Self-Assembly of Charge-Containing Copolymers at theLiquid–Liquid Interface

摘要

Quantitatively understanding the self-assembly of amphiphilic macromolecules at liquid–liquid interfaces is a fundamental scientific concern due to its relevance to a broad range of applications including bottom-up nanopatterning, protein encapsulation, oil recovery, drug delivery, and other technologies. Elucidating the mechanisms that drive assembly of amphiphilic macromolecules at liquid–liquid interfaces is challenging due to the combination of hydrophobic, hydrophilic, and Coulomb interactions, which require consideration of the dielectric mismatch, solvation effects, ionic correlations, and entropic factors. Here we investigate the self-assembly of a model block copolymer with various charge fractions at the chloroform–water interface. We analyze the adsorption and conformation of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) and of the homopolymer poly(2-vinylpyridine) (P2VP) with varying charge fraction, which is controlled via a quaternization reaction and distributed randomly along the backbone. Interfacial tension measurements show that the polymer adsorption increases only marginally at low chargefractions (<5%) but increases more significantly at higher chargefractions for the copolymer, while the corresponding randomly chargedP2VP homopolymer analogues display much more sensitivity to the presenceof charged groups. Molecular dynamics (MD) simulations of the experimentalsystems reveal that the diblock copolymer (PS-b-P2VP)interfacial activity could be mediated by the formation of a richset of complex interfacial copolymer aggregates. Circular domainsto elongated stripes are observed in the simulations at the water–chloroforminterface as the charge fraction increases. These structures are shownto resemble the spherical and cylindrical helicoid structures observedin bulk chloroform as the charge fraction increases. The self-assemblyof charge-containing copolymers is found to be driven by the associationof the charged component in the hydrophilic block, with the hydrophobicsegments extending away from the hydrophilic cores into the chloroformphase.