A facile one-pot method is proposed for the fabrication of yolk–shell mesoporous silica nanoparticles with high special surface area. The particle size can be well controlled by moderately tuning some experimental parameters.

Because of the unique architectures and promising potential applications of biomimetic helical structures in biotechnology and nanotechnology, the design and fabrication of these structures by experimentally realizable anisotropic colloidal particles remain one of the most challenging tasks in materials science. Here we show how soft Janus particles self-assemble into supracolloidal helices with distinctive structural characteristics, including single helices, double helices, and Bernal spirals, by appropriately tuning the particle softness. We further examine the kinetic mechanisms governing the formation of different helical structures by using particle-based dynamics simulations. Our results provide a new way for experimentally fabricating structure-controllable supracolloidal helices solely from the self-assembly of soft Janus particles.

Whether nucleation is triggered by density or by bond-orientational order is one of the most hotly debated issues in recent investigations of the crystallization process. Here, we present a numerical study of the relationship between them for soft particles within the isothermal–isobaric ensemble. We compress the system and thus obtain the fluid-solid transition. By investigating locally dense-packed particles and particles with a relatively high bond-orientational order in the compressing process, we find a sharp increase of the spatial correlations for both densely packed particles and highly bond-orientational ordered particles at the phase transition point, which provide new characterization methods for the liquid–crystal transition. We also find that it is the bond-orientational order rather than density that triggers the nucleation process. The relationship between the local density and the bond-orientational order parameter is strongly affected by the characterization methods used. The local bond order parameter (q6) shows clear correlation with the local density (ρ) in the fluid stage, while the coarse-grained form (6) does not correlate with ρ at all, owing to the comparable spatial scales of q6 and ρ. Nevertheless, 6 shows an obvious advantage in distinguishing between solid and liquid particles in our work. These results may elevate our understanding of the mechanism of the crystallization process.

To achieve simulations on large spatial and temporal scales with high molecular chemical specificity, a hybrid particle–field method was proposed recently. This method is developed by combining molecular dynamics and self-consistent field theory (MD-SCF). The MD-SCF method has been validated by successfully predicting the experimentally observable properties of several systems. Here we propose an efficient scheme for the inclusion of electrostatic interactions in the MD-SCF framework. In this scheme, charged molecules are interacting with the external fields that are self-consistently determined from the charge densities. This method is validated by comparing the structural properties of polyelectrolytes in solution obtained from the MD-SCF and particle-based simulations. Moreover, taking PMMA-b-PEO and LiCF3SO3 as examples, the enhancement of immiscibility between the ion-dissolving block and the inert block by doping lithium salts into the copolymer is examined by using the MD-SCF method. By employing GPU-acceleration, the high performance of the MD-SCF method with explicit treatment of electrostatics facilitates the simulation study of many problems involving polyelectrolytes.

We propose a simple and general mesoscale soft patchy particle model, which can felicitously describe the deformable and surface-anisotropic characteristics of soft patchy particles. This model can be used in dynamics simulations to investigate the aggregation behavior and mechanism of various types of soft patchy particles with tunable number, size, direction, and geometrical arrangement of the patches. To improve the computational efficiency of this mesoscale model in dynamics simulations, we give the simulation algorithm that fits the compute unified device architecture (CUDA) framework of NVIDIA graphics processing units (GPUs). The validation of the model and the performance of the simulations using GPUs are demonstrated by simulating several benchmark systems of soft patchy particles with 1 to 4 patches in a regular geometrical arrangement. Because of its simplicity and computational efficiency, the soft patchy particle model will provide a powerful tool to investigate the aggregation behavior of soft patchy particles, such as patchy micelles, patchy microgels, and patchy dendrimers, over larger spatial and temporal scales.

We propose a simple and effective boundary model in a nonequilibrium molecular dynamics (NEMD) simulation to study the out-of-equilibrium dynamics of polymer fluids. The present boundary model can effectively weaken the depletion effect and the slip effect near the boundary, and remove the unwanted heat instantly. The validity of the boundary model is checked by investigating the flow behavior of dilute polymer solution driven by an external force. Reasonable density distributions of both polymer and solvent particles, velocity profiles of the solvent and temperature profiles of the system are obtained. Furthermore, the studied polymer chain shows a cross-streaming migration towards center of the tube, which is consistent with that predicted in previous literatures. These numerical results give powerful evidences for the validity of the present boundary model. Besides, the boundary model can also be used in other flows in addition to the Poiseuille flow.

The scaling behavior of the second virial coefficient of ring polymers at the theta temperature of the corresponding linear polymer (θL) is investigated by off-lattice Monte Carlo simulations. The effects of the solvents are modeled by pairwise interaction between polymer monomers in this approach. Using the umbrella sampling, we calculate the effective potential U(r) between two ring polymers as well as the second virial coefficient A2 of ring polymers at θL, which results from a combination of 3-body interactions and topological constraints. The trend in the strength of the effective potential with respect to chain length shows a non-monotonic behavior, differently from that caused only by topological constraints. Our simulation suggests that there are three regimes about the scaling behavior of A2 of ring polymers at θL: 3-body interactions dominating regime, the crossover regime, and the topological constraints dominating regime.

A simple and facile one-pot sol–gel method is proposed for the fabrication of hollow mesoporous silica particles. Both the particle size and the shell thickness can be well controlled by moderately tuning some experimental parameters.

Structural relaxation in binary hard spherical particles has been shown recently to exhibit a wealth of remarkable features when size disparity or mixture composition is varied. In this paper, we test whether or not similar dynamical phenomena occur in glassy systems composed of binary hard ellipses. We demonstrate via event-driven molecular dynamics simulation that a binary hard-ellipse mixture with an aspect ratio of two and moderate size disparity displays characteristic glassy dynamics upon increasing density in both the translational and the rotational degrees of freedom. The rotational glass transition density is found to be close to the translational one for the binary mixtures investigated. More importantly, we assess the influence of size disparity and mixture composition on the relaxation dynamics. We find that an increase of size disparity leads, both translationally and rotationally, to a speed up of the long-time dynamics in the supercooled regime so that both the translational and the rotational glass transition shift to higher densities. By increasing the number concentration of the small particles, the time evolution of both translational and rotational relaxation dynamics at high densities displays two qualitatively different scenarios, i.e., both the initial and the final part of the structural relaxation slow down for small size disparity, while the short-time dynamics still slows down but the final decay speeds up in the binary mixture with large size disparity. These findings are reminiscent of those observed in binary hard spherical particles. Therefore, our results suggest a universal mechanism for the influence of size disparity and mixture composition on the structural relaxation in both isotropic and anisotropic particle systems.

The structure and rheological properties of graphene-based particle (GP-x)/polydimethylsiloxane (PDMS) composites are investigated as the surface oxygen content of graphene-based particle is varied, i.e., from 6.6% (GP-1) to 15.3% (GP-2), 25.5% (GP-3) and 43.1% (GP-4). Interestingly, the dispersion state of graphene-based particles in PDMS does not change monotonically with increasing surface oxygen content. The size of layered stacks and aggregates first decreases from GP-1 to GP-3 and then increases from GP-3 to GP-4 with increasing surface oxygen content. The larger size of layered stacks and aggregates in GP-1 and GP-4 suspensions results from strong inter-particle π–π and hydrogen bonding interactions. Under weak shear, GP-1 and GP-4 form larger aggregates in PDMS, which align along the vorticity direction, inducing negative normal stress differences (ΔN) in the composites. However, GP-2 and GP-3 do not further aggregate under weak shear and the ΔN is almost zero. It is further inferred that the strong inter-particle attractive interaction leads to the vorticity alignment of aggregates under weak shear.

Using off-lattice Monte Carlo simulation, we investigate the effects of topological constraints on the free energy and metric properties of an unknotted ring polymer without exclude volume interactions confined in a slit with width d, as well as the effect of confinement on the probability of forming an unknot in a freely jointed ring. Because of the topological constraints, the polymer size of an unknotted ring is shown to behave differently from that of a freely jointed ring: the in-plane radius of gyration Rg∥ increases with increasing confinement. However, the free energy of an unknotted ring follows the same scaling law as a freely jointed ring for strong confinement. This abnormal phenomenon is explained on the basis of the fact that the length of subchains inside the confinement blobs is smaller than the topological blob size, i.e., the characteristic length below which topological constraints become unimportant. As in the bulk, the probability of forming an unknot decreases exponentially with the chain length, but the decay length decreases with decreasing confinement length. We propose an efficient method for calculating the probability of forming unknot from a freely jointed ring in confinement.

The structure and rheological properties of carbon-based particle suspensions, i.e., carbon black (CB), multi-wall carbon nanotube (MWNT), graphene and hollow carbon sphere (HCS) suspended in polydimethylsiloxane (PDMS), are investigated. In order to study the effect of particle shape on the structure and rheological properties of suspensions, the content of surface oxygen-containing functional groups of carbon-based particles is controlled to be similar. Original spherical-like CB (fractal filler), rod-like MWNT and sheet-like graphene form large agglomerates in PDMS, while spherical HCS particles disperse relatively well in PDMS. The dispersion state of carbon-based particles affects the critical concentration of forming a rheological percolation network. Under weak shear, negative normal stress differences (ΔN) are observed in CB, MWNT and graphene suspensions, while ΔN is nearly zero for HCS suspensions. It is concluded that the vorticity alignment of CB, MWNT and graphene agglomerates under shear results in the negative ΔN. However, no obvious structural change is observed in HCS suspension under weak shear, and accordingly, the ΔN is almost zero.

•We report a facile method for synthesizing resin spheres and carbon spheres.•Carbon spheres feature high nitrogen contents and high specific surface area.•The size and uniformity of particles can be well regulated.3-Aminophenol/formaldehyde (AF) resin colloidal spheres with narrow size distribution and high nitrogen content are synthesized in the presence of urea. The obtained particles that indicated by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) are spherical morphology and uniform. It can be further carbonized into carbon spheres preserving high nitrogen percent. The particle size is tunable from 300 nm to 850 nm by appropriately varying the concentration of precursor or water/ethanol volume ratio. Even using the water as an only solvent, we can also obtain spherical particles with different size. Typically, the nitrogen percent in the obtained polymer and carbon particles is as high as 10.39 wt% and 8.95 wt%, respectively. The typical surface area of resulted carbon particles obtained from nitrogen adsorption measurement is 459 m2 g−1. X-ray diffraction demonstrates the obtained carbon spheres are amorphous, which are expected to have practical application in the field of energy devices. The method can be considered as a low cost and facile method for mass production.Graphical abstract

The design and fabrication of two-dimensional (2D) well-ordered nanostructures by a facile and effective strategy remain a major scientific and technological challenge, hitherto achieved mainly through the aid of interfaces or substrates with an ordered arrangement. Here we introduce a new concept in achieving template-free fabrication of diverse 2D ordered nanostructures by utilizing anisotropic characteristics of soft triblock Janus particles. Our numerical investigation demonstrates how particle softness and controllable directional attraction interplay to generate a number of fascinating non-close-packed 2D nanostructures and even three-dimensional (3D) vesicles. These non-close-packed nanostructures are of great interest for scientific reasons and lead to promising applications in soft nanotechnology and biotechnology.

The structure and rheological properties of multiwall carbon nanotube (MWNT)/polydimethylsiloxane (PDMS) composites under shear are investigated, as the molecular weight of PDMS, aspect ratio and concentration of MWNT are systematically varied. Negative normal stress differences (ΔN) are observed at low shear rates for samples with low molecular weight (Mw) of PDMS (lower than the critical entanglement molecular weight (Mc)), whereas positive ΔN is found in samples with high molecular weight of PDMS (Mw > Mc). More interestingly, negative ΔN is also observed for some samples under confinement when the molecular weight of PDMS is higher than the critical value (Mw > Mc). Moreover, the aspect ratio and concentration of MWNT show negligible influence on the sign of ΔN. Based on the results of optical-flow experiments, a phase diagram for the structures of samples under shear is obtained. It is concluded that the vorticity banding of MWNT aggregates results in the negative ΔN under shear through relating the evolution of structure and the rheological properties of samples under shear.

We examined the effect of interfacially active particles on the morphology and rheology of droplet/matrix blends of two immiscible homopolymers. Experiments were conducted on polybutadiene/polydimethylsiloxane (10/90) blend and the inverse system. The effects of fumed silica nanoparticles, at low particle loadings (0.1–2.0 wt%), were examined by direct flow visualization and by rheology. Fumed silica nanoparticles were found to significantly affect the morphology of polymer blends, inducing droplet cluster structure and decreasing the droplet size, regardless of which phase wets the particles preferentially. This is surprising in light of much past research that shows that particles are capable of bridging and thus induce droplet cluster structure in droplet/matrix systems only when they are preferentially wetted by the continuous phase. Therefore, there should exist other possible mechanisms responsible for these droplet cluster structures except for the bridging mechanism. We proposed a particle-flocculating mechanism based on the fact that fumed silica particles readily flocculate due to their high aspect ratio, fractal-like shape, or interparticle attractions. Optical microscopy also reveals that the clustering structure becomes more extensive, and the droplet sizes in the clusters become smaller when the particle loading is increased. Rheologically, the chief effect of particles is to change the flow behavior from a liquid-like rheology to gel-like behavior. This gel-like behavior can be attributed to droplet clustering. Moreover, it should be emphasized that such gel-like behavior can be seen in the blends regardless of which phase wets the particles preferentially, suggesting that, once again, bridging is not the only cause of droplet clustering.

•We proposed the relationship between structural gel and mechanical gel.•We found that chain composition affected the gelation behavior greatly for strong solvophobic system.•We found three typical gelation processes together with different mechanical responses.•We gave an explanation why the system showed three different gelation processes.Polymer gels, defined either from the structural point of view (structural gel) or by their mechanical properties (mechanical gel), are ubiquitous in our daily life. In our previous work (J. Phys. Chem. B, 2011, 115, 11345), we reported that, the mechanical gel formed by strong solvophobic ABA block copolymers with fixed chain compositions shows a strong mechanical response, which meant the formed gel had a high modulus. In this work, we focus on the effect of chain composition on the relationship between structural gel and mechanical gel, where the chain length of block copolymer is lower than its entanglement chain length for simplicity. Our results show that the chain composition has a great effect on the mechanical response of the ABA copolymer solutions with a strong solvophobicity. On the other hand, for the structural gel formed by weak solvophobic block polymers, we do not find any strong mechanical responses even we change the chain composition in a wide range. Moreover, we find three typical gelation processes, companied with three kinds of different mechanical responses. These results may provide us an effective method to control the mechanical property of a polymer gel as expected.

•Graphene oxide disperses better in higher molecular weight of PDMS.•Negative normal stress differences are observed in low Mw PDMS composites.•Positive normal stress differences are observed in high Mw PDMS composites.•Vorticity alignment of GO clusters is observed in low Mw PDMS composites.The structure and rheological properties of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites are examined as the molecular weight of PDMS and concentration of GO are varied. Clusters formed by GO sheets get smaller and disperse better with increasing molecular weight of PDMS, which results in the higher critical concentration to form network (Ccr). Moreover, at GO concentration just above Ccr, the plateau modulus of samples decreases with the molecular weight of PDMS. During shear experiments, negative normal stress differences (ΔN) are observed in composites with PDMS molecular weight lower than critical entanglement molecular weight (Mc). However, positive ΔN is found in samples with PDMS molecular weight above Mc. It can be concluded that the vorticity alignment of GO clusters induces the negative ΔN based on the optical shear experiments. The possible mechanism for the positive ΔN is also proposed.

•Percolation threshold of GC/silicon oil suspensions was investigated.•Negative normal stress was found in pseudo-steady and transient shear measurements.•Strain hardening of G″ and strain softening of G′ in oscillatory shear were observed.•The rheological properties of different carbon materials were compared.The rheological properties of amorphous carbon suspensions have attracted great attention, but they are still not fully understood due to the non-equilibrium nature of the structure. In this work, the linear and nonlinear rheological properties of ginger-like amorphous carbon (GC) filled silicon oil suspensions are investigated. The percolation threshold of GC/silicon oil suspensions is 1.2 wt.% based on linear viscoelasticity and percolation theory. Moreover, a viscosity plateau and apparent negative normal stress differences are observed during pseudo-steady shear experiments for samples with GC concentration above 6 wt.%. Furthermore, constant-rate shear flow confirms the evolution of structure as functions of shear rate and time. Additionally, strain softening of storage modulus and strain hardening of loss modulus are observed during strain sweep experiments for samples with GC concentration above the percolation threshold. Relating the rheological results with the structure observed by an in situ optical shearing cell, the change of viscosity and negative normal stress differences under pseudo-steady shear is supposed to result from the structure reorganization of GC networks.

To achieve simulations on large spatial and temporal scales with high molecular chemical specificity, a hybrid particle–field method was proposed recently. This method is developed by combining molecular dynamics and self-consistent field theory (MD-SCF). The MD-SCF method has been validated by successfully predicting the experimentally observable properties of several systems. Here we propose an efficient scheme for the inclusion of electrostatic interactions in the MD-SCF framework. In this scheme, charged molecules are interacting with the external fields that are self-consistently determined from the charge densities. This method is validated by comparing the structural properties of polyelectrolytes in solution obtained from the MD-SCF and particle-based simulations. Moreover, taking PMMA-b-PEO and LiCF3SO3 as examples, the enhancement of immiscibility between the ion-dissolving block and the inert block by doping lithium salts into the copolymer is examined by using the MD-SCF method. By employing GPU-acceleration, the high performance of the MD-SCF method with explicit treatment of electrostatics facilitates the simulation study of many problems involving polyelectrolytes.

A simple and facile one-pot sol–gel method is proposed for the fabrication of hollow mesoporous silica particles. Both the particle size and the shell thickness can be well controlled by moderately tuning some experimental parameters.

How to create novel desired structures by rational design of building blocks represents a significant challenge in materials science. Here we report a conceptually new design principle for creating supracolloidal fullerene-like cages through the self-assembly of soft patchy particles interacting via directional nonbonded interactions by mimicking non-planar sp2 hybridized carbon atoms in C60. Our numerical investigations demonstrate that the rational design of patch configuration, size, and interaction can drive soft three-patch particles to reversibly self-assemble into a vast collection of supracolloidal fullerene-like cages. We further elucidate the formation mechanisms of supracolloidal fullerene-like cages by analyzing the structural characteristics and the formation process. Our results provide conceptual and practical guidance towards the experimental realization of supracolloidal fullerene-like cages, as well as a new perspective on understanding the fullerene formation mechanisms.

A facile one-pot method is proposed for the fabrication of yolk–shell mesoporous silica nanoparticles with high special surface area. The particle size can be well controlled by moderately tuning some experimental parameters.