Interfacial Effects and Mechanics of Liquid Crystalline Dispersions

液晶分散体的界面效应和力学

• 批准号: 0517890
• 负责人: Morton Denn
• 金额: --
• 依托单位: CUNY City College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0517890&HistoricalAwards=false
• 关键词: Interfacial; Effects; Mechanics; Liquid; Crystalline; Interfacial; Effects; Mechanics; Liquid; Crystalline

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.

拟议活动的智力化含量系统的智力优点对于各种技术应用，包括展示技术，自我增强复合材料和电学应用程序，对各种液晶分散阶段来说是感兴趣的。液晶结构不仅通过thedispersed阶段的批量特性表现出来，而且（有时甚至是）通过液晶度对静态界面区域和界面特性的影响（有时甚至是）表现出来。拟议的研究探讨了液晶/各向同性液体界面对形态和流动的影响，尤其是在近晶型系统中。在将近晶苯基碳二硝基（8CB）与聚（二甲基硅氧烷）混合时，获得了具有纳米级尺寸的双连续凝胶样液晶散布。 TheGel通过列明权稳定，然后在列明 - 异分过渡时自发过渡到分散的形态。液滴的形态是元稳定的，并且随着温度降低而对凝胶的正式形式进行了证明。我们计划进行以下实验，以前对这种非凡的动力学捕获的系统有了了解，并将液晶分散体的间接和大量力学放置在胶体凝胶的更广泛背景下：（i）光学显微镜； （ii）非线性流变学和双连续性动力学的确定； （iii）凝胶和液滴形态中的宽带介电实验。混合物中近晶相的界面力学本质上是未知的。我们计划测量针对PDM的近晶8CB的种子间质量，并对PDMS Matrix.Theotical的各向同性，nematic和enectic Sectimes的8CB液滴进行液滴变形的系统研究。该力学最终取决于液晶定向弹性的表面排序与散肌之间的相互作用。我们将在液体晶相中采用模拟退火方法进行检出分布。 8CB/PDMS系统中凝胶散热器的机制似乎是表面张力驱动的现象。由于系统似乎处于元稳定状态，并且似乎在近晶型转变处发生，并且相似的动力学捕获似乎可以防止自发的形态转化以恢复液晶凝胶。我们将研究扩展和球形同型液体晶体阶段嵌入了Aviscous Matrix中的界面张力转变的机制。在促进教学，训练和学习的同时，拟议的Activity Activitivance Advisionaldisvance发现和理解的影响。校长评估者拥有培训博士学位的既定记录。学生和博士后研究员以及将本科生纳入他的研究小组。该研究小组是本杰明·本杰明·列维奇（Benjamin Levich）物理化学水力学研究所的一部分，以及用于中学建模和模拟的NSF-Crestcenter，并且来自化学工程，生物工程，生物学工程学，机械工程，机械，机械工程和物理学和物理学和物理学和物理学和物理学和物理学的教职员工和学生之间的相互作用很大。 Denn教授是关于软材料中多尺度现象的NSF igertprogron的主要研究者，其研究小组的成员通过常规的联合研讨会和一系列新的软材料课程（包括Twolaboratoration Course的新软材料课程）与参与者进行互动。扩大了代表性不足的群体的参与。城市学院是一个城市机构，拥有85％的少数族裔学生，其中包括许多返回的学生，通常承担家庭责任。本科生定期参加软材料研究活动。我们将寻求每年最多包括两名本科生，他们成功完成了三年级运输顺序的第一部分，并希望从事本科独立研究或夏季研究。我们将从已经运作的许多计划的校园内的校园中与本科生联系，以增强科学和工程中代表性不足的团体的参与，包括有兴趣攻读博士学位的本科生的群体计划计划。计划。对社会的支持。拟议的研究解决了与各种重要技术相关的问题，并在重要材料的重要领域提供了培训机会。