Programmable Colloids with Analogous Hypercoordination Complex Architectures.

Colloidal molecule clusters (CMCs) are promising building blocks with molecule-like symmetry, offering exceptional synergistic properties for applications in plasmonics and catalysis. Traditional CMC fabrication has been limited to simple molecule-like structures utilizing isotropic particles. Here, we employ molecular dynamics simulation to investigate the co-assembly of anisotropic nanorods (NRs) and the stimulus-responsive polymer (SRP) via reversible adsorption. The results of the simulation show that it is possible to fabricate hypercoordination complex structures with high symmetry from the co-assembly of NRs and the SRP, even in analogy to the Th(BH4)4 structure. The coordination number of these CMCs can be precisely programmed by adjusting the shape and size of the ends of the NRs and the SRP cohesion energy. Furthermore, a finite-difference time-domain simulation indicates these hypercoordination structures exhibit significantly enhanced optical activity and plasmonic coupling effects. These findings introduce a new design approach for complex molecule-like structures utilizing anisotropic nanoparticles and may expand the applications of CMCs in photonics.

Chemically Specific Systematic Coarse-Grained Polymer Model with Both Consistently Structural and Dynamical Properties.

The coarse-grained (CG) model serves as a powerful tool for the simulation of polymer systems; its reliability depends on the accurate representation of both structural and dynamical properties. However, strong correlations between structural and dynamical properties on different scales and also a strong memory effect, enforced by chain connectivity between monomers in polymer systems, render developing a chemically specific systematic CG model a formidable task. In this study, we report a systematic CG approach that combines the iterative Boltzmann inversion (IBI) method and the generalized Langevin equation (GLE) dynamics. Structural properties are ensured by using conservative CG potentials derived from the IBI method. To retrieve the correct dynamical properties in the system, we demonstrate that using a combination of a Rouse-type delta function and a time-dependent short-time kernel in the GLE simulation is practically efficient. The former can be used to adjust the long-time diffusion dynamics, and the latter can be reconstructed from an iterative procedure according to the velocity autocorrelation function (ACF) from all-atomistic (AA) simulations. Taking the polystyrene as an example, we show that not only structural properties of radial distribution function, intramolecular bond, and angle distributions can be reproduced but also dynamical properties of mean-square displacement, velocity ACF, and force ACF resulted from our CG model have quantitative agreement with the reference AA model. In addition, reasonable agreements are observed in other collective properties between our GLE-CG model and the AA simulations as well.

Ultrasmall Single-Chain Nanoparticles Derived from Amphiphilic Alternating Copolymers.

The collapse or folding of an individual polymer chain into a nanoscale particle gives rise to single-chain nanoparticles (SCNPs), which share a soft nature with biological protein particles. The precise control of their properties, including morphology, internal structure, size, and deformability, are a long-standing and challenging pursuit. Herein, a new strategy based on amphiphilic alternating copolymers for producing SCNPs with ultrasmall size and uniform structure is presented. SCNPs are obtained by folding the designed alternating copolymer in N,N-dimethylformamide (DMF) and fixing it through a photocatalyzed cycloaddition reaction of anthracene units. Molecular dynamics simulation confirms the solvophilic outer corona and solvophobic inner core structure of SCNPs. Furthermore, by adjusting the length of PEG units, precise control over the mean size of SCNPs is achieved within the range of 2.8 to 3.9 nm. These findings highlight a new synthetic strategy that enables enhanced control over morphology and internal structure while achieving ultrasmall and uniform size for SCNPs.

Exploring the interplay of liquid crystal orientation and spherical elastic shell deformation in spatial confinement.

The application of liquid crystal technology typically relies on the precise control of molecular orientation at a surface or interface. This control can be achieved through a combination of morphological and chemical methods. Consequently, variations in constrained boundary flexibility can result in a diverse range of phase behaviors. In this study, we delve into the self-assembly of liquid crystals within elastic spatial confinement by using the Gay-Berne model with the aid of molecular dynamics simulations. Our findings reveal that a spherical elastic shell promotes a more regular and orderly alignment of liquid crystals compared to a hard shell. Moreover, during the cooling process, the hard-shell confined system undergoes an isotropic-smectic phase transition. In contrast, the phase behavior within the spherical elastic shell closely mirrors the isotropic-nematic-smectic phase transition observed in bulk systems. This indicates that the orientational arrangement of liquid crystals and the deformations induced by a flexible interface engage in a competitive interplay during the self-assembly process. Importantly, we found that phase behavior could be manipulated by altering the flexibility of the confined boundaries. This insight offers a fresh perspective for the design of innovative materials, particularly in the realm of liquid crystal/polymer composites.

Correction: A non-sacrificial method for the quantification of poly(ethylene glycol) grafting density on gold nanoparticles for applications in nanomedicine.

[This corrects the article DOI: 10.1039/C8SC02847H.].

Exploring mechanical properties and failure mechanisms of aramid and PBO crystals through molecular dynamics simulations.

Molecular dynamics simulations were used to analyze the mechanical properties and failure processes of poly(p-phenylene-terephthalamide) (PPTA), poly(p-phenylene-benzimidazole-terephthalamide) (PBIA), PBIA-PPTA (formed by 1:1 copolymerization of PPTA and PBIA), and poly(p-phenylene-benzobisoxazole) (PBO) crystals at different strain rates and temperatures. The failure stress and strain were found to be linear with the temperature and logarithmic strain rate. Moreover, based on the kinetic theory of fracture and the comprehensive simulation results, we formulated a model that describes the failure stress of the aforementioned crystals under varying strain rates and temperatures. Through the analysis of the failure process, we found that in PPTA, PBIA, and PBIA-PPTA crystals, the bond failure probability is correlated with the strain rate and temperature. The examination of bond lengths and angles unveiled that bonds with larger initial aligning angles are more susceptible to failure during the strain process. Intriguingly, the stretching process induced a conformational change in the PBO molecular chain, leading to a deviation from the linear relation in its stress-strain curve.

Horizontal to perpendicular transition of lamellar and cylinder phases in block copolymer films induced by interface segregation of single-chain nanoparticles during solvent evaporation.

How to fabricate perpendicularly oriented domains (PODs) of lamellar and cylinder phases in block copolymer thin films remains a major challenge. In this work, via a coarse-grained molecular dynamics simulation study, we report a solvent evaporation strategy starting from a mixed solution of A-b-B-type diblock copolymers (DBCs) and single-chain nanoparticles (SCNPs) with the same composition, which is capable of spontaneously generating PODs in drying DBC films induced by the interface segregation of SCNPs. The latter occurs at both the free surface and substrate and, consequently, neutralizes the interface selectivity of distinct blocks in DBCs, leading to spontaneous formation of PODs at both interfaces. The interface segregation of SCNPs is related to the weak solvophilicity of the internal cross-linker units. A mean-field theory calculation demonstrates that the increase in the chemical potential of SCNPs in the bulk region drives their interface segregation along with solvent evaporation. We believe that such a strategy can be useful in regulating the PODs of DBC films in practical applications.

Molecular Origin of the Reinforcement Effect and Its Strain-Rate Dependence in Polymer Nanocomposite Glass.

We investigate the molecular origin of mechanical reinforcement in a polymer nanocomposite (PNC) under a glass state via molecular dynamics simulations. The strength of the PNC system is found to be reinforced mainly via reduced plastic deformations of the nanoparticle neighborhood (NN). Such a reinforcement effect is found to decay with an increase in the strain rate. The Arrhenius-Eyring relation is used to analyze its origin. The amplitude of the reinforcement is found to be determined by the difference between the energy barrier (ΔE) for the activation of NN and the work (W) done by the applied stress to conquer that barrier. A larger strain rate is found to result in a larger W and, hence, a weaker reinforcement effect. Such a strain-rate dependence is verified in the experimental tensile tests of a poly(vinyl alcohol)/SiO2 composite system. These results not only provide a new understanding of the molecular origin of the reinforcement effect in the PNC system, but also pave the way for a better design of the PNC material properties.

Janus polymer-grafted nanoparticles mimicking membrane repair proteins for the prevention of lipid membrane rupture.

Plasma membrane rupture often leads to cell damage, especially when there is a lack of membrane repair proteins near the wounds due to genetic mutations in organisms. To efficiently promote the repair of the injured lipid membrane, nanomedicines may act as a promising alternative to membrane repair proteins, but the related research is still in its infancy. Herein, using dissipative particle dynamics simulations, we designed a class of Janus polymer-grafted nanoparticles (PGNPs) that can mimic the function of membrane repair proteins. The Janus PGNPs comprise both hydrophobic and hydrophilic polymer chains grafted on nanoparticles (NPs). We track the dynamic process of the adsorption of Janus PGNPs at the damaged site in the lipid membrane and systematically assess the driving forces for this process. Our results reveal that tuning the length of the grafted polymer chains and the surface polarity of the NPs can efficiently enhance the adsorption of Janus PGNPs at the site of the damaged membrane to reduce membrane stress. After repair, the adsorbed Janus PGNPs can be successfully detached from the membrane, leaving the membrane untouched. These results provide valuable guidelines for designing advanced nanomaterials for the repair of damaged lipid membranes.

Automatic Multiscale Method of Building up a Cross-linked Polymer Reaction System: Bridging SMILES to the Multiscale Molecular Dynamics Simulation.

An automatic method is introduced to generate the initial configuration and input file from SMILES for multiscale molecular dynamics (MD) simulation of cross-linked polymer reaction systems. Inputs are a modified version of SMILES of all the components and conditions of coarse-grained (CG) and all-atom (AA) simulations. The overall process comprises the following steps: (1) Modified SMILES inputs of all the components are converted to 3-dimensional coordinates of molecular structures. (2) Molecular structures are mapped to the coarse-grained scale, followed by a CG reaction simulation. (3) CG beads are backmapped to the atomic scale after the CG reaction. (4) An AA productive run is finally performed to analyze volume shrinkage, glass transition, and atomic detail of network structure. The method is applied to two common epoxy resin reactions, that is, the cross-linking process of DGEVA (diglycidyl ether of vanillyl alcohol) and DHAVA (dihydroxyaminopropane of vanillyl alcohol) and that of DGEBA (diglycidyl ether of bisphenol A) and DETA (diethylenetriamine). These components form network structures after the CG cross-linking reaction and are then backmapped to calculate properties in the atomic scale. The result demonstrates that the method can accurately predict volume shrinkage, glass transition, and all-atom structure of cross-linked polymers. The method bridges from SMILES to MD simulation trajectories in an automatic way, which shortens the time of building up cross-linked polymer reaction model and suitable for high-throughput computations.

Nanoscopic Characterization Reveals that Bulk Amorphous Elementary Boron Is Composed of a Ladder-like Polymer with B4 as the Structural Unit.

As the initially discovered allotrope of boron, amorphous elementary boron (AE-B) has been reported for more than two centuries. Several possible structures of AE-B have been proposed during the past decades. Due to its noncrystalline nature, however, the structure of AE-B has not yet been determined. We notice that AE-B can be dissolved in organic solvents, although the solubility is very low. After surface adsorption from solution, the individual or the self-assembled structure of AE-B molecules can be characterized at the single-molecule or nanoscopic level, which may be helpful to reveal the molecular structure of AE-B. Atomic force microscopy (AFM) imaging shows that AE-B is a chain-like molecule with a thickness (or height) of 0.17 ± 0.01 nm, which agrees well with the diameter of a B atom, demonstrating that the structure of an AE-B molecule contains only one layer of B atoms. Results from high-resolution transmission electron microscopy (HRTEM) indicate that AE-B molecules can be self-assembled into a nanosheet with parallel lines. The width of each line is 0.27 nm, and the periodical length along the chain axial direction is 0.32 ± 0.01 nm. These results indicate that AE-B is composed of a ladder-like inorganic polymer with B4 as the structural unit. This conclusion is supported by the single-chain elasticity obtained by single-molecule AFM and quantum mechanical calculations. We expect that this fundamental study is not only an ending of the two-century-old scientific mystery but also the beginning of the research and applications of AE-B (ladder B) as a polymeric material. The research strategy may be also used to study other amorphous inorganic materials.

Carbonized Polymer Dots Assemble in Proton-Conducting Channels to Enhance the Conductivity and Selectivity Simultaneously for High-Performance Fuel Cells.

Fabricating polymer electrolyte membranes (PEMs) simultaneously with high ion conductivity and selectivity has always been an ultimate goal in many membrane-integrated systems for energy conversion and storage. Constructing broader ion-conducting channels usually enables high-efficient ion conductivity while often bringing increased crossover of other ions or molecules simultaneously, resulting in decreased selectivity. Here, the ultra-small carbon dots (CDs) with the selective barriers are self-assembled within proton-conducting channels of PEMs through electrostatic interaction to enhance the proton conductivity and selectivity simultaneously. The functional CDs regulate the nanophase separation of PEMs and optimize the hydration proton network enabling higher-efficient proton transport. Meanwhile, the CDs within proton-conducting channels prevent fuel from permeating selectively due to their repelling and spatial hindrance against fuel molecules, resulting in highly enhanced selectivity. Benefiting from the improved conductivity and selectivity, the open-circuit voltage and maximum power density of the direct methanol fuel cell (DMFC) equipped with the hybrid membranes raised by 23% and 93%, respectively. This work brings new insight to optimize polymer membranes for efficient and selective transport of ions or small molecules, solving the trade-off of conductivity and selectivity.

Effect of the polar group content on the glass transition temperature of ROMP copolymers.

Polar groups have long been recognized to greatly influence the glass transition temperature (Tg) of polymers, but understanding the underlying physical mechanism remains a challenge. Here, we study the glass formation of ring-opening metathesis polymerization (ROMP) copolymers containing polar groups by employing all-atom molecular dynamics simulations. We show that although the number of hydrogen bonds (NHB) and the cohesive energy density increase linearly as the content of polar groups (fpol) increases, the Tg of ROMP copolymers increases with the increase of fpol in a nonlinear fashion, and tends to plateau for sufficiently high fpol. Importantly, we find that the increase rate of Gibbs free energy for HB breaking gradually slows down with the increase of fpol, indicating that the HB is gradually stabilized. Therefore, Tg is jointly determined by NHB and the strength of HBs in the system, while the latter dominates. Although NHB increases linearly with increasing fpol, the HB strength increases slowly with increasing fpol, which leads to a decreasing rate of increase in Tg.

Non-equilibrium Nanoassemblies Constructed by Confined Coordination on a Polymer Chain.

Biological systems employ non-equilibrium self-assembly to create ordered nanoarchitectures with sophisticated functions. However, it is challenging to construct artificial non-equilibrium nanoassemblies due to lack of control over assembly dynamics and kinetics. Herein, we design a series of linear polymers with different side groups for further coordination-driven self-assembly based on shape-complementarity. Such a design introduces a main-chain confinement which effectively slows down the assembly process of side groups, thus allowing us to monitor the real-time evolution of lychee-like nanostructures. The function related to the non-equilibrium nature is further explored by performing photothermal conversion study. The ability to observe and capture non-equilibrium states in this supramolecular system will enhance our understanding of the thermodynamic and kinetic features as well as functions of living systems.

Platelet Aggregation Before Aspirin Initiation in Pediatric Patients With Congenital Heart Disease at High Risk of Thrombosis.

Background: Aspirin following unfractionated heparin is the most common anticoagulation strategy for pediatric patients who experienced cardiac surgery at high risk of thrombosis. The platelet aggregation test is the golden method to evaluate the aspirin effect on platelet function. However, the platelet aggregation basal status before postoperative aspirin initiation and the related clinical influencing factors hasn't been investigated systemically in this population. Methods: In a prospective cohort of 247 children, arachidonic acid-induced platelet aggregation (PAG-AA) was measured by means of light transmission aggregometry (LTA) before the first dose of aspirin after cardiac surgical procedure and the perioperative variables were also collected. Distribution of this population's PAG-AA basal status was described. Univariate and multivariate logistic regression analysis were performed to identify the main influencing factors of PAG-AA. Results: The median time of aspirin administration was 2 (1-27) days after surgery and the corresponding median value of basal PAG-AA was 20.70% (1.28-86.49%), with 67.6% population under 55% and 47.8% population under 20%. Patients undergoing cardiopulmonary bypass (CPB) had a significantly lower basal PAG-AA than those without (30.63 ± 27.35 vs. 57.91 ± 27.58, p = 0.013). While patients whose test done within 3 days after CPB had a significantly lower PAG-AA than those out of 3 days (25.61 ± 25.59 vs. 48.59 ± 26.45, p = 0.001). Univariate analysis implied that the influencing factors of the basal PAG-AA including CPB use, test time point, cyanosis, and platelet count. Multivariate regression analysis indicated that only CPB use, test time point, and platelet count were the main independent influencing factors for the basal PAG-AA. Conclusion: The majority of children have impaired basal platelet aggregometry responses before postoperative aspirin initiation. The main influencing factors are CPB use, test time point, and platelet count. To establish the platelet aggregometry baseline prior to commencement of aspirin therapy, testing should be performed 3 days later following the procedure when effect of CPB is basically over.

Nanoparticle cluster formation mechanisms elucidated via Markov state modeling: Attraction range effects, aggregation pathways, and counterintuitive transition rates.

Nanoparticle clusters are promising candidates for developing functional materials. However, it is still a challenging task to fabricate them in a predictable and controllable way, which requires investigation of the possible mechanisms underlying cluster formation at the nanoscale. By constructing Markov state models (MSMs) at the microstate level, we find that for highly dispersed particles to form a highly aggregated cluster, there are multiple coexisting pathways, which correspond to direct aggregation, or pathways that need to pass through partially aggregated, intermediate states. Varying the range of attraction between nanoparticles is found to significantly affect pathways. As the attraction range becomes narrower, compared to direct aggregation, some pathways that need to pass through partially aggregated intermediate states become more competitive. In addition, from MSMs constructed at the macrostate level, the aggregation rate is found to be counterintuitively lower with a lower free-energy barrier, which is also discussed.

Physisorption of Poly(ethylene glycol) on Inorganic Nanoparticles.

Poly(ethylene glycol) (PEG) is the most widely used polymer to decorate inorganic nanoparticles (NPs) by the "grafting-to" method for antifouling properties. PEG also shows diverse supramolecular interactions with nanoparticle surfaces and polar molecules, suggesting that the physisorption between PEG chains and NPs cannot be ignored in the "grafting-to" process. However, the effect of physisorption of PEG to NPs on the process of chemisorption has been rarely studied. Herein, we report that unfunctionalized PEG is physically adsorbed on various NPs by polyvalent supramolecular interactions, adopting "loop-and-train-tail" conformations. We investigated the effect of molecular weight of PEG and ligands of the NPs on the conformation of PEG chains by experimental methods and simulation. It is demonstrated that the physisorption of PEG on NPs can facilitate the chemisorption in the initial stages but delays it in the later stages during the "grafting-to" process. This work provides a deeper understanding of the conformation of physisorbed PEG on NPs and the relationship between physisorption and chemisorption.

Intercluster Exchange-Stabilized Novel Complex Colloidal χc Phase.

Designing complex cluster crystals with a specific function using simple colloidal building blocks remains a challenge in materials science. Herein, we propose a conceptually new design strategy for constructing complex cluster crystals via hierarchical self-assembly of simple soft Janus colloids. A novel and previously unreported colloidal cluster-χ (χc) phase, which resembles the essential structural features of α-manganese but at a larger length scale, is obtained through molecular dynamics simulations. The formation of the χc phase undergoes a remarkable two-step self-assembly process, that is, the self-assembly of clusters with specific size dispersity from Janus colloids, followed by the highly ordered organization of these clusters. More importantly, the dynamic exchange of particles between these clusters plays a critical role in stabilizing the χc phase. Such a conceptual design framework based on intercluster exchange has the potential to effectively construct novel complex cluster crystals by hierarchical self-assembly of colloidal building blocks.

Supercooled melt structure and dynamics of single-chain nanoparticles: A computer simulation study.

By using coarse-grained molecular dynamics simulations, we have investigated the structure and dynamics of supercooled single-chain cross-linked nanoparticle (SCNP) melts having a range of cross-linking degrees ϕ. We find a nearly linear increase in glass-transition temperature (Tg) with increasing ϕ. Correspondingly, we have also experimentally synthesized a series of polystyrene-based SCNPs and have found that the measured Tg estimated from differential scanning calorimetry is qualitatively consistent with the trend predicted by our simulation estimates. Experimentally, an increase in Tg as large as ΔTg = 61 K for ϕ = 0.36 is found compared with their linear chain counterparts, indicating that the changes in dynamics with cross-links are quite appreciable. We attribute the increase in Tg to the enlarged effective hard-core volume and the corresponding reduction in the free volume of the polymer segments. Topological constraints evidently frustrate the local packing. In addition, the introduction of intra-molecular cross-linking bonds slows down the structural relaxation and simultaneously enhances the local coupling motion on the length scales within SCNPs. Consequently, a more pronounced dynamical heterogeneity (DH) is observed for larger ϕ, as quantified by measuring the dynamical correlation length through the four-point susceptibility parameter, χ4. The increase in DH is directly related to the enhanced local cooperative motion derived from intra-molecular cross-linking bonds and structural heterogeneity derived from the cross-linking process. These results shed new light on the influence of intra-molecular topological constraints on the segmental dynamics of polymer melts.

Understanding of supramolecular emulsion interfacial polymerization in silico.

The composition and structure of a membrane determine its functionality and practical application. We study the supramolecular polymeric membrane prepared by supramolecular emulsion interfacial polymerization (SEIP) on the oil-in-water droplet via the computer simulation method. The factors that may influence its structure and properties are investigated, such as the degree of polymerization and molecular weight distribution (MWD) of products in the polymeric membranes. We find that the SEIP can lead to a higher total degree of polymerization as compared to the supramolecular interfacial polymerization (SIP). However, the average chain length of products in the SEIP is lower than that of the SIP due to its obvious interface curvature. The stoichiometric ratio of reactants in two phases will affect the MWD of the products, which further affects the performance of the membranes in practical applications, such as drug release rate and permeability. Besides, the MWD of the product by SEIP obviously deviates from the Flory distribution as a consequence of the curvature of reaction interface. In addition, we obtain the MWD for the emulsions whose size distribution conforms to the Gaussian distribution so that the MWD may be predicted according to the corresponding emulsion size distribution. This study helps us to better understand the controlling factors that may affect the structure and properties of supramolecular polymeric membranes by SEIP.