A simulation study of twisted crystal growth in organic thin films has recently been published in Physical Review E [view pdf or view at publisher]. We developed a phase-field model that energetically favors twisting of the 3D crystalline orientation about and along particular axes, allowing us to simulate a variety of morphologies, including banded spherulites, curved dendrites, and “s”-shaped or “c”-shaped needle crystals. In curved dendrites, we find that the twisting rate affects not only the morphology but also the kinetics of crystallization.
Our investigation of the assembly dynamics of membraneless biological organelles was published this week in the online Early Edition of Proceedings of the National Academy of Sciences [view pdf or view at publisher]. In collaboration with Stephanie Weber, Nilesh Vaidya, and Cliff Brangwynne from the Department of Chemical and Biological Engineering, we have shown that the assembly dynamics of liquid-phase nuclear bodies (condensed droplets rich in RNA and protein) in C. Elegans embryos can be explained by classical models of phase separation and coarsening long associated with nonliving condensed matter – namely Brownian coalescence and, to a lesser degree, Ostwald ripening. Our findings also indicate that highly nonequilibrium biological activity such as rRNA transcription, rather than fundamentally altering the passive phase separation mechanisms, can act to locally modulate the thermodynamic parameters governing phase separation, thus locally fine tuning organelle size and stability in response to developmental or environmental conditions.
A study of capillary effects in channel-guided crystallization of organic thin films was recently published in APL Materials [view pdf or view at publisher]. An analytical expression was derived for the growth velocity of crystallization guided along a channel defined by differential growth rates. The equation was validated with phase-field simulations and then fit to experimental data for solvent vapor annealed thin films of TES ADT, which yielded the ratio of interfacial energy to bulk thermodynamic driving force and the minimum feature size that can be patterned with this technique.
A study of bulk metallic glass systems from the group has recently been published in the journal “Modelling and Simulation in Materials Science and Engineering.” This work addresses the problem of catastrophic failure via intense plastic strain localization. Employing a non-linear continuum model, we show that the precipitation of crystalline particles yields microstructures that delay the propagation of incipient shear bands and ultimately result in improved ductility characteristics. See the research page for more information on this topic.
At this year’s MAE research day, an annual event where graduate students in the department share their research, Alta represented the materials area and won first place for her talk on modeling crystallization in organic thin films. At the MAE welcome back BBQ, Alta was also recognized for receiving the Larisse Rosentweig Klein Memorial Award, which is presented to a post-general female graduate student who shows outstanding promise in graduate research.
“Blossoming Crystals”, Alta’s video entry in the 2014 Princeton Art of Science competition, was one of 12 videos selected as finalists from over 50 submissions. The video is being displayed in the Friend Center at Princeton University through April 2015. Learn more about how phase-field modeling was used to produce the variety of crystal morphologies shown in the video by reading this publication in Physical Review E.
A recent study of metallic phase coarsening in the anode of solid-oxide fuel cells has been published in Acta Materialia. [R. Davis, F. Abdeljawad, J. Lillibridge, M. Haataja. Acta Materialia 78, 2014.] Using phase field methods, this investigation revealed a strong dependence of performance-critical microstructural features on the interfacial wetting properties of the anode materials. These efforts open a new avenue towards the optimization of anode performance and advance microstructural characterization of composite materials. The image to the left shows a representative metallic structure resulting from simulation with the interface colored by contours of surface curvature.
Mikko was invited to speak at the CECAM workshop “Multiscale modeling of materials with atomic scale resolution using phase-field-crystal methods (MULTIMAT)” which took place May 21-23 on the campus of EPFL in Lausanne, Switzerland. Joel stood in for Mikko and gave a talk entitled “Atomistic Modeling of Crystal Plasticity and Creep Deformation with the Phase Field Crystal Approach”. A week full of familiar faces – and in a beautiful location.
Joel attended the MRS spring meeting this April in San Francisco and presented a talk entitled “Physically-Based Modeling of Redox Reactions and Mechanical Instability in SOFC Anode Materials“. His talk covered new results and work in progress concerned with extending Abdel’s model for redox damage. The Li-ion battery and SOFC modeling sessions were well-attended all week, a great time to be in San Francisco!