Lincoln Materials Science Platform
School of Mathematics and Physics
Dr Kostas Daoulas
Max Planck Institute for Polymer Research, Mainz, Germany
Monday 3rd November 2014
Studying soft materials for specific technological applications with “top-down” coarse-grained models
Studying soft matter on large time and length scales with computer simulations requires drastically coarse-grained models. Frequently their development benefits from concepts of universality, relying on separation between microscopic details and mesoscopic behaviour. The latter can be then studied with simple models where the choice of the coarse-grained representation, interactions, and parameters is motivated by some characteristic thermodynamic, structural, and/or dynamical properties of the system. Here we will highlight special “top-down” strategies where the control of the thermodynamic and material properties is facilitated by linking the particle-based model to frameworks akin to the classical density functional theory of liquids. The presentation of the modelling concept will be conducted in context of several technological applications based on soft mater materials.
First we will consider block-copolymer assembly guided by chemically patterned substrates. The topic is of significant importance for microelectronics industry as a potential strategy for creating nanoscale elements of electric circuits. We will focus on the robustness of replication of polymer morphologies to local imperfections of the substrate pattern directing the assembly. For this purpose, a generic particle-based description will be employed traced back to the classical Edwards model. The modelling predictions  on the effects of line edge roughness (LER) of the pattern on the shape of the assembled structures will be compared with experimental data .
Subsequently, we will discuss the extension of top-down models to cases where mesoscale behaviour remains coupled across the length scales to fine details of molecular architecture and interactions. We will address liquid crystalline (LC) mesophases of polymeric semiconductors considering as a test case poly(3-alkylthiophenes). Top-down models describing uniaxial  and biaxial  nematic LC mesophases will be elaborated. Based on experimental data available in the literature, we will demonstrate that the models offer a realistic description of material properties in polymer nematics. These include the effect of molecular weight on phase behaviour and the Frank elastic constants. In the biaxial morphologies we will investigate the distribution of lengths of conjugated segments discussing how collective orientation and planarization of polymer chains can affect properties related to charge transport.
More applications will be briefly reviewed in the conclusions.
 K. Ch. Daoulas, M. Müller, M. P. Stoykovich, H. Kang, J. J. de Pablo, and P. F. Nealey, Langmuir 2008, 24, 1284
 M. P. Stoykovich, K. Ch. Daoulas, M. Müller, H. Kang, J.J. de Pablo, and P. F. Nealey, Macromolecules 2010, 43, 2334
 K. Ch. Daoulas, V. Rühle, and K. Kremer, J. Phys.-Condens. Mat. 2012, 24, 284121
 P. Gemünden, C. Poelking, K. Kremer, D. Andrienko, and K.Ch. Daoulas, Macromolecules 2013, 46, 5762