Self-assembly of shape-tunable oblate colloidal particles into orientationally ordered crystals, glassy crystals and plastic crystals.

The shapes of colloidal particles are crucial to self-assembled superstructures. Understanding the relationship between the shapes of building blocks and the resulting crystal structures is an important fundamental question. Here, we demonstrate that, by using particles whose shape interpolates between a flat disc and a sphere, not only are self-assembled superstructures but also their orientations sensitively dependent on the particle shape. By changing the shape gradually from a flat disc to a spherical shape, a crystal sequence from orientationally ordered crystals to orientationally disordered crystals with frozen and more free rotations are found. The latter two phases are identified as a glassy crystal and a plastic crystal, respectively. By combining theoretical model calculations, the formed crystal structures and the occurring transitions are found to be dictated by the interplay between particle shape and particle-particle interaction as well as particle-wall interaction. In particular, for quasi-spherical shapes, when the strong attraction dominates, a glassy crystal forms, or otherwise a plastic crystal forms. These results demonstrate that the interplay between the particle shape and the interaction can be used to tune crystallization and further fabricate colloid-based new structured and dynamic materials.

Regulation Mechanism of Bubbling Deformation and Fracture Toughness of the Membrane by Asymmetric Phospholipids: A Model System Study.

Dynamic regulation of the deformation modulus and fracture toughness of a membrane is critical to organelles and cells for matching their conflicting needs of resilient and fractured behaviors. These properties implement the protection of the function in the normal condition and the fission function in the endocytosis condition of a membrane. Naturally, a membrane contains phospholipids that have different hydrophilic and hydrophobic group length. The diffusion and aggregation of the phospholipids with asymmetry of the hydrophilic-hydrophobic ratio on the membrane play a key role in regulating the mechanical behaviors passively to the external force. In present work, the effects of the asymmetry of phospholipids on the bubbling deformation and fracture toughness of the membrane to external stretching are investigated in a model system. A disk-shaped micelle formed from the blend of symmetric and asymmetric diblock copolymers in a selective solvent is considered as the membrane sheet. Its mechanically responsive behaviors are investigated by self-consistent field theory. By analyzing the evolution of different components during the stretching process, the mechanism of formation of the bubbling structure is revealed. Moreover, the fracture toughness depending on the asymmetry of the phospholipids is determined quantitatively.

Theoretical Study of the Optimal Design of a UV-Controllable Smart Surface Decorated by a Hybrid Azobenzene-Containing Polymer Layer.

Although grafting polymers onto surfaces is widely suggested for designing smart systems, optimizing the performance of such systems is not simple. In this article, we investigate an azo-polymer-based smart surface using the single-chain-in-mean-field theory. Through the numerical simulations, we study the adhesion/erasion transition of the system and show that the performance of the smart surface can be characterized by the difference between the effective nanoparticle-surface interactions in the UV-on and UV-off states. Further exploring the optimization of the smart surface, we find that the distribution function of the receptor can have typical bimodal characteristics, which is crucial for optimizing the position of the azo-bond along the azo-polymer, f. Moreover, the presence of the homopolymer is also essential for the optimal performance of the smart surface, and we build a reference map for the good combinations of f and the homopolymer design fhomo.

Bistable adhesion behavior of an anisotropic particle on a sliding polymer brush.

Bistable adhesion behavior of an anisotropic particle adsorbed on a sliding polymer brush was found by a single chain in mean field theory (SCMFT) study. Adjacent to the normal adhesion state at which the entropy is depressed, an additional abnormal adhesion state appears. The numerical results demonstrate that the physical mechanism of the bistable adhesion behavior is from the cooperation of the reptation motion of the sliding polymers and the rotating motion of the anisotropic particle. In the abnormal adhesion state, the orientational entropy of the anisotropic particle dominates the adhesion behavior, although the translational entropy is depressed. This bistable adhesion behavior works like a lasso rope in that the abnormal state provides a wide, sensitive, and responsive range, and the normal state furnishes stable adhesion depending on the particle anisotropy.

Single Chain Mean-Field Theory Study on Responsive Behavior of Semiflexible Polymer Brush.

The application of single chain mean-field theory (SCMFT) on semiflexible chain brushes is reviewed. The worm-like chain (WLC) model is the best mode of semiflexible chain that can continuously recover to the rigid rod model and Gaussian chain (GC) model in rigid and flexible limits, respectively. Compared with the commonly used GC model, SCMFT is more applicable to the WLC model because the algorithmic complexity of the WLC model is much higher than that of the GC model in self-consistent field theory (SCFT). On the contrary, the algorithmic complexity of both models in SCMFT are comparable. In SCMFT, the ensemble average of quantities is obtained by sampling the conformations of a single chain or multi-chains in the external auxiliary field instead of solving the modified diffuse equation (MDE) in SCFT. The precision of this calculation is controlled by the number of bonds Nm used to discretize the chain contour length L and the number of conformations M used in the ensemble average. The latter factor can be well controlled by metropolis Monte Carlo simulation. This approach can be easily generalized to solve problems with complex boundary conditions or in high-dimensional systems, which were once nightmares when solving MDEs in SCFT. Moreover, the calculations in SCMFT mainly relate to the assemble averages of chain conformations, for which a portion of conformations can be performed parallel on different computing cores using a message-passing interface (MPI).

What links to psychological needs satisfaction and excessive WeChat use? The mediating role of anxiety, depression and WeChat use intensity.

BACKGROUND: Excessive online social network sites (SNSs) use, such as Facebook or WeChat overuse, has become a severe problem and have caused negative consequences. It is especially important to examine what causes excessive WeChat use in the Chinese population. This study explored the critical role of affective states and WeChat use intensity in the relationship between psychological needs satisfaction and excessive WeChat use based on the self-determination theory and the emotional motivation theory. METHODS: 952 Chinese college students aged 18 to 25 completed an online survey that measured psychological needs satisfaction, depression, anxiety, WeChat use intensity, and excessive WeChat use. RESULTS: Path analysis demonstrated that anxiety, depression, and WeChat use intensity mediated the effect of psychological needs satisfaction on excessive WeChat use. More importantly, the chain mediation model indicated that psychological needs satisfaction could influence excessive WeChat use through the "anxiety-WeChat use intensity" path, but not the "depression-WeChat use intensity" path. CONCLUSION: The current study could not only contribute to theoretical development, but also guide mental health practice by showing that improving psychological needs satisfaction may restrain excessive WeChat use through regulating affective states and Wechat use intensity.

Differences in Reward Sensitivity between High and Low Problematic Smartphone Use Adolescents: An ERP Study.

BACKGROUND: Problematic smartphone use is highly prevalent in adolescent populations compared to other age groups (e.g., adults and young children). Previous studies suggested that higher levels of reward sensitivity were associated with problematic smartphone use. Therefore, the current study investigated the neural processing of monetary and social reward and punishment feedbacks between high and low problematic smartphone use adolescents. METHODS: 46 adolescents participated in the current study and they were categorized into two groups based on their level of problematic smartphone use: those who obtained low scores on the measure of problematic smartphone use were categorized as Low Problematic Smartphone Use (LPSU), and those who obtained high scores on the measure of problematic smartphone use were categorized as High Problematic Smartphone Use (HPSU). Electrocortical activities were recorded during the processing of monetary and social reward and punishment feedback. RESULTS: (1) LPSUs evoked larger P3 in the social punishment condition than in the monetary punishment condition. HPSUs evoked larger P3 in the social reward condition than in the monetary condition. (2) The feedback-related negativity (FRN) amplitudes in the reward condition were significantly larger than those in the punishment condition. (3) HPSUs induced larger reward positivity in social feedback conditions than in monetary feedback conditions, while there were no significant differences between the two types of conditions in the LPSUs. DISCUSSION: The results provide neural underpinning evidence that high sensitivity to social rewards may be related to problematic smartphone use in adolescence.

Enhanced Heterogeneous Diffusion of Nanoparticles in Semiflexible Networks.

The transport of nanoparticles in semiflexible networks, which form diverse principal structural components throughout living systems, is important in biology and biomedical applications. By combining large-scale molecular simulations as well as theoretical analysis, we demonstrate here that nanoparticles in polymer networks with semiflexible strands possess enhanced heterogeneous diffusion characterized by more evident hopping dynamics. Particularly, the hopping energy barrier approximates to linear dependence on confinement parameters in the regime of moderate rigidity, in contrast to the quadratic dependence of both its soft and hard counterparts. This nonmonotonic feature can be attributed to the competition between the conformation entropy and the bending energy regulated by the chain rigidity, captured by developing an analytical model of a hopping energy barrier. Moreover, these theoretical results agree reasonably well with previous experiments. The findings bear significance in unraveling the fundamental physics of substance transport confined in network-topological environments and would provide an explanation for the dynamics diversity of nanoparticles within various networks, biological or synthetic.

Scattering and Gaussian Fluctuation Theory for Semiflexible Polymers.

The worm-like chain is one of the best theoretical models of the semiflexible polymer. The structure factor, which can be obtained by scattering experiment, characterizes the density correlation in different length scales. In the present review, the numerical method to compute the static structure factor of the worm-like chain model and its general properties are demonstrated. Especially, the chain length and persistence length involved multi-scale nature of the worm-like chain model are well discussed. Using the numerical structure factor, Gaussian fluctuation theory of the worm-like chain model can be developed, which is a powerful tool to analyze the structure stability and to predict the spinodal line of the system. The microphase separation of the worm-like diblock copolymer is considered as an example to demonstrate the usage of Gaussian fluctuation theory.