Complex fluids and theoretical polymer physics seminars

We run a regular seminar series, with a mixture of internal and external speakers.

Our aim is to provide the chance to engage with the different research projects going on and to stimulate discussions and new ideas. Therefore, we want this seminar to be informal and lively, with the emphasis on explaining ideas, plans and problems.

2026

14 May

16:00 to 17:00 Maths 108

12 February

14:00 to 15:00 Maths 108

Speaker: Hanan Hozan (with Mike Baines and Alex Lukyanov)

Title: Oil slick dynamics on wavy sea surface in the convective limit of the model

Abstract: The main idea of the study is to rigorously understand the dynamics of oil slicks freely floating on the surface of water in the presence of water-wave motion. The mathematical model, we discuss and apply, is based on the thin film approximation developed by making use of the small parameter present in the problem, which is the ratio of the oil layer thickness to characteristic horizontal dimensions. The resultant governing equations are of diffusion-advection type, where the effective diffusion results from coupled action of gravity and viscous forces and the advection terms come from the water-wave dynamics. In the presentation, we are going to demonstrate, interpret and compare two limiting cases: strong diffusion and weak advection, and negligible diffusion with dominant advective forcing.

2024

30 August

14:30 to 15:30 Maths 104

Speaker: Prof Mark Matsen, Department of Physics & Astronomy, Department of Chemical Engineering, and Waterloo Institute for Nanotechnology, University of Waterloo, Waterloo, Canada

Title: Development of quantitatively accurate simulations for block copolymer materials

28 May

10:00 to 11:00 Maths 212

Speaker: Prof Yuichi Masubuchi, Nagoya University, Japan

Title: Relationship between fracture of networks and the cycle rank

Abstract: The influence of node functionality (f) on the fracture of polymer networks remains unclear. While many studies have focused on multifunctional nodes with f > 4, recent research suggests that networks with f = 3 exhibit superior fracture properties compared to those with f = 4. To clarify this discrepancy, we conducted phantom chain simulations for star-polymer networks varying f between 3 and 8. Our simulations utilized equimolar binary mixtures of star branch prepolymers with a uniform arm length. We employed a Brownian dynamics scheme to equilibrate the sols and induce gelation through end-linking reactions. We prevented the formation of odd-order loops algorithmically, owing to the binary reaction and second-order loops. We stored network structures at various conversion ratios (φc) and minimized energy to reduce computation costs induced by structural relaxation. We subjected the networks to stretching until fracture to determine stress and strain at break and work for fractures, εb, σb, and Wb. These fracture characteristics are highly dependent on φc for networks with a small f but relatively insensitive for those with a large f. Thus, the networks with small f exhibit greater fracture properties than those with large f at high φc, whereas the opposite relationship occurs at low φc. We analyzed εb, σb, and Wb concerning cycle rank ξ and broken strand fraction φbb. We found that εb, σb/φbb, and Wb/φbb monotonically decrease with increasing ξ, and the data for various f and φc superpose with each other to draw master curves. These results imply that the mechanical superiority of the networks with small f comes from their smaller ξ that gives higher εb, σb/φbb, and Wb/φbb than the networks with large f.

25 April

14:00 to 15:00 Maths 108

Speaker: Nuofei Jiang (Université Catholique de Louvain, Belgium)

Title: Potential Universal Extensional Rheology in Concentrated Polymeric Liquids

Abstract: Polymer dynamics is universal in the linear viscoelastic regime, while the recent experiments show that the nonlinear extensional rheology of polymer melts is highly sensitive to the chemical composition and thus has the non-universal feature. To understand this transition, in this work, the variation of inter-chain interaction in the coarse-grained (CG) molecular dynamics (MD) simulation systems of polymer melts is investigated in terms of the frictional coefficient, which is thought to be the critical factor in explaining the observed non-universality. The frictional coefficients in the simulation systems are quantified from the expressions we proposed very recently (Jiang, N.; van Ruymbeke, E., Macromolecules 2023, 56 (8), 2911-2929.), which are based on the analytical relationships between the frictional coefficient and the observable quantities. After the validation of the CG MD simulation with experimental data and our expressions, it is shown that those frictional coefficients can be universally related to the projection areas of the polymer coils. Moreover, this projection-friction relationship indicates a Kuhn-scale criterion of extensional viscosity, which suggests a universal extensional rheological response will be observed when the samples have the same number of Kuhn segments N_k and the same reduced density n_k defined as the ratio of the Kuhn length to the packing length. This criterion is tested on a series of new simulation systems designed to show universal nonlinear extensional rheology, as well as the existing experimental data in the literature. The results in this work provide a helpful guideline in searching for the potential universal nonlinear flow behaviors in the experimental samples.