Amphiphilic Hybrid Nano Building Blocks with Surfactant-Mimicking Structures.

Abstract

We report the preparation and self-assembly of amphiphilic hybrid nano building blocks (NBBs) with surfactant-mimicking structures. These NBBs, composed of hydrophilic silica-like heads tethered with well-defined one or two hydrophobic polystyrene (PS) tails, were prepared by efficient intramolecular cross-linking via silane chemistry. Using a series of "AB" diblock copolymers (BCPs) and "ABA" tri-BCPs of PS and poly(tert-butyl acrylate-co-3-(trimethoxysilyl)propyl methacrylate) (P(tBA-co-TMSPMA)), the intramolecular self-folding of P(tBA-co-TMSPMA) blocks and the deprotection of tert-butyl groups were demonstrated to be an efficient method to prepare amphiphilic NBBs with a hydrophilic silica head tethered by one or two PS tails. The formation of NBBs was carefully studied by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. The self-assembly of these amphiphilic NBBs was further investigated by fixing the molecular weight of PS tails and varying the size of hydrophilic heads. The intramolecular cross-linking of hydrophilic heads that shifted the hydrophilic/hydrophobic balance of polymers resulted in morphological transitions from bilayered vesicles to spherical micelles. Spherical micelles prepared from NBBs with large hydrophilic heads were found to have surface protrusions that differed from the self-assembly of linear BCPs. We also observed that the chain conformation of PS tails was critical for the self-assembly of NBBs, where the bitailed NBBs with highly stretched PS tails favored bilayered vesicle structures.