Self-Enhancement of Scalar and Vector Holographic Gratings in Azobenzene Molecular Glassy Films

Self-enhancement (SE) effect of scalar and vector holographic gratings (HG) recorded in three different azobenzene molecular glassy films is experimentally studied in both transmission and reflection modes at 532 and 633 nm. The maximal SE factor (the ratio of diffraction efficiency to its initial value) SEF = 42 has been achieved. It is shown that the model of complementary HG can be applied also in scalar transmission thin HG case to explain coherent SE. The possibility of vector HG coherent SE in transmission mode is experimentally demonstrated for the first time (SEF = 4.3). The possibility of coherent HG SE in reflection mode is also established for the first time (SEF = 21). HG recording processes as well as coherent SE processes are found to be independent in transmission and reflection modes being determined by volume and surface relief HG, respectively. The permittivity gradient mechanism is proposed to explain the coherent SE of surface relief HG. Both HG recording and coherent SE efficiencies strongly decrease when HG period is decreased from 2 mm to 0.5 mm. No relaxational SE effect is found. Coherent SE effect in molecular glasses is found to be weaker than in inorganic materials.

Chemically Amplified Resist Based on Dendritic Molecular Glass for Electron Beam Lithography

A novel dendritic molecular glass(MG)containing adamantane core(AD-15)was synthesized and characterized.It exhibits good solubility in common organic solvents and a stable amorphous state at room temperature,which contributes to forming films with different thicknesses by spin-coating.The thermal analysis of AD-15 indicates that no apparent glass transition temperature(Tg)is observed before the thermal decomposition temperature(Td=160℃).The good thermal resistance suggests that it can satisfy the lithographic process and is a candidate for photoresist materials.The patterning properties of AD-15 resist were evaluated by electron beam lithography(EBL).By optimizing the lithographic process parameters,AD-15 resist can achieve 40 nm half-pitch patterns with a line-edge roughness of 4.0 nm.The contrast and sensitivity of AD-15 resist were 1.9 and 67µC/cm^(2),respectively.Compared with the commercial PMMA(950k)electron beam resist,the sensitivity of AD-15 resist increases by 6 times.This study provides a new example of molecular glass resist with high resolution and sensitivity for EBL.

Outgassing analysis of molecular glass photoresists under EUV irradiation

A device was designed and assembled to analyze the outgassing of molecular glass(MG)photoresists under extreme ultraviolet(EUV)exposure.The outgassing of the photoresists with different components and different concentrations of tert-butoxycarbonyl(t-Boc),photo-generated acid(PAG),and acid quencher was systematically investigated.Based on experiments,some solutions for reducing the outgassing of MG photoresists were proposed.

Single-component chemically amplified i-line molecular glass photoresist based on calix[4]resorcinarenes

Calix[4]resorcinarene, prepared by the acidcatalyzed condensation of resorcinol and paraldehyde, was used as the core of the molecular glass compound. The hydroxyl groups of calix[4]resorcinarene were partly protected by tert-butoxycarbonyl(t-BOC) and then esterified with 2-diazo-1-naphthoquinone-4-sulfonyl chloride(2,1,4-DNQ-Cl). Upon irradiation to 365 nm light, the 2,1,4-DNQ groups undergo photolysis to generate a small quantity of sulfonic acid other than indene carboxylic acid. The generated sulfonic acid can further catalyze the deprotection of the t-BOC group. So, a new type of single-component chemically amplified i-line positive photoresist can be formed by the molecular glass compounds. The lithographic performance of the resist was evaluated with high resolution and photosensitivity with an i-line stepper.

Immobilization of radioactive fluoride waste in aluminophosphate glass:a molecular dynamics simulation

Molecular dynamics(MD) simulations were conducted to investigate the structural and chemical environment of aluminum in aluminophosphate glasses.Such glasses have the potential for application in the disposal of radioactive fluoride waste from molten salt reactors(MSR).Due to the risks of studying these materials and the limitations of realistic research conditions,MD simulations were used as an alternative method to study the vitrification of radioactive fluoride waste.In the past decades,aluminophosphate glasses have been studied and they exhibit certain favorable properties for high-level radioactive waste management.This work focuses on the effects of fluorine addition on structural changes in the glass.We observed that glass with composition P_2O_5–Al_2O_3–Na_2O–CaO exhibited a good performance in immobilizing fluoride at low F concentrations(approximately under25 mol%).Significant changes were observed where PO_3F_2 units replaced PO_3F units in the glass.The fourcoordinated AlO_4 units were increasingly converted into five-coordinated [AlO_xF_y] with the increasing F content.The radionuclide Sr in the simulation had the tendency to form six-coordinated octahedrons in the glass.We conclude that the structural changes resulting from the fluoridewaste added to aluminophosphate glasses does not adversely affect their chemical stability at relatively low F concentrations,i.e.,under 25 mol%.Hence,the use of phosphate glasses is a potential alternative method of fluoride waste disposal.

Epoxy-based azo molecular glasses with four-arm architecture:Preparation, characterization and holographic recording

In this study,a series of epoxy-based azo molecular glasses with four-arm architecture was synthesized based on an intermediate(MDGA-AN),which was obtained from ring-opening reaction between 4,4'-methylene-bis(N,N’-diglycidylaniline)and N-methylaniline.The azo compounds were then synthesized through azo-coupling reaction between MDGA-AN and diazonium salts of 4-nitroaniline,4-aminobenzonitrile,4-aminobenzoic acid,4-fluoroaniline and 4-methoxyaniline,respectively.The azo compounds were thoroughly characterized and the photoresponsive properties of their solid films were investigated at three different wavelengths(λex=488,532 and 589 nm).The results show that the electron-withdrawing groups on the azo chromophores can significantly affect the absorption band positions in visible light range,which shift to the longer wavelength with the enhanced push-pull effect.Both photoinduced birefringence and surface-relief-grating formation are closely related to the electronwithdrawing groups and excitation wavelengths of the actinic light,which show significant influences on the growth rates and saturated values of the photoinduced variations.In this series,the azo molecular glasses containing cyano and carboxyl groups as the electron-withdrawing groups show the significantly higher efficiency for both the photoinduced birefringence growth and the SRG formation compared with others under the same light irradiation conditions.The capability of the materials as a photo-storage medium is demonstrated by holographic recording.

Icosahedral medium-range order formed in Mg_(70)Zn_(30) metallic glass: a larger-scale molecular dynamics simulation

A larger-scale Mg70Zn30 alloy system including 100000 atoms has been simulated by using the molecular dynamics method to investigate the icosahedral medium-range order (IMRO) formed in the Mg70Zn30 metallic glass. It is found that the simulated pair distribution function of Mg70Zn30 metallic glass is in good agreement with the experimental results. The glass transition temperature Tg is near 450 K under the cooling rate of 1×1012 K/s. The icosahedral local structures play a critical role in the formation of metallic glass, and they are the dominant local configurations in the Mg70Zn30 metallic glass. The IMRO in the Mg70Zn30 metallic glass is characterized by certain types of extended icosahedral clusters combined by intercross-sharing atoms in the form of chains or dendrites. The size distributions of these IMRO clusters present a magic number sequence of 19, 23, 25, 27, 29, 31, 33, 35, 37, 39,. . . , and the magic clusters can be classified into three types according to their compactness. The IMRO clusters grow rapidly in a low-dimensional way with cooling, but this growth is limited near Tg.

Molecular Dynamic Simulation Study on Glass Transition Temperature of DGEBA-THPA/SWCNTs Composites

Molecular dynamic (MD) simulations were carried out to predict the thermo-mechanical properties of the cured epoxy network composed of diglycidyl ether bisphenol A (DGEBA) epoxy resin and tetrahydrophthalic anhydride (THPA) curing agent and their single-walled carbon nanotubes (SWCNT) reinforced the epoxy matrix composites. Different characters such as the density of the materials and mean square displacements (MSDs) were calculated to estimate the glass transition temperatures (Tgs) of of the materials. 365 K and 423 K of the Tgs were obtained respectively, whereas the latter is much higher than the former. The simulation results indicated that the incorporation of SWCNTs in the epoxy matrix can significantly improve the Tg of the cured epoxy. The approach presented in this study is ready to be applied more widely to a large group of candidate polymers and nanofillers.

Molecular Dynamics Simulation of Glass Transition Behavior of Polyimide Ensemble

The effect of chromophores to the glass transition temperature of polyimide ensemble has been investigated by means of molecular dynamics simulation in conjunction with barrier analysis. Simulated Tg results indicated a good agreement with experimental value. This study showed the MD simulation could estimate the effect of chromophores to the Tg of polyimide ensemble conveniently and an estimation approach method had a surprising deviation of Tg from experiment. At the same time, a polyimide structure with higher barrier energy was designed and validated by MD simulation.

Ab initio molecular dynamics study on the local structures in Ce_(70)Al_(30) and La_(70)Al_(30) metallic glasses

Ab initio molecular dynamics simulations were performed to investigate the effect of similar elements on the shortto medium-range atomic packing features in Ce_(70)Al_(30) and La_(70)Al_(30) glass-forming alloys. 4 f electrons of Ce element in Ce_(70)Al_(30) alloy were properly treated in electronic calculations. The local atomic structures in both alloys are qualitatively similar. However, the local environments of Al atoms in Ce_(70)Al_(30) alloy show fluctuation with temperature in the cooling process, which could result from 4 f electrons of Ce elements. Surprisingly, the medium-range atomic packing features of Al atoms in both MGs are quite different, although Ce and La elements are similar. These findings are useful for understanding the enhanced glass-forming ability by similar element substitution in RE-based MGs from a medium-range structure perspective.

退火处理对Pt基块体金属玻璃塑性动力学行为的影响

采用退火的热诱导方法向Pt基块体金属玻璃(Pt-BMG)基体内原位引入纳米晶,通过纳米压痕实验,考察了Pt-BMG在铸态和在玻璃转变温度Tg之上(250℃)退火15 min,2 h和6 h的力学性能和塑性动力学行为.研究结果表明,退火时间从15 min增加到6 h时,Pt-BMG的结晶度从34%增加到57%,平均晶粒尺寸从25.6 nm增加到38.3 nm,硬度和折合模量分别从5.66 GPa和133.83 GPa增加到8.65 GPa和182.89 GPa,同时载荷-位移曲线上的锯齿流变行为呈现从可明显观察到不连续的位移突变到比较平滑的变化规律.通过分子动力学模拟进一步证明,随着纳米晶尺寸的增加,剪切转变区的激活与剪切带的成核呈现先促进后抑制、先增加后减小的趋势.这是由于金属玻璃在塑性变形过程中,小尺寸纳米晶会被剪切带所包裹或溶解,促进了金属玻璃塑性变形的形成;而大尺寸纳米晶在承受载荷时,在晶体内部产生了位错和滑移,进一步抑制了剪切带的成核与传播.本文结合纳米压痕实验和分子动力学模拟,从原子尺度上揭示了纳米晶的尺寸影响非晶合金塑性变形的内在机理,为设计理想性能的金属玻璃提供了有效的实验基础与理论支撑.

非晶合金结构演变影响玻璃形成能力的分子动力学研究

通过分子动力学方法模拟了Ti_(75)Al_(25)、Ni_(50)Zr_(50)和Cu_(50)Zr_(50)非晶合金的玻璃转变过程,得到并分析了平均原子体积和双体分布函数等结构参数,并应用Voronoi多面体指数分析法统计了玻璃转变过程中二十面体及类二十面体团簇的数量,通过分析团簇在玻璃转变过程中种类和数量的涨落趋势,研究了非晶原子由短程序连接至中程序再至长程无序的动力学演化过程.结果表明,非晶合金的玻璃形成能力以及塑性变形能力与动力学演化过程中Voronoi团簇的种类和数量密切相关.在玻璃转变过程中局部五次对称性高的团簇倾向于连接在一起形成链,从而密排整个空间,降低系统的动力学行为从而提高玻璃形成能力.塑性形变倾向于发生在局部五次对称性较低的区域.在玻璃转变温度附近团簇种类和数量的突变反映出非晶合金的自组织临界行为,蕴含着丰富的非线性动力学现象.

基于分子动力学模拟下CuZr金属玻璃的局域连接度对拉伸性能的影响

二十面体连接网络是由二十面体相互连接而形成的中程有序结构。利用分子动力学模拟方法研究了CuZr金属玻璃在拉伸过程中的二十面体连接网络的演变。结果表明,二十面体连接网络会因为变形而断裂,从而出现孤立的二十面体,或是转变成其他团簇。高的米瑟斯应力和屈服时更少的连接度数量百分比可以解释Cu含量低的样品中的较低强度和良好塑性。此外,在Cu含量高的样品中,低连接度在变形后更倾向于向高连接度转变,让样品在变形后仍保持着较高的连接度,呈现为强度高、塑性低的力学性能。

热氧老化对马来酸酐接枝聚丙烯的结构与性能的影响

以自制的马来酸酐接枝聚丙烯(PP-g-MAH)为研究对象,研究了PP-g-MAH对玻璃纤维增强聚丙烯材料性能的影响以及热氧老化对PP-g-MAH分子结构和性能的影响。结果表明,自制的PP-g-MAH大幅度提高了30%玻纤增强聚丙烯材料的力学性能;随着热氧老化时间的延长,PP-g-MAH的MFR不断增加,对玻璃纤维增强聚丙烯材料的力学性能的提升作用不断降低;通过凝胶色谱仪(GPC)、红外光谱(IR)和马来酸酐(MAH)接枝率测定结果的分析,热氧老化过程没有对PP分子链接枝的马来酸酐产生明显的影响,而是引起了聚丙烯分子链的断裂,造成PP-g-MAH分子量下降,导致自身力学性能下降,使得PP与玻璃纤维之间的界面强度下降,使得PP-g-MAH对玻璃纤维增强聚丙烯材料的力学性能提升作用下降。

中空玻璃干燥剂钾交换率的测定——原子吸收分光光度法

介绍了一种中空玻璃干燥剂钾交换率测定的新方法。中空玻璃干燥剂经研磨、混合酸溶解后,消除待测溶液中铝对钾钠离子的干扰,采用原子吸收分光光度法测定溶液中氧化钾、氧化钠的含量后折算出钾交换率。

Simulations of the flipping images and microparameters of molecular orientations in liquids according to the molecule string model

The relaxation dynamics of liquids is one of the fundamental problems in liquid physics,and it is also one of the key issues to understand the glass transition mechanism.It will undoubtedly provide enlightenment on understanding and calculating the relaxation dynamics if the molecular orientation flipping images and relevant microparameters of liquids are studied.In this paper,we first give five microparameters to describe the individual molecular string(MS) relaxation based on the dynamical Hamiltonian of the MS model,and then simulate the images of individual MS ensemble,and at the same time calculate the parameters of the equilibrium state.The results show that the main molecular orientation flipping image in liquids(including supercooled liquid) is similar to the random walk.In addition,two pairs of the parameters are equal,and one can be ignored compared with the other.This conclusion will effectively reduce the difficulties in calculating the individual MS relaxation based on the single-molecule orientation flipping rate of the general Glauber type,and the computer simulation time of interaction MS relaxation.Moreover,the conclusion is of reference significance for solving and simulating the multi-state MS model.

Molecular dynamics of amorphous pharmaceutical fenofibrate studied by broadband dielectric spectroscopy

Fenofibrate is mainly used to reduce cholesterol level in patients at risk of cardiovascular disease.Thermal transition study with the help of differential scanning calorimetry(DSC) shows that the aforesaid active pharmaceutical ingredient(API) is a good glass former.Based on our DSC study,the molecular dynamics of this API has been carried out by broadband dielectric spectroscopy(BDS) covering wide temperature and frequency ranges.Dielectric measurements of amorphous fenofibrate were performed after its vitrification by fast cooling from a few degrees above the melting point(T_m=354.11 K) to deep glassy state.The sample does not show any crystallization tendency during cooling and reaches the glassy state.The temperature dependence of the structural relaxation has been fitted by single Vogel–Fulcher–Tamman(VFT) equation.From VFT fit,glass transition temperature(T_g) was estimated as 250.56 K and fragility(m) was determined as 94.02.This drug is classified as a fragile glass former.Deviations of experimental data from Kohlrausch–Williams–Watts(KWW) fits on high-frequency flank of α-peak indicate the presence of an excess wing in fenofibrate.Based on Ngai's coupling model,we identified the excess wing as true Johari–Goldstein(JG) process.Below the glass transition temperature one can clearly see a secondary relaxation(γ) with an activation energy of 32.67 kJ/mol.

Thermodynamic and structural properties of polystyrene/C60 composites: A molecular dynamics study

To tailor properties of polymer composites are very important for their applications.Very small concentrations of nanoparticles can significantly alter their physical characteristics.In this work,molecular dynamics simulations are performed to study the thermodynamic and structural properties of polystyrene/C60(PS/C60)composites.The calculated densities,glass transition temperatures,and coefficient of thermal expansion of the bulk PS are in agreement with the experimental data available,implying that our calculations are reasonable.We find that the glass transition temperature Tg increases accordingly with an added concentration of C60 for PS/C60 composites.However,the self-diffusion coefficient D decreases with increase of addition of C60.For the volumetric coefficients of thermal expansion(CTE)of bulk PS and PS/C60 composites,it can be seen that the CTE increases with increasing content of C60 above Tg(rubbery region).However,the CTE decreases with increasing content of C60 below Tg(glassy region).

Liquid-to-glass transition of tetrahydrofuran and 2-methyltetrahydrofuran

Both tetrahydrofuran(THF) and 2-methyltetrahydrofuran(MTHF) are studied systematically at desired temperatures using molecular dynamics simulations.The results show that the calculated densities are well consistent with experiment.Their glass transition temperatures are obtained:115K ～ 130K for THF and 131K ～ 142K for MTHF.The calculated results from the dipolar orientational time correlation functions indicate that the "long time" behavior is often associated with a glass transition.From the radial and spatial distributions,we also find that the methyl has a direct impact on the structural symmetry of molecules,which leads to the differences of physical properties between THF and MTHF.