Yongmin Huang

Simulation of Morphologies and Mechanical Properties of A/B Polymer Blend Film

Abstract The effects of blend composition and micro-phase structure on the mechanical behavior of A/B polymer blend film are studied by coupling the Monte Carlo (MC) simulation of morphology with the lattice spring model (LSM) of micro mechanics of materials. The MC method with bond length fluctuation and cavity diffusion algorithm on cubic lattice is adopted to simulate the micro-phase structure of A/B polymer blend. The information of morphology and structure is then inputted to the LSM composed of a three-dimensional network of springs to obtain the mechanical properties of polymer blend film. Simulated results show that the mechanical response is mainly affected by the density and the composition of polymer blend film through the morphology transition. When a force is applied on the outer boundary of polymer blend film, the vicinity of the inner cavities experiences higher stresses and strains responsible for the onset of crack propagation and the premature failure of the entire system.

Mechanical properties of high-performance elastomeric nanocomposites: a sequential mesoscale simulation approach

The incorporation of nanoparticles into elastomeric block copolymers affords engineers an opportunity to obtain polymer nanocomposites that potentially rival the most advanced materials in nature. A computationally efficient simulation method that utilized MesoDyn for the morphologies and the lattice spring model (LSM) for the mechanical properties was adopted in this work. The simulation results show that the selective distribution of nanoparticles in hard or soft segment microdomains of block copolymers will narrow the phase domain size in bicontinuous structures. The Zener model was incorporated into pure elastic LSM to capture the stress relaxation behavior. Mechanical tests reveal that the stress transfer between the polymer matrix and nanoparticles in different composites is critical to the stiffness enhancement. In dispersed structures, adding nanoparticles in a hard microdomain can increase the elastic modulus and maintain high extensibility without impairing its viscosity dramatically. The methods developed in this work yield guidelines for formulating elastomeric nanocomposites with desired macroscopic mechanical responses.

Transport of mixed solvents in glassy polymer membrane

Transport of mixed solvents in polymer membrane was investigated using quartz spring weighing method. Absorption kinetic curves for two mixed solvent systems, ethanol/1,2-dichloroethane and ethanol/ethyl acetate, in polyurethane (PU) were measured. Solubility of solvent in PU membrane was studied using a model that incorporates Henry law and BET adsorption theory. Taking into account the interactions between different solvents, a dual-mode transport model for mixed solvents in glassy polymer membrane was developed to fit the experimental data. The correlation is satisfactory. The same set of parameters can be used to fit the data over a wide range of concentrations indicating the prediction potential of the model.

Multiscale simulation of shear-induced mechanical anisotropy of binary polymer blends

Mechanical properties of polymer blends are not only determined by characteristics of individual polymer but also depend significantly on processing such as shear fields. A sequential mesoscopic simulation method was adopted to study the influence of shear processing on morphology orientation and mechanical responses. This method utilizes mesoscopic dynamic simulation (MesoDyn) for structural evolution and lattice spring model (LSM) for correlating the structure and mechanical behaviour. The dispersed phase in meso-structures moves from spherical to elliptical and then to columnar structure with the increase of shear rates. The morphology orientation leads to the anisotropy of elastic modulus. During the tensile test, different fracture processes were observed with two kinds of toughness relationship in blends which correspond to brittle phases dispersed in a ductile matrix and in reverse ductile phases dispersed in a brittle matrix. The tensile strength along shear processing direction increases with the increase of shear rates when the dispersed phase is ductile, while the strength decreases when the dispersed phase is brittle. The strength perpendicular to shear processing direction is mainly related to the soft matrix and interfacial strength. The morphologies of polymer blends at different shear rates and their corresponding mechanical behavior are well correlated by the mesoscopic simulation. The simulation results also yield guidelines to manufacture desired polymer blends with shearing process, e.g. extrusion or injection molding.

Effect of Polymer-Substrate Interactions on the Surface Morphology of Polymer Blend Thin Films: Comparison between Simulation and Experiment

Microphase and macrophase separation phenomena can simultaneously appear in ABA/C copolymer blend systems due to the immiscibility among monomers A, B, and C. In this work, the surface morphologies and compositions of ABA/C blend thin films confined between two walls, which were used to mimic SEBS/PMMA films, have been simulated by a lattice Monte Carlo (MC) method. The effect of the polymer-wall interaction on the surface morphologies and compositions of thin films was investigated as a function of blend composition and film thickness. It is shown that the simulated surface morphologies of thin films resulting from the macrophase separation between copolymer ABA and homopolymer C and the microphase separation between block A and block B in ABA copolymer are similar to the experimental surface morphology of SEBS/PMMA polymer blend films observed by atomic force microscope (AFM). The effect of substrate on the surface morphologies by MC simulation is qualitatively consistent with the experimental results. The composition profiles of thin films are given to characterize the micro- and macrophase separation in thin films. It is indicated that the surface energy of the substrate (substrate/air) plays a crucial role on the surface composition. For a fixed surface, the adsorptions of polymer on the substrate and film thickness are also important.

Electrical Properties and Stability of Poly(N-isopropylacylamide-co-methacrylic Acid) Core-Shell Microgel

Graphical Abstract: A doubly responsive microgel with core shell shape was prepared by seed polymerization. The electrical properties were characterized. The latex stability was evaluated and discussed according to the colloid theory. A core-shell microgel of poly(N-isopropylacylamide-co-methacrylic acid) was prepared by seeded polymerization. Dynamic light scattering measurements indicated that the microgel had a narrow size distribution. Zeta potential decreased gradually with increasing ionic strength, and when salinity reached a certain concentration the surface charge was almost screened out. Further addition of salt led to the shrinking and final flocculation. For increasing temperature, the zeta potential under higher ionic strength exhibited an abrupt change for trending to zero. Total interaction energy between particles was calculated with colloid theory. Meanwhile, thermal stability was evaluated and interpreted the experimental phenomenons.

Micro-phase separation and configuration of ABC triblock copolymer in ultra-thin film by Monte Carlo simulation

A Monte Carlo simulation using the bond fluctuation and cavity diffusion algorithms was adopted to investigate the micro-phase separation of ABC triblock copolymer in ultra-thin film on simple cubic lattice. Simulations reveal that the morphologies of ABC copolymer films are dependent on not only the volume fraction of the middle block B (f B) but also on the ratio of interaction between different kinds of blocks (ϵ(AC)/ϵ(AB)). As for the molecular orientation, the copolymers stretch parallel to the flat surface at lower f B, but tend to align perpendicularly along z direction at higher f B. Furthermore, the chain configuration was discussed in detail. Smaller ϵ(AC)/ϵ(AB) is beneficial to the formation of a “loop” configuration, whereas, larger ϵ(AC)/ϵ(AB) would result in a “bridge” configuration of ABC triblock copolymer chains. The formation of micro-phase structures was illustrated intuitively by the molecular orientation and the chain configuration.

Molecular Thermodynamic Models for Fluids of Chain-Like Molecules, Applications in Phase Equilibria and Micro-Phase Separation in Bulk and at Interface

Abstract Molecular thermodynamic models based on lattice framework have been widely applied to study the thermodynamic properties and the phase behaviors of chain-like fluids. Recently, we have developed a new molecular thermodynamic model by combining statistical mechanics theory with computer simulation. The effects of branching, coordination number, chain stiffness, composition, hydrogen bonding and pressure on thermodynamic properties and phase behaviors can be well described by the new model. Satisfactory agreement is obtained between the predicted results and Monte Carlo (MC) simulation data for multicomponent Ising and Flory–Huggins lattice systems. The model can be used to satisfactorily correlate phase equilibria including vapor–liquid and liquid–liquid equilibria for the mixtures of ordinary fluids, polymers, and ionic liquids. Incorporated with density functional theory (DFT) for nonuniform fluids and weighted-density approximation (WDA), the model can also be used to describe the adsorption of polymer at solid–liquid interface and conformation distributions at interfacial regions. For the morphologies of micro-phase separation of diblock copolymers confined in curved surfaces, a framework has been developed based on the strong segregation limit (SSL) theory. The SSL predictions agree well with simulation and experimental results on multilayer transitions. Upon comparison between theoretical predictions and MC simulations, we have established a numerical calculation method of the Helmholtz energy for a special structure called the complex multilayered sector column (CMSC) structure. Finally, the detailed theoretical studies together with simulations indicate that the CMSC structure tends to be formed at higher thickness, while the mutually competing concentric cylinder barrel and the sector column structures appear at lower thickness.