No abstract

Immobilized polymer fractions have been claimed to be of pivotal importance for the large mechanical reinforcement observed in nanoparticle-filled elastomers but remained elusive in actual application-relevant materials. We here isolate the additive filler network contribution to the storage modulus of industrial styrene–butadiene rubber (SBR) nanocomposites filled with silica at different frequencies and temperatures and demonstrate that it is viscoelastic in nature. We further quantify the amount of immobilized polymer using solid-state NMR and establish a correlation with the mechanical reinforcement, identifying a direct, strongly nonlinear dependence on the immobilized polymer fraction. The observation of a temperature-independent filler percolation threshold suggests that immobilized polymer fractions may not necessarily form contiguous layers around the filler particles but could only reside in highly confined regions between closely packed filler particles, where they dominate the bending modulus of aggregated particles.

No abstract

The electrospinning technique was used successfully to fabricate one-dimensional arrays of Au nanoparticles within nanofibers in which the intrinsic nature of the semicrystalline polymer poly(ethylene oxide) (PEO) was employed as a template for the controlled nanoscale organization of nanoparticles. Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy, UV-visible spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy (TEM) were performed to characterize the resulting electrospun fibers in comparison with pure PEO and PEO/Au nanocomposite before electrospinning. By choosing chloroform as the solvent in this work the observed electrospun fibers were about 400-650 nm in diameter and revealed a well-defined Gaussian distribution. Thermal analysis showed that the dodecanethiol-capped Au nanoparticles preferentially act as heterogeneous nucleating agents for PEO crystallization. Conformational changes occurred by incorporating Au nanoparticles as well as electrospinning. The most common helical structure of PEO was transformed into a trans zigzag planar structure due to the high extensional flow caused by electrospinning. As a striking result, fairly long and one-dimensional chainlike structures consisting of Au nanoparticles within the electrospun fibers were observed by TEM. The present findings demonstrate that the electrospinning process provides not only a fundamental understanding of the conformational changes upon process conditions, but also a straightforward and cost-effective technique to fabricate one-dimensional arrays of nanoparticles for future nanodevices with unique properties in various applications, such as biological sensors, single-electron transistors, photonic materials, etc.

Abstract. Thermally induced shape-memory effect (SME) in tensile mode was investigated in binary and ternary blends of two ethylene-1-octene copolymers with a degree of branching of 30 and 60 CH3/1000C and/or nearly linear polyethylene cross-linked after melt mixing with 2 wt% of liquid peroxide 2,5-dimethyl-2,5-di-(tert.butylperoxy)-hexane at 190°C. The average cross-link density estimated by means of the Mooney-Rivlin equation on the basis of tensile test data was characterized between 130 and 170 mol·m -3 depending on the blend composition. Thermal analysis points out multiple crystallization and melting behavior of blends caused by the existence of several polyethylene crystal populations with different perfection, size and correspondingly different melting temperature of crystallites. That agrees well with the diversity of blends phase morphology characterized by atomic force microscopy. However, triple-and quadruple-SME could be observed only after two-and accordingly three-step programming of binary and tertiary blends, respectively, at suitable temperatures and strains. Compared to performances obtained for the same blend after single-step programming above the maximal melting temperature the significantly poorer characteristics of SME like strain fixity and strain recovery ratio as well as recovery strain rate occurred after multi-step programming. Vol.2, No.7 (2008) [461][462][463][464][465][466][467][468][469][470][471][472][473] Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2008.56 Strain fixity (R f ) and strain recovery ratios (R r ) are defined according to [4] by Equations (1): (1) where ε p is the strain caused by programming, ε v is the strain that remains after programming, cooling and unloading of specimen and ε rec,m is the residual strain that resides after thermal induced recovery (shrinkage) at maximum temperature of experiment. The investigation of the SM effect of covalent cross-linked semicrystalline polymers and in particular of peroxidic cross-linked ethylene copolymers [7][8][9][10] showed a strong correlation between the melting temperature T m ≡ T trans of the crystalline phase and the response temperature T res , namely T res ≈ T m . Thus, it may be assumed that the existence of several 'n' crystalline phases or/and crystal populations with different perfection, size and correspondingly with distinctly different melting temperatures T m.i in one polymeric material results presumably in a multiple SM behavior, i.e. in the appearance of the same or lower number of recovery strain ε rec (T) steps and accordingly dε rec (T)/dt maxima with response temperatures T res.i ≈ T m.i where 1 ≤ i ≤ n (i is an even number). The triple-shape memory behavior for two different complex polymer network systems which were prepared by photoinduced copolymerization of a methacrylate-monomer and poly(ε-caprolactone) dimethacrylate was already recently described by Bellin et al. [11]. These polymer network systems are formed from two types of chain sections/ domains of ...