Swelling behavior and mechanical properties of endlinked poly (dimethylsiloxane) networks and randomly crosslinked polyisoprene networks

Measurements of the equilibrium degree of swelling and of the equilibrium modulus were performed on poly(dimethylsiloxane) networks (PDMS) and on polyisoprene vulcanizates. The results support the concept that topological interactions between network chains, e.g. entanglements or the like, have a large influence on the rubber elastic behavior, at least within a certain range of network densities.PDMS networks having network chains of different lengths and varying functionlities of the crosslinks were prepared in bulk by endlinking fractionated ,-divinyl PDMS via multifunctional hydrogen-siloxanes (f=3 to 22). Natural rubber (NR) and synthetic liquid polyisoprene (IR) were cured in bulk with various amounts of dicumyl peroxide to give randomly crosslinked samples.The experimentally determined moduli and degrees of swelling were compared with theoretical predictions based on the phantom network theory and affine network theory, taking into account only chemical crosslinks. The observed discrepancies can be traced back to a contribution of topological interactions (trapped entanglements) to the total effective network density. The modulus and swelling data are consistent, thus ruling out non-equilibrium effects.     

Precise and accurate quantitative C NMR with reduced experimental time

In order to detect small variations in ¹³C isotopomers concentrations, high sensitivity, accuracy and precision have to be achieved. To assess such criteria, when using ¹³C NMR, ¹³C bi-labelled ethanol has been proposed as a molecular probe. Advantage has been taken of the pre-established structural relationship between the peak areas of the ¹³C NMR spectrum of this molecule, i.e. the ratio of signal areas is set to a fixed value. It is shown that the quality performance, required by quantitative ¹³C NMR spectroscopy, is not affected by a large reduction of the repetition delay using relaxation reagents.     

H and H NMR studies of cyclohexane nanocrystals in controlled pore glasses

The formation and behaviour of cyclohexane and cyclohexane-d₁₂ nanocrystals in mesoporous solids of well-defined dimensional constraints are studied by ¹H and ²H NMR. The NMR line widths, spin–spin relaxation times (T₂), spin–lattice relaxation times (T₁) and diffusivities (D) were measured as a function of temperature, and the results are discussed with reference to the values obtained for the bulk materials. The confined solids exhibit substantial changes in the phase behaviour and molecular dynamics. Thus, the line-shape measurements reveal a two-phase system consisting of a highly mobile component at the surface of the pore and a plastically crystalline phase in the centre of the pore. The liquid-like surface layer in the mesopores is observable well below the reduced transition temperature of the confined cyclohexane. However, the T₂ and diffusion measurements show that the mobile phase also embraces a minor component attributed to non-frozen liquid in pockets or offshoots.     

Influence of high pressure treatment on rheological and other properties of egg white

Abstract

The paper deals with the influence of high pressure treatment of fresh egg white on its properties and protein composition (individual amino-acids predicted as a function of pressure and time levels). The rheological properties are changed by high pressure from Newtonian to non-Newtonian behaviour, with increasing apparent viscosity as the pressure and time increased. The pH, whipping ability, foam stability, gel strength of heat induced gels after treatment and the whole protein content, were also predicted.

The results showed that the foam stability is increased with increasing pressure and time of processing. The foam volume is also increased with pressure. The pH did not change with pressure or time of processing. Composition of proteins as indicated by individual amino-acids did not exhibit statistically important changes. Gel strength of heat induced gels prepared from previously pressured liquid whites showed no important change of values with pressure or time of treatment. The modulus of elasticity showed a decrease for samples pressured to 400 MPa for 5 up to 15 minutes.     

Study of Temperature and UV Wavelength Range Effects on Degradation of Photo-Irradiated Polyethylene Films Using DMA

Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure.     

Wrinkle morphologies with two distinct wavelengths

Wrinkles with two distinct wavelengths formed sequentially on the same surface are investigated. A series of aligned wrinkles are formed through local strain application on a partially crosslinked elastomer. After the formation of these primary wrinkles, the elastomer is fully crosslinked, and a mechanical compressive strain is applied to the sample orthogonal to the primary wrinkles. This mechanical strain results in smaller secondary wrinkles superimposed on the larger primary aligned wrinkles. Resulting biaxial morphologies suggest that the primary pattern directs the formation of the smaller wrinkles. The modulus mismatch of the substrate on primary and secondary wrinkle formation dictates the ratio between the two resulting wavelengths, as well as the specific biaxial morphologies, ranging from zigzag ridges to ellipsoidal bumps or corn‐on‐the‐cob structures to the classic herringbone. The sequential strain wrinkling process has the potential to be used on an industrial scale for the facile formation of surface topography with two discrete, tunable lateral dimensions over large surface areas. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Preparation and Characterization of Isotactic Polypropylene Reinforced with Hydroxyapatite Nanorods

Isotactic polypropylene (PP) composites filled with hydroxyapatite nanorods (nHAs) were fabricated using a melt compounding process. The effects of nHA additions on the structure, thermal, and mechanical properties as well as bioactivity of PP were investigated. Wide-angle X-ray diffraction and differential scanning calorimetry results showed that PP crystallized exclusively in the α-form when adding nHAs. Dynamic mechanical analysis showed that nHAs enhanced the storage modulus of PP. Mechanical measurements showed that nHAs stiffened and reinforced PP but reduced its tensile ductility and impact strength considerably. Furthermore, the PP/nHA nanocomposites were found to exhibit excellent bioactivity upon immersion in a simulated body fluid solution. This was attributed to the formation of apatite mineral crystals on the nanocomposite surfaces as revealed by scanning electron microscopy and energy dispersive X-ray analysis.     

A reduced simulation applied to the viscoelastic fatigue of polymers

The paper extends the use of the PGD method to viscoelastic evolution problems described by a large number of internal variables and with a large spectrum of relaxation times. The internal variables evolution is described by a set of linear differential equations that involve many time scales. The feasibility and the robustness of the method are discussed in the case of a polymer in a non-equilibrium state under creep and cyclic loading. The relationships between different time scales (loading and internal variables) are also discussed.     

Electrical Impedance Spectroscopic Study of CNT/Ethylene-alt-CO/Propylene-alt-CO Polyketones Nanocomposite

Impedance spectroscopy was utilized to investigate the dielectric properties, ac conductivity and charge transport mechanisms in propylene-alt-CO/ethylene-alt-CO (EPEC) random terpolymer filled with multi-walled carbon nanotubes (MWCNT) as a function of nanofiller content, frequency, and temperature. Equivalent resistor-capacitor (RC) circuit models were proposed to describe the impedance characteristics of the unfilled terpolymer and the nanocomposite at different temperatures. For the nanocomposites, the ac conductivity tended to be frequency independent at low frequencies. At high frequencies, the ac conductivity increased with frequency. The dc conductivity (i.e., plateau of the ac conductivity at low frequencies) at room temperature increased from 10^?9 (Ω·m)^?1 for the unfilled polymer to l0^?3 (Ω·m)^?1 for the 6 wt% MWCNT/EPEC nanocomposite. At low temperatures, the equivalent RC model for EPEC-0 and EPEC-2 was found to consist of a parallel RC circuit. However, for 6 wt% MWCNT/EPEC nanocomposite, an RC model consisting of an R/constant phase element (CPE) circuit and a resistor in series was required to describe the impedance behavior of the nanocomposite.     

Reconstructing the relaxation dynamics induced by an unknown heat bath

In quantum state tomography, one potential source of error is uncontrolled contact of the system with a heat bath whose detailed properties are not known, and whose impact on the system moreover varies between different runs of the experiment. Precisely these variations provide a handle for reconstructing the system?s effective relaxation dynamics. I propose a pertinent estimation scheme which is based on a steepest-descent ansatz and maximum likelihood. After reconstructing the relaxation dynamics, the original quantum state of the system can be constrained to a curve in state space.