Two multi‐walled carbon nanotubes (MWCNTs) having relatively high aspect ratios of 313 and 474 with approximately the same diameter were melt mixed with polycarbonate (PC) in a twin‐screw conical micro compounder. The effects of aspect ratio on the electrical, mechanical, and thermal properties of the PC/MWCNT composites were investigated. Electrical conductivities and storage moduli of the filled samples are found to be independent of the starting aspect ratio for these high aspect ratio tubes; although the conductivities and storage moduli are still significantly higher than values of composites made with nanotubes having more commercially common aspect ratios of ∼100. Transmission electron microscopy results suggest that melt‐mixing reduces these longer nanotubes to the same length, but still approximately two times longer than the length of commercially common aspect ratio tubes after melt‐mixing. Molecular weight measurements show that during melt‐mixing the longer nanotubes significantly degrade the molecular weight of the polymer as compared to very similar nanotubes with aspect ratio ∼100. Because of the molecular weight reduction glass transition temperatures predictably show a large decrease with increasing nanotube concentration. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 73–83
A thermodynamic scaling law for the relaxation times of complex liquids as a function of temperature and volume has been proposed in the literature: τ(T,V) = f(TV(γ)), where γ is a material-dependent constant. We test this scaling for six materials, linear polystyrene, star polystyrene, two polycyanurate networks, poly(vinyl acetate), and poly(vinyl chloride), and compare the thermodynamic scaling to T-T(g) scaling, where τ = f(T-T(g)). The thermodynamic scaling law successfully reduces the data for all of the samples; however, polymers with similar structures but different glass transition (T(g)) and pressure-volume-temperature (PVT) behavior, i.e., the two polycyanurates, cannot be superposed unless the scaling law is normalized by T(g)V(g) (γ). On the other hand, the T-T(g) scaling successfully reduced data for all polymers, including those having similar microstructures. In addition, the T-T(g) scaling is easier to implement since it does not require knowledge of the PVT behavior of the material. The relationship between T(g)V(g) (γ)∕TV(γ) and T-T(g) scaling is clarified and is found to be weakly dependent on pressure.
Purpose To understand why the penetration of handset-based mobile payment in most countries is still low has been an important research topic for the last 15 years, and it has been analyzed from different perspectives. However, the analysis of a single aspect cannot provide a sophisticated answer to the complicated underlying question. The purpose of this paper is to understand how a relatively successful m-payment ecosystem is created and sustained through the coopetition of various actors. Design/methodology/approach To that end, the authors analyze the case of Alipay wallet, the m-payment service provider with the largest market share in China, and focus on understanding the motivations and subsequent actions of the organizations cooperating in the Alipay wallet core ecosystem. Findings The results show that actors with heterogeneous and complementary resources can forge sustainable collaboration. Within an ecosystem, although always constrained by resources and capabilities, the actions that the core actors take and the resulting power imbalances are dynamically changing, reflecting actors’ aim of reducing uncertainty. Research limitations/implications The main limitation of this case is that it was conducted in a Chinese context, which has specific features that may not apply to other cases. In addition, this study is based on a single case study in a single country, without comparing the results to any other cases or countries. Therefore, some modifications may have to be made when applying the framework and generalizing the results. Practical implications With regards to the practical perspective, the Alipay case may serve as an example that other providers follow, taking similar actions to increase the dependency of others and reduce their own dependency on others. It is helpful to take a keystone strategy to create value within the ecosystem and share this value with other participants. Moreover, Alipay acts as the platform provider, in addition to managing value creation within the ecosystem and sharing that value with the other participants. Alipay focuses on the business and strategic needs of the core actors, without threatening their main business, for example, Alipay focuses on micro-payments, which does not pose a direct competition to banks, who mainly rely on macro-payments to generate profit. Micro-payments are often related to high transaction costs for banks. In addition, although it is difficult to define the boundaries of actors in the ecosystem, the core business of every actor is the key competitive or even survival condition. This notion should be taken into consideration by actors whose actions affect the business of other ecosystem partners. For instance, Alipay will not aim to become a bank, as they know that if they do so, they cannot connect any other bank to their platform. In other words, the scope and boundary of the actors are clearly identified so that the core business will not be threatened. Sords, we can learn from Alipay that it pays off to focus on one area, and not to let your competitors challenge you. Originality/value The authors proposed the StReS framework for analyzing a business ecosystem by combining resource-based review, resource dependency theories and network analysis for investigating the motivations of the organizations cooperating in the core ecosystem and the actions they have taken to reduce dependency and uncertainty.
The bulk and shear rheological properties of a symmetric three‐arm star polystyrene were measured using a self‐built pressurizable dilatometer and a commercial rheometer, respectively. The bulk properties investigated include the pressure–volume–temperature behavior, the pressure‐dependent glass transition temperature (Tg), and the viscoelastic bulk modulus and Poisson's ratio. Comparison with data for a linear polystyrene indicates that the star behaves similarly but with slightly higher Tgs at elevated pressures and slightly higher limiting bulk moduli in glass and rubbery states. The Poisson's ratio shows a minimum at short times similar to what is observed for the linear chain. The horizontal shift factors above Tg obtained from reducing the bulk and shear viscoelastic responses are found to have similar temperature dependence when plotted using T − Tg scaling; in addition, the shift factors also exhibit a similar temperature dependence to linear polystyrene. The retardation spectra for the bulk and shear responses are compared and show that the long time molecular mechanisms available to the shear response are unavailable to the bulk. At short times, the two spectra have similar slopes, but the short‐time retardation spectrum for the shear response is significantly higher than that for the bulk, a finding that is, as yet, unexplained. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
Multiwalled carbon nanotubes (MWCNTs) with aspect ratios (ARs) ranging from 94 to 474 were incorporated into polystyrene (PS)/poly(methyl methacrylate) blends using solution mixing and melt mixing. Also, two functionalized MWCNTs were prepared from the nanotubes having AR 94: one was oxidized by nitric acid while the other was further modified with amine‐terminated PS attached to carboxyl groups to form amides. The two functionalized MWCNTs (1 wt %) were used to show that which phase the carbon nanotubes (CNTs) were located in could be controlled with nanotube surface chemistry. When nanotubes were confined to the minor phase, the size of the minor domain first decreased with adding low AR CNT as expected due to the increased viscosity of the minor phase. However, at higher ARs, the size increased beyond the size for the minor domain with no nanotubes, and at high enough AR, the shape of the minor domain changed from spherical to an elongated irregular shape. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3500–3510, 2015
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