1. Greg Grason (polymer science & engineering) : soft matter theory/polymer physics Filamentous Assemblies: How do small, flexible molecules pack themselves? -Filaments are both nanoscopic (~1-10 nm diameter) and microscopic (~1  m) length -Filaments have well defined structure, chemistry and mechanical properties -Thermal forces and packing constraints gives rise to a host of complex assembly properties growth cone of axon mitotic spindle bundles of protein filaments polymer-based nano-rods ordered assembly Moon & McCarthy, Macromolecules (2003). How does Nature generate such robust & functional assemblies?? How can one design/functionalize synthetic filaments to achieve desired assembly??

2. Statistical mechanics: melting to states of intermediate order Grelet, Phys. Rev. Lett. (2008). phase behavior or rod-like fd virus low-temperature, high-density crystal high-temperature, low-density columnar liquid crystal inhomogenous structure along filament backbone longitudinal thermal fluctuations -density variation locks into registry -breaks symmetry along backbone direction -non-zero shear modulus -thermal fluctuations along filaments to slide freely -fluid symmetry -shear modulus vanishes Questions: -what are critical properties? -how does melting influence mechanical properties of assemblies?

3. Geometry & frustration: 2D packings of flexible screws Claessens, Semmrich, Ramos & Bausch, PNAS (2007). bundles of filamentous actin Bundles of helical filaments want twist & 2D order Can they have both? Biological filaments (like DNA) have helical, screw-like structure… …and molecular screws exert a mutual twist, inducing relative tilt Questions: -how does local twist packing dictate assembly properties (size) of bundles? -other twisted assembly motifs? writhing bundles? planar assemblies of short filaments?

4. Better filament packing with defects: 5-fold disclinations drive twisting writhing conformations Questions: What is state of densely packed DNA? Crystalline or liquid crystalline? What type of defect structures accommodate packaging? DNA in bacteriophage capsid (EM) DNA in bacteriophage capsid (simulation) Petrov, Locker & Harvey, PRE (2009). Leforestier & Livolant, PNAS (2009).

5. Homin: postdoc Stephanie: PSE Wei: PSE Raw materials: espresso Apparatus: “belafonte” currently seeking graduate student www.pse.umass.edu/ggrason/ grason@mail.pse.umass.edu Badel: postdoc