Improving properties of natural rubber/polyamide 12 blends through grafting of diacetone acrylamide functional group

The aim of the present study was to improve the compatibility in blends of natural rubber (NR) and polyamide 12 (PA12) by grafting NR with hydrophilic monomer, diacetone acrylamide (DAAM), via seeded emulsion polymerization. The increase in polarity of NR after grafting modification was confirmed by a considerable increase in the polar component of its surface energy. Blends of graft copolymers of NR and poly(diacetone acrylamide) prepared using 10 wt% of DAAM (NR‐g‐PDAAM10) and PA12 were prepared at a 60/40 blend ratio (wt%) using simple blend and dynamic vulcanization techniques. The mechanical and rheological properties of the resulting blends were subsequently investigated and compared with those of the corresponding blends based on unmodified NR. The results show that dynamic vulcanization led to a significant increase in both mechanical and rheological properties of the blends. It was also observed that the dynamically cured NR‐g‐PDAAM10/PA12 blend had smaller particle size of vulcanized rubber dispersed in the PA12 matrix than observed for the dynamically cured NR/PA12 blend. This is due to the compatibilizing effect of DAAM groups present in NR‐g‐PDAAM10 molecule, which decreases the interfacial tension between the two polymeric phases. Therefore, it can be stated that the interfacial adhesion between NR and PA12 was improved by the presence of DAAM groups in NR molecule. This was reflected in the higher tensile properties observed in the dynamically cured NR‐g‐PDAAM10/PA12 blend. Copyright © 2017 John Wiley & Sons, Ltd.     

Effects of Structural Variations on the Cellular Response and Mechanical Properties of Biocompatible,Biodegradable, and Porous Smectic Liquid Crystal Elastomers

The authors report on series of side‐chain smectic liquid crystal elastomer (LCE) cell scaffolds based on star block‐copolymers featuring 3‐arm, 4‐arm, and 6‐arm central nodes. A particular focus of these studies is placed on the mechanical properties of these LCEs and their impact on cell response. The introduction of diverse central nodes allows to alter and custom‐modify the mechanical properties of LCE scaffolds to values on the same order of magnitude of various tissues of interest. In addition, it is continued to vary the position of the LC pendant group. The central node and the position of cholesterol pendants in the backbone of ε‐CL blocks (alpha and gamma series) affect the mechanical properties as well as cell proliferation and particularly cell alignment. Cell directionality tests are presented demonstrating that several LCE scaffolds show cell attachment, proliferation, narrow orientational dispersion of cells, and highly anisotropic cell growth on the as‐synthesized LCE materials.

     

Stress relaxation of large amplitudes and long timescales in soft thermoplastic and filled elastomers

We propose a model for describing mesoscale relaxation mechanisms in soft thermoplastic elastomers and also in the high-temperature regime of filled rubbers. The model consists of hard spheres embedded in an elastic matrix. It is solved by dissipative particle dynamics. We study the response of the model to deformations of various amplitudes. We show that it displays slow relaxation processes of large amplitudes that are related to irreversible reorganizations at a mesoscopic scale. We characterize these reorganizations as buckling of instabilities that change the local environment of the hard inclusions. Paper presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece.     

Adhesion of nonplanar wrinkled surfaces

Topological patterns on polymer surfaces can significantly alter and control adhesion. In this study, the effect of surface wrinkles on a spherical surface on adhesion has been studied. Surface wrinkling induced by swelling of a crosslinked polydimethylsiloxane elastomer constrained by a stiff, thin surface layer (silicate) is used to produce topographic features of various length scales over a large curved area. By controlling the properties of the stiff layer and the applied strain conditions, surface wrinkles of varying amplitude and wavelength are obtained. The effect of wrinkle morphology on adhesion is quantified, and the results display a transition from enhancement of adhesion to decrease depending upon wrinkle dimensions. A simple phenomenological model is proposed that describes the change of adhesion behavior as a function of wrinkle morphology. Our results provide a critical understanding toward tuning the adhesion behavior of nonplanar surfaces consisting of periodic topographic structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Temporary shape development in shape memory nanocomposites using magnetic force

Direct mechanical force is used to create a temporary shape in shape memory polymers. This can become difficult in situations where the sample is not directly accessible such as interior in the body. In these cases it is not possible to use a direct mechanical force to deform the sample into temporary shape; therefore other alternative routes should be proposed. The magnetic force is a good candidate for inducing remote deformation. The ability of magnetic field to cause deformation in soft matters has already been revealed. To prove the hypothesis of using magnetic force to create temporary shape, magnetic field active shape memory polymeric nanocomposites were manufactured by incorporation of NdFeB ferromagnetic micro particles in a nanocomposite based on crosslinked low density polyethylene loaded with 2 wt.% of organoclay. The results indicate that as the NdFeB content increases, the reversible temporary deformation induced in the samples by the magnetic force increases. The effect of NdFeB concentration on the shape recovery progress and the possibility of heat induction in NdFeB filled samples through the application of an alternating magnetic field were also examined.     

Thermophysical properties of o-ring elastomers at pressures to 200 MPA

Abstract

Results on the temperature- and pressure dependence of the specific volume, thermal expansivity and compressibility of elastomeric compounds are reported.     

Electrical and mechanical behavior of filled rubber. III. Dynamic loading and the rate of recovery

Following the earlier articles in this series, the changes in the electrical resistivity and mechanical behavior as a result of static and dynamic deformation have been studied. Cyclic shear and tensile loading were used to follow the changes in stress and resistivity with strain, including the recovery with time from the effects of a large strain as monitored by the small‐strain behavior. The recovery of resistivity from a prestrain was not complete even after 7 days at room temperature or at 50 °C, but swelling with a solvent and subsequent drying produced rapid recovery. It appears from the detailed results that there are two strain regions. Below about 10% the resistance and the modulus are strongly dependent on the filler–filler structure, which can break down and reform fairly readily, but the changes at higher strains are probably influenced by changes in the elastomer matrix and also by slippage at the filler–rubber interface. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1649–1661, 2005     

Swollen-collapsed transition in random hetero-polymers

A lattice model of a hetero-polymer with random hydrophilic-hydrophobic charges interacting with the solvent is introduced, whose continuum counterpart has been proposed by Garel, Leibler and Orland [#!GLO!#]. The transfer matrix technique is used to study various constrained annealed systems which approximate at various degrees of accuracy the original quenched model. For highly hydrophobic chains an ordinary -point transition is found from a high temperature swollen phase to a low temperature compact phase. Depending on the type of constrained averages, at very low temperatures a swollen phase or a coexistence between compact and swollen phases are found. The results are carefully compared with the corresponding ones obtained in the continuum limit, and various improvements in the original calculations are discussed. Received: 10 April 1998 / Revised: 4 June 1998 / Accepted: 1st July 1998     

Two-dimensional polymer networks at a mixed boundary: Surface and wedge exponents

We provide general formulae for the configurational exponents of an arbitrary polymer network connected to the surface of an arbitrary wedge of the two-dimensional plane, where the surface is allowed to assume a general mixture of boundary conditions on either side of the wedge. We report on a comprehensive study of a linear chain by exact enumeration, with various attachments of the walk's ends to the surface, in wedges of angles and , with general mixed boundary conditions. Received: 20 October 1997 / Accepted: 13 May 1998