Dear soft matter colleagues,

Welcome to the May newsletter, we are featuring quite a range of topics this month including block copolymers, granular materials and some novel liquid crystal based capsules, read below to find out more. Thinking about a postdoc or grad school? Take a look at our global map and the updated conference deadlines to find out where soft matter sci-ence is happening! Have a great May and enjoy reading.

Directed self-assembly of block copolymers for universal nanopatterningBong Hoon Kim, Ju Young Kim and Sang Ouk Kim. Soft Matter, 2013, 9, 2780. 10.1039/C2SM27535J

Block copolymers (BCPs) can be used in various tech-nological fields as a self-assembling material. They can form ordered build-ing blocks and nanoscale structures, but are limited in scope by dense defects and slow structure formation. Recently, they have been investigated as a nanopat-terning method compli-mentary to existing photo-lithographic methods. The authors of this review ad-dress current uses, limita-tions, and improvements in the use of BCPs.

Two methods have been developed to combat the formation of defects that occur when a self-assem-bled BCP thin film forms on a planar surface (figure 1A). Epitaxial (figure 1B) self-assembly involves creating a chemically pre-patterned surface to direct the self-as-sembly of the BCP. The oth-er method, graphoepitaxy (figure 1C), creates a series of trenches to form the de-sired pattern. The trenches

confine the BCP and force it into the desired shape. A form of this method, re-ferred to as "soft" grapho-epitaxy, uses organic nega-tives, allowing the substrate pattern to be removed. This allows the manufacture of metallic and semiconductor nanowire arrays without a trace of the mold.

Low surface energy sub-strates, such as Teflon, can-not be modified to have neutral surfaces by conven-tional methods, such as spin casting of an organic layer and thermal treatment. The use of dopamine as an ad-hesive was inspired by the adhesive secreted by the common marine mussel. Immersing any substrate in a solution of dopamine forms a polydopamine net-work on the surface, allow-ing for application of BCP lithography to low surface energy substrates. Using this strategy, Teflon nanow-ires and other unconven-tional nanostructures can be grown directly on mate-

rials such as gold.

BCP nanopatterning has been used in semicon-ductor patterning, mag-netic storage, and more recently for virus filtration membranes and memris-tors. Future expansion of the uses of the material require low cost and large scale supply of suitable block copolymers, which are primarily produced in lab-scale quantities. Cur-rent lithographic methods allow arbitrary patterns, while BCPs create periodic

patterns, leading the au-thors of this review to sug-gest BCP nanopatterning will not replace the current lithography method, but complement it. If defects can be suitably controlled, these materials could be used in the manufacture of commercial devices.

The article can be found here.

-Michael Lane

Figure 1: (Aa) Surface parallel (left) and perpendicular (right) lamellar nanostructures self-assembled in BCP thin films on preferential and neutral substrates. (Ab) SEM im-age of randomly oriented BCP lamellar morphology self-assembled on a homogeneous neutral substrate. (Ba) Schematic illustration of epitaxial self-assembly. (Bb) SEM images of defect-free lamellar and (Bc) hexagonal cylinder patterns attained by epitaxial self-as-sembly. (Ca) Schematic illustration of graphoepitaxy. (Cb) SEM images of highly aligned lamellar and (Cc) hexagonal cylinder patterns prepared by graphoepitaxy.

The web's foremost resource on soft condensed matter.

Examples pf the ellipsoidal-shaped core-shell particles at room temperature. See "Micropump" article on page 2. Credits: Jagerwall et al. (DOI: 10.1038/ncomms2193)

2012/2013 Softmatterworld.org

Newsletter

May | 2013 | Issue #52

Modeling a washboard road: From experimental measurements to linear stability analysisPercier, B., Manneville, S., & Taberlet, N. (2013). Physical Review, 87(1), 012203-1-012203-7. doi: 10.1103/PhysRevE.87.012203

Washboard roads are made of sand or gravel and de-velop deep groves after being driven over several times causing vehicles to lose traction. A research team from the Université de Lyon has created a washboard instability model based on the lift force acting on a blade as it plows through a mound of sand.

The team started by deriving an equation for the dy-namics of the plow based on previous experimental data. The results showed that when the plow did not reach the critical velocity of the system, the sand bed flattened when plowed. When the plow exceeded the critical velocity, the rippled pattern would become regular after several pas-sages of the plow increasing in amplitude until a saturated value was reached by the system. The Université de Lyon research team discovered that the critical velocity increas-es as the mass of the plow increases.

The current experiment tested what the sand bed would experience if a plow moved through a mound of sand. The general set up included a large circular track filled with sand granules. The plow was attached to an arm that al-lowed the plow to rotate freely or remain immobile on a translational stage. This experimental set up allowed the team to test more parameters including how the system responded to sinusoidal excitations.

The mechanical response of the system was determined

based on the effects of sinusoidal excitation. After several plowed rotations, the indentation pattern of the sand bed would either disappear or increase depending on the wavelength and velocity of the plow.

The research team was able to produce a linear stabil-ity analysis based on the lift force that acts on the plow as it moved circularly in sand. This fundamental experiment could be modified in the future to include a wheel. That way, the compaction of sand and the suspension of a ve-hicle tire could be taken into account.

To read more about the article please click here. You can also watch a video uploaded by the authors of the experi-ment in action at our youtube channel.

-Amanda Baijnauth

Figure 2: An experimental setup showing a plow moving in a bed of sand.(Bitbol, A., Taberlet, N., Morris, S., & McElwaine, J. (2009). Scaling and dynamics of washboard road. Physical Review E, 79(6), 061308-1 Ð 061308-10. doi: 10.1103/PhysRevE.79.061308)

One-piece micropumps from liquid crystalline core-shell particlesEva-Kristina Fleischmann, Hsin-Ling Liang, Nadia Kapernaum, Frank Giesselmann, Jan Lagerwall & Rudolf Zentel (2013). Nature Communications, 3:1178. doi: 10.1038/ncomms2193.

Responsive polymers are used as low-cost and flexible micro-mechani-cal devices such as micro-actuators. If such devices can be produced more economically, lab-on-a-chip systems can be made more affordable.

Researchers from Germany and South Korea recently collaborated to develop and demonstrate a manu-facturing process of spherical one-piece micropumps constructed from a liquid crystal elastomer shell and a liquid core. The apparatus they cre-ated consisted of a cylindrical glass tube nested within a square glass capillary which was housed within a circular Teflon cover (Figure 3). This configuration allowed three fluids to flow simultaneously and exit the three

Figure 3: The triple co-flowing apparatus used, showing the three fluids being combined, and the polymerization of the monomer.

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tubes at the same point. The inner tube contained glycerol, the liquid core of the micropump. The square tubing con-tained the liquid crystal elastomer that formed the shell of the pump, and the outer tube provided a continuous flow of silicon oil to contain and separate the individual pumps. This resulted in glycerol droplets encapsulated by an el-lipsoid monomer shell, all contained within silicon oil. The monomer was then polymerized with ultraviolet light.

The researchers tested the mechanism by puncturing an individual pump with a glass capillary. This assembly was lowered towards a hot plate, bringing the temperature of the micropump from 90ºC to 130ºC. This shifted the elas-tomer within the shell from the nematic to the isotropic phase. This produced a deformation in the shell, pushing the glycerol core into the inserted capillary. Upon removal from the heating element, the shell returned to the nematic phase and its original volume, returning the glycerol to the

core.

WAXS (wide-angle X-ray scattering) was used to de-termine the director configuration of the elastomer shell. There were two defects within the shell, one at either pole of the ellipsoid, which lead to the initial shape. The direc-tor configuration was the result of the shear flow produced by the silicon oil during polymerization.

The group acknowledges the limitations of temperature-actuated mechanisms for lab-on-chip applications but explain that the method of production they successfully demonstrated should allow for any desired monomer to be used, including light-sensitive elastomers.

The full article can be found here.

-Michael Lane

CONFERENCE LISTINGS listed below are all of the conferences which have abstract/registration deadlines this may/june

may 10th

  11th International Conference on Materials Chemistry   IUPAC World Chemistry Congress

may 15th   Statistical Physics of Quantum Matter   Thermodynamics 2013

may 16th

  International Symposium on Polyelectrolytes

may 17th

  STATPHYS 25

may 19th

  GRC presents: Liquid Crystals

may 20th

  12th European Conference on Liquid Crystals, ECLC-2013

may 24th

  Physics of Glassy and Granular Materials   RSC presents: Faraday Discussion 165   6th International Granulation Workshop

may 31st

  1st International Workshop on Theo-retical and Computational Physics   CECAM 849   Innovation in Polymer Science and Technology 2013

june 1st

  I-CAMP 2013 Summer School

SITE UPDATES global research network back online

After a 4 month hiatus, the soft matter world Global Re-search Network Interactive map is back online! Over the next few months we strongly encourage any of our regis-tered users to please check if your group is correctly listed on the map.

If not please send an email to the webmaster at:

aossowski@softmatterworld.org

with "Global Network Group Update" in the subject line.

Read more about the global map and how to get in-volved in the "News" section of the website.

-Adam Ossowski

check back every week for up-dates to the summer conferences

2012/2013 Softmatterworld.org All rights reserved 3

We hope you enjoy broWsing and come back soon

Linda S. Hirst & Adam P. Ossowski

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