Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Y14: Nonequilibrium and Templated Assembly |
Hide Abstracts |
Sponsoring Units: DFD Chair: Jack Douglas, National Institute of Standards and Technology Room: 315 |
Friday, March 20, 2009 8:00AM - 8:12AM |
Y14.00001: Speeding up the understanding of Vertical Deposition of Diluted Colloids Wenceslao Gonz\'alez-Vi\~nas, Maximiliano Giuliani, Moorthi Pichumani We measured the speed of contact line in vertical deposition of diluted micron sized polymeric colloids. We correlated these results with the obtained morphologies for the deposits. We show that low velocities correspond to the formation of monolayer and high velocities to multilayer. These new results are explained in terms of the local concentration of particles in the suspension near the contact line and the porosity of the pre-deposited structure. The effect of an applied electric field to the system is also reported. [Preview Abstract] |
Friday, March 20, 2009 8:12AM - 8:24AM |
Y14.00002: Kinetics of formation and disintegration of ionic and non-ionic spherical micelles Gunjan Mohan, Dmitry Kopelevich Dynamics of self-assembly and structural transitions in amphiphilic systems play an important role in various industrial and biological processes. Main challenge in computational modeling of these dynamics is a complex interplay between various length- and time-scales. In this talk, we discuss development of a multi-scale model for formation and disintegration of non-ionic and ionic spherical micelles. This study is performed under the assumption that the dominant mechanism of micelle formation (disintegration) is a stepwise addition (removal) of individual surfactant monomers to (from) a surfactant aggregate. A series of molecular dynamics simulations is used to develop reduced stochastic models for these elementary processes. It is demonstrated that these processes involve complex interactions of the translational degree of freedom (i.e., distance between centers of mass of the aggregate and the monomer) with degrees of freedom corresponding to the monomer orientation and the micellar shape and microstructure. [Preview Abstract] |
Friday, March 20, 2009 8:24AM - 8:36AM |
Y14.00003: Using fluid flow to control the structure of soluble surfactants deposited through receding contact lines. Benjamin Beppler, Kalyani Varanasi, Stephen Garoff, Kristina Woods, Guennadi Evmenenko Moving contact lines are often used to deposit soluble organic molecules in applications such as spin coating and dip coating. In this study, we demonstrate that altering the flow field near such a contact line fundamentally changes the deposited surfactant structure. At slow contact line speeds, the substrate emerges dry. The rolling fluid motion near the contact line deposits a densely packed, tilted monolayer of surfactant along the emerging solid-vapor interface. Above a critical contact line speed, an evaporating thin film is entrained on the emerging substrate. Surfactant concentration constantly increases in this confined environment due to solvent evaporation. Monodisperse crystalline islands nucleate and grow on the surface with sizes and shapes controlled by varying the deposition conditions. These results contrast with disordered deposits that result from evaporation at a pinned contact line. Our results suggest that dip-coating with control of dipping speed and evaporation rate produces unique assembled structures and may provide better control of deposition through moving contact lines. [Preview Abstract] |
Friday, March 20, 2009 8:36AM - 8:48AM |
Y14.00004: Rapid Convective Deposition For Fabrication of Microlens Arrays James Gilchrist, Pisist Kumnorkaew, Nelson Tansu, Yik-Khoon Ee Micron-sized microspheres were deposited into thin films via rapid convective deposition, similar to the `coffee ring effect' using a similar method to that studied by Prevo and Velev, Langmuir, 2003. By varying deposition rate and blade angle, the optimal operating ranges in which 2D close-packed arrays of microspheres existed were obtained. Previous models do not consider the effect of blade angle and blade surface energy on the deposition rate. Using a confocal laser scanning microscope, dynamic self-assembly of colloidal particles under capillary force during solvent evaporation was revealed. The resulting microstructure controlled by varying the macroscale parameters and interaction between substrate and colloidal particles played an important role in formation of ordered crystalline arrays. These interactions were explored through a model comparing the residence time of a particle in the thin film and the characteristic time of capillary-driven crystallization to describe the morphology and microstructure of deposited particles. Fabricated microlens arrays assembled on LEDs using this process were demonstrated to enhance performance by 300{\%}. [Preview Abstract] |
Friday, March 20, 2009 8:48AM - 9:00AM |
Y14.00005: Permanent Flow-Induced Phase Transitions in Wormlike Surfactant Micelle Solutions Mukund Vasudevan, Eric Buse, Amy Shen, Bamin Khomami, Radhakrishna Sureshkumar It is well known that certain wormlike micelle solutions form flow-induced structures under shear flow. This structure transition is typically accompanied by an enhancement in the shear viscosity and the emergence of a new gel phase. However, such transitions are generally believed to be reversible, i.e., upon flow stoppage, the structure relaxes to equilibrium. In this work, we show that by subjecting translucent wormlike micelle solutions to high flow deformation over a rapid time scale, permanent flow-induced structures can be formed. We will discuss the phenomenology and plausible physical mechanisms underlying this discovery. [Preview Abstract] |
Friday, March 20, 2009 9:00AM - 9:12AM |
Y14.00006: Understanding the structure of porous materials created by freeze casting Stephen Barr, Erik Luijten When a suspension of colloidal particles in water freezes, dendrites of ice with high aspect ratios are formed which can either engulf or reject the particles based on their size and the velocity of the advancing ice front. As the particles are pushed between the dendrites, concentrated regions of colloidal particles are formed. Recent experiments have shown that this can be exploited to create strong, lightweight, porous materials. We investigate this process using molecular dynamics simulations, focusing on the effect of the ice front velocity on the structure of the resulting material. We develop a simulation model which accounts for particle engulfment or rejection by the dendrites. We study both columnar and lamellar geometries. Our main finding is that variation of the front velocity not only affects the particle concentration in the interdendritic regions, but also the degree of order of the resulting solid. [Preview Abstract] |
Friday, March 20, 2009 9:12AM - 9:24AM |
Y14.00007: End-Functionalized Triblock Copolymers as a Guide for Nanoparticle Ordering Rastko Sknepnek, Joshua Anderson, Monica Lamm, Joerg Schmalian, Alex Travesset Using molecular dynamics simulations we show that triblock copolymers, designed to have specific affinity for nanoparticles at the chain ends, can successfully mediate assembly of nanoparticle/copolymer composites. In this talk, we will present a detailed investigation of the phase diagram of these nanocomposites as a function of both nanoparticle size and concentration. We find a rich phase diagram with two striking features. The first is the existence of an unconventional square columnar phase of two interpenetrating line-lattices of micellar cylinders and aligned nanoparticles, and the second is a drastically enhanced stability of the gyroid phase. We interpret the origin of the square columnar phase by making an analogy to the packing of binary mixtures of disks. Based on the analysis of stretching of copolymers we argue that nanoparticles help stabilize gyroid order and drastically widen the region of its stability. Our study suggests that combining nanoparticles with functionalized block copolymers can provide a simple and efficient tool for assembling novel materials with nanometer scale resolution. [Preview Abstract] |
Friday, March 20, 2009 9:24AM - 9:36AM |
Y14.00008: Unexpectedly wide distributions in the stochastic synthesis of functionalized nanoparticles. Jack Waddell, Douglas Mullen, Bradford Orr, Mark Banaszak Holl, Leonard Sander Functionalized nanoparticles are promising devices with a variety of applications, such as the targeted delivery of chemotherapy drugs to cancer cells. Their properties depend on the specifics of the distribution of functional groups on the nanoparticle. Stochastic ligand conjugation is an efficient strategy for synthesizing large quantities of functionalized nanoparticles. We developed a kinetic model for the study of ligand distribution on a generation 5 poly(amidoamine) dendrimer, as measured by HPLC and SPR. We found a cooperative effect in single species ligation, leading to a broader-than-Poisson distribution of ligands on nanoparticles, and suggesting a high spatial correlation of functional groups. [Preview Abstract] |
Friday, March 20, 2009 9:36AM - 9:48AM |
Y14.00009: Self assembly of silica nanoparticles in a surfactant mesophase K. Sharma, K. Guruswamy, O. Mondain-Monval, I. Ly We examine the organization of silica particles in a hexagonal mesophase of a non-ionic surfactant, C$_{12}$E$_{9}$ in water. The mesophase has a characteristic length scale (cylinder center-to-center distance, a $\sim $ 5.7 nm). We vary the size of the silica particles from $\sim $ 2 nm ($<$ a) to $\sim $500 nm ($>>$ a), to examine the effect of particle size, and use a combination of SAXS, freeze fracture TEM and optical microscopy to characterize our materials. We show that particles $<$ a behave like a solvent and template the mesophase. Particles with a size $\sim $ a are partitioned into a dispersed phase and into strand-like aggregates. Particles $>$ a phase separate from the mesophase and form strand-like aggregates that organize into a network. The formation of this network is reversible and heating into the high temperature isotropic phase leads to dispersion of the particles. Unusually an \textit{increase} in hexagonal-isotropic transition temperature is seen for the mesophase-particle composites. We show that the network forms by expulsion of the particles from growing hexagonal phase domains -- as these domains grow, the particles are concentrated in the isotropic regions until they jam to form the network. We show that we are able to tune the mesh size of the particulate networks by changing the cooling rate. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700