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表面活性剂和聚合物减阻溶液流变特性的实验研究含开题报告及任务书,表面活性剂,聚合物,溶液,流变,特性,实验,研究,开题,报告,任务书

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常州大学毕业设计（论文）中期报告题 目：表面活性剂和聚合物减阻溶液流变特性的实验研究 学 院： 机械工程学院 专 业： 过程装备与控制工程 学 号： 14403118 姓 名： 卢文斌 手 机： 15261179537 指导教师： 庞明军 教师职称： 副教授 填表日期： 2018.4.26 教务处制题目名称表面活性剂和聚合物减阻溶液流变特性的实验研究题目来源 国家、省（部）级 市、校级 企业（公司 ） 其他题目类型 工程设计 应用研究 基础研究 其他一、毕业设计（论文）概述添加剂湍流减阻技术可有效减少流体输送过程中的摩擦阻力，是目前减阻的重要方式之一。添加剂湍流减阻技术可有效减少流体输送过程中的摩擦阻力，是目前减阻的重要方式之一，但是其减阻机理目前还未完全理解,两者的联合研究更少。然而，采用流变试验的手段可以表征CTAC和PEO的微观结构的变化，因此本文将对常用的减阻添加剂（表面活性剂CTAC和高聚物PEO）进行流变测量，通过溶液的流变特性来预测剪切率和浓度（CTAC浓度：30-1000ppm、PEO浓度：15-1000ppm）对减阻添加剂微观结构的影响，找出流变规律，进而总结出一些有价值的减阻机理。从目前的实验结果来看，可以发现，表面活性剂稀溶液在剪切作用下会出现剪切增稠转变，即随着剪切率的增加，溶液的粘度会产生稀化、稠化再稀化的过程。当溶液浓度的增加，CTAC剪切增稠转变越来越弱。当浓度达到1000ppm时，不再有剪切增稠转变发生。与之相似，PEO高分子聚合物的水溶液在剪切作用下，同样产生剪切稀化、稠化以及破坏这三个明显现象，但是其粘度曲线产生最大粘度时的剪切率相比CTAC而言要更高，这意味着PEO抵抗剪切的能力较表面活性剂来说更好。当将这二者相联合，对其水溶液进行相关流变测量，又会产生不一样的现象和规律。分析其规律产生的原因。对得到的规律和形成原因进行推导总结，就是本篇论文的重点，也是主要的内容。二、毕业设计（论文）整体安排及进度 周 次工 作 内 容检 查 方 式第七学期17课题内容理解，查阅文献、完成开题报告随时沟通，遇问题及时解决18翻译外文文献，学习和总结文献资料译文准确、通畅19修改外文文献和翻译译文上传至系统第八学期1理解流变仪的工作原理和熟悉操作过程及时交流2购置所需表面活性剂、高分子聚合物和实验器材定性分析计算结果，及时检查3-5测量不同浓度CTAC表面活性剂溶液表观黏度随剪切率的变化情况定性分析计算结果，及时检查6-8测量不同浓度PEO高分子聚合物溶液表观黏度随剪切率的变化情况定性分析计算结果，及时检查9-11测量不同混合比例高聚物PEO和表面活性剂CTAC溶液表观黏度随剪切率的变化情况定性分析计算结果，及时检查12-13整理实验数据，归纳流变规律，总结相关的流变机理，并撰写毕业论文需经严格审核14论文查重15答辩准备，答辩必须经指导教师审核通过 （3 10周中安排实习）三、毕业设计（论文）已完成的研究部分针对本次毕业设计，根据任务书要求，目前已经完成开题报告和外文翻译的相关内容，并掌握MCR302流变仪测量表面活性剂溶液和高聚物水溶液测量的相关操作，同时掌握对溶液的配制、OriginPro绘图软件绘图以及对图中出现的规律得出总结和定性分析的能力，完成了一部分的结果分析处理。在论文撰写方面，前言中表面活性剂部分已大致完成，主要内容上已完成对表面活性剂和高分子聚合物PEO流动曲线的绘制，并找出相关规律，结合所阅读文献，完成对发现的不同现象的定性分析。截至目前，已经完成对表面活性剂溶液、PEO溶液以及部分表面活性剂和PEO相联合溶液的剪切测量，也基本完成对PEO的温度变化实验测量，得出相关数据，绘制相应曲线图，总结出相关规律。四、下一部分的工作安排在四月末，完成PEO在40下的剪切实验，得出相关数据，并与10、20、30进行比较，找出变化规律。五月初，完成对CTAC/NaSal+PEO联合溶液的测量，并比较相同浓度下的CTAC、PEO以及联合试剂间的相同剪切率下粘度的变化情况，找出规律得出结论，并完成结果分析。实验结束后，进行高聚物的前言书写，完成前言。完成主要内容，初步完成毕业论文。初步完成后进行，交流讨论查重修改，完成毕业论文，进行答辩。五、毕业设计（论文）工作中存在的问题实验中对实验过程和得出的结果反思考虑不充分，对某些较细节的曲线分析处理不太到位，应当及时改正；测量所得的曲线有出现突然突出的部分，未发现其原因，应当加以重视；曲线绘制时，同种粘度的应力-剪切率曲线同粘度-剪切率曲线中图标不一致，以及表面活性剂的重复性较差，通过多次测量和仪器校准，现已改正。学生（签字） 年 月 日 指导教师（签字） 年 月 日 序号: XX 学号: XXXX 实 习 报 告实习课程名称： 毕业实习 学 生 姓 名： XXXXX 学 院： XXXX 专 业 班 级： XXX 校内指导教师： XX 专业技术职务： XXX 实 习 单 位： 常州市东方锅炉压力容器制造有限公司 实习时间： 20XX 年 5 月 2 日 20XX年 5 月 5 日实习报告1 实习目的按照教学计划的安排，我校过程装备与控制工程专业的学生，跟随毕业设计环节的进行，为加强对压力容器（包括塔器、换热器等）的直观了解，加深对设计加工工艺过程的认识，深刻地理解图纸与实际加工过程中的要求，使得毕业设计环节可以高效、准确地完成对压力容器的尺寸设计和图纸绘制，特此进行对常州市东方锅炉压力容器制造有限公司的场内实习。通过实地考察、导师讲解、拍照记录和同学交流等方式开展实习活动，提升自己的专业素养，促进毕业设计环节的有效进行。2 实习时间2018年5月2日-2018年5月5日3 实习地点常州市东方锅炉压力容器制造有限公司4 公司简介常州市东方锅炉压力容器制造有限公司地处长江三角洲经济发达区的常州市东郊，毗邻沪宁铁路和沪宁高速公路，交通便利，具有得天独厚的经济地理位置，处于发展经济、对外贸易的最佳之地。公司具有悠久历史，最早成立于1958年，是江苏最早取得锅炉压力容器制造许可证单位之一，经过几十年企业员工的共同努力已成为初具规模的现代化企业。我公司现有员工200多人，其中工程技术人员占30%，高级工程师5名，工程师20多名，高级技师、技工5名及一大批高素质人材。公司现占地面积2.4万多平方米，拥有固定资产3000多万元，其中各类专用设备300多台套。具有完善的检测手段，配备有力学试验室、化学性能试验及无损探伤室等。经几十年的发展，公司的主要产品：有机热载体加热炉、各类非标压力容器已广泛用于化工、医药、石油、食品、印染、造纸、塑料、木业加工、油脂、碳素、油漆、家电、汽车等行业。5 实习内容本次的实习活动的开展大致可以分为四个部分，即厂房考察、导师和工人讲解、拍照记录以及师生交流。以下是拍照记录的相关内容：图5.1 换热管板换热管板和换热管管孔，可以清晰地看见换热管和管板之间的连接采用了内孔焊的焊接形式。这样的焊接形式，使得原来的交接接头转变为对接接头，优化了换热管与管板连接处的应力状态，大大减小了边缘应力。对于有应力腐蚀、或间隙腐蚀介质的换热器非常实用。此外，可以看出该换热器使用了一块分层隔板，壳程被分隔，形成了双管程结构。图5.2 管板焊接这是工人采用内孔焊的焊接方式进行管板焊接，使用脉冲焊机和氩气保护，这对工人的焊接要求较高，任何焊接缺陷都将导致整台换热器的报废，因为无法返修。图5.3 法兰和折流板图片上包含两样东西，分别是法兰和折流板。对于法兰，它是用螺栓的两个密封面相互挤压法兰垫片从而实现密封要求。而远处的折流板，可以看见是采用的横向弓形（圆缺形）折流板，在列管式换热器中，该样式的折流板有以下作用；增强流体在管间流动的湍流程度；增大传热系数；提高传热效率。同时它还起支撑管束的作用。图5.4 固定管板换热器由图可见尺寸型号、壳程设计不一的固定管板式换热器，图示为未安装封头的筒体结构。工人正在进行换热管与管板间的焊接。图5.5 U形换热管图示为U形管换热器中的换热管，U形管式换热器每根管子均弯成U形，流体进、出口分别安装在同一端的两侧，封头内用隔板分成两室，每根管子可自由伸缩，来解决热补偿问题。这样的换热器结构简单，只有一个管板，密封面少，运行可靠，造价低;管束可抽出，管间(壳程)清洗方便。但管板利用率低;内层管子不能更换，报废率高。图5.6 U型管插管图示表现的是对U形管换热器进行穿管的过程，图片中包括了拉杆、拉杆固定的折流板等的部件。图5.7 膨胀节 图5.8 膨胀节挠性元件上述两图，均为换热器中的膨胀节结构。膨胀节为补偿因温度差与机械振动引起的附加应力，而设置在容器壳体或管道上的一种挠性结构。利用其工作主体波纹管的有效伸缩变形，以吸收换热管与管板间由线性热膨胀差而产生的尺寸变化，或其轴向位移。图5.9 小型固定管板式换热器 图5.10 接管法兰图示是一个小型的固定管板式换热器，虽然体积很小，但是一般大型换热器具有的部件它全都具备，包括筒体、管板、膨胀节、接管、长颈法兰、支座、密封面、补强部分，可谓“麻雀虽小，五脏俱全”。就其中的长颈法兰部分进行讨论，即图5.10，可见法兰开孔并不在沿筒体方向的水平线上，而是与筒体轴线呈一定的角度。原因是根据换热器的力学性能要求，与轴线呈一定角度，其承载性能会更好。 图5.11 双层叠式换热器图示为两个竖直方向叠加在一起的用接管连通的固定管板式换热器，它们的铭牌标注完全一致。通过将两个换热器竖直向上进行叠加，可以有效降低换热器的占地空间，使得换热器更小型化，有效降低因壳程的增大而导致的换热器体型较大，但是仍然可以获得同大体型换热器一样的换热效果。图5.12 塔体裙座左图是一塔设备，从照片主体而言，可以看见这是塔体的裙座部分。该裙座部分采用圆锥形结构，该结构主要用于细高型塔设备的支承。在化工设备中，裙座是很好的固定支承装置，虽然它不是受压元件，但是对于整个塔器至关重要，其设计标准要求与受压元件相同。6 实习心得通过这短短几天的生产实习，让我学到了很多课堂上学不到的知识，可以说是受益匪浅了。压力设备的生产实习是一个重要的理论联系实际的教学环节，借由实习的机会，培养了自己理论联系实际、解决实际问题的能力，将所学的基础理论知识与专业知识，在生产实践中一一验证。通过压力容器厂间的生产参观，可以看到压力容器生产工艺的全过程，例如：U形管换热器的管子插管、折流板的安装、管板的焊接（主要参观的是内孔焊的焊接形式）、筒体法兰的固定、筒体的焊接。除此之外，还见到了许多已经装配完成的压力容器，有卧式换热器，包括U形管换热器、固定管板式换热器、容积式换热器等等；还有塔设备，塔径大大小小的塔设备摆放在车间里，人进去仿佛显得尤其矮小。其中有一个在竖直方向上将两个换热器进行堆叠的作为一个整体工作的换热设备，在占地面积较小的情况下依然可以获得较好的换热效果。同时，随行的导师和厂里的工作人员为我们进行压力容器实际生产的要求和工艺设计的讲解，开拓了我们的视野。让我印象深刻的是一个体型尺寸较小的压力容器，体型并不能说明一切的形容极为贴切。其中有一个接管长颈法兰，它的开孔并不在沿着换热器轴线方向和它的垂线上，而是开在与轴线有一定的角度的方向上。这样开孔的原因也比较多见，因为根据换热器的力学性能要求，开孔与轴线互成一定角度能够承受更大的压力，获得较好的承压性能。最后，虽然本次实习只有短短几天，但是通过本次实习，使我对压力容器的生产有了更加深入更为广泛的认识，对自己即将从事的工作渐渐憧憬起来。通过观察实践，让我认识到一个压力容器的制造需要各个岗位的工人们共同完成，对压力容器的设计、焊接工艺、热处理、无损检测等过程都理解了很多，对我的毕业设计和工作都提供了很大的帮助。9Behavior of wormlike micellar solutions formed withoutany additives from semi-fluorinated quaternaryammonium saltsGennifer Padoan,abElisabeth Taffin de Givenchy,aAlessandro Zaggia,bSonia Amigoni,aThierry Darmanin,aLino Conteband Fr ed eric Guittard*aIn the present work a series of fluorinated quaternary ammonium salts were synthesized in two steps. Thephysical properties of the obtained surfactants were characterized by DLS, zeta potential, viscosity, andCryo-SEM. The surfactants with a long fluorinated chain form long and highly flexible aggregates thatlead to highly viscous solutions and the formation of an entangled network made of flexible worm-likemicelles. The viscoelastic properties of the surfactants that form hydrogels without any additives werecharacterized along with zeta potential and Cryo-SEM observations. They present a maximum viscosityas a function of worm-like micelles formation. The increase of the fluorinated and hydrocarbon chainlengths contributes to the enhancement of this viscoelastic behavior.IntroductionSurfactant solutions represent a well-documented class of self-assembled structures providing a powerful tool for severalapplications in pharmaceutical and cosmetics industries.15The addition of an inorganic,6a strongly binding organic salt,7or an oppositely charged surfactant leads to the growth ofaggregates. This growth generally leads to highly viscoussolutions and the formation of an entangled network made ofexible worm-like micelles, oen referred to as thread-likemicelles.8The length of these aggregates can reach up to 1 mm,but the diameters are only a few times the length of theconstituent molecules.Prudhomme and Warr investigated the behavior of solu-tions of tetradecyltrimethylammonium salicylate9and theyobserved a rheological behavior of wormlike micelles in thesurfactant solution similar to that of exible polymers. Yet,above a critical concentration (c*), few weight percent, wormlikemicelles entangle into a transient network similar to a solutionof exible polymers; they behave in exactly the same way as theequivalent macromolecules and entangle with each other toform transient networks, which display remarkable viscoelasticproperties in a manner analogous to semi-dilute polymersolutions.Wormlike micelles are dynamic systems and the aggregatesare constantly breaking and recombining, making them livingpolymers and proving an increase in viscosity with shear rate.10The polymer analogy has been the catalyst for recent theo-retical advances in understanding the properties of the aniso-metric micellar solutions. By incorporating the dynamic natureof micelles into polymer solution theories, Cates11has been ableto predict scaling laws for both equilibrium and dynamicproperties of these systems. Because the micelles are in ther-modynamic equilibrium with the surrounding solvent, they arenot geometrically xed like polymer molecules. As a conse-quence, the connecting or branching points of the micelles areable to move along the primary axis of the micelles.Theselivingpolymershaveoneextrapropertythatthenormalpolymer system lacks (and hence their name): if either polymerchains or surfactant worm-like micelles are subjected to a highextensional force, they can be snapped in half. While polymerfragments always remain thereaer at this lower (halved)molecular weight, the broken surfactant micelles can reformundermorequiescentconditions,sincetheyarethermodynamicobjects held together by reversible bonds. If elastic liquids areneeded to withstand continual damage, and yet survive, thenthese micellar systems are much more mechanically robust.Micellar microstructures have a strong inuence on therheological properties of aqueous surfactant solutions.12Thetransition to a shear-thickened uid is commonly attributed tothe formation of shear-induced structures, where phase sepa-ration takes place between a surfactant-rich and a surfactant-poor phase. Their unique viscoelastic behavior is exploited totune the rheology in numerous applications with or without theuse of polymers or additives. For this reason they have beensuggested for drag reducing uids in central-heating systems.13aUniv. Nice Sophia Antipolis, CNRS, Laboratoire Physique Mati ere Condens ee, UMR7336, Parc Valrose, 06100 Nice, France. E-mail: guittardunice.fr; Fax: +33492076156; Tel: +33 492076159bDipartimento di Ingegneria Industriale, University of Padua, Via Marzolo, 9-35131,Padua, Italy Electronic supplementary information (ESI) available: Characterizations, yieldsand cmc for the synthesized surfactants, complementary graphs of rheology, zetapotential and Cryo-SEM images. See DOI: 10.1039/c3sm51591eCite this: Soft Matter, 2013, 9, 8992Received 7th June 2013Accepted 25th July 2013DOI: 10.1039/c3sm51591e/softmatter8992 | Soft Matter, 2013, 9, 89928999This journal is The Royal Society of Chemistry 2013Soft MatterPAPERPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article OnlineView Journal | View IssueLike all brous microstructures, the viscosity is high when thesystem is randomly dispersed in space and highly entangled,but once the ow has aligned the microstructures, the viscosityis quite low.This change from very high to very low viscosity takes placeover a narrow range of stress or temperature. These self-assembled structures may reduce friction energy loss inturbulent ow by up to 90% at relatively low surfactantconcentrationsunderappropriateowandtemperatureconditions. This phenomenon is called drag reduction (DR)and it has signicant potential impacts on uid transport andon the environment.14The self-assembly of surfactant DRadditives (DRAs) permits them to be used in recirculationapplications such as in district heating/cooling systems.15,16Cationic surfactants have been extensively investigated and itseems that they are the most effective surfactant drag reducersproviding the proper conditions (such as the chemical struc-tures and concentrations of surfactant and counter-ion). Somecationic surfactants can spontaneously pack into cylindricalstructures without any additives at room temperature. Most ofthe time, the addition of inorganic salts to ionic surfactants isneeded to promote micellar growth and viscoelastic proper-ties.17The mechanism involved is primarily the screening ofthe electrostatic repulsion between the charged head-groups,which results in reduction of the optimal molecular area at thehydrocarbonwater interface, leading to an increase in the end-cap energy.18Rather, little is known about uorosurfactants, inparticular cationic uorosurfactants, despite the technicalinterest of their potential usefulness due to their stronghydrophobicity and efficient surface activity. Solutions of thesesurfactants have a number of peculiar properties because theirmicellar structures are formed due to weak non-covalentinteractions and easily change in response to external actions.The introduction of uorinated chains in surfactants is verypromising, thanks to their high hydrophobicity and stiffness,for the formation of structures with relatively little curvature,such as cylindrical micelles.14,19A schematic representation of the synthesized uoro-surfactants is given in Scheme 1. We report on the synthesis ofthese surfactants, zeta potential and rheological measurements.Moreover, viscoelastic properties of concentrated solutions ofthese hybrid surfactants as a function of temperature, stressand strain were studied along with Cryo-SEM observations.Materials and methods3-Peruorobutyl-1,2-epoxypropane, 3-peruorohexyl-1,2-epoxy-propane and 3-peruorooctyl-1,2-epoxypropane were synthe-sized according to the previous procedure.20For the synthesis ofhybrid surfactants, iodomethane and all chemicals werepurchased from Aldrich and used without further purication.Unless specied, the solvents were used as received. Conr-mation of the structures of the intermediates and products wasobtained by nuclear magnetic resonance (NMR) realized with aBruker W-200 MHz instrument and mass spectrometry (MS) 80using a Thermo TRACEGC instrument from Thermoscher81Corp. tted with an Automass III Multi spectrometer (elec-tron ionization at 70 eV).Preparation of the semiuorinated tertiary amines (Anm)3-Peruoroalkyl-1,2-epoxypropane(0.02mol)alkylbutyl(n4),hexyl (n 6), and octyl (n 8) was added under stirring todialkylamine (0.022 mol) alkyl methyl or ethyl in methanol.The mixture was heated at 60?C for 6 to 15 h. Purication ofthe red liquid by column chromatography on silica gel (dichlor-omethane : methanol99 : 1)gaveaminesAnmasyellowliquids.The experiments were reproduced several times. In all cases, theyields (see details in the ESI) were reproducible (?3%).General procedure for the synthesis of the hybrid surfactants(FnHm)A mixture of a tertiary amine (Anm) and an excess of iodo-methane was reuxed in acetonitrile at 60?C for over 24 h.Scheme 1Synthetic route towards the studied surfactants FnHm.This journal is The Royal Society of Chemistry 2013Soft Matter, 2013, 9, 89928999 | 8993PaperSoft MatterPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article OnlineIodomethane and acetonitrile were removed by evaporation, theresidue was washed several times with anhydrous diethyl etherand recrystallized several times from a mixture of methanol anddiethyl ether, and then the residue was washed several timeswith petroleum ether to give FnHmin the form of white solids(seeyields,chemicalcharacterizations,criticalmicellarconcentration (cmc) and surface tensions (gS) in the ESI).Dynamic light scattering experimentsTheZ-averagediameteristhemeanhydrodynamicdiameterandthe polydispersity index is an estimate of the width of distribu-tion. Both of these parameters were calculated according to theInternational Standard on dynamic light scattering (ISO13321).All the measurements were done at a temperature of 25?C,whichwas controlled bymeans of a thermostatusing a ZetasizerNano-ZSmodel3600(MalvernInstrumentsLtd)equippedwithaHeNe laser (l 633 nm, 4.0 mW). Measurements of the size ofthe surfactant aggregates wereperformed byDLS to examine thestate of aggregation in aqueous solution. The aqueous solutionswere prepared using deionizated water and ltered through a0.45 mm lter. The time-dependent correlation function of thescattered light intensity was measured at a scattering angle of90?relative to the laser source (red-scattering detection).Measurements were repeated several weeks aer prepara-tion, and no modication of the sizes was visualized. DLSdiffusion coefficients (D) were evaluated by tting the equationof StokesEinstein:D (kBT )/6phr(1)where kBis Boltzmanns constant, T is the absolute tempera-ture, and h is the viscosity of the solvent. The radius (r) of theparticles was estimated from their diffusion coefficient (D).Zeta potential measurementsZeta potential measurements of the surfactant complex werecarried out using a Malvern Instruments Ltd NanoZs by takingthe average of three measurements at the stationary level. Thecell used was a 5 mm ? 2 mm rectangular quartz capillary. Thetemperature of the experiments was 298.15 ? 0.01 K controlledby a proportional temperature controller HETO. The zetapotential z were calculated from the electrophoretic mobilities(mE) using the Henry equation:21z 3mEh2303r1fka(2)where 30is the permittivity of vacuum, 3rand h are the relativepermittivity and viscosity of the medium, respectively, a is theparticle radius, and k is the Debye length. The function f (ka)depends on the particle shape and for our systems it wasdetermined byfka 1:5 ?92ka752k2a2?330k3r3(3)The Henry function is appraised to be 1 for small kr and 1.5for large kr. Hence, for larger aggregates of relatively smallpotential, eqn (2) can be used to determine the zeta potential ofa particle. Then, k is related to the ionic strength of electrolytesolution according tok (2000F2)/(303rRT)1/2I1/2(4)where F is the Faraday constant, 30the permittivity of a vacuum,3rthe relative permittivity, R the gas constant, T the tempera-ture, and I the ionic strength of the electrolyte solution.22Rheological measurementsThe rheological properties of the samples were measured usingan Anton Parr Physica MCR-301 rheometer. Cone geometry wasused in each case (50 mm diameter, 1 angle). The gap was0.05mm.Asolventtrapwasusedtominimizewaterevaporation.Experiments were performed at 20, 30, 40, and 50 ? 1?C. Theviscosityofthesamplewasobtainedfromsteady-shearmeasurements with the shear ranging from 0.3 to 500 s?1.Frequencysweepmeasurementswereperformedatagivenstressin the frequency region varying from 0.01 to 100 rad s?1. All therheology/viscosity data given in this paper are average values oftwomeasurements;thedeviationswereintherangeof?0.01Pas.Microscopic observationsCryogenic scanning electron microscopy (Cryo-SEM) imageswere obtained with an FESEM6700F JEOL microscope (Japan).One drop of the sample was rapidly frozen in nitrogen slush at?220?C and transferred under vacuum into the cryofractureapparatus (Alto 2500 GATAN UK) chamber where it was frac-tured at ?100?C and maintained at this temperature for 7 minfor sublimation. It was then metallized with AuPd and intro-duced into the microscope chamber where it was maintained at?100?C during the observation. To ensure reproducibility, themicrographs presented in this article were chosen from a largenumber of negatives.Results and discussionDynamic light scattering discussionFig. 1 shows the diameter (D) of the population of aggregates asa function of the solution concentrations for F4H1and F4H2. Dincreases as the concentration and the value of D was higher forF4H2suggesting the inuence of the head size (N+Me3for F4H1against N+MeEt2for F4H2) on larger aggregates.Fig. 2 shows the diameter D of the aggregates in solution (atve times the cmc) as a function of the uorinated chain length:it can be observed that higher values of D are reached withlonger uorinated chains. It reects the ability of uorinatedsurfactants to form aggregates with lengths as long as severalmicrometers. These ndings are consistent with the earlierobservations by Zana and co-workers10for hybrid surfactantshaving a very strong propensity for micellar growth andformation of micelles of very low curvature.Moreover, in our case, the presence of big counter-ions I?near to the polar head-groups of the surfactant moleculesdecreases the repulsion force between the head-groups. This8994 | Soft Matter, 2013, 9, 89928999This journal is The Royal Society of Chemistry 2013Soft MatterPaperPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article Onlinereduction in the repulsion allows the surfactant molecules toapproach each other more closely and form larger aggregates.However, the electrostatic effect of the I?counter-ionbinding on ionic micelles and the change in the hydrocarbon-bonded structure of water cause hydrophobic interactionsbetween surfactant molecules.23Also, due to Ostwald ripening,24aggregates of larger curvature realized themselves into singlespecies due to their higher chemical potential and the liberatedsingle species adsorb to the aggregates of smaller curvature tomake them further larger in size. DLS analyses clearly show thepresence in the solution of different sizes of aggregates and thetransition from monomodal to bimodal structure with anincrease in the uorinated chain length (see DLS curves in theESI).25The effect of a long uorinated chain on packing ofsurfactants is expected to affect strongly the curvature of asurfactant layer and the incorporation of a uorinated chaininto the core provides a bimodal distribution for the longuorinated chains (F8Hmand F6Hm).In fact, it may be assumed that with an increasing number ofcarbon atoms in the uorinated chain, the hydrophobic interac-tions become more intensive and larger aggregates can beobserved.Thesemeasurementssuggestspontaneousorganizationinlargeaggregates(vesiclesorcylinders)forallofthesynthesized surfactants.Zeta potential discussionZeta potential (z) measurements for F8H1and F8H2as a func-tion of concentration for 20 (C1), 30 (C2), and 40 (C3) times thecmc were carried out; these concentrations were chosen toobserve the behavior until the maximal solubility of thesynthesized surfactants was reached. The concentration over 40times the cmc of F8H1was not realized because the surfactant isinsoluble at this concentration. The main peak was found to bepositive and it corresponds to the positive change of headgroups in these quaternary ammonium surfactants.25The main positive peak is probably attributed to largeaggregates with a low degree of curvature and a weak adsorptionof I?counter-ions at the micelle surface.Here, the positive zeta potential of F8H1and F8H2decreaseswith increasing surfactant concentration due to the formationof entangled networks of wormlike micelles caused by higherhydrophobic interactions.Also, zeta potential measurements were carried out at aconcentration twice the cmc of FnHmwith n 4, 6, 8 and m 1,2 in order to study the inuence of the uorinated chains. Themeasured values for the synthesized surfactants are summa-rized in Table 1. All values were positive, due to the head group,and the values increased on increasing the uorinated chainlength. The uorinated chain enhances the hydrophobicinteractions leading to an increase in the value of the zetapotential.Rheological discussionThe stiffness of the uorocarbon chain sometimes has an effecton the packing17leading uorinated surfactants, in aqueoussolutions, to form cylindrical micelles with lengths as long asseveral micrometers, where analogous hydrocarbon would formspherical aggregates. The packing constraints of the per-uoroalkyl chain are responsible for the formation of exibleaggregates in water at low concentrations and low tempera-tures.Surfactantsolutionscommonlyexhibitviscoelasticproperties only at low temperatures because heating enhancesthermal vibrations in micelles and the chains are morefrequently breaking and their average length oen decreases.Some surfactants reach a maximum viscosity at a specictemperature and then decrease with increasing temperature.6These surfactants are called thermo-responsive viscoelasticsurfactants.The synthesized surfactants F8H1, F8H2and F6H2formedhydrogels in pure water. Then, to investigate the importance ofFig. 1Aggregate diameters as a function of concentration for F4H1and F4H2.Fig. 2Aggregate diameters as a function of the fluorinated chain length (redleft scale for FnH1and blue right scale for FnH2surfactants).Table 1Values of the zeta potential of surfactants FnHmSurfactantz (mV)Surfactantz (mV)F8H165.9F8H258.3F6H124.4F6H238.9F4H111.3F4H29.5This journal is The Royal Society of Chemistry 2013Soft Matter, 2013, 9, 89928999 | 8995PaperSoft MatterPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article Onlineuorocarbon and hydrocarbon chains to give viscoelasticproperties, rheological measurements were carried out. Nopeculiar hydrogel behavior was observed for the solutions ofFnHmwith n 4, 6 and m 1, 2. Only F8H1, F8H2, and F6H2showed tendency to form hydrogels in pure water above theircmc and only F8H1and F8H2showed high viscosity. However, toinvestigate concentrated solutions of F8H1and F8H2, rheolog-ical measurements under different conditions were carried out.Viscosity as a function of temperature for F8Hm. Fig. 3 and 4show viscosity as a function of temperature for F8H1and F8H2atconcentrations of 20 (C1), 30 (C2) and 40 (C3) times the cmc. Wecanobservethermo-responsiveviscoelasticityforalltheconcentrations. Also, the value of the maximal viscosity and thetemperature at which the maximal viscosity appeared seem tobe dependent on the surfactant concentration and the hydro-carbon chain length.6In particular, the maximum value was T 19?C at C1 20times cmc and T 26?C at C2 30 times cmc for F8H1, andT 32?C at C1 20 times cmc, T 42?C at 40 times cmc, andT 37?C times cmc at 40 times cmc for F8H2.As schematized in Fig. 5, there is a thermodynamic expla-nation usually proposed for this increasedecrease in viscosity.The increase of viscosity with temperature can be understood interms of a decrease in the mean size of the micelles or theformation of cross-linked micellar networks.7ConsideringthereptationmodelofCates,11relaxationofchainconformationsoccursbythegradualdisengagementofanygivenchain, by curvilinear diffusion along its own contour26from atube-like environment. Cates also deduced the rheological prop-ertiesofexiblesurfactantmicelles.Inparticular,thenormalizednumber density C(L) of micelles of length L is given by eqn (5):CL eLL(5)where C(L) is the normalized number density of micelles oflength L and the mean length?L is related to the volume fraction4 and to temperature T by eqn (6):L4;T 412eEbreak=2kBT(6)where Ebreakis the scission energy required to break a micelleinto two parts.Thistemperaturedependenceofthemicellarlengthproduces a decrease in micellar size and thus a greater resis-tance to the ow. However, networks have to be, in some way,similar to exible polymers with their stress relaxation partlycontrolled by the motion of micelles along its own contour andby a reversible scission of the micelles. The formation of aninter-micellar junction may be viewed as a fusion reactionbetween the end cap of one cylindrical micelle and the mainbody of another, forming a Y-like joint.10Also, Fig. 3 and 4 show that the trend of the viscosity vs.temperature curve is similar to the increasing surfactantconcentration, but the temperature at which the maximumviscosity is reached gradually shis to lower values. Then, theyshow that highly viscoelastic solutions are formed at a lowtemperature and at a high surfactant concentration. In fact,Fig. 4 shows that the value of maximal viscosity for F8H2at C3ishigher than the value at C1and C2because the viscosityincreases with the surfactant concentration due to an increasein the mean micellar length. As the contour length decreases,the viscosity is predicted to decrease because of a reduction inthe extent of entanglement of micelles. Therefore, changes insolution concentrations can lead to the formation of other self-assembled structures and the formation of a micellar networktakes place at a lower temperature. Also, as shown in Fig. 4 themaximal viscosity is higher for F8H2for all concentrations,Fig. 3Viscosity as a function of temperature at concentrations C1, C2, and C3forF8H2.Fig. 4Viscosity as a function of temperature at concentrations C1and C2forF8H1.Fig. 5Change of micelles and viscosity as a function of temperature.8996 | Soft Matter, 2013, 9, 89928999This journal is The Royal Society of Chemistry 2013Soft MatterPaperPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article Onlineindicating that an increase of hydrophobicity leads to theformation of larger molecular assemblies in solution; in fact, ifthe aggregates are located in the vicinity of the micelle surfacethey are likely to actively participate in the hydrophobic inter-micellar interaction, thereby forming large molecular assem-blies through the gathering of small molecular assemblies. Fora saturated network the reptation model breaks down, whichsuggests that the system becomes very uid and so F8H1at C3shows a low viscosity and no hydrogel behavior.Viscoelastic measurementsTemperature sweep. The storage modulus (G0) and the lossmodulus (G00) as a function of temperature at a xed frequency of1 Hz and 20% strain for the concentrations C1, C2, and C3werealso analyzed. The results at low frequencies are somewhat scat-teredbecausetherheometerwasoutofitsmeasuringrange.Intherangeoftemperaturesused(T1070?C)theplotsarelinearandthe value of G0isalways largerthanG00, then the storagemodulusshows no frequency dependency in the range of 1070?C. In thisrange, analyzed surfactants F8H1and F8H2present a viscoelasticbehavior. In the ESI, examples of measurements are given.Frequency sweep. The storage modulus (G0) and the lossmodulus (G00) as a function of frequency at 20, 30, 40 and 50?Cand 20% xed strain were analyzed to calculate the evolution ofrelaxation times as a function of temperature. Fig. 6 shows anexample of measurements for F8H1at C1. All the values aregathered in Fig. 7 and 8.Reptation and breaking timeThe relaxation time can be correlated with reptation time srepand breaking time sbof Catess model. In fact, the relaxationtime is the geometric mean of two characteristic times, formicellar breakingrecombination and for micellar reptation, asproposed by the reptation-reaction model. However, the repta-tion time (srep) is dened in eqn (7):srep?L43/2(7)it is the time required to form a worm-micelle of contour length?L to pass through a hypothetical tube, with 43/2volume fraction.At srep, the formation of the aggregate is associated with thecreation of an interface between its hydrophobic domain andwater. The surfactant head-groups are brought to the aggregatesurface, giving rise to steric repulsion between them.Then, the breaking time is dened in eqn (8)sb (kr?L)?1(8)it is the average time necessary for a chain of average length tobreak into two pieces by a reversible scission characterized by atemperature-dependent rate constant krper unit time and perunit arc length, which is the same for all elongated micelles andis independent of time and of volume fraction.27Fig. 7 and 8 show a correlation between the relaxation timeand change of viscosity as a function of temperature. At lowtemperatures either not all of the surfactants in the solutionform wormlike micelles, or not all of the wormlike micelles werelarge enough to entangle. Therefore, the relaxation time wasvery low at low temperatures because surfactant micellesexchange slowly at lower temperatures and they have stronghydrophobic interactions with single micelles. Then, with anincrease of the temperature a very small reduction of repulsionbetween the head-groups and the hydrophobic micellar aggre-gates (interactions between the hydrophobic chains locatedFig. 6G0and G00as a function of frequency for F8H1at C1.Fig. 7Correlation between viscosity and relaxation time of F8H2at C3.Fig. 8Correlation between viscosity and relaxation time of F8H2at C1.This journal is The Royal Society of Chemistry 2013Soft Matter, 2013, 9, 89928999 | 8997PaperSoft MatterPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article Onlinenear to the micelle surface) determines the increase of molec-ular aggregates. Then, the aggregates accomplish cylinder toworm-like micelles increasing the viscosity and allowing thesystem to release the stress quickly.28Similarly, an increase ofthe micelle length oen leads to lower viscosity due to fasterrelaxation, because the triggering tricks consist essentially ofreducing the preferred curvature of the micelles.Moreover, for an entangled network of wormlike micelles,junctions provide a mean relax stress to increase the viscosity.Hence, at the maximum viscosity, uorocarbon chains areremoved from contact with water and are subjected to packingconstraints because of the polar head group requirements thatshould remain at the aggregatewater interface and the micellecore should have the hydrocarbon chains in the liquid.Consequently, they are incorporated into the micelle coreand the surfactant forms compact micelles with increasingrelaxation time. Then, an increase of temperature determinesthe degradation process of micelles leading to a decrease ofviscosity and relaxation time.Cryo-SEM discussionCryo-SEM selected images were presented to establish themorphologies associated with the surfactant solutions. Fig. 9ashows a Cryo-SEM image (scale bar 100 nm) of F8H1solution inwater at 20 timesthe cmc. The predominant structural feature inthisimageissphericalnodules,withlittleevidenceofbranchesorcylindricalaggregates.Fig.9bshowsagiantcylindricalmicelleinthe medium of a small spherical nodule. Fig. 9c (scale bar 1 mm)shows small cylindrical aggregates linked together at junctions.Fig. 10 (scale bar 1 mm) shows small branched cylindricalaggregates observed for F8H2at a concentration of about 5 timesthe cmc. The basic structural element of the random networkappears to be approximately cylindrical, with a diameter of 50100 nm, consistent with the dimensions extracted from theform factor scattering. Although it is impossible to determinethe aspect ratio with any certainty, these cylinders appear to berather long, with length-to-radius exceeding at least 3040 nm.This image reveals a densely connected, random, networkmorphology. Strands of surfactants, roughly 4050 nm inlength, are linked together at junctions that range from simple3-fold unions to larger, at, multifunctional connections. Thesame results were found for F8H1as shown in Fig. 11 (scale barFig. 9Representative Cryo-SEM micrographs of F8H1(20? cmc); (a and b) scale bar 100 nm; (c) scale bar 1 mm.Fig. 10Representative Cryo-SEM micrographs of F8H2(5? cmc); scale bar 1 mm.Fig. 11RepresentativeCryo-SEMmicrographsofF8H1(7?cmc);scalebar10mm.8998 | Soft Matter, 2013, 9, 89928999This journal is The Royal Society of Chemistry 2013Soft MatterPaperPublished on 29 July 2013. Downloaded on 02/12/2017 01:48:19. View Article Online10 mm). In contrast to spheres, cylinders, and vesicles, there isno way to continuously expand (dilate) a three-dimensionalnetwork formed from bulk (hydrophobic) cylindrical struts andmultifunctional branches. The preferred local structure isdominated by Y-junctions, thus leading to the formation of adense network under equilibrium conditions.Branching in cylindrical micelles is less obvious with shorterhydrocarbon chains due to the chain packing constraintsassociated with the formation of Y-junctions.ConclusionsAs compared to existing systems29the synthesized uorinatedquaternary ammonium salts have a thermoresponsive visco-elasticbehaviorwithouttheadditionofaninorganicorastronglybinding organic salt. They form large and highly exible aggre-gates30,31that lead to highly viscous solutions and the formationof an entangled network made of exible worm-like micelles.They present a thermoresponsive behavior able to increasethe viscosity as a function of temperature due to the formationand breaking of entangled micelles.Theyalsopresentamaximumviscosityasafunctionofworm-like micelle formation. The increase of the uorinated andhydrocarbon chain lengths contributes to the enhancement ofthis viscoelastic behavior and therefore increases the size of themicellar aggregates. The preferred local structure