Non-Technical Abstract: Despite their natural abundance and wide industrial applications, such as red blood cells and clay, disks are least studied compared to spheres and rods. This condensed matter physics project will establish the long waited model micro-disks using unique methodology, shape transformation of liquid crystal emulsions and exfoliation of layered inorganic crystals. Micro-disks will be mass-produced with unprecedented uniformity in size and shape, and unprecedented flexibility in the control of size, shape, size-polydispersity and aspect ratio. Underlining the unique flow characteristics and applications of disk materials, the discotic liquid crystal phase transitions will be investigated experimentally and theoretically regarding their dependence on inter-disk interactions, disk aspect ratio and polydispersity. The achievement of controlled organization of discotic molecules and colloids will impact industries such as pharmaceuticals, medicine, oil refining, chemical process, solar energy, nano-composite engineering and photonics. Colloidal discotics will help to unleash the educational power of complex fluids as models of atomic discotic liquid crystals and tangible elements of the macroscopic world. This project will use visualization and multimedia tools to train graduates, to build educational modules for undergraduates, and to attract k-12 students into scientific research. It will also establish collaborations around the world to enhance the global impact of its research and education program.

Technical Abstract

This condensed matter physics project will use unique methodology (shape transformation of liquid crystal emulsions and exfoliation of layered inorganic crystals) to mass-produce micro-disks with unprecedented uniformity in size and shape, and unprecedented flexibility in the control of size, shape, size-polydispersity and aspect ratio. The discotic liquid crystal phase transitions isotropic or liquid-like to orientationally order or nematic (I-N), nematic to crystal (N-C), and nematic to ordered layer-like or smectic (N-S) will be investigated experimentally. The nematic-to-smectic (N-S) transition is one of the main unsolved problems in statistical physics. Theory will be constructed and experimentally tested regarding the dependence of phase transitions on inter-disk interactions (screened electrostatic repulsion, depletion attraction), aspect ratio and polydispersity. The achievement of controlled organization of discotic molecules and colloids will impact industries such as pharmaceuticals, medicine, oil refining, chemical process, solar energy, nano-composite engineering and photonics. Colloidal discotics will help to unleash the educational power of complex fluids as models of atomic discotic liquid crystals and tangible elements of the macroscopic world. This project will use visualization and multimedia tools to train graduates, to build educational modules for undergraduates, and to attract K-12 students into scientific research. It will also establish collaborations around the world to enhance the global impact of its research and education program.

Project Report

Despite their natural abundance and wide industrial applications, such as red blood cells and clay, disks are least studied compared to spheres and rods. By unprecedented control of nanoplate morphology (shape, size, thickness and their distribution), this project created a model system to develop discotic liquid crystal research to its full fledge. The project has yielded 15 peered reviewed Journal publications, and contributed to the development of one technology "nanoplate surfactants" based on the surface modification. It has contributed to the further understanding, engineering and utilization of the soft condensed matter. The project has revealed the control role of aspect ratio (thickness over size) in the phase behavior of colloidal disks, i.e., the formation of isotropic (I) phase , Nematic (N) and other possible liquid crystal phases, including twisted nematic (N*), Twisted Grain Boundary (TGB), tilted Smectic (SC), and Smetic (SA). It has discovered that size polydispersity broadens the I-N transition. It has established optical method to directly observe the nucleation and growth of the liquid crystal phases, and the dynamics of defects in the liquid crystals. X-ray densitometry measured the equation of state of the isotropic phase and revealed the I-N transition. The project discovered the phase behavior sensitively depends on charge, temperature, depletion attraction. It found surprising chiral structures for apparently non-chiral plates, presumably due to the charge decoration on the surface. The N-S transition is also sensitive to the charge screening by salt in the solvent. The project has fabricated temperature responsive disk using gamma-ray initiated graft of PNIPAM on the disk surface and discovered soft disks can form liquid crystal at less-degree of anisotropy than charged disks. The nanoplate surfactants developed (Janus and Gemini nanoplates) are ideal surface active particles, having the highest "interfacial area per atom", for making Pickering emulsions and foams, which has applications in enhanced oil recovery, fire fighting for LNG and others, nano-encapsulation for Phase changing materials, drugs and vaccines. The achievement of controlled organization of discotic molecules and colloids will impact industries such as pharmaceuticals, medicine, oil refining, chemical process, solar energy, nano-composite engineering and photonics. The project has supported two female PhD and one Hispanic male PhD students. Each student received training in soft matter physics (colloidal and surface science, liquid crystal experiments and theories, polymer science, microfluidics, electrospray, nanocomposites), nano material synthesis and functionalization, microscopy (optic, confocal, polarizing, SEM,TEM), light and x-ray scattering, data and image analysis, technical writing and publishing, and presentation of results (AICHE and APS meetings). Students mentor undergraduate students, a great training toward academic career or leadership position in industrial settings. Both female students are now postdoc fellows aiming to pursue a faculty position in the near future. The Hispanic student, among many distinguished honor, has been honored the inaugural Dwight Look College of Engineering Outstanding Graduate Student Award, only two students in the college have been awarded. He is now working in the Shell Oil Research Lab at Houston. Nine undergraduate students have worked in the PI lab on tasks related to this project (surface functionalization of ZrP platelets, fabrication of wax disks, and synthesis of nematic hydrogels) via honored class, directed research, international internship, or REU program. All of them have the hands-on experience on scientific research for the first time. They are in close interaction with the graduate students and other group members, very good introduction to their possible graduate studies. Several of them have been co-authors of peer-reviewed Journal publications. One high school student has worked on the fabrication of Li battery using MoS2 disks in his science project which is closely related to this project. He has hands on experience with the nano-particle synthesis, complex fluids handling, and a 'peek' into discotic liquid crystals. This will be a great introduction to his college education. Two high school students have received training in scientific research via this project. One of them has attend the school science and Engineering fair using the research results she obtained and awarded honorable mention, an internship opportunity at Houston Museum of Natural Science and qualification of the international science fair (I-SWEEEP) in May 2012. In 2010, she won the bronze medal at ISWEEEP for a project titled "Disk stabilized emulsions" that was carried out in the PI’s lab. She is now in College. Teamed with Prof. Philip Galanter at TAMU we have created colorful art work from the discotic liquid crystals: Dynamic paintings, which enhanced the educational value of our project. Based on the research accomplished in this project, a microgravity project "Liquid Crystals of Nanoplates," is established in response to NASA’s Research Announcement, Research Opportunities in Complex Fluids and Macromolecular Biophysics. The PI has established strong international collaborations in Spain, Norway and China through this project. He organized an annual symposium of "China Soft Matter Day", which has been held so far 3 times.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Application #
1006870
Program Officer
Guebre X. Tessema
Project Start
Project End
Budget Start
2010-07-15
Budget End
2014-06-30
Support Year
Fiscal Year
2010
Total Cost
$294,000
Indirect Cost
Name
Texas Engineering Experiment Station
Department
Type
DUNS #
City
College Station
State
TX
Country
United States
Zip Code
77845