Confined Polymers in Solution: Advanced Optical Investigations Under Extreme Confinement – CoPinS

The Confined Polymers in Solution (CoPinS) project aims to uncover polymer solution dynamics with macromolecular-scale resolution in three dimensions near surfaces. In the context of near-surface dynamics, the solutions studied will be semi-dilute which, up to now, have been investigated much less compared to their counterparts in the melt –for which there is no solvent– and for dilute solutions where the molecules are independent from one another. This relatively complex situation, with concentrations intermediate to melts and dilute solutions, gives rise to a continuously varying bulk length scale (i.e. the correlation length, CL) which can be controlled by changing the concentration of polymers. The CL can range from a few nanometers to hundreds of nanometers. In the bulk this length scale is well-understood concerning its impact on morphological (microscopic) and rheological (macroscopic) properties. However, the CL’s impact on near-surface transport is relatively unknown as revealed in several recent reviews. Moreover, near-surface, semi-dilute dynamics is relevant to flows in many industrial settings (filtration, coatings, energy) yet a fundamental understanding of the underlying physics is lacking.

The complexity of interfacial, semi-dilute solutions arises partly from how the interplay of energies between the two liquid species (polymer, solvent) leads to a preferential one at the surface, and how the resulting hydrodynamics is thus impacted. It is furthermore not known how hydrodynamic interactions change this preference. A lack of understanding persists even while semi-dilute polymers are an extremely important class of materials, finding uses in global energy production, to focus on just one example. In this context, semi-dilute polymer solutions are forced through porous media in which surfaces are a salient, even defining, feature of the flows. The degree to which solutions stick to or slip along the confining surfaces plays a dominant role in the success of the energy production process, yet a basic understanding remains elusive. To overcome this lack of understanding, the CoPinS project will allow us to investigate in detail semi-dilute polymer flows in microfluidic devices (i.e. model pores) at nanometric distances from surfaces. The microfluidic devices will be tailored with various physico-chemical surfaces (hydro-phobic, -phillic, grafted and adsorbed polymers) and over a wide range of polymer molecular weight and concentration, thus scanning a large range of the CL.

Furthermore, knowing that in many biological and medical contexts, polymer flows are driven not only by pressure gradients, but also by chemical, thermal and electrical gradients, a large portion of the project will thus be focused on understanding how different driving mechanisms can impose various interfacial flows. Since the physics is not well understood for pressure driven flows, this diverse driving portion of the project is completely open to investigating polymer interfacial mobility, and all results will be novel.

The main tool of our experimental investigations will be objective-based, total internal reflection fluorescence (TIRF), permitting 3D tracer tracking to determine flow properties at the nanoscale. TIRF has a long history in surface-specific biological science, and was developed into a high-performance soft-matter probe over the last three decades. However, only recently did it become capable of measuring flows with macromolecular resolution, providing an exciting opportunity for the CoPinS project to target polymer interfacial dynamics. The project brings together a broad team of polymer scientists who are well-positioned to undertake the project. The funding will enable the creation of an independent research group that collaborates with this team to uncover molecular-scale polymer dynamics at interfaces in a field of high impact and tremendous current interest.