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An atom is cooled by a standing-wave light field between two high-quality mirrors. Cavity cooling avoids the usual light scatter into the surroundings. Instead, the light leaking out of the mirrors is blue-shifted to a higher frequency (image credit: Pepijn Pinkse Max Planck Institute of Quantum Optics)
Artist's impression of an atom cooling device
NECF Meeting Abstracts

57th New England Complex Fluids Meeting
Boston University | Friday, December 13, 2013
Registration deadline: Wednesday, December 11, 2013

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Abstracts for Invited Talks and Sound Bites:

Invited Talks

Sound Bites

1. Adams; Thomas Kodger and David Weitz

Harvard University
"Chiral Double Emulsions: Breaking Symmetry with Microfluidics"
A surprisingly robust route for the bias production of single handed chiral structures has been found in generating non-spherical, multi-component double emulsions using glass micro‡fluidic devices. I will show that channeling aqueous fl‡uids through narrow orifices of a multi-bore injection capillary and encapsulating these different fluids as drops inside an ultra-thin sheath of oil is sufficient to produce micron-size chiral structures that break left-right symmetry.
Keywords: breaking symmetry; chirality; microfluidics; double emulsions

2. Ban; Catalin R. Picu

Rensselaer Polytechnic Institute
"Strength of DNA Sticky End Links"
Two DNA molecules can be linked by association of dangling bases at their ends. This forms a DNA sticky end link. Such structures are observed in artificial self-assembled DNA crystals as well as in cells during homologous recombination. Here the strength of these structures is studied for links of various length and base sequences. The links are divided into two groups based on their stability and mechanism of failure. Also a specific sequence is introduced that gives unusual stability to the links.
Keywords: DNA Slef-Assembly, Molecular Dynamics Simulation, Mechanics

3. Bartlett; James Bird

Boston University
"Drainage of Bare Ultra-Viscous Bubbles"
Liquid films, such as those found in soap bubbles, have previously been studied for their impact in meteorology, disease transfer, and physics. When a gas bubble rises to the surface from a bulk liquid it is expected to eventually pop. Prior to popping the bubble forms a thin spherical cap that drains slowly over time. Eventually, the film becomes sufficiently thin and ruptures. Depending on the dynamics following the rupture, the film may either rapidly disintegrate into droplets, retract and form wrinkles, or deflate and collapse back into the bulk. Theories describing these rupture dynamics are largely based on the film thickness profile at the time of popping. However, a model describing the complete film thickness during the drainage process consistent with experiments is not available. Here we demonstrate a universal model for film drainage up to the time of rupture consistent with experimental results for a range of bubble sizes. Additionally, we find viscous bubble films to be orders of magnitudes thicker than previously thought. Knowledge of film thickness profiles will better the understanding of post-rupture dynamics.
Keywords: bubble drainage, ultra viscouse

4. Basu; Dave Weitz

SEAS, Harvard University; Broad Institute
"Simulating flow in Microfluidic devices using COMSOL"
Estimating flow conditions in microfluidic devices for complex, multiphase systems is challenging. We use a commercial software, COMSOL that uses finite element analysis to estimate flow behavior in different geometries and at different fluid velocities and mixing ratio. This can be used as a tool to estimate device design and flow conditions.
Keywords: laminar, two-phase, reverse emulsion

5. Burke; Badel Mbanga, Timothy Atherton

Tufts University
"Packing on ellipsoids: curvature, dislocations, and symmetries"
Arrested relaxation occurs when an emulsion droplet is prevented from relaxing to an equilibrium spherical shape due to the jamming of colloidal particles adsorbed on its surface. We generated simulated packings of spheres on ellipsoidal surfaces in order to understand the influence of curvature on the jammed structures that form. A nontrivial coupling between dislocation density and Gaussian curvature is observed. For systems with few particles (n<200), we characterize the symmetries of the resulting configurations.

6. Farah; Dipti Sharma

Lasell College
"“RPPTM” Teaching Model to Health Sciences Majors"
Teaching Physics to Health Science (HS) majors is a challenging task. It is hard to find a connection between traditional laboratory investigations and physical concepts for non-major students taking a general physics course. To attempt to relate physics content to allied health practices, we are introducing a new teaching model termed “RPPTM”. Within this model, we required a research based project as part of the laboratory course in order to engage students in observing actual physical actions/reactions and then applying physics principles. Students conducted a short literature review, defined variables, developed a methodology prior to beginning their experimental work, performed experiments using real time data loggers and digital video analysis method and concluded with a semester end presentation. Some of the real life projects are as follows: forces exerted by athletic shoes during plyometric jumping exercise; the effect of jump height on a horse’s legs during cross-country eventing; and concussive forces resulting from the impact of a lacrosse ball on helmet.
Keywords: Physics, Health Science, Teaching Methods, Non-majors, Teaching Model

7. Foster; Dan Needleman

School of Engineering and Applied Sciences, Harvard University
"Self-Organization of Microtubule Structure in Xenopus Egg Extract"
Recently, there has been great interest in studying active matter systems, which are collections of components that interact in a way that locally consumes energy. These non-equilibrium systems are characterized by collective organization and pattern formation on a length scale much larger than the component size. Examples of active matter systems include flocking birds, nematics of vibrating rods, and systems of purified motors and cytoskeletal filaments. In this talk, I will present preliminary results on the collective organization of microtubules in Xenopus llaevis oocyte extract. Xenopus extracts contain biologically relevant concentrations of motor proteins and cross-linking proteins, and are capable of assembling the meiotic spindle, a biologically important microtubule based structure that segregates DNA at cell divisions. Through studying these collective interactions, we hope to gain insight into both spindle self-organization and active matter systems in general.
Keywords: microtubules, active matter, cytoskeleton, self-organization

8. Geng; Prof. Ophelia Tsui

Boston University
"Viscosity of high molecular weight polymer films under nano-confinement"
Our previous experiment shows that low molecular weight polystyrene nanometer films have reduced viscosity with decreasing film thickness and a two-layer model is able to explain the data. In this talk, I shall report new data obtained from high molecular weight polystyrene films indicating that a mechanism different from the two-layer model operates in bringing the viscosity reduction.
Keywords: two-layer model, nano-confinement, chain pinning

9. Gottesman; Efi Efrati, Shmuel Rubinstein

School of Engineering and Applied Sciences, Harvard University
"Furrows in the wake of propagating d-cones"
We investigate the formation dynamics of plastic creases in thin elasto-plastic sheets. In contrast to the commonly accepted description of crumpled thin sheets, which asserts that creases form only by elastic interaction between two d-cones, the creases we study in this letter are created by plastic deformations left in the wake of a single propagating d-cone. Upon application of load, a d-cone initially remains stationary and responds by deforming globally. However, above a critical load, the d-cone undergoes a sharpening transition that focuses the stresses at its tip, allowing it to propagate along the sheet, leaving a furrow-like scar in its wake. Our results show that the dynamics of plastic defect creation are important for predicting the final geometry and statistics of a defect network in a crumpled thin sheet.
Keywords: Thin sheets, plasticity, crumpling, d-cones

10. Gruver; R. Glynn Holt

Boston University
"Acoustic levitation of gels: a proof-of-concept for thromboelastography via levitation"
Current thromboelastography in the clinic is flawed by its extensive contact between the measurement apparatus and the blood being studied. An alternative technique employs levitation of a small droplet to limit contact with the blood sample to air alone. In the past, ultrasonic levitation has been used to study the material properties of aqueous solutions. In this study, ultrasonic acoustic levitation was used to levitate small viscoelastic samples (approximately one cubic millimeter in volume). Gelatin was used as a stand-in for blood to establish the validity of the ultrasonic levitation technique on viscoelastic materials. Liquid data was first taken to benchmark the apparatus, then studies were performed on set and setting gelatin gels. Relationships between gelling time/concentration and gel firmness were demonstrated.
Keywords: Gels, Acoustic Levitation, Thromboelastography

11. Hardcastle; Rama Bansil

Boston University
"Influence of Cell Shape on the Motility of Helicobacter Pylori"
Bacteria's body shape plays an important role in motility by effecting chemotaxis, swimming mechanisms, and swimming speed. A prime example of this is the bacteria Helicobacter Pylori; whose helical shape has long been believed to provide an advantage in penetrating the viscous mucus layer protecting the stomach lining, its niche environment. To explore this we have performed bacteria tracking experiments of both wild-type bacteria along with mutants, which have a straight rod shape. A wide distribution of speeds were found, reflecting both temporal variation and different shape morphologies in the bacterial population. Body shape appears to play less of a role in a simple fluid, while in a more viscous solution the helical shape results in increased swimming speeds. In addition, we use experimentally obtained cell shape measurements to model the hydrodynamic influence of cell shape on swimming speed using resistive force theory.
Keywords: Bacteria Motility, Bacteria Shape, Mucin

12. Jones; William Hanna, Jonathan Celli

University of Massachusetts Boston
"Investigating the mechanical microenvironment of 3D pancreatic tumor models using particle tracking microrheology "
Recent advances in cancer biology highlight mechanotransduction as an important mechanism in tumor growth and metastasis. Building off of established particle tracking microrheology protocols, we have adapted a method for measuring longitudinal, intra-sample variations in the mechanical properties of 3-dimensional tumor models in order to better understand the interactions between rheology, tumor behavior, and treatment response. To validate our methods, we have explored the effect of fibroblasts and the broad spectrum matrix metalloproteinase inhibitor, Marimastat on the invasive progression of Panc-1 tumor spheroids embedded in collagen. These experiments coupled with custom automated image analysis software to measure treatment response may prove to be a useful tool in describing the physical mechanisms at the heart of photodynamic therapy.
Keywords: particle tracking microrheology, 3D tumor models, stroma, photodynamic therapy, matrix metalloproteinase inhibitor

13. Mbanga; Marcelo A. Dias, Timothy J. Atherton, Thomas Powers

Tufts University
"Programmed shape change of thin sheets of Nematic Liquid Crystal Elastomers"
Nematic liquid crystal elastomers are synergetic materials that show a strong coupling between orientational order and the elasticity of the polymer matrix; thus they are viewed as excellent candidates for soft actuators and artificial muscles. We report on recent analytical and numerical studies of thin sheets of nematic liquid crystal elastomers undergoing prescribed macroscopic shape change.
Keywords: Nematic, Elastomer

14. Milas; B.D. Gamari, S. Rahmanseresht

"Single-Molecule-Sensitive FRET in Attoliter droplets"
Single molecular-pair fluorescence resonance energy transfer (spFRET) has become an cross-disciplinary tool for understanding molecular folding and interactions. While providing detailed information about the individual members of a molecular ensemble, this technique is always limited by fluorophore brightness and stability. In the case of diffusing molecules, the experiment is further limited by the number of photons that can be collected during the time it takes for a molecule to diffuse across the detection volume. To maximize the number of photons it is common to either increase the detection volume at the expense of increased background, or increase the diffusion time by adding glycerol or sucrose to increase viscosity. Here we demonstrate that FRET from attoliter volume (100 nm radius) aqueous droplets in perfluorinated oil has significantly higher signal-to-noise and a much wider dynamic range than FRET from molecules diffusing in solution. However, our measurements also reveal a droplet environment that is dramatically modified from that of the bulk.
Keywords: single molecule, nanodroplet, microfluidics, droplet fluidics, FRET, RNA

15. Perry; Nica Franklin, Vinothan N. Manoharan

Harvard University
"Partition functions of colloidal clusters in liquids"
Partition functions that we learn in classes were derived for molecules in a vacuum. Where does this leave us when we apply statistical mechanics to colloidal clusters surrounded by liquid? I am currently starting experiments on clusters of mixed spheres with different densities in order to figure out the role of mass in the partition functions of this low Reynold's number system.
Keywords: Colloid, Statistical Mechanics, Fluid Dynamics

16. Senbil; W. He, B. Davidovitch, A.D. Dinsmore

"Hysteresis of the Contact Angle around Spheres Adsorbed at Curved Fluid Interfaces "
Force on the particles adsorbed at the fluid interface is related with the contact angle between the particle itself and the shape of the interface. There is hysteresis in contact angle, which is defined as advancing and receding contact angles. We find that, surprisingly, hysteresis highly depends on the shape of the interface. In our experiments, we use millimeter-sized glass spheres coated with PDMS adsorbed at the water-air interface. Our results are important for understanding interactions between particles at interfaces and may shed new light on the origin of contact-angle hysteresis. This work is funded by the NSF through CBET-0967620 and by the Gulf of Mexico Research Initiative through the C-MEDS consortium.
Keywords: contact angle, hysteresis, interfaces

17. Sharma

Liquid Crystals (LCs) are unique materials that exhibit characteristics of both liquid and crystalline phases simultaneously at certain temperatures. Because of these characteristics LCs have many applications in Liquid Crystal Display (LCD) including television screens, touch panels for mobile devices, highly accurate thermometers, optical imaging, and more. This study explores the calorimetric results of Crystalline to Smectic-A (K-SmA) phase transitions of 4-Decyl-4-biphenylcarbonitrile (10CB) liquid crystal during heating and cooling. The thermodynamic study was performed from -20oC to 70oC at various heating and cooling cycles. The size, shape and appearance of the transition changed from heating to cooling. A clear and attracting inclination effect in K-SmA transition was observed in cooling scans, which is completely absent on heating scans. The transition peak shifts with heating ramp rates as well as the inclination of the peak also changes as function of ramp rates. Cooling of the K-SmA phase transition of 10CB brings the effect of “time lag” when compared with the heating scans. The study of “time lag” may bring the possible solutions to the existing drawbacks of LCD in the research and industrial areas1and may also provide a better future direction of studies and career to undergraduate students in Physics and Chemistry. 1.D. Sharma, “Effect of Alignment on N-I Phase Transition of 8CB Liquid Crystal Brings Possible Solutions to LCD Drawback”, APL, 94, 134103 (2009),
Keywords: Keywords: Calorimetry, Liquid Crystals, Heating and Cooling, Specific heat capacity, 10CB, Crystalline to Smectic A phase transition, Time lag, Thermodynamics.

18. Walls; James Bird

Boston University
"Measuring the change in particle concentration in draining bubbles"
The knowledge of particle concentration in bubbles at a free liquid surface is important to several industries including biotech and mining. Previous studies have mainly focused on the jet drop concentration as an indication of bubble film concentration. We instead use high speed imaging techniques to directly observe particles and their motion over the life of the bubbles. Using this information will enable us to determine precisely how the concentration changes over time, whether it increases, decreases or remains constant.
Keywords: bubble drainage, particles

19. Wang; Nicolas G. Hadjiconstantinou

"Predicting Anomalous Water Densities in Carbon Nanotubes"
Confined fluids exhibit a number of surprising properties that have been demonstrated in simulations and experiments, but that are not well understood theoretically. One particular phenomenon of interest is the anomalously low density of water confined in a carbon nanotube as compared to water in the bulk. We present early findings in a study of this phenomenon using simple statistical mechanical models, including comparisons to results from molecular dynamics simulations.
Keywords: Confined fluids, carbon nanotubes

20. Zeinali; Katherine Y. Zhang

Boston University
"Regional variations in mechanical properties of aortic tissue using a structurally motivated constitutive model"
Arterial wall extracellular matrix, mainly composed of collagen and elastin, plays an important role in the biomechanics of arteries, and thus the pathogenesis of arterial diseases. Arterial constituents are known to vary in quantity and organization throughout the arterial tree, making some regions more susceptible to the development of arterial diseases. In this study, we have investigated the regional variation of mechanical properties of porcine thoracic aorta and relate that to the microstructural organization of the constituents using a structurally motivated constitutive model as well as multiphoton microscopic imaging.
Keywords: Vascular Tissue Mechanics; Structural-based Constitutive Models

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