Crystallographic Domain Engineering of Ferroelectric Single Crystals

Friday, November 19, 2010 3:00 pm – 4:00 pm (1 of 2 speakers)
Room 610, M&M Building

Jie Zhou
Graduate Student
Materials Science and Engineering
Michigan Technological University

Abstract

Phase field modeling and computer simulation is performed to study the mechanisms ofcrystallographic domain engineering technique for ferroelectrics. It is found that both domainconfigurations and domain sizes in ferroelectric single crystals can be controlled throughsophisticated thermal and electrical conditions imposed on the materials during ferroelectricphase transformations. The simulations reveal that minimal domain sizes and highest domainwall densities are obtained with intermediate magnitude of electric field applied along non-polaraxis of ferroelectric crystals, while lower and higher fields produce coarser domains and lowerdomain wall densities. It is found that temperature also plays an important role in domain sizecontrol. The simulations show that selection of polar domain variants by external electric fieldduring nucleation stage of ferroelectric phase transition significantly affects subsequent domaingrowth and evolution kinetics and controls the formation and sizes of twin-related lamellardomains. It is also found that the long-range electrostatic and elastostatic interactions generateinsurmountable energy barrier to isolated ferroelectric nucleation, and independent nucleation offerroelectric phase in the context of classical nucleation theory is impossible. In order tocircumvent such an energy barrier, ferroelectric nucleation exhibits strong spatial correlation andself-organization behaviors, and ferroelectric phase transformation proceeds via spatial andtemporal evolution of self-accommodating domains that provide a low-energy kinetic pathwaythroughout the entire phase transformation process.

Particles at Fluid Interfaces and Effects on Coarsening Kinetics

Friday, November 19, 2010 3:00 pm – 4:00 pm (1 of 2 speakers)
Room 610, M&M Building

Tianle Cheng
Graduate Student
Materials Science and Engineering
Michigan Technological University

Abstract

A newly developed diffuse interface field approach (DIFA) is employed to perform simulationstudy of particles assembly at fluid interfaces. The model employs diffuse interface fields todescribe arbitrary particle shapes as well as multi-phase fluid. It takes into account capillaryforces associated with fluid interfaces, inter-particle short-range repulsions due to mechanicalcontact and/or steric force, hydrostatic force, and Brownian motion force. The model is appliedto simulate particle self-assembly in fluid that undergoes spinodal decomposition. It is shownthat particles stabilize the two-phase fluid morphology by slowing down the coarsening kinetics,and the fluid interfaces are finally arrested by particles closely packed at the interfaces. Inparticular, the effects of particles on the curvature of the fluid interfaces are discussed. It isfound that capillary force and pressure both play important roles in equilibrium of particles atfluid interfaces as well as the interface curvature. The latter is essential for coarsening kineticsof spinodal decomposition.

The Theory of Wetting Including the Fundamentals of Designing the Superlyophobic State of Materials

Tuesday, November 9, 2010 10:00 am – 11:00 am
Room 610, M&M Building

Prof. Ludmila Boinovich
Russian Academy of Science
Moscow, Russia

Abstract

The dominant role of the long-range surface forces in wetting phenomena is widely accepted. Theoretical grounds of the design of hydrophobic materials and coatings and the specificfeatures of the superhydrophobic state of the surface will be discussed on the basis ofthermodynamic and using the concept of surface forces which are characterized by the isothermof disjoining pressure. This concept allows one to explain the peculiarities of wetting and toshow that in general, bulk liquid (drop or concave meniscus) coexists with the substrate which isnot dry, but coated by wetting or adsorption film of liquid. The problems of ageing anddegradation of syperhydrophobic coatings will be outlined.

Biography

Scientific career of Ludmila Boinovich began in 1980s in the laboratory of famous Russian scientistB.V. Derjaguin. Her research activities, both theoretical and experimental, have been centered on molecular andsurface physics. She has discovered and studied several new physical mechanisms of surface forces including thephonon mechanism of surface forces, explaining the influence of confining phases on inter- and intramolecularinteractions in the intervening liquid layer. She has introduced the notion on dynamic structure of liquid innanosystems, characterized by the density of vibrational states. The analysis of the dispersion systems withmulticomponent dispersion phase allowed her to made pioneering advances at the theoretical level, for imagecharge mechanism of surface forces, associated with the polarization of confining phases by the electrostatic fieldof solute molecules. Her studies on phase transitions in nano-sized systems lead to establishing the physicochemical parameters determining the shift of melting/freezing temperatures at the interfaces, in wetting films,aerosols and porous matrices. Ludmila Boinovich and her team have developed a series of new spectroscopicmethods and devices for studying the structure of liquids in nanosize systems and have found experimentally thethickness dependent deviation of liquid structure in thin layers.

Among various awards and honors she received the Gold medal of ICEPEC (Institut Communautaire Europeenpour la Promotion des Enterprices Commerciales) for her contribution to the promotion of scientific results inengineering applications. She has earned a reputation as an outstanding lecturer and teacher who has motivatedand inspired the younger generations of Russian surface and colloid physicists. In 2006 Prof. Boinovich waselected to be a Corresponding Member of Russian Academy of Sciences.

The Modern State of the Theory of Surface Forces in Colloid Systems and Thin Liquid Films

Monday, November 8, 2010 3:00 pm – 4:00 pm
Room 610, M&M Building

Prof. Ludmila Boinovich
Russian Academy of Science
Moscow, Russia

Abstract

A modern physical theory, which describes the state and stability of liquid films and thedispersed and colloid systems, is based on the analysis of the surface forces acting across thinliquid films separating particles or macroscopic bodies. The major recent advances in the theorywill be considered. Limitations intrinsic in the conventional DLVO theory will be briefly outlined.Studies devoted to the analysis and calculations of non-DLVO interactions of different nature willbe reviewed. Particular attention will be paid to the forces caused by the inhomogeneity of liquidinterlayers. The applicability of the known approaches for solving the nanotechnologychallenges will be discussed.

Biography

Scientific career of Ludmila Boinovich began in 1980s in the laboratory of famous Russian scientistB.V. Derjaguin. Her research activities, both theoretical and experimental, have been centered on molecular andsurface physics. She has discovered and studied several new physical mechanisms of surface forces including thephonon mechanism of surface forces, explaining the influence of confining phases on inter- and intramolecularinteractions in the intervening liquid layer. She has introduced the notion on dynamic structure of liquid innanosystems, characterized by the density of vibrational states. The analysis of the dispersion systems withmulticomponent dispersion phase allowed her to made pioneering advances at the theoretical level, for imagecharge mechanism of surface forces, associated with the polarization of confining phases by the electrostatic fieldof solute molecules. Her studies on phase transitions in nano-sized systems lead to establishing the physicochemical parameters determining the shift of melting/freezing temperatures at the interfaces, in wetting films,aerosols and porous matrices. Ludmila Boinovich and her team have developed a series of new spectroscopicmethods and devices for studying the structure of liquids in nanosize systems and have found experimentally thethickness dependent deviation of liquid structure in thin layers.

Among various awards and honors she received the Gold medal of ICEPEC (Institut Communautaire Europeenpour la Promotion des Enterprices Commerciales) for her contribution to the promotion of scientific results inengineering applications. She has earned a reputation as an outstanding lecturer and teacher who has motivatedand inspired the younger generations of Russian surface and colloid physicists. In 2006 Prof. Boinovich waselected to be a Corresponding Member of Russian Academy of Sciences.

Electromechanical Molecular Actuators Based Quantum Mechanical Mechanisms

Thursday, November 4, 2010 11:00 am – 12:00 pm
Room 610, M&M Building

Prof. Miklos Kertesz
Department of Chemistry
Georgetown University
Washington DC

Abstract

Charged or neutral radicals often display π-stacking geometries that show signs ofintermolecular covalent bonding based on the partial occupancy of π-orbitals. This interaction issensitive to the number of π-electrons available for this bonding and goes beyond van derWaals interactions. We analyze known cases of intermolecular π-bonding in various radicaldimers and chains and connect the intermolecular bonding properties to observed properties.The simulations involve molecular and periodic first principles density functional theorycalculations. Various stacked chains are analyzed for their suitability as electrochemically drivenactuating molecules and compared with other mechanisms of electrochemical actuationincluding those based on polyacetylene and carbon nanotubes as well as those based onlocalized 2 center/3 electron bonds.

Relevant references

“Dimensional Changes as a Function of Charge Injection in Single Walled Carbon Nanotubes”Sun, G.Y.; Kürti, J.; Kertesz, M.; R. H. Baughman,  J. Am. Chem. Soc. 2002, 124, 15076-15080.

“Electronic Structure of Helicenes, C2S Helicenes, and Thiaheterohelicenes”Yong-Hui Tian, Gyoosoon Park, Miklos Kertesz, Chem Mater. 2008, 20, 3266-3277.

“Molecular Actuators Designed with S…N(sp(2)) Hemibonds Attached to a ConformationallyFlexible Pivot“ Tian, Y.-H.; Kertesz, M. Chem. Mater. 2009, 21, 2149-2157.

“Is There a Lower Limit to the CC Bonding Distances in Neutral Radical ?-Dimers? The Case ofPhenalenyl Derivatives”, Tian, Y.-H.; Kertesz, M. J. Am. Chem. Soc. 2010. 132, 10648-10649.