疏水基支链化对甜菜碱表面扩张流变性质的影响

利用悬挂滴方法研究了同分异构的直链（C₁₆PB）和支链（C₁₆GPB）十六烷基羟丙基羧酸甜菜碱的表面扩张流变性质,考察了时间、表面压、工作频率及体相浓度对扩张模量和相角的影响.研究发现,羟丙基甜菜碱分子在溶液表面上吸附时,整个亲水基团倾向于平铺在表面上,造成较高的表面扩张模量,表面膜性质由亲水基团取向变化等膜内过程控制.甜菜碱分子疏水烷基的支链化造成分子间相互作用增强,不仅能增大模量,而且在高浓度条件下出现动态模量的最大值现象,说明表面膜的强度与分子排布密切相关,并非单纯由表面分子浓度决定.     

沥青质对塔河稠油黏度的影响机理研究

本文研究了沥青质对塔河稠油黏度的影响机理.首先对不同沥青质含量的稠油的黏度进行了测试,研究结果表明稠油的黏度随沥青质含量的增加而增大;其次,对不同沥青质含量的稠油进行了储能模量的测试,实验结果表明,随着沥青质含量的增加,稠油的储能模量和黏度呈现同步增大的趋势,说明大量的沥青质在稠油内部形成了空间网状聚集体,导致稠油的弹性和黏度增大;最后,对沥青质空间网状结构的成因以及沥青质对稠油黏度的影响机理进行了深入分析.通过甲基化改性实验,脱除沥青质分子上的活泼氢,以此减弱与活泼氢相关的氢键等沥青质分子间作用力,对比了改性前后沥青质分子聚集体的变化以及稠油黏度的变化.实验结果表明,在众多沥青质分子间作用力中,与活泼氢相关的分子间作用力更有利于沥青质空间网状结构的形成,对稠油黏度的影响也更大.     

一种超支化疏水缔合聚合物的制备与性能评价

首先制备了疏水单体2-丙烯酰胺基十四烷磺酸,在此基础上又以改性Si O2功能单体为反应核制备了超支化疏水缔合聚合物(HBPAM),结构经红外光谱(FTIR)和核磁共振氢谱(1H NMR)表征证实。HBPAM在低浓度时主要是分子内缔合,表观黏度低,随着浓度的增加,分子内缔合逐渐变为分子间缔合,又因其独特的三维立体网状结构,溶液黏度显著增加。与梳形KYPAM相比,HBPAM在耐温抗盐及抗剪切方面有较高的优势:升温到85℃时黏度保留率为62.2%;100000mg·L-1Na Cl、150000 mg·L-1Na Cl、500 mg·L-1Mg Cl2、1000 mg·L-1Mg Cl2、500 mg·L-1Ca Cl2、1000 mg·L-1Ca Cl2时的黏度保留率分别为233.0%、132.9%、64.4%、26.1%、66.2%、15.7%;3400rpm/min剪切30s后HBPAM的黏度保留率为69.8%,比KYPAM高10.9%。在60℃烘箱中的30d老化实验证明,HBPAM比KYPAM有明显抗老化能力,尤其是在高矿化度条件下优势更明显。     

溶剂效应制备核壳纳米银及荧光素金属增强荧光

直链或支链高分子可用来制备和稳定纳米材料,具有丰富羟基的高分子通过分子间和分子内氢键作用形成分子级别的"胶囊",用作生长纳米颗粒的模板[1].可溶性淀粉主要是直链淀粉,是由多个葡萄糖单元构成的含有丰富羟基的高分子,同时具有疏水性和亲水性[2].     

不同结构驱油聚合物的界面剪切流变性质

利用双锥法研究了油田现场用超高分子量部分水解聚丙烯酰胺(PHPAM)和疏水改性聚丙烯酰胺(HMPAM)溶液与航空煤油间的界面剪切流变性质,考察了时间、应变幅度和剪切频率对不同浓度PHPAM和HMPAM溶液界面剪切流变参数的影响.结果表明,只有在适宜的剪切频率条件下,流变数据才能反映界面膜的结构信息.HMPAM分子具有界面活性,能吸附在界面上,其界面膜的强度随时间变化逐渐增强,且在高浓度时以黏性为主;PHPAM分子不具有界面活性,其剪切流变参数没有时间依赖性,界面层以弹性为主.HMPAM能通过疏水作用形成界面网络结构,界面膜的剪切复合模量明显高于PHPAM界面层.HMPAM界面层中网络结构在剪切形变作用下的破坏与重组这一慢弛豫过程是其强度较高的原因.     

不同结构烷基苯磺酸钠水溶液的泡沫性能及动态表面张力

研究了一系列直链三取代和支链双取代烷基苯磺酸钠水溶液的动态表面张力(DST)和泡沫性能, 考察了分子结构变化对烷基苯磺酸钠水溶液的DST和泡沫性能的影响. 探讨了动态表面张力参数(t*, n, R1/2)的变化规律及其与泡沫性能的关系. 结果表明, 随着取代烷基链长度增加, t*和n值增大, R1/2减小, 动态表面活性降低. 由于双取代支链烷基苯磺酸钠分子具有特殊的柔性长支链, 使得吸附膜排列紧密、膜弹性增大, 因而其泡沫稳定性明显优于多取代直链烷基苯磺酸钠的稳定性. 在气流法产生泡沫的过程中, 动态表面张力是控制起泡高度的关键因素.     

聚醚类破乳剂的界面扩张流变性质

采用悬挂滴方法研究了不同结构聚醚类破乳剂与煤油间的界面张力及界面扩张流变性质. 结果表明, 4种聚醚类破乳剂均具有较强的降低界面张力能力, 且支链化程度越低分子在界面上排列越紧密, 直线型破乳剂在低浓度条件下界面张力最低. 破乳剂的分子尺寸较大, 慢弛豫过程控制界面膜性质, 吸附膜以弹性为主. 同时, 柔性聚氧乙烯链和聚氧丙烯链对界面膜性质的影响较大, 随着支链化程度增大, 界面分子间相互作用增强, 界面膜弹性增强, 黏性降低.     

直链型与支链型疏水缔合水凝胶的机械性能与溶胀行为

以丙烯酰胺(AM)为亲水单体,脂肪醇聚氧乙烯醚丙烯酸酯(AEO-AC-n-m,n为疏水端烷基链碳的数目,m为亲水端PEG链的长度,n,m=13,5;10,5;13,10)为疏水单体,十二烷基硫酸钠(SDS)为表面活性剂,过硫酸钾(KPS)为引发剂,通过胶束聚合制备了3种聚丙烯酰胺-co-脂肪醇聚氧乙烯醚丙烯酸酯(AM-co-AEO-AC)疏水缔合水凝胶.以疏水烷基链为直链的疏水单体AEO-AC-13-5合成的直链型水凝胶的网络结构均匀且强度高,其形态在水中可维持180 d.而以疏水烷基链为支链的疏水单体AEO-AC-10-5与AEO-AC-13-10合成的支链型水凝胶的机械性能较弱,60 d内即溶解于水中.在相同条件下,直链型水凝胶断裂时的最大应力是支链型水凝胶的4~5倍.利用弹性橡胶理论中的新胡克方程计算了直链型和支链型水凝胶的有效交联密度ν0和有效交联点间的分子量Mc.     

二维纳米材料作为润滑油添加剂的研究进展[1]

二维纳米材料因其独特的分子结构和润滑性能而在摩擦学领域得到了广泛的研究。同一层内原子间的高强度和较低的层间剪切强度使其成为一种优异的减摩抗磨添加剂。本文分别从石墨烯类二维纳米材料、过渡金属二硫化物和其它的二维纳米材料三方面综述了二维纳米材料作为润滑油添加剂的摩擦学性能,阐述了二维纳米材料的摩擦机理,并指出二维纳米材料作为高性能润滑材料仍需解决的问题及未来的研究趋势。     

石油化学粗粒化分子力学/分子动力学力场：Ⅰ.烷烃的粗粒化模型

提供了一种用以描述石油中烷烃分子的通用型粗粒化模型.依据石油中烷烃的结构特征,划分出从A1到A7共7种粗粒化珠子.7种烷烃的粗粒化珠子含有3～6个碳原子,与之相对应的既有直链烷烃,也有支链烷烃.这些基本结构单元以不同的组合方式可以得到石油中从C3～C40各种烷烃的粗粒化分子.为了获得精确的力场参数,采用密度泛函方法优化...     

Impact of molecular structure on the lubricant squeeze-out between curved surfaces with long range elasticity

The properties of butane (C4H10) lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and elastic properties of the solid surfaces. We consider the linear n-butane and the branched isobutane. For the linear molecule, well defined molecular layers develop in the lubricant film when the width is of the order of a few atomic diameters. The branched isobutane forms more disordered structures which permit it to stay liquidlike at smaller surface separations. During squeezing the solvation forces show oscillations corresponding to the width of a molecule. At low speeds (<0.1 ms) the last layers of isobutane are squeezed out before those of n-butane. Since the (interfacial) squeezing velocity in most practical applications is very low when the lubricant layer has molecular thickness, one expects n-butane to be a better boundary lubricant than isobutane. With n-butane possessing a slightly lower viscosity at high pressures, our result refutes the view that squeeze-out should be harder for higher viscosities; on the other hand our results are consistent with wear experiments in which n-butane were shown to protect steel surfaces better than isobutane.     

Degradation mechanisms and environmental effects on perfluoropolyether, self-assembled monolayers, and diamondlike carbon films

The degradation mechanisms and durability of selected lubricants and environmental effects on the lubricants which could be used for microelectromechanical/nanoelectromechanical systems (MEMS/NEMS) applications were studied in this paper. The degradation of perfluoropolyether (Z-DOL), four self-assembled monolayers (SAMs)-hexadecane thiol, perfluoroalkylsilane, and alkylsilane (C8 and C18)-and diamondlike carbon (DLC) films was investigated in high vacuum. Gaseous products and friction force were detected using a quadrupole mass spectrometer and strain gauges. It is believed that triboelectrical reaction and mechanical scission cause the degradation of Z-DOL. SAMs are believed to degrade by cleavage at an interfacial bond accompanied with triboelectrical reactions. DLC is believed to degrade by mechanical shear and thermal oxidation. Environmental effects on lubricant films were studied in high vacuum, argon, and air at various humidity levels. It was found that the environment has a significant influence on the lubricant performance. The lubricant films exhibit high friction and low durability in high vacuum. Oxygen in the air can cause the thermal oxidation of SAMs and DLC films. Water molecules can act as a lubricant for Z-DOL films at a moderate humidity level, while they can penetrate the Z-DOL films at a high humidity level. Water molecules can detach the SAM molecules from the substrate, whereas, for DLC films, water molecules can act as a lubricant.     

Nonequilibrium molecular dynamics of the rheological and structural properties of linear and branched molecules. Simple shear and poiseuille flows; instabilities and slip

Nonequilibrium molecular-dynamics simulations are performed for linear and branched chain molecules to study their rheological and structural properties under simple shear and Poiseuille flows. Molecules are described by a spring-monomer model with a given intermolecular potential. The equations of motion are solved for shear and Poiseuille flows with Lees and Edward's [A. W. Lees and S. F. Edwards, J. Phys. C 5, 1921 (1972)] periodic boundary conditions. A multiple time-scale algorithm extended to nonequilibrium situations is used as the integration method, and the simulations are performed at constant temperature using Nose-Hoover [S. Nose, J. Chem. Phys. 81, 511 (1984)] dynamics. In simple shear, molecules with flow-induced ellipsoidal shape, having significant segment concentrations along the gradient and neutral directions, exhibit substantial flow resistance. Linear molecules have larger zero-shear-rate viscosity than that of branched molecules, however, this behavior reverses as the shear rate is increased. The relaxation time of the molecules is associated with segment concentrations directed along the gradient and neutral directions, and hence it depends on structure and molecular weight. The results of this study are in qualitative agreement with other simulation studies and with experimental data. The pressure (Poiseuille) flow is induced by an external force F(e) simulated by confining the molecules in the region between surfaces which have attractive forces. Conditions at the boundary strongly influence the type of the slip flow predicted. A parabolic velocity profile with apparent slip on the wall is predicted under weakly attractive wall conditions, independent of molecular structure. In the case of strongly attractive walls, a layer of adhered molecules to the wall produces an abrupt distortion of the velocity profile which leads to slip between fluid layers with magnitude that depends on the molecular structure. Finally, the molecular deformation under flow depends on the attractive force of the wall, in such a way that molecules are highly deformed in the case of strong attracting walls.     

Tracking lubricants during single screw extrusion of uPVC

Lubrication is one of the most important parameters in unplasticized polyvinyl chloride (uPVC) processing apart from the PVC resin and processing equipment. Lubricants are used in specific ratios to ensure effective fusion of PVC particles. The exact mechanism on how these lubricants interact is not yet fully understood. A widely accepted theory is the interaction mechanism proposed by Rabinovic et al. where lubricants are said to act as surfactants and slip agents. In this study a method for tracking lubricants, by simulating the extrusion process within a single screw extruder, was proposed. A three stage fusion simulation consisted of the feeding zone (stage 1), the compression zone (stage 2) and the metering zone (stage 3). The association interactions between the individual components of a typical uPVC formulation were followed throughout the three stages. External polar and nonpolar lubricants in combination with an internal lubricant was studied. Lubricants were successfully tracked using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). In conclusion it was found that the use of an internal lubricant promotes dispersion of external lubrication towards PVC. It was also found that there is a competition between the internal lubricant and polar external lubricant.     

Conformational and adsorptive characteristics of albumin affect interfacial protein boundary lubrication: From experimental to molecular dynamics simulation approaches

The lifetime of artificial joints is mainly determined by their biotribological properties. Synovial fluid which consists of various biological molecules acts as the lubricant. Among the compositions of synovial fluid, albumin is the most abundant protein. Under high load and low sliding speed articulation of artificial joint, it is believed the lubricants form protective layers on the sliding surfaces under the boundary lubrication mechanism. The protective molecular layer keeps two surfaces from direct collision and thus decreases the possibility of wear damage. However, the lubricating ability of the molecular layer may vary due to the conformational change of albumin in the process. In this study, we investigated the influence of albumin conformation on the adsorption behaviors on the articulating surfaces and discuss the relationship between adsorbed albumin and its tribological behaviors. We performed the friction tests to study the effects of albumin unfolding on the frictional behaviors. The novelty of this research is to further carry out molecular dynamics simulation, and protein adsorption experiments to investigate the mechanisms of the albumin-mediated boundary lubrication of arthroplastic materials. It was observed that the thermal processes induce the loss of secondary structure of albumin. The compactness of the unfolded structure leads to a higher adsorption rate onto the articulating material surface and results in the increase of friction coefficient.     

Interfacial friction and adhesion of polymer brushes

A bead-probe lateral force microscopy (LFM) technique is used to characterize the interfacial friction and adhesion properties of polymer brushes. Our measurements attempt to relate the physical structure and chemical characteristics of the brush to their properties as thin-film, tethered lubricants. Brushes are synthesized at several chain lengths and surface coverages from polymer chains of polydimethylsiloxane (PDMS), polystyrene (PS), and a poly(propylene glycol)-poly(ethylene glycol) block copolymer (PPG/PEG). At high surface coverage, PDMS brushes manifest friction coefficients (COFs) that are among the lowest recorded for a dry lubricant film (μ ≈ 0.0024) and close to 1 order of magnitude lower than the COF of a bare silicon surface. Brushes synthesized from higher molar mass chains exhibit higher friction forces than those created using lower molar mass polymers. Increased grafting density of chains in the brush significantly reduces the COF by creating a uniform surface of stretched chains with a decreased surface viscosity. Brushes with lower surface tension and interfacial shear stresses manifest the lowest COF. In particular, PDMS chains exhibit COFs lower than PS by a factor of 3.7 and lower than PPG/PEG by a factor of 4.7. A scaling analysis conducted on the surface coverage (σ) in relation to the fraction (ε) of the friction force developing from adhesion predicts a universal relation ε ~ σ(4/3), which is supported by our experimental data.     

Effect of molecular structure on polyethylene melt rheology. I. Low-shear behavior

The melt rheological properties of both linear and branched polyethylene were investigated by use of narrow molecular weight distribution fractions and experimentally polymerized samples. Studies carried out in steady shear and in oscillatory shear yielded information concerning both the melt viscosity and the melt elasticity as a function of molecular structure, where the latter was characterized by various solution property techniques. The 3.4–3.5 power dependence of the low shear limiting viscosity on molecular weight was confirmed for linear polyethylene. The effect of long-chain branching on rheological properties was defined both at constant molecular weight and at constant molecular weight distribution and coupled with variation of molecular weight.     

Preparation and Tribological Behaviors of Lubricants—Oil Based on Modified Microbial Oil with Nano-Schiff Base Copper Complex

A W/O microemulsion reactor was used to prepare four kinds of modified lubricants: (i) modified lubricant 1, modified epoxidized microbial oil + rape oil in volume ratio of 1:1; (ii) modified lubricant 2, modified esterified microbial oil + rape oil in volume ratio of 1:3; (iii) modified lubricant 3, modified epoxidized rape oil; and (iv) modified lubricant 4, modified PAO. The individual modified lubricants were further modified with 0%, 0.5%, 1%, and 2% content of nano-Schiff base copper complex (nano-SBCC). A microtribometer was used to evaluate the friction coefficient between ball/flat point contacts immersed in the modified lubricants and operated in reciprocating and linear sliding mode. A comparison of the values of the friction coefficient with the lubricants further modified with nano-SBCC with those of their individual 0% nano-SBCC counterparts indicated significant decrease: (i) almost 19.18% was obtainable for the modified lubricant 1 with 2% of nano-Schiff base copper complex, (ii) almost 16.5% was obtainable for the modified lubricant 2 with 0.5% of nano-Schiff base copper complex; (iii) almost 7.42% was obtainable for the modified lubricant 3 with 1% of nano-SBCC; and (iv) almost 7.01% was obtainable for the modified lubricant 4 with 0.5% of nano-SBCC. These suggested that the addition of nano-Schiff base copper complex can efficiently decrease the friction coefficient of epoxidized or esterified microbial oil. Analyses of two-dimensional images, average profiles (across the mid-section y = 0 of the reciprocating sliding path), and three-dimensional topographies by confocal white light microscope for the worn surfaces of flats immersed in modified lubricant 1 and modified lubricant 2 suggested better wear-resistance of the modified lubricant 2 than that of the modified lubricant 1. The ability of wear resistance for the modified lubricant became better with the increasing content of nano-Schiff base copper complex from 0% to 2%. The study revealed the modification of epoxidized microbial oil + rape oil (1:1 volume ratio) and esterified microbial oil + rape oil (1:3 volume ratio) with Cu(II) chelate of bis(salicylaldehyde)ethylenediamine, reducing the magnitude of friction and wear because of their respective wear self-repairing ability. Such self-repairing ability furnishes the suitability of epoxidized microbial oil or esterified microbial oil to be effectively modified by nano-Schiff base copper complex and to substitute ordinary base oil as a mixture with rape oil.     

Rheology of linear and branched styrene–acrylonitrile copolymers. Similarities and differences

A comprehensive investigation of rheological properties of linear and branched styrene-acrylonitrile copolymer specimens with similar molecular characteristics has been carried out. During the steady-state shear flow, the viscosity properties of both specimens are described by the Cross equation. In this case, the branched copolymer is characterized by a higher viscosity and shear thinning degree as well as by substantially lower shear rate values corresponding to transition to the non-Newtonian flow region. The elasticity of the branched copolymer melt (estimated from the value of the first normal stress difference) is considerably higher than that of the linear. This is reflected on the characteristics of occurrence of unstable flow at high shear rates. Rougher extrudate surface distortions are characteristic for the branched copolymer, and the shear rate corresponding to their occurrence is noticeably lower than for the linear copolymer. The dynamic characteristics of the copolymers being compared also attest to a greater elasticity of the branched specimen. An investigation of the viscoelastic properties in a wide temperature range allowed constructing a generalized frequency dependence of dynamic moduli encompassing various regions of the relaxation states of the copolymer specimens. Continuous relaxation spectra were calculated by means of the Mellin transform. It is shown that relaxation phenomena caused by segmental mobility doesn’t depend on the presence of branchings, whereas branching of the chain has a substantial effect on translation mobility of the chain as a whole. Branching leads to a noticeable increase of transient elongation viscosity but has almost no effect of strain hardening of the melt.     

Oil‐Soluble Polymer Brush Grafted Nanoparticles as Effective Lubricant Additives for Friction and Wear Reduction

The development of high performance lubricants has been driven by increasingly growing industrial demands and environmental concerns. Herein, we demonstrate oil‐soluble polymer brush‐grafted inorganic nanoparticles (hairy NPs) as highly effective lubricant additives for friction and wear reduction. A series of oil‐miscible poly(lauryl methacrylate) brush‐grafted silica and titania NPs were synthesized by surface‐initiated atom transfer radical polymerization. These hairy NPs showed exceptional stability in poly(alphaolefin) (PAO) base oil; no change in transparency was observed after being kept at ?20, 22, and 100 °C for ≥55 days. High‐contact stress ball‐on‐flat reciprocating sliding tribological tests at 100 °C showed that addition of 1 wt % of hairy NPs into PAO led to significant reductions in coefficient of friction (up to ≈40 %) and wear volume (up to ≈90 %). The excellent lubricating properties of hairy NPs were further elucidated by the characterization of the tribofilm formed on the flat. These hairy NPs represent a new type of lubricating oil additives with high efficiency in friction and wear reduction.