Weihua Li

Fudan University

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Depletion interactions in binary mixtures of repulsive colloids

Chinese Physics B (2010)

Weihua Li Qiu Feng

Acceptance ratio method, which has been used to calculate the depletion potential in binary hard-sphere mixtures, is extended to the computation of the depletion potential of non-rigid particle systems. The repulsive part of the Lennard-Jones pair potential is used as the direct pair potential between the non-rigid particles. The depletion potential between two big spheres immersed in a suspension of small spheres is determined with the acceptance ratio method through the application of Monte Carlo simulation. In order to check the validity of this method, our results are compared with those obtained by the Asakura-Oosawa approximation, and by Varial expansion approach, and by molecular dynamics simulation. The total effective potential and the depth of its potential well are computed for various softness parameters of the direct pair potential.

Pair potential

Hard spheres

Lennard-Jones potential

Suspension

Particle (ecology)

Colloidal particle

10.1088/1674-1056/19/10/108204

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Citations (4)

鉱化ゴミバイオリアクター中の細菌多様性を分析した。【JST・京大機械翻訳】

Huanjing Gongcheng (2016)

Sun Yingjie Yang Qiang Rongxing Bian Weihua Li Ziliang Liu

Source

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Effects of Chain Topology on the Self-Assembly of AB-Type Block Copolymers

Macromolecules (2018)

Wenbo Jiang Yicheng Qiang Weihua Li Feng Qiu An‐Chang Shi

The effects of chain topology on the self-assembly of block copolymers are examined using an ABAT block copolymer, composed of an AB diblock copolymer with an extra A block tethered onto the B block, as a model system. The topology of the ABAT block copolymer is regulated by the tethering point, such that the block copolymer changes continuously from linear ABA triblock copolymer to A2B miktoarm star copolymer as the tethering position moves from the B end to the AB junction. The phase diagrams of ABAT copolymers of different tethering positions are constructed using the self-consistent field theory. The theoretical results reveal that the phase behavior of the system depends sensitively on the topology of the ABAT copolymers. In particular, a considerably wide stable region of the perforated lamellar (PL) phase is predicted for ABAT with proper tethering positions. The PL phase could even completely replaces the gyroid phase at relatively strong segregation. Furthermore, a large window of the hexagonally close-packed (hcp) spherical phase, as well as a direct transition from hcp to the cylindrical phase, is predicted. An analysis of the distributions of the different blocks reveals that the local segregation of the two different B blocks occurs to accommodate the topological constraints due to the chain architecture, which in turn regulates the local interfacial curvature and chain packing resulting in the different phase behaviors.

Gyroid

Tethering

Chain (unit)

10.1021/acs.macromol.7b02389

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Citations (47)

Quadruple-hole multiplication by directed self-assembly of block copolymer

Zhiyong Wu Jiacheng Luo Qingshu Dong Jiaxiang Li Xingran Xu

Directed Self-Assembly (DSA) of cylindrical block copolymer with graphoepitaxy strategy offering significant potential for contact hole multiplication in semiconductor manufacturing at technology nodes below 7 nm (sub-7 nm). This technique allows precise control over the number of DSA-generated holes and their critical dimensions (CD) by manipulating the guiding template geometry and size. The results indicate that DSA quadruple-hole multiplication patterns aligned top-bottom and left-right, with a long-axis spacing of 55-65 nm and a short-axis spacing of 30-40 nm could be achieved through precisely designing template holes with long-axis dimension and short-axis dimension. The formed DSA pattern was successfully transferred to the underlying hard mask layer, creating a large-area quadruple-hole array with a CD of approximately 17 nm. A comprehensive investigation of guiding template size and morphology on multiplication hole patterning enhances the understanding of the self-assembly behavior in confined elliptical spaces. In conclusion, this work highlights the importance of optimizing guiding template size for contact hole multiplication in integrated circuit fabrication.

10.1117/12.3055274

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Thermodynamics and Kinetics of Defect Motion and Annihilation in the Self-Assembly of Lamellar Diblock Copolymers

Macromolecules (2016)

Weihua Li Marcus Müller

The thermodynamics of dislocations in thin films of lamella-forming diblock copolymers and their climb and glide motions are investigated using single-chain-in-mean-field (SCMF) simulations and self-consistent field theory (SCFT) in conjunction with the string method. The glide motion of a defect perpendicular to the stripe pattern is characterized by large free energy barriers. The barriers not only stem from altering the domain topology; an additional barrier arises from a small-amplitude but long-range domain displacement. In contrast, the climb motion along the stripes does not involve a free energy barrier in accord with the continuous translational invariance along the stripe. Thus, the perpendicular distance ("impact parameter") between a pair of defects is approximately conserved. Dislocation pairs with opposite Burgers vectors attract each other and move toward each other ("collide") via climb motion. We find that the forces between apposing defects significantly depend on system size, and the Peach–Koehler force in smectic structures only becomes accurate for extremely large system sizes. Moreover, we observe in SCMF simulations that the defect annihilation time qualitatively and nonmonotonously depends on the defects' perpendicular distance and rationalize this finding by the collective kinetics along the minimum free energy path (MFEP) and the single-chain dynamics in an inhomogeneous environment.

Annihilation

10.1021/acs.macromol.6b01088

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Citations (44)

Emergence and Stability of Helical Superstructures in ABC Triblock Copolymers

Macromolecules (2011)

Weihua Li Feng Qiu An‐Chang Shi

The emergence and stability of superstructured cylindrical phases in frustrated ABC linear triblock copolymers are investigated by the self-consistent field theory. Our results reveal that the complex single/double/triple helices-on-cylinder phases are formed when the straight cylinders-on-cylinder and rings-on-cylinder phases are frustrated due to packing constraints. A free energy comparison indicates that the double and triple helical phases are stable, whereas the other cylinders-on-cylinder phases are metastable. In addition, the chirality and rotation for the helical supercylinders are considered in our calculations. Our theoretical prediction is consistent with a number of experimental observations.

Metastability

Chirality

10.1021/ma2023952

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Citations (76)

Origins of low-symmetry phases in asymmetric diblock copolymer melts

Proceedings of the National Academy of Sciences (2018)

Kyungtae Kim Akash Arora Ronald M. Lewis Meijiao Liu Weihua Li

Cooling disordered compositionally asymmetric diblock copolymers leads to the formation of nearly spherical particles, each containing hundreds of molecules, which crystallize upon cooling below the order-disorder transition temperature (

10.1073/pnas.1717850115

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Citations (122)

Emergence and Stability of a Hybrid Lamella–Sphere Structure from Linear ABAB Tetrablock Copolymers

ACS Macro Letters (2017)

Bin Zhao Wenbo Jiang Lei Chen Weihua Li Feng Qiu

The self-assembly of linear A1B1A2B2 tetrablock copolymers is studied using the self-consistent field theory, aiming to target the formation of stable hybrid structures composed of lamellar and spherical domains of the same component, i.e., the lamella–sphere (LS) phase. Two types of lamellar morphologies, regular (L) and sandwich-like (L′), are observed, and their transition is identified as first-order. The formation of L′ is a prior condition for the formation of LS because the disordered short A2-blocks sandwiched in the B domain in L′ aggregate into spheres as χN increases, leading to the formation of LS. The separation of A2-blocks from A1-blocks in L′ or LS causes extra interfacial energy, which is compensated by the gain of configurational entropy. The tail B2-block is demonstrated to play a critical role in enlarging the gain of configurational entropy. In a word, the formation of L′ is driven by entropy, while the transition from L′ to LS is driven by enthalpy.

Lamella (surface anatomy)

10.1021/acsmacrolett.7b00818

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Citations (31)

Regulate the Stability of Gyroids of ABC-Type Multiblock Copolymers by Controlling the Packing Frustration

ACS Macro Letters (2020)

Qiong Xie Yicheng Qiang Weihua Li

We propose to regulate the stability of gyroids of ABC-type multiblock copolymers by controlling the packing frustration of majority-component B-blocks. Accordingly, we investigate the self-assembly behaviors of the BABCB linear terpolymer with a variable length ratio τ of the middle B-block relative to the total B-blocks using self-consistent field theory. It is observed that the gyroid region exhibits a maximal width with respect to τ, which is attributed by the nonmonotonical change of the packing frustration of three B-blocks in the morphology of discrete domains, for example, cylinders. Then we further purposely design another ABC-type copolymer composed of an ABC linear triblock tethered by another B-block at the middle of the B-block. In contrast, the packing frustration of B-blocks of the second terpolymer drops down continuously as the middle B-block shortens, thus, expanding the stable regions of cylinders and spheres while contracting those of lamella and gyroid.

Gyroid

Lamella (surface anatomy)

10.1021/acsmacrolett.9b00966

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Citations (29)

Flow-driven translocation of comb-like copolymer micelles through a nanochannel

Soft Matter (2023)

Yingjie He Luyang Li Mingming Ding Weihua Li

Using hybrid lattice-Boltzmann molecular dynamics simulations, we investigate the flow-driven translocation of comb-like copolymer micelles through a nanochannel, in particular, making a detailed comparison with micelles formed by the corresponding diblock copolymers. Our results demonstrate that the critical flow flux of micelles formed by the comb-like copolymers is higher than that of micelles formed by the corresponding diblock copolymers, which is more pronounced with increasing side chain lengths or grafting densities, as evidenced by the free energy computed by self-consistent field theory. Our work indicates that the impact of chain topology on the stability of micelles, especially with the same size, can be well characterized using the critical flow fluxes, which provides a theoretical basis for designing self-assembling micelles for various applications.

Lattice Boltzmann methods

10.1039/d3sm01241g

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Citations (1)