Mesophase Separation of Diblock Copolymer Confined in a Cylindrical Tube Studied by Dissipative Particle Dynamics

Summary: The morphologies of diblock copolymers confined in a cylindrical tube have been investigated by the dissipative particle dynamics (DPD) method. Results indicate that the morphology depends on the volume ratio of the immiscible blocks, the diameter of the cylindrical tube and the interactions between the blocks and between the confinement wall and blocks. For symmetric diblock copolymers, when the tube wall is uniform toward the two blocks, perpendicular lamellae or a stacked disk morphology are generally formed except when the diameter of the cylindrical tube is very small; in that case, a special bi‐helix morphology forms because of the entropy effect. When the tube wall is non‐uniform, as the diameter of the tube increases, perpendicular lamellae are first formed, then changing to parallel lamellae and, finally, back to perpendicular lamellae again. An intermediate morphology characterizing the transition between perpendicular and parallel lamellae is observed. If the non‐uniformity of the wall is further enhanced, only parallel lamellae can be found. In the case of asymmetric diblock copolymers, more complex morphologies can be obtained. Multi‐cylindrical micro‐domains and a multilayer helical phase as well as other complex pictures are observed. Generally, the morphologies obtained could find their counterparts from experiments or Monte Carlo simulations; however, differences do exist, especially in some cases of asymmetric diblock copolymers.

Bi‐helix and stacked disks morphologies of A₅B₅ diblock copolymer confined in two different neutral nanocylinders.     

无界算子扰动下随机发展系统的稳定性

柱布朗运动是布朗运动在无穷维空间上的一种重要实现。考虑一类实可分Hilbert空间上被无界算子扰动的关于柱布朗运动的随机发展系统的稳定性问题。运用线性算子半群理论给出了分别使得此系统稳定、使其L^2－连续发展解指数稳定及使其发展解指数稳定的状态反馈控制律,且稳定关于无界扰动算子族是一致的。     

Advanced functional safeguarding composites with enhanced anti-impact and excellent thermal properties

Personal safety protection has played an important role in daily life. Developing advanced functional safeguarding composites with enhanced anti-impact and excellent thermal properties will be a significant development for body armor. Herein, Kevlar fiber reinforced polymers (KFRP) were fabricated by introducing short Kevlar fibers (KFs) into a shear stiffening elastomer (SSE). The storage modulus of KFRP with 15 wt% KFs (KFRP-15%) increased from 222.8 kPa to 830.8 kPa when the shear frequency varied from 0.1 Hz to 100 Hz. KFRP-15% achieved a higher tensile strength (2.65 MPa) and fracture toughness (11.95 kJ/m2) than SSE in the vertical type, showing superior tear resistance. Additionally, KFRP-15% exhibited promising anti-impact properties, which could dissipate the drop hammer impact force from 1.74 kN to 0.56 kN and remained intact after 10 consecutive impacts. Moreover, KFRP-15% also presented excellent stab-resistant performance. In addition, KFRP-15% also showed improved heat transfer properties, flame retardancy, and smoke suppression capabilities. Finally, functional bracers based on KFRP-15% for protection, thermal-dissipation, and flame-retardant were successfully prepared.     

X-ray investigations concerning the physical structure of cross-linking in segmented urethane elastomers

In the X-ray diagrams of some segmented urethane elastomers, so-called hard-segment interferences can be observed which indicate a defined geometrical accumulation of the hard segments. These interferences can easily be traced back to a system of hydrogen bridges between the hard segments. They allow an insight into the geometrical structure of the cross-linking as well as into the mechanism of elongation and thermosetting.     

空间圆柱形目标的热效应研究

应用热网络法和数值分析法,对空间圆柱形目标的热效应作了初步研究,并对两种不同形状气球的热效应进行了对比。     

RATE DEPENDENT STRESS-STRETCH RELATION OF DIELECTRIC ELASTOMERS SUBJECTED TO PURE SHEAR LIKE LOADING AND ELECTRIC FIELD

The performance of dielectric elastomer(DE) transducers is significantly affected by viscoelastic relaxation-induced electromechanical dissipations.This paper presents an experimental study to obtain the rate dependent stress-stretch relation of DE membranes(VHB TM 9473) subjected to pure shear like loading and electric loading simultaneously.Stretching rate dependent behavior is observed.The results also show that the tensile force decreases as the voltage increases.The observations are compared with predictions by a viscoelastic model of DE.This experiment may be used for further studies of dynamic electromechanical coupling properties of DEs.     

VISCOELASTICITY AND POROELASTICITY IN ELASTOMERIC GELS

An elastomeric gel is a mixture of a polymer network and a solvent.In response to changes in mechanical forces and in the chemical potential of the solvent in the environment,the gel evolves by two concurrent molecular processes:the conformational change of the network,and the migration of the solvent.The two processes result in viscoelasticity and poroelasticity,and are characterized by two material-specific properties:the time of viscoelastic relaxation and the effective diffusivity of the solvent through the network.The two properties define a materialspecific length.The material-specific time and length enable us to discuss macroscopic observations made over different lengths and times,and identify limiting conditions in which viscoelastic and poroelastic relaxations have either completed or yet started.We formulate a model of homogeneous deformation,and use several examples to illustrate viscoelasticity-limited solvent migration,where the migration of the solvent is pronounced,but the size of the gel is so small that the rate of change is limited by viscoelasticity.We further describe a theory that evolves a gel through inhomogeneous states.Both infinitesimal and finite deformation are considered.     

SOLUTIONS FOR CYLINDRICAL CAVITY IN SATURATED THERMOPOROELASTIC MEDIUM

Based on the thermodynamics of irreversible processes, the mass conservation equation and heat energy balance equation are established. The governing equations of thermal consolidation for homogeneous isotropic materials are presented, accounting for the coupling effects of the temperature, stress and displacement fields. The case of a saturated medium with a long cylindrical cavity subjected to a variable thermal loading and a variable hydrostatic pressure （or a variable radial water flux） with time is considered. The analytical solutions are derived in the Laplace transform space. Then, the time domain solutions are obtained by a numerical inversion scheme. The results of a typical example indicate that thermodynamically coupled effects have considerable influences on thermal responses.     

Multicriteria optimization of a composite cylindrical shell subjected to longitudinal thermal stresses and buckling under the action of torque

The multicriteria optimization of the structure and geometry of a multilayer cylindrical shell under the action of external torque and longitudinal thermal stresses is considered. From known monolayer properties of the composite and given values of variable structural and geometric parameters, the thermoelastic properties of the anisotropic layered composite are determined. The criteria to be optimized — the critical external torque and thermal stresses — depend on two variable parameters and temperature. In the space of optimization criteria, the domain of allowable solutions and the Pareto-optimal subdomain are found. Translated from Mekhanika Kompozitnykh Materialov, Vol. 45, No. 2, pp. 223–230, March–April, 2009.     

Reports on progress in polymer physics in Japan

The Calm microbalance system for plasticizer absorption in PVC resin has been used to study the different absorption behaviors of two different plasticizer systems [diisodecyl phthalate (DidP) and a mixed system] on resins of various origins [50-gal reactor and the large reactor pilot plant (LRPP)] and polymerization conditions [different killing pressures (conversion) and two different chemical additives]. The results show that these two chemical additives do not affect the plasticizer capacity of resin but do increase the maximum rate of plasticizer absorption. Killing pressure (conversion) affects both capacity and rate of absorption.