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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


54th New England Complex Fluids Meeting
Yale University | Friday, March 15, 2013
Registration deadline: Wednesday, March 13, 2013

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Abstracts for Invited Talks and Sound Bites:

Invited Talks

1. Invited; Dr. Rob Style

Yale University
"Wetting on Soft Substrates"
TBA
Keywords: 

2. Invited; Prof. Carmel Majidi

Carnegie Mellon University
"Adhesion and Spontaneous Deformation of Thin Elastic Sheets"
TBA
Keywords: 

3. Invited; Prof. Doug Holmes

Virginia Technical Institute
"Using Thin Films of Rubber to Move Thin Films of Fluid"
TBA
Keywords: 

4. Invited; Prof. Pedro Reis

MIT
"Mechanics of Shells"
TBA
Keywords: 

5. Invited; Prof. Zhigang Suo

Harvard University
"Mechanics of Hydrogels"
TBA
Keywords: 


Sound Bites

1. Amstad; David A. Weitz

Harvard University
"The microfluidic nebulator: Production of sub-30 nm nanoparticles"
Many orally administered pharmaceutically relevant drugs are hydrophobic and therefore poorly water soluble. This severely limits their bioavailability and thus their effectiveness as medication. One possibility to increase their solubility is to formulate them as nanoparticles. However, the formulation of drug nanoparticles with sizes below 100 nm still presents a major challenge. I will present a microfluidic spray drier, a so-called microfluidic nebulator, that allows the formulation of nanoparticles with diameters below 30 nm.
Keywords: microfluidics, spray drying, drug formulation

2. Arriaga; David A. Weitz

Harvard University
"Filling lipid vesicles with non-ideal polymer mixtures"
The use of microfluidic technologies allows for controlled and efficient encapsulation of polymer mixtures inside the inner aqueous cores of microfluidic-templated vesicles. These polymer mixtures phase separate rapidly in the vesicles due to the smaller volumes and larger areas available for the polymers in the vesicles as compared to the bulk. Additionally, the permeability of the lipid bilayer to water allows for changes in the concentration of the polymers upon changes in external osmolarity. We are currently studying the membrane deformations that accompany those changes.
Keywords: microfluidics, vesicles, phase separation

3. Ban; Catalin R. Picu

Rensselaer Polytechnic Institute
"An Unusually Stable DNA Sticky End Link"
Two DNA molecules can be connected by association of unpaired bases at their ends. This leads to formation of a sticky end link. Sticky end links is used in self-assembling DNA structures. Here we investigate the stability of these links by testing their axial stretch using Molecular Dynamics simulations. First we compare the simulations against existing simulations of double stranded DNA and crystallographic structures of sticky end links. Then we perform stretch of sticky end links with different lengths and base sequences. A group of the tested sticky ends are unusually stable. In all of them we observe a specific complex of bases that maintains the link’s stability until dissociation.
Keywords: DNA, Self-Assembled Structures, Sticky Ends, Stability, Mechanics, Stretch, Strength, Thermodynamics

4. Basu; Alex Shalek, Evan Macosko, Steve McCarroll, Aviv Regev, David Weitz

School of Engineering and Applied Science, Harvard University; Broad Institute of MIT and Harvard
"Single-cell Genomics using Emulsion Microfluidics"
Single-cell Transcriptomics using Emulsion Microfluidics Anindita Basu*,†, Alex Shalek*,†, Evan Macosko‡, Steve McCarroll‡, Aviv Regev†, David Weitz* *School of Engineering and Applied Science, Harvard University ‡Harvard Medical School, Harvard University †Broad Institute of MIT and Harvard We study the transcriptomics of single cells in isolation using a droplet-based microfluidic setup. We can follow a cell in response to its micro-environment by (a) uniquely bar-coding the genomic information from a given cell, (b) encapsulating one cell per emulsion droplet, and (c) using state-of-the-art sequencing techniques. This enables study of cellular behavior in response to its micro-environment in the emulsion droplet.
Keywords: single-cell, RNAseq, barcoding, microfluidics

5. Baykal; Igor Kaltashov, Paul Dubin

University of Massachusttes, Amherst
"Counterion condensation on heparin oligomers"
The electropherogram of native heparin shows a broad distribution of mobilities µ which truncates abruptly at a notably high µ = 4.7x10-4 cm2V-1s-1. This highly skewed mobility distribution is also found for the 20-saccharide chain which shows from mass spectrometry a more uniform (symmetrical) with respect to sulfation level. Since a partially degraded heparin exhibits oligomer peaks with µ> 5x10-4 cm2V-1s-1 (appearing to escape the limitation of the mobility value for native heparin), we examined the electrophoretic behavior of chain-length monodisperse heparin oligomers. Their mobilities varied inversely with the logarithm of the contour length L, for L from 3 to 10 nm and reached an asymptotic limit for L> 20 nm. The generality of this effect was indicated by similar behavior for oligomers of poly(styrenesulfonate). A recent theory of polyelectrolyte end effects (Manning, G. S. Macromolecules 2008, 41, 6217-6227.), in which chain termini exhibit reduced counterion condensation was found to account quantitatively for these results. A qualitative explanation for the anomalously high value of µ of native heparin, 10-20% higher than those seen for synthetic polyelectrolytes of higher linear charge density is suggested on the basis of similar junction effects (Manning, G. S. Macromolecules 2008, 41, 6217-6227.), which reduce counterion condensation at the interfaces of regions of high and low sulfation. We suggest that these effects should be considered in models for the biofunctionality of the regulated high and low sulfation (NS/NA) domains of heparan sulfate.
Keywords: Heparin; oligomers; counterion condensation; effective charges; end effects; junctions

6. Boltyanskiy; Katie Rosowski, Valerie Horsley, Jay Humphrey, Eric Dufresne

Yale University, Department of Physics
"Mechanical Response of Living Cells to Stretch"

Keywords: 

7. Chang; H. Zhang, A. Rotem

Harvard University
"Droplet-based Microfluidics for Directed Viral Evolution"
We are applying droplet-based microfluidic techniques to isolate viral progeny and accelerate viral evolution. We show that viruses replicate in individual droplets containing host cells, and these isolated progeny are passaged through several generations of replication. Results obtained from next-generation sequencing methods show interesting results of increased genetic diversity, and the emergence of viral sequences that have escaped under selective pressure. These emergent sequences will allow for a better understanding of viral evolution.
Keywords: Viruses, Evolution, Microfluidics, Sequencing

8. Choo; Manesh Gopinadhan, Prashant Deshmukh, Rajeswari Kasi and Chinedum Osuji

Yale University
"Nanoporous Templates by Magnetic Field Alignment"
Here we introduce a novel densely packed cylinder forming soft-etchable liquid crystalline brush block copolymer (LCBCP). Using a high magnetic field, the material was aligned over large area and macroscopic thicknesses. Crosslinking the LC matrix and subsequent removal of PLA domains by hydrolytic degradation results in a nanoporous polymer template which can be further utilized for variety of applications.
Keywords: PLA-LC Brush Block Copolymer, Magnetic Field Alignment, Nanoporous Template

9. Cunsolo

"A new generation Inelastic X Ray Scattering spectrometer at NSLS II"
A new generation Inelastic X Ray Scattering spectrometer with unprecedented narrow and sharp resolution is soon to be available at the forthcoming synchrotron source, NSLS-II, at Brookhaven National Laboratory. Its working principle is based upon the use of extremely asymmetric Bragg back reflections from Si crystals. The instrument has an energy resolution function with 1 meV bandwidth and sharp, nearly Gaussian, tails and is expected to open new scientific opportunities, particularly in areas of liquid, disordered and bio-molecular systems.
Keywords: 

10. Datta; Alireza Abbaspourrad, David A. Weitz

Department of Physics, Harvard University
"Exploding Microcapsules"
Spherical microcapsules are important for the encapsulation, delivery, and controlled release of a variety of active materials. In many cases, the utility of such a microcapsule critically depends on its mechanical response to an external stimulus. While the pressure-induced deformations of a microcapsule are well understood, studies of how microcapsules deform under electrostatic forces are lacking. We use microfluidics to make spherical microcapsules with thin, hybrid shells composed of a mixture of a pH-sensitive polymer, which becomes highly charged under basic conditions, and another, pH-inert, polymer. When exposed to a very high pH, the microcapsules expand uniformly; this behavior can be understood by coupling electrostatics, shell theory, and Darcy's law for flow through the porous shell. Surprisingly, as the pH is reduced, the microcapsules begin to disintegrate; eventually, holes form in their shells, and the microcapsules expand into large, crumpled sacs. The origin of this behavior is a puzzle.
Keywords: 

11. Dias; Thomas R. Powers

Brown University
"Swimming near a deformable interface"
It is a known fact that swimmers behave differently near deformable soft tissues than when near a rigid surface. Motivated by this class of problems, we investigate swimming microorganisms near flexible walls. We calculate the speed of an infinitely long swimmer near an interface between two viscous fluids. Part of the calculation of the speed is the calculation of the shape of the free boundary. The swimming speed is controlled by the competition between surface and viscous effects, where two limits are observed. When the surface tension vanishes, we get Taylor’s result for a swimmer with no walls. When the surface tension is infinite, the problem is like that of a swimmer near a rigid wall.
Keywords: 

12. DiMasi

Brookhaven National Laboratory
"New Soft-Matter Interfaces X-ray Beamline at NSLS-II"
A beamline for x-ray scattering from Soft Matter Interfaces is in the works at the new synchrotron, NSLS-II, under construction at Brookhaven National Laboratoty. The SMI beamline specializes in surface and interface scattering: grazing incidence SASX/WAXS and the liquid reflectivity geometry. Systems of interest include polymers, liquid crystals, organic films, nanostructured mineral-organic composites, and biomaterials; also liquid-vapor, liquid-solid, and liquid-liquid interfaces and micro/nano fluidics. Notably, the energy range from 2.1 to 24 keV enables new resonance experiments, and a microbeam mode will be implemented. As lead scientist can describe our designs and goals for this beamline, scheduled to take beam in late 2016.
Keywords: synchrotron x-ray liquid interface

13. Fan; David A. Weitz

Harvard University
"Structural transition in dense packings of drops"
Dense packings of monodisperse bubbles or drops exhibit ordered structures in confinements: variation of the shape of confinement and the volume fraction lead to different packing structures. However, the geometrical effect on packing structure and the physical mechanism for the transition between different structures at different volume fractions has not been fully understood. We study these problems using emulsion drops confined to a few layers at high volume fractions, showing that the transition from the wet beehive to wet Toth structures with the volume fraction of drops increases is governed by the structural instability of the beehive structure.
Keywords: drops, packing structure, structural transition

14. Gopinadhan; Helen Tran, Pawel Majewski, Ryan Shade, Victoria Steffes, Chinedum Osuji,and Luis M. Campos

Yale University
"Large Area Monoliths of Semiconducting Block Copolymers by Magnetic Alignment"
Fabrication of large-area, aligned and ordered semiconducting organic molecules is crucial in improving the performance of organic electronics. Several approaches are employed to align semiconducting choromophores, yet remain a non-trivial problem. Herein, we demonstrate a supramolecular route combined with a magnetic field directed self-assembly to obtain long range order in these materials. Hydrogen bonding between a perylene based rigid choromophone (PDI) and a diblock copolymer generated a hexagonally packed PS domains surrounded by PAA/PDI matrix. Application of the magnetic field when the complex was cooled from the disordered state results in monoliths of highly oriented semiconducting ligands. This synergistic introduction of both functional properties and the means of controlling alignment by supramolecular attachment of mesogenic species to polymer backbones offer intriguing new possibilities for the modular design of functional nano-structured materials.
Keywords: n-type semiconductors, magnetic-field alignment, organic monoliths, block copolymer self-assembly.

15. Hanna; J Guven, M M Müller

UMass Amherst
"Whirling Skirts"
I will discuss a simple model of steady conical waves on rotating sheets.
Keywords: flexible rotordynamics

16. Hohlfeld; Phillip L. Geissler

UMass Amherst, Lawrence Berkeley Nattional Lab, UC Berkeley
"Extremely Fast Actin Gels"
Growing, dendritic actin gels can propel small objects such as bacteria and microbeads. I will discuss the surprising roles of extreme fluctuations and many-body correlations in this nonequilibrium process.
Keywords: acin, gel, nonequilibrium, Brownian ratchet

17. Hu; Sofia Rangou, Myungwoong Kim, Padma Gopalan, Volkan Filiz, Apostolos Avergopoulos, Chinedum Osuji

Yale Univ.
"Continuous Equilibrated Growth of Ordered Block Copolymer Thin Films by Electrospray Deposition"
Deposition of block copolymer thin films is most often accomplished in a serial process where material is spin coated onto a substrate and subsequently annealed, either thermally or by solvent vapor, to produce a well-ordered morphology. Here we show that under appropriate conditions, well-ordered block copolymer films may be continuously grown under substrate equilibrated conditions by slow deposition of discrete sub-attoliter quantities of material using electrospray. We conduct time-resolved observations and investigate the effects of process parameters that underpin film morphology including solvent selectivity, substrate temperature, block-substrate selectivityand flow rate of the feed solution. For a PEO cylinder-forming poly(styrene-b-ethylene oxide) block copolymer, we uncover a wide temperature window from 90 ºC to 150 ºC and an ideal flow rate of 2 µL/min for ordered film deposition from dilute acetone solutions. PEO cylinders aligned with their long axes perpendicular to the film-air interface at optimal spray conditions. Using poly(styrene-b-methyl methacrylate) deposited onto neutrally selective surfaces, we show that the substrate-equilibrated process results in vertically oriented microdomains throughout the film, indicating a preservation of the initial substrate-dictated morphology during the film deposition. Electrospray offers a new and potentially exciting route for controlled, continuous growth of block copolymer thin films and manipulation of their microstructure.
Keywords: block copolymer; thin films; electrospray; film growth; self-assembly

18. Jang; Simon G. Mochrie

Post Doctoral Associate
"MICROSTRUCTURE AND PHASE BEHAVIOR STUDY OF POLY(STYRENE-b-ISOPRENE) DIBLOCK COPOLYMER MELTS USING SMALL ANGLE X-RAY SCATTERING AND X-RAY PHOTON CORRELATION SPECTROSCOPY"
X-rays are widely used to study the block copolymer nanostructure; however, a conventional X-ray beam source limits the detection of the nanostructure and dynamic behavior. The present research uses a third generation coherent synchrotron X-ray source – the Advanced Photon Source at Argonne National Laboratory – to study the nanostructural evolution and dynamic behavior of poly(styrene10,000-b-isoprene16500) diblock copolymer. The block copolymer was found to exhibit phase coexistence of double-gyroid and orthorhombic Fddd structures for temperatures from 115 to 120 C. Above 130 C, in the disordered phase, the temperature dependence of the static structure factor exhibits deviations from the behavior expected for ideal Gaussian chains. The scattering over a wide range of wavevectors is well-described as the linear sum of a model due to Burger and Semenov1 and a modified Lorentzian function peaked at zero wavevector. In addition, the dynamic behavior of the disordered state was investigated using X-ray photon correlation spectroscopy, and the disordered-phase structural relaxation time characterized as a function of temperature.
Keywords: Block Copolymer, X-Ray

19. Jensen; Eliza J. Morris; David A. Weitz; Jeffrey R. Moore

Boston University, Harvard University
"Mechanism of calponin stabilization of cytoskeletal actin networks"
Calponin, an actin-binding protein present in both smooth muscle and non-muscle cells, is thought to stabilize actin structures in the cell under stress; however, the underlying mechanism is unknown. Our previous work has shown that calponin reduces the flexural rigidity of individual actin filaments. Here, I present bulk rheology data demonstrating that calponin delays the strain-stiffening onset in a crosslinked actin network, and increases the yield stress and strain of the network even when actin is decorated with tropomyosin. I also compare our experimental data to a simple simulation of a network of linear springs under affine strain and show that our data can be fully explained by calponin reducing the flexural rigidity of actin filaments. Together, this provides a compelling model for calponin stabilization of actin in vivo.
Keywords: Actin, calponin, rheology, network mechanics

20. Jensen; D.A. Weitz, F. Spaepen

Harvard University
"Defects in sheared and quiescent colloidal glasses"
We report experiments on 1.55-µm-diameter, hard-sphere silica colloidal glasses with and without applied shear. We measure the strain both locally and globally, and observe the development of a quadrupolar signature in local strain correlations. This indicates the presence of shear defects in the material that can be characterized as Eshelby inclusions: local regions of high plastic strain that couple elastically to the surrounding material. Interestingly, we observe that these shear defects exist in the glass even when there is no applied or bulk strain.
Keywords: glass, colloid, deformation, defect

21. Jin; Lihua Jin, Dayong Chen, Ryan C. Hayward, and Zhigang Suo

Harvard SEAS and UMass Amherst
"Creases on the interface between two soft materials"
Calculations and experiments are presented to show that an interface between two soft materials under compression can form creases, a type of bifurcation distinct from wrinkles. While creases bifurcate from a state of flat interface by a deformation localized in space and large in amplitude, wrinkles bifurcate from a state of flat interface by a deformation non-local in space and small in amplitude. The interfacial creases set in at a lower critical compression than interfacial wrinkles, but higher than surface creases. The condition for the onset of interfacial creases is calculated in terms of elastic moduli, pre-strains and applied strains.
Keywords: 

22. Kalakonda; P. KALAKONDA, G. S. IANNACCHIONE, G.Y. Georgiev

Worcester Polytechnic Institute
"Nano Structure-Transport Relationship in Oriented Polymer-Carbon Nanotubes films"
The internal structure of anisotropic nanocomposites determines the anisotropy of their macroscopic properties. Nanoscale oriented carbon nanotubes (CNTs) in a polymer matrix allow for anisotropy of thermal and electrical transport and their control by varying concentration, alignment methods and temperature. A better understanding of the transport of energy through such unique systems will improve the applications of these materials. We choose isotactic PolyPropylene (iPP) as one of the most widely used polymer and mixed it with different concentration of CNT from 0, 1, 2 and 5wt%. We oriented thin film samples of these nanocomposites using melt-shear at 200 0C and 1 Hz in a Linkan Microscope shearing hot stage. We present a series of complementary experiments exploring the macroscopic thermanl and electrical transport in iPP/CNT thin films as function of shearing, temperature and CNT concentration. Using a DC method, the thermal and electrical conductivity of sheared and un-sheared of iPP/CNT samples were measured over a wide range of temperature. The percolation threshold is clearly observed in both electrical and thermal conductivities but at different concentration of CNT depending on shear treatment. This work provides evidence for a physical model that connect the CNT dispersion and orientation to energy transport. This will further our abilities to nano-engineer material for many important applications.
Keywords: iPP, CNT, thermal conductivity, Electrical conductivity

23. Kang; Michael Bradley, Brannon McCullough, Elena Grintsevich, Emil Reisler, Enrique De La Cruz

Yale University
"Actin-Bound Cations Modulate Filament Mechanics and Cofilin Severing Activity"
The regulation of actin assembly and modulation of filament mechanical properties are critical for actin function. It is well established that physiological salt concentrations promote actin assembly and alter the overall bending mechanics of assembled filaments and networks. However, the molecular origins of these salt-dependent effects, particularly if they involve non-specific ionic strength effects or specific ion binding interactions, are unknown. Here, we demonstrate that specific cation binding at two discrete sites situated between adjacent subunits along the long-pitch helix drive actin polymerization and determine the filament bending rigidity. We classify the two sites as “polymerization” and “stiffness” sites based on the effects that mutations at the sites have on salt-dependent filament assembly and bending mechanics, respectively. Cofilin binding is coupled to dissociation of filament-associated cations, stiffness site reorganization and enhanced actin filament bending and twisting dynamics, consistent with displacement of stiffness site cations underlying the effects of cofilin on actin filament mechanics. The work presented reveals the molecular mechanism of salt-dependent actin assembly and cofilin-mediated changes in actin filament bending mechanics and severing.
Keywords: Actin mechanics, Severing, Ion-linkage

24. Kaufman; Chinedum Osuji

Yale University
"Hollow microcapsules synthesis by droplet microfluidics solvent extraction "
Understating the dynamics of deformable particles in microfluidic networks is imperative for clinical assays of a wide range of diseases including sickle cell anemia, malaria, and cancer. However, the field of separation of particles based on deformability still poses several important questions such as how path selection in a microfluidic device is dependent on particle deformability. Our goal is to design a microfluidic device that will allow high throughput particle separation based on deformability. The first step toward this goal is to design a model system of deformable particles with fluid core and viscoelastic shell. This talk discusses a microfluidic approaches for achieving this goal. The approach involved microfluidic formation of double emulsion of water-in organic solvent-in water (W/O/W), followed by formation of elastic polyelectrolyte membrane through solvent extraction. The double emulsion was produced through two consecutive flow focusing junctions. In the first junction, we formed the inner droplets of polyelectrolyte solution-sodium alginate in alcohol followed by engulfing these droplets by an outer droplet of a polyelctrolyte solution with opposite charge-poly4vynilpyrodiine to form the W/O/W. Upon removal of the middle phase through solvent extraction hollow microcapsule with polymeric elastic shell was formed. The double emulsion method to form hollow microcapsules can be extended to various other polyelectrolyte pairs with opposite charge such as chitosan/alginate and polystyrene sulfonate/poly(allylamine hydrochloride).
Keywords: Microfluidic,Microcapsules

25. Khalkhal; Ajay S. Negi and Chinedum Osuji

Yale University
"Scaling behavior of elasticity in weakly attractive surfactant stabilized colloidal gels"
Effective dispersion of attractive colloidal particles often relies on controlling the interaction potential between the particles by the addition of surfactants that provide steric or electrostatic stabilization. We combine careful determinations of adsorption isotherms with rheological experiments to evaluate the dependence of colloidal gel elasticity on particle volume fraction and exploit the adsorption efficiency of surfactants. The current research indicates the significance of rheological investigations coupled with accurate determinations of surface coverage to engineer new dispersants.
Keywords: adsorption, attractive colloids, aggregation, rheology, fractal gels

26. Kodger; Adrien Demongeot, David A. Weitz

Harvard University
"Delayed sedimentation in colloidal gels"
Colloidal gels are networks of aggregated particles that impart an elastic mechanical response to an otherwise fluid dispersion. Typically, the gel responds to gravity by creaming or sedimenting. It has been observed that this response can exhibit a marked delay; the time may be several hours or days. We will present data that shows this delayed response is greatly affected by the boundary conditions on the fixed container walls.
Keywords: colloids, gravitational collapse, delay

27. Kramel; Rui Ni, Greg Voth

Wesleyan University
"3D Particle tracking with scanned laser illumination for simultaneous measurement of velocity gradients and rod dynamics in turbulence"
We have built a system that allows us to measure the velocity gradient tensor for 3D turbulence. We illuminate a narrow slab of the volume of interest and scan the illuminated slab through the entire volume, taking sequential images. This technique enables us to greatly increase the concentration of tracer particles while simultaneously decreasing the particle size. Our experimental setup consists of an octagonal shaped tank with two grids oscillating in phase that produces a low Reynolds number flow (Re ~ 200). The detection volume is centered in our tank. The scanning motion of the light sheet is generated by a piezo-electric steering mirror which, combined with four high speed cameras, allows us to scan the detection volume in multiple steps while keeping the temporal resolution high.
Keywords: Particle tracking, Turbulence

28. Lee; Mo Chen, Tian Gan, Patrick Doyle, and Nicholas Fang

MIT
"Adaptive Digital Optofluidic Synthesis of Information-Rich Microparticles"
Novel in-flow digital lithography for massive and high throughput synthesis of microparticles is developed. Microfluidic environment offers great platform to transport multiple functional materials in the flow stream. By innovative application of a digital dynamic display, geometrically and chemically anisotropic microparticles are rapidly fabricated in a microfluidic channel where photocurable resin is flowing. Multiple functional units with different optical, chemical, or mechanical properties can be possibly integrated into the particles. Furthermore, taking advantage of the versatility of the dynamic mask, particle-specific patterns are generated in real-time based on the visual information of the particles suspended in the solution. This digital optofluidic lithography could potentially lead to adaptive encapsulation of cells with labels loaded with cell-specific information.
Keywords: particle synthesis, encapsulation, lithography, optofluidics

29. MacMinn; Eric R. Dufresne and John S. Wettlaufer

Yale University
"Mechanics of fluid injection into soft porous materials"
The mechanical deformation of rocks and sediments due to fluid injection plays an important role in carbon sequestration and enhanced oil and gas recovery. Here, we study this process experimentally in a simple model system.
Keywords: poroelasticity, porous materials, granular materials, fluid mechanics

30. Massenburg; Prof. David Weitz

Harvard University
"Understanding the Process of Pore Clogging"
Understanding the clogging behavior of microchannels represents a tremendous burden upon the burgeoning field of microfludics while also gaining understanding into the function of pore filtration. Here we show that the apparent randomness of clogging can be mitigated by careful surface treatment and then clogging can be harnessed to study effect of channel geometry on the propensity to clog.
Keywords: Microfluidic, clogging,

31. McFann

Unilever R&D, Trumbull, CT
"LAOS Fingerprinting of Personal Care Products"
Many if not most personal care products, for example creams and lotions, shampoos, body washes, deodorants, and toothpastes, are complex fluids. In general they are elastoviscoplastic colloids whose flow behavior is described by the Herschel-Bulkley model. Standard rheological characterization techniques such as amplitude and frequency sweeps show little of interest. However, when large amplitude oscillatory shear (LAOS) data are analyzed by the Chebyshev decomposition technique of McKinley et al. [J. Rheol., 52, 1427 (2008)], a variety of material responses become visible.
Keywords: LAOS, rheology, consumer products

32. Meng; David A. Weitz; Yunker Peter; Jianhong Xu; Rui Xie

Harvard university
"Interfacial Mass Transfer in Droplet-based Aqueous Two-phase Microfluidic Systems"
Droplet-based microfluidics with aqueous two-phase systems (ATPSs) enhancing mass transfer by spherical liquid-liquid interface in a highly biocompatible environment, has great advantages in bioseparations. In order to reveal the basic principles of the ATPSs droplet flow interface intensifying the two-phase mass transfer on microscale, the fundamental research on improvement mass transfer process has been conducted in this study by setting up ATPSs droplet flow platform and investigating the transfer characteristics of protein and small molecule across the interface.
Keywords: Mass Transfer, Droplet, ATPS, Microfluidic

33. Momani; H.H. Winter

University of Massachusetts Amherst Chemical Engineering
"Temperature Dependence in a Self-Exfoliating Nanocomposite"
Exfoliating layered materials in a polymer matrix to form a nanocomposite typically requires elaborate processing. However, montmorillonite organoclays have been found to self-exfoliate when gently mixed into a telechelic dicarboxy-terminated polybutadiene melt. No shear or sonication is needed and the exfoliation can reach completion in less than one hour. This study examined the temperature dependence of the self-exfoliation process using SAOS (small amplitude oscillatory shear) rheology and SAXS (small angle x-ray scattering). An unexpected temperature dependence was found with a maximum rate occurring around 80°C with sharp drops in rate below 35°C or above 85°C.
Keywords: Nanocomposite, self-exfoliation

34. Ni; Stefan Kramel, Greg Voth, Nicholas Ouellette

Wesleyan University; Yale University
"The dynamics of rods motion in turbulence"
We report on an experimental investigation of the dynamics of anisotropic particles in the turbulent flow. The rods are rigid nylon fibers, which are 30 μm in diameter and ~700 μm in length. Our previous experiments have been focused on the rotational dynamics of single rods. Our current studies extend in two directions. First, we measure the dynamics of multiple rods. We measure the alignment between two nearby rods that results from the competition between turbulent randomization and alignment by the strain in the flow. Second, we simultaneously measure the orientation of a single rod and the velocity of many tracer particles around it to investigate the alignment of the rods with the coarse-grained velocity gradient tensor.
Keywords: turbulence, particle tracking

35. Parsa; Greg Voth

Wesleyan University
"Accessing Statistics of Different Scales of Turbulence with Single Particle Measurement"
We study how the rotational statistics of rod-like particles in turbulent fluid flow depend on rod length. We show that the rotation rate scales with the time-scale of eddies of the length of rods. The Lagrangian auto-correlation of rotation rate depends on the length of the rods and the auto-correlation time for rods of length L scales like turn over time of this length-scale. The mean squared rotation rate of rods decreases as the length of the rods increases and in the inertial range the mean square rotation rate approaches an inertial range scaling of L^ -4/3.
Keywords: Turbulence, Rod, Rotation rate

36. Peterson

Mount Holyoke College
"Evolution of surface data"
The evolution equations are given for the first and second fundamental forms of a surface in Lagrangian coordinates under arbitrary differentiable deformation.
Keywords: Surface geometry

37. Schreck; Rob Hoy, Mark Shattuck, Corey O'Hern

Yale University
"Shear Reversibility in Model Granular Media"
Athermal particulate systems such as foams and granular media are out-of-thermal equilibrium and therefore must be externally driven using shear or vibration to explore different configurations. Of particular interest is being able to predict and control the structural and mechanical properties of athermal systems as a function of the driving mechanism. In this work, we show numerically how particle collisions in cyclically sheared hard sphere systems can lead to microreversibility. We map out the steady-state "phase diagram" as a function of packing fraction ($\phi$) and strain amplitude ($\gamma_{max}$), and identify "point-reversible" states at low $\phi$ and $\gamma_{max}$ in which particles do not collide over the course of a shear cycle, and "loop-reversible" states at intermediate $\phi$ and $\gamma_{max}$ in which particles undergo numerous collisions but return to their initial positions at the end of each shear cycle. Loop-reversiblity is a novel form of self organization that gives rise to non-fluctuating dynamical states over a broad range of packing fractions from contact percolation to jamming, i.e. $\phi_P=0.55$ to $\phi_J=0.84$ in two dimensions.
Keywords: Granular media, suspensions, reversibility

38. Shao; Manesh Gopinadhan, Golden Kumar, Sundeep Mukherjee, Yanhui Liu, Corey O’Hern, Jan Schroers and Chinedum Osuji

Yale University
"Size-Dependent Viscosity in the Supercooled Liquid State of a Bulk Metallic Glass"
We experimentally investigate the role of sample size on the viscosity of a bulk metallic glass by examining pressure driven flows in nm-scale confinement. A Pt57.5Cu14.7Ni5.3P22.5 metallic glass in the supercooled liquid state is extruded into isolated cylindrical pores of varying sub-micron dimensions, down to 39 nm. The apparent viscosity of the liquid as a function of the sample size is determined from the filling depth by appropriate corrections to the Hagen-Poiseuille equation. We observe a striking, sudden increase of the apparent viscosity for dimensions below ca. 100 nm. Results are discussed in the framework of collective shear events.
Keywords: Viscosity, Bulk Metallic Glasses

39. Sharma; N. Chau, K. McDonough and D. Sharma

Simmons College
"THERMODYNAMICS OF CRYSTALLINE (K) TO SMECTIC A (SmA) PHASE TRANSITION OF nCB LIQUID CRYSTALS"
This study explores a comparative thermodynamics of Crystalline (K) to Smectic A (SmA) phase transition of nCB Liquid Crystals. We have compared 4-Octyl-4-cyanobiphenyl (8CB) and 4-Decyl-4-cyanobiphenyl (10CB) liquid crystals. Fresh and degassed samples of 8CB and 10CB were used to run in Differential Scanning Calorimetry (DSC) from -20 oC to 50 oC at ramp rate of 5 oC/min rate keeping all the environmental conditions same. We have detected a significant shift in transition temperature and transition time of K-SmA phase transition for 10CB and 8CB. The K-SmA transition occurs later in temperature and times when compared with 8CB on heating scans. Comparative ramp rate dependence in K-SmA transition is also observed in 10CB and 8CB. It is found that 10CB shows a slower temperature shift with increasing ramp rates from 5oC/min to 20oC/min when compared with 8CB transitions and shows higher activation. The thermodynamic behavior of K-SmA phase transitions of nCB can be discussed in terms of mobility and size of molecules.
Keywords: Thermodynamics, Heat flow, Liquid Crystal, Phase Transition, Molecular Structure

40. Sharma; K. McDonough, N. Chau and D. Sharma

Simmons College
"HEATING AND COOLING EFFECT ON K- SmA PHASE TRANSITION OF 4-DECYL-4-BIPHENYLCARBONITRILE LIQUID CRYSTAL USING CALORIMETRIC TECHNIQUE"
A non-isothermal heating and cooling study was performed for 4-Decyl-4-Biphenylcarbonitrile (10CB) liquid crystal using calorimetric technique. A small amount 7 mg of fresh sample of 10CB was used to run on Differential Scanning Calorimetry (DSC) where heating scans were performed from -20 oC to 50 oC and cooling scans were performed from 50 oC to -20 oC. A clear difference between heating and cooling scans for Crystalline to smectic A (K-SmA) transition was observed. The size, shape and appearance of K-SmA trasition change 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 transition shows a time lag when compared with the heating scans. The results can be discussed in terms of the density and nature of the material.
Keywords: Calorimetry, Heating and Cooling, Specific Heat Capacity, 10CB, Crystalline to Smectic A phase Transition, Time lag

41. Winter

Department of Chemical Engineering and Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003
"Glass Transition as the Rheological Inverse of Gelation"
This is a comparative study in search for common patterns in the relaxation dynamics of amorphous materials in the approach of a liquid-to-solid transition from the liquid side. Observations with two representative materials provide guidance for the study. The first material, a concentrated colloidal suspension, represents the glass transition. The second material is a cross-linking polymer far above its glass transition; it represents gelation. The entire study is founded in Boltzmann’s constitutive equation of linear viscoelasticity; the stress is caused by a wide range of relaxation modes where, as argued here, fast modes dominate gelation and slow modes dominate the glass transition. For both classes of amorphous materials, the relaxation time spectrum broadens and adopts powerlaw format, but the powerlaw exponent is positive for the glass transition and negative for gelation, i.e. the relaxation patterns of gelling fluids and glass formers are inverse near the transition. Several examples are shown for each class of materials in order to test the proposed transition behavior for glasses (colloidal and molecular) on the one side and chemical/physical gels on the other. Among several results, this experimental study provides a decisive criterion that distinguishes the glass transition from gelation. It also shows a relation between the zero shear viscosity and the diverging longest relaxation time for both materials. To appear in ‘Macromolecules’ 2013.
Keywords: gelation, soft glass, colloids, viscoelasticity

42. Zhang; Minglei Wang, Stefanos Papanikolaou, Yanhui Liu, Jan Schroers, Mark D. Shattuck, and Corey O'Hern

Yale University
"Computational studies of the glass-forming ability of model bulk metallic glasses"
Bulk metallic glasses are produced by rapidly thermally quenching supercooled liquid alloys below the glass transition temperature at rates faster than the critical cooling rate $R> R_c$ to avoid crystallization. Better glass-formers have low values of $R_c$. We need to understand what determines $R_c$. We perform coarse-grained molecular dynamics simulations of model metallic glass-forming systems to understand $R_c$. We perform simulations of binary Lennard-Jones mixtures over a wide range of stoichiometry, particle size difference and attraction strength. A good glass former tends to have large particle size difference and stoichiometry close to 50:50. Weaker attraction for the smaller particle is found to facilitate glass formation. A small negative heat of mixing in experimentally relevant regime does not cause noticeable reduce in $R_c$. Our findings are compared and discussed with experimental results on numerous binary metallic glass formers.
Keywords: bulk metallic glass, glass-forming ability, critical cooling rate, Lennard-Jones

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