Understanding Multicompartment Micelles Using Dissipative Particle Dynamics Simulation

Multicompartment micelles are a new class of nanomaterials that may find wide applications in the fields of drug delivery, nanotechnology and catalysis. Due to their structural complexity, as well as the wide parameter space to explore, experimental investigations are a difficult task, to which molecular simulation may contribute greatly. In this paper, the application of the dissipative particle dynamics simulation technique to the understanding of multicompartment micelles is introduced, illustrating that DPD is a powerful tool for identifying new morphologies by varying block length, block ratio and solvent quality in a systematic way. The formation process of multicompartment micelles, as well as shear effects and the self-assembly of nanoparticle mixtures in multicompartment micelles, can also be studied well by DPD simulation. The present work shows that DPD, as well as other simulation techniques and theories, can complement experiments greatly, not only in exploring properties in a wider parameter space, but also by giving a preview of phenomena prior to experiments. DPD, as a mesoscopic dynamic simulation technique, is particularly useful for understanding the dynamic processes of multicompartment micelles at a microscopic level.

     

Multicompartment Micellar Solutions in Shear: A Dissipative Particle Dynamics Study

Summary: Dissipative particle dynamics simulations were performed to study the effect of shear on the rheological behavior of multicompartment micellar solutions, demonstrating that both shear thickening and thinning can occur, and the macroscopic behavior was elucidated at a molecular level. In addition, a novel shear‐induced morphology of “sphere‐on‐rod” was observed. This work provides useful information towards a complete understanding of the properties and morphologies of multicompartment micelles that is useful for future rational synthesis of novel micelles.

Shear‐induced morphological transitions and rheological behavior in multicompartment micellar solutions formed from star triblock copolymers.     

Multicompartment Micelles From π-Shaped ABC Block Copolymers

Dissipative particle dynamics simulations were performed on the morphology and structure of multicompartmerit micelles formed from n-shaped ABC block copolymers in water. The influences of chain architectures were studied in a systematic way, and a rich variety of morphologies were observed, such as spherical, wormlike, X-shaped, Y-shaped, ribbon-like, layered rod-like, layered disk-like, as well as network morphologies. The simulations show that the distance between the two grafts plays an important role in control of the morphology. Since n-shaped ABC block copolymers can be reduced to linear ABC and star ABC block copolymers, they are good model copolymers for studying the self-assembly of complex block copolymers into micelles. The knowledge obtained in this work as well as the new morphologies identified provide useful information for future rational design and synthesis of novel multicompartment micelles.     

Self‐Assembly of Two Agents in a Core‐Shell‐Corona Multicompartment Micelle Studied by Dissipative Particle Dynamics Simulations

Summary: Dissipative particle dynamics simulations are performed on the distributions of two agents in a core‐shell‐corona multicompartment micelle. The simulated results show that when the agents are weakly hydrophobic, their distributions in the multicompartment micelle are largely affected by the interactions between the agents and the blocks; while for strongly hydrophobic agents, the self‐assembly of solubilized species in the micelle is also affected largely by the interactions between the species. This work confirms that a multicompartment micelle can store two agents within separate nanoscopic compartments simultaneously, and shows that the distributions of the agents can be tailored easily by changing the interactions presented. This provides molecular‐level information that is useful for the future rational design of new micellar systems with tailored properties.

Simulated cross sections of the multicompartment micelles with strongly hydrophobic solubilized agents (the solvent and block A are omitted for clarity, block B is dark gray, block C is light gray, agent P is white, and agent Q is black).     

Novel Two‐Compartment Micelles Formed by Self‐Assembly of Linear Pentablock Copolymers in Selective Solvents

In this work, the formation of two‐compartment micelles from symmetric pentablock copolymers in selective solvents was studied using the dissipative particle dynamics simulation technique, and the effects of block lengths and solvent quality were investigated. The simulations revealed several new morphologies and their formation mechanisms were elucidated at the molecular level, providing useful information that may contribute to the future rational design and synthesis of novel multicompartment micelles with tailored structures.

     

三嵌段共聚物和两嵌段共聚物在水溶液中共混自组装成多室胶束结构的耗散粒子动力学模拟(英文)

利用耗散粒子动力学模拟研究了在水溶液中混合不同的线形三嵌段共聚物AxByCz和线形两嵌段共聚物AmBn对多室胶束的形貌多样性的影响.通过改变线形的三嵌段共聚物和两嵌段共聚物的链长来寻找多室胶束的形成条件.由线形三嵌段共聚物和线形两嵌段共聚物的不同混合形成的多室胶束结构是多种多样的,例如"蠕虫状"胶束、"汉堡包"胶束、"球上球"胶束、"核-壳-壳"胶束等等.多室胶束的整体形貌和内部结构的控制都可以从线形三嵌段共聚物和两嵌段共聚物的二元共混得到.为了表征获得的多室胶束结构,我们计算了密度图和成对分布函数图.在此工作中,可以获得和观察到复杂的多室胶束.结果表明,简单地混合线形的三嵌段共聚物和线形的两嵌段共聚物是一个控制多室胶束形貌和结构的有效方法,在工程实验中可以更简单更经济地形成多室胶束结构.因此,在设计新的多室胶束方面,聚合物共混仍然是未来值得更加关注的一个话题.     

Cooperative Self‐Assembly of Nanoparticle Mixtures in Lamellar Diblock Copolymers: A Dissipative Particle Dynamics Study

Summary: Dissipative particle dynamics simulations are performed on the distribution of binary nanoparticle mixtures in lamellar diblock copolymers. The results show that the self‐assembly of nanoparticle mixtures in polymer matrix is a cooperative assembly that is affected by various factors, providing molecular‐level information for the rational design of new polymer nanocomposites with tailored properties.

The simulated polymer nanocomposite structure (the polymer matrix was omitted for clarity; P, gray; Q, black).     

Nanoparticle-filled ABC Star Triblock Copolymers: A Dissipative Particle Dynamics Study

Chinese Journal of Polymer Science - The phase behavior of nanoparticle-filled ABC star triblock copolymers was investigated by dissipative particle dynamics simulation. Two typical structures, the...     

梳状-线性共聚物自组装的耗散粒子动力学模拟

梳状-线性共聚物在选择性溶剂中可以自组装形成两种不同类型的聚集体, 其中第I类的自组装发生在亲、疏溶剂链之间, 而第II类发生在线性链和梳状亚结构之间. 本工作利用耗散粒子动力学方法, 分别研究了梳状-线性共聚物在侧链和主链选择性溶剂中形成的这两类聚集体, 探讨了侧链长度和侧链数量等对聚集体类型及形貌的影响. 研究表明, 第II类聚集体在侧链长度较短且侧链数量较多时容易形成. 将模拟结果与文献报道的实验结果相比较, 发现两者能较好地吻合. 此外, 本研究获得了一些在实验中较难得到的信息, 有助于进一步理解梳状-线性共聚物的自组装行为.     

Dissipative Particle Dynamics Simulations on the Self-Assembly of New Segmented Random-Block Copolymers in Selective Solvents

Dissipative particle dynamics simulation was applied to investigate the self-assembly of new segmented random-block copolymers (A-co-B)-b-B in selective solvents. The coarse-grained models of random-block copolymers were built. The effects of the composition of the copolymer, the interaction parameters, the volume fractions, as well as the ratio of hydrophilic particles to hydrophobic particles in the random segment, on the morphology of the aggregations were systematically investigated. The results showed that new segmented random-block copolymers (A-co-B)-b-B could self-assemble into rodlike micelle, spherical micelle and two-compartment micelle. Oval-shaped micelle and spherical micelle could be formed at different volume fractions. The simulation results provide an important reference to the design and synthesis of specific micelles.     

Formation of Vesicles from Amphiphilic Random Copolymers in Solution: A Dissipative Particle Dynamics Simulation Study

Five coarse-grained models were built for amphiphilic random copolymers. The self-assembly of amphiphilic random copolymers in selective solvent was investigated via dissipative particle dynamics simulations. The simulation results showed that the content of hydrophilic particles and the repulsive parameter between solvent and copolymer particles were two key factors of the vesicle formation. We report herein on how to control the self-assembled morphology evolution. The two mechanisms of vesicle formation from amphiphilic random copolymers are found through investigating the dynamic processes of vesicle formation, which is in accordance with the experiment and simulation results of amphiphilic block copolymer reported in the literature.      

PEO—PPO—PEO三嵌段共聚物自组装行为的耗散粒子动力学模拟

采用耗散粒子动力学方法（DPD）,模拟了聚氧乙烯-聚氧丙烯-聚氧乙烯（PEO—PPO—PEO）三嵌段共聚物在乙醇溶液中的自组装行为,考察了该共聚物的体积分数和聚氧乙烯（PEO）嵌段链长对介观形貌的影响。当F88（PEO104-PPO39-PEO104）体积分数为20％时,胶柬由初始的均衡分散态逐渐聚合,最终形成PPO为核、PEO为壳的平衡态柱状团聚体。改变共聚物的体积分数和PEO链的长度,会形成不同的介观结构,如：球状、柱状、立体网络、层状和穿孔状结构等。结果表明,DPD方法是研究三嵌段共聚物自组装行为和介观结构形成机理的有效工具,对合成具有特定结构性能的材料有一定的指导意义。     

Core-Corona Micelles Formed by Self-Assembly of Random Copolymer and Homopolymer Mixtures: Dissipative Particle Dynamics Simulations

Dissipative particle dynamics simulation was applied to investigate the cooperative aggregation of amphiphilic random copolymer and homopolymer mixtures in selective solvents. The amphiphilic random copolymers were set to contain more hydrophilic segments. The effects of the contents of homopolymers, the chain length of amphiphilic random copolymers, the interaction parameters, as well as the simulation time, on the cooperative aggregation were systematically studied with dissipative particle dynamics simulation method. The results showed that core-corona micelles could be formed with the addition of homopolymers, where the homopolymers accumulate at the core and the amphiphilic random copolymers as the corona. This work demonstrated that the morphology and the size of the micelles could be tuned by the controlled addition of homopolymers in the process of self-assembly.     

ABC三嵌段共聚物胶束从多间隔结构到多核结构转变的Monte Carlo模拟

采用Monte Carlo模拟方法研究了疏水-亲水-疏水(H-P-H)型ABC三嵌段共聚物在B嵌段的选择性溶剂中的自组装行为. 模拟结果表明, 通过调节A嵌段和C嵌段的疏水性和二者之间的不相容性, 体系中可以形成多种形貌各异的胶束. 根据胶束中疏水核结构的特点, 这些胶束大体上可以被分为多核型胶束和多间隔型胶束两种类型. 通过增强疏水嵌段的疏水性或降低A嵌段和C嵌段间的不相容性, H-P-H型ABC三嵌段共聚物胶束能够发生从多核型胶束向多间隔型胶束的转变. 进一步分析胶束中聚合物的链构象等微观结构信息发现, A嵌段和C嵌段间的排斥作用和疏水作用之间存在竞争关系, 而这种竞争关系是影响体系中形成多核型胶束还是多间隔型胶束的决定性因素.     

Dissipative Particle Dynamics Simulation of Microphase Separation and Properties of Linear–Dendritic Diblock Copolymer Melts under Steady Shear Flow

Summary: Dissipative particle dynamic simulations were performed on the microphase separation, end‐to‐end distance, and shear viscosity of linear–dendritic diblock copolymers under steady shear flow. The results show that their microstructure and properties depend on both the shear rate and the degree of branching, and they can incorporate the characteristics of both linear and dendritic polymers to lead to new materials with unique properties.

Schematic structure for the linear‐dendritic copolymer G4 described in this work.     

Microphase Separation of Phenylene Oligomers with Polymeric Side Chains: A Dissipative Particle Dynamics Study

The microphase‐separated morphologies of p‐phenylene oligomers with POx, PCL, PS, and PEO side chains are studied using DPD simulations. It is shown that the microphase‐separated morphologies depend significantly on the degree of chemical incompatibility between the components as indicated by the Flory‐Huggins interaction parameters. The good agreement of the microphase separated morphologies as simulated by DPD with the experimentally determined thin film morphologies suggests that DPD can produce convincing morphological information at the nanoscale. The results show that grafting of polymeric side chains can be an important tool to control the morphology of polymers with a rigid backbone.

     

Phase Behavior of Amphiphilic Molecules in the Presence of One Solvent: A Dissipative Particle Dynamics Study

We simulate the phase behavior of amphiphilic molecules in the presence of one solvent by DPD. In general, DPD has successfully captured most of the effects of composition of amphiphilic molecules, solvent selectivity, and solvent amount, on the phase transition behavior obtained by both SCMF calculations and experiments. When a neutral good solvent is added, the solutions undergo a lyotropic transition analogous to the thermotropic transition in the melts. Furthermore, the order‐disorder transition results obtained via DPD are in good agreement with theoretical predictions by including the fluctuation effects, as well as with experiments. In the selective solvents, various transitions from the “normal” phases (i.e., the minority blocks form the minor domains) to even the “inverted” phases (formed by the majority blocks) have been observed by varying solvent selectivity and solvent amount. Since the packing order of the spheres is greatly affected by the finite size of the simulation box, it becomes difficult to examine the most stable packing array of spheres via DPD as has been predicted by SCMF theory. However, DPD reveals a possible spherical order of A15, which has been ignored in current SCMF work but observed in some amphiphilic molecule systems.

     

Dissipative Particle Dynamics Simulations of Polymer Brushes: Comparison with Molecular Dynamics Simulations

Summary: The structure of polymer brushes is investigated by dissipative particle dynamics (DPD) simulations that include explicit solvent particles. With an appropriate choice of the DPD interaction parameters , we obtain good agreement with previous molecular dynamics (MD) results where the good solvent behavior has been modeled by an effective Lennard–Jones potential. The present results confirm that DPD simulation techniques can be applied for large length scale simulations of polymer brushes. A relation between the different length scales and is established.

Polymer brush at a solid–liquid interface.     

嵌段共聚物组成对薄膜形貌影响的多体耗散粒子动力学研究

利用多体耗散粒子动力学(Multibody Dissipative Particle Dynamics, Multibody DPD)方法研究了在溶剂蒸发条件下, 嵌段共聚物在表面自组装形成薄膜的过程, 分别考虑了两嵌段共聚物和三嵌段共聚物及不同组成对薄膜形貌的影响. 模拟得到了无序状薄膜和层状薄膜, 并计算了这些薄膜的序参量和薄膜厚度随时间的演化. 结果表明, 嵌段共聚物的组成对薄膜厚度几乎没有影响, 当某种组分的链段很短时, 只能形成序参量较小的无序薄膜, 相反, 则可以得到序参量较大的层状薄膜.