PolySMart: a general coarse-grained molecular dynamics polymerization scheme

Molecular Insight into the Effect of Polymer Topology on Wettability of Block Copolymers: The Case of Amphiphilic Polyurethanes

The microstructure design of multiblock copolymers is essential for achieving desired interfacial properties in submerged applications. Two major design factors are the chemical composition and polymer topology. Despite a clear relationship between chemical composition and wetting, the effect of polymer topology (i.e., linear vs cross-linked polymers) is not very clear. Thus, in this study, we shed light on the molecular origins of polymer topology on the wetting behavior. To this end, we synthesized linear and three-dimensional (3D) cross-linked network topologies of poly(ethylene glycol) (PEG)-modified polycarbonate polyurethanes with the same amount of hydrophilic PEG groups on the surface (confirmed by X-ray photoelectron spectroscopy (XPS)) and studied the wetting mechanisms through water contact angle (WCA), atomic force microscopy (AFM), and molecular dynamics (MD) simulations. The linear topology exhibited superhydrophilic behavior, while the WCA of the cross-linked polymer was around 50°. AFM analysis (performed on dry and wet samples) suggests that PEG migration toward the interface is the dominant factor. MD simulations confirm the AFM results and unravel the mechanisms: the higher flexibility of PEG in linear topology results in a greater PEG migration to the interface and formation of a thicker interfacial layer (i.e., twice as thick as the cross-linked polymers). Accordingly, water diffusion into the interfacial layer was greater in the case of the linear polymer, leading to better screening of the underneath hydrophobic (polycarbonate) segments.

Reactive Martini: Chemical Reactions in Coarse-Grained Molecular Dynamics Simulations

Chemical reactions are ubiquitous in both materials and the biophysical sciences. While coarse-grained (CG) molecular dynamics simulations are often needed to study the spatiotemporal scales present in these fields, chemical reactivity has not been explored thoroughly in CG models. In this work, a new approach to model chemical reactivity is presented for the widely used Martini CG Martini model. Employing tabulated potentials with a single extra particle for the angle dependence, the model provides a generic framework for capturing bonded topology changes using nonbonded interactions. As a first example application, the reactive model is used to study the macrocycle formation of benzene-1,3-dithiol molecules through the formation of disulfide bonds. We show that starting from monomers, macrocycles with sizes in agreement with experimental results are obtained using reactive Martini. Overall, our reactive Martini framework is general and can be easily extended to other systems. All of the required scripts and tutorials to explain its use are provided online.