Self-assembly Of Colloidal Particles Research Articles

Evolution of self-assembled amphiphilic colloidal particles in strong-flavor Chinese baijiu

This study proposed the evolution of self-assembled amphiphilic colloidal particles in Strong-Flavor (SF) Baijiu based on Ostwald ripening for the first time. The evolution process occurs in two stages: disordered amphiphilic molecules self-assemble into small colloidal particles and subsequently undergo Oswald ripening to form larger hydrophobic particles. Microscopic observations revealed the average size of oil-like spherical colloidal particles in Baijiu increased from 1.86 μm to 2.96 μm while the number of particles decreased by 39.50% during the 16-year cellaring process of SF Baijiu, consistent with the particle size trend observed via laser scattering. During fusion process, the charge-to-mass ratio of positively charged colloidal particles decreased, leading ζ-potential decreased from 23.7 mV to 4.66 mV within 16 years of storage. The electrochemical impedance spectroscopy approach tracked the unidirectional variation in the dielectric constant during evolution of SF Baijiu, reflecting the gradual expansion of colloidal particles, which aligns with the evolution trend observed in molecular dynamics simulations. By integrating direct microscopic observations of amphiphilic colloidal particles with electrochemical techniques, the evolution of Baijiu samples is capable to be evaluated in-situ, laying the foundation for intelligent Baijiu aging monitoring technology.

Assembly of Covalent Organic Frameworks into Colloidal Photonic Crystals.

Self-assembly of colloidal particles into ordered superstructures is an important strategy to discover new materials, such as catalysts, plasmonic sensing materials, storage systems, and photonic crystals (PhCs). Here we show that porous covalent organic frameworks (COFs) can be used as colloidal building particles to fabricate porous PhCs with an underlying face-centered cubic (fcc) arrangement. We demonstrate that the Bragg reflection of these can be tuned by controlling the size of the COF particles and that species can be adsorbed within the pores of the COF particles, which in turn alters the Bragg reflection. Given the vast number of existing COFs, with their rich properties and broad modularity, we expect that our discovery will enable the development of colloidal PhCs with unprecedented functionality.

Porous Self-Assemblies Mediated by Dumbbell Particles as Cross-Linking Agents.

Self-assembly of colloidal particles is emerging as a promising approach for producing novel materials. These colloidal particles can be synthesized with protrusions (lobes) on their surfaces that allow the formation of porous structures with a wide range of applications. Using Langevin dynamics simulations, we studied self-assembly in the binary mixtures of lobed colloidal particles with variations in their lobe sizes to investigate the feasibility of using dumbbell particles (with two lobes) as cross-linkers to increase the porosity in self-assembled morphologies. Each binary system was formed by mixing the dumbbell particles with one of the following types of particles: trigonal planar (three lobes), tetrahedral (four lobes), trigonal bipyramidal (five lobes), and octahedral (six lobes). We observed that the lobe size on each particle can be tuned to favor the formation of random aggregates and spherical aggregates when the lobes are larger and well-ordered crystalline structures when the lobes are smaller. We also observed that these polydisperse systems form self-assembled structures characterized by porosities higher than those of the structures formed by the monodisperse systems. These results indicate that the lobe size is an important design feature that can be optimized to achieve desired structures with distinct morphologies and porosities, and the dumbbell particles are effective cross-linking agents to enhance the porosity in self-assembled structures.

Nanoparticle localization within chiral liquid crystal defect lines and nanoparticle interactions.

Self-assembly of colloidal particles into predefined structures is a promising way to design inexpensive manmade materials with advanced macroscopic properties. Doping of nematic liquid crystals (LCs) with nanoparticles has a series of advantages in addressing these grand scientific and engineering challenges. It also provides a very rich soft matter platform for the discovery of unique condensed matter phases. The LC host naturally allows the realization of diverse anisotropic interparticle interactions, enriched by the spontaneous alignment of anisotropic particles due to the boundary conditions of the LC director. Here we demonstrate theoretically and experimentally that the ability of LC media to host topological defect lines can be used as a tool to probe the behavior of individual nanoparticles as well as effective interactions between them. LC defect lines irreversibly trap nanoparticles enabling controlled particle movement along the defect line with the use of a laser tweezer. Minimization of Landau-de Gennes free energy reveals a sensitivity of the ensuing effective nanoparticle interaction to the shape of the particle, surface anchoring strength, and temperature, which determine not only the strength of the interaction but also its repulsive or attractive character. Theoretical results are supported qualitatively by experimental observations. This work may pave the way toward designing controlled linear assemblies as well as one-dimensional crystals of nanoparticles such as gold nanorods or quantum dots with tunable interparticle spacing.

Water-in-water emulsions stabilized by self-assembled chitosan colloidal particles

Dextran (Dex) and poly(ethylene glycol) (PEG)-based aqueous emulsions were stabilized using the self-assembled chitosan colloidal particles (CS CPs). Besides, the effects of pH, CS CPs concentration, polymer concentration, volume ratio of PEG solution to Dex solution, temperature, homogenizing speed and homogenizing time on the property of the W/W emulsions were investigated, respectively. In order to enhance the stability of the PEG-Dex emulsion, sodium tripolyphosphate was used to cross-link the CS CPs at the interface of emulsion droplets, which resulted in the stability duration for >1 year. Finally, the CS CPs were used as a support to immobilize urease and bovine serum albumin and a stabilizer to prepare W/W emulsion, which were then adopted as a catalysis system and as a spinning solution to fabricate drug-loaded nanofiber. This strategy potentially provides a new opportunity to encapsulate the active molecules at the water-water interface, and enrich the types of usable active molecules in the encapsulation in the W/W emulsions.

Chiral Plasmonic Shells: High-Performance Metamaterials for Sensitive Chiral Biomolecule Detection.

Low-cost and large-area chiral metamaterials (CMs) are highly desirable for practical applications in chiral biosensors, nanophotonic chiral emitters, and beyond. A promising fabrication method takes advantage of self-assembled colloidal particles, onto which metal patches with defined orientation are created using glancing angle deposition (GLAD). However, using this method to make uniform and well-defined CMs over macroscopic areas is challenging. Here, we fabricate a uniform large-area colloidal particle array by interface-mediated self-assembly and precisely control the structural handedness of chiral plasmonic shells (CPSs) using GLAD. Strong chiroptical signals arise from twisted currents at the main, corner, and edge of CPSs, allowing a balance between strong chiroptical and high transmittance properties. Our shell-like chiral geometry shows excellent sensor performance in detecting chiral molecules due to the formation of uniform superchiral fields. Systematic investigations optimize the interplay between peak and null point resonances in different CPSs and result in a record consistency chiral sensor parameter U, i.e., 3.77 for null points and 0.0867 for peaks, which are about 54 and 1.257 times larger than the highest value (0.068) of previously reported CMs. The geometrical chirality, surface plasmonic resonance, chiral surface lattice resonance, and chiral sensor performance evidence the chiroptical effect and the excellent chiral sensor performance.

Extreme mechanics of colloidal polymers under compression: Buckling, creep, and break-up

Self-assembling patchy colloidal particles form a promising platform to create designer soft materials. To dress such systems with mechanical functionality, one can take inspiration from biological structures such as the cell's cytoskeleton, which consists of semiflexible filaments, whose mechanical behavior give the cell its unique mechanical properties. Here we present mechanical experiments on analogs of biological fibers, semiflexible ``colloidal polymers'' made from bonded patchy colloidal particles. We use optical tweezers to probe their extreme mechanics under increasingly high compressions and we reveal a rich nonlinear mechanical response involving buckling, viscoelastic creep, and ultimately break-up. We characterize and model this response using elastic and viscoelastic models involving Euler buckling and stress relaxation. This allows us to identify the critical Euler buckling force, and relate the critical bending at break-up to the finite patch size of the colloids. These results demonstrate the crucial role of the patch-patch interactions in the mechanics of self-assembled colloidal materials, and they provide mechanical relationships that are essential to design functional colloidal architectures inspired by nature.

Preparation and Emulsification Properties of Self-assembled Colloidal Particles Based on Alginic Acid

Preparation and Emulsification Properties of Self-assembled Colloidal Particles Based on Alginic Acid

Colloidal Particles with Triangular Patches.

Self-assembling colloidal particles into clathrate hydrates requires the particles to have tetrahedral bonds in the eclipsed conformation. It has been suggested that colloidal particles with eclipsed triangular-shaped patches can form clusters in the eclipsed conformation that leads to colloidal clathrate hydrates. However, in experiments, patches have been limited to circular shapes due to surface energy minimization. Here, we extend the particle synthesis strategy and show that colloidal particles with triangular patches can be readily fabricated by controlling the viscosity of the liquid oil droplets during a colloidal fusion process. The position, orientation, curvature, shape, and size of the patches are all exclusively determined by the intrinsic symmetry of the colloidal clusters, resulting in dipatch particles with eclipsed patches and tetrahedral patchy particles with patch vertices pointing toward each other. Patch curvature can be controlled by tuning the viscosity of the oil droplets and using different surfactants. Using strain-promoted azide-alkyne cycloaddition, single-stranded DNA can be selectively functionalized on the patches. However, after annealing these particles, dipatch particles form chains because the patches are too small to form clathrate hydrates. Under certain conditions, tetrahedral triangular patchy particles should prefer the eclipsed conformation, as it maximizes DNA hybridization. However, we observe random aggregates, which result from having triangular patches that are too big. We estimate that tetrahedral patchy particles that can crystallize need to be less than 1 μm in diameter.

Inverse Design of Self-Assembling Diamond Photonic Lattices from Anisotropic Colloidal Clusters.

Colloidal nanoparticles with anisotropic interactions are promising building blocks for the fabrication of complex functional materials. A challenge in the self-assembly of colloidal particles is the rational design of geometry and chemistry to program the formation of a desired target structure. We report an inverse design procedure integrating Langevin dynamics simulations and evolutionary algorithms to engineer anisotropic patchy colloidal clusters to spontaneously assemble into a cubic diamond lattice possessing a complete photonic band gap. The combination of a tetrahedral cluster geometry and optimized placement of a single type of anisotropic interaction patch results in a colloidal building block predicted to assemble a cubic diamond lattice with more than 82% yield. This design represents an experimentally viable colloidal building block capable of high-fidelity assembly of a cubic diamond lattice.

Self-assembly of colloidal particles into amorphous photonic crystals

This review focuses on the introduction, fabrication, and applications of amorphous photonic crystals.

Self-Assembly of Monodispersed Closely Packed Composite Superstructures by Anchoring Nanoparticles into Multihierarchical Frameworks

Self-assembly of colloidal particles into superstructures is a simple but effective way to prepare composite materials, which is of widespread interest for particle engineering. Here, we establish ...

Colloidal diamond.

Self-assembling colloidal particles in the cubic diamond crystal structure could potentially be used to make materials with a photonic bandgap1-3. Such materials are beneficial because they suppress spontaneous emission of light1 and are valued for their applications as optical waveguides, filters and laser resonators4, for improving light-harvesting technologies5-7 and for other applications4,8. Cubic diamond is preferred for these applications over more easily self-assembled structures, such as face-centred-cubic structures9,10, because diamond has a much wider bandgap and is less sensitive to imperfections11,12. In addition, the bandgap in diamond crystals appears at a refractive index contrast of about 2, which means that a photonic bandgap could be achieved using known materials at optical frequencies; this does not seem to be possible for face-centred-cubic crystals3,13. However, self-assembly of colloidal diamond is challenging. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches14-16. But this approach lacks a mechanism to ensure that the patchy spheres select the staggered orientation of tetrahedral bonds on nearest-neighbour particles, which is required for cubic diamond15,17. Here we show that by using partially compressed tetrahedral clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion in combination with a steric interlock mechanism that selects the required staggered bond orientation. Photonic bandstructure calculations reveal that the resulting lattices (direct and inverse) have promising optical properties, including a wide and complete photonic bandgap. The colloidal particles in the self-assembled cubic diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. This makes these structures suitable templates for forming high-dielectric-contrast photonic crystals with cubic diamond symmetry.

Dielectrophoretic crossover frequency of individual pearl chains formed by bonded colloidal spheres

Dielectrophoresis (DEP) has emerged as a viable means of fabricating functional materials and devices via self-assembly of colloidal particles, and has attracted much attention. Despite the extensive studies, how the crossover frequency of a pearl chain changes with the number of forming spheres is still unclear. Here we investigate the crossover frequency of individual two-sphere particles using the optical-tweezer-based phase-shift method and the volumetric polarization and integration (VPI) model. The phase shift method, based on reversal of particle oscillating movement, is capable of measuring the crossover frequency of individual particles with high accuracy; the VPI model considers the electric field distortion due to the particles and the electric double layer. We find that a two-sphere particle possesses a lower crossover frequency than the single sphere due to the competing effect of volume and surface area. Also, there exists an intriguing relationship between the crossover frequency of an n-sphere chain and that of its composing single sphere as follows: fn-sphere = n―0.095fsingle. This relationship is independent of the sphere size, medium conductivity, and functional group. Our results provide a rational framework for understanding the DEP behavior of pearl chains and may be useful for future applications using DEP self-assembly technology.

Role of Entropy in Colloidal Self-Assembly.

Entropy plays a key role in the self-assembly of colloidal particles. Specifically, in the case of hard particles, which do not interact or overlap with each other during the process of self-assembly, the free energy is minimized due to an increase in the entropy of the system. Understanding the contribution of entropy and engineering it is increasingly becoming central to modern colloidal self-assembly research, because the entropy serves as a guide to design a wide variety of self-assembled structures for many technological and biomedical applications. In this work, we highlight the importance of entropy in different theoretical and experimental self-assembly studies. We discuss the role of shape entropy and depletion interactions in colloidal self-assembly. We also highlight the effect of entropy in the formation of open and closed crystalline structures, as well as describe recent advances in engineering entropy to achieve targeted self-assembled structures.

Modified karaya gum colloidal particles for the management of systemic hypertension

This study undertakes the development of colloidal carriers for the purpose of oral delivery of bosentan and subsequent management of systemic hypertension. Karaya gum, a natural polymer was carboxymethylated to improve its hydrophilic character and then the carboxymethyl gum was hydrophobically modified by forming propyl ethers. The modified polymer acquired amphiphilic property and self-aggregated in water to form amphiphilic colloidal particles (ACPs) at critical concentration of 3.35 mg/L with spherical shape (<200 nm) and smooth surface morphology. The colloidal particles could entrap >90% drug in the lipophilic domain. The ionic crosslinking of the hydrophilic shell of ACPs imparted greater stability to the colloidal system. The crosslinking extended the duration of drug release under simulated gastrointestinal fluids. The crystalline drug physically turned into amorphous state after hosting into the lipophilic cores of ACPs. The entrapment resulted in significant improvement of drug dissolution rate. The polymer relaxation contributed to the diffusion process of drug from ACPs. Pre-clinical testing via oral route demonstrated that the crosslinked colloidal particles could effectively control the systemic hypertension over a period of 12 h. Hence, bosentan-loaded self-assembled colloidal particles may advance the management of systemic hypertension.

Charge-, salt- and flexoelectricity-driven anchoring effects in nematics

ABSTRACT We investigate the effects of electric double layers and flexoelectricity on the surface anchoring in general nematic fluids. Within a simplified model, we demonstrate for a nematic electrolyte how the surface anchoring strength can be affected by the surface charge, bulk ion concentration and/or flexoelectricity, effectively changing not only the magnitude of the anchoring but also the anchoring type, such as from planar to tilted. In particular, we envisage possible tuning of the anchoring strength by the salt concentration in the regime where sufficiently strong electrostatic anchoring, as controlled by the (screened) surface charge, can compete with the non-electrostatic anchoring. This effect is driven by the competing energetic-torque couplings between nematic director and the emergent electrostatic potential, due to surface charge, ions and flexoelectricity. Our findings propose a way of influencing surface anchoring by using electrostatic effects, which could be used in various aspects, including in the self-assembly of colloidal particles in nematic fluids, optical and display patterns, and sensing.

Shape Complementarity Modulated Self-Assembly of Nanoring and Nanosphere Hetero-nanostructures.

Shape complementarity is of paramount importance in molecular recognition, but has rarely been adopted in the self-assembly of colloidal particles, especially in the case of nanoparticles of different shapes. Here, we demonstrated a simple, yet powerful strategy for fabricating gold nanoring-based heterogeneous nanostructures (AuNR-HNs) with well-defined geometries and high yield. The assembly of various geometries of AuNR-HNs is modulated by the shape complementarity of plasmonic nanorings and nanospheres. We also present experimental evidence of dark quadrupolar ring mode excitation in AuNR-HNs through single-particle optical measurements. Our strategy will be beneficial in the study of nanoparticle assembly, photonic element interaction, and the development of plasmon-based optical devices.

Redox-Responsive Colloidal Particles Based on Coordination Polymers Incorporating Viologen Units.

Colloidal particles based on supramolecular polymers are emerging as promising functional materials because of their intrinsic dynamic features and the possibility of stimuli responsivity. In this work, ≈200 nm self-assembled redox-responsive colloidal particles made of 1D-coordination polymers were readily prepared. In these metallopolymers, organic entities made of bis(viologen) groups covalently associated with terpyridine units are spontaneously bridged by Zn2+ cations through the formation of coordination bonds. The properties of these particles were analyzed and their redox activities investigated. Upon reduction of the viologen units, the formation of π-dimers between the reduced viologen moieties was demonstrated by spectroscopic experiments. It was shown that intermolecular π-dimers (i.e., between different polymer chains) that do not exist in homogeneous polymer solutions were, nevertheless, formed in the particle's structure because of the effects of confinement. The presence of these π-dimers allows stabilization of the charge in the colloids.

Recent developments in nano micelles as drug delivery system

Targeting of the drug directly to the cells, tissues, or organs with no impact on healthy cells is a challenge. In the current era, it's been made possible by therapeutic interventions. The novel drug delivery systems such as nano particulates, liposomes, aquasomes, phytosomes, dendrimers, nano sponges, nano micelles are developed. Nano micelles are developed for efficient targeting and are currently in trend as therapeutic carriers of water-insoluble drugs. Micelles are self-assembling Nano-sized colloidal particles with a hydrophobic core and hydrophilic shell. Among the micelle-forming compounds, amphiphilic copolymers, i.e., polymers consisting of hydrophobic block and hydrophilic block, are gaining increasing attention. Polymeric micelles possess high stability both in vitro and in vivo with good biocompatibility. Nano micelles are used widely because of the smaller size range of 10 to 100nm, with greater drug loading capacity. Advantages over other dosage forms include solubilization of poorly soluble drugs, sustained release, protection of drugs from degradation and metabolism. The property discussed includes CMC, size, and aggregation number, and stability. CMC is the minimum polymer concentration required for micelle formation. Aggregation number (Nₐ) is the number of polymeric chains required to form micelles, and it ranges between tens to hundreds. Thermodynamic stability is based on size, the optical clarity of solution, viscosity, and surface tension. Kinetic stability accounts for micellar integrity. This review will discuss some recent trends in using micelles as pharmaceutical carriers such as to deliver drugs in conditions such as TB, cancer, ocular complications, etc.