Self‐Assembly of Nanoparticles in 2D and 3D: Recent Advances and Future Trends

Versatility of the Templated Surface Assembly of Nanoparticles from Water-in-Oil Microemulsions in Equivalent Hybrid Nanostructured Films

Water-in-oil microemulsions, as stable colloidal dispersions from quasi-ternary mixtures, have been used in diverse applications, including nanoreactors for confined chemical processes. Their use as soft templates not only includes nanomaterial synthesis but also the interfacial assembly of nanoparticles in hybrid nanostructures. Especially the hierarchical arrangement of different types of nanoparticles over a surface in filament networks constitutes an interesting bottom-up strategy for facile and tunable film coating. Herein, we demonstrate the versatility of this surface assembly from microemulsion dispersions. Transmission and Scanning Electron Microscopy, in addition to UV-Vis Transmittance Spectroscopy, proved the assembly tunability after solvent evaporation under different conditions: the nanostructured films can be formed over different surfaces, using different compositions of liquid phases, as well as with the incorporation of different nanoparticle materials while keeping equivalent surface functionalization. This offers the possibility of adapting different components and conditions for coating tuning on a larger scale with simple procedures.

Quantifying the Microstructure of Dried Deposits Using Height-Height Correlation Function

Colloidal self-assembly has garnered significant attention in recent research, owing to applications in medical and engineering domains. Understanding the arrangement of particles in self-assembled systems is crucial for comprehending the underlying physics and synthesizing complex nano- and microscale structures. In this study, we introduce a novel methodology for analyzing the spatial distribution of particles in colloidal assemblies, focusing specifically on quantifying the microstructure of deposits formed by the evaporation of colloidal particle-laden drops. Utilizing a height-height correlation-function-based approach, we quantify variations in the height profile of deposits in radial and azimuthal directions. This approach enables the classification of the patterns into typical examples encountered in an evaporation-driven assembly. The method is demonstrated to be robust for quantifying synthetic and experimentally obtained deposit patterns, exhibiting excellent agreement in the estimated parameters. The mapping developed between pattern morphology and the quantitative measures introduced in this work may be used in a variety of applications including disease diagnosis as well as in developing pattern recognition tools.

Self-Assembly Pathways of Triblock Janus Particles into 3D Open Lattices

The self-assembly of triblock Janus particles is simulated from a fluid to 3D open lattices: pyrochlore, perovskite, and diamond. The coarse-grained model explicitly takes into account the chemical details of the Janus particles (attractive patches at the poles and repulsion around the equator) and it contains explicit solvent particles. Hydrodynamic interactions are accounted for by dissipative particle dynamics. The relative stability of the crystals depends on the patch width. Narrow, intermediate, and wide patches stabilize the pyrochlore-, the perovskite-, and the diamond-lattice, respectively. The nucleation of all three lattices follows a two-step mechanism: the particles first agglomerate into a compact and disordered liquid cluster, which does not crystallize until it has grown to a threshold size. Second, the particles reorient inside this cluster to form crystalline nuclei. The free-energy barriers for the nucleation of pyrochlore and perovskite are ≈10 kBT, which are close to the nucleation barriers of previously studied 2D kagome lattices. The barrier height for the nucleation of diamond, however, is much larger (>20 kBT), as the symmetry of the triblock Janus particles is not perfect for a diamond structure. The large barrier is associated with the reorientation of particles, i.e., the second step of the nucleation mechanism.

Stimuli-responsive nanoparticle self-assembly at complex fluid interfaces: a new insight into dynamic surface chemistry

The self-assembly of core/shell nanoparticles (NPs) at fluid interfaces is a rapidly evolving area with tremendous potential in various fields, including biomedicine, display devices, catalysts, and sensors. This review provides an in-depth exploration of the current state-of-the-art in the programmed design of stimuli-responsive NP assemblies, with a specific focus on inorganic core/organic shell NPs below 100 nm for their responsive adsorption properties at fluid and polymer interfaces. The interface properties, such as ligands, charge, and surface chemistry, play a significant role in dictating the forces and energies governing both NP-NP and NP-hosting matrix interactions. We highlight the fundamental principles governing the reversible surface chemistry of NPs and present detailed experimental examples in the following three key aspects of stimuli-responsive NP assembly: (i) stimuli-driven assembly of NPs at the air/liquid interface, (ii) reversible NP assembly at the liquid/liquid interface, including films and Pickering emulsions, and (iii) hybrid NP assemblies at the polymer/polymer and polymer/water interfaces that exhibit stimuli-responsive behaviors. Finally, we address current challenges in existing approaches and offer a new perspective on the advances in this field.

2D superlattices via interfacial self-assembly of polymer-grafted Au nanoparticles

Nanoparticle (NP) superlattices are periodic arrays of nanoscale building blocks. Because of the collective effect between functional NPs, NP superlattices can exhibit exciting new properties that are distinct from those of individual NPs or corresponding bulk materials. In particular, two-dimensional (2D) NP superlattices have attracted increasing attention due to their emerging applications in micro/opto-electronics, catalysis, sensing, and other fields. Among various preparation methods, evaporation-induced interfacial self-assembly has become the most popular method for preparing 2D NP superlattices because it is a simple, low-cost, and scalable process that can be widely applied to various NPs. Introducing soft ligands, such as polymers, can not only provide convenience in controlling the self-assembly process and tuning superlattice structures but also improve the properties of 2D NP superlattices. This feature article focuses on the methods of evaporation-induced self-assembly of polymer-grafted Au NPs into free-standing 2D NP superlattice films at air/liquid interfaces and 2D NP superlattice coatings on substrates, followed by studies on in situ tracking of the self-assembly evolution process through small-angle X-ray scattering. Their application in nano-floating gate memory devices is also included. Finally, the challenges and perspectives of this direction are discussed.

Tailored Morphology in Polystyrene/Poly(lactic acid) Blend Particles: Solvent's Effect on Controlled Janus/Core-Shell Structures

Controlling the morphology of polymeric particles is vital for their diverse applications. In this study, we explored how solvent composition influences the morphology of poly(styrene)/poly(lactic acid) (PS/PLA) particles prepared via the emulsion solvent evaporation method. We used toluene, dichloromethane (DCM), and various mixtures to prepare these particles. We investigated phase separation within the PS/PLA/solvent system using the Flory-Huggins ternary phase diagram and MesoDyn simulation, revealing pronounced immiscibility and phase separation in both PS/PLA/DCM and PS/PLA/toluene systems. We employed scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to characterize the resulting morphologies. Our study unveiled the substantial impact of solvent composition on particle structure. Using pure toluene resulted in acorn-shaped Janus particles. However, incorporating DCM into the solvent induced a transition from Janus to core-shell morphology. Remarkably, core-shell particles exhibited a single-core structure in a mixed toluene/DCM solvent, indicating thermodynamic stability. In contrast, pure DCM favored kinetically controlled multicore morphology, leading to lower PLA crystallinity due to increased PS-PLA interfaces. Samples with high Janus balance formed a self-assembled, two-dimensional (2-D) monolayer film, demonstrating the interfacial activity of the Janus particles. This 2-D monolayer film exhibits desirable emulsification properties with potential applications in various fields. Our study combines theoretical and experimental analyses, shedding light on the profound impact of solvent composition on the PS/PLA particle morphology. We observed transitions from Janus to core-shell structures, highlighted the influence of solvent viscosity on particle size, and uncovered the formation of self-assembled 2-D monolayer films. These insights are pivotal for tailoring polymeric particle structures. Furthermore, our findings advance macromolecular science in interface design, offering promising prospects for innovative materials development.

Patterned Nanoparticle Arrays Fabricated Using Liquid Film Rupture Self-Assembly

Self-assembly is an important bottom-up fabrication approach based on accurate manipulation of solid-air-liquid interfaces to construct microscale structures using nanoscale materials. This approach plays a substantial role in the fabrication of microsensors, nanosensors, and actuators. Improving the controllability of self-assembly to realize large-scale regular micro/nano patterns is crucial for this approach's further development and wider applications. Herein, we propose a novel strategy for patterning nanoparticle arrays on soft substrates. This strategy is based on a unique process of liquid film rupture self-assembly that is convenient, precise, and cost-efficient for mass manufacturing. This approach involves two key steps. First, suspended liquid films comprising monolayer polystyrene (PS) spheres are realized via liquid-air interface self-assembly over prepatterned microstructures. Second, these suspended liquid films are ruptured in a controlled manner to induce the self-assembly of internal PS spheres around the morphological edges of the underlying microstructures. This nanoparticle array patterning method is comprehensively investigated in terms of the effect of the PS sphere size, morphological effect of the microstructured substrate, key factors influencing liquid film-rupture self-assembly, and optical transmittance of the fabricated samples. A maximum rupture rate of 95.4% was achieved with an optimized geometric and dimensional design. Compared with other nanoparticle-based self-assembly methods used to form patterned arrays, the proposed approach reduces the waste of nanoparticles substantially because all nanoparticles self-assemble around the prepatterned microstructures. More nanoparticles assemble to form prepatterned arrays, which could strengthen the nanoparticle array network without affecting the initial features of prepatterned microstructures.

Ordered stripes to crack patterns in dried particulates of DNA-coated gold colloids via modulating nanoparticle-substrate interactions

The surface pattern in dried droplets of nanoparticle suspension possesses direct correlation with the evaporation profile, which apart from the bulk parameters, can also be altered by tuning the nanoscale interactions. Here, we show that, for sessile drops of DNA-coated gold nanoparticle (DNA-AuNP) solution, the alteration in evaporation pathway of TPCL (three-phase contact line) from stick-slip to mixed mode leads to a surface morphological transition from concentric rings with stripes to radial crack formation within the coffee ring deposit. A freshly cleaned silicon substrate offers hydrophilic/favorable substrate-nanoparticle interaction and produces multiple ordered stripes due to stick-slip motion of the TPCL. Using a SiO₂/Si substrate with ∼200 nm of oxide layer leads to an increase in the initial water contact angle θ_i-w by ∼40°, due to increased hydrophobicity of the substrate. Three distinct modes of evaporation are observed - constant contact radius (CCR), constant contact angle (CCA) and mixed mode, resulting in the formation of radial cracks on a thick coffee ring structure. The critical thickness (h_c), beyond which the cracks start to appear, was measured to be ∼600 nm and is in close agreement with the theoretical estimate of ∼510 nm. Through in situ contact angle and ex situ SEM measurements, we provide an understanding of the observed surface morphological transition in the dried particulate at various nanoparticle densities. Further analysis of the coffee ring width (d), linear crack density (σ) and crack spacing (λ) provides insight into the mechanism of crack formation for droplets dried on oxide-coated substrates.

Biocatalytic synthesis and ordered self-assembly of silica nanoparticles via a silica-binding peptide

Achieving scalable and economic methods for manufacturing ordered structures of nanoparticles is an ongoing challenge. Ordered structures of SiO2 nanoparticles have gained increased attention due to the great potential they offer in filtering, separation, drug delivery, optics, electronics, and catalysis. Biomolecules, such as peptides and proteins, have been demonstrated to be useful in the synthesis and self-assembly of inorganic nanostructures. Herein, we describe a simple Stöber-based method wherein both the synthesis and the self-assembly of SiO2 nanoparticles can be facilitated by a silica-binding peptide (SiBP). We demonstrate that the SiBP acts as a multirole agent when used alone or in combination with a strong base catalyst (NH3). When used alone, SiBP catalyzes the hydrolysis of precursor molecules in a dose-dependent manner and produces 17-20 nm SiO2 particles organized in colloidal gels. When used in combination with NH3, the SiBP produces smaller and more uniformly distributed submicrometer particles. The SiBP also improves the long-range self-assembly of the as-grown particles into an opal-like structure by changing the surface charge, without any need for further modification or processing of the particles. The results presented here provide a biomimetic route to the single-step synthesis and assembly of SiO2 nanoparticles into colloidal gels or opal-like structures.

Core-Shell Particles: From Fabrication Methods to Diverse Manipulation Techniques

Core-shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core-shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core-shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core-shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core-shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail.

Atomistic mechanisms of phase nucleation and propagation in a model two-dimensional system

We present a computational study on the solid–solid phase transition of a model two-dimensional system between hexagonal and square phases under pressure. The atomistic mechanism of phase nucleation and propagation are determined using solid-state Dimer and nudged elastic band (NEB) methods. The Dimer is applied to identify the saddle configurations and NEB is applied to generate the transition minimum energy path (MEP) using the outputs of Dimer. Both the atomic and cell degrees of freedom are used in saddle search, allowing us to capture the critical nuclei with relatively small supercells. It is found that the phase nucleation in the model material is triggered by the localized shear deformation that comes from the relative shift between two adjacent atomic layers. In addition to the conventional layer-by-layer phase propagation, an interesting defect-assisted low barrier propagation path is identified in the hexagonal to square phase transition. The study demonstrates the significance of using the Dimer method in exploring unknown transition paths without a priori assumption. The results of this study also shed light on phase transition mechanisms of other solid-state and colloidal systems.

The Formation of Self-Assembled Nanoparticles Loaded with Doxorubicin and d-Limonene for Cancer Therapy

Self-assembled nanoparticles present unique properties that have potential applications in the development of a successful drug delivery system. Doxorubicin (DOX) is an important anti-neoplastic anthracycline chemotherapeutic drug widely described. However, it suffers from serious dose-dependent cardiotoxicity. d-Limonene is a major constituent of numerous citrus oils that is considered a specific monoterpene against free radicals producing antioxidant activity. Herein, we aimed to design three types of self-assembled nanodelivery systems (nanoemulsion, niosomes, and polylactide nanoparticles) for loading both DOX and d-limonene to enhance the solubilization of d-limonene and provide antioxidant activity with excellent anticancer activity. As confirmed by dynamic light scattering and transmission electron microscopy, the nanoparticles were prepared successfully with diameter sizes of 52, 180, and 257 nm for the DOX-loaded nanoemulsion, niosomes, and polylactide nanoparticles, respectively. The zeta potential values were above -30 mV in all cases, which confirms the formation of stable nanoparticles. The loading efficiency of DOX was the highest in the case of the DOX-loaded nanoemulsion (75.8%), followed by niosomes (62.8%), and the least was in the case of polylactide nanoparticles with a percentage of 50.2%. The in vitro release study of the DOX-loaded nanoparticles showed a sustained release profile of doxorubicin with the highest release in the case of DOX-loaded PDLLA nanoparticles. The kinetic release model for all developed nanoparticles was the Peppas-Sahlin model, demonstrating DOX release through Fickian diffusion phenomena. Moreover, all developed nanoparticles maintain the antioxidant activity of d-limonene. The cytotoxicity study of the DOX-loaded nanoparticles showed concentration-dependent anticancer activity with excellent anticancer activity in the case of the DOX-loaded nanoemulsion and polylactide nanoparticles. These nanoparticles will be further studied in vivo to prove the cardioprotective effect of d-limonene in combination with DOX.

Fabrication and Characterization of Novel Silk Fiber-Optic SERS Sensor with Uniform Assembly of Gold Nanoparticles

Biocompatible optical fibers and waveguides are gaining attention as promising platforms for implantable biophotonic devices. Recently, the distinct properties of silk fibroin were extensively explored because of its unique advantages, including flexibility, process compatibility, long-term biosafety, and controllable biodegradability for in vitro and in vivo biomedical applications. In this study, we developed a novel silk fiber for a sensitive optical sensor based on surface-enhanced Raman spectroscopy (SERS). In contrast to conventional plasmonic nanostructures, which employ expensive and time-consuming fabrication processes, gold nanoparticles were uniformly patterned on the top surface of the fiber employing a simple and cost-effective convective self-assembly technique. The fabricated silk fiber-optic SERS probe presented a good performance in terms of detection limit, sensitivity, and linearity. In particular, the uniform pattern of gold nanoparticles contributed to a highly linear sensing feature compared to the commercial multi-mode fiber sample with an irregular and aggregated distribution of gold nanoparticles. Through further optimization, silk-based fiber-optic probes can function as useful tools for highly sensitive, cost-effective, and easily tailored biophotonic platforms, thereby offering new capabilities for future implantable SERS devices.

Structural and Dynamical Studies of a Lipid-Nanoclay Composite Layer at the Air-Water Interface

We modulate the adsorption affinities of nanoclay particles for the air-water interface by changing the cationic surface charge composition of the lipid monolayer and thereby tune the attractive electrostatic interaction between the positively charged lipid layer and the zwitterionic nanoclay particles in the water subphase. Our findings emphasize the significance of electrostatic interaction between lipids and the nanoclay, as well as its impact on the structural and viscoelastic features of the composite layer. We use surface pressure (Π)-mean molecular area (A) isotherms, atomic force microscope (AFM), Brewster angle microscopy (BAM), and energy dispersive X-ray spectrsocopy (EDXS) measurements to analyze the structure phases of lipid and lipid-nanoclay composite interfacial layer. The Π-A isotherm curve shows that the lipid-nanoclay composite layer has a larger lift-off area than the neat lipid layer, indicating that nanoparticles adsorb at the lipid layer via electrostatic interaction between lipid and nanoclay molecules. The surface density of the adsorbed nanoclay particles increases with an increase in the composition of the cationic lipid molecules. The stress relaxation response of the composite layer, measured using step compression measurements, exhibits exponential decay and ubiquitous dependence on the cationic dimyristoy-trimethylammonium propane (DMTAP) composition in the lipid layer with crossover to faster relaxation dynamics at DMTAP > 0.75. The power-law study of the frequency-dependent dynamic viscoelastic responses of the interfacial layer, measured using the barrier oscillation method, reveals a transition from glass-like response from neat lipid layer to gel-like dynamic response for the lipid-nanoclay composite layer. A solid-like behavior is evident for all the interface layers with dilation elastic modulus (E') > dilational viscous modulus (E″); however, the dynamic response of the neat layer is largely frequency-independent, whereas lipid-nanoclay composite layers with DMTAP > 0.75 reveal a frequency-dependent dynamic responses. The frequency-dependent power-law exponent of E', E″ increases on increasing the fractional composition of cationic DMTAP from 0.1 to 1.0, which forms a saturated interface of laponite particles and behaves as a viscoelastic gel in 2D.

Interfacial tension driven adsorption of MnO2 nanoparticles at the liquid/liquid interface to tailor ultra-thin polypyrrole sheets

An emerging aspect of research is designing and developing fully tunable metamaterials for various applications with fluid interfaces. Liquid/liquid interface-assisted methods represent an efficient and facile route for synthesizing two-dimensional (2-D) thin films of potential materials. The underlying mechanism behind thin film formation at the liquid/liquid interface involves the preferential adsorption of nano-sized particles at the interface to minimize high interfacial tension. Here, a water/chloroform interface-assisted method is employed for the one-pot synthesis of highly crystalline polypyrrole/manganese dioxide (PPy/MnO₂) sheets. The temporal evolution in the dynamic interfacial tension (from 32 mN m^-1 to 17 mN m^-1) observed in pendant drop tensiometry proved the preferential adsorption of MnO₂ atttached PPy oligomers at the water/chloroform interface. An ultra-thin sheet-like morphology and uniform distribution of ∼6 nm highly crystalline MnO₂ nanoparticles are evidenced by transmission and atomic force microscopy techniques. The predominance of interfacial polymerization in retaining the electrochemical activity of the PPy/MnO₂ sheets is elucidated for the electrochemical detection of nicotine. This study opens a new avenue for the realization of ultra-thin sheets of polymer-nanomaterial hybrids, enabling applications ranging from new classes of sensors to optics.

Nanoparticle and bioparticle deposition kinetics

Mechanisms and kinetic of particle deposition at solid surfaces leading to the formation of self-assembled layers of controlled structure and density were reviewed. In the first part theoretical aspects were briefly discussed, comprising limiting analytical solutions for the linear transport under flow and diffusion. Methods of the deposition kinetics analysis for non-linear regimes affected by surface blocking were also considered. Characteristic monolayer formation times under diffusion and flow for the nanoparticle size range were calculated. In the second part illustrative experimental results obtained for micro- and nanoparticles were discussed. Deposition at planar substrates was analyzed with emphasis focused on the stability of layers and the release kinetics of silver particles. Applicability of the quartz microbalance measurements (QCM) for quantitative studies of nanoparticle deposition kinetic was also discussed. Except for noble metal and polymer particles, representative results for virus deposition at abiotic surfaces were analyzed. Final part of the review was devoted to nanoparticle corona formation at polymer carrier particles investigated by combination of the concentration depletion, AFM, SEM and the in situ electrokinetic method. It is argued that the results obtained for colloid particles can be used as reliable reference systems for interpretation of protein and other bioparticle deposition, confirming the thesis that simple is universal.

Self-Assembly of Upconversion Nanoparticles Based Materials and Their Emerging Applications

In the past few decades, significant progress of the conventional upconversion nanoparticles (UCNPs) based nanoplatform has been achieved in many fields, and with the development of nanoscience and nanotechnology, more and more complex situations need a UCNPs based nanoplatform having multifunctions for specific multimodal or multiplexed applications. Through self-assembly, different UCNPs or UCNPs with other materials could be combined together within an entity. It is more like an ideal UCNPs nanoplatform, a unique system with the properties defined by its individual components as well as by the morphology of the composite. Various designs can show their different desired properties depending on the application situation. This review provides a complete summary on the optimization of the synthesis method for the recently designed UCNPs assemblies and summarizes various applications, including dual-modality cell imaging, molecular delivery, detection, and programmed control therapy. The challenges and limitations the UCNPs assembly faces and the potential solutions in this field are also presented.

Block copolymer self-assembly assisted fabrication of laterally organized- and stacked- nanoarrays

Block copolymer (BCP) self-assembly processes are often seen as reliable techniques for advanced nanopatterning to achieve functional surfaces and create templates for nanofabrication. By taking advantage of the tunability in pitch, diameter and feature-to-feature separation of the self-assembled BCP features, complex, laterally organized- and stacked- multicomponent nanoarrays comprising of gold and polymer have been fabricated. The approaches not only demonstrate nanopatterning of up to two levels of hierarchy but also investigate how a variation in the feature-to-feature gap at the first hierarchy affects the self-assembly of polymer features at the second. Such BCP self-assembly enabled multicomponent nanoarray configurations are rarely achieved by other nanofabrication approaches and are particularly promising for pushing the boundaries of block copolymer lithography and in creating unique surface architectures and complex morphologies at the nanoscale.

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

From Nanoparticle Heteroclusters to Filament Networks by Self-Assembly at the Water-Oil Interface of Reverse Microemulsions

Surface self-assembly of spherical nanoparticles of sizes below 10 nm into hierarchical heterostructures is under arising development despite the inherent difficulties of obtaining complex ordering patterns on a larger scale. Due to template-mediated interactions between oil-dispersible superparamagnetic nanoparticles (MNPs) and polyethylenimine-stabilized gold nanoparticles (Au(PEI)NPs) at the water-oil interface of microemulsions, complex nanostructured films can be formed. Characterization of the reverse microemulsion phase by UV-vis absorption revealed the formation of heteroclusters from Winsor type II phases (WPII) using Aerosol-OT (AOT) as the surfactant. SAXS measurements verify the mechanism of initial nanoparticle clustering in defined dimensions. XPS suggested an influence of AOT at the MNP surface. Further, cryo-SEM and TEM visualization demonstrated the elongation of the reverse microemulsions into cylindrical, wormlike structures, which subsequently build up larger nanoparticle superstructure arrangements. Such WPII phases are thus proven to be a new form of soft template, mediating the self-assembly of different nanoparticles in hierarchical network-like filaments over a substrate during solvent evaporation.

Magnetic-field-assisted deposition of self-assembling crystallite layers of Co2+-containing layered double hydroxides

Precipitation of nanocrystallites of cobalt-aluminium layered double hydroxides in a magnetic field has been studied. In a magnetic field perpendicular to the substrate, dense and homogeneous films have been obtained. Magnetic anisotropy of the crystallites is explained by deviation from the statistical cation distribution in favour of honeycomb-like coordination of cobalt.

Ordered polymer composite materials: challenges and opportunities

Polymer nanocomposites containing nanoscale fillers are an important class of materials due to their ability to access a wide variety of properties as a function of their composition. In order to take full advantage of these properties, it is critical to control the distribution of nanofillers within the parent polymer matrix, as this structural organization affects how the two constituent components interact with one another. In particular, new methods for generating ordered arrays of nanofillers represent a key underexplored research area, as emergent properties arising from nanoscale ordering can be used to introduce novel functionality currently inaccessible in random composites. The knowledge gained from developing such methods will provide important insight into the thermodynamics and kinetics associated with nanomaterial and polymer assembly. These insights will not only benefit researchers working on new composite materials, but will also deepen our understanding of soft matter systems in general. In this review, we summarize contemporary research efforts in manipulating nanofiller organization in polymer nanocomposites and highlight future challenges and opportunities for constructing ordered nanocomposite materials.

Electrostatic pair-interaction of nearby metal or metal-coated colloids at fluid interfaces

In this paper, we theoretically study the electrostatic interaction between a pair of identical colloids with constant surface potentials sitting in close vicinity next to each other at the fluid interface. By employing a simplified yet reasonable model system, the problem is solved within the framework of classical density functional theory and linearized as well as nonlinear Poisson-Boltzmann (PB) theory. Apart from providing a sound theoretical framework generally applicable to any such problem, our novel findings, all of which contradict common beliefs, include the following: first, quantitative and qualitative differences between the interactions obtained within the linear and the nonlinear PB theories; second, the importance of the electrostatic interaction between the omnipresent three-phase contact lines in interfacial systems; and, third, the occurrence of an attractive electrostatic interaction between a pair of identical metal colloids. The unusual attraction we report largely stems from an attractive line interaction, which although scales linearly with the size of the particle can compete with the surface interactions and can be strong enough to alter the nature of the total electrostatic interaction. Our results should find applications in metal or metal-coated particle-stabilized emulsions where densely packed particle arrays are not only frequently observed but also sometimes required.

Self-Assembly of Ag2S Colloidal Nanoparticles Stabilized by MPS in Water Solution

Self-assembly of colloidal Ag₂S nanoparticles (NPs) was studied in the presence of (3-mercaptopropyl)trimethoxysilane (MPS). Solutions with different molar ratios of Ag₂S/MPS were prepared. The appearance of nano- and microtubes was detected. Self-organized NPs were studied with optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HRTEM). Silicon nuclear magnetic resonance spectroscopy (²⁹Si NMR) was used to study polycondensation of MPS molecules. Geometrical parameters of the nano- and microtubes depended on the molar ratio of Ag₂S/MPS. The scheme and mechanism of self-assembly of Ag₂S NPs in nanotubes in the presence of MPS were proposed. The effect of MPS on the preservation of the initial stoichiometry of Ag₂S NPs was discussed.