Polymerization-like kinetics of the self-assembly of colloidal nanoparticles into supracolloidal polymers

The Process-Directed Self-Assembly of Block Copolymer Particles

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrial applications.

Step-growth polymerization of supracolloidal chains from patchy micelles of diblock copolymers

HYPOTHESIS

The formation of supracolloidal chains from the patchy micelles of diblock copolymers bears a close resemblance to traditional step-growth polymerization of difunctional monomers in many aspects, including chain-length evolution, size distribution, and initial-concentration dependence. Thus, understanding the colloidal polymerization based on the step-growth mechanism can offer potential control over the formation of supracolloidal chains in terms of chain structure and reaction rate.

EXPERIMENTS

We analyzed the size evolution of supracolloidal chains of patchy micelles of PS-b-P4VP by investigating a large number of colloidal chains visualized in SEM images. We varied the initial concentration of patchy micelles to achieve a high degree of polymerization and a cyclic chain. To manipulate the polymerization rate, we also changed the ratio of water to DMF and adjusted the patch size by employing PS(25)-b-P4VP(7) and PS(145)-b-P4VP(40).

FINDINGS

We confirmed the step-growth mechanism for the formation supracolloidal chains from patchy micelles of PS-b-P4VP. Based on this mechanism, we were able to achieve a high degree of polymerization early in the reaction by increasing the initial concentration and form cyclic chains by diluting the solution. We also accelerated colloidal polymerization by increasing the ratio of water to DMF in the solution and patch size by using PS-b-P4VP with a larger molecular weight.

Chain Assembly Kinetics from Magnetic Colloidal Spheres

Magnetic colloidal chains are a microrobotic system with promising applications due to their versatility, biocompatibility, and ease of manipulation under magnetic fields. Their synthesis involves kinetic pathways that control chain quality, length, and flexibility, a process performed by first aligning superparamagnetic particles under a one-dimensional magnetic field and then chemically linking them using a four-armed maleimide-functionalized poly(ethylene glycol). Here, we systematically vary the concentration of the poly(ethylene glycol) linkers, the reaction temperature, and the magnetic field strength to study their impact on the physical properties of synthesized chains, including the chain length distribution, reaction temperature, and bending modulus. We find that this chain fabrication process resembles step-growth polymerization and can be accurately described by the Flory-Schulz model. Under optimized experimental conditions, we have successfully synthesized long flexible colloidal chains with a bending modulus, which is 4 orders of magnitude smaller than previous studies. Such flexible and long chains can be folded entirely into concentric rings and helices with multiple turns, demonstrating the potential for investigating the actuation, assembly, and folding behaviors of these colloidal polymer analogues.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

In Situ Supramolecular Polymerization of Micellar Nanoobjects Induced by Polymerization

Supramolecular polymerization offers a fascinating opportunity to develop dynamic soft materials by associating monomeric building blocks via noncovalent interactions. We report that polymerization can spontaneously drive the supramolecular polymerization of nanoscale micellar objects. We constructed the patchy micelles via two-step polymerization-induced self-assembly. A horizontal association between the patches results in a 1D supermicellar chain in situ by minimizing the enthalpic penalty of exposing the growing chains to solvent. Its length grows with increasing degree of polymerization, confirming that the supramolecular polymerization was triggered and controlled by polymerization. Our results highlight the observation that (1) the entire self-assembly process of forming, compartmentalizing, and associating the micelles can be driven by polymerization in a concerted manner and that (2) polymerization-induced self-assembly now can use compartmentalized nanoobjects as substrates beyond block copolymer chains. Polymerization-induced supramolecular polymerization could be useful for the autonomous preparation of hierarchical nanostructures.

DPD simulations on morphologies and structures of blank PLGA-b-PEG-b-PLGA polymeric micelles and docetaxel-loaded PLGA-b-PEG-b-PLGA polymeric micelles

Dissipative particle dynamics (DPD) simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PLGA-b-PEG-b-PLGA) polymeric micelles and the docetaxel (Dtx)-loaded PLGA-b-PEG-b-PLGA polymeric micelles. We focused on the influences of PLGA-b-PEG-b-PLGA copolymer concentration, composition, Dtx drug content and the shear rate on morphologies and structures of the micelles. Our simulations show that the PLGA-b-PEG-b-PLGA copolymers in the aqueous solutions could aggregate and form blank micelles while Dtx drug and PLGA-b-PEG-b-PLGA could aggregate and form drug-loaded micelles. Under different PLGA-b-PEG-b-PLGA concentrations and drug content, the blank and drug-loaded micelles are observed as spherical, onionlike, columnar, and lamellar structures. The onionlike structures are comprised of the PEG hydrophilic core, the PLGA hydrophobic middle layer, and the PEG hydrophilic shell. As the structure of micelles varies from a spherical core–shell structure to a core–middle layer–shell onionlike structure, the distribution of the Dtx drugs diffuses from the core to the PLGA middle layer of the aggregate. In addition, the drug release process of the Dtx-loaded micelles under shear flow is also simulated. And the results show that the spherical micelles turn into a columnar structure under a shear rate from 0.2 to 3.4. When the shear rate increases to 3.5, the Dtx drugs released gradually increase until all are released with time evolution. These findings illustrate the dependence of the structural morphologies on the detailed molecular parameters of PLGA-b-PEG-b-PLGA and Dtx.

Dissipative particle dynamics simulation was used to study the morphologies and structures of blank (no drug) poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) polymeric micelles and the docetaxel-loaded polymeric micelles.

Advances in self-assembling of pH-sensitive polymers: A mini review on dissipative particle dynamics

Dissipative Particle Dynamics (DPD) is a mesoscopic simulation program used to simulate the behavior of complex fluids. This work systematically reviews the use of DPD to simulate the self-assembly process of pH-sensitive drug-loaded nanoparticles. pH-sensitive drug-loaded nanoparticles have the characteristics of good targeting and slow release in the body, which is an ideal method for treating cancer and other diseases. As an excellent simulation method, DPD can help people explore the loading and release laws of drugs with complex molecular structures and has extensive applications in other medical fields. This article reviews the self-assembly process of pH-sensitive polymers under neutral conditions and explores the factors that affect the self-assembly structure. It points out that different hydrophilic-hydrophobic ratios, molecular structures, and component distributions will affect the morphology, stability and drug carrying capacity of micelles. This article also introduces the release mechanism of the drug in detail and introduces the factors that affect the release. This article can help relevant researchers to follow the latest advances in the DPD simulation and pH-sensitive drug nano-carrier and insight people to investigate the further application of DPD simulation in biomedical science.

Porous self-supporting film of semi-flexible supracolloidal chains of diblock copolymer micelles

Patchy micelles of diblock copolymers can be polymerized into a linear supracolloidal chain. We measure the persistence and contour lengths of supracolloidal chains coated on a solid substrate to evaluate their flexibility. Based on the analysis, the chain is semi-flexible, and the conformation is suitably explained by the worm-like chain model. In addition, utilizing a spin-coating technique with the semi-flexible nature of the chains, we produce a self-supporting film of supracolloidal chains having nanoscale pores essentially from colloidal constituents that tend to form dense packing if there is no prior organization of them into a semi-flexible chain.

Entropic factors and structural motifs of triblock-terpolymer-based patchy nanoparticles

A prevalent strategy for synthesizing patchy nanoparticles is through the self-assembly of triblock terpolymers in selective solvents. Since the thermodynamic and kinetic factors that govern the morphology of the particles produced in this way are not fully understood, this strategy usually demands trial-and-error methodologies. We investigate the fundamental mechanisms that produce multiple types of patchy nanoparticles and identify the conditions needed to program the shapes of the nanoparticles and predict their assembly. Our findings demonstrate that particle morphology can be described in a generic fashion by accounting for the energetic balance between the conformation of the polymer coils and the formation of interfaces. This allows us to forecast the synthesis of patchy nanoparticles for systems with different triblock terpolymers and solvents. Since the shape, size, and distribution of the patches influence the growth of larger microscale structures, we construct a library of elemental nanoparticles, or building blocks, suitable for the study of hierarchically larger self-assembled aggregates and useful for streamlining the design of functional materials. Our results provide new insights into the intriguing mechanisms that determine the morphology of soft nanoscale objects, whether synthetic or naturally occurring.

Open and Closed Layered Nanostructures with Sub-10 nm Periodicity Self-Assembled from Hydrophilic [60]Fullerene-Based Giant Surfactants

Giant surfactants have been identified as good candidates to produce sub-10 nm elaborate nanostructures, which could potentially realize complex functions in nanofabrication fields. Our theoretical simulation demonstrates the formation of open layered (pupa-like micelles) and closed layered (onion-like micelles) nanostructures, self-assembled from giant surfactants with comparably sized hydrophilic heads tethered by oligomers in solution. Directed by these simulation results, we synthesized giant surfactants consisting of hydrophilic [60]fullerene heads and oligostyrene (OS₇) tails and produced the predicted nanostructures with periods of 9.5, 8.3, and 7.5 nm, experimentally. Adjusting the polarity of the solvent and corresponding concentration changed the nanostructures from onion-like micelles with closed layers to pupa-like micelles with open layers. The different morphologies and periods were caused by solvent inclusion and the overlap of OS chains. The above layered nanostructures remained stable after annealing at 120 °C. This work provides insights that computer simulation can play an important role in assisting the design and construction of complicated nanostructures in giant surfactant systems.

Reversible Polymerization-like Kinetics for Programmable Self-Assembly of DNA-Encoded Nanoparticles with Limited Valence

A similarity between the polymerization reaction of molecules and the self-assembly of nanoparticles provides a unique way to reliably predict structural characteristics of nanoparticle ensembles. However, the quantitative elucidation of programmable self-assembly kinetics of DNA-encoded nanoparticles is still challenging due to the existence of hybridization and dehybridization of DNA strands. Herein, a joint theoretical-computational method is developed to explicate the mechanism and kinetics of programmable self-assembly of limited-valence nanoparticles with surface encoding of complementary DNA strands. It is revealed that the DNA-encoded nanoparticles are programmed to form a diverse range of self-assembled superstructures with complex architecture, such as linear chains, sols, and gels of nanoparticles. It is theoretically demonstrated that the programmable self-assembly of DNA-encoded nanoparticles with limited valence generally obeys the kinetics and statistics of reversible step-growth polymerization originally proposed in polymer science. Furthermore, the theoretical-computational method is applied to capture the programmable self-assembly behavior of bivalent DNA-protein conjugates. The obtained results not only provide fundamental insights into the programmable self-assembly of DNA-encoded nanoparticles but also offer design rules for the DNA-programmed superstructures with elaborate architecture.

Assembly of silica rods into tunable branched living nanostructures mediated by coalescence of catalyst droplets

Branched nanostructures with tunable arm numbers were prepared through the assembly of silica rods mediated by coalescence of catalyst droplets on the end of the rods. The formed primary branched colloids retain living characteristics similar to the original ones, that is, they can further assemble into multilevel and hierarchical branched structures.

Sequence-Regulated Supracolloidal Copolymers via Copolymerization-Like Coassembly of Binary Mixtures of Patchy Nanoparticles

Synthetic copolymers of molecular systems serve as an inspiration for creation of one-dimensional copolymer-like superstructures via coassembly of anisometric nanoparticles. In contrast to the covalent and molecular copolymers, the details of formation mechanisms of copolymer-like superstructures, as well as the factors determining their length and the sequences of arranged nanoparticles, are still poorly understood. Herein, we propose a joint theoretical-computational framework to probe into the coassembly mechanism and kinetics of binary mixtures of patchy nanoparticles. By applying the coarse-grained molecular dynamics simulations, it is demonstrated that the coassembly of patchy nanoparticles markedly resembles many aspects of molecular step-growth copolymerization, and the sequences of nanoparticles inside the copolymer-like superstructures can be finely regulated by the relative activity and the initial ingredient of patchy nanoparticles as well as the coassembly strategy. A quantitatively copolymerization-like model is developed to account for the coassembly kinetics of patchy nanoparticles and the sequence distribution of arranged nanoparticles, all governed by the elaborate design of lower-level building units. The jointly theoretical and simulated studies offer mechanistic insights into the copolymerization-like kinetics and the sequence prediction for the coassembly of binary mixtures of patchy nanoparticles, paving the way toward the rational design of copolymer-like superstructures with various sequences and functionalities.

Supramolecular step-growth polymerization kinetics of pre-assembled triblock copolymer micelles

Pre-assembled copolymer micelles were found to “polymerize” into hierarchical nanowires, induced by the structural defects on the micelle surfaces.