Selectivity in capillary electrochromatography using native and single isomer anionic cyclodextrin reagents

Separations of naphthalene compounds that differ in position of substitution and type of substituent were accomplished using cyclodextrin distribution capillary electrochromatography. Separation systems composed of running buffers containing mixtures of native neutral and single isomer anionic cyclodextrins (CDs) were employed yielding efficiencies of approximately 200,000 plates/meter. Solute migration rates and relative orders can be readily modified by changing CD types and concentrations. Experiments were performed to determine distribution coefficients between each of the CDs used in these studies and an aqueous running buffer. For this work, naphthalene-CD cavity inclusion is assumed to be the principal mode of interaction. The distribution coefficients for carboxymethyl-beta-cyclodextrin (CM-beta-CD), degree of substitution 1, were 10-70% larger than those for native beta-CD and 75-1800% large than those for gamma-CD. The CM-beta-CD was singly charged and yielded a narrow elution window. Nevertheless, baseline resolution was achieved for several substituted naphthalene compounds using CM-beta-CD in conjunction with beta-CD or gamma-CD. Under certain conditions, the gamma-CD system yielded an elution order that differed from that of the beta-CD system. Heptakis-(2,3-dimethyl-6-sulfato)-beta-CD with its -7 charge produced a much larger elution window. The extensive substitution with sulfonic groups at the truncated bottom of the CD seemed to inhibit inclusion as the distribution coefficients for the naphthalene compounds were generally more than an order of magnitude smaller than those for CM-beta-CD. Moreover, there was evidence that this sulfato-CD interacted with both the capillary wall and neutral beta-CD. This work differs from prior uses of CDs in that relatively complicated mixtures of neutral, achiral compounds are separated using combinations of recently developed single-isomer CDs as running-buffer additives. The single-isomer CDs, as opposed to most highly complex derivatized CD products, facilitate predictions of separation performance for multicomponent samples. In this manner, the ability to use knowledge of distribution coefficients to predict elution characteristics for a ternary CD system is demonstrated.     

Regeneration of critical bone defects with anionic collagen matrix as scaffolds

The aim of this study was to make a histomorphometric evaluation of the osteogenic potential of anionic collagen matrix as scaffolds; either crosslinked in glutaraldehyde or not cross-linked and, implanted in critical bone defects in rat calvaria. Seventy-two rats were randomly distributed in three groups: anionic collagen scaffolds treated for 24 h of selective hydrolysis (ACSH); anionic collagen scaffolds treated for 24 h of selective hydrolysis and 5 min of crosslinking in glutaraldehyde 0.05 % (ACSHGA); empty bone defect (Control), evaluated at the biological points of 15, 45, 90 and 120 days. The results showed that the biomaterials implanted were biocompatible and showed a high osteogenic potential. These biomaterials presented a speed of biodegradation compatible with bone neoformation, which was shown to be associated with angiogenesis inside the scaffolds at all biological points. The percentage of mineralization of ACSH (87 %) differed statistically from that found in ACSHGA (66 %). It was concluded that the regeneration of critical bone defect was more evident in anionic collagen without crosslinking (ACSH).     

类石墨烯单层结构ZnO和GaN的压电特性对比研究

本研究采用基于密度泛函理论的第一性原理计算了类石墨烯单层结构ZnO(g-ZnO)和GaN(g-GaN)的力学、电学和压电性质,重点研究了施加应变后原子坐标弛豫与否的Clamped-ion和Relaxed-ion两种模式的弹性刚度系数和压电张量。结果表明单层g-ZnO和g-GaN均具有半导体属性和较好的弹性。单层g-ZnO和g-GaN的压电系数分别约为9.4和2.2 pm·V^–1,预测这类单层材料在极薄器件中可能具有压电效应,且g-ZnO的压电性能更好。因此,类石墨烯单层ZnO有望用于压力传感器、制动器、换能器及能量收集器等纳米尺度器件。     

聚丙烯孔洞驻极体薄膜的突出压电活性及其应用研究

聚丙烯(PP)孔洞膜可呈现高达1000pC/N的准静态压电d33系数,是久负盛名的铁电聚合物PVDF相应系数的50倍以上,可和压电陶瓷相媲美.基于国内外最新研究成果,综述了PP孔洞膜的制备技术、极化方法、压电活性以及可能的应用前景.     

Piezoelectricity and microstructures of modified lead titanate ceramics

Modified lead titanate ceramics with the composition Pb_0.70 Ca_0.30 Ti_0.94 (Co_1/2W_1/2)_0.06 O₃ with 1 mol% MnO were prepared by the mixed oxide route. By varying the sintering temperature, ceramics with average grain sizes between 2.8 and 5m were obtained. An increase in grain size resulted in an increased electromechanical anisotropy and a decreased dielectric constant. Transmission electron microscopy was used to examine the ferroelectric domain boundaries and intergranular phases. Indications are that during poling favourably oriented domains approximately doubled in size by 90 ° type domain wall switching. Evidence was found for the existence of a vitreous intergranular phase at multiple grain junctions. EDS microanalysis indicated that the amorphous grain boundary phase had a lower lead content than the bulk material.     

Piezoelectricity of ferroelectric perovskites from first principles

The very recent use of first-principles-derived approaches to investigate piezoelectricity in simple and complex ferroelectric perovskites has not only provided a deep microscopic understanding but also has led to the design of materials with striking electromechanical responses.     

聚丙烯孔洞型铁电驻极体薄膜的压电性研究

利用准静态法和激光干涉法测量正、逆压电d33系数,研究了经压力膨化处理的聚丙烯孔洞型铁电驻极体薄膜压电系数的压强和频率特性及其热稳定性.结果表明,聚丙烯薄膜经压力膨化处理后,其压电性能改善的原因是:压力膨化处理既能有效地降低孔洞膜的弹性模量Y,又能增强其储电能力.聚丙烯孔洞膜的压电d33系数在激励信号压强为0.2～4kPa的范围内基本保持恒定,但当其值高于4kPa时,d33系数出现了明显的下降.聚丙烯孔洞膜的压电d33系数随频率上升而下降(即从0.001Hz时的1200pC/N降低到其机械共振频率附近时的350pC/N),是与材料的弹性模量Y随频率的上升而增加直接相关.对不同工艺参数制备的样品,其机械共振频率位于150～400kHz范围内.实验结果还表明:聚丙烯孔洞膜的压电d33系数的热稳定性与非孔洞型聚丙烯驻极体薄膜的电荷储存热稳定性相近.     

Bonding interactions and stability assessment of biopolymer material prepared using type III collagen of avian intestine and anionic polysaccharides

The present study demonstrate bonding interactions between anionic polysaccharides, alginic acid (AA) and type III collagen extracted from avian intestine used for the preparation of thermally stable and biodegradable biopolymer material. Further the study describes, optimum conditions (pH, temperature and NaCl concentration) required for the formation of fibrils in type III collagen, assessment on degree of cross-linking, nature of bonding patterns, biocompatibility and biodegradability of the cross-linked biomaterial. Results revealed, the resultant biopolymer material exhibit high thermal stability with 5–6 fold increase in tensile strength compared to the plain AA and collagen materials. The degree of cross-linking was calculated as 75%. No cytotoxicity was observed for the cross-linked biopolymer material when tested with skin fibroblast cells and the material was biodegradable when treated with enzyme collagenase. With reference to bonding pattern analysis we found, AA cross-linked with type III collagen via (i) formation of covalent amide linkage between –COOH group of AA and ε-NH₂ group of type-III collagen as well as (ii) intermolecular multiple hydrogen bonding between alginic acid –OH group with various amino acid functional group of type-III collagen. Comparisons were made with other cross-linking agents also. For better understanding of bonding pattern, bioinformatics analysis was carried out and discussed in detail. The results of the study emphasize, AA acts as a suitable natural cross-linker for the preparation of wound dressing biopolymer material using collagen. The tensile strength and the thermal stability further added value to the resultant biopolymer.     

Piezoelectricity in Monolayer Hexagonal Boron Nitride

2D hexagonal boron nitride (hBN) is a wide-bandgap van der Waals crystal with a unique combination of properties, including exceptional strength, large oxidation resistance at high temperatures, and optical functionalities. Furthermore, in recent years hBN crystals have become the material of choice for encapsulating other 2D crystals in a variety of technological applications, from optoelectronic and tunneling devices to composites. Monolayer hBN, which has no center of symmetry, is predicted to exhibit piezoelectric properties, yet experimental evidence is lacking. Here, by using electrostatic force microscopy, this effect is observed as a strain-induced change in the local electric field around bubbles and creases, in agreement with theoretical calculations. No piezoelectricity is found in bilayer and bulk hBN, where the center of symmetry is restored. These results add piezoelectricity to the known properties of monolayer hBN, which makes it a desirable candidate for novel electromechanical and stretchable optoelectronic devices, and pave a way to control the local electric field and carrier concentration in van der Waals heterostructures via strain. The experimental approach used here also shows a way to investigate the piezoelectric properties of other materials on the nanoscale by using electrostatic scanning probe techniques.     

Rheological behavior of anionic collagen injectable gels in the presence of rhamsan for plastic surgery applications

The present paper describes the rheological properties of anionic collagen gels and anionic collagen:rhamsan composites gels in the concentration of 0.7, 4 and 6%, estimated to be used as injectable biomaterials for plastic reconstruction. Rheological studies of these gels showed that independently of pH, composition and concentration the viscoelastic behavior was dependent on the frequency, with the storage modulus always greater than the loss modulus (G′ > G″ and δ < 45°). Creep experiments showed that anionic collagen:rhamsan composites equilibrated at pH 7.4 were less elastic and more susceptible to deformation in comparison to gels equilibrated at pH 3.5. Flow experiments indicated that the force needed for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smoother flow, suggesting the association with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations. Finally, on the basis of dynamic viscosity profiles found for different preparations, some of these composites are potential candidates to be utilized in laryngology.     

Piezoelectricity of single- and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct- and inverse-piezoelectric d₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets.     

单层及多层PP蜂窝膜驻极体的压电性

经压力膨化处理后,以正逆压电系数d33测量研究了一种经无栅电晕充电的国产商用聚丙烯蜂窝膜(cellular PP,商品名PQ50)驻极体的压电性.经过优化工艺参数压力膨化处理后的PQ50蜂窝膜呈现600pC/N以上的准静态压电系数,这一量值约为PVDF相关系数的40倍.而通过将单层PQ50蜂窝膜驻极体粘贴形成合理的多层结构,得到的复合膜系压电系数d33高达2010pC/N,约为PZT压电陶瓷相应系数的3倍.从而为拓宽这类新一代的非极性孔洞聚合物压电功能膜应用领域,推动其应用进程提供了一定的理论和技术依据.     

孔洞结构聚丙烯铁电驻极体薄膜的压电性研究

为了提高孔洞结构聚丙烯(cellular PP)铁电驻极体的压电性能,采用高压气体膨化技术对材料进行了改性处理,并利用准静态和干涉仪测量方法,对经处理的cellular PP铁电驻极体薄膜的压电效应进行了研究.结果表明:气体膨化工艺能够明显提高cellular PP铁电驻极体薄膜的压电活性:这种突出的压电活性源干膨化膜杨氏模量Y的降低和电极化能力的提高;压电系数d33随频率的增加呈现下降趋势:从0.01 Hz下的1200 pC/N降低到共振频率附近的350 pC/N;对于不同参数处理的样品,它们的共振频率在150～400 kHz;大多数样品的d33在0.2～10 kPa的范围内没有明显的变化,但是高于10 kPa,d33随之下降;cellular PP铁电驻极体薄膜d33的热稳定性与非孔洞型PP驻极体薄膜的电荷储存热稳定性相当.     

空间电荷聚合物驻极体材料的压电效应

自20世纪70年代空间电荷驻极体压电性概念被提出以来,开发新的聚合物压电材料一直是驻极体界研究的热点.这类材料的压电效应产生机制与传统的极性聚合物压电材料不同,是由于空间电荷在机械应力的作用下非对称性地向电极移动所致.本文从理论和实验两方面,对具有闭合型或开放型空洞结构和"软"、"硬"复合有机聚合物驻极体压电膜的研究现状进行了综述,并对进一步开展这类材料的研究提出了看法.     

Piezoelectricity of single-and multi-layer cellular polypropylene film electrets

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct-and inverse-piezoelectric d ₃₃ coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d ₃₃ coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets. Translated from Journal of Functional Materials, 2006, 37(2): 207–209 [译自: 功能材料]     

Piezoelectricity: old effect, new thrusts

A tutorial synopsis of the piezoelectric effect is presented in the context of its history, traditional uses, and relation to crystal symmetry. Associated effects are briefly noted. Future prospects, particularly in the area of microelectromechanical systems/structures (MEMS) are discussed     

Meshless Local Petrov-Galerkin Method for Plane Piezoelectricity

Piezoelectric materials have wide range engineering applications in smart structures and devices. They have usually anisotropic properties. Except this complication electric and mechanical fields are coupled each other and the governing equations are much more complex than that in the classical elasticity. Thus, efficient computational methods to solve the boundary or the initial-boundary value problems for piezoelectric solids are required. In this paper, the Meshless local Petrov-Galerkin (MLPG) method with a Heaviside step function as the test functions is applied to solve two-dimensional (2-D) piezoelectric problems. The mechanical fields are described by the equations of motion with an inertial term. To eliminate the time-dependence in the governing partial differential equations the Laplace-transform technique is applied to the governing equations, which are satisfied in the Laplace-transformed domain in a weak-form on small subdomains. Nodal points are spread on the analyzed domain and each node is surrounded by a small circle for simplicity. The spatial variation of the displacements and the electric potential are approximated by the Moving Least-Squares (MLS) scheme. After performing the spatial integrations, one obtains a system of linear algebraic equations for unknown nodal values. The boundary conditions on the global boundary are satisfied by the collocation of the MLS-approximation expressions for the displacements and the electric potential at the boundary nodal points. The Stehfest's inversion method is applied to obtain the final time-dependent solutions.     

Piezoelectricity in Multilayer Black Phosphorus for Piezotronics and Nanogenerators

Recently, piezoelectric characteristics have been a research focus for 2D materials because of their broad potential applications. Black phosphorus (BP) is a monoelemental 2D material predicted to be piezoelectric because of its highly directional properties and non-centrosymmetric lattice structure. However, piezoelectricity is hardly reported in monoelemental materials owing to their lack of ionic polarization, but piezoelectric generation is consistent with the non-centrosymmetric structure of BP. Theoretical calculations of phosphorene have explained the origin of piezoelectric polarization among P atoms. However, the disappearance of piezoelectricity in multilayer 2D material generally arises from the opposite orientations of adjacent atomic layers, whereas this effect is limited in BP lattices due to their spring-shaped space structure. Here, the existence of in-plane piezoelectricity is experimentally reported for multilayer BP along the armchair direction. Current–voltage measurements demonstrate a piezotronic effect in this orientation, and cyclic compression and release of BP flakes show an intrinsic current output as large as 4 pA under a compressive strain of −0.72%. The discovery of piezoelectricity in multilayer BP can lead to further understanding of this mechanism in monoelemental materials.     

FEP和多孔PTFE复合膜铁电驻极体的压电性及电荷动态特性

报道了将致密的FEP和多孔PTFE交互层叠在一起，采用热粘合的方法制备出具有孔洞结构的聚合物复合膜，然后经电晕极化处理使该复合膜成为铁电驻极体。最后用准静态方法测量该铁电复合膜的压电系数d33，并通过热刺激电流放电（TSD）电流谱和等温衰减研究了FEP和多孔PTFE复合膜铁电驻极体的电荷动态特性。结果表明：该复合膜的压电系数d33可达200～500pC/N，在0～12kPa的压强范围内呈现出良好的线性，并且在90℃下老化160min后仍保持在原来的43％且趋于稳定；FEP和多孔PTFE复合膜铁电驻极体电荷在热激发脱阱后复合途径主要有2种：一种是沿着固体介质的表面迁移与异性电荷复合，另一种是穿过固体介质层与异性电荷复合。在低温区（7512附近）前者占优，高温区（120℃附近）后者占优。