Polymers and Soft Condensed Matter Dr Edith Sevick

We research the physical properties of polymers, in particular single polymer chains. Our aim is to understand how molecular and structural features of polymer chains give rise to equilibrium and non-equilibrium properties in a variety of conditions for example, when chains are tethered to a surface or sheared by fluid flow. We use a combination of computer simulation, theory and experiments.

Using the latest techniques, such as Atomic Force Microscopy and Optical Tweezers, we are able to manipulate single polymer chains including DNA and proteins. These techniques are capable of imposing nanometre-scale deformations and measuring picoNewton scale forces.

Understanding the physics of polymers at such small scales is important for the development of nanotechnology, particularly for determining how nanomachines can be controlled and calculating the work they are capable of performing.

Current research activities

Thermodynamics of small systems over small timescales

Our laboratory has a specially modified optical tweezer apparatus for the measurement of small forces. It consists of an optical trap that weakly holds a micron-sized bead. The trap is formed by a focused laser beam which is refracted through the transparent bead. The refracted rays exert a force on the bead, drawing it towards the region of highest light intensity. The optical trap 'holds' the bead and allows the measurement of picoNewton forces acting on the bead. This apparatus has been used to demonstrate experimentally, for the first time, that a small system can evolve in a way that is opposite to that predicted by the Second Law of Thermodynamics. This is important as it suggests that nanomachines do not operate as simple scaled-down versions of larger machines.

Mechanical properties of single polymer chains

Using both experiment and simulation, we explore the deformation of single polymer chains when they are stretched and compressed. By attaching latex beads to the ends of a modified DNA molecule, we stretch a single DNA molecule in the optical tweezers apparatus and record the tension in the chain as we elongate it. We measure larger stretching forces in single polymer chains whose ends are attached to the tip of an Atomic Force Microscope and an attractive substrate. We also study the squashing of single polymer chains using computer simulation. Single polymer chains are manipulated in a range of situations such as varying solvent conditions. These are important in understanding the shearing of dilute polymer solutions, the impact of biopolymers attached at a membrane wall, and the properties of DNA in the presence of binding proteins.

Annual Research Report   (PDF format)

Group members

Academic Staff:
Dr Edith Sevick (Leader)   |   Dr Prabhakar Ranganathan   |   Dr Genmiao Wang

PhD Students:
David Carberry   |   James Reid

Key publications

1. E.M. Sevick and D.R.M. Williams, Collision of a Field-Driven Polymer with a Post: Electrophoresis in Microlithographic Arrays, Phys. Rev. Lett.76, 2595-2598, 1996.
2. M.C. Guffond, D.R.M. Williams, and E.M. Sevick, End-Tethered Polymer Chains under AFM Tips: Compression and Escape in Theta Solvents, Langmuir 13, 5691-5696, 1997.
3. E.M. Sevick and D.R.M. Williams, Polymers Grafted onto Strongly Adsorbing Surfaces in Poor Solvents: Stretching, Fission, Phase Separation and Globular Micelles in 2D, Phys. Rev. Lett. 82, 2701-2704, 1999.
4. B.J. Haupt, T.J. Senden, and E.M. Sevick, Experimental Evidence of the Rayleigh Instability in Single Polymer Chains, Langmuir 18, 2174-2182, 2002.
5. G.M. Wang, E.M. Sevick, E. Mittag, D.J. Searles, and D.J. Evans, Experimental Demonstration of Violations of the Second Law of Thermodynamics, Phys. Rev. Lett. 89, 50601-50604, 2002.

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curriculum vitae publications Group Web Pages

Dr E M Sevick Research School of Chemistry, Building 35 Australian National University Canberra ACT 0200 AUSTRALIA Ph: +61 2 6125 0508 Fx: +61 2 6125 0750 E-mail: sevick@rsc.anu.edu.au