From Precision Colloidal Hybrid Materials to Advanced Functional Assemblies

Abstract

Conspectus The concept of colloids encompasses a wide range of isotropic and anisotropic particles with diverse sizes, shapes, and functions from synthetic nanoparticles, nanorods, and nanosheets to functional biological units. They are addressed in materials science for various functions, while they are ubiquitous in the biological world for multiple functions. A large variety of synthetic colloids have been researched due to their scientific and technological importance; still they characteristically suffer from finite size distributions, imperfect shapes and interactions, and not fully engineered functions. This contrasts with biological colloids that offer precision in their size, shape, and functionality. Materials science has searched for inspiration from the biological world to allow structural control by self-assembly and hierarchy and to identify novel routes for combinations of functions in bio-inspiration. Herein, we first discuss different approaches for highly defined structural control of technically relevant synthetic colloids based on guided assemblies of biological motifs. First, we describe how polydisperse nanoparticles can be assembled within hollow protein cages to allow well-defined assemblies and hierarchical packings. Another approach relies on DNA nanotechnology-based assemblies, where engineered DNA structures allow programmed assembly. Then we will discuss synthetic colloids that have either particularly narrow size dispersity or even atomically precise structures for new assemblies and potential functions. Such colloids can have well-defined packings for membranes allowing high modulus. They can be switchable using light-responsive moieties, and they can initiate packing of larger assemblies of different geometrical shapes. The emphasis is on atomically defined nanoclusters that allow well-defined assemblies by supramolecular interactions, such as directional hydrogen bonding. Finally, we will discuss stimulus-responsive colloids for new functions, even toward complex responsive functions inspired by life. Therein, stimulus-responsive materials inspired by biological learning could allow the next generation of such materials. Classical conditioning is among the simplest biological learning concepts, requiring two stimuli and triggerable memory. Therein we use thermoresponsive hydrogels with plasmonic gold nanoparticles and a spiropyran photoacid as a model. Heating is the unconditioned stimulus leading to melting of the thermoresponsive gel, whereas light (at a specified wavelength) originally leads to reduced pH without plasmonic or structural changes because of steric gel stabilization. Under heat-induced gel melting, light results in pH-decrease and chain-like aggregation of the gold nanoparticles, allowing a new plasmonic response. Thus, simultaneous heating and light irradiation allow conditioning for a newly derived stimulus, where the logic diagram is analogous to Pavlovian conditioning. The shown assemblies demonstrate the different functionalitie...

Hierarchical self-assembly in colloidal and molecular length scales in thermotropic zwitterionic liquid crystals

“…A plethora of single-length scale soft matter self-assemblies and underlying applications have already been widely known and exploited based on classic block copolymers, liquid crystals, colloids, and surfactants [1][2][3][4][5] . As the next step towards complexity, hierarchical self-assemblies, and superlattices of soft matter involving order at several length scales attract growing attention for several reasons [6][7][8][9][10][11][12][13][14][15] . An obvious motivation is that they can facilitate multifunctional materials, as different functions can require distinct length scales.…”

“…More conceptually, soft matter hierarchies can promote the understanding of emerging soft complex matter in general, ultimately inspired by quest to progressively harness even biomolecular complexities 16 . In artificial soft matter, hierarchical self-assemblies have been achieved upon engineering different competing structural packing motifs: Selected examples are given by various block architectures in multiblock copolymers, by combinations of mesogenic and polymeric block packings in liquid crystalline polymers, or by combinations of different length scale structural units, such as supramolecular complexation of block copolymers with surfactants or liquid crystals [6][7][8][9][10][11][12][13][14][15] . In low-molecular-weight soft matter, achieving hierarchies becomes especially challenging.…”

Supramolecular assembly of pentamidine and polymeric cyclodextrin bimetallic core–shell nanoarchitectures

“…Noble metal nanoparticles (NPs), in particular those composed of gold and/or silver, are versatile agents endowed with unique physicochemical properties, which recently have drawn great interest for a variety of applications ranging from catalysis to nanomedicine [1][2][3].…”

Nanoswimmers Based on Capped Janus Nanospheres

“…One important class of revolutionary new materials comprises various nanoparticles, which give rise to a plethora of applications [2]. There exist numerous different types of particles and their advanced assemblies [3], each with their own specific implementation across the various fields of science and engineering. One of the most exiting branches of these nanoscopic particles is the various kinds of micro-and nanomotors, or "swimmers" [4,5], that can be created with them.…”