Non-classical crystal growth of inorganic and organic materials

Abstract

Investigation of the early stage morphologies of some organic and inorganic systems has established that their crystal growth does not always follow the classical route established 120 years ago. The classical theory assumes that a highly symmetric crystal develops from the nucleation and repeated attachment of atoms, molecules or ions to a single nucleus. In instances where surfactants or polymers are introduced, the crystal growth is often found, however, to follow a ‘reversed crystal growth’ route. This non-classical growth route is initiated by organic molecules adsorbed onto the surface of the nanocrystallites in the early stages of growth. In the reversed route, these nanocrystallites form large disordered aggregates followed by surface crystallisation to create a thin, highly crystalline, dense shell and, finally, an extension of the crystallisation from the surface to the core. Although systems following a non-classical crystal growth route have been known for many years, their formation mechanisms have a much shorter history. Discovery of the reversed crystal growth route in several hollow, core–shell and twin crystal type morphologies not only assists in the designing of materials for industrial applications but also helps to understand the interactions between organic and inorganic components. This review highlights recent research relating to organic and inorganic systems whose growth follows the reversed crystal growth route.     

无机-有机复合膜应用的研究进展

介绍了近年来发展较快的无机—有机复合膜的研究情况，对其应用领域进行了综述并对将来的发展方向提出了一些看法．     

有机/无机支撑复合膜的制备与应用

从有机膜形成方式、有机膜与无机膜界面相互作用等方面对复合膜的制备技术和应用进行了的综述,并讨论了其潜在的发展和应用.     

Highly water-resistant and organic miscible inorganic/polymer composite luminescent material

A novel highly water-resistant and organic miscible luminescent phosphor has been synthesized by grafting a polymer onto the surface of SrAl₂O₄:Eu²⁺, Dy³⁺ (SAO–ED). A bifunctional ligand, 3-allyl-2, 4-pentanedione (APD) was used as a bridge to introduce the polymer onto the surface of SAO–ED. The coordination of APD with SAO–ED was confirmed by FT–IR spectra. The luminescence property of SAO–ED/polymer composite material was analyzed by spectrometer LS-100. The water resistance and miscibility with organics of the product were also investigated. Compared with traditional inorganic SAO–ED, this novel polymer-grafted SAO–ED has higher brightness, much better water resistance and good miscibility with organic solvents and polymers.     

纳米TiO2表面无机/有机复合改性研究

用液相沉积法对纳米TiO2进行了表面无机/有机复合改性.用XRD、FT-IR进行了包覆膜结构表征,用TEM观察改性后颗粒的形态.测量了有机包覆量对改性样品亲油性的影响.结果表明,液相沉积并经105℃烘干得到的Al2O3膜为非晶态结构,煅烧后才能晶化;有机膜可以在无机膜上生成,其最大包覆量约为7%,且与包覆温度无关;复合包覆后纳米颗粒外形不变,分散性提高;有机包覆量对纳米TiO2的亲油性有非线性影响,包覆量为1.2%时其亲油性最好.     

Synthesis and characterisation of alumina fibres using organic/inorganic composite sol

Abstract

The polyvinyl butyral–Al(NO₃)₃ composite sols and alumina fibres were synthesised by the sol–gel process in an aqueous solution using the polyvinyl butyral (PVB) and Al(NO₃)₃.9H₂O (AN). The viscosity of PVB–AN composite sol increased with increasing AN content and aging time when it was laid at room temperature. The addition of AN leads to the formation of new weak peak and the deviation of diffraction angle to higher degrees according to the X-ray diffraction patterns (XRD). The exothermic peak of PVB disappeared and a weak endothermic peak was observed in differential scanning calorimetry curves of composite powders. The XRD pattern of fibres sintered at 1200°C showed the formation of α-alumina and the fibres showed smooth surface and uniform diameter.     

Synthesis, neutralization and blocking procedures of organic/inorganic hybrid scaffolds for bone tissue engineering applications

Bioactive glasses (BaG) can bind to human bone tissues and have been used in many biomedical applications for the last 30 years. However they usually are weak and brittle. On the other hand, composites that combine polymers and BaG are of particular interest, since they often show an excellent balance between stiffness and toughness. Bioactive glass-poly(vinyl alcohol) foams to be used in tissue engineering applications were previously developed by our group, using the sol-gel route. Since bioactive glass-polymer composite derived from the sol-gel process cannot be submitted to thermal treatments at high temperatures (above 400 degrees C), they usually have unreacted species that can cause cytotoxicity. This work reports a technique for stabilizing the sol-gel derived bioactive glass/poly(vinyl alcohol) hybrids by using glutaraldehyde (GA), NH(4)OH solutions and a blocking solution containing bovine serum albumin. PVA/BaG/GA hybrids were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM/EDX) analyses. Moreover, MTT (3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide) biocompatibility and cytotoxicity assays were also conducted. The hybrids exhibited pore size varying from 80 to 820 mum. After treatments, no major changes in the pore structure were observed and high levels of cell viability were obtained.     

细乳液聚合制备有机-无机复合纳米粒子的研究进展

从细乳液聚合制备有机-无机复合纳米粒子体系的助剂、聚合方法及过程和提高无机纳米粒子包覆率的措施3个方面介绍了采用细乳液聚合法制备有机-无机复合纳米粒子的最新研究进展,并提出其目前存在的问题、今后的研究重点。     

Radiation characteristics of composite inorganic materials with an optically smooth surface

A method is suggested for determining the monochromatic reflectance of a multicomponent inorganic material with an optically smooth surface on the basis of its mineralogical and chemical composition.Translated from Inzhenerno-Fizicheski Zhurnal, Vol. 58, No. 2, pp. 261–264, February, 1990.     

有机/无机共混聚丙烯纤维中无机粉体表面处理效果评价

用钛酸酯偶联剂对TiO2 、ZnO等无机粉体表面处理 ,增加其与聚丙烯基体之间的相容性作用 ,并利用沉降体积这一参数对处理效果进行表征 ,讨论了偶联剂用量对处理效果的影响 ,并通过透射电镜观察、评价了无机填料在有机基体中的分散性。     

Dynamic instability of suddenly heated, thick, composite shells

The parametric resonance type of dynamic instability is investigated for suddenly heated, long circular cylindrical shells of composite material. Particular attention is devoted to the effects of thickness shear flexibility and to mid-surface extensibility. Both long-term and short-term responses are investigated.     

含碳纳米管有机-无机复合涂层的制备与防护性能

为了改善铝合金材料的耐腐蚀性能, 研究了以正硅酸乙酯（TEOS）为主要原料, 加入一定量的KH-550, 并引入部分羟基化的多壁碳纳米管（MWCNTs-OH）进行复合, 以冰乙酸为催化剂, 采用溶胶---凝胶法在铝合金基体表面形成复合涂层。腐蚀电化学测试和扫描电镜分析结果表明, MWCNTs-OH的引入能够明显提高涂层的防护性能, 并有效防止涂层开裂。考察了MWCNTs-OH含量和热处理温度对涂层性能的影响。结果表明: MWCNTs-OH质量分数为0.04%、 热处理温度为130℃时制备的涂层性能最佳, 相应的试样在3.5wt%NaCl溶液中的腐蚀电流密度约为3.056×10-8A/cm2, 而同等实验条件下铝合金基体腐蚀电流密度为7.216×10-5A/cm2, 涂层的存在使腐蚀速率降低了3个数量级, 涂层对铝合金基体具有显著的防护效果。      

Synthesis of inorganic-organic hybrid materials from TEOS, TBT and PDMS

Inorganic-organic hybrid materials have been synthesized by reaction of tetraethoxysilane (TEOS), titanium tetrabutoxide (TBT) and silanol-terminated polydimethylsiloxane (PDMS). The hydrolysis and polymerization reactions of TEOS and PDMS in presence of TBT have been followed by means of FT-IR spectroscopy. Hydrolysis reactions have been characterized by Si—O—C and Ti—O—C bonds and polymerization reactions by Si—O—Si, Si—O—Ti and Ti—O—Ti bonds. The instantaneous hydrolysis of TEOS, the condensation reactions between Si—OH groups forming crosslinked and linear Si—O—Si structures and the copolimerization reactions between Si—OH groups and PDMS molecules have been observed. The reaction between Ti—OH and Si—OH groups or PDMS gives Si—O—Ti bonds. Si—O—Ti bonds are formed during the addition step of TBT and they show a decrease along the reaction time up to gelling. By another hand, the concentration of crosslinked and linear Si—O—Si structures depend on the TBT concentration. High TBT concentration favors the formation of crosslinked chains. TBT influences the hydrolysis and copolymerization reactions between hydrolyzed TEOS and PDMS molecules.     

Synthesis of fluorescent composite macromolecules by using organic/inorganic assemblies as structural units

A synthetic pathway is introduced to construct fluorescent composite macromolecules with supramolecular assemblies as structural units. The supramolecular assembly that contains polymerizable groups is used as a starting "monomer." The supramolecular assembly is composed of nanoparticle core of II - IV group semiconductor and organic ammonium shell. Polymerization of the assemblies yields soluble composite macromolecules. Light scattering data show that the macromolecule has an average size of about 310 nm in diameter in chloroform; AFM image illustrates that the macromolecule has an average diameter of 120 nm and an average height of 35 nm on a mica surface and photoluminescent spectra reveal that the macromolecule performs an extraordinary enhancement in fluorescence intensity of the semiconductor nanoparticles. These observations suggest that construction of macromolecules with supramolecular assembly as starting monomer may produce generations of materials with novel properties.     

Postbuckling of nanotube-reinforced composite cylindrical shells in thermal environments,Part I: Axially-loaded shells

A postbuckling analysis is presented for nanocomposite cylindrical shells reinforced by single-walled carbon nanotubes (SWCNTs) subjected to axial compression in thermal environments. Two kinds of carbon nanotube-reinforced composite (CNTRC) shells, namely, uniformly distributed (UD) and functionally graded (FG) reinforcements, are considered. The material properties of FG-CNTRCs are assumed to be graded in the thickness direction, and are estimated through a micromechanical model. The governing equations are based on a higher order shear deformation theory with a von Kármán-type of kinematic nonlinearity. The thermal effects are also included and the material properties of CNTRCs are assumed to be temperature-dependent. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of axially-loaded, perfect and imperfect, FG-CNTRC cylindrical shells under different sets of thermal environmental conditions. The results for UD-CNTRC shell, which is a special case in the present study, are compared with those of the FG-CNTRC shell. The results show that the linear functionally graded reinforcements can increase the buckling load as well as postbuckling strength of the shell under axial compression. The results reveal that the CNT volume fraction has a significant effect on the buckling load and postbuckling behavior of CNTRC shells.     

Postbuckling of nanotube-reinforced composite cylindrical shells in thermal environments,Part II: Pressure-loaded shells

A postbuckling analysis is presented for nanocomposite cylindrical shells reinforced by single-walled carbon nanotubes (SWCNTs) subjected to lateral or hydrostatic pressure in thermal environments. The multi-scale model for functionally graded carbon nanotube-reinforced composite (FG-CNTRC) shells under external pressure is proposed and a singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium path. Numerical results for pressure-loaded, perfect and imperfect, FG-CNTRC cylindrical shells are obtained under different sets of thermal environmental conditions. The results for uniformly distributed CNTRC shell, which is a special case in the present study, are compared with those of the FG-CNTRC shell. The results show that the linear functionally graded reinforcements can increase the buckling pressure as well as postbuckling strength of the shell under external pressure. The results reveal that the carbon nanotube volume fraction has a significant effect on the buckling pressure and postbuckling behavior of CNTRC shells.     

Synthesis of organic–inorganic hybrid composite and its thermal conversion to porous bioactive glass monolith

We report the synthesis and bioactivity studies of 3-dimensional macro-porous material produced by thermal treatment of organic–inorganic hybrid composite. This is prepared by sol–gel processing of co-poly(methylmethacrylate (MMA)-vinyltriethoxysilane (VTS)) with tetraethoxysilane (TEOS), calcium nitrate and zinc nitrate, ([CH₂C(CH₃)(CO₂CH₃)]_0.8n-[CH₂-CH(Si(OEt)₃]_0.2n-SiO₂-CaO-ZnO) (1). Thermal treatment of this polymer at 600 °C yielded macro-porous bioglass monolith, with pore size distribution between 1 and 5 μm and showed excellent bone bonding ability in simulated body fluid. The ratio of VTS:MMA in the organic polymer can easily be controlled. Since the VTS is the bonding agent, the amount of VTS in the co-polymer can be utilized to increase or decrease the porosity of the hybrid composite. This may be a convenient approach for preparation of bioglass scaffolds especially in tissue engineering of bone.     

Nonlinear viscoelastic analysis of composite plates and shells

A finite element analysis is developed for treating nonlinear viscoelastic response of laminated composites. The analysis uses an eight-node layered shell element. The transient creep compliance in the viscoelastic model is represented as an exponential series plus a steady-flow term. This allows for a simplification of the numerical procedure for handling hereditary effects. Calculations are performed to study the time-dependent redistribution of stress in a flat plate under uniform pressure, a spherical cap under a point load, and a cylindrical shell pinched between two concentrated forces.