Embedding plasmonic nanoparticles in soft crystals: an approach exploiting CTAB-I structures

Embedding nanoparticles with different functionalities into soft substrates is a convenient tool to realize technologically significant multifunctional materials. This study focuses on incorporating bimetallic plasmonic nanoparticles into soft crystals made of cetyltrimethylammonium bromide-iodide. We observed the emergence of a novel symmetry-lowered cetrimonium crystal polymorph that enables the realization of strong interparticle plasmonic coupling in these composite materials. The observed crystal polymorph exhibits a triclinic structure with significantly reduced unit cell volume compared to standard CTAB. Solid-state nuclear magnetic resonance studies revealed an enhanced cetrimonium chain rigidity and a commensurate decrease in the mobility of the methyl groups. This is attributed to iodide incorporation. To study the influence of these interactions on solution phase dynamical properties, we employed light scattering measurements using gold nanospheres as markers, where we observed aggregation of these particles. We then develop a two step synthetic scheme that successfully enables high levels (533 particles per μm2) of incorporation of bimetallic plasmonic particles into the emergent crystal polymorph.

Molecular-scale Insights into Cooperativity Switching of xTAB Adsorption on Gold Nanoparticles

Quantifying adsorption behaviors is crucial for various applications such as catalysis, separation, and sensing, yet it is generally challenging to access in solution. Here, we report a combined experimental and computational study of the adsorption behaviors of alkyl-trimethylammonium bromides (xTAB), a class of ligands important for colloidal nanoparticle stabilization and shape control, with various alkyl chain lengths x on Au nanoparticles. We use density functional theory (DFT) to calculate xTAB binding energies on Au{111} and Au{110} surfaces with standing-up and lying-down configurations, which provides insights into the adsorption affinity and cooperativity differences of xTAB on these two facets. We demonstrate the key role of van der Waals interactions in determining the xTAB adsorption behavior. These computational results predict and explain the experimental discovery of xTAB's adsorption behavior switch from stronger affinity, negative cooperativity to weaker affinity, positive cooperativity when the concentration of xTAB increases in solution. We also show that in the standing-up configuration, bilayer adsorption may occur on both facets, which can lead to different differential binding energies and consequently adsorption crossover between the two facets when the ligand concentration increases. Our combined experimental and computational approaches demonstrate a paradigm for gaining molecular-scale insights into adsorbate-surface interactions.

Imparting pH and temperature dual-responsiveness in a micellar solution of cationic surfactants by introducing a hydrotrope

Over the recent years, intelligent, multi-responsive micelles have received considerable attention due to their promising application in a variety of fields, including biomedical technology, drug delivery, separation, and catalysis. However, the design of such systems with controlled self-assembly is challenging both experimentally and theoretically and is still in the nascent stage. In this study, a novel dual-stimuli triggered wormlike micellar solution is prepared by mixing cationic surfactants 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R₁₆HTAB) and sodium hydrogen phthalate (SHP). The viscoelasticity, aggregate morphology, and pH- and thermo-responsive behavior of the micellar solution are examined by rheological measurements, cryogenic-transmission electron microscopy (cryo-TEM), nuclear magnetic resonance (¹H NMR) spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The dual-sensitive fluid can be switched between a water-like state and a gel-like state by adjusting the pH and temperature. The variations in the flowing behavior are ascribed to the microstructural transition between wormlike micelles, short cylindrical micelles, and spherical micelles. Furthermore, based on the experimental results, dual-responsive behavior of the mixed solution is attributed to the different binding modes between SHP and the surfactant with the variation in the pH and temperature. We hope that the proposed system provides a new route for developing multi-stimuli-responsive materials that are capable of adapting to local environmental variations.

A pH, thermal and light triple-stimuli responsive micellar solution formed by a cationic surfactant and trans-o-hydroxycinnamic acid

Controlling the viscoelastic characteristics of wormlike micelles is of great significance to both basic theory and practical applications. In this article, a novel multi-stimuli responsive wormlike micellar solution was prepared by mixing cationic surfactant 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R₁₆HTAB) with trans-o-hydroxycinnamic acid (OHCA). Rheological studies, nuclear magnetic resonance (¹H-NMR) spectroscopy, UV-vis spectroscopy, and cryogenic-transmission electron microscopy (cryo-TEM) were utilized to investigate the wormlike micellar system's multi-responsive activity. The results showed that the self-assembled structure and viscoelasticity of the mixed system could be regulated by pH, temperature, and light irradiation. With the increasing trans-OHCA concentration, η₀ of the mixed solution increases first and then decreases and the turning point is presented at 30 mM trans-OHCA, indicating the transformation of spherical micelles to wormlike micelles, and then to short micelles. The microstructure of the mixed systems could be reversibly altered by adjusting the pH between 6.41 and 3.90, which was ascertained by cryogenic-transmission electron microscopy (cryo-TEM). The relationship of temperature and η₀ obeys the Arrhenius law, attributed to the decreasing micellar contour length. η₀ of a 40 mM R₁₆HTAB/15 mM OHCA solution sharply increases after UV irradiation, mainly because the cis-isomer could insert into the micelle more easily, and the transition mechanism was studied by UV-vis and ¹H NMR. The multi-responsive self-assembled system may open a new vista for building multi-functional aggregates to adapt to various environmental changes.

Interplay of noncovalent interactions in antiseptic quaternary ammonium surfactant Miramistin

The molecular and crystal structure of the widely used antiseptic benzyldimethyl{3-[(1-oxotetradecyl)amino]propyl}ammonium chloride monohydrate (Miramistin, MR), C26H47N2O+·Cl−·H2O, was determined by a single-crystal X-ray diffraction study and analyzed in the framework of the QTAIM (quantum theory of atoms in molecules) approach using both periodic and molecular DFT (density functional theory) calculations. The various noncovalent intermolecular interactions of different strengths were found to be realized in the hydrophilic parts of the crystal packing (i.e. O—H...Cl, N—H...Cl, C—H...Cl, C—H...O and C—H...π). The hydrophobic parts are built up exclusively by van der Waals H...H contacts. Quantification of the interaction energies using calculated electron-density distribution revealed that the total energy of the contacts within the hydrophilic and hydrophobic regions are comparable in value. The organic MR cation adopts the bent conformation with the head group tilted back to the long-chain alkyl tail in both the crystalline and the isolated state due to stabilization of this geometry by several intramolecular C—H...π, C—H...N and H...H interactions. This conformation preference is hypothesized to play an important role in the interaction of MR with biomembranes.

Ionic Liquid Crystals: Versatile Materials

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Ionic liquid crystals with novel thermal properties formed by the gemini surfactants containing four hydroxyl groups

The ionic liquid crystals formed by the gemini surfactants containing four hydroxyl groups show sustained-release behavior of phase enthalpy.

Bio-based ionic liquid crystalline quaternary ammonium salts: properties and applications

In the present work, we describe the preparation, properties, and applications of novel ionic liquid crystalline quaternary ammonium salts (QSs) of 3-pentadecylphenol, a bio-based low-cost material derived from cashew nut shell liquid. Amphotropic liquid crystalline phase formation in QSs was characterized using a combination of techniques, such as DSC, PLM, XRD, SEM, and rheology, which revealed the formation of one, two, and three dimensionally ordered mesophases in different length scales. On the basis of these results, a plausible mechanism for the formation of specific modes of packing in various mesophases was proposed. Observation of anisotropic ionic conductivity and electrochemical stability suggests their application as a solid electrolyte.

Ether- and alcohol-functionalized task-specific ionic liquids: attractive properties and applications

In recent years, the designer nature of ionic liquids (ILs) has driven their exploration and exploitation in countless fields among the physical and chemical sciences. A fair measure of the tremendous attention placed on these fluids has been attributed to their inherent designer nature. And yet, there are relatively few examples of reviews that emphasize this vital aspect in an exhaustive or meaningful way. In this critical review, we systematically survey the physicochemical properties of the collective library of ether- and alcohol-functionalized ILs, highlighting the impact of ionic structure on features such as viscosity, phase behavior/transitions, density, thermostability, electrochemical properties, and polarity (e.g. hydrophilicity, hydrogen bonding capability). In the latter portions of this review, we emphasize the attractive applications of these functionalized ILs across a range of disciplines, including their use as electrolytes or functional fluids for electrochemistry, extractions, biphasic systems, gas separations, carbon capture, carbohydrate dissolution (particularly, the (ligno)celluloses), polymer chemistry, antimicrobial and antielectrostatic agents, organic synthesis, biomolecular stabilization and activation, and nanoscience. Finally, this review discusses anion-functionalized ILs, including sulfur- and oxygen-functionalized analogs, as well as choline-based deep eutectic solvents (DESs), an emerging class of fluids which can be sensibly categorized as semi-molecular cousins to the IL. Finally, the toxicity and biodegradability of ether- and alcohol-functionalized ILs are discussed and cautiously evaluated in light of recent reports. By carefully summarizing literature examples on the properties and applications of oxy-functional designer ILs up till now, it is our intent that this review offers a barometer for gauging future advances in the field as well as a trigger to spur further contemplation of these seemingly inexhaustible and--relative to their potential--virtually untouched fluids. It is abundantly clear that these remarkable fluidic materials are here to stay, just as certain design rules are slowly beginning to emerge. However, in fairness, serendipity also still plays an undeniable role, highlighting the need for both expanded in silico studies and a beacon to attract bright, young researchers to the field (406 references).