behaviour, then in the nematic phase the backbone adopts a slightly oblate shape resulting from smectic fluctuations.     

Mineralogical Crystallography: Look in the Past,New Trends,and Highlights

Crystallography Reports - Many urgent problems of modern mineralogical crystallography, to which the papers of this thematic issue of the journal Kristallografiya (Crystallography Reports) are...     

左手材料的电磁特性

左手材料就是介电常数ε和磁导率μ同时为负的材料,电磁波在这种材料中传播将具有不同寻常的特性.本文在详细回顾这种新型人工材料背景、研究进展后,着重介绍了左手材料所具有的奇特特性,如负折射特性、逆Doppler效应、逆Cerenkov辐射、负Coos-Hanchen位移和Bragg Regime带移,简要介绍了含左手材料的一维光子晶体.     

多铁性材料的应变调控

多铁性材料是一种同时具有铁电、铁弹、铁磁等两种或者两种以上“铁性”的材料,可以通过多种序参量的耦合产生新的效应,在电子信息、传感、存储、无线网络等领域具备广阔的应用前景。当前在室温下具有强磁电耦合效应的多铁性材料仍然是学者们研究的重点,但基于多铁材料的器件还没有实现应用。应变工程是一种可以有效影响多铁材料物理性质的调控手段,通过晶格与电子、自旋、轨道等的相互作用来影响材料的电、磁、光、声等物理特性,因此通过应变调控多铁性薄膜结构和性能,受到了研究人员的广泛关注。本文通过调研多铁性材料中应变工程的研究,总结了应变调控手段及其对材料物理性能的影响,期望为多铁性材料的研究和发展提供研究思路。     

Materials for high-power fiber lasers

The absorption and emission properties of silica based ytterbium doped preforms, made by Modified Chemical Vapor Deposition, and of the drawn fibers were investigated as a function of the atmosphere during the preform collapsing. Under increasingly reducing conditions for the collapsing atmosphere, a strong UV/VIS absorption is built up, accompanied with an UV excited emission in the visible region, obviously induced by the formation of Yb²⁺ ions. Both the fluorescence lifetime of the Yb³⁺ lasing level and the cooperative fluorescence in the visible are remarkably diminished. Laser power experiments with the different fibers show a strong deterioration of the laser efficiency parallel to the degree of reduction of the doped glasses.     

纳米金刚石材料的研究进展

纳米金刚石不但拥有金刚石材料优异的物理、化学特性,还具备一些在纳米尺度下的特殊性能,如半导体特性、良好的生物相容性及光学特性.其研究吸引了国内外研究人员的广泛关注,且关于纳米金刚石材料的制备、性能表征以及应用的相关研究逐渐开展.前期的研究显示:不同形貌的纳米金刚石材料需要特定的制备方法、且表现出各异的特殊性能,适合于不同的应用领域.文中首先介绍了纳米金刚石颗粒、薄膜、金刚石纳米片及金刚石纳米线的制备方法;其次阐述了各类纳米金刚石材料在光、电、力学等方面的特殊性能,并对纳米金刚石材料在民用、生物医药、军事等领域的应用进行了总结,最后展望了纳米金刚石材料的发展前景.     

Some New Smectic F Materials

In the course of studies on the smectic C phase, we have succeeded in preparing three new compounds each of which exhibits a well defined smectic F phase. In all of these materials, the F phase gives a smectic C phase on heating and a smectic H phase on cooling. Moreover, these three compounds are members of two related homologous series of esters; therefore it seems probable that many more of the other homologues will exhibit smectic F properties.     

Polymeric Precursors for Inorganic Materials

Standard ceramic processing centers around the growth, compaction, and sintering of compact colloidal particles. Recently, however, it has become clear that numerous glass and ceramic processing techniques cannot be understood in terms of standard colloid physics. The purpose of this talk is to demonstrate several areas where polymer concepts are not only necessary for the understanding of ceramic processing, but also provide the insights necessary to tailor the properties of ceramic materials to achieve specific goals. The talk will center on the polymerization of silicates in solution. By control of the growth conditions such as catalysis, pH, and reaction sequence, it is possible to create a variety of structures from dense colloidal particles to randomly branched polymers. By mapping the polymerization process onto simple fractal models, it is possible to identify the essential factors that control the structure.     

LD泵浦激光晶体材料的新发展

近年来,在激光二级管(LD)的迅速发展和外部市场需求的推动下,形成了一道激光晶体材料新的市场风景线.研究更多更适合于LD泵浦的高效率,宽吸收带的激光晶体的工作非常活跃.本文对固态激光晶体材料的发展作了简要的叙述.分别按照1-μm、2-和3-μm发射波长区域和可调谐激光晶体,评述了10种新发展的LD泵浦激光晶体的特性.     

晶体材料的设计与模拟

从化学反应热力学和动力学的角度出发,系统地分析和计算了一些具有代表性的功能晶体材料的生长、结构与性能.研究结果表明,晶体组成化学键的微观参量可以很好地计算、分析及预测其非线性光学倍频效应、生长特性及缺陷控制等宏观物理化学特征.因此,化学键方法与模型可以帮助我们实现光电功能晶体材料的结构设计与模拟、性能预测与模拟等晶体工程领域的研究目标.该工作可以为物理、化学、化工及材料等领域的相关研究提供很好的研究思路.     

Erratum to:Mineralogical Crystallography: Look in the Past,New Trends,and Highlights

Crystallography Reports - An Erratum to this paper has been published: https://doi.org/10.1134/S1063774521340071     

多功能分子基磁性材料研究进展

多功能分子基磁性材料不仅可以表现出单分子磁体的慢弛豫行为,还可以展现出其他丰富多彩的物理或化学性质,如荧光、手性、铁电性、吸附、催化等,在光电以及自旋电子器件等多个领域具有潜在的应用前景.设计和开发新型的多功能分子基磁性材料作为单分子磁体研究领域一个重要的研究方向,引起了研究者广泛的关注.本文主要从合成策略,结构与性能的关系出发,综述了近年来多功能分子基磁性材料的研究进展,并对今后相关领域的发展做出了展望.     

High-k材料研究进展与存在的问题

随着集成电路的飞速发展,SiO2作为传统的栅介质将不能满足MOSFET器件高集成度的要求,需要一种新型High-k材料来代替传统的SiO2,这就要综合考虑以下几个方面问题:(1)介电常数和势垒高度;(2)热稳定性;(3)薄膜形态;(4)界面质量;(5)与Si基栅兼容;(6)工艺兼容性;(7)可靠性.本文综述了几类High-k栅介质材料的研究现状及存在的问题.目前任何一种有望替代SiO2的栅介质材料都不能完全满足上述几点要求.但是,科学工作者们已经发现了几种有希望的High-k候选材料.     

稀土发光材料的研究进展

稀土发光材料已在众多领域获得广泛的应用,并且已成为稀土应用的主要领域之一.本文归纳了白光LED用稀土荧光粉、稀土光转换材料、稀土上转换发光材料、稀土纳米发光材料、真空紫外发光材料、稀土配合物电致发光材料和稀土闪烁体等的研究最新进展,并对未来发展趋势进行了展望.     

Mixed Chalcopyrites as Useful Solar Cell Materials

I1n view of the present global energy crisis the advent of the ternary chalcopyrites with some important useful properties stimulate us to study these compounds together with their mixed versions with a view to find their suitability as efficient solar cell materials. We finally selected out a few promising materials, as some of them have desirable characteristics and satisfy the stringent requirements for photovoltaic energy conversion.     

超声速长波红外整流罩材料研究进展

采用长波红外制导的超声速导弹具有极佳的军事应用前景,但高速飞行的导弹整流罩会承受较高的气动冲击以及砂蚀、雨蚀,极易出现结构和光学性能失效,因此选择与服役环境相匹配的整流罩材料至关重要.基于上述应用现状,本文综述了目前主要研究的几种长波红外整流罩材料,对其光热理化性能及应用前景进行了分析,同时对几款整流罩材料或结构的发展方向进行了展望,旨在为超声速长波红外整流罩的选材提供技术参考.     

高性能GeTe基热电材料的研究进展

随着环境相容性的提出,热电材料除具有优异的性能外,还需要由环境友好型元素构成。GeTe具有无毒无害的特点,因而被作为理想的PbTe替代物广泛研究。近年来,研究者主要以掺杂方式对其进行改善,由于单掺存在局限性,双掺便成了主导,且Pb元素逐渐被Sb、Bi等代替。本文从GeTe的晶体结构及能带结构特点出发,总结了载流子调控、能带调控和结构调控3种优化手段。目前的GeTe热电器件主要以p型单臂为主,n型GeTe热电材料还需要深入研究,同时,解决相变引起的界面断裂问题也是该材料的发展方向之一。     

LiInS2多晶原料的合成与性能

本文研究了高纯LiInS2多晶原料的合成及性能.LiInS2晶体是一种极具吸引力的晶体,可以应用于红外区域的非线性光学频率变换.一般来说,含锂硫族化合物制备非常困难,因为锂极易被氧化,且腐蚀石英管.而且,硫族元素高的蒸气压会导致石英安瓿爆炸.本文采用两种方法合成了LiInS2多晶原料,对所获LiInS2多晶原料进行了X射线粉末衍射和差示扫描量热分析.