Search results for "Tension"
showing 10 items of 2456 documents
Limiting concepts in extensional flow
1975
A characteristic feature of extensional flows is their potential capability of determining a stable, oriented structure in liquid materials containing elongated particles. With reference to flexible linear macromolecules, either in solution or as polymer melts, the limiting conditions under which such an oriented structure is actually possible are critically reviewed. It is seen that orientation can be obtained either when entanglements are present, i.e. when the polymer molecules form some sort of network, or, if the molecules behave entirely individually, only under very special circumstances. Further, if the objective is the “freezing” of the oriented structure in a partly crystalline, h…
Ultra-coarse-graining of homopolymers in inhomogeneous systems
2021
Abstract We develop coarse-grained (CG) models for simulating homopolymers in inhomogeneous systems, focusing on polymer films and droplets. If the CG polymers interact solely through two-body potentials, then the films and droplets either dissolve or collapse into small aggregates, depending on whether the effective polymer–polymer interactions have been determined from reference simulations in the bulk or at infinite dilution. To address this shortcoming, we include higher order interactions either through an additional three-body potential or a local density-dependent potential (LDP). We parameterize the two- and three-body potentials via force matching, and the LDP through relative entr…
Interfacial Assembly and Jamming Behavior of Polymeric Janus Particles at Liquid Interfaces
2017
The self-assembly and interfacial jamming of spherical Janus nanoparticles (JNPs) at the water/oil interface were investigated. Polymeric JNPs, made by cross-linking polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (PS-PB-PMMA), with a high interfacial activity assemble at the water/oil interface. During the self-assembly at the interface, the interfacial energy was reduced and a dynamic interlayer was observed that is responsive to the pH of the aqueous phase. Unlike hard particles, the JNPs are composed of polymer chains that can spread at the liquid-liquid interface to maximize coverage at relatively low areal densities. In a pendant drop geometry, the interfacial area of …
Interfacial Tensions from Drop Retraction versus Pendant Drop Data and Polydispersity Effects
2004
Interfacial tensions sigma were measured by means of both methods for the following polymer pair: polyisobutylene (PIB 3) plus poly(dimethylsiloxane) (PDMS 152) and poly(dimethyl-co-methylphenylsiloxane) (CoP26*) plus PDMS 48. The numbers after the abbreviation state the molar masses in kilograms; the homopolymers exhibit polydispersities on the order of 2. The reliability of the method of drop retraction is backed up by systematic measurements, which demonstrate that it is possible to study the time evolution of sigma. Because of the free choice of the phases (drop or matrix) and the possibility to vary the overall composition of the system in a wide range, drop retraction yields more info…
Effect of random copolymer additives on the interfacial tension between incompatible polymers
1998
Interfacial tensions γ were measured for mixtures of poly(methylphenylsiloxane) (4 kg/mol) and poly(dimethylsiloxane) (24 kg/mol) in the absence and in the presence of small amounts of the random copolymer poly(dimethylsiloxane-ran-methylphenylsiloxane) (89 mol-% of dimethylsiloxane units, 28 kg/mol) from 25 to 110°C. Approximately 1 wt.-% of the copolymer additive suffices to reduce γ from ca. 2.2 to 1.6 mN/m. The time dependence of the apparent γ value in the course of the attainment of equilibria also indicates surface acivity. The hypothesis is formulated that the efficiency of the random copolymer for a reduction of γ is bound to the condition that it is only sparingly soluble in both …
Self-organization of hydrophobized polyzwitterions
1992
Abstract Several series of copolymers of different geometry were synthesized from zwitterionic surfactant monomers and polar non-ionic comonomers. Bulk properties were investigated by d.s.c. and X-ray scattering. The copolymers were amorphous, but exhibited superstructures up to high commonomer contents. Solubility of the copolymers was determined as a function of geometry and composition. From the results, a main chain spacer model has been derived. All water-soluble copolymers exhibited characteristic features of classical polysoaps, as shown by surface tension measurements and by solubilization of pyrene. But gradual differences depending on the polymer geometry were observed for the sol…
Modeling the nonlinear deformation of flax-fiber-reinforced polymer matrix laminates in active loading
2015
In an attempt to fully utilize the mechanical properties of bast fibers in polymer-matrix composites, unidirectional (UD) or quasi-UD flax-fiber-reinforced composites are being developed and characterized. Their response in tension is markedly nonlinear both in on- and off-axis loading. A semiempirical tensor-linear model is applied to describe such deformation nonlinearity in active combined loading. The deformation model of UD ply, combined with an elementary laminate theory, is used to predict the stress–strain curves of laminated composites in tension. Reasonable accuracy of prediction is demonstrated for fiber-dominated layups.
Modeling the non-linear deformation of a short-flax-fiber-reinforced polymer composite by orientation averaging
2013
Abstract The growing usage of short-flax-fiber-reinforced polymer composites in such applications as automotive industry necessitates the prediction of their mechanical response up to and beyond the limit of elasticity. Due to the imperfect, mechanical interlocking-dominated adhesion of natural fibers to most polymers, both fiber debonding and matrix yielding contribute to the non-linear deformation. In the present study, the deformation under an active loading of a short misaligned fiber composite is modeled by the orientation averaging approach, employing an analytical description of the behavior of a unit cell (UC), the parameters of which are determined using a FEM analysis of UC respon…
Evaluation of interfacial shear strength by tensile tests of impregnated flax fiber yarns
2011
Adhesion of flax fibers and polymer matrix as well as mutual bonding of elementary fibers in a technical fiber are among the principal factors governing the mechanical response of flax fiber-reinforced polymer–matrix composites. A method for evaluation of adhesion is proposed based on tension tests of impregnated fiber yarns, with subsequent characterization by optical microscopy of length distribution of fibers pulled out of the yarn fracture surfaces. An elementary probabilistic model is derived relating aspect ratio distribution of the pulled-out fibers to the fiber tensile strength distribution and the effective interfacial shear strength (IFSS). The method was applied to flax fiber/vi…
Model analysis of uniaxial and biaxial stretching of polymer melts
1976
The biaxial extension results byDenson et al. are compared with the predictions of a model of non-linear viscoelasticity. Date of uniaxial extension on the same material (a commercial polyisobutylene) are taken for extending the comparison. The model used seems to adequately describe both types of elongational flow with the same value of the single adjustable parameter.