Item Published version Open AccessInkjet Printed Large-Area Flexible Few-Layer Graphene Thermoelectrics(Wiley, 2018) Juntunen, T; Jussila, H; Ruoho, M; Liu, S; Hu, G; Albrow-Owen, T; Ng, LWT; Howe, RCT; Hasan, T; Sun, Z; Tittonen, I; Tittonen, I [0000-0002-2985-9789]AbstractGraphene‐based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene‐based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet‐printed large‐area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so‐called phonon‐glass electron‐crystal character (i.e., electrical transport behavior akin to that of few‐layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all‐graphene films show a room‐temperature thermoelectric power factor of 18.7 µW m−1 K−2, representing over a threefold improvement to previous solution‐processed all‐graphene structures. The demonstration of inkjet‐printed thermoelectric devices underscores the potential for future flexible, scalable, and low‐cost thermoelectric applications, such as harvesting energy from body heat in wearable applications. Item Open AccessFuture, Opportunities and Challenges of Inkjet Technologies(2013-08-07) Castrejon-Pita, J. R.; Baxter, W. R. S.; Morgan, J.; Temple, S.; Martin, G. D.; Hutchings, I. M. Item Open AccessHow PEDOT:PSS solutions produce satellite-free inkjets(Elsevier BV, 2012) Hoath, SD; Jung, S; Hsiao, WK; Hutchings, IM; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074] Item Open AccessThe matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation(Society of Rheology, 2012) Vadillo, DC; Tembely, M; Morrison, NF; Harlen, OG; MacKley, MR; Soucemarianadin, A Item Open AccessAerodynamic effects in ink-jet printing on a moving web(2012) Hsiao, WK; Hoath, SD; Martin, GD; Hutchings, IM; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074] Item Open AccessVelocity Profiles in a Cylindrical Liquid Jet by Reconstructed Velocimetry(ASME International, 2012-01) Castrejon-Pita, JR; Hoath, SD; Hutchings, IM; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074]An experimental setup and a simple reconstruction method are presented to measure velocity fields inside slightly tapering cylindrical liquid jets traveling through still air. Particle image velocimetry algorithms are used to calculate velocity fields from high speed images of jets of transparent liquid containing seed particles. An inner central plane is illuminated by a laser sheet pointed at the center of the jet and visualized through the jet by a high speed camera. Optical distortions produced by the shape of the jet and the difference between the refractive index of the fluid and the surrounding air are corrected by using a ray tracing method. The effect of the jet speed on the velocity fields is investigated at four jet speeds. The relaxation rate for the velocity profile downstream of the nozzle exit is reasonably consistent with theoretical expectations for the low Reynolds numbers and the fluid used, although the velocity profiles are considerably flatter than expected. Item Open AccessHigh speed shadowgraphy for the study of liquid drops(Springer Berlin Heidelberg, 2013) Castrejón-Pita, JR; Castrejón-García, R; Hutchings, IM; Klapp, Jaime; Medina, Abraham; Cros, Anne; Vargas, Carlos A; Hutchings, Ian [0000-0002-5051-1074]The book contains invited lectures and selected contributions presented at the Enzo Levi and XVII Annual Meeting of the Fluid Dynamic Division of the Mexican Physical Society in 2011. Item Open AccessSelf-similar breakup of near-inviscid liquids.(American Physical Society (APS), 2012-07) Castrejón-Pita, JR; Castrejón-Pita, AA; Hinch, EJ; Lister, JR; Hutchings, IM; Hinch, John [0000-0003-3130-7761]; Hutchings, Ian [0000-0002-5051-1074]The final stages of pinchoff and breakup of dripping droplets of near-inviscid Newtonian fluids are studied experimentally for pure water and ethanol. High-speed imaging and image analysis are used to determine the angle and the minimum neck size of the cone-shaped extrema of the ligaments attached to dripping droplets in the final microseconds before pinchoff. The angle is shown to steadily approach the value of 18.0 ± 0.4°, independently of the initial flow conditions or the type of breakup. The filament thins and necks following a τ(2/3) law in terms of the time remaining until pinchoff, regardless of the initial conditions. The observed behavior confirms theoretical predictions. Item Open AccessBreakup of liquid filaments.(American Physical Society (APS), 2012-02-17) Castrejón-Pita, Alfonso A; Castrejón-Pita, JR; Hutchings, IM; Hutchings, Ian [0000-0002-5051-1074]Whether a thin filament of liquid separates into two or more droplets or eventually condenses lengthwise to form a single larger drop depends on the liquid's density, viscosity, and surface tension and on the initial dimensions of the filament. Surface tension drives two competing processes, pinching-off and shortening, and the relative time scales of these, controlled by the balance between capillary and viscous forces, determine the final outcome. Here we provide experimental evidence for the conditions under which a liquid filament will break up into drops, in terms of a wide range of two dimensionless quantities: the aspect ratio of the filament and the Ohnesorge number. Filaments which do not break up into multiple droplets demand a high liquid viscosity or a small aspect ratio. Item Open AccessDrying and Deposition of Picolitre Droplets of Colloidal Suspensions in Binary Solvent Mixtures(NIP28, 2012) Talbot, EL; Berson, A; Brown, PS; Bain, CD Item Open AccessRegimes of polymer behaviour in drop-on-demand ink-jetting(2012) Hoath, SD; Hutchings, IM; Harlen, OG; McIlroy, C; Morrison, NF; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074]Three regimes of fast DoD jetting behaviour for solutions of mono-disperse linear polymers have been linked to the underlying polymer molecular chains and their fully extended length L in good solvents. This allows scaling laws in molecular weight to be predicted and applied to experimental jetting results from different DoD print heads. The higher extensional flows encountered in high speed jetting in viscous solvents can fully stretch linear molecules outside the nozzle, permitting jetting of higher polymer content than for purely elastic behaviour. These results are significant for DoD printing at raised jet speeds and will apply to any DoD print head jetting linear polymer solutions. Item Open AccessEvaporation of Picolitre Droplets on Surfaces with a Range of Wettabilities and Thermal Conductivities(Physical Review E, 2012) Talbot, EL; Berson, A; Brown, PS; Bain, CD Item Open AccessJetting behavior of polymer solutions in drop-on-demand inkjet printing(Society of Rheology, 2012) Hoath, SD; Harlen, OG; Hutchings, IM; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074]The jetting of dilute polymer solutions in drop-on-demand printing is investigated. A quantitative model is presented which predicts three different regimes of behaviour depending upon the jet Weissenberg number Wi and extensibility of the polymer molecules. In regime I (Wi < ½) the polymer chains are relaxed and the fluid behaves in a Newtonian manner. In regime II (½ < Wi < L) where L is the extensibility of the polymer chain the fluid is viscoelastic, but the polymer do not reach their extensibility limit. In regime III (Wi > L) the chains remain fully extended in the thinning ligament. The maximum polymer concentration at which a jet of a certain speed can be formed scales with molecular weight to the power of (1-3ν), (1-6ν) and -2ν in the three regimes respectively, where ν is the solvent quality coefficient. Experimental data obtained with solutions of mono-disperse polystyrene in diethyl phthalate with molecular weights between 24 - 488 kDa, previous numerical simulations of this system, and previously published data for this and another linear polymer in a variety of “good” solvents, all show good agreement with the scaling predictions of the model. Item Open AccessMicrosecond relaxation processes in shear and extensional flows of weakly elastic polymer solutions(Springer Science and Business Media LLC, 2012-08) Vadillo, DC; Mathues, W; Clasen, C Item Open AccessImpact of picolitre droplets on superhydrophobic surfaces with ultra-low spreading ratios(Langmuir, 2011) Brown, PS; Berson, A; Talbot, EL; Wood, TJ; Schofield, WCE; Bain, CD; Badyal, JPS Item Open AccessThe matching of a "one-dimensional" numerical simulation and experiment results for low viscosity Newtonian and non-Newtonian fluids during fast filament stretching and subsequent break-up(Society of Rheology, 2012) Tembely, M; Vadillo, D; MacKley, MR; Soucemarianadin, A Item Open AccessImbibition dynamics of nano-particulate ink-jet drops on micro-porous media(Nanotech, 2011) Hsiao, W-K; Hoath, SD; Martin, GD; Hutchings, IM; Chilton, NB; Jones, S; Hoath, Steve [0000-0003-1125-579X]; Hutchings, Ian [0000-0002-5051-1074]Ink-jet printing of nano-metallic colloidal fluids on to porous media such as coated papers has become a viable method to produce conductive tracks for low-cost, disposable printed electronic devices. However, the formation of well-defined and functional tracks on an absorbing surface is controlled by the drop imbibition dynamics in addition to the well-studied post-impact drop spreading behavior. This study represents the first investigation of the realtime imbibition of ink-jet deposited nano-Cu colloid drops on to coated paper substrates. In addition, the same ink was deposited on to a non-porous polymer surface as a control substrate. By using high-speed video imaging to capture the deposition of ink-jet drops, the time-scales of drop spreading and imbibition were quantified and compared with model predictions. The influences of the coating pore size on the bulk absorption rate and nano-Cu particle distribution have also been studied. Item Open AccessInkjet printing of non-Newtonian fluids(Proc 27th Int. Conf. on Digital Printing Technologies, NIP27, 2011) Morrison, NF; Harlen, OGJet breakup is strongly affected by fluid rheology. In particular,small amounts of polymer can cause substantially different breakup dynamics compared to a Newtonian jet, influencing in-flight fragmentation and detachment from the nozzle. Significant concentrations may also impede jettability. Furthermore, most commercial and industrial inks are inherently colloidal due to the presence of pigment and other additives. Fluids containing a particulate phase are normally shear-thinning and so may have a different characteristic viscosity within the nozzle compared to the ejected ligament. We have developed numerical simulations using a Lagrangian finite element method that captures the free surface automatically, and admits a variety of viscosity dependences, e.g. on the local shear rate (generalized Newtonian fluid) or on the particle concentration (Krieger-Dougherty type models), in addition to several viscoelastic models for polymeric fluids. This method has been benchmarked against experimental data for Newtonian jets. Appropriate rheological models are discussed, and results are presented alongside comparisons with experimental work. Item Open AccessThe Effect of Inkjet Ink Composition on Rheology And Jetting Behaviour(Proc 27th Int. Conf. on Digital Printing Technologies, 2009) Vadillo, D; Mulji, A; Tuladhar, T; Jung, S; Mackley, M; Hoath, Steve [0000-0003-1125-579X]This work presents recent results on the way linear and non linear viscoelastic properties of the fluids affect the jetting mechanism. Recent progress on quantitative characterising both high frequency linear (LVE) and non-linear (NLVE) viscoelasticity of fluids allows fluids to be assessed for their jettability before using such materials in a DoD print head. In term of linear viscoelastic measurements, the Piezo Axial Vibrator (PAV) was used to probe the rheology of the fluids on a frequency range between 10Hz and 10000Hz. A filament stretching apparatus, called the “Cambridge Trimaster”, was used in combination with high speed cinematography, to characterize the fluids high speed stretching and break-up behaviour. The series of fluids investigated here consist in dilutions of mono disperse polystyrene with different molecular weight (110, 210, 306 and 488 kg/mol respectively) diluted in diethyl phthalate. The choice of polymer weights and concentrations were chosen to match both the complex viscosity and the LVE. However, non linear rheological data experiments exhibit differences in the fluid relaxation time and filament break-up mechanism. Ultra-high speed cinematography of DoD jetting events were correlated with filament break-up experiments and demonstrated that fluid rheology provides valuable information on the jetting quality of the fluids. Item Open AccessHolographic measurement of drop-on-demand drops in flight(Proc 27th Int. Conf. on Digital Printing Technologies, NIP27, 2011) Martin, GD; Castrejón-Pita, JR; Hutchings, IM; Hutchings, Ian [0000-0002-5051-1074]The analysis of images of ink drops in flight can provide information about jet straightness, drop velocity and volume. However trade-offs between field of view, optical and digital resolution and other factors such as depth of field and optical distortion, limit the accuracy and amount of information available from a single image. In-line, digital holograms of drops in flight can capture information from fields of view at least as large as the area of the digital sensor. Using mathematical reconstruction techniques particularly suited to sparse, small objects of regular geometry the accuracy of measurement can potentially be submicrometer on drop position and diameter. This paper describes our experimental apparatus, hologram reconstruction techniques and the results of experiments on imaging drops. We also discuss techniques to improve the accuracy of the technique in the direction of the optical axis.