Interfacial Effects and Mechanics of Liquid Crystalline Dispersions

包含液晶分散相的多相系统在显示技术、自增强复合材料和电流变应用等技术应用中具有重要意义。液晶结构不仅表现在分散相的本体性质上，而且（有时主要是）表现在液晶性对非观界面区域和界面性质的影响上。提出的研究解决了液晶/各向同性液体界面的形态和流动的影响，特别是在近晶体系。将近晶型联苯腈（8 CB）与聚二甲基硅氧烷（PDMS）混合，得到了具有纳米尺度的双连续凝胶状液晶分散体。该凝胶是亚稳定的，通过水热制度，然后经历了一个自发的过渡到disperseddroplet形态在向列-各向同性转变。液滴的形态是亚稳定的，随着温度的降低不会向凝胶转变。我们计划进行以下实验，目的是发展对这种显着的动力学捕获系统的理解，并将液晶分散体的界面和体积力学置于胶体凝胶的更广泛的背景下：（i）光学显微镜;（ii）非线性流变学和双连续形态动力学的测定;（iii）凝胶和液滴形态的宽带介电实验。共混物中近晶相的界面力学基本上是未知的。我们计划测量近晶相8 CB与PDMS的界面张力，并对PDMS基质中各向同性、近晶相和近晶相的8 CB液滴的变形和恢复进行系统的研究。力学最终由液晶取向弹性的表面有序性和体应力之间的相互作用决定。我们将采用模拟退火方法来确定液晶相的取向分布。8 CB/PDMS体系中的凝胶分散液滴转变的机理似乎是一种表面张力驱动的现象;这种转变并不发生在近晶-液晶转变处，因为该体系似乎被动力学捕获在亚稳态中，并且类似的动力学捕获似乎阻止了自发的形态转变以恢复液晶凝胶。我们将研究界面张力驱动的机制之间的延伸和球形垂面液晶相嵌入aviscous matrix.Broader影响的拟议activities推进发现和理解，同时促进教学，培训和学习。主要研究者有培训博士的既定记录。学生和博士后研究员，并将本科生纳入他的研究小组。该研究小组是跨学科的本杰明Levich物理化学流体力学研究所和NSF-CREST中心的介观建模与仿真的一部分，来自化学工程，生物医学工程，机械工程和物理系的教师和学生之间有相当大的互动。Denn教授是NSF-IGERT软材料多尺度现象项目的首席研究员，他的研究小组成员通过定期联合研讨会和一系列新的软材料课程（包括两个实验室课程）与IGERT参与者互动。代表性不足群体的广泛参与。城市学院是一个城市机构，85%的少数民族学生，其中包括许多返回的学生，往往与家庭的责任。本科生定期参加软材料研究活动。我们将寻求包括每年最多两名本科生谁已经成功完成了第三年的运输序列的第一部分，并希望追求本科独立研究或夏季研究。我们将从已经在运作的许多项目的校园中接触本科生，以提高在科学和工程方面代表性不足的群体成员的参与，包括纽约市立大学管道计划，为有兴趣攻读博士学位的本科生。对社会有益。拟议的研究解决了与各种重要技术相关的问题，并提供了软材料重要领域的培训机会。

Intellectual Merit of Proposed ActivityMultiphase systems containing liquid crystalline dispersed phases are of interest for a variety oftechnological applications, including display technology, self-reinforced composites, and electrorheologicalapplications. The liquid crystalline structure manifests itself not only through the bulk properties of thedispersed phase, but also (and sometimes primarily) through the impact of liquid crystallinity on thenanoscopic interfacial region and the interfacial properties. The proposed research addresses the effect ofthe liquid crystal/isotropic liquid interface on morphology and flow, particularly in smectic systems.Experimental. A bicontinuous gel-like liquid crystalline dispersion with nanoscale dimension is obtainedwhen a minor phase of a smectic biphenylcarbonitrile (8CB) is mixed with poly(dimethyl siloxane). Thegel is meta-stable through the nematic regime and then undergoes a spontaneous transition to a disperseddroplet morphology at the nematic-isotropic transition. The droplet morphology is meta-stable and does notreform to the gel with lowering of the temperature. We plan to carry out the following experiments, with agoal of developing an understanding of this remarkable kinetically-trapped system and placing theinterfacial and bulk mechanics of the liquid crystal dispersion in the broader context of colloidal gels: (i)optical microscopy; (ii) nonlinear rheology and determination of the dynamics of the bicontinuousmorphology; (iii) broadband dielectric experiments in the gel and droplet morphologies. The interfacialmechanics of the smectic phase in blends are essentially unknown. We plan to measure the interfacialtension of smectic 8CB against PDMS and to carry out a systematic study of droplet deformation andrecovery for 8CB droplets in isotropic, nematic, and smectic regimes in a PDMS matrix.Theoretical. The mechanics are ultimately determined by the interplay between surface ordering and bulkstresses from the liquid crystalline orientational elasticity. We will employ a simulated annealing method todetermine orientation distribution in the liquid crystalline phase. The mechanics of the gel-disperseddroplet transition in the 8CB/PDMS system seems to be a surface tension-driven phenomenon; thetransition does not occur at the smectic-nematic transition because the system appears to be kineticallytrapped in a meta-stable state, and a similar kinetic trapping appears to prevent a spontaneous morphologytransformation to recover the liquid crystalline gel. We will study the mechanics of the interfacial tensiondriven transition between extended and spherical homeotropic liquid crystalline phases embedded in aviscous matrix.Broader impacts of the proposed activitiesAdvance discovery and understanding while promoting teaching, training, and learning. The PrincipalInvestigator has an established record of training Ph.D. students and postdoctoral fellows and ofincorporating undergraduate students into his research group. The research group is a part of theinterdisciplinary Benjamin Levich Institute for Physico-Chemical Hydrodynamics and the NSF-CRESTCenter for Mesoscopic Modeling and Simulation, and there is considerable interaction among the facultyand students, who come from the Departments of Chemical Engineering, Biomedical Engineering,Mechanical Engineering, and Physics. Professor Denn is the Principal Investigator for an NSF-IGERTprogram on Multiscale Phenomena in Soft Materials, and members of his research group interact withIGERT participants through regular joint seminars and a body of new soft materials courses, including twolaboratory courses. Broaden Participation of Underrepresented Groups. City College is an urban institution with an 85% minority student body that includes many returning students, often with family responsibilities. Undergraduate students participate regularly in the soft materials research activities. We will seek to include up to two undergraduates annually who have successfully completed the first part of the third-year transport sequence and wish to pursue undergraduate independent research or summer research. We will profit in reaching out to undergraduates from the presence on the campus of many programs already in operation to enhance the participation of members of groups underrepresented in science and engineering,including the CUNY Pipeline Program for undergraduates interested in pursuing a Ph.D. program.Benefits to society. The proposed research addresses problems that are relevant to a variety of importanttechnologies, as well as providing training opportunities in the important area of soft materials.