Magneto‐Adaptive Surfactants Showing Anti‐Curie Behavior and Tunable Surface Tension as Porogens for Mesoporous Particles with 12‐Fold Symmetry

Abstract

Gaining external control over self-organization is of vital importance for future smart materials.S urfactants are extremely valuable for the synthesis of diverse nanomaterials. Their self-assembly is dictated by microphase separation, the hydrophobic effect, and head-group repulsion. It is desirable to supplement surfactants with an added mode of long-range and directional interaction. Magnetic forces are ideal, as they are not shielded in water.W er eport on surfactants with heads containing tightly bound transition-metal centers.T he magnetic moment of the head was varied systematically while keeping shape and charge constant. Changes in the magnetic moment of the head led to notable differences in surface tension, aggregate size, and contact angle,which could also be altered by an external magnetic field. The most astonishing result was that the use of magnetic surfactants as structuredirecting agents enabled the formation of porous solids with 12-fold rotational symmetry.The spontaneous formation of organized patterns as an intrinsic property of asystem containing discrete constituents, ap rocess termed self-assembly,h as fascinated scientists for decades.N ature shows the enormous potential of such behavior, since many of the unexcelled properties of biological matter originate from its capacity for adaptive selfassembly.[1] Full exploration of this potential in materials science is still remote,a smost reported examples of selfassembly so far are dictated by internal factors,s uch as thermodynamic equilibrium.[2] Systems reaching as tate of higher order only under constant consumption of energy (dissipative,n on-equilibrium state) have seldom been reported.[3] Apremise for advancing research in this direction is that compounds capable of adaptive self-assembly can be equipped with the ability to be actuated externally.Examples from particle research, such as dispersions of superparamagnetic colloids, [4] demonstrate the promise of manipulation by the use of magnetism, because it can be applied in astatic or dynamic way,a nd unlike electric fields,m agnetism is not damped in aqueous electrolytes.T hus,i ti sw orth exploring the use of external magnetic fields to trigger the selforganization of molecular systems.As model systems for the self-assembly of soft matter, surfactants are the focus of much current interest. Surfactants are molecular species that contain two moieties of opposite solvent compatibility arranged in adipolar geometry.Inpolar solvents,u sually water, concentration-dependents elf-organization takes place.T he amphiphilic properties of surfactants make them suitable for the stabilization of interfaces of many kinds,f or example,f or the generation of nanoparticles or nanoporous materials.[5] Thetypical head group of surfactants is organic in nature and, thus,d iamagnetic.T om ake as urfactant magnetic, one of its constituents should contain ap aramagnetic metal species.T his emerging field was reviewed very recently by Eastoe and co-workers.[6] Most known examples involve surfac...

Ferro-self-assembly: magnetic and electrochemical adaptation of a multiresponsive zwitterionic metalloamphiphile showing a shape-hysteresis effect

“…21,30,31 Some of us have previously reported redox-switchable as well as paramagnetic stimuli-responsive amphiphiles of relevance to the current work. 32,33 We thought that ferrocene would be an ideal building block in order to combine both these kinds of stimuli within one single amphiphile. [34][35][36][37] On oxidation, the diamagnetic, hydrophobic ferrocene nucleus is transformed into a paramagnetic S ¼ 1/2 ferrocenium ion with a distinct hydrophilic character.…”

Hybrid Surfactants with N‐Heterocyclic Carbene Heads as a Multifunctional Platform for Interfacial Catalysis

“…First, 2,6‐dichloro‐4‐iodopyridine ( 2 ) was coupled to the alkyl‐substituted phenylboronic acid ( 1 ) by means of Suzuki coupling, followed by the nucleophilic substitution of the chlorine substituents in 3 with an N ‐substituted imidazole ( 4 ). Because the flexible alkyl chain prevents growing single‐crystals and characterization by X‐ray diffraction methods, electron‐spray ionization mass spectrometry (ESIMS) has proven to be a valuable method for hybrid surfactants . The ESIMS patterns of 5 a,b are shown in the Supporting Information, Figure S1.…”

Multiheaded Cationic Surfactants with Dedicated Functionalities: Design, Synthetic Strategies, Self-Assembly and Performance

“…Several gemini-type magnetic surfactants comprise a group of unconventional surfactants consisting of two hydrophobic chains, three different hydrophilic groups (two quaternary ammonium salts and one hydroxylic group) and two magnetic counterions [121]. A unique group of magnetic surfactants are compounds with metals (e.g., manganese or gadolinium) complexed with the correct number of nitrogen atoms containing ring-type structures [122,123]. Such groups of surfactants exhibit easy tunability in terms of their surface tension and wettability due to anti-Curie behavior.…”