Interactions of magnetic holes in ferrofluid layers
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第6卷 第3期2013年6月 中国光学 Chinese Optics Vol.6 No.3June 2013 收稿日期:2013⁃02⁃17;修订日期:2013⁃04⁃15 基金项目:国家自然科学基金资助项目(No.10834015;No.61077082);陕西省科技新星资助项目(No.2012KJXX⁃27);陕西省光电技术与功能材料省部共建国家重点实验室培育基地基金资助项目(No.ZS12018)文章编号 1674⁃2915(2013)03⁃0283⁃14太赫兹波段超材料的制作、设计及应用潘学聪1,姚泽瀚2,徐新龙1,2∗,汪 力1(1.中国科学院物理研究所北京凝聚态物理国家实验室,北京100190;2.西北大学光子学与光子技术研究所光电技术与功能材料国家重点实验室培育基地,陕西西安710069)摘要:本文从制作方法、结构设计和材料选择几方面综述了超材料在太赫兹波段的电磁响应特性和潜在应用。
首先,介绍了获得不同维度、具有特异电磁响应以及结构可调超材料的各种微加工制作方法,进而分析和讨论了超材料的电磁响应特性。
文中指出,结构设计可以控制超材料的电磁响应特性,如各向异性、双各向异性、偏振调制、多频响应、宽带响应、不对称透射、旋光性和超吸收等。
超材料的电磁响应依赖于周围微环境的介电性质,因而可用于制作对环境敏感的传感器件。
此外,电光、磁光、相变、温度敏感等功能材料的引入可以获得光场、电场、磁场、温度等主动控制的太赫兹功能器件。
最后,简单介绍了超材料在太赫兹波段进一步发展所面临的机遇和挑战。
关 键 词:超材料;太赫兹技术;结构设计;调制;偏振中图分类号:O441;TB34 文献标识码:A doi:10.3788/CO.20130603.0283Fabrication ,design and application of THz metamaterialsPAN Xue⁃cong 1,YAO Ze⁃han 2,XU Xin⁃long 1,2∗,WANG Li 1(1.Beijing National Laboratory for Condensed Matter Physics ,Institute of Physics ,Chinese Academy of Sciences ,Beijing 100190,China ;2.State Key Laboratory Incubation Base of Photoelectric Technology and Functional Materials ,Institute of Photonics &Photon⁃Technology ,Northwest University ,Xi′an 710069,China )∗Corresponding author ,E⁃mail :xlxuphy@ Abstract :In this paper,the electromagnetic responses and potential applications of THz metamaterials are re⁃viewed through the focus on fabrication,unit structure design,and material selection,respectively.It de⁃scribes different kinds of fabrication technologies for obtaining metamaterials with special electromagnetic re⁃sponses such as magnetic resonance and reconfigurable tunability,which is helpful for further understanding of electromagnetic resonances in metamaterials.The paper analyzes the electromagnetic response characteristics in detail and points out that the unit structure design can be used to obtain desired electromagnetic characteris⁃tics,such as anisotropy,bianisotropy,polarization modulation,multiband response,broadband response,asymmetric transmission,optical activity,and perfect absorption,etc .The dependence of electromagnetic re⁃sponses upon surrounding dielectrics can be used not only to control resonant frequency by a proper substrateselection,but also for sensing applications.Furthermore,the introduction of functional materials with control⁃lable dielectric properties by external optical field,electrical field,magnetic field and temperature has the po⁃tential to achieve tunable metamaterials,which is highly desirable for THz functional devices.Finally,the op⁃portunities and challenges for further developments of THz metamaterials are briefly introduced.Key words:metamaterials;THz technology;structure design;modulation;polarization1 引 言 通过对自然材料的裁剪、加工和设计,从而实现对电子、光子以及其他一些元激发准粒子的人为调控,一直是光电科学研究的重点。
核磁苯环特征区的英文表达为:Nuclear magnetic benzene ring characteristic region。
核磁共振(Nuclear Magnetic Resonance,NMR)是一种常用的分析技术,通过观测核磁共振现象来研究物质的结构和性质。
苯环是一个六个碳原子构成的芳香环,具有特殊的电子结构和化学性质。
在核磁共振谱中,苯环的特征区主要包括以下几个方面:
1. 化学位移:苯环中的氢原子具有一定的化学位移,即吸收峰在核磁共振谱上的位置。
苯环上的氢原子通常显示在较低化学位移区域,其化学位移范围通常在7-8.5 ppm之间。
2. 耦合常数:苯环中的氢原子之间存在耦合作用,即它们的共振频率相互影响。
苯环上的氢原子通常呈现出三重ts选项对称的耦合模式,即每个氢原子周围都有两个等距离的耦合氢原子。
这种耦合关系导致了峰的裂分,例如,苯环上的顶氢原子会被四个邻近的耦合氢原子裂分为四个峰。
耦合常数可以通过测量裂分的峰距来确定。
3. 积分强度:苯环中各个氢原子的积分强度可以反映它们的相对数量。
在苯环谱图中,积分强度通常以峰的高度或面积表示,用于计算不同位置氢原子的比例关系。
4. 峰形和峰宽:苯环的核磁共振峰通常呈现出对称的形状,峰宽度较窄。
这是由于苯环具有刚性结构和芳香性质,使得苯环上的氢原子的化学位移和峰形较为稳定。
当然,苯环的核磁共振谱还受到其他因素的影响,例如溶剂效应、取代基和环境条件等。
因此,在解读苯环的核磁共振谱时,需要综合考虑这些因素,以及其他实验条件和样品性质的影响。
物理启蒙英语Introduction to PhysicsPhysics is the study of the natural world and the fundamental principles that govern it. It is concerned with the behavior of matter and energy, and how they interact with each other in different contexts.The study of physics can be divided into several subfields, such as classical mechanics, electromagnetism, thermodynamics, quantum mechanics, and relativity. Each of these subfields deals with a specific aspect of the physical world, and together they form a comprehensive understanding of the universe.Classical mechanics is concerned with the motion of objects under the influence of forces. It is based on the laws of motion, which were first described by Sir Isaac Newton in the 17th century. Classical mechanics explains phenomena such as the motion of planets, balls, and automobiles.Electromagnetism deals with the interactions between electric and magnetic fields. It describes how charged particles interact with electric and magnetic fields and how these fields can be generated by chargedparticles. This is the basis for many modern technologies such as computers, televisions, and cell phones.Thermodynamics is the study of the behavior of matter and energy in systems that involve heat transfer. It is concerned with how heat is transferred from one system to another and how it affects the behavior of matter and energy. Thermodynamics is essential for understanding how energy can be converted from one form to another.Quantum mechanics describes the behavior of matter and energy at the atomic and subatomic level. It is based on the principles of wave-particle duality and the uncertainty principle. Quantum mechanics is essential for understanding phenomena such as atomic and molecular structure, the behavior of light, and the nature of matter.Relativity is concerned with the behavior of matter and energy in extreme conditions, such as those found near black holes or at high velocities. It describes how space and time are affected by gravity and how the speed of light is absolute. Relativity is essential for understanding the behavior of the universe at large.In summary, physics is a fundamental part of our understanding of thenatural world. It helps us comprehend the behavior of matter and energy in different contexts, and it underpins many modern technologies. By studying physics, we can gain a greater appreciation of the world around us and our place in it.。
第52卷第12期表面技术2023年12月SURFACE TECHNOLOGY·315·医用镁合金微弧氧化/有机复合涂层的研究现状及演进方向冀盛亚a,常成b,常帅兵c,倪艳荣a,李承斌a(河南工学院 a.电缆工程学院 b.车辆与交通工程学院c.电气工程与自动化学院,河南 新乡 453003)摘要:医用镁及镁合金过快的降解速率严重缩短了其有效服役时间,过高的析氢速率引发局部炎症,束缚了其临床应用前景。
微弧氧化(MAO)/有机复合涂层良好的抑蚀降析性能,在医用镁及镁合金表面改性领域展现出巨大的应用潜力。
首先,从有机材料(植酸(PA)、壳聚糖(CS)、硬脂酸(SA)、多巴胺(DA)、聚乳酸-乙醇酸共聚物(PLGA)、聚乳酸(PLA)、聚已内酯(PCL))自身的组织及性能特征入手,分析了单一有机涂层提高镁及镁合金耐蚀性的作用机理,并指出单一涂层自身的性能弱点(单一MAO涂层微孔和裂纹的不可避免,单一有机涂层与镁合金结合强度低,易于剥落)限制了对镁合金降解保护效能。
其次,从结合强度、耐蚀性、多功能性(生物安全性、生物相容性、诱导再生性、抑菌抗菌性、载药缓释性等)的角度,详细阐述了各MAO/有机复合涂层的结构特点、优势特征。
在此基础上,明确指出以MAO/PCL (MAO/CS)复合涂层为基底涂层,通过PCL(CS)涂层与其他涂层的交叉组合,是实现医用镁合金植入材料的生物活性及多功能性的最佳路径。
最后,对镁合金MAO/有机复合涂层的演进方向进行了科学展望。
关键词:镁合金;微弧氧化;有机材料;复合涂层;演进方向中图分类号:TG174.4 文献标识码:A 文章编号:1001-3660(2023)12-0315-20DOI:10.16490/ki.issn.1001-3660.2023.12.026Research Status and Evolution Direction of Micro-arc Oxidation/Organic Composite Coating on Medical Magnesium Alloy SurfaceJI Sheng-ya a, CHANG Cheng b, CHANG Shuai-bing c, NI Yan-rong a, LI Cheng-bin a(a. School of Cable Engineering, b. School of Vehicle and Traffic Engineering, c. School of Electrical Engineering andAutomation, Henan Institute of Technology, Henan Xinxiang 453003, China)ABSTRACT: Good biosafety, biocompatibility and valuable self-degradation properties endow medical magnesium and magnesium alloys with great potential to replace inert implant materials in the field of traditional clinical applications.The excessive degradation rate of magnesium alloy, however, leads to its premature loss of structural integrity and mechanical support, being unable to complete the effective service time necessary for tissue healing of the implant site. At the same time, it is also its excessive degradation rate that leads to the intensification of hydrogen evolution reaction of收稿日期:2023-02-01;修订日期:2023-05-14Received:2023-02-01;Revised:2023-05-14基金项目:河南省科技攻关项目(222102310337,222102240104,232102241029);博士科研资金(9001/KQ1846)Fund:Henan Province Science and Technology Research Project (222102310337, 222102240104, 232102241029); Doctoral Research Funding (9001/KQ1846)引文格式:冀盛亚, 常成, 常帅兵, 等. 医用镁合金微弧氧化/有机复合涂层的研究现状及演进方向[J]. 表面技术, 2023, 52(12): 315-334.JI Sheng-ya, CHANG Cheng, CHANG Shuai-bing, et al. Research Status and Evolution Direction of Micro-arc Oxidation/Organic Composite·316·表面技术 2023年12月magnesium alloy. Because it cannot be absorbed by the human body in a short time, the excessive H2 will easily gather around the implant or form a subcutaneous airbag, which will not only cause the inflammation of the implant site, but also hinder the adhesion and growth of cells in the implant, limiting its clinical application prospects. Surface modification technology can effectively delay the degradation rate of medical magnesium and magnesium alloys, and reduce the rate of hydrogen evolution.Firstly, starting from the structure and performance characteristics of organic materials (phytic acid (PA), chitosan (CS), stearic acid (SA), dopamine (DA), polylactic acid glycolic acid copolymer (PLGA), polylactic acid (PLA), and polycaprolactone (PCL)), the mechanism of improving the corrosion resistance of magnesium and magnesium alloys by a single organic coating was analyzed, and the performance weaknesses of a single coating were also pointed out: ①Micro arc oxidation (MAO) is an anodic oxidation process that generates a highly adhesive ceramic oxide coating on the surface of an alloy immersed in an electrolyte through high voltage (up to 300 V) spark discharge. The continuous high voltage discharge and the bubbles generated by the reaction bring about the inevitable occurrence of a large number of volcanic micropores and cracks in the coating. The diversity of discharge modes also gives rise to the unpredictable morphology of micropores and cracks. Therefore, the preparation of a single MAO coating on different alloy surfaces does not only require proper adjustment of MAO electrical parameters (current density, voltage, duty cycle, frequency, oxidation time) and the coupling effect of its electrolyte system to decrease (small) the pores and cracks on the MAO coating surface, but also increases the sealing process at the later stage. ② A single organic coating has a low bonding strength with magnesium alloy, being easy to flake off. These performance weaknesses limit the protection effect of a single coating on magnesium alloy degradation.Secondly, from the perspectives of bonding strength, corrosion resistance, and versatility (biosafety, biocompatibility, induced regeneration, antibacterial and antibacterial properties, drug loading and sustained-release properties, and so on), the structural characteristics and advantages of each MAO/organic composite coating were elaborated in detail. It has revealed that MAO/organic composite coating has an enormous application potentiality in the field of surface modification of medical magnesium and magnesium alloys, thanks to its good corrosion inhibition and degradation performance. On this basis, it is clearly pointed out that, in order to achieve the biological activity and versatility of medical magnesium alloy implant materials, the best way is to adopt the MAO/PCL (MAO/CS) composite coating as the base coating and make the cross combination of PCL (CS) coating and other coatings. Finally, the evolution direction of magnesium alloy MAO/organic composite coating is scientifically predicted.KEY WORDS: magnesium alloy; micro-arc oxidation; organic materials; composite coating; evolution direction作为人体所必须的营养元素,镁不但辅助600多种酶的合成(包括参与、维护DNA和RNA聚合酶的正确结构和活性),而且改善胰岛素稳定和糖类正常代谢、舒张血管、降低冠心病、高血压及糖尿病的患病风险[1]。
IntroductionMagnetic holes in a carrier ferrofluid are micrometric spherical nonmagnetic particles,whose size is orders of magnitudes above that of magnetites(0.01l m),so the ferrofluids appears homogeneous on their scale.In the presence of an external magneticfield,they generate dipolar magnetic perturbations,whose moment is the opposite of that of the ferrofluid displaced[1,2].This induces dipolar interactions between them,which can be tuned through the type of imposed externalfield. This system,first invented by Skjeltorp[1],is confined between two nonmagnetic plates,spaced by afixed distance ranging from one to ten particle diameters. The ability to design and modify the effective interac-tions in this system enables us to grow crystals of such holes and induce order/disorder transitions in them[1], to study aggregation dynamics of these particles[3],or to study the nonlinear dynamics of such magnetic holes in low-frequency rotating magneticfields[4].Under-standing these systems is important for ferrofluid industrial applications[5],or their possible use in biomedicine[6].Nonetheless,there was no satisfactory theoretical description of the effective interactions between holes in magneticfields composed of a high-frequency rotating in-plane component and a constant normal one,and the existence of stable configurations of particles with afinite distance between them[2]remained unexplained.Focusing on the boundary conditions of the magnetic fields along the confining plates,we will derive analyt-ically the pair interaction potential in such oscillating fields,and demonstrate for a wide range of them the existence of a secondary minimum whose position depends continuously on the ratio between out-of-plane and in-planefield magnitudes.We will then compare this theory with experiments where the motion of a particle pair is followed.Progr Colloid Polym Sci(2004)128:151–155 DOI10.1007/b97120ÓSpringer-Verlag2004Renaud Toussaint Jørgen Akselvoll Geir Helgesen Eirik G.Flekkøy Arne T.Skjeltorp Interactions of magnetic holes in ferrofluid layersR.Toussaint(&)ÆJ.AkselvollE.G.FlekkøyÆA.T.Skjeltorp Department of Physics,University of Oslo,P.O.Box1048Blindern,0316Oslo,Norwaye-mail:renaud.toussaint@fys.uio.noJ.AkselvollÆG.HelgesenÆA.T.Skjeltorp Physics Department,Institute for Energy Technology,2027Kjeller,Norway Abstract Nonmagneticmicrospheres in a ferrofluid layerinteract as dipoles in an externalmagneticfield.With a constantfieldnormal to the layer and anoscillating in-planefield,the spheresstabilize atfixed separations,andcan thus be trapped attunablefinite distances.We showanalytically how the susceptibilitycontrast at the system boundary isresponsible for this secondaryminimum of a pair interactionpotential,obtain the effectiveinteraction potential andequilibrium separation as afunction of the appliedfield,andexperimentally validate this theory.Keywords FerrofluidsÆMagneticholesÆRotating magneticfieldsÆEffective interactionsÆConfined systemSystem presentation and derivation of an effectivepair interaction potentialIn the presence of a far-rangefield~H in a ferrofluid of susceptibility v,each hole generates a dipolar perturba-tion of the dipolar moment equal and opposite to that of the displaced ferrofluid,~r¼ÀV v e~H,where V is the volume of the particle,and v e=3v/(3+2v)is the effective susceptibility including a demagnetization factor render-ing for the boundary conditions of the magneticfield along the spherical particle boundary[1,7].The suscep-tibility contrast between the ferrofluid and the two planar nonmagnetic confining plates leads to a different dipolar field perturbation from that in the infinite medium expression.According to the image method[8],the boundary conditions for the magneticfield along the plates are fulfilled if in addition to the infinite space expression,the dipolarfield emitted in an unbounded medium by an infinite series of dipole images is taken into account.This series consists of mirror images in the plane boundaries of the initial dipoles or of some previous image,by multiplying the magnitude of the dipole at each mirror symmetry operation by an attenuation factor j=v/(v+2)–see Fig.1.The instantaneous interaction potential between a pair of confined particles can then be expressed as[7]U¼l8pXi¼j~r iÁ~r jr ijÀ3~r iÁ~r ijÀÁ~r jÁ~r ijÀÁr ij"#ð1Þwhere l is the ferrofluid’s permeability,the i-index runsover both the source and image dipoles,and the j-indexruns only over the two source particles.A detailed analysisshows that the dominant effect for the components of theforces normal to the plates is the interaction between aparticle and its own mirror images,which stabilizes theparticles midway between the plates.This constraint istherefore adopted throughout this paper and in Fig.1.Buoyancy forces have also been checked to be negligiblefor the ferrofluid and particles used in this work.Decomposing the instantaneous far-rangefield into itsin-plane and normal components~H?and~H k,we definethe ratio of their magnitudes as b¼H?=H k,the anglebetween in-plane component and separation vector as u,the particle diameter and interplate separation,respec-tively,as a and h,and the scaled separation as x=r/h.A straightforward analysis of Eq.(1)in the configu-ration of Fig.1leads up to an additive constant to144h3Ulp a6v2eH2k¼Xþ1l¼À1j l j j1þÀ1ðÞl j j b2x2þl2ðÞ3=2À3y cos uþl bðÞy cos uþÀ1ðÞl j j l bx2þl2ðÞ5=22435:ð2ÞThe term l=0corresponds to the source–sourceinteraction term,already used in previous studies[1,2],the other terms correspond to interactions between aparticle and the images of the other one.For all existingferrofluids,j is sufficiently smaller than unity,so theprefactor ensures that the threefirst images are enough toget a relative precision better than1%for the potentialand its derivatives.The imposedfields considered consist of a constantcomponent~H?,while~H k rotates uniformly at sufficientlyhigh frequency(10–100Hz in this work).For themicrometric particles considered here(a¼50l m),inertial terms can be neglected,and a characteristicviscous relaxation time can be obtained as the time toseparate two particles initially in contact by their size,balancing the Stokes drag with the magnetic interactionforces derived from the potential.Retaining themain term l=0in Eq.(1)leads to an estimate ofT c=144g/(lv2eH2)»5s,for the ferrofluid[g=9·10–3Pa s,l=l0(1+v),v=1.9,l0=4p·10–7H m–1]and thetypicalfield H=10Oe considered here.Atfield rotationfrequencies significantly exceeding the inverse relaxationtime,the particle’s motion can be neglected during afieldoscillation,and an effective interaction potential aver-aged over time can be obtained by replacing simply theu-dependent terms in Eq.(2)by their average over anoscillation,while the slowly varying separation vector ismaintained constant,which leads to the dimensionlesseffective interactionpotential: 152u x ðÞ 144h 3Ulp a 6v e H k¼X þ1l ¼À1j l j j1þÀ1ðÞl j j b2x 2þl 2ðÞ3=2À3À1ðÞl j j l 2b 2þy 2=2x 2þl 2ðÞ5=2"#:ð3ÞFor a given ferrofluid and field,this central potential can be of four possible types as illustrated in Fig.2.At low normal field b <b m ,the interactions are purely attractive up to contact;at higher fields b m <b <b c ,a secondary minimum at finite distance appears,later on in the regime b c <b <b u this minimum becomes the only one,and ultimately interactions are purely repulsive for b u <b .For the ferrofluid used,the equilibrium separa-tion for these effective interactions as a function of b are displayed as a continuous line in Fig.3.From Eq.(3),the separating values can be shown to be b c ¼1=ffiffiffi2p ,b u =b c (1+j )/(1–j ),which is a growing function of the susceptibility diverging to infinity when the susceptibility does,and b m a function of the suscep-tibility decreasing regularly from b c at zero susceptibility to 0at infinite susceptibility –for the ferrofluid used here,b m »0.55and b u »2.05.Neglecting the susceptibility con-trast along the plates –terms l …0in Eq.(3)–would correspond to the limiting case j =0,where these three separating values merge,and the interactions are either purely attractive or repulsive.The presence of this susceptibility contrast is thus essential to trap the particles at a given equilibrium distance in this type of field.In order to confront this theory with experiments,the motion of particle pairs initially in contact in a given field was recorded through time.The dynamical equation ruling the particles in this overdamped regime is obtained by balancing the Stokes drag from the embedding fluid with the magnetic interactions,which leads to _x¼Àu 0x ðÞ,where the dot refers to derivation with respect to t ¢=t /T ,the dimensionless time,with T =3T c h 5/a 5,the unit time.The function t ¢(x )wasthen153numerically evaluated as the integral of–1/u¢from the initial a/h to the actual x value of the scaled separation, to obtain the dashed lines of Fig.3and the full line of Fig.4.Experiments and resultsThe experiments were carried using a¼50-l m diameter neutral nonmagnetic polystyrene particles designed by Ugelstad’s technique[9]and produced under the trade-mark Dynospheres by Dyno Particles,Lillestrøm,Nor-way,in a kerozene-based ferrofluid(type EMG905, Ferrofluidics,Nashua,NH,USA).The confining cell consisted of two glass plates70l m from each other,and was obtained by slightly pressing the cells together with a few h¼70-l m-diameter spacers in-between(of the same composition as the holes).The cell was placed in three pairs of Helmholtz coils,and the particle motion was recorded and digitized from optical microscopy data.The particles were initially brought into contact by applying a fast oscillating purely in-planefield,after which the constant normalfield component was added at time zero.The particle pair observed was separated from any other particle or spacer by more than20diameters, so as to avoid perturbations.A typical record of the scaled distance as a function of the scaled time,obtained for afield H jj¼14:2Oe,at b=0.8,is shown in Fig.3.In this case,the unit time is T=32s,and particles come to the predicted equilibrium distance r=2.35h after a few paring this data with the present theory(full line)and with the preexisting expression[1,2] ignoring the effect of the boundary conditions along the nonmagnetic plates(dashed line)we conclusively show the primary importance of this susceptibility contrast in explaining the existence of this secondary minimum.A range of geometric b parameters of the appliedfield was explored in a series of experiments with the same setup,and the resulting scaled separation as a function of b,for various characteristic scaled times,is displayed in Fig.4.The error bars correspond to an experimental error in b reflecting a possible angle up to2.5°of the constant field over the normal direction,which is the maximum variation of thefield orientation over the cell,calculated from its precise geometry with respect to the external coils.This error effect was calculated to be the major one owing to the slight inhomogeneity of thefield along the experimental cell.Once again,in the range b>b m»0.55 experiments and theory agree fairly well.The main discrepancy lies in the small but nonzero separation(x>50/70)for0.3<b<b m»0.55.This is believed to be due to the effect of the non-point-like character of the magnetic holes for the magneticfield, which should generate higher-order terms in a multipolar expansion at moderate separations r/a–qualitatively,the dipolar perturbationfield of a hole does not fulfill proper boundary conditions along the surface of another hole that is close enough,and a repulsive term corresponding qualitatively to taking into account images of one sphere in the other one,similar to the repulsive effect of images in the plane boundaries on its source particle,becomes sensitive at these short distances.ConclusionsWe have established the effective pair interactions of nonmagnetic particles embedded in a ferrofluid layer confined between two nonmagnetic plates,submitted to magneticfields including constant normal components and high-frequency oscillating in-plane components. Owing to the susceptibility contrast along the glass plates,a family of potentials displaying a secondary minimum at afinite separation distance has been proven to exist,which should allow us to trap nonmagnetic bodies at tunable distances via the externalfield.A system with interactions such as those described here should be relevant for any colloidal suspension of electrically or magnetically polarizable particles con-strained in layers.The realization of the detailed effective interaction potentials of this system also makes it a good candidate as an analog model system to study phase transitions[1],aggregation phenomena in complexfluids [4],or fracture phenomena in coupled granular/fluidsystems. 154References1.Skjeltorp AT(1983)Phys Rev Lett51:23062.Helgesen G,Skjeltorp AT(1991)JMagn Magn Mater97:253.Helgesen G,Skjeltorp AT,Mors PM,Botet R,Jullien R(1988)Phys Rev Lett 61:17364.Helgesen G,Pieranski P,Skjeltorp AT(1990)Phys Rev Lett64:14255.Chantrell R,Wohlfart E(1983)J MagnMagn Mater40:16.Hayter T,Pynn R,Charles S,SkjeltorpAT,Trewhella J,Stubbs G,Timmins P(1989)Phys Rev Lett62:16677.Bleaney B,Bleaney B(1978)Electricityand magnetism.Oxford UniversityPress,Oxford8.Weber E(1950)Electromagneticfields:theory and applications,vol1.Wiley,New York9.Ugelstad J,Mork P(1980)Adv ColloidInterface Sci13:101155。