A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

Dynamic oscillatory shear tests are common in rheology and have been used to investigate a wide range of soft matter and complex fluids including polymer melts and solutions, block copolymers, biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions and beyond. More specifically, small amplitude oscillatory shear (SAOS) tests have become the canonical method for probing the linear viscoelastic properties of these complex fluids because of the firm theoretical background [1], [2], [3] and [4] and the ease of implementing suitable test protocols. However, in most processing operations the deformations can be large and rapid: it is therefore the nonlinear material properties that control the system response. A full sample characterization thus requires well-defined nonlinear test protocols. Consequently there has been a recent renewal of interest in exploiting large amplitude oscillatory shear (LAOS) tests to investigate and quantify the nonlinear viscoelastic behavior of complex fluids. In terms of the experimental input, both LAOS and SAOS require the user to select appropriate ranges of strain amplitude (γ₀) and frequency (ω). However, there is a distinct difference in the analysis of experimental output, i.e. the material response. At sufficiently large strain amplitude, the material response will become nonlinear in LAOS tests and the familiar material functions used to quantify the linear behavior in SAOS tests are no longer sufficient. For example, the definitions of the linear viscoelastic moduli G′(ω) and G″(ω) are based inherently on the assumption that the stress response is purely sinusoidal (linear). However, a nonlinear stress response is not a perfect sinusoid and therefore the viscoelastic moduli are not uniquely defined; other methods are needed for quantifying the nonlinear material response under LAOS deformation. In the present review article, we first summarize the typical nonlinear responses observed with complex fluids under LAOS deformations. We then introduce and critically compare several methods that quantify the nonlinear oscillatory stress response. We illustrate the utility and sensitivity of these protocols by investigating the nonlinear response of various complex fluids over a wide range of frequency and amplitude of deformation, and show that LAOS characterization is a rigorous test for rheological models and advanced quality control.     

EVAPS蒸发系统的能源和环境解决方案

介绍了欧洲某家工厂采用9效蒸发系统后，能源和环境绩效都得到了提高。还介绍了另外一家工厂采用LCC分析得出的解决方案，改善了工厂的环境绩效和能源效率。     

Fingerprinting soot (towards source identification): Physical structure and chemical composition

Soot is a highly variable material. Physically the nanostructure can range from amorphous to graphitic to fullerenic. Chemically nearly any element may be included, while the surface functional groups are predominantly oxygen-based. Presented here are HRTEM image analysis results of the physical nanostructure and XPS analysis of the surface chemical composition of soot collected from plant and industrial scale oil-fired boilers, a diesel engine, jet engine and a wildfire. Physically soots from these emission source classes may be differentiated on the basis of carbon lamella length, mean separation and tortuosity. Chemically these soots may also be distinguished by elemental composition and surface functional groups. Together, this suite of parameters can be used to differentiate natural from anthropogenic soots.     

Adolescent substance abuse treatment outcome: The role of substance abuse problem severity, psychosocial, and treatment factors.

A structural equation model incorporating substance abuse problem severity, psychosocial risk and protection, and treatment variables examined adolescent drug abuse treatment outcome pathways across 6- and 12-month follow-up points. Findings on resiliency factors and an empirical method adapted from previous research were used to select and assign 10 psychosocial factors to either a multiple protective factor index or a risk factor index. Gender, substance abuse problem severity, treatment modality, treatment length, and aftercare participation were also examined as outcome predictors. The findings suggest that treatment intensity decisions may be better informed by pretreatment psychosocial risk level rather than by substance abuse problem severity. The present study also suggests that drug-abusing adolescents who receive sufficiently long treatment, participate in aftercare, and possess at least 1 individual or interpersonal protective factor during their recovery process have the best chance to maintain gains made during treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

价值链透视视频消费电子设备的无线连接预计强劲增长Wi-Fi、WiGig和WirelessHD将起飞

据iSuppli公司,消费电子(CE)产业正在进入连接无处不在的新时代,刺激装备高带宽无线视频接口解决方案的视频导向CE设备蓬勃发展.     

Reactive coupling between immiscible polymer chains: Acceleration by compressive flow

It is demonstrated that processing flow affects the kinetics of the interfacial coupling reaction between functional groups that are grafted to polymer chains. At melt temperatures the amine group on the end of nylon 6 chains reacts with maleic anhydride grafted polyethylene (PE‐MA) and forms graft copolymers. Bilayers were made by lamination and coextrusion and adhesion was measured using asymmetric dual cantilever beam (ADCB). The amount of graft copolymer in the interface was quantified by X‐ray photon spectroscopy (XPS). With quiescent lamination, adhesion increased with temperature and the concentration of PE‐MA. The adhesion metric, G_c (critical energy release rate), plotted as a function of Σ (interfacial copolymer density) fell on the same master curve, unifying reaction process, temperature and time. G_c was a linear function of Σ for low‐copolymer coverage and weak adhesion. For relatively high coverage and strong adhesion, G_c scaled with Σ. 2 Coextrusion with compressive flow resulted in a reaction rate strikingly two‐orders of magnitude faster than that without compressive flow. The rate in the noncompressive die was close to quiescent lamination. Even for lamination, when compressive flow was applied normal to the interface, the coupling reaction rate was also greatly accelerated. Several mechanisms are speculated for this remarkable acceleration in polymer chain coupling. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3391–3402, 2013     

Role of entanglements and bond scission in high strain-rate deformation of polymer gels

A key factor that limits the practical implementation of polymer gels is low gel toughness. Here, we present coarse-grained molecular dynamics simulations of the effects of solvent molecular weight on the toughness of entangled and non-entangled polymer gels in the ballistic impact regime. Our results demonstrate that higher molecular weight solvents enhance gel toughness, and that mechanical properties including strength and toughness can be influenced by bond scission. Further, we find a remarkable two-step gel fracture mechanism on the molecular level: network chains undergo scission first (and well before fracture), followed by scission of solvent chains. For strain rates greater than inverse relaxation time of the solvent, long, highly entangled solvent chains provide fracture resistance even after the network chains break by effectively increasing the number of chains that must be broken as a crack propagates.     

Pyrochlore‐Free Ferroelectric 0.64Pb(Ni1/3Nb2/3)O3–0.36PbTiO3 Ceramics Synthesized by the Combustion Method

By adopting Nb₂O₅, HNO₃ and coordination agents EDTA as raw materials, pyrochlore‐free 0.64Pb(Ni_1/3Nb_2/3)O₃–0.36PbTiO₃(0.64PNN–0.36PT) powders were successfully synthesized via a combustion route. Free of pyrochlore phase was realized by the chelation formation of EDTA‐metal ions which isolate niobium and lead oxides and then prevent the formation of pyrochlore phases, therein generate the desired perovskite phases. Comparing the results with similar samples synthesized by the Columbite method, the new 0.64PNN–0.36PT ceramics here shown much better dielectric and ferroelectric performances: a maximum dielectric constant of 22 856 at 1 kHz and a remnant polarization of 21.6 μC/cm² at 40 kV/cm.