360 research outputs found

    The electrorheology of suspensions consisting of Na-Fluorohectorite synthetic clay particles in silicon oil

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    Under application of an electric field greater than a triggering electric field Ec0.4E_c \sim 0.4 kV/mm, suspensions obtained by dispersing particles of the synthetic clay fluoro-hectorite in a silicon oil, aggregate into chain- and/or column-like structures parallel to the applied electric field. This micro-structuring results in a transition in the suspensions' rheological behavior, from a Newtonian-like behavior to a shear-thinning rheology with a significant yield stress. This behavior is studied as a function of particle volume fraction and strength of the applied electric field, EE. The steady shear flow curves are observed to scale onto a master curve with respect to EE, in a manner similar to what was recently found for suspensions of laponite clay [42]. In the case of Na-fluorohectorite, the corresponding dynamic yield stress is demonstrated to scale with respect to EE as a power law with an exponent α1.93\alpha \sim 1.93, while the static yield stress inferred from constant shear stress tests exhibits a similar behavior with α1.58\alpha \sim 1.58. The suspensions are also studied in the framework of thixotropic fluids: the bifurcation in the rheology behavior when letting the system flow and evolve under a constant applied shear stress is characterized, and a bifurcation yield stress, estimated as the applied shear stress at which viscosity bifurcation occurs, is measured to scale as EαE^\alpha with α0.5\alpha \sim 0.5 to 0.6. All measured yield stresses increase with the particle fraction Φ\Phi of the suspension. For the static yield stress, a scaling law Φβ\Phi^\beta, with β=0.54\beta = 0.54, is found. The results are found to be reasonably consistent with each other. Their similarities with-, and discrepancies to- results obtained on laponite-oil suspensions are discussed

    Yield Hardening of Electrorheological Fluids in Channel Flow

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    Electrorheological fluids offer potential for developing rapidly actuated hydraulic devices where shear forces or pressure-driven flow are present. In this study, the Bingham yield stress of electrorheological fluids with different particle volume fractions is investigated experimentally in wall-driven and pressure-driven flow modes using measurements in a parallel-plate rheometer and a microfluidic channel, respectively. A modified Krieger-Dougherty model can be used to describe the effects of the particle volume fraction on the yield stress and is in good agreement with the viscometric data. However, significant yield hardening in pressure-driven channel flow is observed and attributed to an increase and eventual saturation of the particle volume fraction in the channel. A phenomenological physical model linking the densification and consequent microstructure to the ratio of the particle aggregation time scale compared to the convective time scale is presented and used to predict the enhancement in yield stress in channel flow, enabling us to reconcile discrepancies in the literature between wall-driven and pressure-driven flows

    Smart and Functional Polymers

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    This book is based on the Special Issue of the journal Molecules on “Smart and Functional Polymers”. The collected research and review articles focus on the synthesis and characterization of advanced functional polymers, polymers with specific structures and performances, current improvements in advanced polymer-based materials for various applications, and the opportunities and challenges in the future. The topics cover the emerging synthesis and characterization technology of smart polymers, core?shell structure polymers, stimuli-responsive polymers, anhydrous electrorheological materials fabricated from conducting polymers, reversible polymerization systems, and biomedical polymers for drug delivery and disease theranostics. In summary, this book provides a comprehensive overview of the latest synthesis approaches, representative structures and performances, and various applications of smart and functional polymers. It will serve as a useful reference for all researchers and readers interested in polymer sciences and technologies

    Structure evolution in electrorheological fluids flowing through microchannels

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    Enhanced knowledge of the transient behavior and characteristics of electrorheological (ER) fluids subject to time dependent electric fields offers the potential to advance the design of fast actuated hydraulic devices. In this study, the dynamic response of electrorheological fluid flows in rectilinear microchannels was investigated experimentally. Using high-speed microscopic imaging, the evolution of particle aggregates in ER fluids subjected to temporally stepwise electric fields was visualized. Nonuniform growth of the particle structures in the channel was observed and correlated to field strength and flow rate. Two competing time scales for structure growth were identified. Guided by experimental observations, we developed a phenomenological model to quantitatively describe and predict the evolution of microscale structures and the concomitant induced pressure gradient.United States. Defense Advanced Research Projects Agency. Maximum Mobility and Manipulation (M3) Progra

    Sustainable product design with smart materials : a literature review and analysis

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    This Master's thesis explores sustainable product design using smart materials, specifically emphasizing the application of pH-sensitive materials. This work is oriented towards the design of a color-changing compost bin product line, utilizing pH values to promote sustainable waste management. Additionally, the thesis investigates the use of chromic materials in the creation of a color-changing baby bottle product line, harnessing temperature changes to enhance infant care. This Master's thesis employs an extensive literature review and analytical approach to delve into the areas of smart materials, circular design, and design thinking principles. It presents practical design processes and outcomes for both the color-changing compost bin and baby bottle product families, supplemented by several visual simulations. The study explores the potential of pH-sensitive materials for monitoring compost pH levels and the role of chromic materials in temperature-sensitive applications, and provides successful practical design examples of these materials. The results underscore the significance of smart materials in sustainable product design. This research makes a significant contribution to the expanding field of sustainable design, underscoring the potential for additional exploration and utilization of smart materials across a broad range of product categories

    Plasma Science and Technology

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    Plasma science and technology (PST) is a discipline investigating fundamental transport behaviors, interaction physics, and reaction chemistry of plasma and its applications in different technologies and fields. Plasma has uses in refrigeration, biotechnology, health care, microelectronics and semiconductors, nanotechnology, space and environmental sciences, and so on. This book provides a comprehensive overview of PST, including information on different types of plasma, basic interactions of plasma with organic materials, plasma-based energy devices, low-temperature plasma for complex systems, and much more

    SMART MATERIALS

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    NSF/ESF Workshop on Smart Structures and Advanced Sensors, Santorini Island, Greece, June 26-28, 2005: Structural Actuation and Adaptation Working Group

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    This document is a result of discussions that took place during the workshop. It describes current state of research and development (R&D) in the areas of structural actuation and adaptation in the context of smart structures and advanced sensors (SS&AS), and provides an outlook to guide future R&D efforts to develop technologies needed to build SS&AS. The discussions took place among the members of the Structural Actuation and Adaptation Working Group, as well as in general sessions including all four working groups. Participants included members of academia, industry, and government from the US and Europe, and representatives from China, Japan, and Korea
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