Interfacial Activity of Amine‐Functionalized Polyhedral Oligomeric Silsesquioxanes (POSS): A Simple Strategy To Structure Liquids

Amine‐functionalized polyhedral oligomeric silsesquioxane (POSS), the smallest, monodisperse cage‐shaped silica cubic nanoparticle, is exceptionally interfacially active and can form assemblies that jam the toluene/water interface, locking in non‐equilibrium shapes of one liquid phase in another. The packing density of the amine‐functionalized POSS assembly at the water/toluene interface can be tuned by varying the concentration, the pH value, and the degree of POSS functionalization. Functionalized POSS gives a higher interface coverage, and hence a lower interfacial tension, than nanoparticle surfactants formed by interactions between functionalized nanoparticles and polymeric ligands. Hydrogen‐bonded POSS surfactants are more stable at the interface, offering some unique advantages for generating Pickering emulsions over typical micron‐sized colloidal particles and ligand‐stabilized nanoparticle surfactants.     

Gold nanoparticle self-assembly in two-component lipid Langmuir monolayers

Self-assembly processes are considered to be fundamental factors in supramolecular chemistry. Langmuir monolayers of surfactants or lipids have been shown to constitute effective 2D "templates" for self-assembled nanoparticles and colloids. Here we show that alkyl-coated gold nanoparticles (Au NPs) adopt distinct configurations when incorporated within Langmuir monolayers comprising two lipid components at different mole ratios. Thermodynamic and microscopy analyses reveal that the organization of the Au NP aggregates is governed by both lipid components. In particular, we show that the configurations of the NP assemblies were significantly affected by the extent of molecular interactions between the two lipid components within the monolayer and the monolayer phases formed by each individual lipid. This study demonstrates that multicomponent Langmuir monolayers significantly modulate the self-assembly properties of embedded Au NPs and that parameters such as the monolayer composition, surface pressure, and temperature significantly affect the 2D nanoparticle organization.     

Interfacial activity of polymer-coated gold nanoparticles

A systematic study of the interfacial activity of polymer-coated gold nanoparticles was performed with the use of a computer-controlled four-roll mill. The nanoparticle locality within the polymeric domains (bulk or interface) was controlled by means of a mixture of polymeric ligands grafted to the gold nanoparticle core. The bulk polymers were polybutadiene (PBd) and polydimethylsiloxane (PDMS). Monoterminated PDMS and PBd ligands were synthesized on the basis of the esterification of reactive groups (such as hydroxyl or amino groups) with lipoic acid anhydride. The formation of polymer-coated nanoparticles using these lipoic acid-functionalized polymers was confirmed via transmission electron microscopy (TEM), and their interfacial activity was manifested as a reduction of the interfacial tension and in the enhanced stability of thin films (as seen via the inhibition of coalescence). The nanoparticles showed an equal, if not superior, ability to reduce the interfacial tension when compared to previous studies on the effect of insoluble surfactants; however, these particles proved not to be as effective at inhibiting coalescence as their surfactant counterpart. We suggest that this effect may be caused by an increase in the attractive van der Waals forces created by the presence of metal-core nanoparticles. Experimental measurements using the four-roll mill allow us to explore the relationship between nanoparticle concentration at the interface and interfacial tension. In particular, we have found evidence that the interface concentration can be increased relative to the equilibrium value achieved by diffusion alone, and thus the interfacial tension can be systematically reduced if the interfacial area is increased temporarily via drop deformation or breakup followed by recoalescence.     

Functional oligomers for the control and fixation of spatial organization in nanoparticle assemblies

Interactions in nanoparticle assemblies play an important role in modulating their interesting magnetic and optical properties. Controlling and fixing the distance between nanoparticles is therefore crucial to the development of next-generation nanodevices. Here, we show that the interparticle distance in two-dimensional assemblies can be quantitatively controlled by functionalizing the nanoparticles with short polymers containing one functional end group that binds to the nanoparticle. Carboxy-functional poly(dimethylsiloxane) (PDMS) ligands are attached to the nanoparticle surface by a simple ligand exchange process with the oleic acid synthesis ligands. The distance between nanoparticles is manipulated by adjusting either the number of PDMS ligands per molecule or their molecular weight. The use of PDMS ligands is unique in that they provide a means to permanently and robustly fix the spatial distribution of nanoparticles because PDMS is readily converted to silicon oxide by a simple UV/ozone treatment. The distance between nanoparticles can be designed a priori, as it is found to scale well with theoretical predictions for the thickness of the surface-bound polymer brush layer.     

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)‐surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod‐like cellulose nanocrystal (CNC)‐based NP‐surfactants, termed CNC‐surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau–Rayleigh (PR) instabilities of a free‐falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end‐functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC‐surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three‐dimensional (3D) printing, of all‐liquid constructs.     

Role of Capping Ligands on the Nanoparticles in the Modulation of Properties of a Hybrid Matrix of Nanoparticles in a 2D Film and in a Supramolecular Organogel

We incorporate various gold nanoparticles (AuNPs) capped with different ligands in two‐dimensional films and three‐dimensional aggregates derived from N‐stearoyl‐L ‐alanine and N‐lauroyl‐L ‐alanine, respectively. The assemblies of N‐stearoyl‐L ‐alanine afforded stable films at the air–water interface. More compact assemblies were formed upon incorporation of AuNPs in the air–water interface of N‐stearoyl‐L ‐alanine. We then examined the effects of incorporation of various AuNPs functionalized with different capping ligands in three‐dimensional assemblies of N‐lauroyl‐L ‐alanine, a compound that formed a gel in hydrocarbons. The profound influence of nanoparticle incorporation into physical gels was evident from evaluation of various microscopic and bulk properties. The interaction of AuNPs with the gelator assembly was found to depend critically on the capping ligands protecting the Au surface of the gold nanoparticles. Transmission electron microscopy (TEM) showed a long‐range directional assembly of certain AuNPs along the gel fibers. Scanning electron microscopy (SEM) images of the freeze‐dried gels and nanocomposites indicate that the morphological transformation in the composite microstructures depends significantly on the capping agent of the nanoparticles. Differential scanning calorimetry (DSC) showed that gel formation from sol occurred at a lower temperature upon incorporation of AuNPs having capping ligands that were able to align and noncovalently interact with the gel fibers. Rheological studies indicate that the gel–nanoparticle composites exhibit significantly greater viscoelasticity compared to the native gel alone when the capping ligands are able to interact through interdigitation into the gelator assembly. Thus, it was possible to define a clear relationship between the materials and the molecular‐level properties by means of manipulation of the information inscribed on the NP surface.     

Forced desorption of nanoparticles from an oil-water interface

While nanoparticle adsorption to fluid interfaces has been studied from a fundamental standpoint and exploited in application, the reverse process, that is, desorption and disassembly, remains relatively unexplored. Here we demonstrate the forced desorption of gold nanoparticles capped with amphiphilic ligands from an oil-water interface. A monolayer of nanoparticles is allowed to spontaneously form by adsorption from an aqueous suspension onto a drop of oil and is subsequently compressed by decreasing the drop volume. The surface pressure is monitored by pendant drop tensiometry throughout the process. Upon compression, the nanoparticles are mechanically forced out of the interface into the aqueous phase. An optical method is developed to measure the nanoparticle area density in situ. We show that desorption occurs at a coverage that corresponds to close packing of the ligand-capped particles, suggesting that ligand-induced repulsion plays a crucial role in this process.     

Template-free parallel one-dimensional assembly of gold nanoparticles

In this work, we have identified key process parameters to generate parallel unidirectional 1D assemblies of gold nanoparticles with the assistance of organic surfactants. By controlling the surfactant population, metal particle size, and amount of solvent for dispersion, the length of nanoparticle chains and their interchain space can be further tailored. In principle, the general findings of this work can also be extended to large-scale 1D organization of other transition/noble metal nanoparticles using simple organic surfactants.     

Chloride ion effects on synthesis and directed assembly of copper nanoparticles in liquid and compressed alkane microemulsions

Microemulsions are effective media for solution-based synthesis of metallic nanoparticles where surfactants and other ionic species influence the directed assembly of the nanomaterials with specific sizes, geometries, and compositions. This study demonstrates the effects of chloride ion on the synthesis of copper nanoparticles within the sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelle system utilizing both liquid isooctane and compressed propane as the bulk solvent. Copper nanoparticle synthesis can be achieved in the presence of HCl in the micelle core, taking advantage of the buffering action of the AOT surfactant. The concentration of chloride ions influence the particle growth rate and dispersion in liquid isooctane. The presence of chloride ions during particle synthesis in compressed propane has a significant effect on the geometry and structure of the copper nanomaterials produced. Chloride ion addition to the compressed propane/Cu(AOT)(2)-AOT/water reverse micelle system at 20 degrees C and 310 bar results in the formation of diamond-shaped copper nanoparticle assemblies. The copper nanoparticle assemblies exhibit unique structure and retain this structure through repeated solvent processing steps, allowing separation and recovery of the assembled diamond-shaped copper nanoparticle structures.     

Frequency dependence of gold nanoparticle superassembly by dielectrophoresis

Dielectrophoresis is an effective method for capturing nanoparticles and assembling them into nanostructures. The frequency of the dielectrophoretic alternating current (ac) electric field greatly influences the morphology of resultant nanoparticle assemblies. In this study, frequency regimes associated with specific gold nanoparticle assembly morphologies were identified. Gold nanoparticles suspended in water were captured by microelectrodes at different electric field frequencies onto thin silicon nitride membranes. The resultant assemblies were examined by transmission electron microscopy. For this system, the major frequency-dependent influence on morphology appears to arise not from the Clausius-Mossotti factor of the dielectrophoretic force itself, but instead from ac electroosmotic fluid flow and the influence of the electrical double layer at the electrode-solution interface. Frequency regimes of technological interest include those forming one-dimensional nanoparticle chains, microwires, combinations of microwires and nanoparticle chains suitable for nanogap electrode formation, and dense three-dimensional assemblies with very high surface area.     

Synthesis of CdS, ZnS and Ag2S nanoparticles stabilized by sodium bis(2-ethylhexyl)sulfosuccinate and polyoxyethylenesorbitan monooleate in aqueous medium

The effect of synthesis conditions (molar ratio between precursors, concentration of surfactants, synthesis temperature) on the size of CdS, ZnS and Ag₂S nanoparticles (NPs) stabilized by sodium bis(2-ethylhexyl)succinate and polyoxyethylenesorbitan monooleate was studied. It was established that stabilization by polyoxyethylenesorbitan results in formation of smaller NPs (～8 nm) as compared to that in the presence of sodium bis(2-ethylhexyl)sulfosuccinate (14–60 nm), which is due to the difference between the adsorption rates of these surfactants onto the surface of synthesized NPs. The resulting aqueous dispersions of CdS, ZnS and Ag₂S NPs exhibit long-term stability to sedimentation. The nanoparticle size increases insignificantly with temperature increasing to 65–70°C and rises abruptly at higher temperatures. The increase in the ratio between concentrations of precursors (sulfide and metal ions) also results in an increase in NP size, allowing one to synthesize nanoparticles of prescribed sizes. The optical properties of the resulting nanoparticles were studied. The positions of the exciton peaks and the luminescence intensity peaks of the dispersions of synthesized CdS and ZnS NPs were determined.     

Synthetic polymer nanoparticle-polysaccharide interactions: a systematic study

The interaction between synthetic polymer nanoparticles (NPs) and biomacromolecules (e.g., proteins, lipids, and polysaccharides) can profoundly influence the NPs fate and function. Polysaccharides (e.g., heparin/heparin sulfate) are a key component of cell surfaces and the extracelluar matrix and play critical roles in many biological processes. We report a systematic investigation of the interaction between synthetic polymer nanoparticles and polysaccharides by ITC, SPR, and an anticoagulant assay to provide guidelines to engineer nanoparticles for biomedical applications. The interaction between acrylamide nanoparticles (~30 nm) and heparin is mainly enthalpy driven with submicromolar affinity. Hydrogen bonding, ionic interactions, and dehydration of polar groups are identified to be key contributions to the affinity. It has been found that high charge density and cross-linking of the NP can contribute to high affinity. The affinity and binding capacity of heparin can be significantly diminished by an increase in salt concentration while only slightly decreased with an increase of temperature. A striking difference in binding thermodynamics has been observed when the main component of a polymer nanoparticle is changed from acrylamide (enthalpy driven) to N-isopropylacryalmide (entropy driven). This change in thermodynamics leads to different responses of these two types of polymer NPs to salt concentration and temperature. Select synthetic polymer nanoparticles have also been shown to inhibit protein-heparin interactions and thus offer the potential for therapeutic applications.     

Staged Surface Patterning and Self‐Assembly of Nanoparticles Functionalized with End‐Grafted Block Copolymer Ligands

Using two orthogonal external stimuli, programmable staged surface patterning and self‐assembly of inorganic nanoparticles (NPs) was achieved. For gold NPs capped with end‐grafted poly(styrene‐block‐(4‐vinylbenzoic acid)), P(St‐block‐4VBA), block copolymer ligands, surface‐pinned micelles (patches) formed from NP‐adjacent PSt blocks under reduced solvency conditions (Stimulus 1); solvated NP‐remote P(4VBA) blocks stabilized the NPs against aggregation. Subsequent self‐assembly of patchy NPs was triggered by crosslinking the P(4VBA) blocks with copper(II) ions (Stimulus 2). Block copolymer ligand design has a strong effect on NP self‐assembly. Small, well‐defined clusters assembled from NPs functionalized with ligands with a short P(4VBA) block, while NPs tethered with ligands with a long P(4VBA) block formed large irregularly shaped assemblies. This approach is promising for high‐yield fabrication of colloidal molecules and their assemblies with structural and functional complexity.     

Improvement of interfacial adhesion performance of the kevlar fiber mat by depositing SiC/TiO2/Al2O3/graphene nanoparticles

Modern world seeks dramatic progress in composite materials use in numerous applications. Scientists worldwide are researching on fabricating new composites and attempting to have more applications using these materials. Serious attempts have also been taken to improve the properties of these materials. In this circumstance, a conscious attempt has been made in this present work that studies the effect of SiC/TiO₂/Al₂O₃/ graphene nanoparticles (NPs) deposition on Kevlar fiber. In this process, SiC/TiO₂/Al₂O₃/ graphene NPs have been deposited on Kevlar fiber by dip coating process. For the analysis, physical observation has been performed well at first which confirms nanoparticle deposition on the fiber and formation of adhesive bonding. SEM analysis followed by surface topography has been conducted to observe and further analysis of nanoparticle deposition. Atomic bonding mechanism shows how chemical bonding between fiber and nanoparticles. TGA analysis shows thermal improvement of the fiber by NPs deposition where graphene with binder makes 21.6% improvement in decomposition temperature. Tensile strength and young’s modulus of binder inclusion coated kevlar fabric are improved up to 26% and 5.7%, respectively. Finally, the IR-spectra confirms successful deposition of nanoparticles on the fiber.     

Transition‐metal nanoparticles: synthesis,stability and the leaching issue

This perspective examines the state‐of‐the‐art of catalysis by metal nanoparticles. We outline various methods for preparing metal nanoparticle suspensions, and highlight the role of the stabilizers and the stabilizing principles. Subsequently, we examine some catalytic applications of homometallic and bimetallic nanoparticle suspensions in a variety of reactions. The cases are divided according to the stabilizing agent: polymers, dendrimers, ionic liquids, surfactants, micelles and micoremulsions, ligands and solid supports. We explain the importance of atom/ion leaching (all too frequent in nanoparticle catalysis, especially for the catalytically active group VIII metals) and consider ways of minimizing it. The future perspectives of nanoparticles as catalysts are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Two-dimensional self-assemblies of silica nanoparticles formed using the "bubble deposition technique"

Two-dimensional silica nanoparticle assemblies were obtained by deposition of bubble made from a surfactant solution containing nanoparticles onto hydrophobic silicon substrate. The morphologies of the nanoparticle assemblies can be finely controlled by several experimental parameters, including surfactant concentration, nanoparticle concentration, and deposition time. Monolayer of nanoparticles with surface coverage of about 100% can be obtained under appropriate conditions. The method can also be applied to another hydrophobic substrate, HMDS (hexamethyldisilazane)-modified silicon substrate. Furthermore, it can be applied directly to lithography patterned substrates, meaning a high compatibility with the well-developed conventional top-down approaches to nanodevices. This bubble deposition technique is expected to be a promising method in the field of nano-object assembly and organization and has great application potentials.     

Folding Up of Gold Nanoparticle Strings into Plasmonic Vesicles for Enhanced Photoacoustic Imaging

The stepwise self‐assembly of hollow plasmonic vesicles with vesicular membranes containing strings of gold nanoparticles (NPs) is reported. The formation of chain vesicles can be controlled by tuning the density of the polymer ligands on the surface of the gold NPs. The strong absorption of the chain vesicles in the near‐infrared (NIR) region leads to a much higher efficiency in photoacoustic (PA) imaging than for non‐chain vesicles. The chain vesicles were further employed for the encapsulation of drugs and the NIR light triggered release of payloads. This work not only offers a new platform for controlling the hierarchical self‐assembly of NPs, but also demonstrates that the physical properties of the materials can be tailored by controlling the spatial arrangement of NPs within assemblies to achieve a better performance in biomedical applications.     

Tailoring block copolymer and polymer blend morphology using nanoparticle surfactants

Combining the functionality of nanoparticles (NPs) with the processability of polymers offers great promise for designing novel materials. In particular, NPs with tailored surface properties can effectively modify the interface between two distinct fluids and/or different polymer matrices which allows them to function as efficient surfactants. The efficiency of NP surfactants is strongly affected by their size and shape, which influences their adsorption energy to the interface, and the entropic contribution to the system. In this review, the assembly of size- and shape-controlled inorganic NPs at the interface of block copolymers (BCPs) and polymer blends has been focused. First, we discuss the design of size- and shape-controlled NP surfactants and we review the examples of NP surfactant-driven BCPs and polymer blend morphologies. In addition, we review the recent investigations of the morphological transition of BCP emulsion particles induced by NP surfactants. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 228–237     

Hierarchical nanoparticle/block copolymer surface features via synergistic self-assembly at the air-water interface

This work demonstrates the first example of the controlled organization of semiconducting nanoparticles (NPs) using amphiphilic block copolymer self-assembly at the air-water interface. Preferential interactions between polystyrene-functionalized NPs and the polystyrene block of an amphiphilic polystyrene-b-poly(ethylene oxide) block copolymer result in synergistic self-assembly at the air-water interface, forming a range of highly stable one-dimensional NP/polymer surface features, including branched nanowires, nanocables up to 100 microm in length, and nanowires with nanoring connectors. This strategy offers new routes to hierarchical hybrid assemblies with potential photonics applications because the nanoscale organization of NPs is coupled to features with dimensions that are commensurate with optical wavelengths.     

G-quartet-induced nanoparticle assembly

The design and synthesis of a new class of gold nanoparticle with guanosine monophosphate derivatives or G-rich oligonucleotides as their surface ligands are described. These nanoparticles spontaneously form macroscopic assemblies at low temperature and relatively high salt concentrations, which is attributed to the cooperative formation of guanosine quartets and G-quadruplexes between the individual nanoparticles. Significantly, the solution behavior of these nanoparticles is highly controllable by adjusting solution parameters (including temperature, ionic strength, and ion species) and the sequence of the G-rich oligonucleotide