牙科复合树脂转化率的测定方法

光聚充填复合树脂是牙齿修复的主要原料之一,在临床使用中,树脂中有机基质分子上碳碳双键的聚合转化率决定着修复的效果和树脂在口腔中的使用寿命。光聚转化率是树脂性能的主要评价指标之一,因此,在研究和使用过程中,树脂光聚转化率的测定十分重要。确定光聚充填复合树脂转化率的方法有多种,目前主要是采用仪器分析的方法。基于傅里叶变换红外光谱(FT-IR)、傅里叶变换拉曼光谱(FT-Raman)、近红外光谱(NIR)、差热分析(DTA)、核磁共振(NMR)和高效液相色谱(HPLC)等仪器在牙科充填复合树脂光聚转化率测定方面的应用,介绍牙科充填复合树脂光聚转化率的测定方法,并分析了各种方法的特点。     

Synthetic Light‐Curable Polymeric Materials Provide a Supportive Niche for Dental Pulp Stem Cells

Dental disease annually affects billions of patients, and while regenerative dentistry aims to heal dental tissue after injury, existing polymeric restorative materials, or fillings, do not directly participate in the healing process in a bioinstructive manner. There is a need for restorative materials that can support native functions of dental pulp stem cells (DPSCs), which are capable of regenerating dentin. A polymer microarray formed from commercially available monomers to rapidly identify materials that support DPSC adhesion is used. Based on these findings, thiol‐ene chemistry is employed to achieve rapid light‐curing and minimize residual monomer of the lead materials. Several triacrylate bulk polymers support DPSC adhesion, proliferation, and differentiation in vitro, and exhibit stiffness and tensile strength similar to existing dental materials. Conversely, materials composed of a trimethacrylate monomer or bisphenol A glycidyl methacrylate, which is a monomer standard in dental materials, do not support stem cell adhesion and negatively impact matrix and signaling pathways. Furthermore, thiol‐ene polymerized triacrylates are used as permanent filling materials at the dentin‐pulp interface in direct contact with irreversibly injured pulp tissue. These novel triacrylate‐based biomaterials have potential to enable novel regenerative dental therapies in the clinic by both restoring teeth and providing a supportive niche for DPSCs.     

A combined molecular dynamics and Raman spectroscopy approach for designing ice-metal interfaces

Summary Understanding the structure and interatomic interactions of an ice-metal interface plays a fundamental role in the design of deicing coatings. This is demonstrated by a novel approach, combining vibrational results from laser Raman spectroscopy with molecular dynamics simulations to obtain insights into icing on solids which, in turn, lead to design criteria for minimizing adhesion. An atomistic model of ice-copper interaction is constructed based on electronic structure calculations and used to show that reasonable molecular geometry and binding energy at the interface can be obtained. Through molecular dynamics simulations we find that the ice layer adjacent to the copper surface is structurally more disordered than the layers further away, a result which is verified by the Raman spectra of vibrational frequencies. The primary adhesive bond is made by the adsorption of oxygen atoms at the lattice sites of the metal substrate. The information obtained by Raman spectroscopy and molecular dynamics is then exploited to arrive at specific recommendations for designing polymeric deicing coatings and materials.     

A combinatorial characterization scheme for high-throughput investigations of hydrogen storage materials

Abstract

In order to increase measurement throughput, a characterization scheme has been developed that accurately measures the hydrogen storage properties of materials in quantities ranging from 10 ng to 1 g. Initial identification of promising materials is realized by rapidly screening thin-film composition spread and thickness wedge samples using normalized IR emissivity imaging. The hydrogen storage properties of promising samples are confirmed through measurements on single-composition films with high-sensitivity (resolution <0.3 μg) Sievert’s-type apparatus. For selected samples, larger quantities of up to ～100 mg may be prepared and their (de)hydrogenation and micro-structural properties probed via parallel in situ Raman spectroscopy. Final confirmation of the hydrogen storage properties is obtained on ～1 g powder samples using a combined Raman spectroscopy/Sievert’s apparatus.     

Review Polarised Raman spectroscopy for the study of molecular orientation distributions in polymers

Polarised Raman spectroscopy is a vibrational spectroscopic technique that is used widely for the chemical and physical analyses of materials since it is both non-destructive and suitable for remote analysis. In particularly over the last 40 years, the technique has been developed and applied for the study of molecular orientation distributions in polymers. Compared to other analytical techniques, polarised Raman spectroscopy has the following advantages, (1) quantitative and precise measurement of molecular orientation distributions, and (2) study of these distributions in both the crystalline and amorphous phases. Knowledge obtained from the technique is of both academic and industrial interest to study relationships between microstructure and macroscopic physical properties in polymers. In this paper, polarised Raman spectroscopy is reviewed with regard to the study of molecular orientation distributions in polymeric materials. The basis of polarised Raman scattering is first described, and this is followed by the procedure for obtaining spectra. It is shown how Raman scattering intensities for different polarised scattering geometries can be interpreted to give parameters and functions representing quantitative measures of the degree of molecular orientation. Factors affecting the evaluation of these parameters are also summarised. Finally, the usefulness of the technique is demonstrated by practical applications including a study of molecular orientation distributions in poly(ethylene terephthalate) (PET) fibres.     

Facile route to prepare film of poly(3,4-ethylene dioxythiophene)-TiO2 nanohybrid for solar cell application

Composite using poly(3,4-ethylenedioxythiophene) (PEDOT) as electronic conducting polymer and nanocrystalline titanium dioxide (TiO₂) as host matrix were prepared by the template method. We applied an original in situ photopolymerization technique to synthesize PEDOT inside the TiO₂ pore and characterized the polymer and pore filling by different analysis (cyclic voltammetry, atomic force microscopy, spectroscopy and thermogravimetric measurements). Results were compared with those obtained on PEDOT films synthezised by monomer oxidization in the presence of FeCl₃. In situ generation of PEDOT by photopolymerization was observed to be higher and self-limiting after 22% filling of the mesoporous TiO₂ network. Hybrid materials were used to fabricate an indium-tin oxide/nano-crystalline TiO₂/PEDOT/Au device. The current-voltage characteristics indicate that a built-in electrical field has been created at the nano-crystalline TiO₂/PEDOT interface with energy conversion efficiency of 0.09% without dye.     

A combinatorial characterization scheme for high-throughput investigations of hydrogen storage materials

In order to increase measurement throughput, a characterization scheme has been developed that accurately measures the hydrogen storage properties of materials in quantities ranging from 10 ng to 1 g. Initial identification of promising materials is realized by rapidly screening thin-film composition spread and thickness wedge samples using normalized IR emissivity imaging. The hydrogen storage properties of promising samples are confirmed through measurements on single-composition films with high-sensitivity (resolution <0.3 μg) Sievert’s-type apparatus. For selected samples, larger quantities of up to ∼100 mg may be prepared and their (de)hydrogenation and micro-structural properties probed via parallel in situ Raman spectroscopy. Final confirmation of the hydrogen storage properties is obtained on ∼1 g powder samples using a combined Raman spectroscopy/Sievert’s apparatus.     

Structure and Properties of Chemically-reduced Functionalized Graphene Oxide Platelets

Green reduction of graphene oxide(GO) functionalized with 3-aminopropyltriethoxysilane and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide was performed by using ascorbic acid and sodium bisulfite.The obtained materials were characterized by thermo-gravimetric analysis,transmission electron microscopy.X-ray diffraction,UV-Vis,Fourier transform infrared and Raman spectroscopy techniques.The results indicated a strong dependence of the materials properties such as deoxygenation degree,absorption peak shift,crystallite size and functionalization degree on the functionalization approach and reducing agent.     

利用拉曼光谱鉴别优化处理宝玉石

通过对一些宝玉石及其优化处理样品的测试,证明拉曼光谱在检测优化处理宝玉石中具有无可替代的独特优势。拉曼光谱可以检测红外光谱无法透过的闷镶翡翠样品,并可以清楚地检测出充填处理翡翠中的环氧树脂峰;可以明显地将绿松石的上蜡和注胶区分开来,相比于红外光谱,两者的区别更为明显;还可以精确地定位祖母绿裂隙中的充填物质,明确地判定祖母绿是否经充胶或染色处理。拉曼光谱在珠宝检测中的作用越来越重要,将会成为珠宝检测的重要手段之一。     

Curing of visible light-activated dental restorative composites

FTIR spectroscopy and microhardness measurements were employed to follow the degree of curing of visible light activated dental composites. The observed dependence of curing on grade and shade of the materials, exposure time and depth from the light exposed surface have been discussed. Immediately after curing, it was found that direct correlation of microhardness values with that of double bond conversion estimated by FTIR technique could not be established.     

Effect of sonication time on the synthesis of the CdS nanoparticle based multiwall carbon nanotube – maleic anhydride – 1-octene nanocomposites

Effect of sonication time on the synthesis of the CdS nanoparticles within the matrix obtained through the covalent functionalization of multiwall carbon nanotube (MWCNT) with maleic anhydride (MA) – 1-octene copolymer was investigated. Cadmium chloride and thiourea were used as the raw materials. MWCNTs used for the matrix were synthesized by Catalytic Chemical Vapor Deposition using Fe-Co/Al₂O₃ as the catalyst. The obtained nanostructures were characterized by FTIR, XRD, Raman spectroscopy, TEM, SEM, TG and UV-Vis spectroscopy. Electrophysical properties of the polymer nanocomposites obtained using different periods of time for sonication were comparably investigated. The average CdS particle diameter was between 3.9–7.9 nm as confirmed independently by TEM and XRD. UV-Vis spectroscopy revealed that the obtained nanostructures are appropriate base materials for making optical devices.     

Analysis of the fragmentation test for carbon-fibre/epoxy model composites by means of Raman spectroscopy

The interfaces between high-modulus PAN-(T50) and mesophase pitch-based (P55) carbon fibres and an epoxy matrix have been studied by using the conventional fragmentation test in conjunction with polarised-light optical microscopy. Raman spectroscopy has also been used to follow stress transfer from the matrix to the fibres for the same fragmentation geometries. The level of fibre/matrix adhesion and mechanisms by which the stress is transfered from the matrix to the fibres has been determined from both the stress birefringence patterns and strain-induced Raman band shifts in the fibres. The values of interfacial shear strength have been determined by means of both the conventional analysis and the Raman technique. It is found that the Raman method gives a much more detailed picture of stress transfer in the test specimens and that the two methods give somewhat different values of the interfacial shear strength. The values of interfacial shear stress have been discussed with respect to fibre surface energy, surface chemistry and surface morphology. It was found that the surface chemical functional groups appear to have no direct correlation with interfacial shear strength. Furthermore, it appears that mechanical interlocking due to surface roughness could contribute to the higher values of interfacial shear strength determined for the PAN-based fibre.     

The interfacial properties of aramid/epoxy model composites

Many attempts have been made to measure, evaluate and improve the level of interfacial adhesion in aramid/epoxy composites. Different surface treatments have been developed in order to promote chemical bonding between the fibre and the matrix but it is found that most of the surface treatments developed have shown little or no improvement in the level of interfacial adhesion. The interfacial properties of a model composite are often determined by measuring the interfacial shear strength using micromechanical test methods that employ different loading configurations. However, the values of interfacial shear strength determined using different test methods are found to be dependent upon the variation of localized stress in the samples due to the different loading configurations and often give different results. Using Raman spectroscopy it is shown that the strain-dependent shift of the 1610 cm^–1 aramid Raman band can be used to determine the point-to-point variation of axial fibre strain along aramid fibres embedded in epoxy resin matrices from which the interfacial properties can be derived. The interfacial properties of aramid/epoxy model composites have been determined using Raman spectroscopy where the properties of the fibre, including different surface treatments, and the matrix have been changed systematically. The results are reviewed here and compared to those obtained using conventional micromechanical test methods. It is also demonstrated that the Raman technique can be used to characterize the interfacial properties of aramid/epoxy model composites deformed using different micromechanical test methods. In this way the interfacial properties can be determined at different loading levels enabling the progressive failure of the fibre/matrix interface to be monitored and defined accurately.     

Raman spectroscopy for characterization of interfacial debonds between carbon fibers and polymer matrices

A systematic study on Raman spectroscopy of carbon fibers, both experimental and commercial, has been undertaken. The objectives of this study are to (i) use the Raman spectra of carbon fibers to quantify the degree of chemical bonding and interdiffussion across the fiber–matrix interface, and (ii) to characterize interfacial debonds. Key experimental results include: (i) spectra from the same location of a fiber, repeated thrice, (ii) spectra from three different locations of a particular fiber, (iii) spectra from the same location of a fiber as a function of laser power, and (iv) comparison of the spectra of commercial fibers (AS4), manufactured at Hercules, Inc. (presently Hexel), Magna, with those of the experimental fibers, produced in a more controlled laboratory environment at the Hercules Research Center, Wilmington, DE. In the present investigation, the experimentally determined crystallite size (inversely proportional to the ratio of the relative intensities of the Raman peaks corresponding to the week (A_1g) and strong (E_2g) modes) is correlated to the deformation and stress states in the vicinity of the circumferential tip of a fiber–matrix interfacial debond under the combined mode I/II. The experimental results obtained by means of Raman spectroscopy in combination with a three-dimensional eigenfunction approach can provide a powerful tool for characterization of interfacial debond nucleation and propagation in real-life carbon fiber/polymer matrix composites.     

Polymer grafted hydroxyapatite whisker as a filler for dental composite resin with enhanced physical and mechanical properties

The objective of this study was to investigate the effect of surface graft polymerization of hydroxyapatite whisker (HW) on physical and mechanical properties of dental composite resin. Poly bisphenol A glycidyl methacrylate (Poly(Bis-GMA)) was grafted onto silanized hydroxyapatite whisker (SHW) via solution polymerization and the amount of the Poly(Bis-GMA) on the surface was effectively controlled by polymerization time. The obtained poly(Bis-GMA) grafted hydroxyapatite whisker (PGHW) with different polymer contents was filled into a resin matrix respectively, meanwhile the composites with HW and with SHW served as controls. Monomer conversion was characterized by Fourier transform infrared spectroscopy (FTIR) and volume shrinkage of the composite resin was measured with a density tester. Mechanical properties were tested with a universal testing machine. The results indicated that the composite filled with PGHW-1 h (graft ratio of poly(Bis-GMA): 8.5 wt.%) showed lower shrinkage and better mechanical properties, improving flexural strength by 6.5% and 11.9% compared with SHW filled composite and HW filled composite, respectively. However, PGHW with higher graft ratios aggregated seriously and formed defects in the composite, leading to deterioration of mechanical properties. It was revealed that the poly(Bis-GMA) on the surface of PGHW acted as a functional transition layer and enhanced interfacial compatibility and interaction between whisker and resin matrix, which facilitated the dispersion of PGHW in the composite and decreased the composite shrinkage. Thus, the graft polymerization of Bis-GMA on the surface of filler might be a promising modification method for the fabrication of dental materials.     

Structural analysis on photopolymerized dental resins containing nanocomponents

The incorporation of nanoscale layered silicates, as montmorillonite (MMT), into polymers has attracted great attention due to their ability to improve mechanical, thermal, and barrier properties of many polymers. Inserting these nanocomponents into dental resins could lead to materials with improved wearing resistance under masticatory attrition, among other advantages. Thus, the aim of this work was to investigate the process of incorporating layered silicates into dental resins by studying the influence of the concentration of these nanocomponents and the type of chemical species, used to modify the clays, in the morphology of the systems. Three types of clay were inserted in a BisGMA/TEGDMA photopolymerized resin system. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS). FTIR and TGA results confirmed the presence of the modifier agents in MMT. SEM micrographs indicated a homogeneous distribution of the layered silicates throughout the dental resin after photopolymerization and a high degree of interfacial adhesion. SEM micrographs also showed that the mixing process used to add clay into dental monomers was not successful in breaking agglomerates and was also responsible for forming new agglomerates particularly in highly concentrated materials. XRD and SAXS patterns showed the development of a partially exfoliated/intercalated clay structure after photopolymerization of the dental resin. Exfoliation, together with intercalation, was even observed in materials having concentrations of MMT as high as 16 wt.%. Exfoliation in highly filled materials was attributed to the formation of a microstructure composed of large agglomerates, in which most of the MMT layers were concentrated and restricted to exfoliate, and few small particles disseminated throughout the polymer matrix that were able to exfoliate. SAXS results also suggested that the modification of MMT with species containing polar groups was more successful in producing exfoliated structures than MMT having highly hydrophobic incorporated species. The insertion of vinyl groups into MMT galleries led to the production of dental resins containing large and compact agglomerates with intercalated layers, as suggested by determining the fractal number of the materials. The possibility of producing photopolymerized dental resins containing exfoliated nanolayers can potentially be useful in controlling important properties of dental materials such as resistance to attrition, moisture absorption, polymerization shrinkage, coefficient of thermal expansion, among others.     

Effect of cycling on the magnetization of ion exchanged magnetic nanocomposite based on polystyrene

Magnetic nanocomposites containing iron oxide particles embedded in a polymer matrix have been synthesized using the method of ion exchange. They have been characterized by using low temperature and room temperature magnetic measurements and Mössbauer spectroscopy. The iron content in these samples has also been determined. The results have been analysed and explained. The physical and chemical properties of these nanocomposite materials are different from those of the bulk. Some of the unique properties of these materials find application in information storage, color imaging, ferrofluids and magnetic refrigeration.     

Spectrum analysis of the reduction degree of two-step reduced graphene oxide (GO) and the polymer/r-GO composites

In this paper, the reduction degree of graphene oxide (GO) reduced using chemical reduction and thermal reduction methods was characterized by spectrum analysis. The optimized conditions of reducing GO were determined that the hydrazine hydrate is the best reducing agent and the appropriate thermal reduction temperature is at 240 °C. The obtained GO solution was mixed with polystyrene (PS) solution to prepare PS/r-GO composites by using two-step reduction technique under the optimized conditions. The structure and micro-morphology of GO, r-GO and PS/r-GO composites were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) respectively. It is also observed that the two-step reduction pathway is more effective than one-step reduction for improving the reduction degree of GO. Accordingly, the electric conductivity of PS/r-GO composites prepared by two-step reduction technique is as high as 21.45 S m⁻¹, which is much higher than that of composites fabricated by one-step reduction method. The spectrum techniques will highlight new opportunities for investigating the reduction degree of GO in polymer composites.     

Polymer-matrix nanocomposite gas-sensing materials

A new approach has been proposed for producing nanocomposite gas-sensing materials: in situ preparation of a polymer matrix and metal sulfide or oxide nanoparticles through the frontal polymerization of Co(II), Cd(II), Zn(II) and Pb(II) acrylamide complexes. The composition and structure of the nanocomposites thus obtained have been determined using X-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopy. The nanocomposites have been tested as room-temperature liquefied petroleum gas sensors.     

拉曼光谱表征石墨烯结构的研究进展

石墨烯是一种只有一个原子层的二维原子晶体,它是构成零维富勒烯、一维碳纳米管和三维石墨等其他碳同素异形体的基本结构单元,具有很多独特的电子及力学性能,因而吸引了化学、材料及其他领域众多科学家的高度关注。拉曼光谱作为一种灵敏便捷的表征方法,在石墨烯的研究中起到重要的作用。该综述总结了近年来拉曼光谱在石墨烯表征中的应用,在对单层石墨烯的典型特征峰作详细介绍的基础上,通过对拉曼谱图中D峰、G峰和2D峰的强度、位置和半峰宽变化情况的分析,可以快速而准确地表征出石墨烯的层数,并可以对石墨烯的堆垛方式、边缘手性和掺杂程度进行判定。同时,也系统地分析了在石墨烯制备与测试过程中基底、掺杂、温度和激光功率等因素对拉曼谱图中D峰、G峰和2D峰的强度、位置和半峰宽的影响。