Search

Patterning of two or more liquids, either homogeneous in each phase or mixed with particles (including biological matter, such as cells and proteins), by controlling their flow dynamics, is relevant to several applications. Examples include dynamic spatial confinement of liquids in microfluidic systems (such as lab-on-a-chip and organ-on-a-chip devices) or structuring of polymers to modulate various properties (such as strength, conductivity, transparency and surface finishing). State-of-the-art strategies use various technologies, including positioners, shakers and acoustic actuators, which often combine limited versatility of mixing with significant inefficiency, energy consumption, and noise, as well as tendency to increase the temperature of the liquids. Here, we describe a new kind of robotic mixers of liquids, based on electro-responsive smart materials (dielectric elastomer actuators). We show for the first time how an efficient soft robotic device can be used to produce, via combinations of rotations and translations, various spatial patterns in liquids and maintain them stable for a few minutes. Moreover, we show that, as compared to a conventional orbital shaker, the new type of robotic device can mix liquids with a higher efficacy (~ 94% relative to ~ 80%, after 8 min of mixing) and with a significantly lower increase of the liquids' temperature (+ 1 °C relative to + 5 °C, after 6 h of mixing). This is especially beneficial when mixing should occur according to controllable spatial features and should involve temperature-sensitive matter (such as biological cells, proteins, pre-polymers and other thermolabile molecules). [ABSTRACT FROM AUTHOR]

Compounds incorporating hydrogenated acrylonitrile butadiene rubber (HNBR) are widely adopted in applications that operate under extreme conditions such as at high temperatures, often whilst in contact with oil and other chemicals. They also work effectively when subjected to high strains and high strain rates. The detailed mechanisms that allow these materials to perform so well under these specific conditions are not yet fully understood. In this study a high acrylonitrile (ACN) content HNBR is incorporated into four different rubber compounds that are subjected to different thermal ageing conditions to investigate their impact on fatigue crack growth resistance of the cured compound. The resulting compounds are subjected to detailed DSC, TGA and FTIR analysis to help understand the changes that take place in the compounds during ageing for the first time. Counterintuitively, in this work ageing under specific set of conditions can produce an increase in the fatigue crack resistance in some of the elastomer compounds and when this happens it is observed that this occurs when the HNBR compounds develop knottier tearing profiles. Analysis of the DSC, FTIR and TGA results confirm that during ageing there is a steady evolution of the some of the ingredients in the compound such as the processing oils and the plasticiser which appears to have a significant effect on the fatigue properties of the HNBR materials. [ABSTRACT FROM AUTHOR]

The possibility to electrically tune the optical transparency of thin membranes is of significant interest for a number of possible applications, such as controllable light diffusers and smart windows, both for residential and mobile use. As a difference from state-of-the-art approaches, where with an applied voltage the transparency can only increase or decrease, this paper presents the first concept to make it electrically tuneable to both higher and lower values, within the same device. The concept is applicable to any soft insulating membrane, by coating both of its surfaces with a circular transparent stretchable conductor, surrounded by a stretchable annular conductor. The two conductors are used as independently addressable electrodes to generate a dielectric elastomer-based actuation of the membrane, so as to electrically control its surface topography. We show that the optical transmittance can electrically be modulated within a broad range, between 25% and 83%. This approach could be especially advantageous for systems that require such a broad tuning range within structures that have to be thin, lightweight and acoustically silent in operation. [ABSTRACT FROM AUTHOR]

Carbon black particulate reinforcement of rubber is examined in terms of linear viscoelasticity and the dynamics of the filler particle network. First, it is demonstrated that for the case of purely hydrodynamic reinforcement, the dynamics of the filled rubber are equivalent to those of the corresponding unfilled material. A breakdown in thermorheological simplicity is observed with the onset of filler networking in reinforced compounds. The dynamics of the filler network are initially examined by strain sweep/recovery experiments performed on uncrosslinked materials. The role of the surface activity of carbon black in defining the rate and magnitude of flocculation is explored and various models to describe this process are reviewed. The dynamics of carbon black filler networks in crosslinked materials are probed using small strain torsional creep experiments. Physical ageing (structural relaxation) of filled compounds at temperatures well above the glass transition temperature of the rubber matrix is observed and the ageing rate is found to scale with the level of filler networking in the various compounds. Physical ageing is the result of non-equilibrium, slow dynamics, which sheds light on the physical origin of the filler network. Furthermore, the implications of physical ageing of highly filled rubbers on typical linear viscoelastic time–temperature superposition experiments are discussed. [ABSTRACT FROM AUTHOR]

The holy grail of reconfigurable optics for microscopy, machine vision and other imaging technologies is a compact, in-line, low cost, refractive device that could dynamically tune optical aberrations within a range of about 2–5 wavelengths. This paper presents the first electrically reconfigurable, fully elastomeric, tuneable optical lenses with motor-less electrical controllability of astigmatism in the visible range. By applying different voltage combinations to thin dielectric elastomer actuator segments surrounding a soft silicone lens, we show that the latter can be electrically deformed either radially or along selectable directions, so as to tune defocus or astigmatism, up to about 3 wavelengths. By mounting the new lenses on a commercial camera, we demonstrate their functionality, showing how electrically reconfiguring their shape can be used to dynamically control directional blurring while taking images of different targets, so as to emphasize directional features having orthogonal spatial orientations. Results suggest that the possibility of electrically controlling aberrations inherent to these smart lenses holds promise to develop highly versatile new components for adaptive optics. [ABSTRACT FROM AUTHOR]