Selected Publications

Instability and structural transitions arise in many important problems involving dynamics at molecular length scales. Buckling of an elastic rod under a compressive load offers a useful general picture of such a transition. However, the existing theoretical description of buckling is applicable in the load response of macroscopic structures, only when fluctuations can be neglected, whereas membranes, polymer brushes, filaments, and macromolecular chains undergo considerable Brownian fluctuations. We analyze here the buckling of a fluctuating semiflexible polymer experiencing a compressive load. Previous works rely on approximations to the polymer statistics, resulting in a range of predictions for the buckling transition that disagree on whether fluctuations elevate or depress the critical buckling force. In contrast, our theory exploits exact results for the statistical behavior of the worm-like chain model yielding unambiguous predictions about the buckling conditions and nature of the buckling transition. We find that a fluctuating polymer under compressive load requires a larger force to buckle than an elastic rod in the absence of fluctuations. The nature of the buckling transition exhibits a marked change from being distinctly second order in the absence of fluctuations to being a more gradual, compliant transition in the presence of fluctuations. We analyze the thermodynamic contributions throughout the buckling transition to demonstrate that the chain entropy favors the extended state over the buckled state, providing a thermodynamic justification of the elevated buckling force.
Polymers

We demonstrate the ability to simulate complex flows of entangled polymer melts using a high-fidelity slip-link model. Given the strong connections of the underlying molecular model to an atomistic description, nearly ab initio predictions of complex processing are feasible. Moreover, the method retains sufficient information which might allow extraction of detailed polymer chain conformations imposed by the flow. The macroscopic transport equations are solved using smoothed-particle hydrodynamics consistently with the stresses calculated using stochastic simulation of an ensemble of polymer chains in each particle. The polymer model uses only a single adjustable parameter whose value is determined from equilibrium stress relaxation. All other parameters are determined from atomistic simulation. Thereafter, nonlinear rheology predictions are made without any parameter adjustment. As a demonstration, we simulate journal-bearing flow of a moderately entangled polymer. Although the flows considered here are two dimensional, the required computational resources demonstrate that three dimensional flow calculations are accessible.
In Molecular Systems Design & Engineering.

Building up gradually from first principles, this unique introduction to modern thermodynamics integrates classical, statistical and molecular approaches, and is especially designed to support students studying chemical and biochemical engineering. In addition to covering traditional problems in engineering thermodynamics in the context of biology and materials chemistry, students are also introduced to the thermodynamics of DNA, proteins, polymers and surfaces. It includes over 80 detailed worked examples, covering a broad range of scenarios such as fuel cell efficiency, DNA/protein binding, semiconductor manufacturing, and polymer foaming, emphasising the practical real-world applications of thermodynamic principles; more than 300 carefully tailored homework problems, designed to stretch and extend students' understanding of key topics, accompanied by an online solution manual for instructors; and all the necessary mathematical background, plus resources summarising commonly used symbols, useful equations of state, microscopic balances for open systems, and links to useful online tools and datasets.
Cambridge Series in Chemical Engineering

Recent Publications

More Publications

  • Reexamination of multi-component non-ideal polymer solution based on the general equation for nonequilibrium reversible-irreversible coupling
    The Journal of Chemical Physics

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  • Buckling a Semiflexible Polymer Chain under Compression
    Polymers

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  • A multi-chain polymer slip-spring model with fluctuating number of entanglements: Density fluctuations, confinement, and phase separation
    The Journal of Chemical Physics

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  • A boundary integral method for computing forces on particles in unsteady Stokes and linear viscoelastic fluids
    International Journal for Numerical Methods in Fluids

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  • Nanomechanics of Type I collagen
    Biophysical journal

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  • Challenging Tube and Slip-Link Models: Predicting the Linear Rheology of Blends of Well-Characterized Star and Linear 1, 4-Polybutadienes
    American Chemical Society

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  • Microrheological Study of Physical Gelation in Living Polymeric Networks
    In Macromolecules

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  • Smoothed particle hydrodynamics simulation of viscoelastic flows with the slip-link model
    In Molecular Systems Design & Engineering.

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  • Identifying distinct nanoscopic features of native collagen fibrils towards early diagnosis of pelvic organ prolapse
    Nanomedicine: Nanotechnology, Biology and Medicine

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  • Determination of linear viscoelastic properties of an entangled polymer melt by probe rheology simulations
    American Physical Society

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Recent & Upcoming Talks

Software

Code for calculating the primitive-path length distribution for a monodisperse linear polymer melt (Rudi Steenbakkers):

README_pp_discrete_msm.txt

PI_Kuhnchain.m

pp_discrete_msm.m

Analytic Slip-link Expressions for Universal Dynamic Modulus Predictions of Linear Monodisperse Polymer Melts (Maria Katzarova):

Download Mathematica notebook

GPU DSM (Marat Andreev, Konstantin Taletskiy):

Source code

GUI for Linux

Lab Members

Lab Members

Group photo in 2014

Projects

Mechanical properties measurements

Measurements of the elastic modulus of type I rat-tail collagen

Polymer rheology

Modeling of dynamics of associating polymers and entangled polymers

Contact