Abstract:

I will present the phase separation behavior of different sequences of a coarse-grained model for sequence defined macromolecules. They exhibit a surprisingly rich phase behavior, and not only conventional liquid-liquid phase separation is observed, but also reentrant phase behavior. Most sequences form open phases consisting of large, interconnected aggregates (e.g. string-like or membrane-like clusters), rather than a conventional dense liquids. Minor alterations in the sequence may lead to large changes in the overall phase behavior, a fact of significant potential relevance for biology and for designing self-assembled structures using block copolymers. I will also discuss recent results from unsupervised manifold learning (UMAP) to classify the different aggregate types and what we can learn from machine learning. Using a bidirectional Recurrent Neural Network (RNN), we can now predict which sequence will self-assemble into what aggregate structure. With this framework, we can investigate the effects of dispersity and sequence errors, which is of immediate importance for experimental investigations.

Additionally, I will briefly discuss how block copolymers interact with biological lipid membranes to form hybrid membranes. Hybrid phospholipid block copolymer bilayers display many properties, seen in biomembranes such as selective transport phenomena, synergistic elastic properties, and structural phase transformations. Just like in biomembranes, these fundamental properties of hybrid bilayers are often regulated by lateral phase separation. Understanding the molecular and physical cues that determine the formation of rafts or domains in hybrid membranes, their size, and morphology is paramount to elucidating and programming their function. We find that at low polymer content, a new structure develops in which the bilayer leaflets unzip (but remain continuous) to incorporate nanodomains of hydrophobic butadiene globules. Our findings offer new insights into the morphology of biomembranes upon the insertion of transmembrane proteins with bulky hydrophobic residues.