Search

Spatial gradient materials occupy an important research position in the field of functional materials with their unique porous structure. Gradient changes in pore size and density distribution have received extensive attention in the fields of biomimetic and smart materials. The gradient transition law is mathematically related to the driving force of isomerization reaction and component phase separation. In this study, a dissipative particle dynamics simulation is used to introduce photoisomerization reactions into the system. Lambert's law is used to construct a reaction model for the variation of light intensity with irradiation depth, and a gradient structure with a spatial transition law is obtained. The effects of the extinction coefficient ε, the initial reaction probability Pr0, and the interactions α(A,B) between the isomerized molecules as well as the viscosity on the formation of the gradient structure are investigated in detail. Furthermore, the mathematical proportionality between the size of the phase region and interfacial energy of the two phases is elucidated. This study provides preliminary computational insights into the factors affecting the photoinduced phase separation process of polymeric gradient materials. It may help to develop effective strategies to improve the phase separation and properties of polymer gradient materials in subsequent studies. [ABSTRACT FROM AUTHOR]

Lignin, a renewable aromatic polymer, has great potential as a synthetic building block for functional materials. The effects of quaternary ammonic methylation of alkali lignin (AL) on the morphologies and ofloxacin antibiotic (OA) removal application from water are investigated by using the dissipative particle dynamics (DPD) simulation method. Untreated AL can form spherical aggregates, but the phenylpropane units of untreated AL and loaded broad‐spectrum OA molecules are randomly distributed in aggregates. However, if quaternary ammonic groups are grafted onto all orthopositions of the phenolic hydroxyl groups (100‐QAMAL), then multilamellar spherical aggregates are obtained and OA molecules are entrapped in the aggregates. To prepare multilamellar spherical aggregates with an ordered and regular layered structure, <15 v% of 100‐QAMAL and low molecular weights of AL (≈4700–9400 Da) are suggested to be used. Lignin‐based multilamellar spherical aggregates can be adopted as potential functional carriers for removing pollutant OA from water. [ABSTRACT FROM AUTHOR]

Poly(aryl ether sulfone ketone) (PPESK) is an engineering plastic with high strength, good heat resistance, insulation, and chemical corrosion resistance. The properties of PPESK fiber prepared by centrifugal melt electrospinning can be improved, and the method is efficient and environmentally friendly. This article employs a systematic analysis to investigate the impact of process parameters on the jet formation process, jet motion, fiber diameter, fiber yield, and changes in molecular chain orientation of PPESK. The analysis uses dissipative particle dynamics simulation to reveal that PPESK fibers can attain a certain degree of refinement, and fiber yield can be increased with an appropriate increase in rotational speed, temperature, and electric field force. Moreover, for PPESK with different chain lengths, longer molecular chains impede the untwisting of the molecular chains within the fiber, weakening the fiber orientation, increasing fiber diameter, and resulting in a slower fiber yield increase. These simulation results provide theoretical guidance for preparing PPESK ultrafine fibers with the required performance, shortening the exploration process of actual spinning, and saving time and labor. [ABSTRACT FROM AUTHOR]

The suitability of dissipative particle dynamics simulations is investigated to predict the dynamics of polymer chains in dilute polymer solutions. The authors find that the predictions depend on the value of the repulsive parameter for bead‐bead pairwise interactions used in the DPD simulations (aij). For all systems, the chain sizes and the relaxation time spectrum are analyzed. For aij = 0, theta solvent behaviour is obtained, whereas the dynamics at equilibrium agrees well with the predictions of the Zimm model. For higher values of aij, the static properties of the chain show good solvent behaviour. However, the scaling laws for the chain dynamics at equilibrium show wide variations, with consistent results obtained only at an intermediate value of aij = 25. At higher values of the repulsive parameter (aij ⩾ 25), the simulations are also able to predict the abrupt cut‐off in the relaxation spectrum, which has been observed earlier in experiments of dilute solutions. To verify further, the chain dynamics in shear flow using DPD simulations is studied. Specifically, the variation of the chain is analysed stretch and end‐over‐end tumbling with shear rates. Overall, the trends obtained from DPD simulations agree well with those observed in earlier BD simulations. [ABSTRACT FROM AUTHOR]

Given the importance of preserving the mechanical properties of recycled isotactic polypropylene (iPP) during its processing, this work provides an improved understanding of the contribution of introducing physical or chemical crosslinks using the dissipative particle dynamics (DPD) method, which makes it possible to model iPP structures with a realistic range of crosslink densities. First, the protocol to build a coarse‐grained model of iPP from an all‐atom expression by Bayesian optimization is described. A Bayesian optimization procedure employing two different cutoff distances successfully provides optimal DPD parameters reproducing iPP's properties compared to the all‐atom system. Then, the coarse‐grained iPP model with optimal DPD parameters is applied to study structures containing a realistic range of crosslink densities to evaluate their mechanical properties. These calculations demonstrate that the mechanical properties such as the Young's modulus and ultimate strength increase while the fracture strain decreases with an increase in the crosslink density, which is consistent with experimental observations. The results also show that there is a critical crosslink density above which these properties start to be improved due to the introduction of crosslinks. These findings can help us to obtain targeted properties of recycled iPP by introducing physical or chemical crosslinks. [ABSTRACT FROM AUTHOR]

The general lack of knowledge on the dynamics of polymer vesicles under flow field has confounded their applications in drug delivery and other fields. Therefore, dissipative particle dynamics (DPD) simulations on the dynamic behavior of diblock copolymer vesicles in a nanochannel under Poiseuille flow are conducted. The simulation results show that the block copolymer vesicles with hydrophobic blocks of different rigidities exhibit significantly different mechanical stabilities under the flow fields. With increasing the Reynolds number, the coil–coil block copolymer vesicles undergo a shape transition from spherical to bullet‐like to asymmetric and eventually split into two parts. In contrast, the rod–coil block copolymer vesicles deform from spherical to bullet‐like to parachute‐like structures and ultimately ruptured. The flow‐induced distortion and reorganization of copolymers mainly cause the deformation of vesicles. The distinguished motions of the block copolymers with different rigid blocks lead to the distinct performance of the vesicles. The findings could help understand the flow behavior of polymer vesicles in a nanochannel or a blood vessel and assist the design of bio‐functional polymersomes. [ABSTRACT FROM AUTHOR]

Proton transport in proton exchange membrane is considered to depend on the hydrophilic domain formed by the microphase separation between hydrophobic and hydrophilic segments of the membrane. Therefore, the study of hydrated morphologies is crucial to understand proton transport. Here, the mesoscopic structure of sulfonated polyether ether ketone (SPEEK) membrane and SPEEK/polyethersulfone (PES) blend membrane is investigated by dissipative particle dynamics (DPD) simulation. The degree of sulfonation, water content, and PES content are considered to affect proton transport. Results show that the hydrophilic particles combine with water and are separated from hydrophobic particles to form clusters of different sizes. For the SPEEK membrane, with the increase in the sulfonation degree, clusters become large and begin to connect. Compared with isolated clusters at low water content, water clusters become large with increased water content. When water content λ = 16, the cluster size is the largest. The addition of PES accelerates the phase separation in the membrane and increases the size of water clusters. When SPEEK/PES = 4:6, the cluster size is the largest and provides the best proton transport pathway. [ABSTRACT FROM AUTHOR]

The problem of slowing down the rate of DNA translocation through a nanopore so as to facilitate detection of the genetic information remains a major challenge. In this study, the effectiveness of employing corrugated nanopores to reduce the polymer translocation velocity is investigated using dissipative particle dynamics (DPD) simulations. The average translocation time, <τ>, increases with the pore length and extent of variation of the pore cross‐sectional area. A systematic comparison of <τ> between flat and corrugated nanopores with walls that are either neutral or attractive for the polymer is performed. The value of <τ> for a corrugated nanopore with an attractive wall is 158% greater than that for a flat pore with a neutral wall. The extent of increase in <τ> obtained by manipulating either the geometry of the pore or the nature of its interaction with the polymer alone is significantly smaller. This is because the combined effect of monomer‐pore interactions and the spatial variation of the electric field strength significantly slows down the entry and escape of the chain from the pore. [ABSTRACT FROM AUTHOR]

Blends prepared by mixing incompatible homopolymers with a compatibilizing copolymer attract high technological interest due to their self‐assembling behavior. In the present work, 281 dissipative particle dynamics (DPD) simulations are performed in order to evaluate the influence of copolymer microstructure and concentration on properties of these systems. The results show that alternate copolymers are arranged between the homopolymeric phases while nanodomains rich in each of the components are formed in the copolymeric matrix. Dispersion in block lengths increases the size of these nanodomains, so that they can properly allocate homopolymer chains. Besides, dispersions in chain lengths and chemical compositions of diblock copolymers, which can form self‐assembled mesostructures, also lead to development of larger mesophase domains. Larger dispersions of chain lengths and chemical compositions cause the increase of the amount of copolymers necessary to bring about changes in the mixing behavior, when compared to non‐dispersed copolymers. It can be concluded that microstructural properties of the copolymer exert a decisive impact on molecular interactions and, consequently, on the characteristics of the mesophases generated during the blending process. Therefore, microstructure control methods, stemming from both polymer‐reaction engineering and polymer‐purification techniques, are important for the design and resulting performance of the analyzed blends. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics (DPD) is used to predict the mechanical properties of crosslinking-polyisoprene (PI) reinforced by single-walled carbon nanotube (SWCNT). The role of the increasing concentration of SWCNT up to 8% in morphology of PI composite is investigated. The carbon nanotube (CNT) restricts the polymer movement as indicated by the reduction of mean square displacement and the end-to-end distance. The analysis of CNT bundle reveals that the CNT forms bundle of many sizes depending on its concentration. The mechanical reinforcement of the PI composites is attributed to the restricted motion of crosslinked entangled polyisoprene and to the alignment of aggregated CNT along the elongation direction. However, the DPD alone fails to account for the change in Young's modulus of the composite system as a function of the SWCNT concentration. Using the modified segmental repulsive potential (mSRP), which prevents polymeric chain crossing and enhances polymer entanglement, can address this shortcoming. The mSRP is necessary for correct description of mechanical reinforcement in a polymer composite system. To obtain quantitative agreement with the experimental modulus, the polyisoprene interaction parameter is modified from the published value by 10%. This modified parameter is found to work well for the simulation of polyisoprene composites. [ABSTRACT FROM AUTHOR]

Abstract: In this study, dissipative particle dynamics is employed to investigate the complexation of poly(amido amine) dendrimer and single‐stranded DNA (ssDNA). A coarse‐grained model for ssDNA is constructed, which reproduces correctly the conformational behavior of the ssDNA molecules. The effects of pH, dendrimer generation, ionic strength, and dendrimer/ssDNA charge ratio on DNA–dendrimer complexes are explored. Simulation results show that ssDNA molecules can be significantly condensed by dendrimers and stable complexes are obtained by regulating the pH value. The ssDNA chain penetration would complicate its release from dendrimer, while this can be tuned by different generations of dendrimer. Salt concentration affects the size and stability of the complexes through ion screening effect. Dendrimer/ssDNA charge ratio can be used to control the size and morphology of the complex. This work can help design dendrimer‐based gene vectors. [ABSTRACT FROM AUTHOR]

The formation of channel membrane of polystyrene- block-poly(4-vinyl pyridine) block copolymer is studied by computer simulations with the nonsolvent induced phase separation (SNIPS) method. Dissipative particle dynamics is employed to study the microphase separation process and the SNIPS mechanism. Simulation results indicate that polymer concentration has a significant effect on the membrane structure. Channel membranes form in the copolymer concentration range of 44-58%. Block ratio plays an important role in shaping the membrane structure. Solvent exchange rate also affects the degree of microphase separation at each evolution stage of simulation. The time evolution of morphologies shows that the microphase separation processes happen with the following sequences: the polymer self-assembled and many small pores appear, then they form irregular cavities and cross-link gradually, finally the channel membrane forms. These results throw light on the formation mechanism of polymer membranes and provide insightful guidance for future membrane design and preparation. [ABSTRACT FROM AUTHOR]

Dissipative particle dynamics (DPD) models of orientation of weakly-interacting silicate particles in a polymer matrix are presented. To examine the DPD models, the evolution of orientation under shear flow is compared with the predictions of the standard orientation models, namely, the Folgar-Tucker (FT) and the strain reduction factor (SRF) models. While the orientation patterns are the same in all models, the slow orientation kinetics observed in previous experiments is only predicted in the DPD and SRF models. Since the coefficients of the SRF model are in good agreement with the experiments, the good tally between the DPD and SRF models supports the capability of DPD to successfully simulate the orientation process. The orientation in a large cell constructed from unit cells with various averaged initial orientation angles is evaluated from evolutions in the unit cells based on the affine deformation assumption. The good agreement between such calculations and SRF model predictions supports that the affine deformation assumption in the large cell is reasonable. It is argued that the nonaffine deformation originated from the particle-based nature of DPD models at the lower scale could be combined with the affine deformation at the upper scale to yield appropriate estimations of the orientation state. [ABSTRACT FROM AUTHOR]

Polydisperse linear polymers are studied in startup of steady shear flow simulations using dissipative particle dynamics. The results show that with an increase in polydispersity the stress overshoot declines while the steady-state stress increases. Various physical characteristics of the systems are studied including frequency of nonbonded interactions, gyration radius data, flow alignment angles, and average bond lengths. The patterns in the data suggest higher forces are necessary to orient and stretch long chain fractions in the flow direction. Relaxation modulus data prove the broad range of relaxation mechanisms in polydisperse systems. Linear viscoelasticity theory is used to quantify the relaxation spectrum. The results indicate an increase in the longest relaxation time in systems with higher polydispersity. The steady-state shear viscosity results show higher viscosities with an increase in polydispersity at all shear-rates. The good agreement of the characteristic behaviors of modeled polydisperse polymers with experiments is encouraging for future work. [ABSTRACT FROM AUTHOR]

The orientation of a three-layered silicate particle in uncompatibilized and compatibilized polymer melts is studied under shear flows utilizing dissipative particle dynamics (DPD). Based on trajectories, pair distribution functions are calculated in orthogonal planes. Regardless of the applied flow direction, it is shown that the layers rearrange themselves so that their surfaces would be normal to the velocity gradient direction. The maximum shear stress values fall in numerical uncertainties in uncompatibilized systems while they show a characteristic overshoot in compatibilized counterparts. This overshoot is shown to be a result of (i) the large interfaces between the silicate layers and the matrix due to the exfoliation, and (ii) the increased energy dissipation due to friction at the interface. [ABSTRACT FROM AUTHOR]

Influence of size and shape of simulation box on lamellar morphology in DPD simulation is systematically studied. The 3D Voronoi Tessellation and cluster analysis is employed. It is shown that orientation and number of lamellar planes determines the value of lamellar spacing in box with periodic boundary conditions. The role of initial conditions and relaxation scenario on lamellar morphology is also studied. Scaling the box dimensions and equalizing the diagonal pressure tensor components is used to obtain natural lamellar spacing. Where the estimation of natural lamellar spacing is unclear, the intersection of the off-diagonal components of the pressure tensor is used. Finally, examples where maximum lamellar spacing achieved by scaling of the box is smaller than the natural lamellar spacing are presented. [ABSTRACT FROM AUTHOR]

Herein, a new coarse-grained methodology for modeling and simulations of polyelectrolyte systems using implicit solvent ionic strength (ISIS) with dissipative particle dynamics (DPD) is presented. This ISIS model is based on mean-field theory approximation and the soft repulsive potential is used to reproduce the effect of solvent ionic strength. The capability of the ISIS model is assessed via two test cases: dynamics of a single long polyelectrolyte chain and the self-assembly of polyelectrolyte diblock copolymers in aqueous solutions with variable ionic strength. The results are in good agreement with previous experimental observations and theoretical predictions, which indicates that our polyelectrolyte model can be used to effectively and efficiently capture salt-dependent conformational features of large-scale polyelectrolyte systems in aqueous solutions, especially at the salt-dominated regime. [ABSTRACT FROM AUTHOR]

Polymer materials are normally constituted by chains of different sizes and compositions due to the stochastic nature of most polymerization mechanisms. For this reason, dissipative particle dynamics (DPD) simulations are carried out in the present work to investigate the effect of chain length distribution (CLD), chemical composition distribution (CCD), and block length distribution (BLD) on the process of self‐assembly of diblock copolymers. Flory and Poisson distributions are used to study CLD and BLD effects and bidispersed distributions are used for the study of CCD effects. Visual inspection and the static structure factor S(q) are used to evaluate the obtained structures. The results show that high dispersion in the CCD and different levels of dispersion in the BLDs of different components of the system increase the sizes of the segregated domains and decisively affect the structure and the purity of the formed mesophases. [ABSTRACT FROM AUTHOR]

In order to explore the relationship between drug grafting ratio of polymeric prodrug and its drug loading efficiency, molecular dynamics simulation is utilized to calculate the compatibility of polymeric prodrug with 5‐aminolevulinic acid methyl ester (m‐ALA) and H2O first. Then, dissipative particle dynamics simulation is used to observe the morphologies of drug‐loaded micelles. Then, designed polymeric prodrugs are synthesized, drug‐loaded micelles and blank micelles are prepared by dialysis method, and the drug loading content (DLC) and encapsulation efficiency are measured. The computer simulation shows that polymer–drug compatibility gets better as the m‐ALA grafting ratio increases from 0% to 100%. Experimental results show that the DLC of micelle changes from 4.05% (0% grafting ratio) to 8.99% (100% grafting ratio). Through comparison, the experimental results are proven to be consistent with the computer simulation results, revealing that the drug loading efficiency of polymer micelles could be improved by grafting drugs. [ABSTRACT FROM AUTHOR]

Front Cover: The channel membrane was successfully prepared by simulations for the first time. Dissipative particle dynamics (DPD) was used to simulate the block copolymer self‐assembly with the non‐solvent induced phase separation (SNIPS) method and effects of polymer concentration, block ratio and solvent exchange rate on the polymer self‐assembly process were investigated. This is reported by Chu Wang, Xuebo Quan, Mingrui Liao, Libo Li, and Jian Zhou* in article number 1700027. [ABSTRACT FROM AUTHOR]