Molecular dynamic simulations of elastomer structure and its influence on anisotropic stress under time-varying strain

We investigate the evolution of polymer structure and its influence on uniaxial anisotropic stress under time-varying uniaxial strain, and the role of external control variables such as temperature, strain rate, chain length, and density, using molecular dynamics simulation. At temperatures higher than glass transition, stress anisotropy in the system is reduced even though the bond stretch is greater at higher temperatures. There is a significant increase in the stress level with increasing density. At higher densities, the uncoiling of the chains is suppressed and the major contribution to the deformation is by internal deformation of the chains. At faster rates of loading stress anisotropy increases. The deformation mechanism is mostly due to bond stretch and bond bending rather than overall shape and size. Stress levels increase with longer chain length. There is a critical value of the functionality of the cross-linkers beyond which the uniaxial stress developed increases caused primarily by bond stretching due to increased constraint on the motion of the monomers. Stacking of the chains in the system also plays a dominant role in the behaviour in terms of excluded volume interactions. Low density, high temperature, low values of functionality of cross-linkers, and short chain length facilitate chain uncoiling and chain slipping in cross-linked polymers.

A preliminary investigation of Elastomer Visible Implant (EVI)tag retention rates and the effect of tagging on the growth and survival of barbel (Barbus barbus L.).

The Elastomer Visible Implant system (EVI) is a relatively new technique for batch marking fish. The aim of this study was to assess retention rates and the possible effects of tagging on the growth and mortality of barbel, Barbus barbus, (81-197mm, fork length) over approximately 2 months using a syringe injection system.

Computational analysis of liquid crystalline elastomer membranes: Changing Gaussian curvature without stretch energy

Liquid crystalline elastomers (LCEs) can undergo extremely large reversible shape changes when exposed to external stimuli, such as mechanical deformations, heating or illumination. The deformation of LCEs result from a combination of directional reorientation of the nematic director and entropic elasticity. In this paper, we study the energetics of initially flat, thin LCE membranes by stress driven reorientation of the nematic director. The energy functional used in the variational formulation includes contributions depending on the deformation gradient and the second gradient of the deformation. The deformation gradient models the in-plane stretching of the membrane. The second gradient regularises the non-convex membrane energy functional so that infinitely fine in-plane microstructures and infinitely fine out-of-plane membrane wrinkling are penalised. For a specific example, our computational results show that a non-developable surface can be generated from an initially flat sheet at cost of only energy terms resulting from the second gradients. That is, Gaussian curvature can be generated in LCE membranes without the cost of stretch energy in contrast to conventional materials. © 2013 Elsevier Ltd. All rights reserved.

Dewetting of polymethyl methacrylate on the patterned elastomer substrate by solvent vapor treatment

The dewetting evolution process of polymethyl methacrylate (PMMA) film on the flat and prepatterned polydimethylsiloxane (PDMS) substrates (with square microwells) by the saturated solvent of methyl ethyl ketone (MEK) treatment has been investigated at room temperature by the optical microscope (OM) and atomic force microscope (AFM). The final dewetting on the flat PDMS substrate led to polygonal liquid droplets, similar to that by temperature annealing. However, on the patterned PDMS substrate, depending on the microwells' structure of PDMS substrate and defect positions that initiated the rupture and dewetting of PMMA, two different kinds of dewetting phenomena, one initiated around the edge of the microwells and another initiated outside the microwells, were observed. The forming mechanism of these two different dewetting phenomena has been discussed. The microwells were filled with liquid droplets of PMMA after dewetting due to the formation of fingers caused by the pinning of the three-phase-line at the edge of the microwells and their rupture.

Synthesis and characterization of a novel biodegradable, thermoplastic polyurethane elastomer

A series of biodegradable, thermoplastic polyurethane elastomers poly (epsilon-caprolactone-co-lactide)polyurethane [PCLA-PU] were synthesized from a random copolymer Of L-lactide (LA) and epsilon-caprolactone (CL), hexamethylene diisocyanate, and 1,4-butanediol. The effects of the LA/CL monomer ratio and hard-segment content on the thermal and mechanical properties of PCLA-PUs were investigated. Gel permeation chromatography, IR, C-13 NMR, and X-ray diffraction were used to confirm the formation and structure of PCLA-PUs. Through differential scanning calorimetry, tensile testing, and tensile-recovery testing, their thermal and mechanical properties were characterized. Their glass-transition temperatures were below -8 degrees C, and their soft domains became amorphous as the LA content increased. They displayed excellent mechanical properties, such as a tensile strength as high as 38 MPa, a tensile modulus as low as 10 MPa, and an elongation at break of 1300%. Therefore, they could find applications in biomedical fields, such as soft-tissue engineering and artificial skin.

Toughening PA1010 with a functionalized saturated polyolefin elastomer

Polyamide (PA)1010 is blended with a saturated polyolefin elastomer, ethylene-cu-olefin copolymer (EOCP). To improve the compatibility of PA1010 with EOCP, different grafting rates of EOCP with maleic anhydride (MA) are used. The reaction between PA1010 and EOCP-g-MA during extrusion is verified through an extraction test. Mechanical properties, such as notched Izod impact strength, elongation at break, etc., are examined as a function of grafting rate and weight fraction of elastomer. It was found that in the scale of grafting rate (0.13-0.92 wt %), 0.51 wt % is an extreme point for several mechanical properties. Elastomer domains of PA1010/ EOCP-g-MA blends show a finer and more uniform dispersion in the matrix than that of PA1010/EOCP blends. For the same grafting rate, the average sizes of elastomer particles are almost independent on the contents of elastomer, but for different grafting rates, the particle sizes are decreased with increasing grafting rate. The copolymer formed during extrusion strengthens the interfacial adhesion and acts as an emulsifier to prevent the aggregation of elastomer in the process of blending. (C) 2000 John Wiley & Sons, Inc.

Brittle-tough transition in elastomer toughening thermoplastics: effects of the elastomer stiffness

The effect of the elastomer stiffness on brittle-tough transition in elastomer toughening thermoplastics was quantitatively studied. A correlation between brittle-tough transition temperature and the elastomer stiffness was obtained. The calculation from this correlation showed that the brittle-tough transition temperature (T-bt) Of elastomer toughening thermoplastics slowly increased up to one tenth of the modulus of matrix, thereafter it increased rapidly with increasing the modulus of elastomer. The results indicated that the modulus of the elastomer must be one-tenth or less of that of the matrix in order to be effective at low temperature. (C) 2001 Elsevier Science Ltd. All rights reserved.

Studies on water-swellable elastomer .1. Synthesis and characterization of amphiphilic polymer

A new amphiphilic polymer i.e., polyethylene glycol (PEG) grafted crystalline neoprene, which was used as compatibilizer to improve the compatibility of elastomer and water-absorbent resin, has been investigated. The synthesis was based on the reaction between chlorine in neoprene and sodium salts of PEG. PEGs with molecular weights of 600 and 2000 were used. The grafting percent and the PEG content were calculated through elemental analysis of chlorine in the resulted copolymers. The maximum grafting percent of copolymers was ca. 24.80%. The molecular parameters such as number-average molecular weight and the average number of grafting chains on one CR backbone were also calculated and discussed. (C) 1996 John Wiley & Sons, Inc.

Self-lubricating silicone elastomer biomaterials

Silicone has a relatively high coefficient of friction and silicone medical devices therefore lack inherent lubricity, leading to pain on device insertion and potential tissue trauma. In this study, higher molecular weight tetra(alkoxy) silanes, particularly tetra(oleyloxy) silane, have been used as crosslinkers in the condensation cure of a hydroxy end-functionalised linear poly(dimethylsiloxane). The resulting elastomers displayed a persistent lubricous surface of oleyl alcohol, and coefficients of friction (static and dynamic) approaching zero. Chemical structures of the synthesised silanes and surface alcohol exudate were confirmed by nuclear magnetic resonance spectroscopy. Mechanical properties of the elastomers, which were chemically identical to conventionally cured systems, suggested that an 80/20 mixture of tetra(oleyloxy) silane and tetra(propoxysilane) gave the best compromise between desirable mechanical and frictional properties.