In‐Situ Formation of Viscoelastic Wormlike Micelles in Mixtures of Non‐Surface‐Active Compounds

Viscoelastic fluids based on surfactant self‐assembled wormlike micelles have been in focus over the past decade. In this work, we report wormlike micellar solutions formed in situ by simply mixing two non‐surface‐active compounds, N‐(3‐(dimethylamino)propyl)palmitamide (C16AMPM) and salicylic acid (HSal), without specialized organic synthesis of a surfactant. In the absence of HSal, C16AMPM is poorly soluble in pure water; after introducing HSal, C16AMPM is protonated into quaternary ammonium, behaving like a cationic surfactant with a low critical micellar concentration (0.25 mM) and a small area per molecule, which favors the formation of long cylindrical wormlike micelles. Above the overlapping concentration (~28 mM), the wormlike micelles formed entangle each other into viscoelastic networks, enhancing the viscosity by several orders of magnitude. In contrast to the worms formed by a single ultra‐long‐chain surfactant, the current system shows the advantages of a smaller flow activation energy and end‐cap energy, simpler formulation and lower cost, which make it more suitable for practical use.     

pH对油酸钠/盐酸三乙胺蠕虫状胶束流变性质的影响

用流变学方法研究了pH对油酸钠/盐酸三乙胺(NaOA/Et3NHCl)蠕虫状胶束溶液流变性质的影响。通过稳态剪切和动态流变实验发现,30℃时,NaOA(0.12 mol/L)/Et3NHCl(0.2 mol/L)溶液在pH=8.20~9.40循环变化时,pH对溶液黏度的改变具有"开关"效应,可实现黏度在3~27 649 mPa·s时反复变化3次以上。体系在pH=8.55~9.02时为蠕虫状胶束,其流变行为符合Maxwell模型。这种溶液流变性对pH的响应行为是由于pH对反离子Et3NH+与NaOA的相互作用影响而产生的。当pH降低时,反离子Et3NH+的离子势增大,导致胶束表面电荷密度降低,蠕虫状胶束进一步增长。当pH=8.64,胶束因相互吸引而析出。而在初始条件下,升高pH=9.40,反离子Et3NH+从胶束中解吸出来,蠕虫状胶束受到破坏。     

反胶团技术应用研究进展

反胶团具有独特的优良性能,有着十分广阔的应用前景,近年来正越来越多地受到关注。该文介绍了反胶团理论的最新研究进展,综述了反胶团技术在酶催化反应、萃取分离、纳米粒子的制备等方面的应用研究进展, 提出了反胶团技术目前存在的问题,并对其应用前景作了展望。引用文献22篇。     

Extraction of L-synephrine by Bis(2-ethylhexyl)phosphoric acid/n-octanol Reversed Micelles

In this study, reversed micelles of Bis(2-ethylhexyl)phosphoric acid/n-octanol was prepared to investigate the purification of L-synephrine in Citrus aurantium fruit crude extract. The reverse micellar system formed was confirmed with atomic force microscopy and the effect of important factors on extraction efficiency, such as the pH of the aqueous phase, molar ratio of water to surfactant, surfactant concentration, cationic ion concentration, and extraction time, was studied. Under the optimal operational conditions, the purity of L-synephrine was improved to be >85% and the total yield >98%. Mathematic analysis and experimental results exhibited that the extraction process in this system was effectuated mainly via electrostatic interactions between L-synephrine and the surfactant.     

Modeling the rheology of gelatin gels for finite deformations. Part 2. Viscoelastic solid model

The viscoelastic solid model proposed in this work can predict the rheological responses of gelatin gels for finite deformations. This rheological model considers a degree of physical cross-links at a given maturation time, which is partially attained from those links totally available when a pure elastic network is achieved. Thus, both an elastic network formed by permanent links on the average and a viscoelastic network composed of the remaining adaptive links are described at each maturation time. This model for gelatin gels considers appropriately the interplay between the networks involving: (a) viscoelastic relaxation as a consequence of an imposed mechanical history, (b) average degree of physical cross-links in the partially generated permanent network acting in the short-term mechanical response. In this context of analysis the standard viscoelastic solid is obtained asymptotically for small deformations. Also the effect of shear rate on the shear test is studied and the braking phenomenon is analysed in relation to the formation of microstructure by considering viscoelastic parameters.     

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

Viscoelastic surfactants (VES) are used in various oilfield applications such as matrix stimulation and enhanced oil recovery. The loss of surfactants during the propagation of VES could result in a significant reduction in the permeability of the rock (formation damage). The objective of the current work was to identify the effect of rheological behavior of the VES on the formation damage using core‐flooding experiments, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analysis. A combination of core‐flooding, NMR, and SEM techniques was used to quantify and identify the location of formation damage in carbonate core samples. The viscosity and storage modulus strongly depend on the nature and concentration of salts. The viscosity increased by increasing the salt concentration up to a specific point (15 wt% CaCl₂) and then starts decreasing. The VES formulations that displayed the maximum and minimum viscosities were used to identify the impact of rheological behavior on formation damage. Core‐flooding experiments were performed to assess the formation damage due to high‐viscosity and low‐viscosity VES formulations. The reduction in the permeability of carbonate rocks reaches more than 90% of the initial permeability. It was found that low‐viscosity VES caused more damage compared with high‐viscosity VES when they were used at constant concentrations. NMR and core‐flooding results revealed that the damage took place both in pore body and pore throat. However, most of the surfactant was retained at the pore throat.     

Viscoelastic Properties of a Biological Hydrogel Produced from Soybean Oil

Hydrogels formed from biopolymers or natural sources have special advantages because they may have biodegradable and biocompatible properties. The viscoelastic properties of a newly developed biological hydrogel made from epoxidized soybean oil (ESO) were investigated. The material called HPESO is a hydrolytic product of polymerized ESO (PESO). HPESO exhibited viscoelastic solid or gel behavior above 2% (wt. %) concentration at room temperature and viscous liquid behavior at 55 °C. The thermal assembly disassembly reassembly function of the HPESO hydrogel was completely reversible. The viscoelastic properties of HPESO were dependent on concentration. Analysis of modulus and concentration dependence and stress relaxation measurement indicated that HPESO was a physical gel where the cross-linkers between the molecules were physical junctions. HPESO hydrogel also exhibited fast initial recovery of its viscoelastic properties after being subjected to mechanical shear disruption. The function and behavior of the HPESO hydrogel suggest that this biomaterial may be suitable for applications in drug delivery and scaffolds of bioengineering and tissue engineering. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.     

羧酸盐型表面活性剂对功能化Gemini表面活性剂流变性质的影响

利用稳态和动态剪切实验考察了功能化Gemini表面活性剂1,3双-(二羟乙基十二烷基溴化铵)-丙烷[简写为12(2OH)-3-12(2OH)·2Br]与传统阴离子表面活性剂(十二酸钠、十四酸钠和十六酸钠)混合体系在25℃下的流变性质。12(2OH)-3-12(2OH)·2Br的浓度为50 mmol/L时,十二酸钠、十四酸钠和十六酸钠均可以增强溶液的黏弹性。十二酸钠与12(2OH)-3-12(2OH)·2Br的混合摩尔比β为0.3时,溶液的零剪切黏度η0出现最大值,为12.35 Pa·s,平台模量G'∞为31.88 Pa;β=0.4时,G'∞值为14.67 Pa。混合体系的黏弹性顺序为:十二酸钠/12(2OH)-3-12(2OH)·2Br十四酸钠/12(2OH)-3-12(2OH)·2Br十六酸钠/12(2OH)-3-12(2OH)·2Br。改变12(2OH)-3-12(2OH)·2Br的浓度到60 mmol/L且十二酸钠/12(2OH)-3-12(2OH)·2Br的混合摩尔比β为0.3时,零剪切黏度η0和平台模量G'∞均增大,分别为33.92 Pa·s和46.41 Pa。     

NaSal/NaCl诱导阳离子蠕虫状胶束的形成及流变性研究

以阳离子三联表面活性剂双(2-羟基-二亚甲基醚)-α,ω,γ-三(十六烷基二甲基氯化铵)(TrimerC16)为主剂,水杨酸钠(Na Sal)为有机反离子,氯化钠(Na Cl)为无机反离子,制备了阳离子蠕虫状胶束体系。利用电导率-表观黏度法研究了TrimerC16的相行为,考察了不同有机反离子Na Sal、苯甲酸钠(Na BENZ)及甲酸钠(Na FM)对TrimerC16克拉夫特温度(Tk)的影响,通过动态流变手段研究了TrimerC16/Na Sal/Na Cl的流变行为,并采用表观黏度法考察了温度(T)及剪切时间(ts)对该体系表观黏度(ηa)的影响。结果表明:TrimerC16的临界囊泡浓度(CVC)为0.015 mmol?L?1,临界胶束浓度为0.042mmol?L?1;三种有机反离子对TrimerC16的Tk影响大小顺序为:Na SalNa BENZNa FM;剪切速率(r′)为100 s?1时,TrimerC16/Na Sal/Na Cl体系的黏度仍高达70 m Pa·s;T=100℃时,转速为50 r?min?1下,TrimerC16/Na Sal/Na Cl体系的ηa为61.8 m Pa?s,而同一测试条件下,相同摩尔浓度的单链表面活性剂胶束体系的ηa已接近水的黏度。TrimerC16/Na Sal/Na Cl蠕虫状胶束体系耐较高温、耐剪切且破胶彻底。     

A Study on Tunable Viscoelastic Properties of Xhantan Gum and Sodium Alginate Hyrogelling System

Theoretical Foundations of Chemical Engineering - In this study, viscoelastic properties of xhantan gum (XG) and sodium alginate (SA) hydrogelling system were investigated at a definite range of...     

The Viscoelastic Properties of Chinese Fir During Water-Loss Process Under Hydrothermal Conditions

In this article, the viscoelastic properties of water-swollen Chinese fir during a water-loss process under different hydrothermal conditions (30–90°C, 40–80% RH) were investigated. After the 300 min hydrothermal process at 70 or 90°C, the moisture contents (MCs) of the specimens were well below the MC value at the fiber saturation point. During the hydrothermal process, normalized E′ increased at first, and then leveled off at temperatures above 50°C. The wood specimens were softened due to the hydrothermal effect. The glass transition of hemicellulose appeared at 50°C. Lignin transition was observed at 70 and 90°C. Superposition of transitions of lignin and hemicellulose moved to low storage modulus E′ with increasing temperature and RH level.     

Viscoelastic, Thermal and Mechanical Properties of Dicyclopentadiene Bisphenol Diyanate Ester / Epoxy Co-polymers

Summary Dicyanate ester containing dicyclopentadiene cycles and epoxy co-polymers were prepared by copolymerization between epoxy and dicyclopentadiene bisphenol cyanate esters (DCPDCE). Viscoelastic properties of the co-polymers were characterized by the technique of dynamic mechanical analysis (DMA), which indicated that the introduction of E51 in the co-polymers would effectively improve the toughness of DCPDCE, while the thermal dimensional stability would be weakened. Results from thermogravimetric analysis (TGA) are in good accordance with the T_g values from DMA curves. Mechanical testing of the cured co-polymers shows that E51 can improve the mechanical properties of the co-polymers while its usage is controlled among 5% to 15%.     

Creep Effects in Nanometer-scale Contacts to Viscoelastic Materials: A Status Report

Effects of creep on the behavior of nanometer-scale contacts to viscoelastic materials are described from the viewpoint of the contact mechanics theory developed by Ting. The two most important effects are: (1) The time at which maximum contact area and maximum deformation occur can be delayed substantially from the time of maximum applied load. (2) The deformation at separation is related to the loss tangent. These long-range effects due to creep are distinct from the much shorter-range crack tip effects induced by adhesion at the periphery of the contact and associated with the names Barquins and Maugis. Consideration of relevant time scales reveals that creep effects are expected to dominate in SFM-scale contacts for a wide range of compliant viscoelastic materials. Guidelines for selection of optimal experimental parameters for nanometer-scale studies are presented. The need for a comprehensive theory is emphasized.     

Creep Effects in Nanometer-scale Contacts to Viscoelastic Materials: A Status Report

Effects of creep on the behavior of nanometer-scale contacts to viscoelastic materials are described from the viewpoint of the contact mechanics theory developed by Ting. The two most important effects are: (1) The time at which maximum contact area and maximum deformation occur can be delayed substantially from the time of maximum applied load. (2) The deformation at separation is related to the loss tangent. These long-range effects due to creep are distinct from the much shorter-range crack tip effects induced by adhesion at the periphery of the contact and associated with the names Barquins and Maugis. Consideration of relevant time scales reveals that creep effects are expected to dominate in SFM-scale contacts for a wide range of compliant viscoelastic materials. Guidelines for selection of optimal experimental parameters for nanometer-scale studies are presented. The need for a comprehensive theory is emphasized.     

刺云实胶/魔芋葡甘聚糖复合凝胶流变性能研究

为了获得性能更优良的食品凝胶体系,本研究将刺云实胶(TG)与魔芋葡甘聚糖(KGM)按一定比例复配制得复合凝胶,通过旋转流变仪研究其流变性能,用统计力学和动力学相结合的方法,对KGM与TG分子链的链间作用进行深入研究。实验结果表明,TG/KGM凝胶在高温下为假塑性流体,二者具有良好的相容性,复配溶胶体系的剪切应力和黏度均随着KGM组分比例的增加而增加,抗剪切能力有所增强。在选定的频率范围0.1~100 rad/s内,TG/KGM的损耗模量G”低于其储能模量G’,KGM的添加使得模量上升。而在85~25℃的降温过程中,随着KGM的增加,复配体系中G’和G”模量下降,溶胶向凝胶的转化温度点发生右移,以上表明相比于单一多糖,适量的KGM与TG复配,可以大大提高凝胶耐热性,形成稳定性高的凝胶。分析得出,在不同质量比的TG/KGM凝胶体系中,当m(TG):m(KGM)=0.9:0.6（即TK6）时,可得到综合性能优异、胶凝能力强、稳定性高且黏度适中的凝胶体系。研究表明,制备的TG/KGM凝胶有望成为一种新型食品凝胶,可以为TG和KGM的合理应用提供理论指导。     

Measurement of the Adhesion of a Viscoelastic Sphere to a Flat Non-Compliant Substrate

The adhesion between a single polystyrene bead (radius, 27 μm) and a flat silica surface has been measured with an atomic force microscope as a function of two variables: (a) The maximum applied load and, (b) the loading time at a constant maximum applied load. Analysis of the results indicates significant plastic deformation of the bead under the action of the load forces. There is also evidence for time-dependent viscoelastic effects as a load is exerted on the bead. The contact zone of the polystyrene bead used for these experiments was examined using Scanning Electron Microscopy. The microscope images revealed a surface covered in small polymer beads with a radius of only 115 nm. In the contact zone these beads had undergone substantial and permanent deformation as a function of the applied load. Basic geometric analysis reveals that the large sphere is not contacting the flat surface under any load. The results presented here indicate the value of being able to measure adhesion using an atomic force microscope. The importance of being able to characterise the contact zone accurately is also highlighted.     

Measurement of the Adhesion of a Viscoelastic Sphere to a Flat Non-Compliant Substrate

The adhesion between a single polystyrene bead (radius, 27 μm) and a flat silica surface has been measured with an atomic force microscope as a function of two variables: (a) The maximum applied load and, (b) the loading time at a constant maximum applied load. Analysis of the results indicates significant plastic deformation of the bead under the action of the load forces. There is also evidence for time-dependent viscoelastic effects as a load is exerted on the bead. The contact zone of the polystyrene bead used for these experiments was examined using Scanning Electron Microscopy. The microscope images revealed a surface covered in small polymer beads with a radius of only 115 nm. In the contact zone these beads had undergone substantial and permanent deformation as a function of the applied load. Basic geometric analysis reveals that the large sphere is not contacting the flat surface under any load. The results presented here indicate the value of being able to measure adhesion using an atomic force microscope. The importance of being able to characterise the contact zone accurately is also highlighted.     

A Study of the Viscoelastic and Rheological Properties of PVC/CPE Blends Modified by Using Polylauryllactam

Abstract

Polylauryllactam was used to improve the impact strength of polyvinylchloride (PVC)/chlorinated polyethylene (CPE) blends without sacrificing their tensile properties. The enhancement of the impact strength increased with the increase of the CPE content in the PVC/CPE blends due to the formation of intermolecular hydrogen bonds among PVC, polylauryllactam and CPE macromolecules. A doubled impact strength of the PVC/CPE blend with 20 weight percent of CPE was obtained after the addition of 1.5 phr polylauryllactam. The PVC/CPE blends with polylauryllactam have a better dimensional stability compared with the PVC/CPE blends without the additive, according to their viscoelastic characteristics. Polylauryllactam shortened the processing time to reach a minimum melt viscosity in the processing of the PVC/CPE blends.     

Rheological Properties of Wormlike Micelles Formed in Aqueous Systems of 3‐Alkoxy‐2‐hydroxypropyl Trimethyl Ammonium Bromides in the Presence of Sodium Octanoate

The rheological properties of aqueous systems composed of each of the four homologous cationic surfactants (3‐alkoxy‐2‐hydroxypropyl trimethyl ammonium bromides, C_nHTAB, n = 12, 14, 16 and 18) in the presence of an anionic surfactant, sodium octanoate (SO), have been studied by using steady state and frequency sweep rheological measurements. The effects of surfactant concentration, hydrophobic chain length and temperature were investigated. In C₁₄HTAB solution, the viscosity shows shear thinning in the concentration range of C_C14HTAB >320 mmol/kg. Addition of SO promotes the micellar growth and results in the generation of wormlike micelles. Zero‐shear viscosity (η₀) of the binary surfactant system exhibits a maximum point in the investigated concentration range, suggesting the interaction between C₁₄HTAB and SO molecules is strongest at the optimal ratio of C₁₄HTAB with SO. The decrease in viscosity was attributed to be the transition from entangled wormlike micelles to branching micelles after the maximum point, cryo‐TEM images revealed the changes in the structure of the wormlike micelles.     

Physicochemical,Textural and Viscoelastic Properties of Palm Diacylglycerol Bakery Margarine During Storage

Physicochemical, textural and viscoelastic properties of palm diacylglycerol (PDG) bakery margarines (DOS720, DOS721 and DOS711) and commercial margarine (CM) throughout a 3-month storage period were evaluated and compared. All the margarines had significant (P < 0.05) increments in slip melting point (SMP), solid fat content (SFC) and hardness during storage with CM having the highest overall increment followed by margarines DOS711, DOS 721 and DOS720. The smaller increments are mainly due to the ability of PDG to delay polymorphic transformation from β′ to β form. In terms of viscoelastic properties, all margarines had a higher degree of firmness which may probably be due to rearrangement of the fat crystals into a three-dimensional scaffolding network upon storage. In terms of melting behavior, storage has no effects on all margarines with the exception of margarine DOS711. The melting behavior of margarine DOS711 displayed a probability of oil exudation during storage. As for polymorphic transformation, CM had the earliest polymorphic transformation with only β crystals after 8 weeks of storage. PDG bakery margarines managed to retard the transformation to more than 10 weeks of storage for DOS711 and 12 weeks of storage for DOS720 and DOS721.