Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

Infrared (IR) and Raman spectroscopic features of silicate glasses are often interpreted based on the analogy with those of smaller molecules, molecular clusters, or crystalline counterparts; this study tests the accuracy and validity of these widely cited peak assignment schemes by comparing vibrational spectral features with bond parameters of the glass network created by molecular dynamics (MD) simulations. A series of sodium silicate glasses with compositions of [Na₂O]_x[Al₂O₃]₂[SiO₂]_98−x with x = 7, 12, 17, and 22 were synthesized and analyzed with IR and Raman. A silica glass substrate and a crystalline quartz were also analyzed for comparison. Glass structures with the same compositions were generated with MD simulations using three types of potentials: fixed partial charge pairwise (Teter), partial diffuse charge potential (MGFF), and bond order-based charge transfer potential (ReaxFF). The comparison of simulated and experimental IR spectra showed that, among these three potentials tested, ReaxFF reproduces the concentration dependence of spectral features closest to the experimentally observed trend. Thus, the bond length and angle distributions as well as Si–Qⁿ species and ring size distributions of silica and sodium silicate glasses were obtained from ReaxFF-MD simulations and further compared with the peak assignment or deconvolution schemes—which have been widely used since 1970s and 1980s—(a) correlation between the IR peak position in the Si–O stretch region (1050-1120 cm⁻¹) and the Si–O–Si bond angle; (b) deconvolution of the Raman bands in the Si–O stretch region with the Qⁿ speciation; and (c) assignment of the Raman bands in the 420-600 cm⁻¹ region to the bending modes of (SiO)_n rings with different sizes (typically, n = 3-6). The comparisons showed that none of these widely used methods is congruent with the bond parameters or structures of silicate glass networks produced via ReaxFF-MD simulations. This finding invokes that the adequacy of these spectral interpretation methods must be questioned. Alternative interpretations are proposed, which are to be tested independently in future studies.     

The influence of hBN crystallinity and additive Lithium hydride on cBN synthesis in Li3N–hBN system

In this paper, the influence of hBN crystallinity and additive Lithium hydride (LiH) on cBN synthesis with Lithium nitride (Li₃N) as catalyst was investigated under the pressure of 4.5–5 GPa and the temperature of 1500–1700 °C. hBN with different crystallinities was obtained by the same hBN. Some were explored to high pressure and high temperature, and others were subjected to heat treatment with alkali. X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectronic spectroscopy (XPS) were used to characterize the property of the starting materials. The synthesized samples were observed by optical microscopy (OM). The results indicated that besides the crystallinity of hBN, which is a general parameter for controlling the structural quality of hBN powders, some other factors such as the content of B⁺ at the surface of hBN and additive LiH all strongly influence the synthesis of cBN.     

Theoretical investigation of the hBN(0001)/cBN(111) interface

The interface between the (0001) surface of the hexagonal boron nitride (hBN) and the (111) surface of the cubic boron nitride (cBN) is studied through first principles plane-wave pseudopotentials within the density functional theory. Four different structural models for the pseudomorphic growth of the cBN on hBN have been investigated, two with tetrahedral and two with hexagonal arrangements of the atoms at the interface. The interfaces with N-terminated cBN(111) surface are seen to have the lowest formation energies. The studied interface models present a metallic character, with the levels at Fermi energy spatially confined in the interface region. The band offsets show type I band lineups, with large valence and conduction band discontinuities.     

Quantitative analogies between the linear and non-linear viscoelastic functions

A method of determination of linear and non-linear viscoelastic functions is proposed. Through this method it is possible to calculate the non-linear functions P₁₁ - P₂₂ and η(γ) assuming that linear viscoelastic function (ω) is known. Alternatively from the function P₁₁ - P₂₂ we are able to calculate η(γ) and y'(ω) etc. The method is based on the assumption that the change from linear to non-linear functions is proportional to a molecular deformation for shear stress components P₁₂, and is dependent on the square of the deformation for the first normal stress difference, P₁₁ - P₂₂. The obtained results suggest straightforward modification of equations of state, this being demonstrated with the White-Metzner model of the convected Maxwell element. Consideration of available experimental data shows that this theory is capable of predicting the various functions, at least as well as currently available constitutive equations, while requiring less experimental information.     

Combustion synthesis in the Ni-Al-W system: Some structural features

Explored was combustion synthesis in the Ni-Al-W system with special emphasis on structural features of the process. Using SHS in the 1500–1700°C temperature range, we observed the diffusion-induced processes at the interface between synthesized NiAl and W particles resulting in the formation of W₂Ni and W-Ni intermetallics.     

An empirical correlation between glass transition temperatures and structural parameters for polymers with linear and branched alkyl substituents

A new quantitative model is proposed to correlate glass transition temperatures with bond radii-based structural parameters for poly(p-alkyl styrenes), poly-olefins, poly(alkyl methacrylates), and poly(alkyl acrylates). The model provides a consistent prediction of the glass transition temperatures for both the linear and highly branched polymers up to the entanglement offset points for long side groups. Polymers with highly branched side chains, such as t-butyl and t-pentyl groups that contain quaternary C groups, are predicted to have much higher glass transition temperatures, followed by the methylated, the unsubstituted, and the linearly alkylated polymers. The predictions are confirmed by the experimental results from the authors' research and literature. The current model also allows the extraction of the contribution of hydrogen bonding to glass transition temperatures in polymethacrylates and polyacrylates by comparing differences between the modeled hydrogen-bonding free values with the experimental data. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 507–517, 1997     

网络器结构参数与网络加工的关系

从网络器的进气孔和丝道的形状、尺寸等结构参数以及合理配置,阐述了其与网络加工的关系,可作为网络器设计的依据;同时还介绍了复式网络器的结构参数,网络器的间距对网络加工的影响,长丝加工过程中,应依照振动谐波运动规律调节网络器间距。     

Effect of B2O3 and hBN Crystallinity on cBN Synthesis

Four kinds of BN powders—amorphous BN with B₂O₃, partially crystallized BN without B₂O₃, well-crystallized hBN with B₂O₃, and well-crystallized hBN without B₂O₃—were prepared to determine the effect of B₂O₃ on the crystallization of amorphous BN and the effect of BN crystallinity on the formation of cBN under high pressure (4–5 GPa) and at high temperature (1350–1450°C). The amorphous BN with B₂O₃ easily crystallized and transformed to cBN in the presence of A1N catalyst, while the partially crystallized BN without B₂O₃ did not. The well-crystallized hBN transformed very slowly to cBN without B₂O₃, in contrast to fast transformation with B₂O₃. It is thus found that the transformation from hBN to cBN in the presence of AIN catalyst is determined by the degree of BN crystallinity as well as the presence of B₂O₃. Cubic BN can be synthesized only from crystallized hBN under the experimental conditions used. The formation of cBN from amorphous BN is possible through its prior crystallization, which can occur in the presence of B₂O₃.     

Inorganic phosphate in crude palm oil: Quantitative analysis and correlations with oil quality parameters

A convenient method, not involving ashing or acid digestion, for the determination of inorganic phosphorus content in crude palm oil, is developed. Direct extraction from solvent-diluted palm oil by dilute acid allows the inorganic phosphates to be analyzed by the usual phosphomolybdenum blue complex. Using this method, phosphate analyses in palm oil samples were correlated with other oil quality parameters and the results discussed.     

Total phospholipids in crude palm oil: Quantitative analysis and correlations with oil quality parameters

Phospholipids, selectively extracted from crude palm oil and free of colored carotenoids, can be quantitatively determined by the phospholipid-molybdenum blue complex in hexane. A study of the phospholipid in crude palm oil in relationship to other components affecting oil quality shows that they have a beneficial effect while any detrimental effect may be of an indirect nature.     

Three-dimensional diamond growth film simulations: correlations between nucleation and surface parameters

The development of a three-dimensional simulation of the diamond nucleation and growth presented in a previous paper has been used in this study to determine surface parameters such as the roughness, R_a, and porosity (filling factor Q) of diamond film, according to the crystal size (via the radius R) and the nucleation density N. Evolutions of these surface parameters are compared to values obtained by a statistical treatment (Poisson's law) based on the random nucleation and subsequent growth of hemispheres. In particular, we study the roughness variations with the parameter λ=πR²N, which seems to be the key variable in the case of coatings whose nucleation and growth are in agreement with the Volmer–Weber mechanism. From these results, it is possible to calculate some surface parameters that are useful for tribological and optical applications and whose evolutions with synthesis time have not been reported to our knowledge.     

Mutual correlations between parameters characterizing the miscibility,structure and mechanical properties of polymer blends

Polymer blends were prepared in the whole composition range using polymers of different polarity. Mechanical properties were characterized by tensile measurements. Surface and interfacial properties were measured and calculated and parameters characterizing the miscibility were determined. A correlation was found between the yield stress and the thermodynamic quantities characterizing the degree of miscibility. Since both the degree of miscibility and morphology are influenced by the interfacial tension, it can be regarded as the best candidate to correlate polymer/polymer interaction and mechanical properties in polymer blends.     

Asynchronous synthesis method of waterborne polyurethane with the differences of structural features and thermal conductivity

Waterborne polyurethane (WPU) was successfully synthesized with two ways of one-step method and two-step method, mainly focusing on the effects of asynchronous synthesis method on WPU films’ structural features and thermal conductivity. Compared to the one-step synthesis method of WPU (OS-WPU), the two-step synthesis method of WPU (TS-WPU) showed a high thermal conductivity and approximately 1.4-fold higher than OS-WPU. In addition to this, the water- and solvent-resistance properties and crystallinity of TS-WPU also displayed a better performance than that of OS-WPU. Instrumental analyses of FTIR, DSC, DMA, AFM, SEM and XRD indicated that TS-WPU had an evenly phase separation and lots of microcrystal domains, which is owing to the more ordered structures existed in hard and soft segment domains. In short, the long-range order, short-range order and microcrystal domains existed in WPU can facilitate the phonon propagation, and that is corresponding to the increasing of thermal conductivity.

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Graphic abstract Novelty: Focusing on two synthetic methods to study the structural features and thermal conductivity of WPU. Results show that WPU synthesized by two-step method displays a higher thermal conductivity, phase separation and crystallization behavior than one-step method.

     

On the relationship between the adhesive properties and the structural features of fibrin sealants

The relationship between the adhesive properties and network architecture of fibrin sealants was studied at various fibrinogen, thrombin and calcium ion concentrations. Network features were characterized using Scanning Electron Microscopy at cryogenic temperature (cryo-SEM). This technique allows examination of the hydrated gel without drying. It was shown that by gradually increasing the calcium ion concentration, at constant thrombin and fibrinogen concentrations, the network appearance changed dramatically, from an almost isotropic structure at low concentration to highly oriented fibers at higher concentration of 7 mM CaCl₂. In addition, it was found that further increase in the calcium ion concentration induced fiber aggregation and formation of large clusters, co-existing with fine fibers. Changes in thrombin concentration at constant calcium and fibrinogen concentrations induced only slight changes in the gel appearance. Adhesive properties of fibrin sealants were measured using the shear-lap test and were correlated with structural features of the network. Holding fibrinogen and thrombin concentrations constant and varying the CaCl₂ concentration, maximal shear strength was found with 7 mM CaCl₂, corresponding to an oriented network. Holding fibrinogen and calcium chloride concentrations constant, a slight increase in shear strength was observed with increase in thrombin concentration, demonstrating again the correlation between the network structure and its adhesive properties.     

Relationship between migration potential and structural parameters in crosslinked polyethylenes

Interactions between water and crosslinked polyethylenes (XPE) pipes are subject to regulatory control. In line with this, the objective of our work has been to identify some methods enabling to predict the behaviour of XPE vis à vis its contents. In our study, series of PEHD were crosslinked by β-irradiation at various crosslinking densities. With regard to the structural parameters measured for XPE, we were led to select the evaluation of crystallinity by DSC, the evaluation of crosslink density through its gel fraction and through dynamic mechanical analysis in the rubbery state. These properties are supposed to have a significant effect on the migration potential. With regard to the measurement of the migration potential, an organic solvent was used to accelerate the migration process and the quantity of migrating species was evaluated using gas chromatography. Our results show that irradiation increase the degree of crosslinking, which has the effect of reducing the potential of migration. It comes out of these conclusions that the measurement of structural characteristics of XPE may be a relevant way to predict their potential migration.     

Facile synthesis of a carbon-rich SiAlCN precursor and investigation of its structural evolution during the polymer-ceramic conversion process

A liquid carbon-rich SiAlCN precursor is facilely synthetized by hydrosilylation between liquid polyaluminocarbosilane (LPACS) and 1,3,5,7-tetravinyl- 1,3,5,7-tetramethylcyclotetrasilazane {[CH₃(CH₂CH₂)SiNH]₄} (TeVSZ). The structural evolution during the polymer-ceramic conversion process is investigated by various methods. The results show that the main cured mechanism is β-addition on hydrosilylation, although α-addition on hydrosilylation, polymerization of vinyl groups and dehydrocoupling reaction between N–H bonds also occur during the cured process. During the pyrolysis process, dehydrogenation and dehydrocarbonation condensation reactions, transamination reactions occur, leading to formation of a three-dimensional network inorganic structure at 400–800 °C, where part of Al–O bonds convert to Al–N bonds. Then the network inorganic structure undergoes demixing and separation into amorphous SiAlCN(O) phase, where the amorphous turbostratic free carbon phase also form at 800–1200 °C. With demixing and decomposition of the amorphous carbon-rich SiAlCN(O) phase, the crystalline β-SiC and graphitic carbon start to form at about 1400 °C, the crystalline sizes of them both enlarge with increasing temperature. However, the crystal growth of β-SiC is distinctly inhibited due to existence of the rich carbon phase, tiny amounts of Al₂O₃ and AlN. In addition, a small amount of AlN can promote the formation of α-SiC at 1800 °C.     

On the effects of the sol-gel synthesis parameters on textural and structural characteristics of TiO2

The effects of alcohol/alkoxide, water/alkoxide molar ratios, acid addition, type of solvent, reaction temperature and calcination temperature on textural, structural and morphological characteristics of TiO₂ were studied. The results show that surface area, pore size distribution and crystalline phases were very sensitive to preparation conditions.     

立方氮化硼晶体生长与三大基材的关系

文章将复合传压介质的特性、六方氮化硼的纯净性及Ca、Li基触媒三大基础材料的组成与立方氮化晶体生长的关系进行了论述.指出,传压介质的化学特征组成与特性对稳定的压力场的建立是有着重要影响的;六方氮化硼的晶体结构及其中的氧含量对其生长率与品质是至关重要的;触媒的类型则是决定立方氮化硼晶体生长热力学参数变化的因素.     

Branched poly(ethylene terephthalate) correlations between viscosimetric properties and polymerization parameters

Samples of poly(ethylene terephthalate) (PET) modified with small amounts of trimesic acid groups and hence containing long chain branching have been prepared. From the content of trifunctional modifier and from the experimental value of the extent of reaction, the weight-average molecular weight $\text{M}\text{?}{}_{\mathrm{w}}$ and branching density $\text{B}\text{?}{}_{\mathrm{w}}$ have been calculated, assuming that all the end-groups are equally reactive and intramolecular reactions are absent. The values of $\text{M}\text{?}{}_{\mathrm{w}}$ and $\text{B}\text{?}{}_{\mathrm{w}}$ have been correlated with the experimental values of intrinsic viscosity [η] and the Newtonian melt viscosity η₀. General relations of the following type have been obtained:

$\text{f}{}_1\text{([η],}\text{M}{}_{\mathrm{w}}\text{,}\text{B}{}_{\mathrm{w}}\text{) = 0; f}{}_2\text{(η}{}_0\text{,}\text{M}{}_{\mathrm{w}}\text{,}\text{B}{}_{\mathrm{w}}\text{) =0; f}{}_3\text{(η}{}_0\text{, [η],}\text{B}{}_{\mathrm{w}}\text{) = 0; f}{}_4\text{(η}{}_0\text{, [η],}\text{M}{}_{\mathrm{w}}\text{) = 0;}$

In particular, [η] and η₀ increase on increasing $\text{M}\text{?}{}_{\mathrm{w}}$ and decrease on increasing $\text{B}\text{?}{}_{\mathrm{w}}$, but, at equal [η] values, η₀ increases with $\text{B}\text{?}{}_{\mathrm{w}}$. Through the last relation, the reliability limits of which should be experimentally checked, and from measurements of [η] and η₀, it is possible to calculate $\text{M}\text{?}{}_{\mathrm{w}}$ of a branched PET.