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Calcium sulfate is one of the most important construction materials. Today it is employed as high-performance compound in medical applications and cement mixtures. We report a synthesis for calcium sulfate nanoparticles with outstanding dispersibility properties in organic solvents without further functionalization. The nanoparticles (amorphous with small γ-anhydrite crystallites, 5-50 nm particle size) form long-term stable dispersions in acetone without any sign of precipitation. 1H NMR spectroscopic techniques and Fourier-transform infrared spectroscopy (FTIR) reveal absorbed 2-propanol on the particle surfaces that induce the unusual dispersibility. Adding water to the nanoparticle dispersion leads to immediate precipitation. A phase transformation to gypsum via bassanite was monitored by an in situ kinetic FT-IR spectroscopic study and transmission electron microscopy (TEM). The dispersibility in a volatile organic solvent and the crystallization upon contact with water open a broad field of applications for the CaSO4 nanoparticles, e.g., as nanogypsum for coatings or the fabrication of hybrid composites. [ABSTRACT FROM AUTHOR]

This work describes the synthesis and characterization of metal-surfactant complexes. Dioctyl sulfosuccinate and dodecylbenzenesulfonate are associated with multivalent aluminum, iron, and vanadium ions using an ion exchange reaction. The metal complexes are dispersible in various organic solvents. In solvents with low polarity, the complexes form "inverse" macromolecular structures with multiple metal ions. In contrast, in alcohols, the complex size is reduced, showing a more disperse conformation. The metal and surfactant ions are still strongly bonded to each other in all the solvents probed. Small-angle X-ray and neutron scattering (SAXS and SANS) are used to characterize the structures. Simultaneous fitting of neutron and X-ray scattering spectra is performed in order to obtain an accurate description of the system. Scattering results are also validated by performing molecular dynamics (MD) simulations. The conductive and electrochemical properties of the complexes in solution are also evaluated. The dispersion of metal-organic complexes significantly increases electric conductivity, and some metal ions in the core of the complexes are shown to be electrochemically active in apolar solvents. [ABSTRACT FROM AUTHOR]

Recent studies have successfully measured surface forces using atomic force microscope (AFM) and modeled surface deformations using the Stokes-Reynolds-Young-Laplace (SRYL) equations for particle-droplet, particle-bubble, droplet-droplet, and bubble-bubble systems in various solutions. The current work focuses on interactions between spherical silica particles and a viscoelastic interface of water droplets in crude oil. The self-assembly of surface active natural polyaromatic molecules (NPAMs) at the oil-water interface has previously been shown to change a viscous dominant oil-water interface to an elastic dominant interface upon aging, due to gradual formation of rigid interfacial networks. AFM was used to measure the interactions between a small silica sphere (D ≈ 8 μm) and a deformable water droplet (D ≈ 70 μm), which exhibits time-dependent interfacial viscoelasticity in NPAM solutions. Unlike the systems studied previously, the measured deformation shown as a repulsive force over the region of constant compliance could not be modeled adequately by the conventional SRYL equations which are applicable only to purely Laplacian interfaces. As the water droplet ages in NPAM solutions, a rigid "skin" forms at the oil-water interface, with the interface exhibiting increased elasticity. Over a short aging period (up to 15 min in NPAM-in-toluene solution), interfacial deformation is well predicted by the SRYL model. However, upon further exposure to the NPAM solution, droplet deformation is overpredicted by the model. Physical properties of this mechanical barrier as a function of interfacial aging were further investigated by measuring interfacial tension, dilatational rheology, and interfacial "crumpling" (non-smooth, non-Laplacian interface) upon droplet volume reduction. By introducing a viscoelasticity parameter to account for interfacial stiffening and using experimentally determined elasticity, we are able to correct this discrepancy and predict droplet deformation under AFM cantilever compression. This parameter appears to be important for modeling non-Laplacian systems of significant viscoelastic contributions, such as biological cell membranes or polymer blends. [ABSTRACT FROM AUTHOR]

Slippery liquid-infused porous surfaces (SLIPS) have potential impact on a wide range of industries, including healthcare, food packaging, and automobile. A tremendouseffort has been focused on developing novel fabrication methods for making SLIPS. However, current fabrication methods usually involve harsh conditions and complicated postfabrication modifications or are limited to specific substrates. Presented here is a novel method for the fast and facile fabrication of SLIPS. Layer-by-layer (LBL) assembly of branched polyethylenimine and Nafion, a perfluorinated polyelectrolyte, is performed with methanol as the solvent. Hierarchically rough and superhydrophobic surface is obtained directly without further modification on various substrates. The surface properties are shown to highly depend on the LBL assembly parameters, including deposition cycles, dipping time, rinsing time, and drying time between baths. The polyelectrolyte multilayers obtained with this method are infused with Krytox 100 to form SLIPS surfaces, which show excellent omniphobic, antifouling, self-cleaning, flexible, and optical properties. The result of this study not only simplifies the fabrication of SLIPS surfaces, but also provides great insight for making LBL films with specific morphologies. [ABSTRACT FROM AUTHOR]

An axial-substituted silicon phthalocyanine derivative, SiPc(OR)2 (R = C4H9), that is soluble in organic solvent is conveniently synthesized. This silicon phthalocyanine derivative reacts with a hydroxyl group on a substrate and then with another phthalocyanine derivative under mild conditions. The accumulation number of the phthalocyanine molecules on the substrates is easily controlled by the immersion time. On the basis of AFM (atomic force microscopy) images, the surface of the phthalocyanine-modified glass substrate has uneven structures on the nanometer scale. ITO electrodes modified with the composition of the phthalocyanine derivative and PCBM show stable cathodic photocurrent generation upon light irradiation. [ABSTRACT FROM AUTHOR]

The well-known Marangoni effect perfectly supports the dynamic mechanism of organic solvent-swollen gels on water. On this basis, we report a series of energy conversion processes of concentrated droplets of polyvinylidene fluoride/dimethyl formamide (PVDF/DMF) that can transfer chemical-free energy to kinetic energy to rapidly rotate itself on water. This droplet (22.2 mg) is capable to offer kinetic energy of 0.099 μJ to propel an artificial paper rocket of 31.8 mg to move over 560 cm on water at an initial velocity of 7.9 cm s-1. As the droplet increases to 35.0 mg, a paper goldfish of 10.6 mg can be driven to swim longer at a higher initial velocity of 20 cm s-1. The kinetic energy of the droplet can be further converted to electrical energy through an electromagnetic generator, in which as a 0.5 MΩ resistor is loaded, the peak output reaches 6.5 mV that corresponds to the power density of 0.293 μW kg-1. We believe that this report would open up a promising avenue to exploit energies for applications in miniature robotics. [ABSTRACT FROM AUTHOR]

Thisstudy provides experimental evidence that di(1-pyrenylmethyl)ether or DiPyMe, a well-known fluorescent probe employed to determinethe microviscosity of surfactant or polymeric micelles, is being hydrolyzedin the presence of water upon UV irradiation. This effect was establishedfrom a careful analysis of the fluorescence spectra and decays acquiredwith aqueous solutions of DiPyMe dissolved in micelles of sodium dodecylsulfate (SDS). The size of the SDS micelles could be adjusted froman aggregation number (Nagg) of 70 to172 by increasing the ionic strength of the aqueous solution from0.0 to 0.5 M NaCl. The hydrolysis of DiPyMe was much reduced in thelarger SDS micelles. While the degradation of DiPyMe in aqueous solutionsof SDS micelles affected the analysis of the fluorescence spectra,model-free analysis (MFA) of the fluorescence decays of DiPyMe couldreliably retrieve the rate constant ⟨k⟩of excimer formation for DiPyMe. After calibration with mixtures oforganic solvents of known macroscopic viscosity, the ⟨k⟩ values obtained for DiPyMe yielded the microviscosity(μη) of the SDS micelles as a functionof salt concentration. The μηwas foundto increase from 4.0 to 8.8 mPa·s as the salt concentration increasedfrom 0.0 to 0.5 M. This study demonstrated that, regardless of theproblem of its hydrolysis that jeopardizes its use in steady-statefluorescence experiments, DiPyMe remains an extremely valuable probefor describing the microviscosity of hydrophobic domains in aqueoussolution as long as its decays are analyzed with a model that accountsfor the presence of degradation products as the MFA does. [ABSTRACT FROM AUTHOR]

A methodology based on light scattering and spectrophotometry was developed to evaluate the effect of organic surfactants on the size and yield of eutectic gallium/indium (EGaIn) nanodroplets formed in organic solvents by ultrasonication. The process was subsequently applied to systematically evaluate the role of headgroup chemistry as well as polar/apolar interactions of aliphatic surfactant systems on the efficiency of nanodroplet formation. Ethanol was found to be the most effective solvent medium in promoting the formation and stabilization of EGaIn nanodroplets. For the case of thiol-based surfactants in ethanol, the yield of nanodroplet formation increased with the number of carbon atoms in the aliphatic part. In the case of the most effective surfactant system-octadecanethiol-the nanodroplet yield increased by about 370% as compared to pristine ethanol. The rather low overall efficiency of the reaction process along with the incompatibility of surfactant-stabilized EGaIn nanodroplets in nonpolar organic solvents suggests that the stabilization mechanism differs from the established self-assembled monolayer formation process that has been widely observed in nanoparticle formation. [ABSTRACT FROM AUTHOR]

Both chiral OFm monosubstituted cyclo(l-Glu-l-Glu) and cyclo(d-Glu-d-Glu) display a robust gelation ability in a variety of organic solvents and water. In contrast to an individual enantiomer, their racemate can form rapidly recoverable thixotropic hydrogels with a remarkably shorter thixotropic recovery time. This unexpected thixotropic behavior is induced by the random arrangement of d- and l-enantiomers in the cell units, leading to the formation of "pseudoracemate", noncrystalline self-assemblies in the resulting 3D fibrous network. [ABSTRACT FROM AUTHOR]

The phase transfer of nanoparticles (NPs) from water to organic solvents by an amphiphilic room-temperature ionic liquid (IL) was reported. The geminal IL modified with Pluronic P123 stabilizes a variety of NPs of different size and nature, such as Pd, Au, Ag, and SiO2 NPs. Their phase transfer into a hydrophobic environment was realized by raising the temperature and adding salts (such as NaCl and KBr), both of which have a common effect of breaking the hydrogen bonds of the IL with H2O. A more straightforward method of using an organic solvent working as a hydrogen bond donor (such as butyl alcohol) was then proposed. In this case, NaCl was no longer required. To further apply this strategy to the organic solvents that are generally incapable of forming hydrogen bonds (e.g., toluene), a small quantity of benzoic acid was added to the organic phase. By forming hydrogen bonds from benzoic acid to the IL, an even more facile approach was provided. FT-IR confirmed the hydrogen bonding between them. The phase-transfer protocol does not rely on coordination bonding of ligands with a specific metal and is capable of the phase transfer of objects with large sizes and different natures. Thus, it has the potential for wide application. [ABSTRACT FROM AUTHOR]

Supramolecular gelation provides an efficient way of fabricating functional soft materials with various nanostructures. Amphiphiles containing naphthyl group and dialkyl l-glutamide with a methylene spacer, 1NALG and 2NALG, have been designed and their self-assembly in various organic solvents were investigated. Both of these compounds formed organogels in organic solvents. In the case of the alcohol solvents, the initially formed organogel underwent gel-precipitate transformation, which process was monitored by the UV-vis, CD spectra, and SEM observation. It was revealed that both the compounds formed the nanofiber structures in gel phases. Interestingly, in alcohol solvents, during the phase transition from the gel to precipitates, the nanofibers gradually transformed into a series of long coaxial solid nanotoruloid, a unique nanostructure that has never been observed in other self-assembly systems. In addition, during the gel formation, the nanofibers with supramolecular chirality or M-chirality were obtained. However, the coaxial nanotoruloid showed an inversed P-chirality. Comprehensive analysis based on various data and the gelator structure, substituent position, type of organic solvents, it was suggested that the synergistic interactions between the amide H-bond and π-π stacking of the naphthyl groups played important roles in the formation of the gels as well as the nanofiber, while the H-bonding ability of alcohol to the amide group can subtly regulate the gelator-gelator interactions and lead to the dynamic and hierarchical evolution of the unique nanostructures. [ABSTRACT FROM AUTHOR]

A C3-symmetric molecule was found to form organic nanotubes through supramolecular gel formation in organic solvents. These nanotubes can be dispersed in toluene without destroying the tubular nanostructures. Using the dispersions of these organic nanotubes as "spreading solutions", Langmuir-spreading films of these nanotubes were formed. Through repeated compression and expansion cycles, the nanotubes can be aligned to a certain extent. The formed Langmuir films could be subsequently transferred to a solid substrate, and the well-aligned nanotube films were constructed by Langmuir-Blodgett film deposition technique. Interestingly, many guests including polymers, water-soluble or oil-soluble organic molecules can be encapsulated into the nanotubes and further spread on a water subphase. Through elaborate control, large-scale parallel alignment of self-assembled organic nanotubes encapsulated by guests was also realized. This study implies that 2D hierarchical alignment of one-dimensional organic nanostructures can be realized using a simple method. [ABSTRACT FROM AUTHOR]

The structure and frictional properties of glycerol monooleate (GMO) in organic solvents, with and without water impurity, confined and sheared between two mica surfaces are examined using molecular dynamics simulations. The structure of the fluid is characterized in various ways, and the differences between systems with nonaggregated GMO and with preformed GMO reverse micelles are examined. Preformed reverse micelles are metastable under static conditions in all systems. In n-heptane under shear conditions, with or without water, preformed GMO reverse micelles remain intact and adsorb onto one surface or another, becoming surface micelles. In dry toluene, preformed reverse micelles break apart under shear, while in the presence of water, the reverse micelles survive and become surface micelles. In all systems under static and shear conditions, nonaggregated GMO adsorbs onto both surfaces with roughly equal probability. Added water is strongly associated with the GMO, irrespective of shear or the form of the added GMO. In all cases, with increasing shear rate, the GMO molecules flatten on the surface, and the kinetic friction coefficient increases. Under low-shear conditions, the friction is insensitive to the form of the GMO added, whereas the presence of water is found to lead to a small reduction in friction. Under high-shear conditions, the presence of reverse micelles leads to a significant reduction in friction, whereas the presence of water increases the friction in n-heptane and decreases the friction in toluene. [ABSTRACT FROM AUTHOR]

A technique to solubilize fine magneticinorganic particles ingeneral organic solvents is proposed via surfaces modification bylong-chain carboxylic acids. This organic modification should overcomethe relatively weak van der Waals interactions between the nanoparticles,allowing the formation of ordered arrangements of the modified Fe3O4and CoFe2O4materials.Using nanodispersions of these organo-modified magnetic nanoparticlesas “spreading solutions”, Langmuir monolayers of theseparticles were formed. Multiparticle layered structures were constructedby the Langmuir–Blodgett (LB) technique. The fabrication ofsingle- and multiparticle layers of organo-modified magnetic nanoparticleswas investigated using surface pressure–area (π–A) isotherms, out-of-plane X-ray diffraction (XRD), in-planeXRD, and atomic force microscopy (AFM). The out-of-plane XRD profileof a single-particle layer of organo-modified Fe3O4clearly showed a sharp peak which was attributed to the distancebetween Fe3O4layers along the c-axis. The AFM image of single-particle layer of organo-modifiedCoFe2O4revealed integrated particle organizationwith a uniform height; these aggregated particles formed large two-dimensionalcrystals. For both nanoparticle species, regular periodic structuresalong the c-axis and high-density single-particlelayers were produced via the Langmuir and LB techniques. [ABSTRACT FROM AUTHOR]

Polydopamine (PDA)-based surface modification has been used in a variety of fields. However, a vague impression on the stability of PDA still exists due to a lack of systematic studies. To ascertain the issue and make better use of this surface modification method, a technique of surface plasmon resonance imaging (SPRi) was exploited to study the stability of PDA coated on gold surface. The results showed that PDA-coating stability was largely dependent on the pH of aqueous solutions, giving detachment ratios up to 66% and 80% at pH 1.0 and pH 14.0, respectively. However, increasing the ionic strength of aqueous solutions could reduce the detachment of PDA in strong acid and strong alkali conditions. Besides, organic solvents also made a difference on the PDA-coating stability. Among the tested 10 kinds of organic solvents, including n-hexane, toluene, ethyl ether, tetrahydrofuran, ethyl acetate, isopropanol, acetone, acetonitrile, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), DMSO caused the most serious detachment of PDA, up to 56%, followed by DMF with a detachment ratio of 31%. Ultrasonication caused less than 10% detachment of the coated PDA. It should be mentioned that the PDA coatings deposited on gold surface were not detached completely in all the test conditions, even at pH 14.0 (ca. 20% PDA retained). In alkaline conditions, detachment competes with further polymerization, which gave a slight increase of the SPRi signals at pH 9.0-11.0. Based on the obtained information about PDA-coating stability, thickness-controllable and alkali-resistant PDA coatings were prepared. Moreover, the alkali-resistant PDA coatings remained reactive to biomolecules, supporting further functionalization of PDA coatings. [ABSTRACT FROM AUTHOR]

Low-molecular-weight gelators are interesting small molecules with potential applications as advanced materials. Carbohydrate-based small molecular gelators are especially useful because they are derived from renewable resources and are more likely to be biocompatible and biodegradable. Various 4,6-benzylidene acetal protected α-methyl 2-D-glucosamine derivatives have been found to be effective low-molecular-weight gelators. To understand the influence of the 4,6-benzylidene acetal functional group toward molecular self-assembly and to obtain effective molecular gelators, we synthesized and analyzed a new series of D-glucosamine derivatives in which the phenyl group of the acetal is replaced by a benzyl group. The homologation of the acetal protection from aromatic to aliphatic functional groups allows us to probe the effect of increasing structural flexibility on molecular self-assembly and gelation. In this study, nine representative amides and nine urea analogs were synthesized, and their gelation properties were analyzed in a series of organic solvents and aqueous solutions. The resulting amide and urea derivatives are versatile organogelators forming gels in toluene, ethanol, isopropanol, ethylene glycol, and aqueous mixtures of organic solvents. More interestingly, the amide analogs are also effective gelators for pump oil and engine oil. NMR spectroscopy at variable temperatures was used to analyze the molecular assemblies and intermolecular forces. The selected gelators with several drug and dye molecules in DMSO and water were studied for their effectiveness of encapsulation and release of these agents. [ABSTRACT FROM AUTHOR]

Block copolymers have attracted much attention as potentially interesting building blocks for the development of novel nanostructured materials in recent years. Herein, we report a new type of self-assembling block copolymer with changeable polymer backbone structure, poly(Fmoc-Ser)ester-b-PSt, which was synthesized by combining the polycondensation of 9-fluorenylmethoxycarbonyl-serine (Fmoc-Ser) with the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St). This block copolymer showed the direct conversion of the backbone structure from polyester to polypeptide through a multi O,N-acyl migration triggered by base-induced deprotection of Fmoc groups in organic solvent. Such polymer-to-polymer conversion was found to occur quantitatively without decrease in degree of polymerization and to cause a drastic change in self-assembling property of the block copolymer. On the basis of several morphological analyses using FTIR spectroscopy, atomic force, and transmission and scanning electron microscopies, the resulting peptide block copolymer was found to self-assemble into a vesicle-like hollow nanosphere with relatively uniform diameter of ca. 300 nm in toluene. In this case, the peptide block generated from polyester formed β-sheet structure, indicating the self-assembly via peptide-guided route. We believe the findings presented in this study offer a new concept for the development of self-assembling block copolymer system. [ABSTRACT FROM AUTHOR]

To control the surface properties of a commonly used polymer, poly(methyl methacrylate) (PMMA), poly(perfluoromethyl methacrylate)s (PFMMAs) with short perfluorinated side groups (i.e., −CF3, −CF2CF3, −(CF3)2, −CF2CF2CF3) were used as blend components because of their good solubility in organic solvents, low surface energies, and high optical transmittance. The surface energies of the blend films of PFMMA with the −CF3 group and PMMA increased continuously with increasing PMMA contents from 17.6 to 26.0 mN/m, whereas those of the other polymer blend films remained at very low levels (10.2-12.6 mN/m), similar to those of pure PFMMAs, even when the blends contained 90 wt %PMMA. Surface morphology and composition measurements revealed that this result originated from the different blend structures, such as lateral and vertical phase separations. We expect that these PFMMAs will be useful in widening the applicable window of PMMA. [ABSTRACT FROM AUTHOR]

Colloidal stability of graphene oxide (GO) is studied in aqueous and organic media accompanied by an improved aggregation model based on Derjaguin-Landau-Verwey- Overbeek (DLVO) theory for ultrathin colloidal flakes. It is found that both magnitude and scaling laws for the van der Waals forces are affected significantly by the two-dimensional (2D) nature of GO. Experimental critical coagulation concentrations (CCC) of GO in monovalent salt solutions concur with DLVO theory prediction. The surface charge density of GO is largely affected by pH. However, theoretical calculations and experimental observations show that the colloidal stability of the 2D colloids is less sensitive to the changes in the surface charge density compared to the classical picture of 3D colloids. The DLVO theory also quantitatively predicts the colloidal stability of reduced GO (rGO). The origin of lower stability of rGO compared to GO is rooted in the higher van der Waals forces among rGO sheets, and particularly, in the removal of negatively charged groups, and possibly formation of some cationic groups during reduction. GO also exfoliates in the polar organic solvents and results in stable dispersions. However, addition of nonpolar solvents perturbs the colloidal stability at a critical volume fraction. Analyzing the aggregation of GO in mixtures of different nonpolar solvents and N-methyl-2-pyrrolidone proposed that the solvents with dielectric constants of less than 24 are not able to host stable colloids of GO. However, dispersions of GO in very polar solvents shows unexpected stability at high concentration (>1 M) of salts and acids. The origin of this stability is most probably solvation forces. A crucial parameter affecting the ability of polar solvents to impart high stability to GO is their molecular size: the bigger they are, the higher the chance for stabilization. [ABSTRACT FROM AUTHOR]

Centimeter-scale gold nanoparticle (Au NP) monolayer films have been fabricated using a water/organic solvent self-assembly strategy. A recently developed approach, drain to deposit, is demonstrated to be most effective in transferring the Au NP films from the water/organic solvent interface to various solid substrates while maintaining their integrity. The interparticle spacing was tuned from 1.4 to 3.1 nm using alkylamine ligands of different lengths. The ordering of the films increased with increasing ligand length. The surface plasmon resonance and the in-plane electrical conductivity of the Au NP films both exhibit an exponential dependence on the interparticle spacing. These findings show great potential in scaling up the manufacturing of high-performance optical and electronic devices based on two-dimensional metallic nanoparticle superlattices. [ABSTRACT FROM AUTHOR]

Capillary suspensions are ternary systems including a solid and two liquid phases representing a novel formulation platform for pastes with unique processing and end-use properties. Here we have investigated aqueous suspensions of non-Brownian graphite particles including different polymers commonly used as thickening agents or binders in paste formulations. We have studied the interaction between these additives and organic solvents in order to elucidate its effect on the characteristic formation of a particle network structure in corresponding ternary capillary suspension systems. Organic solvents with different polarity have been employed, and in the presence of nonadsorbing poly(ethylene oxide), all of them, whether they preferentially wet the graphite surface or not, induce the formation of a network structure within the suspension as indicated by a strong change in rheological properties. However, when the adsorbing polymers carboxymethylcellulose and poly(vinylpyrrolidone) are included, the drastic change in rheological behavior occurs only when polar organic solvents are used as secondary liquids. Obviously, these solvents can form pendular bridges, finally resulting in a sample-spanning particle network. Vibrational sum frequency spectroscopy provides evidence that these polar liquids remove the adsorbed polymer from the graphite particles. In contrast, nonpolar and nonwetting solvents do not force polymer desorption. In these cases, the formation of a percolating network structure within the suspensions is presumably prevented by the strong steric repulsion among graphite particles, not allowing for the formation of particle clusters encapsulating the secondary liquid. Accordingly, polymeric additives and secondary fluids have to be carefully selected in capillary suspension formulations, then offering a new pathway to customize paste formulations. The polymer may serve to adjust an appropriate viscosity level, and the capillary bridging induces the desired degree of shear thinning. Alternatively, the polymer may be selected with respect to its binding properties in the final dry product, and capillary bridging may be used to control the flow and processing behavior of the wet paste. [ABSTRACT FROM AUTHOR]

Anoriginal protocol of simultaneous surface modification and transferfrom aqueous to organic phases of anatase TiO2nanoparticles(NPs) using alkylphosphonic acids (PAs) is studied. The influenceof the solvent, the nature and concentration of the PA, and the size,concentration, and aggregation state of the TiO2NPs wasinvestigated. Complete transfer was observed for linear alkyl chains(5, 8, 12, and 18 C atoms), even at very high sol concentrations.After transfer, the grafted NPs were characterized by 31P solid-state MAS NMR. The dispersion state of NPs before and afterphase transfer was monitored by dynamic light scattering (DLS). Small-angleneutron scattering (SANS) was used to characterize the structure ofPA-grafted NPs in the organic solvent. Using a quantitative core–shellmodel cross-checked under different contrast conditions, it is foundthat the primary particles making up the NPs are homogeneously graftedwith a solvated PA-layer. The nanometric thickness of the latter isshown to increase with the length of the linear carbon chain of thePA, independent of the size of the primary TiO2NP. Interestingly,a reversible temperature-dependent aggregation was evidenced visuallyfor C18PA, and confirmed by DLS and SANS: heating the sampleinduces the breakup of aggregates, which reassemble upon cooling.Finally, in the case of NPs agglomerated by playing with the pH orthe salt concentration of the sols, the phase transfer with PA iscapable of redispersing the agglomerates. This new and highly versatilemethod of NP surface modification with PAs and simultaneous transferis thus well suited for obtaining well-dispersed grafted NPs. [ABSTRACT FROM AUTHOR]

We present a general route for the transfer of Au and Ag nanoparticles of different shapes and sizes, from water into various organic solvents. The experimental conditions for each type of nanoparticles were optimized by using a combination of thiolated poly(ethylene glycol) and a hydrophobic capping agent, such as dodecanethiol. The functionalized nanoparticles were readily transferred into organic dispersions with long-term stability (months). Such organic dispersions efficiently spread out on water, leading to self-assembly at the air/liquid interface into extended nanoparticle arrays which could in turn be transferred onto solid substrates. The dense close packing in the obtained nanoparticle monolayers results in extensive plasmon coupling, rendering them efficient substrates for surface-enhanced Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

In this work, we have designed andsynthesized a series of fattyacid amphiphiles that have the same structural skeleton but differenthydrogen-bonding (H-bonding) functional groups in the hydrocarbonchain. To examine the importance of the H-bonding interaction on theformation of a one-dimensional (1D) aggregate in organic solvents,we have compared the gelation behavior of these amphiphiles in somecommon organic solvents at room temperature. Despite the structuralsimilarity, the amphiphiles were observed to exhibit different gelationbehavior. The organogels were characterized using conventional techniquessuch as field emission scanning electron microscopy, X-ray diffraction,and rheology. A systematic analysis of the FT-IR and 1HNMR spectral data, gel melting temperatures, and mechanical strengthsof the organogels in a given solvent suggested the importance of H-bondingas well as van der Waals interaction in the gelation process. In thisstudy, we have made an attempt to estimate qualitatively the relativecontribution of H-bonding and van der Waals interactions between gelatormolecules forming organogels. The results suggest that strong andweaker H-bonding affects the gelation ability of gelators. However,when the H-bonding interaction is weak, an increase in van der Waalsinteractions can result in gelation, but when both H-bonding and vander Waals interactions are weak, that is, when the amphiphiles areliquid and semisolid, no gelation is observed. It is concluded thata balance between H-bonding and van der Waals interactions is necessaryfor physical gelation. [ABSTRACT FROM AUTHOR]

The well-known Leidenfrost effectis the formation of a vapor layerbetween a liquid and an underlying hot surface. This insulating vaporlayer severely degrades heat transfer and results in surface dryout.We measure the heat transfer enhancement and dryout prevention benefitsaccompanying electrostatic suppression of the Leidenfrost state. Interfacialelectric fields in the vapor layer can attract liquid toward the surfaceand promote wetting. This principle can suppress dryout even at ultrahightemperatures exceeding 500 °C, which is more than 8 times theLeidenfrost superheat for organic solvents. Robust Leidenfrost statesuppression is observed for a variety of liquids, ranging from lowelectrical conductivity organic solvents to electrically conductingsalt solutions. Elimination of the vapor layer increases heat dissipationcapacity by more than 1 order of magnitude. Heat removal capacitiesexceeding 500 W/cm2are measured, which is 5 times thecritical heat flux (CHF) of water on common engineering surfaces.Furthermore, the heat transfer rate can be electrically controlledby the applied voltage. The underlying science is explained via amultiphysics analytical model which captures the coupled electrostatic-fluid-thermaltransport phenomena underlying electrostatic Leidenfrost state suppression.Overall, this work uncovers the physics underlying dryout preventionand demonstrates electrically tunable boiling heat transfer with ultralowpower consumption. [ABSTRACT FROM AUTHOR]

This paper presents the effect of end groups, chain structure, and stereocomplexation on the microparticle and nanoparticle morphology and thermal properties of the supramolecular triblock copolyesters. Therefore, the series of the triblock copolymers composed of l,l- and d,d-lactide, trimethylene carbonate (TMC), and e-caprolactone (CL) with isopropyl (iPr) or 2-ureido-4-[1H]-pyrimidinone (UPy) end groups at both chain ends were synthesized. In addition, these copolymers were intermoleculary stereocomplexed by polylactide (PLA) blocks with an opposite configuration of repeating units to promote their self-assembly in various organic solvents. The combination of two noncovalent interactions of the end groups and PLA enantiomeric chains leads to stronger interactions between macromolecules and allows for alteration of their segmental mobility. The simple tuning of the copolymer microstructure and functionality induced the self-assembly of macromolecules at liquid/liquid interfaces, which consequently leads to their phase separation in the form of particles with diameters ranging from 0.1 µm to 10 µm. This control is essential for their potential applications in the biomedical field, where biocompatible and well-defined microparticles and nanoparticles are highly desirable. [ABSTRACT FROM AUTHOR]

There are emerging demands for single-digit nanoscale particles in multidisciplinary fields, such as nanomedicine, optics, catalysis, and sensors, to create new functional materials. Here, we report a novel route to prepare silica nanoparticles less than 3 nm in size via the evaporation-induced self-assembly of silicate species and quaternary trialkylmethylammonium surfactants, which usually form reverse micelles. The solvent evaporation induces a local concentration increase and simultaneous polycondensation of silicate species within the hydrophilic region of the surfactant mesophases. Extremely small silica nanoparticles in the silica–surfactant mesostructures can be stably dispersed in organic solvents by destroying the mesostructure, which is in clear contrast to the preparation of silica nanoparticles using the conventional reverse micelle method. The surface chemical modification of the formed silica nanoparticles is easily performed by trimethylsilylation. The particle size is adjustable by changing the ratio of the surfactants to the silica source because the hydrophobic/hydrophilic ratio determines the curvature and diameter of the resulting spherical silica–surfactant domains in the mesostructure. The versatility of this method is demonstrated by the fabrication of very small titania nanoparticles. These findings will increase the designability of oxide nanoparticles at the single-digit nanoscale because conventional methods based on the generation and growth of nuclei in a solution cannot produce such nanoparticles with highly regulated sizes. [ABSTRACT FROM AUTHOR]

Polyelectrolyte microcapsules are versatile compartments for encapsulation, protection, and controlled/triggered release of active agents. Conventional methods of polyelectrolyte microcapsule preparation require multiple steps or do not allow for efficient encapsulation of active agents in the lumen of the microcapsule. In this work, we present the fabrication of hollow polyelectrolyte microcapsules with a salt-responsive property based on surfactant organized nanoscale interfacial complexation in emulsions (SO NICE). In SO NICE, polyelectrolyte microcapsules are templated by water-in-oil-in-water (W/O/W) double emulsions. One polyelectrolyte is dissolved in the inner water droplet of the W/O/W double emulsions, whereas the second polyelectrolyte is dissolved in the organic phase by hydrophobic ion paring with an oppositely charged hydrophobic surfactant. Interfacial complexation of the two polyelectrolytes generates a few hundred-nanometer thick film at the inner water-oil interface of the W/O/W double emulsions. SO NICE microcapsules can be triggered to release their cargo by increasing the ionic strength of the solution, which is a hallmark of polyelectrolyte-based microcapsules. By enabling dissolution and interfacial complexation of polyelectrolytes in organic solvents, SO NICE widens the pallet of polymers that can be used to generate functional polyelectrolyte microcapsules with high encapsulation efficiency for applications in encapsulation and controlled/triggered release. [ABSTRACT FROM AUTHOR]

Here, we propose to modify the hydrophilicity of metal-organic framework (MOF) particles by an interfacial assembling route, which is based on the surface-active nature of MOF particles. It was found that hydrophilic UiO-66-NH2 particles can be converted to hydrophobic particles through an oil-water interfacial assembling route. The underlying mechanism for the conversion of UiO-66-NH2 was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was revealed that the close assembly of UiO-66-NH2 particles at the oil-water interface strengthens the coordination between organic ligands and metal ions, which results in a decrease in the proportion of hydrophilic groups on UiO-66-NH2 particle surfaces. Hydrophobic UiO-66-NH2 particles show improved adsorption capacity for dyes in organic solvents compared with pristine UiO-66-NH2 particles. It is expected that the interfacial assembling route can be applied to the synthesis of different kinds of MOF materials with tunable hydrophilicity or hydrophobicity required for diverse applications. [ABSTRACT FROM AUTHOR]

We have developed a new class of thermoresponsive colloids that can exhibit a sharp reversible transition between dispersion and aggregation in binary BuAc/EtOH solvents based on the UCST (upper critical solution temperature)-type phase separation. This is realized by grafting linear PMMA-BA (random) copolymer onto the colloidal particles. We have selected TiO2/PS hybrid spheres (HSs) as a model system to demonstrate our general design concept. By grafting the linear PMMA-BA copolymer onto the HS surface, with the molecular weight from 30 to 40 kDa, we found that the thermoresponsive transition between dispersion and aggregation is fast, sharp, and reversible. At high mass fractions of the HSs, we have even observed a sharp transition between dispersion and gelation (or phase separation). The transition temperature can be tuned by varying the binary solvent composition, BuAc/EtOH, and the molecular weight of the grafted linear copolymer in the range from 5 to 55°C. One of the most important features of this work is that the thermoresponsive materials used in organic solvents are initially synthesized in water with widely applied conventional (instead of research-based) techniques, thus being well suited for industrial production. In addition, the proposed approach is rather general and applicable to realizing the thermoresponsive transition for various types of colloids and nanoparticles. [ABSTRACT FROM AUTHOR]

Silk is a natural polymer with a broad range of potential applications in textiles, advanced materials, biomedical devices, and drug delivery. The ability to control the morphology and assembly of silk fibroin is essential for the fabrication of silk-based structured materials. Here, we report an effective and simple approach based on droplet dissolution for weaving silk fibroin into spheres of several hundred micrometers in diameter. The spheres possess regular wrinkled microstructures on the surface and switchable transparency for visible light. To produce these silk spheres, we immersed a sessile microdrop of the silk fibroin aqueous solution in a surrounding phase of ethanol in toluene at low concentration (<10%). The droplet experienced a two-phase process: the first phase of volume expansion due to the intake of organic solvents from the surrounding phase and the second phase of droplet dissolution. The dissolution rate is closely related to the dynamics of the droplet, while the resulting microstructure of the silk microsphere is simply adjusted by the composition of the surrounding solution. At high concentrations of ethanol, silk fibroin formed a thin shell around the droplet during the initial expansion of the droplet in volume. As the droplet shrank at a later stage, the shell around the droplet wrinkled and crumpled, leading to regular ridges and crevices on the microsphere surface. This work demonstrates that controlled droplet dissolution may be explored as a novel and effective way to tailor microstructures of silk assemblies. The as-prepared silk microspheres may be potentially used as optical units or microcarriers. [ABSTRACT FROM AUTHOR]

We studied the synthesis of poly(4-vinylpyridine) and poly(2-hydroxyethyl methacrylate) polymer particles in silicone oil using a sequential vapor phase polymerization method in which monomer droplets were first condensed onto a layer of silicone oil and subsequently polymerized via a free radical mechanism. The viscosity of the silicone oil was systematically varied. At lower viscosities, a heterogeneous particle size distribution was produced where small particles were formed by engulfment of the monomer droplets at the liquid surface and large particles were formed by coalescence of the monomer droplets inside the liquid layer. Coalescence could be inhibited by increasing the viscosity of the silicone oil leading to a decreased average radius and a narrower size distribution of the polymer particles. The advantages of our method for the fabrication of polymer particles are that it does not require surfactants or organic solvents. [ABSTRACT FROM AUTHOR]

We are reporting a spontaneous supramolecular assembly of backbone engineered γ-peptide scaffold and its utility in the immobilization of semiconductor quantum dots and in cell culture. The stimulating feature of this γ-peptide scaffold is that it efficiently gelates both aqueous phosphate buffers and aromatic organic solvents. A comparative and systematic investigation reveals that the greater spontaneous self-aggregation property of γ-peptide over the α- and β-peptide analogues is mainly due to the backbone flexibility, increased hydrophobicity, and π-π stacking of γ-phenylalanine residues. The hydrogels and organogels obtained from the γ-peptide scaffold have been characterized through field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), FT-IR, circular dichroism (CD), wide-angle X-ray diffraction, and rheometric study. Additionally, the peptide hydrogel has displayed a stimuli-responsive and thixotropic signature, which leads to the injectable hydrogels. 2D cell culture studies using normal and cancer cell lines reveal the biocompatibility of γ-peptide hydrogels. Further, the immobilization of semiconductor core-shell quantum dots in the transparent γ-peptide organogels showed ordered arrangement of quantum dots along the peptide fibrillar network with retaining photophysical property. Overall, γ-peptide scaffolds may serve as potential templates for the design of new functional biomaterials. [ABSTRACT FROM AUTHOR]

Particle-stabilized bubbles and foams have been observed and used in a wide range of industrial sectors and have been exploited as a technology platform for the production of advanced functional materials. The stability, structure, shape, and movement of these bubbles and foams can be controlled by external stimuli such as the pH, temperature, magnetic fields, ultrasonication, mechanical stress, surfactants, and organic solvents. Stimuli-responsive modes can be categorized into three classes: (i) bubbles/foams whose stability can be controlled by the adsorption/desorption/dissolution of solid particles to/from/at gas-liquid interfaces, (ii) bubbles/foams that can move, and (iii) bubbles/foams that can change their shapes and structures. The stimuli-responsive characteristics of bubbles and foams offer potential applications in the areas of controlled encapsulation, delivery, and release. [ABSTRACT FROM AUTHOR]

A simple and eco-friendly procedure of esterification of graphite oxide (GO), which uses acetic anhydride as a model reagent and ethyl acetate as a green solvent, is reported. The procedure leads to high functionalization degrees (at least up to 4.5 mol % of acetyl groups, referred to as graphitic C atoms) and it is much more effective than the literature method based on pure acetic anhydride. Surprisingly, our acetylation procedure does not destroy or reduce GO crystallinity but, irrespective of a substantial increase of distance between GO layers (from 0.84 nm up to 0.95 nm), leads to an increased order in the direction perpendicular to the graphitic planes. This phenomenon indicates that acetyl groups of acetylated GO (AcGO) are easily accommodated between graphitic layers, even improving interlayer order. The esterification procedure is generally applicable with various anhydrides providing differently functionalized graphite oxide. Dispersion of crystalline functionalized GO in volatile organic solvents followed by solvent fast removal, can easily lead to complete exfoliation. [ABSTRACT FROM AUTHOR]

Host-guest chemistry in two-dimensional (2D) space, that is, physisorbed monolayers of a single atom or a single molecular thickness on surfaces, has become a subject of intense current interest because of perspectives for various applications in molecular-scale electronics, selective sensors, and tailored catalysis. Scanning tunneling microscopy has been used as a powerful tool for the visualization of molecules in real space on a conducting substrate surface. For more than a decade, we have been investigating the self-assembly of a series of triangle-shaped phenylene-ethynylene macrocycles called dehydrobenzo[12]annulenes (DBAs). These molecules are substituted with six alkyl chains and are capable of forming hexagonal porous 2D molecular networks via van der Waals interactions between interdigitated alkyl chains at the interface of organic solvents and graphite. The dimension of the nanoporous space or nanowell formed by the self-assembly of DBAs can be controlled from 1.6 to 4.7 nm by simply changing the alkyl chain length from C6 to C20. Single molecules as well as homoclusters and heteroclusters are capable of coadsorbing within the host matrix using shape- and size-complementarity principles. Moreover, on the basis of the versatility of the DBA molecules that allows chemical modification of the alkyl chain terminals, we were able to decorate the interior space of the nanoporous networks with functional groups such as azobenzenedicarboxylic acid for photoresponsive guest adsorption/desorption or fluoroalkanes and tetraethylene glycol groups for selective guest binding by electrostatic interactions and zinc-porphyrin units for complexation with a guest by charge-transfer interactions. In this Feature Article, we describe the general aspects of molecular self-assembly at liquid/solid interfaces, followed by the formation of programmed porous molecular networks using rationally designed molecular building blocks. We focus on our own work involving host-guest chemistry in integrated nanoporous space that is modified for specific purposes. [ABSTRACT FROM AUTHOR]

Shape-controlled nanocrystals, such as nanowires and nanoflowers, are attractive because of their potential novel optical and catalytic properties. However, the dispersion and morphological stabilities of shape-controlled nanocrystals are easily destroyed by changing the dispersion solvent and temperature. Methods of support and the silica coating are known to improve the dispersion and morphological stabilities of metal nanocrystals. The silica-coating method often causes morphological changes in shape-controlled nanocrystals because the silica coating is formed in mixed solutions of water and organic solvents such as ethanol, and this results in aggregation due to changes in the dispersion solvent. Furthermore, ligand exchange, designed to improve the dispersion stability in the solvent, often causes morphological changes. This article introduces a method for the preparation of highly stable silica-coated Au nanoflowers (AuNFs) supported on Al2O3. The method of support prevents the aggregation and precipitation of AuNFs when the solvent is changed from water to water/ethanol. Through stability improvement, silica coating of AuNFs/Al2O3 was conducted in water/ethanol without ligand exchange that causes morphological changes. Furthermore, silica-coated AuNFs/Al2O3 exhibit high morphological stability under high-temperature conditions compared to uncoated AuNFs/Al2O3. These results are very useful when preparing highly morphologically stable, silica-coated, shape-controlled nanocrystals without ligand exchange. [ABSTRACT FROM AUTHOR]

Mussel-inspired polydopamine (PDA) coatings have been broadly exploited for constructing functional membrane surfaces. One-step codeposition of PDA with antifouling polymers, especially zwitterionic polymers, has been regarded as a promising strategy for fabricating antifouling membrane surfaces. However, one challenge is that the codeposition is usually a slow process over 10 h or even several days. Herein, we report that CuSO4/H2O2 is able to notably accelerate the codeposition process of PDA with poly(sulfobetaine methacrylate) (PSBMA). In our case, PSBMA is facilely anchored to the polypropylene microporous membrane (PPMM) surfaces within 1 h with the assistance of PDA because of its strong interfacial adhesion. The PDA/PSBMA-coated PPMMs show excellent surface hydrophilicity, high water permeation flux (7506 ± 528 L/m²·h at 0.1 MPa), and an outstanding antifouling property. Moreover, the antifouling property is maintained after the membranes are treated with acid and alkali solutions as well as organic solvents. To recap, it provides a facile, universal, and time-saving strategy for exploiting high-efficiency and durable antifouling membrane surfaces. [ABSTRACT FROM AUTHOR]

A simple method for covalent functionalization of Fréchet-type dendron nanoparticles (FDNs) using tris-bipyridylruthenium(II) is described. Covalent functionalization is achieved by chemically reducing the diazo derivative of a ruthenium(II)bipyridine complex in the presence of FDNs wherein the radical species generated gets covalently linked to the nanoparticle surface. Simplicity, rapidity, and robustness are the advantages offered by the present approach. The nanoparticles, post functionalization, were characterized using transmission electron microscopy, thermogravimetric analysis, and infrared, energy-dispersive X-ray, UV-visible, and nuclear magnetic resonance spectroscopic techniques. Depending on the solvent, the ruthenium complex-linked FDN displays a range of morphologies, including nanoparticles, fiber-networks, and nanocapsules. In the nanocapsules and fiber-networks observed in organic solvents, the ruthenium complex is confined within the interior domain of the aggregate, whereas in the nanoparticles observed in water, it is present on the periphery. The formation of predictable morphologies in different solvents plays a key role in using such self-assembled structures for various applications such as sensing, catalysis, and light harvesting. Characterization of these nanoaggregates using different spectroscopic and microscopic techniques is also described. [ABSTRACT FROM AUTHOR]

Physical gelation behaviors of a series of novel bisurea-based derivatives bearing fatty alkyl tertiary amine moieties have been explored in water and common organic solvents. One of these amines exhibits very good thixotropic gels in apolar aromatic solvents (e.g., xylenes). The corresponding sol-gel transition is instantaneous and could be repeated for at least 50 cycles. Interestingly, the elasticity and strength of the resulting gels can be remarkably enhanced initially by the addition of a trace amount of tetrabutylammonium acetate (TBA) followed by a subsequent drop with further salt addition. Temperature-dependent ¹H NMR confirmed that hydrogen bonding is the main driving force for the physical gelation. TEM, rheology, ¹H NMR titration, and examination of critical gelation concentration (CGC) reveal that the phenomenon is due to the dominated effects, the salting out effect at lower TBA concentration, or the anion-urea hydrogen bonding at higher TBA concentration. Furthermore, the obtained transparent gels in this work can be used as good media for growing crystals of several organic semiconductors. [ABSTRACT FROM AUTHOR]

When a solute is present in an aqueous droplet, the water activity in the droplet and the rate of droplet dissolution are both decreased (as compared to a pure water droplet). One of the main parameters that controls this effect is the dynamically changing solute concentration, and therefore water activity and chemical potential, at the droplet interface. This work addresses the importance of understanding how water activity changes during solution droplet dissolution. A model for dissolution rate is presented that accounts for the kinetic effects of changing water activity at the droplet interface during the dissolution of an aqueous salt solution microdroplet into a second immiscible liquid phase. The important underlying question in this model is whether the dissolving component can be considered in local equilibrium on both sides of the droplet interface and whether this assumption is sufficient to account for the kinetics of dissolution. The dissolution model is based on the Epstein-Plesset equation, which has previously been applied to pure gas (bubble) and liquid (droplet) dissolution into liquid phases, but not to salt solutions. The model is tested by using the micropipet technique to form and observe the dehydration of single NaCl solution microdroplets in octanol or butyl acetate. The model successfully predicts the droplet diameter as a function of time in both organic solvents. The NaCl concentration in water is measured well into the supersaturated area >5.4 M, and the supersaturation limit at which NaCl nucleation happens is reported to be 10.24 ± 0.31 M. [ABSTRACT FROM AUTHOR]

Fluorescently labeled DNA adsorbed on graphene oxide (GO) is a well-established sensing platform for detecting a diverse range of analytes. GO is a loosely defined material and its oxygen content may vary depending on the condition of preparation. Sometimes, a further reduction step is intentionally performed to decrease the oxygen content, and the resulting material is called reduced GO (rGO). In this study, DNA adsorption and desorption from GO and rGO is systematically compared. Under the same salt concentration, DNA adsorbs slightly faster with a 2.6-fold higher capacity on rGO. At the same time, DNA adsorbed on rGO is more resistant to desorption induced by temperature, pH, urea, and organic solvents. Various lengths and sequences of DNA probes have been tested. When its complementary DNA is added as a model target analyte, the rGO sample has a higher signal-to-background and signal-to-noise ratio, whereas the GO sample has a slightly higher absolute signal increase and faster signaling kinetics. DNAs adsorbed on GO or rGO are still susceptible to nonspecific displacement by other DNA and proteins. Overall, although rGO adsorbs DNA more tightly, it allows efficient DNA sensing with an extremely low background fluorescence signal. [ABSTRACT FROM AUTHOR]

Supramolecular self-assembly of low molecular mass amphiphiles is of topical interest with the urge to achieve precise control over the formation of various self-aggregated structures. Particularly, fabrication of multifarious nanostructures from single molecular backbone would be highly advantageous for task specific applications of the self-aggregates. To this end, the present study reports the solvent triggered evolution of hierarchical self-assembled structures of cholesterol based glucose appended amphiphiles and the pathway of structural transition. The amphiphiles formed bilayered vesicles in water and gels in different organic solvents. In DMSO-water solvent mixture, it showed gradual transition in the morphology of self-aggregates from vesicle-to-fiber and intermediate morphologies depending on the solvent compositions. Microscopic and spectroscopic investigations showed that morphological transformation took place through fusion, elongation and twisting of self-aggregates owing to the reorganization of the amphiphiles (H-type to J-type) in varied solvent polarity. Moreover, sheetlike molecular organization originating from hydrogen bonding and solvophobic interaction played a vital role in the formation of nanoribbons that led to the formation of gel fibril network. This study endows a new strategy to develop solvent induced multistructured self-aggregates from a single molecular scaffold, unraveling the route of forming hierarchical self-assembly. [ABSTRACT FROM AUTHOR]

Citrate-stabilized silver nanoparticles (AgNPs) were functionalized with a pH-responsive amphiphile, 3-[(2-carboxy-ethyl)-hexadecyl-amino]-propionic acid (C16CA). At pH ~ 4, the zwitterionic C16CA assembled into lamellar structures due to the protonation of the amine groups of the amphiphile that neutralized the anionic charge of the carboxylate groups. The lamellar supramolecules incorporated the AgNPs into their 3D network and extracted them from water. C16CA supramolecules dissolved into water (at pH > 6) and organic solvents; consequently, the recovered C16CA-AgNPs were redispersed not only to water but also to chloroform and tetrahydrofuran without any additional functionalization. C16CA acted as a pH-responsive stabilizer of AgNPs and formed a solvent-switchable molecular layer such as a bilayered structure in water and densely packed monolayer in chloroform and tetrahydrofuran. Redispersion of the AgNPs was achieved in different solvents by changing the solvent affinity of the adsorbed C16CA molecular layer based on the protonation of the amine groups of the pH-responsive amphiphile. The morphology of redispersed AgNPs did not change during the recovery and redispersion procedure, due to the high steric effect of the network structure of C16CA supramolecules. These observations can lead to a novel solvent-exchange method for nanocrystals without aggregation and loss of nanocrystals, and they enable effective preparations of stimuli-responsive plasmonic nanomaterials. [ABSTRACT FROM AUTHOR]