Nanoparticle translocation through polymer brush decorated nanochannels: General principles

• Applicant: Dr. Holger Merlitz
• Subject Area: Experimental and Theoretical Physics of Polymers ; Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449432865

Material properties of polymers can be changed via the conformational transition of the chains. This offers unique possibilities to obtain chemically switchable devices. A particular interesting example is the polymer brush which consists of polymers grafted to a substrate. It is known that thermoresponsive polymers or polymers which display a co-nonsolvency transition in mixed solvents display a jump-like collapse/volume transition caused by a minor variation in temperature or solvent composition, respectively. If such polymer brushes are covering the inner wall of a nanochannel, new aspects due to the concave cylindrical geometry come into play. Moreover, such a layout can have interesting applications as switchable gates in microfluidic devices or switchable pores for filtering of nanoobjects. In the proposed research project, the physical principles behind the gating behavior of polymer-decorated nanochannels and the translocation of objects (macromolecules or nanoparticles) through these channels will be explored; analytical models for their function will be developed. The polymers are forming an environment-responsive brush which reversibly switches between a swollen state (gate 'closed') and a collapsed state (gate 'open'). Properties of the involved transitions are studied through mean-field theory and coarse-grained molecular simulations. Here, previously developed and successfully applied molecular dynamics methods will be available. The permeability of such a channel is investigated for freely diffusing particles but also for pressure-driven and self-propelling (active Brownian) particles. Key aspects are the exploration of jump-like opening/closing transitions due to the cylindrical geometry, in which the interplay between brush-properties and surface tension plays a key role. Previously developed models for the nucleation of pores in membranes will be adapted for that task. Furthermore, driven systems can cause new types of transition and even spatial-temporal patterns, such as pulsed droplets formed in a continuous flow field. While the main goal of this project is to develop concepts of polymer physics for this system, the results of this project can offer guidelines for the technical design of nano-fluidic devices and also to improve the basic understanding of related biological processes, such as protein-translocations through nuclear pore complexes.

• DFG Programme: Research Grants