Soft Matter World

Newsletter
March | 2012 | Issue 39

Dear Soft Matter Colleagues,
Welcome to our March newsletter. This month we are featuring Dr. Dhara's group from Hyderabad, India, andstudies on how the behavior of foams, ponytails, and spider webs can be modeled. Have a pleasant March anda great read.

Soft Matter Physics Group at the University of Hyderabad
Dr. Surajit Dhara’s group in theDepartment of Physics at the University of Hyderabad, Hyderabad,
India investigates the molecular dynamics of liquid crystals using field
cycled nuclear magnetic resonanceand Monte Carlo simulation. The
group consists of Dr. Dhara and fiveresearchers. Their three research interests are:
• Structures and Properties of Liq
uid Crystalline Phases of Unconventional Mesogens
The phase transitions and visco
elastic properties are investigatedin liquid crystals composed ofbent, T-shaped, or hockey-stick
shaped molecules. The physicalproperties and the electro optical responses in unconventionalliquid crystals are drastically different from those of conventional
thermotropic liquid crystals.
• Liquid Crystal-Nanoparticle Composites
The curvature elasticity, rotational viscosity, and the rheologicalproperties of liquid crystal nanocomposites is experimentally investigated. Dilute nanosuspen-sions seem to behave in a similar
way to a pure liquid crystal, theirunique electro-optical and magneto-optical properties have attracted much recent attention fordisplay applications.
• Rheology of Complex Fluids
An overarching theme in thegroup’s research, rheology, structures, and dynamics of complex
liquid crystals, liquid crystalnanoparticle composites, andpolymers are investigated.
Dr. Dhara’s lab setup optimallyenables precise liquid crystal sample preparation and observation.

Dr. Dhara's group specializes
in synthesizing liquid crystals andmeasuring their behavior on irregular substrates with a lab setup
designed to enable precise liquid
crystal sample preparation and observation. Images of liquid crystal
phase transitions from the lab havebeen featured in the kaleidoscope
image gallery of European PhysicalJournal E, in particular, one of theseimages documents the discontinuous anchoring transition of a nematic liquid crystal on an amorphous
perfluoropolymer surface. In 2010,
Dr. Dhara was awarded the MichiNakata Prize by the International
Liquid Crystal Society for Early Career Achievement for the discoveryof this transition. Dr. Dhara has received another award from the Indian Physics Association. He is also
visiting scientist of the Jozef Stefan
Institute in Ljubljana, Slovenia andof the Department of Organic andPolymeric Materials in Tokyo Institute of Technology in Tokyo, Japan.
To read more, visit Dr. Dhara’swebsite.

Soft Matter World Newsletter
Shape of a Ponytail and the Statistical Physics of Hair Fiber Bundles
R aymond E. G old s tein , Pa t r i c k B . War re n, and R obi n C . Bal l . P hy s ic a l R ev iew L et t er s , 2 0 1 2 , Vo l. 1 0 8 , I s s u e 7 , D O I : 1 0 . 1 1 0 3 / P hy s R evLett. 108. 078101

In his notebooks, Leonardo daVinci remarked that human hairresembles fluid streamlines. British researchers have reduced themany-body problem of a ponytail
envelope into a one- body problemof swelling pressure, characterized
by an “equation of state” (EOS).
The EOS modifies the envelope
shape from that of a single hairbent by gravity. It describes a force

 Superimposed rotationally averaged
outlines hair switches. The EOS equation
predicts shape through calculating envelope pressure from unit fiber density

balance on a length element of thenotionally equivalent single fiber as
the sum of four dimensionless terms
which are, respectively, an elastic
restoring force, a ‘‘string tension’’contribution, a weight term, and aradial swelling force corresponding
to a pressure gradient per unit fiberdensity.
Read more in Physical Review
Letters.

Simulations of two-dimensional foam rheology: Localization in Linear
Couette Flow and the Interaction of Settling Discs
A . Wyn, I.T. Da vies , a n d S . J . C ox . Europ e an P hy s i cs J our nal E , 2 0 0 8 , Vo l. 2 6 , Nu m b er 1 - 2 , D O I : 1 0 . 1 1 4 0 / ep je/ i2 0 0 7 - 1 0 2 8 6 - 0

Changes in bubble topologythat occur during plastic flow andthe sedimentation of two circular
discs under gravity are investigatedthrough Surface Evolver simulationsin an ideal two dimensional foam.
Researchers from Aberystwyth University in Wales and LaboratoireSpectrometrie Physique in France
investigate the challenge of deter-mining localization from the initialstructure of a foam through five parameters- the average of bubble
coordinates, bubble area average,
average foam disorder around bubbles, texture tensor, and the average of a line that spans a bubble.
Results indicate localization in thelinear Couette shear of a 2D foam
is highly dependent on the polydis-

Nonlinear Material Behaviour OfSpider Silk Yields Robust Webs
St eve n W. Cra n d ford , Anna Tarak anov a, N i col a M . Pug no , a n d Ma rk u s
J.B ue hl er. Na tu re , Vol. 482, D O I : 10. 1038/ nat ure 10739

 (from left to right) A comparison of linear elastic, elastic–perfectly plastic behaviours, and derived dragline silk. Web behaviour under distributed (global) wind loading.

persity in bubble areas. When twodiscs, slightly larger than the bubbles, are placed close to or above
one another, small discs move faster in the wake of the other. For sufficiently close pairs of discs, one is
attracted into the wake of the other.
Read more in the European Physical Journal E.

The properties of spider silk have been thoroughly investigated down to the primary amino acid sequence. However, the many elastic properties of a spider web are due to geometry as well as the silk itself.
Researchers from MIT and Cornell have investigated
how a spider web responds to stress in light of its geometry and materials composition through computermodeling and experiment. Results indicate spider silk
softens and stiffens in a nonlinear manner with entropic
unfolding, stiffening, and stick slip regimes progressing with increasing stress after an initial yield point. Aspider web distributes stress by sacrificing threads, allowing the spider to repair rather than rebuild if failure
occurs. This use of sacrificial elements may see application in engineering.
Read more in Nature.

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Soft Matter World Newsletter
Warwick Polymers 2012
Warwick 2012 will be held July 9-12th, 2012 at theWarwick conference center in Warwick, UK. Submit abstracts no later than April 30, 2012. Over the course of
three days, there will be twelve plenary lectures andeighty invited lecturers, a poster session, and evening
events. A very saturated conference, Warwick Polymers
has a high rating among soft mater professionals internationally.
Register and read the program on the site.

24th International Liquid Crystal ConferenceThis biannual conference brings together
a broad scientificcommunity
linkedtogether by the interest in various
aspects of soft matter and working
in the interdisciplinary field of liquid crystals, or more broadly, mesophases. This community includes
spanning classical synthetic chem-istry, theoretical physics, structural
biology, and engineering. LiquidCrystals are almost omnipresent inmany very different fields. This conference provides a common platform for demonstrating and discussing new developments.
ILCC 2012 will be held in theConvention Center Rheingoldhalle
in Mainz, Germany August 19th -24th 2012 and will consist of talks,seminars, social events, and a poster session. All abstracts must be
submitted not later than March 9,2012.
Look through all twenty conference topics, register, and read moreon the website.

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