Molecular Brush Surfactants: Versatile Emulsifiers for Stabilizing and Structuring Liquids

Associative Liquid-In-Liquid 3D Printing Techniques for Freeform Fabrication of Soft Matter

Shaping soft materials into prescribed 3D complex designs has been challenging yet feasible using various 3D printing technologies. For a broader range of soft matters to be printable, liquid-in-liquid 3D printing techniques have emerged in which an ink phase is printed into 3D constructs within a bath. Most of the attention in this field has been focused on using a support bath with favorable rheology (i.e., shear-thinning behavior) which limits the selection of materials, impeding the broad application of such techniques. However, a growing body of work has begun to leverage the interaction or association of the two involved phases (specifically at the liquid-liquid interface) to fabricate complex constructs from a myriad of soft materials with practical structural, mechanical, optical, magnetic, and communicative properties. This review article has provided an overview of the studies on such associative liquid-in-liquid 3D printing techniques along with their fundamentals, underlying mechanisms, various characterization techniques used for ensuring the structural stability, and practical properties of prints. Also, the future paths with the potential applications are discussed.

Alternating Terpolymers through Cyclopolymerization and Subsequent Orthogonal Functionalization

A method for the synthesis of functionalized alternating copolymers by reversible deactivation radical polymerization was developed. Copolymerization by reversible addition-fragmentation chain transfer of hexenyl vinyl ether with a novel fluorinated divinyl monomer yields alternating cyclopolymers that can be chemoselectively modified by three distinct orthogonal functionalization reactions. Along the thiol-ene click reaction and amidation, a third functionalization was achieved via NHC-catalyzed transesterification or acylation resulting in a small library of ABC-type alternating terpolymers.

Biologically Relevant Micellar Nanocarrier Systems for Drug Encapsulation and Functionalization of Metallic Nanoparticles

The preparation of new and functional nanostructures has received more attention in the scientific community in the past decade due to their wide application versatility. Among these nanostructures, micelles appear to be one of the most interesting supramolecular organizations for biomedical applications because of their ease of synthesis and reproducibility and their biocompatibility since they present an organization similar to the cell membrane. In this work, we developed micellar nanocarrier systems from surfactant molecules derived from oleic acid and tetraethylene glycol that were able to encapsulate and in vitro release the drug dexamethasone. In addition, the designed micelle precursors were able to functionalize metallic NPs, such as gold NPs and iron oxide NPs, resulting in monodispersed hybrid nanomaterials with high stability in aqueous media. Therefore, a new triazole-derived micelle precursor was developed as a versatile encapsulation system, opening the way for the preparation of new micellar nanocarrier platforms for drug delivery, magnetic resonance imaging, or computed tomography contrast agents for therapeutic and diagnostic applications.

Reconfiguration and Reorganization of Bottlebrush Polymer Surfactants

Bottlebrush random copolymers (BRCPs), having randomly distributed hydrophilic and hydrophobic side chains, are shown to reconfigure into hydrophilic-rich and hydrophobic-rich conformations at liquid-liquid interfaces to reduce interfacial energy. Both the degree of polymerization (N_BB ) and extent of grafting in these BRCPs were found to impact surface coverage and assembly kinetics. The time-dependence of the interfacial tension is described as the sum of two exponential relaxation functions characterizing BRCP diffusion, interfacial adsorption, and reorganization. Interfacial tension (γ) and fluorescence recovery after photobleaching (FRAP) results showed that higher molecular weight BRCPs require longer time to adsorb to the water-oil interface, but less time for interfacial reorganization. Overall, this work describes fundamental principles of BRCP assembly at liquid-liquid interfaces, with implications pertaining to polymer design with enhanced understanding of emulsification, adhesion, and related properties in fluids and at interfaces.

The Assembly and Jamming of Nanoparticle Surfactants at Liquid-Liquid Interfaces

Using the interactions between nanoparticles (NPs) and polymeric ligands to generate nanoparticle surfactants (NPSs) at the liquid-liquid interface, the binding energy of the NP to the interface can be significantly increased, irreversibly binding the NPSs to the interface. By designing a simplified NPS model, where the NP size can be precisely controlled and the characteristic fluorescence of the NPs be used as a direct probe of their spatial distribution, we provide new insights into the attachment mechanism of NPSs at the liquid-liquid interface. We find that the binding energy of NPSs to the interface can be reduced by competitive ligands, resulting in the dissociation and disassembly of NPSs at the interface, and allowing the construction of responsive, reconfigurable all-liquid systems. Smaller NPSs that are loosely packed (unjammed) and irreversibly bound to the interface can be displaced by larger NPSs, giving rise to a size-dependent assembly of NPSs at the interface. However, when the smaller size NPSs are densely packed and jam at the interface, the size-dependent assembly of NPSs at the interface can be completely suppressed.

Responsive Interfacial Assemblies Based on Charge-Transfer Interactions

Charge transfer (CT) interactions have been widely used to construct supramolecular systems, such as functional nanostructures and gels. However, to date, there is no report on the generation of CT complexes at the liquid-liquid interface. Here, by using an electron-deficient acceptor dissolved in water and an electron-rich donor dissolved in oil, we present the in situ formation and assembly of CT complex surfactants (CTCSs) at the oil-water interface. With time, CTCSs can assemble into higher-order nanofilms with exceptional mechanical properties, allowing the stabilization of liquids and offering the possibility to structure liquids into nonequilibrium shapes. Moreover, due to the redox-responsiveness of the electron-deficient acceptor, the association and dissociation of CTCSs can be reversibly manipulated in a redox process, leading to the switchable assembly and disassembly of the resultant constructs.