表面活性剂溶液粗粒化模型couette流动模拟

本文主要利用粗粒化分子动力学方法对不同浓度下表面活性剂水溶液在couette流动过程中胶束的形成、速度分布与流变性规律进行了研究。结果表明,对于相同浓度的表面活性剂溶液,随着剪切速率的增大,胶束完全动态平衡时间越来越小;而随着表面活性剂分子浓度的增加,胶束动态平衡时间也越来越小,形成胶束越来越快。在剪切速率与溶液剪切黏度关系方面,保持表面活性剂分子浓度不变情况下,随着剪切速率的增大,剪切黏度逐渐减小,呈现剪切稀化特征。     

在相反电荷表面活性剂存在下阳离子瓜尔胶水溶液流变行为

合成了阳离子瓜尔胶(CG),研究了其水溶液在十二烷基硫酸钠(SDS)存在下的流变行为．测定结果表明,随SDS浓度的增加,溶液零切黏度增加了3个数量级以上．小幅振荡剪切实验结果表明模量几乎和SDS浓度无关,但是驰豫时间则随着SDS浓度增加而迅速增加．因此,SDS的加入将会使交联点的强度增加,但是不会改变交联点密度．SDS对CG流变行为的影响可以用两阶段模型加以描述．在SDS存在下CG水溶液流变行为主要受到由SDS胶束形成的交联点的控制．根据Arrhenius公式得到的瓜儿胶水溶液的流动活化能在将SDS分子疏水尾端从胶束移到水相之中所需能量是一致的.     

PS_(3000)-b-PAA_(5000)球形胶束温度效应的原位小角X射线散射技术研究

应用小角X射线散射技术(SAXS)对两亲嵌段共聚物聚苯乙烯聚丙烯酸(PS-b-PAA)胶束形貌的温度影响进行了原位表征.SAXS结果表明:随着水含量的增加,粒子尺寸相应增加;对于水含量10%的PS_(3000)-b-PAA_(5000)胶束溶液,发现了明显的SAXS双峰现象;双峰的位置不随着温度的变化而改变,但是peak 1和peak 2的相对强度随着温度发生了减弱和增强的交错变化;相邻的SAXS双峰说明在PS_(3000)-b-PAA_(5000)胶束溶液中最初形成的粒子尺寸并不是均匀的,主要分为尺寸极其相近的两种球形粒子;随着温度的升高,粒径大小不同的两种粒子存在着一种消融和生长的过程,并且保持着一个相同的归一化动态平衡速率.     

β-环糊精对含有十二烷基硫酸钠的甲基纤维素水溶液凝胶化行为的影响

测定了甲基纤维素在SDS溶液、和SDS与β-CD混合溶液中的凝胶化温度,讨论了SDS与MC之间疏水相互作用和SDS与β-CD之间包合作用对MC溶液凝胶化行为的影响. 结果表明,SDS与β-CD之间的包合作用远大于SDS与MC链上甲基之间疏水相互作用,在β-CD存在下,SDS对MC溶液凝胶化行为的影响可以被完全屏蔽掉. 由此可以进一步计算出在MC存在下SDS与β-CD之间的包合比是1:1,与在聚乙烯基吡咯烷酮存在下的包合比完全一致,但是与在带相反电荷聚电解质存在下的包合比并相同,主要是因为SDS与MC相互作用的方式和与聚电解质相互作用的方式有着本质的区别.     

利用超声光栅研究声速与液体性质

设计并搭建了超声光栅,观察了激光经过光栅形成的衍射斑纹,测量了声速;并利用超声光栅测定了不同温度、不同浓度的NaCl溶液中的声速,给出了声速-水温和声速-溶液浓度的依赖关系.水的温度每升高1℃,3.974 MHz的超声波的声速增加2.09 m/s,16.574 MHz的超声波的波速增加2.04m/s;声速随着NaCl溶液浓度的增大线性增加,NaCl溶液浓度每升高1%,3.974 MHz的超声波声速增加13.637 m/s,16.574 MHz的声波声速增加11.757 m/s.在此基础上,分析了不同频率的超声波对实验规律的影响,认为不同频率的超声波在相同条件下测量的溶液中声速大小的不同源于测量的随机误差.     

Preparation and Unimolecular-Micellization Behavior of Homopolymer of Surface-Active Monomer AMC14AB

采用水溶液均聚合方法,制备了阳离子型表面活性单体(2-丙烯酰胺基)乙基十四烷基二甲基溴化铵(AMC14AB)的均聚物,使用荧光探针法、表面张力测定及电导测定法,重点考察了均聚物P(AMC14AB)在水溶液中的胶束化行为与表面吸附现象. 在水溶液中,均聚物P(AMC14AB)呈现单分子链胶束的聚集形态,具有零临界胶束浓度,从开始加入P(AMC14AB)起,水溶液中随即产生单分子链胶束,不存在Krafft温度. P(AMC14AB)在溶液表面也发生表面吸附,使水的表面张力下降,即P(AMC14AB)也具有表面活性;随着浓度增大,表面吸附量增大,水的表面张力持续下降;当表面吸附达饱和时,表面张力～浓度曲线上出现突变点,该点定义为饱和的表面吸附浓度,而不应该再称为临界胶束浓度. P(AMC14AB)单分子链胶束溶液对疏水有机物(甲苯)的增溶情况,明显不同于普通小分子表面活性剂十六烷基溴化铵(CTAB)的多分子胶束溶液,甲苯增溶量～P(AMC14AB)浓度的关系曲线上无突变点,而且对甲苯的增溶能力高于CTAB的多分子胶束溶液.     

柠檬酸钠对谷氨酰胺转移酶山羊乳凝胶特性影响的光谱学分析

运用多重光散射光谱、多散斑扩散波光谱和动态光散射光谱分析了柠檬酸钠(TSC)对谷氨酰胺转移酶(TG酶)山羊乳凝胶特性的影响。将浓度分别为0,20,40,60和80 mmol·L-1 的TSC加入到脱脂羊乳中,经过TG酶处理后进行酸化凝乳。凝乳形成过程中,动态光散射光谱显示,随着TSC浓度的增加,酪蛋白胶束的直径从(142.0±11.2) nm下降到(24.4±2.1) nm;在凝胶形成的前5 h内,在不同TSC浓度条件下,样品的背散射光强度分别从41.9%±0.3%,35.8%±0.4%,25.3%±0.5%,10.6%±0.3%和5.3%±0.4%,增加到55.8%±0.6%,49.5%±0.5%,41.9%±0.4%,37.8%±0.4%和30.8%±0.3%,表明TSC的浓度越高,凝胶体系中颗粒的尺寸越小,形成的凝胶构筑单元越小;同时,多散斑扩散波光谱的均方位移曲线显示,凝胶的突变时间分别为31,74,98,151和226 min,表明TSC的浓度越高,山羊乳凝胶形成时间越长;凝胶的持水力与硬度值分析发现,TSC将羊乳酪蛋白胶束分解成更小的颗粒,在TG酶作用下形成更多的共价键连接位点,形成的凝胶具有更高的硬度和持水能力。     

癸基萘磺酸钠胶束中分子动态的质子核磁共振研究

在298、303和313 K下对浓度为0.82 和2.59 mmol/L的癸基萘磺酸钠的重水溶液中质子的自旋-自旋弛豫（T₂）时间进行了测量. 浓度为0.82 mmol/L 的溶液(临界胶束浓度CMC以下)中的所有质子的T₂值均随温度上升而增长，说明整个分子运动变的更自由. 然而，浓度在CMC以上(2.59 mmol/L)时，分子中一部分参与形成栅栏层的质子的T₂值却表现出相反的效应，它们的运动随温度上升而变慢，说明在高温下为防止水分子进入疏水胶束壳内，这些栅栏层的质子堆积的更紧密. 同时分子中其他质子的T₂值随温度上升而增长，表现出正常的分子运动的温度效应.     

Effect of Short Chain Alcohols upon Viscosity of TTAB Solution

研究了不同条件下乙醇、丙醇和丁醇对十四烷基三甲基溴化铵(TTAB)溶液粘度行为的影响． 结果表明, 在无KBr存在下,TTAB溶液相对粘度随着醇的加入线性增加,说明醇分子没有增溶到TTAB胶束之中;在KBr存在下,TTAB溶液相对粘度随着乙醇的加入不断减小,但是会随着丙醇和丁醇的加入出现最大值,说明丙醇和丁醇的加入会促进TTAB胶束的增长;在KCl存在下,丙醇和丁醇的加入对TTAB胶束的影响几乎可以忽略不计．一种可能的解释是：KBr的存在促进了TTAB胶束的增长．因此,TTAB胶束内核的疏水程度有所增加,导致在特定浓度条件下丙醇和丁醇溶解到胶束中进一步促进了TTAB胶束的增长．     

激光光散射研究二醋酸纤维素在丙酮中的聚集

采用激光光散射研究了二醋酸纤维素的溶液性质. 发现在丙酮中二醋酸纤维素除了以单链形式存在外,还形成了胶束以及胶束簇集体. 随着浓度的增加,平均流体力学半径线性增加,而均方根回旋半径与平均流体力学半径的比值线性减小,表明由于二醋酸纤维素分子间的相互作用,胶束之间发生聚集,并形成胶束簇集体.     

CoFe2O4纳米颗粒的结构、磁性以及离子迁移

聚乙烯醇(PVA)溶胶凝胶法制备出CoFe₂O₄纳米微粉，用X射线衍射研究了铁氧体纳米颗粒的结构.测量了CoFe₂O₄纳米颗粒80—873 K的变温穆斯堡尔谱，发现纳米颗粒的磁转变温度范围为793—813 K，比块体材料的磁性转变温度要低.CoFe₂O₄纳米颗粒的德拜温度θ_A=674 K，θ_B=243 K，比块体材料要小.CoFe₂O₄纳米颗粒超精细场H_f随温度的变化符合T^3/2+T^5/2定理.当温度较高时，平均同质异能移IS随温度的升高而减小，并呈线性关系. 关键词： 纳米颗粒 磁性 穆斯堡尔谱     

Multicanonical Monte Carlo simulations on intramolecular micelle formation in copolymers

The formation of intramolecular micelles in copolymers with periodic sequence, where hydrophobic units (stickers) are periodically placed along the chain, is studied by using multicanonical Monte Carlo computer simulations for an off-lattice bead-rod model in three dimensions. With decreasing the temperature, a transition from random-coil conformations to micelles occurs and flower-type micelles are formed via the transition. The number of stickers forming a micelle core is limited by the excluded-volume effect of loop chains around micelle cores. By this effect, two intramolecular micelles are formed for long polymer chains with 60 bonds via the coil-to-micelle transition. By further decreasing the temperature, we find that another transition, i.e., a micelle-to-micelle transition, takes place. At this transition point, the two intramolecular micelles merge into one micelle. Furthermore, we extend the multicanonical MC method to study elastic properties of single polymer chains with strong attractive interactions under external force fields, and study how the intramolecular micellization affects the elastic property of single polymer chains.     

Phase transition of DNA compaction in confined space: Effects of macromolecular crowding are dominant

With a view of detecting the effects of macromolecular crowding on the phase transition of DNA compaction confined in spherical space, Monte Carlo simulations of DNA compaction in free space, in confined spherical space without crowders and in confined spherical space with crowders were performed separately. The simulation results indicate that macromolecular crowding effects on DNA compaction are dominant over the roles of multivalent counterions. In addition,effects of temperature on the phase transition of DNA compaction have been identified in confined spherical space with different radii. In confined spherical space without crowders, the temperature corresponding to phase transition depends on the radius of the confined spherical space linearly. In contrast, with the addition of crowders to the confined spherical space, effects of temperature on the phase transition of DNA compaction become insignificant, whereas the phase transition at different temperatures strongly depends on the size of crowder, and the critical volume fraction of crowders pertains to the diameter of crowder linearly.     

Transition from rigid to flexible structures in micelles of Undecylammonium chloride in aqueous solutions of NaCl

Small angle neutron scattering (SANS) data for Undecylammonium chloride (UAC) in heavy water in the presence of NaCl 0.0428 and 0.3422 M are consistent with the presence of elongated micelles. This micellar shape has been adopted to analyze viscosity data of UAC in water in the presence of NaCl. The results obtained from this last technique are consistent with the increase of the micelle aggregation number with increasing the surfactant concentration. Micelles change from prolate ellipsoidal shape to cylindrical and wormlike shapes by increasing the added NaCl concentration and surfactant concentrations. The differences between results for the micelle aggregation number calculated from viscosity, SANS and light scattering data have been attributed to the solvent effect on micelle formation as well as changes in the size, shape and flexibility of the micelle. Viscosity data provide qualitative information on the effect of the added NaCl concentration and surfactant concentration on the size, shape, flexibility of the micelles in diluted solutions.     

Sphere-to-rod transition of triblock copolymer micelles at room temperature

A room temperature sphere-to-rod transition of the polyethylene oxide-polypropylene oxide-polyethylene oxide-based triblock copolymer, (PEO)₂₀(PPO)₇₀ (PEO)₂₀ micelles have been observed in aqueous medium under the influence of ethanol and sodium chloride. Addition of 5–10% ethanol induces a high temperature sphere-to-rod transition of the micelles, which is brought to room temperature upon addition of NaCl. The inference about the change in the shape of the micelles has been drawn from small-angle neutron scattering (SANS) and viscosity studies.     

Structural investigation of viscoelastic micellar water/CTAB/NaNO<Subscript>3</Subscript> solutions

A highly viscoelastic worm-like micellar solution is formed in hexadecyltrimethylammonium bromide (CTAB) in the presence of sodium nitrate (NaNO₃). A gradual increase in micellar length with increasing NaNO₃ was assumed from the rheological measurements where the zero-shear viscosity (η ₀) versus NaNO₃ concentration curve exhibits a maximum. However, upon increase in temperature, the viscosity decreases. Changes in the structural parameters of the micelles with addition of NaNO₃ were inferred from small angle neutron scattering measurements (SANS). The intensity of scattered neutrons in the low q region was found to increase with increasing NaNO₃ concentration. This suggests an increase in the size of the micelles and/or decrease of intermicellar interaction with increasing salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential between micelles indicate that addition of NaNO₃ leads to a decrease in the surface charge of the ellipsoidal micelles which induces micellar growth. Cryo-TEM measurements support the presence of thread-like micelles in CTAB and NaNO₃.      

Adsorption behaviour of NaCl solution on the surface of MgO: a molecular dynamics study

Magnesium alloy is one of the most promising biomaterials in vascular clogging and bone injury. But it still has some defects to overcome and the key task is to control the degradation velocity. In this study, the reaction between NaCl solution and MgO is simplified as the first stage of the degradation of magnesium alloy stent, and the adsorption properties of NaCl solution on the MgO surface are investigated by MD simulation. The distribution of each component of the solution perpendicular to the MgO surface is analysed and the diffusion coefficient is calculated. Besides, a parameterised analysis is carried out. The results show that there is a solution layer formed at the surface of the MgO, and the existence of metal oxide restricts the diffusion of the solution. The adsorption capacity and the diffuse rate have an opposite variation tendency with the change of temperature, concentration and velocity. The self-diffusion coefficient of the solution increases with the increase in temperature as well as velocity, inversely adsorption capacity decreases with the increase in velocity. Besides, the influence of temperature on the adsorption capacity is small. What is more, the diffusion coefficient decreases while the adsorption capacity increases with the increase in concentration.     

Hydrophobic switching nature of methylcellulose ultra-thin films: thickness and annealing effects

We have studied the thermosensitive property of methylcellulose (MC) thin films supported on Si substrate by static sessile drop contact angle measurements, and their surface properties and thin film structure by x-ray reflectivity (XRR) and atomic force microscopy (AFM) techniques. From the static sessile drop contact angle measurements, the MC thin films showed the characteristic hydrophilic-to-hydrophobic transition at ～70?°C, which is the lower critical solution temperature of the bulk solution volume phase separation transition. For films with thickness d ≤ R(g), the onset of such a transition is affected by the film thickness while very thick films, d ? R(g), yielded higher contact angles. Annealing the MC thin films with thicknesses ～200 ? (near the radius of gyration, R(g), of the polymer) below the bulk glass transition temperature (T(g) ～ 195?° C) would not change the hydrophobic switch nature of the film but annealing 'at' and above the bulk T(g) would change its surface property. From surface topography images by AFM, there were no significant changes in either the roughness or the film texture before and after annealing. With XRR data, we were able to determine that such changes in the surface properties are highly correlated to the film thickness changes after the annealing process. This study, we believe, is the first to examine the thermal annealing affects on the thermal response function of a thermoresponsive polymer and is important for researching how to tailor the hydrophobic switching property of MC thin films for future sensing applications.     

Study of acoustic nonlinearity parameter B/A for seawater

I.Introductionlnthcearlyfifties,thercweremanyresearchworksonpropagatingmechanismofultrasonicwaveinseawater,itssoundve1ocity,absorptionandattenuation.Withthedevelop-mcntandapp1icationofhigh-powersoundsourcc,suchasSONARinnavy,thenonlinearacousticaleffectscausedbyfiniteamplitudeu1trasonicwavetravellingthroughseawaterbecomemoreevident.Thcrcfore,tostudythesenonlinearacousticaleffectsandtheirinfluenccsalsobecomcsmuchmoreimportant.Moreover,ithasbeenexpccted'foralongtimetogetalowfrequencyandhighlydi…