Advances in Colloidal Building Blocks: Toward Patchy Colloidal Clusters

Surface Orthogonal Patterning and Bidirectional Self-Assembly of Nanoparticles Tethered by V-Shaped Diblock Copolymers

We investigated the surface orthogonal patterning and bidirectional self-assembly of binary hairy nanoparticles (NPs) constructed by uniformly tethering a single NP with multiple V-shaped AB diblock copolymers using Brownian dynamics simulations in a poor solvent. At low concentration, the chain collapse and microphase separation of binary polymer brushes can lead to the patterning of the NP surface into A- and B-type orthogonal patches with various numbers of domains (valency), n = 1-6, that adopt spherical, linear, triangular, tetrahedral, square pyramidal, and pentagonal pyramidal configurations. There is a linear relationship between the valency and the average ratio of NP diameter to the polymers' unperturbed root-mean-square end-to-end distance for the corresponding valency. The linear slope depends on the grafting density and is independent of the interaction parameters between polymers. At high concentration, the orthogonal patch NPs serve as building blocks and exhibit directional attractions by overlapping the same type of domains, resulting in self-assembly into a series of fascinating architectures depending on the valency and polymer length. Notably, the 2-valent orthogonal patch NPs have the bidirectional bonding ability to form the two-dimensional (2D) square NP arrays by two distinct pathways. Simultaneously patching A and B blocks enables the one-step formation of 2D square arrays via bidirectional growth, whereas step-by-step patching causes the directional formation of 1D chains followed by 2D square arrays. Moreover, the gap between NPs in the 2D square arrays is related to the polymer length but independent of the NP diameter. These 2D square NP arrays are of significant value in practical applications such as integrated circuit manufacturing and nanotechnology.

Recent advances in photonic crystal-based chemical sensors

The increasing attention towards environmental quality, food safety, public security and medical diagnosis demands high requirements and standards for chemical sensors with merits of rapid response, high precision, long-term stability and reusability. In this case, a prominent innovation in sensory materials holds potential to realize new generations of chemical sensor technologies. Specifically, photonic crystals (PCs) as structured dielectric materials with spatially periodic ordered arrangements offer unique advantages in improving the sensing performance of chemical sensors. Consequently, the promising properties of PCs promote research on their implementation as an integral part of chemical sensors. This review highlights the integration of PCs into chemical sensors including a range of building blocks for the construction of PCs with versatile opal or opal inverse structural architectures and a delicate choice of surface functionality with associated sensing interfaces for target recognition and signal transduction. Subsequently, based on their synthesis and functionality, we focus on introducing the sensing principles of recent advances in PC-based chemical sensors, such as reflection spectra-based sensing, visual colorimetric sensing, fluorescence sensing, surface-enhanced Raman spectroscopy (SERS)-based sensing and other integrated sensing. Finally, the future prospects and challenges are discussed for the further improvement of PC-based chemical sensors.

Spearheading a new era in complex colloid synthesis with TPM and other silanes

Colloid science has recently grown substantially owing to the innovative use of silane coupling agents (SCAs), especially 3-trimethoxysilylpropyl methacrylate (TPM). SCAs were previously used mainly as modifying agents, but their ability to form droplets and condense onto pre-existing structures has enabled their use as a versatile and powerful tool to create novel anisotropic colloids with increasing complexity. In this Review, we highlight the advances in complex colloid synthesis facilitated by the use of TPM and show how this has driven remarkable new applications. The focus is on TPM as the current state-of-the-art in colloid science, but we also discuss other silanes and their potential to make an impact. We outline the remarkable properties of TPM colloids and their synthesis strategies, and discuss areas of soft matter science that have benefited from TPM and other SCAs.

Orientation and stretching of supracolloidal chains of diblock copolymer micelles by spin-coating process

Supracolloidal chains consisting of nano- or micro-scale particles exhibit anisotropic properties not observed in individual particles. The orientation of the chains is necessary to manifest such characteristics on a macroscopic scale. In this study, we demonstrate the orientation of supracolloidal chains composed of nano-scale micelles of a diblock copolymer through spin-coating. We observed separate chains coated on a substrate with electron microscopy, and analyzed the orientation and stretching of the chains quantitatively with image analysis software. In drop-casting, the chains were coated randomly with no preferred orientation, and the degree of stretching exhibited an intrinsic semi-flexible nature. In contrast, spin-coated chains were aligned in the radial direction, and the apparent persistence length of the chain increased, confirming the stretching of the chain quantitatively. Furthermore, by incorporating fluorophores into supracolloidal chains and confirming the oriented chains with confocal fluorescence microscopy, it is demonstrated that oriented chains can be utilized as a template to align functional materials.

Polymorphic Self-Assembly with Procedural Flexibility for Monodisperse Quaternary Protein Structures of DegQ Enzymes

As large molecular tertiary structures, some proteins can act as small robots that find, bind, and chaperone target protein clients, showing the potential to serve as smart building blocks in self-assembly fields. Instead of using such intrinsic functions, most self-assembly methodologies for proteins aim for de novo-designed structures with accurate geometric assemblies, which can limit procedural flexibility. Here, a strategy enabling polymorphic clustering of quaternary proteins, exhibiting simplicity and flexibility of self-assembling paths for proteins in forming monodisperse quaternary cage particles is presented. It is proposed that the enzyme protomer DegQ, previously solved at low resolution, may potentially be usable as a threefold symmetric building block, which can form polyhedral cages incorporated by the chaperone action of DegQ in the presence of protein clients. To obtain highly monodisperse cage particles, soft, and hence, less resistive client proteins, which can program the inherent chaperone activity of DegQ to efficient formations of polymorphic cages, depending on the size of clients are utilized. By reconstructing the atomic resolution cryogenic electron microscopy DegQ structures using obtained 12- and 24-meric clusters, the polymorphic clustering of DegQ enzymes is validated in terms of soft and rigid domains, which will provide effective routes for protein self-assemblies with procedural flexibility.

Surface Engineering and Programmed Self-Assembly of Silica Nanoparticles with Controllable Polystyrene/Poly(4-vinybenzyl azide) Patches

The programmed self-assembly of patchy nanoparticles (NPs) through a bottom-up approach is an efficient strategy for producing highly organized materials with a predetermined architecture. Herein, we report the preparation of di- and trivalent silica NPs with polystyrene (PS)/poly(4-vinylbenzyl azide) (PVBA) patches and assemble them in a THF mixture by lowering the solvent quality. Silica-PS/PVBA colloidal hybrid clusters were synthesized through the seeded growth emulsion copolymerization of styrene and 4-vinylbenzyl azide (VBA) in varying ratios. Subsequently, macromolecules on silica NPs originating from the copolymerization of growing PS or PVBA chains with the surface-grafted MMS compatibilizer are engineered by fine-tuning of polymer compositions or adjustment of solvent qualities. Moreover, multistage silica regrowth of tripod and tetrapod allowed a fine control of the patch-to-particle size ratio ranging from 0.69 to 1.54. Intriguingly, patchy silica NPs (1-, 2-, 3-PSNs) rather than hybrid clusters are successfully used as templates for multistep regrowth experiments, leading to the formation of silica NPs with a new morphology and size controllable PVBA/PS patches. Last but not least, combined with mesoscale dynamics simulations, the self-assembly kinetics of 2-PSN and 3-PSN into linear colloidal polymers and honeycomb-like lattices are studied. This work paves a new avenue for constructing colloidal polymers with a well-defined sequence and colloidal crystals with a predetermined architecture.

Simultaneous and independent topological control of identical microparticles in non-periodic energy landscapes

Topological protection ensures stability of information and particle transport against perturbations. We explore experimentally and computationally the topologically protected transport of magnetic colloids above spatially inhomogeneous magnetic patterns, revealing that transport complexity can be encoded in both the driving loop and the pattern. Complex patterns support intricate transport modes when the microparticles are subjected to simple time-periodic loops of a uniform magnetic field. We design a pattern featuring a topological defect that functions as an attractor or a repeller of microparticles, as well as a pattern that directs microparticles along a prescribed complex trajectory. Using simple patterns and complex loops, we simultaneously and independently control the motion of several identical microparticles differing only in their positions above the pattern. Combining complex patterns and complex loops we transport microparticles from unknown locations to predefined positions and then force them to follow arbitrarily complex trajectories concurrently. Our findings pave the way for new avenues in transport control and dynamic self-assembly in colloidal science.

Solidification-Controlled Compartmentalization of Bismuth-Tin Colloidal Particles

Nucleation and growth are the main steps of microstructure formation. Nucleation occurs stochastically in a bulk material but can be controlled by introducing or removing catalytic sites, or creating local gradients. Such manipulations can already be implemented to bulk materials at a high level of sophistication but are still challenging on micrometer or smaller scales. Here, we explore the potential to transfer this vast knowledge in classical metallurgy to the fabrication of colloidal particles and report strategies to control phase distribution within a particle by adjusting its solidification conditions. Benefiting from the core-shell structure of liquid metals and the constrained volume of particles, we demonstrate that the same alloy particle can be transformed into a lamellar, composite, Janus, or striped particle by the felicitous choice of the phase separation process pathway. This methodology offers an unprecedented opportunity for the scalable production of compartmentalized particles in high yields that are currently limited to inherently unscalable methods.

Self-Assembling of Nonadditive Mixtures Containing Patchy Particles with Tunable Interactions

Mixtures of nanoparticles (NPs) with hybridizing grafted DNA or DNA-like strands have been of particular interest because of the tunable selectivity provided for the interactions between the NP components. A richer self-assembly behavior would be accessible if these NP-NP interactions could be designed to give nonadditive mixing (in analogy to the case of molecular components). Nonadditive mixing occurs when the mixed-state volume is smaller (negative) or larger (positive) than the sum of the individual components' volumes. However, instances of nonadditivity in colloidal/NP mixtures are rare, and systematic studies of such mixtures are nonexistent. This work focuses on patchy NPs whose patches (coarsely representing grafted hybridizing DNA strands) not only encode selectivity across components but also impart a tunable nonadditivity by varying their extent of protrusion. To guide the exploration of the relationship between phase behavior and nonadditivity for different patches' designs, the NP-NP potential of mean force (PMF) and a nonadditive parameter were first calculated. For one-patch NPs, different lamellar morphologies were predominantly observed. In contrast, for mixtures of two-patch NPs and (fully grafted) spherical particles, a rich phase behavior was found depending on patch-patch angle and degree of nonadditivity, resulting in phases such as the gyroid, cylinder, honeycomb, and two-layered crystal. Our results also show that both minimum positive nonadditivity and multivalent interactions are necessary for the formation of ordered network mesophases in the class of models studied.

Pursuing colloidal diamonds

The endeavor to selectively fabricate a cubic diamond is challenging due to the formation of competing phases such as its hexagonal polymorph or others possessing similar free energy. The necessity to achieve this is of paramount importance since the cubic diamond is the only polymorph exhibiting a complete photonic bandgap, making it a promising candidate in view of photonic applications. Herein, we demonstrate that due to the presence of an external field and delicate manipulation of its strength we can attain selectivity in the formation of a cubic diamond in a one-component system comprised of designer tetrahedral patchy particles. The driving force of such a phenomenon is the structure of the first adlayer which is commensurate with the (110) face of the cubic diamond. Moreover, after a successful nucleation event, once the external field is turned off, the structure remains stable, paving an avenue for further post-synthetic treatment.

Programmed Self-Assembly of Single Colloidal Gyroids for Chiral Photonic Crystals

Gyroid structures are of extensive interest because they provide a rich platform for chiroptics as well as topological photonics. While the double-gyroid morphology as a bicontinuous structure is not uncommon in self-assembled soft materials, direct self-assembly of single-network gyroids has proven elusive. Here, an enantiomorphic pair of single-gyroid crystals comprising colloidal spheres is presented, and two distinct routes are demonstrated for programmed self-assembly of each single colloidal gyroid enantiomorph from rationally designed patchy spheres. The designer colloidal patchy spheres, which closely hew to their synthetic feasibility, are chiral, having either two staggered rectangular patches at opposite poles or four circular patches arranged in a well-defined geometry. The single colloidal gyroid, as well as its inverse structure, is shown to support a wide complete photonic bandgap in addition to exhibiting rich chiroptical properties, making them attractive chiral photonic crystals. The versatility of this single colloidal gyroid, the bottom-up routes devised here in silico, and the robustness of the design space for the chiral colloidal patchy spheres together make a strong case for single colloidal gyroids to supersede colloidal diamond, as a target for programmed self-assembly, in the quest for photonic crystals operating at optical frequencies.

Amphiphilic Janus Particles Confined in Symmetrical and Janus-Like Slits

We use Monte Carlo simulations to investigate the behavior of Janus spheres composed of attractive and repulsive parts confined between two parallel solid surfaces. The slits with identical and competing walls are studied. The adsorption isotherms of Janus particles are determined, and the impact of the density in the pore on the morphology is discussed in detail. So far, this issue has not been systematically investigated. New, unique structures are observed along the isotherms, including the bilayer and three-layer structures located at different distances from the walls. We analyze how selected parameters affect the positional and orientational ordering in these layers. In some cases, the particles form highly ordered hexagonal lattices.

Molecular Engineering of Colloidal Atoms

Creation of architectures with exquisite hierarchies actuates the germination of revolutionized functions and applications across a wide range of fields. Hierarchical self-assembly of colloidal particles holds the promise for materialized realization of structural programing and customizing. This review outlines the general approaches to organize atom-like micro- and nanoparticles into prescribed colloidal analogs of molecules by exploiting diverse interparticle driving motifs involving confining templates, interactive surface ligands, and flexible shape/surface anisotropy. Furthermore, the self-regulated/adaptive co-assembly of simple unvarnished building blocks is discussed to inspire new designs of colloidal assembly strategies.