The matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation

this work was supported by EPSRC grant number RG5560

Automated Force Volume Image Processing for Biological Samples

Atomic force microscopy (AFM) has now become a powerful technique for investigating on a molecular level, surface forces, nanomechanical properties of deformable particles, biomolecular interactions, kinetics, and dynamic processes. This paper specifically focuses on the analysis of AFM force curves collected on biological systems, in particular, bacteria. The goal is to provide fully automated tools to achieve theoretical interpretation of force curves on the basis of adequate, available physical models. In this respect, we propose two algorithms, one for the processing of approach force curves and another for the quantitative analysis of retraction force curves. In the former, electrostatic interactions prior to contact between AFM probe and bacterium are accounted for and mechanical interactions operating after contact are described in terms of Hertz-Hooke formalism. Retraction force curves are analyzed on the basis of the Freely Jointed Chain model. For both algorithms, the quantitative reconstruction of force curves is based on the robust detection of critical points (jumps, changes of slope or changes of curvature) which mark the transitions between the various relevant interactions taking place between the AFM tip and the studied sample during approach and retraction. Once the key regions of separation distance and indentation are detected, the physical parameters describing the relevant interactions operating in these regions are extracted making use of regression procedure for fitting experiments to theory. The flexibility, accuracy and strength of the algorithms are illustrated with the processing of two force-volume images, which collect a large set of approach and retraction curves measured on a single biological surface. For each force-volume image, several maps are generated, representing the spatial distribution of the searched physical parameters as estimated for each pixel of the force-volume image

The matching of polymer solution fast filament stretching, relaxation, and break up experimental results with 1D and 2D numerical viscoelastic simulation

this work was supported by EPSRC grant number RG5560

Evaluation of the inkjet fluid's performance using the "Cambridge Trimaster" filament stretch and break-up device

This paper describes the design and initial results from the "Cambridge Trimaster," a recently developed high speed filament stretch and break-up device that can be used for viscoelastic fluids with shear viscosities as low as 10 mPa s. Extensional viscosity and filament break-up behavior were studied optically using a high speed camera and extensional viscosity values determined for a series of mono-disperse polystyrene solutions up to a weight concentration of 5 wt % were measured as a function of the polymer loading. The transient stretching and break-up profiles recorded with the apparatus were observed and correlated with drop formation for drop-on-demand inkjet printing fluids. This allowed the filament break-up behavior to be ranked in terms of satellite drop and droplet filament behavior. Correlation with previous work on the jetting of similar low viscosity viscoelastic polymer solutions demonstrated the ability of this apparatus to characterize inkjet fluids.open115366sciescopu

FORMULATION, QUALITY, CLEANING AND OTHER ADVANCES IN INKJET PRINTING

This article describes a series of modern developments carried out by the inkjet community in its quest to improve material compatibility, printing quality, and reliability. Recent progresses in rheology have advanced our understanding of liquids at the time scales that are characteristic of inkjet printing processes. As a result, microsecond rheology now permits the formulation of inks with tailored viscosities that vary according to the time-scale of their dynamics, i.e. low effective viscosity during jetting but high at break up and landing. These advances have permitted the community to assess, and often predict, the ink jetting behaviour, at a given printing frequency, based on the linear or non-linear viscoelasticity and other fluid characteristics. Advances in fluidic systems and in waveform design have now enabled the printing of high viscous inks that were previously impossible to jet on demand. This capability is opening up new markets and opportunities for inkjet, from the printing of glues to the use of heavily loaded ceramic inks. Advances in printhead design, and the assessment of printing patterns using common standards, now allow the verifiable and reliable operation of industrial-scale digital inkjet printing in a wide range of environments. Recent improvements on printhead cleaning protocols, have contributed to an increase in printing speed and operating time by reducing the production of mist and satellite droplets neighbouring the printhead region. Thanks to these improvements, inkjet is displacing traditional technologies, such as offset and screen printing, in large markets including graphics, packaging and labelling

Jetting complex fluids containing pigments and resins

We have previously studied DoD jetting of complex model fluids based on dilute polymer solutions, resulting in the identification of a new regime of polymer jetting and some basic rules for predicting the limiting polymeric concentrations under real conditions such as print head nozzle diameter, jetting speed, solvent quality and polymer molecular weights [1, 2]. There has been no systematic experimental study of the effect of particles on DoD scale jetting, despite the ground-breaking work by Furbank and Morris [3] as reported in NIP17 for the effects of particles on dripping, although theoretical modelling for liquid bridges/filaments containing particles has been recently published [4] and could be relevant to local thinning of DoD ligaments. A series of pigmented inks in the solvent dipropylene glycol methyl ether (DPM) has been used to help study effects of pigment particle size (dm = 3.6, 2.6, 1.6, 1.0, 0.8 pan) on DoD jetting. These inks contained 35 wt% of the inorganic black pigment copper chromite and had a low shear-rate viscosity of ∼ 15 mPa s. Ink characterisation used a high frequency rheometer [5] and a novel fast (5 m/s) filament stretching device [6, 7], while the DoD jetting used MicroFab 80 pan diameter nozzles [8]. Jetting experiments were performed at 100 Hz to avoid nozzle clogging. We report the first systematic experimental studies for DoD scale jets of characterized inks comprising (a) particles in DPM; (b) resin DPM; and (c) combinations of particles and resins in DPM [9, 10]. These results will provide new insights into the jetting of pigmented inks and be important for new applications