We critically review dissipative particle dynamics (DPD) as a mesoscopic simulation method. We have established useful parameter ranges for simulations, and have made a link between these parameters and χ-parameters in Flory-Huggins-type models. This is possible because the equation of state of the DPD fluid is essentially quadratic in density. This link opens the way to do large scale simulations, effectively describing millions of atoms, by firstly performing simulations of molecular fragments retaining all atomistic details to derive χ-parameters, then secondly using these results as input to a DPD simulation to study the formation of micelles, networks, mesophases and so forth. As an example application, we have calculated the interfacial tension σ between homopolymer melts as a function of χ and N and have found a universal scaling collapse when σ/ρkBTχ0.4 is plotted against χN for N>1. We also discuss the use of DPD to simulate the dynamics of mesoscopic systems, and indicate a possible problem with...

https://www.physics.iitm.ac.in/~iol/lecture_notes/groot-warren.pdf

Dissipative particle dynamics : bridging the gap between atomistic and mesoscopic simulation

The dissipative particle dynamics (DPD) simulation method has been used to study mesophase formation of linear (AmBn) diblock copolymer melts. The polymers are represented by relatively short strings of soft spheres, connected by harmonic springs. These melts spontaneously form a mesocopically ordered structure, depending on the length ratio of the two blocks and on the Flory–Huggins χ-parameter. The main emphasis here is on validation of the method and model by comparing the predicted equilibrium phases to existing mean-field theory and to experimental results. The real strength of the DPD method, however, lies in its capability to predict the dynamical pathway along which a block copolymer melt finds its equilibrium structure after a temperature quench. The present work has led to the following results: (1) As the polymer becomes more asymmetric, we qualitatively find the order of the equilibrium structures as lamellar, perforated lamellar, hexagonal rods, micelles. Qualitatively this is in agreement wi...

Dynamic simulation of diblock copolymer microphase separation

Strategies for compatibilization of polymer blends

The use of supercritical carbon dioxide as a processing solvent for the physical processing of polymeric materials is reviewed. Fundamental properties of CO2/polymer systems are discussed with an emphasis on available data and measurement techniques, the development of theory or models for a particular property, and an evaluation of the current state of understanding for that property. Applications such as impregnation, particle formation, foaming, blending, and injection molding are described in detail including practical operating information for selected topics. The review concludes with some forward-looking discussion on the future of CO2 in polymer processing.

A Review of CO2 Applications in the Processing of Polymers

The thermodynamic and dynamic properties of a partially deuterated poly(ethylene‐propylene)–poly(ethylethylene)(PEP–PEE) diblock copolymer containing 55% by volume PEP were characterized above and below the order–disorder transition (ODT) by small‐angle neutron scattering (SANS) and rheological measurements, respectively. Both experimental techniques produced unambiguous evidence of composition fluctuations well above TODT(T−TODT≲50 °C) in the disordered state, which increase in magnitude as the weak first‐order transition is approached. Based on the SANS results, which are nearly predicted by a recent fluctuation theory, we conclude that the (equilibrium) instantaneous morphology in the disordered state closely resembles a spinodally decomposed binary mixture. Below TODT, long‐range order can be obtained by the application of a shear field as evidenced by the resulting highly anisotropic (one‐dimensional) SANS pattern. As the ODT is approached in the shear‐oriented ordered state, an isotropic scattering ...

Fluctuation effects in a symmetric diblock copolymer near the order–disorder transition

Etude en fonction de la concentration de l'additif pour le systeme ternaire polystyrene/polybutadiene-1,2/poly(styrene-block-butadiene-1,2)

Compatibilizing effect of block copolymers added to the polymer/polymer interface

: Interfacial tensions between immiscible homopolymers are measured using an automated pendant drop apparatus, which utilizes Video Digital Image Processing techniques. A recently developed robust shape analysis algorithm is used to analyze the experimental drop profiles. The data show the effect of temperature and number average molecular weight (Mn) on the interfacial tension for the immiscible blends polystyrene-poly(methyl methacrylate), polybutadiene-poly(dimethyl siloxane) and polystyrene-hydrogenated 1,2 polybutadiene. Interfacial tension decreases linearly with temperature and increases with molecular weight. The data for all three systems can be approximated by an empirical relationship. The interfacial tension data for the latter blend system are compared with thermodynamic theories of polymeric interfaces. A square gradient theory approach, in conjunction with the Flory-Huggins expressions for the free energy of mixing, predicts a magnitude and temperature dependence of interfacial tension which are in reasonable agreement with experimental data, and does predict a molecular weight dependence which roughly follows the empirical relationship.

https://apps.dtic.mil/sti/pdfs/ADA192463.pdf

Interfacial tension of immiscible polymer blends: temperature and molecular weight dependence

The influence of morphological transitions on the hydrogen-bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The materials examined are a noncrystalline polyurethane hard segment, a crystallizable polyurethane hard segment, and a segmented polyurethane block copolymer containing crystallizable hard segments. Integrated absorbance data show that the hydrogen-bonding behavior is insensitive to crystalline transitions within the hard segment microdomains, but that it does reflect morphological transitions in the block copolymer that are associated with intersegmental mixing. In addition, the spectral data show conclusive evidence for reversal of the urethane reaction at high temperatures.

The effects of morphological transitions on hydrogen bonding in polyurethanes: Preliminary results of simultaneous DSC–FTIR experiments

Etude par DSC et SAXS des copolymeres PS/polyisoprene, PS/polybutene et PS/polybutadiene-1,2. Comparaison des profils de diffusion obtenus avec les valeurs prevues par Leibler afin d'evaluer les parametres d'interaction et leur variation avec la temperature

Investigation of the microphase separation transition in low molecular weight diblock copolymers

: Solid state deuterium NMR spectroscopy is used to address phase separation i specifically labeled polyurethanes. The hard segment is 4,4'-diphenyl-methane diisocyanate (MDI) chain extended with 2,2,3,3,-D SUB 4 butanediol and the soft segment is polyoxypropylene end-capped with oxyethylene. The samples contain 100, 70, 60 and 50 wt% hard segment. The results show 1) that the core of the hard segment microdomains is identical to the pure hard segment material with respect to molecular motion; 2) that the amount of hard segment in the interfacial regions can be quantified; 3) that the NMR and SAXS data are in good agreement concerning the fraction of interfacial hard segment; and 4) that the interfacial hard segments undergo nearly isotropic motion on a 10,000,000/s time scale, suggesting that there are few long-lived interrurethane hydrogen bonding interactions in the interfacial area. Author keywords include: Polyurethanes; Small Angle X-ray Scattering; Microphase Separation; Deuterium NMR.

Irena Gancarz

Papers

Compatibilizing effect of block copolymers added to the polymer/polymer interface

Interfacial tension of immiscible polymer blends: temperature and molecular weight dependence

The effects of morphological transitions on hydrogen bonding in polyurethanes: Preliminary results of simultaneous DSC–FTIR experiments

Investigation of the microphase separation transition in low molecular weight diblock copolymers

Phase separation in polyurethanes. A deuterium NMR study