Size-dependent mechanical behavior of nanoscale polymer particles through coarse-grained molecular dynamics simulation

Anisotropic conductive adhesives (ACAs) are promising materials used for producing ultra-thin liquid-crystal displays. Because the mechanical response of polymer particles can have a significant impact in the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry. The objective of this research is to use a coarse-grained molecular dynamics model to verify and gain physical insight into the observed size dependence effect in polymer particles. In agreement with experimental studies, the results of this study clearly indicate that there is a strong size effect in spherical polymer particles with diameters approaching the nanometer length scale. The results of the simulations also clearly indicate that the source for the increases in modulus is the increase in relative surface energy for decreasing particle sizes. Finally, the actual contact conditions at the surface of the polymer nanoparticles are shown to be similar to those predicted using Hertz and perfectly plastic contact theory. As ACA thicknesses are reduced in response to reductions in polymer particle size, it is expected that the overall compressive stiffness of the ACA will increase, thus influencing the manufacturing process.     

Precision grinding of a microstructured surface on hard and brittle materials by a microstructured coarse-grained diamond grinding wheel

Microstructured surfaces on hard and brittle materials are widely used in a series of scientific and industrial applications, such as micro-electro-mechanical systems, nano-electro-mechanical systems, electronic devices, and medical products. However, the efficient precision machining of microstructured surfaces on hard and brittle materials faces great challenges. In this study, a new machining technology for high-efficiency precision fabrication of microstructured surface on hard and brittle materials was developed by a microstructured coarse-grained diamond grinding wheel. Initially, the laser microstructuring of the conditioned coarse-grained diamond grinding wheel was introduced. The influence of the laser-machined microstructure geometry on the form accuracy of the final, ground microstructured surface was theoretically analysed. Subsequently, the ductile regime grinding of the microstructured surface was examined for WC cermet and BK7 optical glass. The ground surfaces mainly under the ductile regime material removal were successfully achieved, especially in the case of WC ceramic. Finally, different linear and square microstructured surfaces with high form accuracy, sharp microstructure edge, and nanoscale surface roughness were efficiently fabricated on WC and BK7 optical glass by the method developed in the study.     

Distribution of cooperative interactions in barnase at different time windows by coarse-grained simulations

The backbone dynamics of barnase has been studied by a recently developed off-lattice Monte Carlo (MC)/Metropolis simulation technique, where a low-resolution model (virtual-bond model) is used together with knowledge-based potentials, with the main emphasis on its cooperative motions at different time windows. The conformations generated around the native state are analysed by time-dependent auto- and cross-conformational correlation functions of the virtual bonds. There exists a correlation between the long time auto-correlated behaviour of the bond rotations and the potential stability of the respective regions. The analysis at different time windows reveals that there are cooperative motions between the bond rotations, which are only near neighbours and basically local motions at all time windows. However, as the time window widens, a progressive increase in the number of correlated pairs, which are separated far along the sequence and are not necessarily close in space, is observed. The structural distribution of these motions shows that the cooperative interactions are not bi-directional and that different residues have a different role within the network of interactions. Thus, the conditions yielding global motion coherence can be accounted for by the existence of anisotropic cooperative long-range interactions among the units in cooperation with the short-range interactions.     

Adulteration detection of Brazilian gasoline samples by statistical analysis

Unfortunately, addition of organic solvents (heavy aliphatic, light aliphatic and aromatic hydrocarbons) in Brazilian gasoline is very frequent, and this illegal practice does not guarantee gasoline quality. Organic solvent adulterations of gasoline samples have been investigated. For characterization and comparison of these samples, physico-chemical parameters together with gas chromatographic analyses data were proposed as the factors for multivariate analysis. Hierarchical clusters analysis was used to improve the detection of the type of solvent and their relative proportion used for this practice. More detailed information of their compositions was revealed. It was found that using physico-chemical properties of gasoline samples together with statistical analysis are a useful method to adulteration detection.     

Weibull statistical analysis of the mechanical strength of a glass eroded by sand blasting

In Saharian regions, the erosion of glass by sand particles during sandstorms is a regular phenomenon. The progressive loss of matter on surface affects both the optical transmission and mechanical strength. In this work, the influence of sand impacts on glass strength was simulated in laboratory. We used Weibull distribution function to characterize statistically the variation of the mechanical strength of a soda-lime glass in the as received state and eroded by sand blasting during 30 and 60 min. From the failure probabilities distributions, we notice an important drop in strength values (about 13%) after 30 min and a tendency to level out with a much reduced dispersion after 60 min. The Weibull plots for the as-received state and for the 30 min eroded state present curves with a knee. They were considered as bimodal forms (two straigth lines) denoting the presence of two kinds of defects that control strength. The Weibull plot for the 60 mins eroded state sample presents one straight line (unimodal form) that indicates the predominance of erosion defects. From micrographical observations on eroded specimen, we observed a tendency toward a damaging homogeneity of the surfaces exposed to sand blasting. This explains the uniformity of the strength values obtained after 1 h of sand blasting.     

Polymers and oligomers derived from pyrrole and N-hydroxymethylpyrrole: A theoretical analysis of the structural and electronic properties

This work reports a theoretical investigation about the structural and electronic properties of polymers constituted by pyrrole and N-hydroxymethylpyrrole in both neutral and p-doped states. Ab initio quantum mechanical calculations were performed on neutral and positively charged oligomers to evaluate the bond length alternation pattern in the π-system, the molecular conformation, the π-π* transition energies and the ionization potential. Results, which have been extrapolated to infinite polymer chains, allow analyze the influence of N-hydroxyalkylation of polypyrrole on these properties.     

Analysis of structural determinants of the stability of thermolysinlike proteases by molecular modelling and site-directed mutagenesis

The thermolysin-like protease (TLP) produced by Bacillus stearothermophilusCU21 (TLP-ste) differs at 43 positions from the more thermallystable thermolysin (containing 316 residues in total). Of thesedifferences, 26 were analysed by studying the effect of replacingresidues in TLP-ste by the corresponding residues in thermolysin.Several stabilizing mutations were identified but, remarkably,considerable destabilizing mutational effects were also found.A Tyr-rich three residue insertion in TLP-ste (the only deletional/insertionaldifference between the two enzymes) appeared to make an importantcontribution to the stability of the enzyme. Mutations withlarge effects on stability were all localized in the ßpleatedN-terminal domain of TLP-ste, confirming observations that thisdomain has a lower intrinsic stability than the largely -helicalC-terminal domain. Rigidifying mutations such as Gly58 Alaand Ala69 Pro were among the most stabilizing ones. Apart fromthis observation, the analyses did not reveal general rulesfor stabilizing proteins. Instead, the results highlight theimportance of context in evaluating the stability effects ofmutations.     

Critical operating factors of a jetting dispenser driven by piezostack actuators: statistical analysis of experimental results

In this work, critical operating factors of a jetting dispenser driven by a dual type of the piezostack actuators are experimentally identified. As a first step, geometrical information and working principle of the jetting dispenser are briefly addressed. Subsequently, in order to investigate jetting performance eight important operating (or working) factors of the dispenser such as exciting stroke and frequency are chosen based on two levels for each factor. Then, in order to reduce the number of experiments, one-sixteenth fractional factorial design method is adopted and an experimental apparatus to measure the weight of a single dot is established. After measuring the weight of a single dispensed dot under each test condition, the effect of each operating factor on the jetting performance is analyzed using a statistical program. The main effects and interaction effects on the average and standard deviation of the weight of a single dispensed dot are then analyzed and discussed in details. In addition, the analysis of variance results for average single dot weight is undertaken to determine the specific values of the critical factors which can provide optimal jetting performances. Consequently, critical operating factors for a small amount and small weight variation of a single dot are identified, which directly represent the performances of a non-contact jetting dispenser driven by piezostack actuators such as dotting accuracy and dotting speed.     

Cross-sectional structural analysis of C60 nanowhiskers by transmission electron microscopy

Cross-sectional observations of C₆₀ nanowhiskers (C₆₀NWs) were successfully conducted using the focused ion beam (FIB) method. The C₆₀NWs were observed to possess the core-shell structures with porous cores and dense surface thin layers. The size and number of pores decreased from the center to the surface, showing that the densification of C₆₀NWs proceeds from the surface to the center upon drying. A cross-sectional high-resolution transmission electron microscopy (HRTEM) image of a C₆₀NW showed a disordered structure comprising the domains with sizes on the order of 10 nm. The most frequently observed cross-sections were hexagons, reflecting the solvated hexagonal crystal structures of as-grown C₆₀NWs. From the observation of various cross-sectional shapes of C₆₀NWs with different diameters and crystallographic surface analysis, it is suggested that C₆₀NWs grow longer above a critical diameter D_c with the development of low-energy crystal surfaces.     

Hydrodynamics of three-phase fluidized bed systems examined by statistical, fractal, chaos and wavelet analysis methods

Hydrodynamic studies were conducted in gas-liquid-solid systems (0.1 m ID, 2 m high) of 3.0 mm glass beads and of 2.1 mm polypropylene low-density particles, with particles densities of 2471 and 1290 kg/m³, respectively. Simultaneous measurement of differential pressure and bubble conductivity probe signals sampled at 500 Hz for 60 s enabled the investigation of the change in flow structure in relation to the flow regime transitions. Superficial gas velocities ranged between 0.010 and 0.052 m/s for polypropylene particles, and extended to 0.12 m/s for glass beads, while the superficial liquid velocities covered the ranges of 0.0007-0.045 m/s for polypropylene particles, and ranged up to 0.056 m/s for glass beads.Spectral analysis of the pressure fluctuations revealed a transition from dispersed to coalesced bubbling flow with decreasing liquid velocity for a given superficial gas velocity. The use of a conductivity probe facilitated characterization of the local flow structure in terms of bubble movement. The measurements were extensively analyzed using fractals and chaos, power spectra frequency analysis and wavelet decomposition in addition to the standard statistical analyses. The coefficient of variation of the bubble probe signals was found to be the most effective in deducing the transition velocity between coalesced and dispersed bubbling flow regimes, while wavelet energy confirmed the similarity in the distribution between two axial positions once operated in the dispersed flow regime. Comparison of the flow structure between glass beads and polypropylene particles showed that both the minimum liquid fluidization velocity and the transition velocity between the bubble flow regimes were much higher for the glass beads than for the lighter polypropylene particles. Furthermore, the standard deviations of the decomposed bubble probe signals through wavelet transformation successfully highlighted the difference between the two systems of particles.     

Quick assessment of the thermal decomposition behavior of lignocellulosic biomass by near infrared spectroscopy and its statistical analysis

The application of near infrared (NIR) spectroscopy for the prediction of the thermal decomposition behavior of lignocellulosic biomass (three types of woody biomass and three types of herbaceous biomass) was successfully performed along with statistical analysis. The thermal degradation behaviors of the woody and herbaceous biomass were different because of their different chemical compositions. Herbaceous biomass was degraded at lower temperature than woody biomass. The weight‐loss profiles as a function of temperature were obtained by thermogravimetric analysis (TGA) at a heating rate of 25°C/min under nitrogen gas. The weight‐loss percentage at 10 temperatures in the range 150–600°C was predicted by a wavelet partial least squares (PLS) model, which showed significantly better predictive performance than the ordinary PLS model. The results show that the data predicted by the wavelet PLS model was well fitted to the original data by TGA, in which the root‐mean‐square error in prediction values less than 5.5 suggested that NIR spectroscopy was applicable for rapid analysis to characterize the thermal decomposition behavior of lignocellulosic biomass for energy production. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A study on the effects of reaction conditions on the characteristics of resol resins for foams by statistical analysis

A two-level full factorial experimental design with three variables, formaldehyde-to-phenol (F/P) molar ratios, hydroxy-to-phenol (OH/P) wt%, and reaction temperature was implemented to determine the effect of the variables on the properties of phenol-formaldehyde (PF) resol resins for insulation foam. Ten resins were prepared with F/P molar ratios between 1.5 and 2.5, OH/P wt% between 0.5 and 1.5 and reaction temperature between 80 and 90 ‡C. The effect of three independent variables on the resin properties was analyzed by using three-way ANOVA of SPSS. All three production variables had a significant effect on resin properties. The F/P molar ratio and OH/P wt% were found to have the most frequent effect on resin properties. F/P molar ratio and OH/P wt% had an increasing effect, while reaction temperature showed a decreasing effect on free formaldehyde. The present study confirms that experimental design is a very valuable and capable tool for evaluating multiple variables in resin production.     

分子筛脱蜡模拟移动床工业过程的模拟计算与分析

针对分子筛脱蜡工业生产的模拟移动床过程,基于TMB建模策略,建立了描述模拟移动床过程的数学模型,模型求解采用有限元配置的数值计算方法PDECOL软件包。结果表明:在验证模型计算正确性的基础上,模型模拟计算值与过程设计值相一致,可以用描述分子筛脱蜡工业生产的模拟移动床过程。探讨了模拟移动床过程中的进料流速、提取液的提取速度、旋转阀的切换周期以及脱附液的用量等操作参数对过程性能的影响,为过程的优化提供了基础。     

Optimization of BaZrO3 sintering by control of the initial powder size distribution; a factorial design statistical analysis

A factorial design statistical analysis has been conducted in order to obtain the optimum conditions in the solid state sintering process of barium zirconate bulk materials, optimum with respect to density, closed and open porosities. The optimized heat treatment permits to sinter a 99% dense barium zirconate sample at 1650 °C during only 2 h. When the temperature is higher than 1650 °C or when the heating time is longer than 2 h, a decrease in density is observed.     

Conformational analysis of a dermatan sulfate-derived tetrasaccharide by NMR, molecular modeling, and residual dipolar couplings

The solution conformation behavior of a dermatan-derived tetrasaccharide--Delta HexA-(1-->3)-GalNAc4S-beta-(1-->4)-IdoA-alpha-(1-->3)-red-GalNAc4S (S is a sulfate group)--has been explored by means of NMR spectroscopy, especially by NOE-based conformational analysis. The tetrasaccharide was present as four species, two of which are chemically different in the anomeric orientation of the reducing 2-deoxy-2-acetamido-galactose (red-GalNAc) residue, while the other two are the result of different conformations of the iduronic acid (IdoA) unit. The two alpha-beta-interconverting anomers were present in a 0.6:1 ratio. Ring conformations have been defined by analysis of (3)J(H,H) coupling constants and interresidual NOE contacts. Both 2-deoxy-2-acetamido-galactose (GalNAc) residues were found in the (4)C(1) chair conformation, the unsaturated uronic acid (Delta-Hex A) adopts a strongly predominant half-chair (1)H(2) conformation, while the IdoA residue exists either in the (1)C(4) chair or in the (2)S(0) skewed boat geometries, in a 4:1 ratio. There is a moderate flexibility of Phi and Psi torsions as suggested by nuclear Overhauser effects (NOEs), molecular modeling (MM), and molecular dynamics (MD) studies. This was further investigated by residual dipolar couplings (RDCs). One-bond C--H RDCs ((1)D(C,H)) and long-range H-H ((3)D(H,H)) RDCs were measured for the tetrasaccharide in a phage solution and interpreted in combination with restrained MD simulation. The RDC-derived data substantially confirmed the validity of the conformer distribution resulting from the NOE-derived simulations, but allowed an improved definition of the conformational behavior of the oligosaccharides in solution. In summary, the data show a moderate flexibility of the four tetrasaccharide species at the central glycosidic linkage. Differences in the shapes of species with the IdoA in skew and in chair conformations and in the distribution of the sulfate groups have also been highlighted.     

Conformation analysis of aspartame-based sweeteners by NMR spectroscopy, molecular dynamics simulations, and X-ray diffraction studies

We report here the synthesis and the conformation analysis by 1H NMR spectroscopy and computer simulations of six potent sweet molecules, N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-S-tert-butyl-L-cysteine 1-methylester (1; 70 000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-beta-cyclohexyl-L-alanine 1-methylester (2; 50 000 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-4-cyan-L-phenylalanine 1-methylester (3; 2 000 times more potent than sucrose), N-[3,3-dimethylbutyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (4; 5500 times more potent than sucrose), N-[3-(3-hydroxy-4-methoxyphenyl)propyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (5; 15 000 times more potent than sucrose), and N-[3-(3-hydroxy-4-methoxyphenyl)-3-methylbutyl]-alpha-L-aspartyl-(1R,2S,4S)-1-methyl-2-hydroxy-4-phenylhexylamide (6; 15 000 times more potent than sucrose). The "L-shaped" structure, which we believe to be responsible for sweet taste, is accessible to all six molecules in solution. This structure is characterized by a zwitterionic ring formed by the AH- and B-containing moieties located along the +y axis and by the hydrophobic group X pointing into the +x axis. Extended conformations with the AH- and B-containing moieties along the +y axis and the hydrophobic group X pointing into the -y axis were observed for all six sweeteners. For compound 5, the crystal-state conformation was also determined by an X-ray diffraction study. The result indicates that compound 5 adopts an L-shaped structure even in the crystalline state. The extraordinary potency of the N-arylalkylated or N-alkylated compounds 1-6, as compared with that of the unsubstituted aspartame-based sweet taste ligands, can be explained by the effect of a second hydrophobic binding domain in addition to interactions arising from the L-shaped structure. In our examination of the unexplored D zone of the Tinti-Nofre model, we discovered a sweet-potency-enhancing effect of arylalkyl substitution on dipeptide ligands, which reveals the importance of hydrophobic (aromatic)-hydrophobic (aromatic) interactions in maintaining high potency.     

Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar

Hydrogenated amorphous silicon carbide (a-SiC_x:H) films were prepared by the decomposition of tetramethylsilane (TMS) with microwave discharge flow of Ar. When radio-frequency (RF) bias voltage (− V_RF) was applied to the substrate, the film hardness increased as (2.39 ± 1.12)-(9.15 ± 0.55) GPa for − V_RF = 0-100 V. The a-SiC_x:H films prepared under various − V_RF conditions were analyzed by the carbon-K near edge X-ray absorption fine structure (NEXAFS), by the elastic recoil detection analysis (ERDA), and by the X-ray photoelectron spectroscopy (XPS). From a quantitative analysis of NEXAFS, the sp²/(sp²+ sp³) ratios of C atoms were evaluated as 67.9 ± 2.0, 55.4 ± 2.7, and 51.7 ± 0.7% for − V_RF = 0, 60, and 100 V, respectively. From ERDA, hydrogen content of the film prepared under the condition of − V_RF = 100 V was found to decrease 28% comparing with that under − V_RF = 0 V. It is suggested that the cause of the increase of the film hardness when applying − V_RF is predominantly the growth of the sp³-hybridized structure of C atoms accompanied by the decrease of hydrogen terminations.     

Hydrocarbon structural group analysis of Athabasca asphaltene and its g.p.c. fractions by C n.m.r.

Asphaltene from the Athabasca oil sand bitumen separated according to molecular weight by gel permeation chromatography was examined by high resolution solution-state ¹³C and ¹H and solid state ¹³C n.m.r. Integration of the inverse gated decoupled solution state and CP/MAS ¹³C n.m.r. spectra gave the aromaticity of each fraction as well as the relative number of carbon atoms responsible for well resolved signals in the aliphatic portion of the spectra. A two-pulse spin-echo ¹³C n.m.r. sequence in the solution state, and dipolar dephasing in the solid state, permitted the assignment of each aliphatic carbon signal to a methyl, methylene, or methine carbon; no quaternary aliphatic carbons were observed. These signals show that the aromatic core of the asphaltene is surrounded by alkyl chains with a mean length of 7.7 for the lowest molecular weight fraction (MW 1200), increasing to 12 for the highest MW fraction (MW 16900). Aromaticity of the fractions obtained from solution spectra ranged from 34 to 48%, the highest aromaticity being associated with the lowest molecular weight asphaltenes. In the solid state, the aromaticity ranged from 31 to 42 %. The degree of branching ranged from 0.5 per chain for the low MW asphaltene to 1.0 for the high MW fraction. The highest naphthenic carbon content was found in the high MW fractions; the 1200 MW fraction appeared to be nearly devoid of such carbon, this fraction having a much higher aromaticity than the second-lowest MW fraction.