Estimation of molecular diffusivity in aqueous solution of acetonitrile by the Wilke-Chang equation

It was tried to estimate the molecular diffusivity (D(m)) of solutes in the mixtures of acetonitrile (ACN) and water by the Wilke-Chang equation. Although the information about association coefficient (α) is necessary for the calculation, it has never been proposed for ACN. The value of α was estimated as 1.37 from D(m) of benzene in ACN at 303 K experimentally measured by the peak parking method. The values of α, i.e. 2.6, 1.9, 1.5, and 1.0, which have respectively been proposed for four solvents, i.e. water, methanol, ethanol, and benzene, were correlated with two physico-chemical parameters of the solvents, i.e. solubility parameter and E(T) value. The α value for ACN was plotted around the two correlations, indicating its appropriateness. The values of D(m) calculated by the Wilke-Chang equation using the α value for ACN were compared with those measured by the peak parking method and the Aris-Taylor method in aqueous solutions of ACN. The mean square deviation of the estimation of D(m) was calculated as 8.8 and 14%. It was demonstrated that the Wilke-Chang equation can be used for estimating D(m) with a reasonable accuracy in the mixtures consisting of ACN and water.     

湍流运动论中的化学反应速率扰动

在分子与分子之间发生碰撞时,如果分子的动能足够大,当超过一定的阈值E时,分子碰撞就会发生化学反应.然而气体分子化学反应速率是受到一定因素影响的,诸如分子数密度n、温度T以及速度V.日本学者Sagara于上世纪70年代曾对分子数密度n和温度T对反应速率的变化做了深入的探究.主要是在此基础上利用二粒碰撞机理论对速度以及温度和速度的共同作用来研究反应速率的变化情况.     

Effect of residual copper on stability of molecular brushes prepared by atom transfer radical polymerization

Effect of residual copper on stability of molecular brushes with poly(n-butyl acrylate) (PBA) side chains was studied. The brushes were prepared by atom transfer radical polymerization (ATRP) using the grafting-from approach. Although the copper concentration was decreased down to below ten ppm levels by passing through alumina column, further removal was required to prevent crosslinking reactions. Further removal was performed by dialysis or precipitation.     

Selective extraction of triazine herbicides based on a combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction

A selective extraction technique based on the combination of membrane assisted solvent extraction and molecularly imprinted solid phase extraction for triazine herbicides in food samples was developed. Simazine, atrazine, prometon, terbumeton, terbuthylazine and prometryn were extracted from aqueous food samples into a hydrophobic polypropylene membrane bag containing 1000μL of toluene as the acceptor phase along with 100mg of MIP particles. In the acceptor phase, the compounds were re-extracted onto MIP particles. The extraction technique was optimised for the type of organic acceptor solvent, amount of molecularly imprinted polymers particles in the organic acceptor phase, extraction time and addition of salt. Toluene as the acceptor phase was found to give higher triazine binding onto MIP particles compared to hexane and cyclohexane. Extraction time of 120min and 100mg of MIP were found to be optimum parameters. Addition of salt increased the extraction efficiency for more polar triazines. The selectivity of the technique was demonstrated by extracting spiked cow pea and corn extracts where clean chromatograms were obtained compared to only membrane assisted solvent extraction or only molecularly imprinted solid phase extraction. The study revealed that this combination may be a simple way of selectively extracting compounds in complex samples.     

The missing link between the Hydration Force and interfacial water: Evidence from computer simulations

In this article I briefly review Molecular Dynamics Simulations studies relevant to the understanding of the physical origin of the controversial Hydration Force. The focus of the review is in simulations of realistic models of hydrophilic surfaces. The results reviewed here show a molecular perspective on how this repulsive, stabilizing force comes from interfacial water.     

Molecular dynamics comparative study of methane–nitrogen and methane–nitrogen–ethane systems

This work concerns the site–site interaction study of 256 particles using the Buckingham potential model. We have calculated the new parameters of the Buckingham potential using an iterative algorithm with a mean square method. This adapted model allows determining the characteristics for each state point. We have applied this model to study the liquefied natural gas LNG properties for methane-nitrogen and methane–nitrogen–ethane mixtures by molecular dynamics. We have calculated the thermodynamic, dynamic and structural properties for both the microcanonical NVT and the isothermal-isobaric NPT ensembles of binary and ternary systems from the SP₁ to SP₉ points. Then, we have compared the results between binary and ternary systems. We have obtained a good prediction on transport properties. From the calculated values of self-diffusion coefficient and viscosity, we have confirmed the liquid state of the liquefied natural gas LNG system.     

The interlayer shear effect on graphene multilayer resonators

Graphene nanostrips with single or few layers can be used as bending resonators with extremely high sensitivity to environmental changes. In this paper we report molecular dynamics (MD) simulation results on the fundamental and secondary resonant frequencies f of cantilever graphene nanostrips with different layer number n and different nanostrip length L. The results deviate significantly from the prediction of not only the Euler-Bernoulli beam theory (f∝nL⁻²), but also the Timoshenko's model. Since graphene nanostrips have extremely high intralayer Young's modulus and ultralow interlayer shear modulus, we propose a multibeam shear model (MBSM) that neglects the intralayer stretch but accounts for the interlayer shear. The MBSM prediction of the fundamental and secondary resonant frequencies f can be well expressed in the form f−f_mono∝[(n-1)/n]^bL^−2(1−b), where f_mono denotes the corresponding resonant frequency as the layer number is 1, with b=0.61 and 0.77 for the fundamental and secondary resonant modes. Without any additional parameters fitting, the prediction from MBSM agrees excellently with the MD simulation results. The model is thus of importance for designing multilayer graphene nanostrips based applications, such as resonators, sensors and actuators, where interlayer shear has apparent impacts on the mechanical deformation, vibration and energy dissipation processes therein.     

基于超疏水高黏附结构的痕量农药分子现场检测SERS基底研究

多种农药,包括孔雀石绿（MG）作为禁用兽药,存在食用致癌的风险。由于MG低廉的价格和极好的药效,在渔业养殖中一直被不法商贩非法使用,使得鱼类生鲜中时有MG残留检出。针对MG分子痕量残留的检测,目前一般是抽取少量养殖水样,再利用高效液相色谱柱、液相色谱-光谱等方法来评估其是否超标。这类传统的检测方法一般需要依赖价格昂贵的大型设备,且检测过程操作繁琐复杂,单次检测耗时长、价格高,因而与农贸市场中商品流通量大、速度快、价格需亲民低廉等特点和要求不相符合。近年来,表面增强拉曼散射（SERS）检测技术以及便携式拉曼光谱仪的出现,有望实现对痕量农药分子的现场快速检测,进而很好地解决这一问题。SERS检测技术利用金属纳米结构的表面等离激元效应感应位于其结构表面附近的分子,得到分子种类和浓度信息。为了降低可检测的浓度极限,一般会在SERS基底上利用咖啡环效应或其他手段将待测分子蒸发富集,以获得足够高的信号强度。针对亲水基底,液滴与基底相接触后,会在基底表面摊开,使其分布面积扩大,导致其咖啡环周长变长,分子分布浓度随之降低。而当采用疏水基底富集时,由于常规的疏水基底表面黏附性小,液滴在其表面处于随处滚动无法抓取的状态,极大增加了操作的难度。以MG分子痕量残留的检测为例,由于农贸市场人员众多、无专业实验平台,磕碰撞击时有发生,在此环境下采用疏水SERS基底对农药分子进行检测显然是不可取的。该研究提出一种基于超疏水高黏附纳米森林结构的SERS基底用于痕量MG分子的快速现场检测。相比于超疏水SERS基底,所提出的超疏水高黏附基底利用其高黏附性可牢固抓取待测液滴,解决了以往超疏水基底在实际现场检测中存在液滴滚动无法操作的问题。此外,与亲水基底相比,超疏水高黏附基底由于接触角大,可将咖啡环面积缩小5.73倍,继而使分子的富集浓度提高5.73倍,最终使检测极限浓度降低了至少两个数量级。研究所提出的超疏水高黏附SERS基底有望在痕量农药分子快速现场检测中得到应用。