Self-Assembly of Polymer Tethered Molecular Nanoparticle Shape Amphiphiles in Selective Solvents

Co-assembly of Amphiphilic Triblock Copolymers with Nanodrugs and Drug Release Kinetics in Solution

Polymeric vesicles present great potential in disease treatment as they can be featured as a structurally stable and easily functionalized drug carrier that can simultaneously encapsulate multiple drugs and release them on-demand. Based on the dissipative particle dynamics (DPD) simulation, the drug-loaded vesicles were designed by the co-assembly process of linear amphiphilic triblock copolymers and hydrophobic nanodrugs in solvents, and most importantly, the drug release behavior of drug-loaded vesicles were intensively investigated. The drug-loaded aggregates, such as vesicles, spherical micelles, and disk-like micelles, were observed by varying the size and concentration of nanodrugs and the length of the hydrophobic block. The distribution of nanodrugs in the vesicles was intensively analyzed. As the size of the nanodrugs increases, the localization of nanodrugs change from being unable to fully wrap in the vesicle wall to the uniform distribution and finally to the aggregation in the vesicles at the fixed concentration of nanodrugs. The membrane thickness of the drug-loaded polymeric vesicle can be increased, and the nanodrugs localized closer to the center of the vesicle by increasing the length of the hydrophobic block. The nanodrugs will be released from vesicles by varying the interactions between the nanodrug and the solvent or the hydrophobic block and the solvent, respectively. We found that the release kinetics conforms to the first-order kinetic model, which can be used to fit the cumulative release rate of nanodrugs over time. The results showed that increasing the size of nanodrugs, the length of hydrophobic block, and the interaction parameters between the hydrophobic block and the solvent will slow down the release rate of the nanodrug and change the drug release process from monophasic to biphasic release model.

Self-assembly of rigid amphiphilic graft cyclic-brush copolymers to nanochannels using dissipative particle dynamics simulation

The synthesis of specific artificial nanochannels remains a formidable challenge in the field of nanomaterials and synthetic chemistry. In particular, the preparation of artificial nanochannels using amphiphilic graft cyclic-brush copolymers (AGCCs) as monomers has garnered substantial attention. Nevertheless, because of the constrained time and length scales inherent in traditional molecular dynamics simulations, a comprehensive theoretical understanding of the morphological regulation mechanism governing the self-assembly of AGCCs into nanochannels remains elusive. In this study, we employed the dissipative particle dynamics (DPD) method to explore the self-assembly mechanism considering factors such as the DPD interaction parameters, concentrations, and sizes of AGCCs. By calculating the phase diagrams, we predicted the emergence of four distinct nanochannel types: short independent, long independent, parallel, and disordered channels. Importantly, the formation of these nanochannels is highly contingent on specific environmental conditions. Furthermore, we extensively discussed self-assembly processes that lead to different types of nanochannels. The self-assembly of AGCCs is revealed as a multistep process primarily influenced by the interaction parameters. However, while the monomer size and concentration do not introduce novel self-assembly morphologies, they do influence the final aggregation state. The elucidation of the self-assembly mechanism presented in this study deepens our understanding of AGCC nanochannel formation. Consequently, this is a valuable guide for the preparation of copolymer materials with specific functionalities, offering insights into targeted copolymer material design.

Hybrid Polymer-Surfactant Wormlike Micelles for Concurrent Use for Oil Recovery and Drag Reduction

We report on the effect of a hydrocarbon (n-dodecane) on the rheological properties and shapes of the hybrid wormlike micelles (WLMs) of a surfactant potassium oleate with an embedded polymer poly(4-vinylpyridine). With and without hydrocarbon solutions, the hybrid micelles exhibit the same values of viscosity at shear rates typical for hydraulic fracturing (HF) tests, as solutions of polymer-free WLMs. Therefore, similar to WLMs of surfactants, they could be applied as thickeners in HF fluids without breakers. At the same time, in the presence of n-dodecane, the hybrid micelles have much higher drag-reducing efficiency compared to microemulsions formed in polymer-free systems since they form "beads-on-string" structures according to results obtained using cryo-transmission electron microscopy (cryo-TEM), dynamic-light scattering (DLS), and small-angle X-ray scattering (SAXS). Consequently, they could also act as drag-reducing agents in the pipeline transport of recovered oil. Such a unique multi-functional additive to a fracturing fluid, which permits its concurrent use in oil production and oil transportation, has not been proposed before.

Solution Self-Assembly of Amphiphilic Tadpole-like Giant Molecules Constructed by Monotethering Diblock Copolymer Chain onto a Nanoparticle

The self-assembly behavior of a tadpole-like giant molecule (TGM) constructed from a hydrophobic nanoparticle (NP) monotethered by a single amphiphilic AB diblock copolymer chain was investigated by combining self-consistent field theory and density functional theory in solution. The effects of the hydrophobicities of the B blocks and NPs (i.e., solvent properties) on the self-assembly behavior of the TGMs were investigated in the cases of weak and strong intramolecular interactions (i.e., incompatibilities) between the components of giant molecules, respectively. Besides conventional ordered aggregates (such as spheres, rings, and vesicles) with hydrophobic B-cores covered by NP shells, several aggregates with novel hierarchical structures, including vesicles with NP-inserted hydrophobic walls, bead-string-like micelles, and long cylindrical micelles with NP bumps, were obtained by tuning the solvent properties under different intramolecular interactions. Noteworthy that the simulation results show that the arrangement of the NP bumps on the long cylindrical micelles may have a certain degree of helicity, which means that these micelles may have some unique electromagnetic features such as circular dichroism. Phase diagrams as a function of the hydrophobicities of the B blocks and NPs were constructed to show the formation conditions of these novel structures. These findings can not only offer new insights into understanding of the self-assembly behavior of the TGM in solution but also provide useful guidance for simple and efficient regulation of the morphology, as well as the NP distribution and arrangement of the ordered aggregates in experiments.

Controlling the two components modified on nanoparticles to construct nanomaterials

Nanoparticle self-assembly technology has made great progress in the past 30 years. Many kinds of self-assembly strategies of modifiable nanoparticles have been developed and used to construct nano-aggregates by designing the shape, size and type of nanoparticles and controlling the components modified on nanoparticles. These strategies are widely used in many fields, such as medical diagnosis, biological detection, drug delivery, materials synthesis and sensors. The modified components can be DNA chains, polymer chains, proteins, and even organic molecules based on different molecular conformations and chemical properties. In recent years, the self-assembly of two-component modified nanoparticles has gradually attracted more attention. Nanoparticles modified with two components of different DNA strands can self-assemble to produce a variety of nano arrangement structures, such as BCC, FCC and other cubic crystals, which can be used in crystal materials. Two-component modification of hydrophilic and hydrophobic polymers can produce vesicular aggregates, which can be used for drug delivery. In this review, we summarize the latest experimental progress and theoretical simulation of self-assembly of two-component modified nanoparticles including different DNA chains, different polymer chains, DNA and polymer chains, proteins and polymer chains, and different organic molecules. Their self-assembly characteristics and application prospects were discussed. Compared with single-component modified nanoparticles, two-component nanoparticles have different tethered molecules or molecular chains, which can be multifunctional by regulating different modified components and types of nanoparticles and ultimately expand the scope of applications.

Selective membrane wrapping on differently sized nanoparticles regulated by clathrin assembly: A computational model

Nanoparticles (NPs) enter cells via multiple pathways, all of which are NP size dependent. Previous studies indicated that the clathrin-mediated endocytosis has different selectivity for the NP size, but the regulatory mechanism remains unclear and difficult to study at the molecular scale in vivo. By means of computer simulation, here we design membrane wrapping on differently sized NPs with mimic clathrin assembly at the opposite membrane side. With relatively large NPs readily wrapped by a pure membrane as manifested, clathrin modulates the process and tunes the size selectivity. Although finite curvature can be generated by cage-like clathrin assembly to facilitate membrane wrapping on relatively small NPs, the clathrin assemblage has a certain range of size, which is mismatched with larger NPs. Besides, the local membrane patch is rigidified by clathrin to increase the barrier of membrane wrapping on larger NPs. Competition of these items determines whether membrane wrapping on NPs is promoted or suppressed, and can be tuned by the NP-membrane adhesion strength, clathrin concentration, and inter-NP distance. Our results highlight the significance of complex environment in altering the nature of NP interaction with cell membranes, and are expected to help design NPs for biomedical applications requiring precise control of NP uptake or cell membrane attachment.

Computer simulations of self-assembly of anisotropic colloids

Computer simulations have played a significant role in understanding the physics of colloidal self-assembly, interpreting experimental observations, and predicting novel mesoscopic and crystalline structures. Recent advances in computer simulations of colloidal self-assembly driven by anisotropic or orientation-dependent inter-particle interactions are highlighted in this review. These interactions are broadly classified into two classes: entropic and enthalpic interactions. They mainly arise due to shape anisotropy, surface heterogeneity, compositional heterogeneity, external field, interfaces, and confinements. Key challenges and opportunities in the field are discussed.

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.

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

This review article is addressed to a broad community of polymer scientists. We outline and analyse the fundamentals of the dissipative particle dynamics (DPD) simulation method from the point of view of polymer physics and review the articles on polymer systems published in approximately the last two decades, focusing on their impact on macromolecular science. Special attention is devoted to polymer and polyelectrolyte self- and co-assembly and self-organisation and to the problems connected with the implementation of explicit electrostatics in DPD numerical machinery. Critical analysis of the results of a number of successful DPD studies of complex polymer systems published recently documents the importance and suitability of this coarse-grained method for studying polymer systems.

An Efficient Random Number Generation Method for Molecular Simulation

We propose a new random number generation method, which is the fastest and the simplest of its kind, for use with molecular simulation. We also discuss the possibility of using this method with various other numerical calculations. To demonstrate the significant increases in calculation speeds that can be gained by using our method, we present a comparison with prior methods for dissipative particle dynamics (DPD) simulations. The DPD method uses random numbers to reproduce thermal fluctuations of molecules. As such, an efficient method to generate random numbers in parallel computing environments has been widely sought after. Several random number generation methods have been developed that use encryption. In this study, we establish for the first time that random numbers with desirable properties exist in the particle coordinates used in DPD calculations. We propose a method for generating random numbers without encryption that utilizes this source of randomness. This is an innovative method with minimal computational cost, since it is not dependent on a complicated random number generation algorithm or an encryption process. Furthermore, our method may lead to faster random number generation for many other physical and chemical simulations.

Charge-Driven Self-Assembly of Polyelectrolyte-Grafted Nanoparticles in Solutions

Nanoparticle self-assembly in solution has gained immense interest due to the enhanced optical, chemical, magnetic, and electrical properties which manifest at the macroscale. Material properties in bulk are a direct consequence of the morphology of these nanoparticles in solutions. Precise control on the orientation, spatial arrangement, shape, size, composition, and control over the interactions of individual nanoparticles play a key role in enhancing their properties. While previous studies have used asymmetry in the nanoparticle and/or the use of linker grafts, nanoparticles grafted with polyelectrolyte grafts provide us a wide parameter space to control and tune their self-assembly in solutions. In this study, we have performed coarse-grained molecular dynamics simulations to understand the charge-driven self-assembly of spherical nanoparticles grafted with polyelectrolyte chains. Nanoparticles grafted with either positively or negatively charged polyelectrolyte chains self-assemble to different structures driven by both excluded volume and electrostatic interactions. Our study shows that by tuning the graft density, the chain length, and the charge density of the grafts, we could build and control a variety of self-assembled structures ranging from rings, dimers, strings, coil-like aggregates, and disordered-to-ordered aggregates.

The influence of random number generation in dissipative particle dynamics simulations using a cryptographic hash function

The tiny encryption algorithm (TEA) is widely used when performing dissipative particle dynamics (DPD) calculations in parallel, usually on distributed memory systems. In this research, we reduced the computational cost of the TEA hash function and investigated the influence of the quality of the random numbers generated on the results of DPD calculations. It has already been established that the randomness, or quality, of the random numbers depend on the number of processes from internal functions such as SHIFT, XOR and ADD, which are commonly referred to as “rounds”. Surprisingly, if we choose seed numbers from high entropy sources, with a minimum number of rounds, the quality of the random numbers generated is sufficient to successfully perform accurate DPD simulations. Although it is well known that using a minimal number of rounds is insufficient for generating high-quality random numbers, the combination of selecting good seed numbers and the robustness of DPD simulations means that we can reduce the random number generation cost without reducing the accuracy of the simulation results.

Self-assembly of polymer-tethered nanoparticles with uniform and Janus surfaces in nanotubes

In this study, a coarse-grained molecular simulation was performed to investigate the morphologies and phase diagrams of self-assembled polymer-tethered nanoparticles (NPs) confined in nanotubes (NTs). Unlike ordinary NPs, polymer-tethered NPs have two distinct characteristic lengths, which are key factors that determine their self-assembly. Herein, two distinct types of NT walls and three types of polymer-tethered NPs were considered: hydrophilic and hydrophobic walls, and hydrophilic, hydrophobic, and Janus surfaces. First, the qualitative phase diagrams of the axial pressure, Pz, versus the ratio of the NT radius to the NP radius, L, were derived. The results revealed that diverse self-assembled morphologies, which are not formed in non-tethered NPs, were observed in the polymer-tethered NPs. For example, three types of ordered structures with different structural characteristic lengths, depending on Pz, were obtained. In addition, the effect of the chemical nature of the polymer-tethered NP surface on the self-assembled morphology confined in NTs was investigated. Clusters of water molecules were formed, particularly in the hydrophobic polymer-tethered NPs, and these clusters caused the structural distortion of the NP. Moreover, in the polymer-tethered NPs with the Janus amphiphilic surface, the hydrophobic and hydrophilic polymer tethered NPs assembled in the axial direction to form an ordered structure, and a double-helix structure was formed at L = 3.0 in the hydrophobic NT. The results of these simulations indicate that the self-assembly behaviours of polymer-tethered NPs can be qualitatively predicted based on the chemical nature of the NT walls and the surface design of the polymer-tethered NP.

Self-Assembly of Single-Polymer-Tethered Nanoparticle Amphiphiles upon Varying Tail Length

We systematically investigated the roles of tail length on the self-assembly of shape amphiphiles composed of a hydrophobic polymer chain (tail) and a hydrophilic nanoparticle in selective solvent using Brownian dynamics simulations. The shape amphiphiles exhibited a variety of self-assembled aggregate morphologies which can be tuned by changing tail length (n) in combination with amphiphile concentration (φ) and system temperature (T*). Specifically, at high φ with T*=1.4, the morphology varied following the sequence "spheres → cylinders → vesicles" upon increasing n, agreeing well with experimental observations. At low φ with T*=1.4 or at high φ with T*=1.2, the morphology sequence becomes "spheres or spheres and cylinders mixture → cylinders → vesicles → spheres" upon increasing n, which has not been found experimentally. Two morphological phase diagrams depending on n and φ were constructed for T*=1.4 and 1.2, respectively. The rich phase behaviors on varying tail length could provide the feasible routes to fabricate target aggregate morphologies in various applications, especially for the vesicles with tunable thickness of membranes that are crucial in drug and gene delivery.

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.

Dissipative Particle Dynamics Simulations of a Protein-Directed Self-Assembly of Nanoparticles

Design and fabrication of multifunctional porous structures play key roles in the development of high-performance energy storage devices. Our experiments demonstrated that nanostructured porous components, such as electrodes and interlayers, generated from the protein-directed self-assembly of nanoparticles can significantly improve the battery performances. The protein-directed assembly of nanoparticles in solution is a complex process involving the complicated interactions among proteins, particles, and solvent molecules. In this paper, we investigate the effects of coating proteins and specific solvent environments on the assembled porous structures. Comprehensive dissipative particle dynamics (DPD) simulations have been implemented to explore the molecular interactions and uncover the fundamental mechanisms in a gelatin-directed self-assembly of carbon black particles under different solvent conditions. Our simulations show that compact triple-strand "rod-like" structures are formed in water while loose curved "sheet-like" structures are formed in an acetic acid/water mixture. The structural difference is mainly due to the redistribution of the charges on the gelatin side chains under specific acid-solvent conditions. The strong and flexible "sheet-like" structures lead to a homogenous porous structure with high porosity and with large functionalized surfaces. Our simulations results can reasonably explain the experimental observations; this work demonstrates the great potential of DPD as a powerful tool in guiding future experimental design and optimization.

Non-dependence of dodecamer structures on alkyl chain length in Platonic micelles

When the micellar aggregation number (Nagg) is sufficiently small (Nagg < 30), the micelle shows an abnormal aggregation behavior: monodispersity without any distribution in Nagg, whose values coincide with the vertex number of a regular polyhedral structure, i.e., they are termed Platonic solids. Micelles with these characteristics are named "Platonic micelles". In this study, we investigated the aggregation behavior of calixarene-based micelles bearing primary amines-the first example of Platonic micelles-with increasing alkyl chain length by small-angle X-ray scattering, asymmetrical flow field flow fractionation coupled with multiangle light scattering, and analytical ultracentrifugation measurements. Morphological transition of the micelles from spherical to cylindrical was observed when the alkyl chain length was increased in this calixarene-based micellar system, which is similar to the case of conventional systems and is acceptable in terms of the packing parameter principle. However, although the micellar Nagg normally increases with an increase in the alkyl chain length, the structure of calixarene-based Platonic micelles bearing butyl (C4), heptyl (C5), and hexyl (C6) chains remains at 12-mer. This is presumably due to the relationship between the thermodynamic stability of the Platonic micelles and the coverage ratio defined by the Tammes problem.

Controllable Self-Assembly of Amphiphilic Tadpole-Shaped Polymer Single-Chain Nanoparticles Prepared through Intrachain Photo-cross-linking

We report the use of intramolecular cross-linking chemistry as a tool to control the self-assembly of amphiphilic diblock copolymers (di-BCPs). Two amphiphilic di-BCPs of poly( N, N'-dimethylacrylamide)- block-polystyrene (PDMA- b-PS) with photo-cross-linkable cinnamoyl groups in either hydrophobic or hydrophilic blocks were prepared using reversible addition-fragmentation chain transfer polymerization. Intramolecular photo-cross-linking of cinnamoyl groups led to the formation of tadpole-shaped polymer single-chain nanoparticles (SCNPs) consisting of a self-collapsed block as the "head" and an un-cross-linked block as the "tail". When intramolecular photo-cross-linking was carried out in hydrophobic PS blocks, a clear morphological transition from branched cylindrical micelles (for the linear di-BCP) to completely spherical micelles at a dimerization degree of ∼63% was observed. A pattern of morphological transitions from cylindrical micelles to spherical micelles is observed through stepwise downsizing the length of cylindrical micelles when increasing the self-collapse degree of PS blocks, whereas, in case of photo-cross-linking carried out in hydrophilic PDMA blocks, the size of micelles showed a dramatic increase due to the shift of hydrophobic-to-hydrophilic balance. When the cross-linking degree of PDMA blocks reached >60%, tadpole-shaped SCNPs assembled into nonconventional aggregates with a nonsmooth surface. Our results illustrate the impact of chain topologies on the self-assembly outcomes of amphiphilic di-BCPs, which likely opens a door to control the micellar morphologies from just one parent linear di-BCP, rather than resynthesizing BPCs with different volume fractions of the two blocks.

Extracting lipid vesicles from plasma membranes via self-assembly of clathrin-inspired scaffolding nanoparticles

Single-cell analysis is a new and rapidly expanding field, the goal of which is obtaining fresh information from individual cells to understand the regulatory mechanisms of cell development and diseases. Conventional approaches generally rely on the cell lysis which, however, is destructive to cells and against multiple sampling from the living cell. Here, we propose and design a scaffolding nanoparticle (NP) system that enables us to sample cytoplasmic contents without rupturing the cellular membrane, by mimicking the unusual features of clathrin. Our simulation results reveal the design principles, following which scaffolding NPs can extract lipid vesicles from plasma membranes, with both the pathway and the mechanism resembling the clathrin-mediated endocytosis, i.e. multiple NPs deposit at the membrane, assembling into cage-like structures to deform the membrane into a vesicle shape. As important design parameters, the interaction between different NPs should be properly stronger than that between each NP and the membrane to ensure the cage formation, and optimal NP concentration and the membrane surface tension are also requisite for extracting lipid vesicles. Our results provide useful guidelines for design of bio-inspired scaffolding NPs as an intelligent machine for practical use in but not limited to the single-cell analysis.

Computer simulation study on the self-assembly of tethered nanoparticles with tunable shapes

We built a tethered nanoparticle (TNP) model that is composed of a nanoparticle with a hydrophobic tethered polymer chain. The shape of the nanoparticle can be tuned from a pure rigid cube to a soft sphere, mimicking the increase of grafting density on the nanocube surfaces. With this model, we study the self-assembly of TNPs in dilute solution using a dissipative particle dynamics simulation technique, and especially focus on the influence of particle shape, tethered chain length, and grafting density on the self-assembly structures. Some intriguing aggregates such as spherical micelles, pearl-necklace-like structures, cubic columnar structures, handshake structures, core–shell–corona micelles, and four-patch micelles have been observed when varying the interactions between cubes and solvents and the lengths of tethered chain. Modifying the nanocube surface with some hydrophilic grafted chains helps the TNPs form small micelles. Increased steric repulsion due to chain overlapping at larger grafting densities results in shape transformation of the nanoparticle from a rigid cube to a soft sphere. In these cases, the self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

The self-assembled structures are characterized by the packing of nanoparticles on the micelle surface, and the typical packing mode turns from rectangular (typical for cubes) to hexagonal (typical for spheres).

Dynamic and programmable morphology and size evolution via a living hierarchical self-assembly strategy

Recent advances in the preparation of shape-shifting and size-growing nanostructures are hot topics in development of nanoscience, because many intelligent functions are always relied on their shape and dimension. Here we report a tunable manipulation of sequential self-assembled transformation in situ via a hierarchical assembly strategy based on a living thiol-disulfide exchange reaction. By tailoring the external stimuli, the reactive points can be generated at the ends of initially unimolecular micelles, which subsequently drive the pre-assemblies to periodically proceed into the hierarchically micellar connection, axial growth, bending, and cyclization processes from nanoscopic assemblies to macroscopic particles. Of particular interest would be systems that acquired the shape control and size adjustment of self-assemblies after termination or reactivation of disulfide reshuffling reaction by regulating external stimuli whenever needed. Such a hierarchical strategy for self-assembled evolution is universally applicable not only for other disulfide-linked dendritic polymers but also for exploitation of biological applications.

Effect of chain microstructure on self-assembly and emulsification of amphiphilic poly(acrylic acid)-polystyrene copolymers

In this study, a series of random copolymer poly(acrylic acid-co-styrene) (P(AA-co-St)) and block copolymer poly(acrylic acid)-b-polystyrene (PAA-b-PSt) with similar chemical composition but different chain microstructure were synthesized. The self-assembly behavior of random and block copolymers in selective solvent was investigated, and the structural evaluation of random and block copolymers micelles was carried out by transmission electron microscopy (TEM), dynamic light scattering (DLS) measurement, and X-ray photoelectron spectroscopy (XPS). Moreover, together with experimental characterization, the theoretical method dissipative particle dynamics (DPD) approach was applied to investigate the morphological structures of micelles composed from random and block copolymers. Results revealed that the structure of polymeric micelles is significantly affected by the distribution sequence of hydrophilic and hydrophobic monomers in copolymer chains. Furthermore, polymeric micelles based on P(AA-co-St) and PAA-b-PSt with about 50 mol% hydrophilic composition were chosen as the model to investigate the influence of micellar structure on emulsifying performance. For PAA-b-PSt micelles (B48), stable water-in-oil (w/o) emulsions could only obtained when the pH values were lower than 5. As a comparison, the P(AA-co-St) micelles (R49) had an excellent emulsification performance at 4-10 pH, and the pH-induced phase inversion derived from obtained emulsions observed at pH higher than 6. Preliminary results confirm that the micellar structure controlled by chain microstructure plays an important role in the interface behavior of polymer micelles. Compared with PAA-b-PSt micelles, P(AA-co-St) micelles have better interfacial performance and are more tailorable and controllable; thus they can be used as a model for further study of polymeric particulate emulsifiers. This paper provides new insight into the principles governing extremely high emulsifying efficiency of polymeric particulate emulsifiers and pH-responsive properties of the formed emulsions.

pH-Induced evolution of surface patterns in micelles assembled from dirhamnolipids: dissipative particle dynamics simulation

Dissipative particle dynamics (DPD) simulation is used to study the effect of pH on the morphological transition in micelles assembled from dirhamnolipids (diRLs), and analyze the pH-driven mechanism and influence factors of micellar surface patterns.

Nanoparticle encapsulation in vesicles formed by amphiphilic diblock copolymers

We investigated the co-assembly of nanoparticles P and amphiphilic diblock copolymers AB in selective solvents using a dissipative particle dynamics (DPD) method. By controlling the nanoparticle concentration and the interaction parameter between the hydrophobic blocks and the solvents, we found that the aggregation morphology can be changed from rod-like micelles to disk-like micelles and further to vesicles. The ratio of the hydrophobic/hydrophilic block and the nanoparticle concentration largely affects the structural characteristics of vesicles and the dispersion of nanoparticles. Copolymers with a longer hydrophobic block length are more likely to form vesicles with a smaller aqueous cavity size and vesicle size as well as a thicker wall. At the same time, the nanoparticles in the hydrophobic membrane tend to locate closer to the center of the vesicle and they become more compactly organized. A significant discovery has found that the larger the nanoparticle concentration, the smaller the aqueous cavity and the larger the vesicle size. We can also locate the nanoparticles at the center of spherical micelles or the hydrophobic membranes of vesicles by varying the nanoparticle concentration. This provides an effective and simple method to prepare size-controlled vesicles containing nanoparticles, project the localization of nanoparticles within the vesicles, and even tune the distance between the nanoparticles.

Hierarchical Colloidal Polymeric Structure from Surfactant-Like Amphiphiles in Selective Solvents

We investigated the self-assembly of surfactant-like amphiphiles consisting of a hydrophilic head and a hydrophobic tail using the dissipative particle dynamics method. By controlling the interaction parameter between the hydrophilic head and the solvent, the length of the hydrophobic tail, the size of the hydrophilic head, and the polymer concentration, we found seven self-assembled morphologies, including spherelike micelles, pomegranate-like micelles, hierarchical colloidal polymeric (HCP) structures, pomegranate-like columnar structures, branched hybrid structures, disklike micelles, and vesicles. Importantly, the HCP structure widely existing in this system has a regular two-component alternating structure and prospective application in soft-matter nanotechnology. The formation process and the structural properties of the HCP structure are intensively studied. The dimension of the HCP structure is largely controlled by the hydrophobic tail and the polymer concentration.

Extremely asymmetric phase diagram of homopolymer-monotethered nanoparticles: Competition between chain conformational entropy and particle steric interaction

The phase behaviors of homopolymer-monotethered nanoparticles (HMNs) in melt are investigated via a theoretical method combining self-consistent field theory for polymers and density functional theory for hard spheres. An extremely asymmetric phase diagram is observed: (i) microphases are only possible for the volume fraction of the tethered polymer f_A > 0.35; (ii) in addition to lamellar phase, the system can only self-assemble into various morphologies with a polymer-rich matrix, including gyroid phase, cylindrical phase, and spherical phase. In the frame of this theory, the critical point for HMNs' microphase separation is significantly lower than that of linear diblock copolymers. Furthermore, the characteristic length of microphase-separated structures of HMNs is much smaller than that of linear diblock copolymers with the same molecular weight. Our calculation results on morphologies and characteristic length agree well with recent simulations and experimental observations.

Computer simulation study on the self-assembly of unimodal and bimodal polymer-grafted nanoparticles in a polymer melt

By performing comprehensive molecular dynamics simulations, the self-assembly behavior of polymer-grafted nanoparticles in a polymer matrix is investigated in this study. Short grafted chains on bimodal grafted NP surfaces favor the dispersion of NPs in the polymer matrix.

Directed assembly of functionalized nanoparticles with amphiphilic diblock copolymers

We theoretically propose a simple approach to achieve soft nanoparticles with a self-patchiness nature, which are further directed to assemble into a rich variety of highly ordered superstructures.

Spontaneous onion shape vesicle formation and fusion of comb-like block copolymers studied by dissipative particle dynamics

The formation of an onion shape vesicle.

Dynamic evolution of a vesicle formed by comb-like block copolymer-tethered nanoparticles: a dissipative particle dynamics simulation study

Vesicles are well-sealed capsules that can store or transport substances.

Amphiphilic nanosheet self-assembly at the water/oil interface: computer simulations

The self-assembly of amphiphilic Janus triangular-plates at the water/oil interface is simulated for the first time.

Self-Assembly Behavior of Ultrahighly Charged Amphiphilic Polyelectrolyte on Solid Surfaces

The adsorption process of a geminized amphiphilic polyelectrolyte, comprising double elementary charges and double hydrophobic tails in each repeat unit (denoted as PAGC₈), was investigated and characterized by means of quartz crystal microbalance with dissipation (QCM-D), ellipsometry, and atomic force microscopy (AFM). By comparison, the self-assembly behaviors of a traditional polyelectrolyte without hydrophobic chains (denoted as PASC₁) and an amphiphilic polyelectrolyte with a single hydrophilic headgroup and hydrophobic tail in each repeat unit (denoted as PASC₈) at the solid/liquid interface were also investigated in parallel. A two-regime buildup was found in both amphiphilic systems of PASC₈ and PAGC₈, where the first regime was dependent on electrostatic interactions between polyelectrolytes and oppositely charged substrates, and the rearrangements of the preadsorbed chains and their aggregation behaviors on surface dominated the second regime. Furthermore, it was found that the adsorbed amount and conformation changed as a function of the charge density and bulk concentrations of the polyelectrolytes. The comparison of the adsorbed mass obtained from QCM-D and ellipsometry allowed calculating the coupling water content which reached high values and indicated a flexible aggregate conformation in the presence of PAGC₈, resulting in controlling the suspension stability even at an extremely low concentration. In order to provide an insight into the mechanism of the suspension stability of colloidal dispersions, we gave a further explanation with respect to the interactions between surfaces in the presence of the geminized polyelectrolyte.

Self-Assembly of Janus Oligomers into Onion-like Vesicles with Layer-by-Layer Water Discharging Capability: A Minimalist Model

A vesicle in a cell is an enclosed structure in which the interior fluid is encompassed by a lipid bilayer. Synthetic vesicles are known as the liposomes. Liposomes with a single phospholipid bilayer are called unilamellar liposomes; otherwise, they are called multilamellar liposomes or onion-like liposomes (vesicles). One prototype synthetic onion-like vesicle, namely, onion-like dendrimersomes, have been recently produced via the self-assembly of amphiphilic Janus dendrimers (Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 1162). Herein, we show computer simulation evidence of another type of onion-like vesicle, namely, onion-like oligomersomes, via the self-assembly of amphiphilic Janus oligomers in water. Specifically, we investigate the minimum-sized oligomers (or minimalist model) that can give rise to the onion-like oligomersomes as well as the composition-dependent phase diagrams. Insights into the formation condition and formation process of the onion-like oligomersomes are obtained. We demonstrate that the discharge of the in-vesicle water is through the remarkable "peeling-one-onion-layer-at-a-time" fashion, a feature that can be utilized for a clinical dosing regimen. The ability to control the formation of onion-like oligomersomes by design can be exploited for applications in drug and gene delivery.