| 1. |
- Oko, Asaf, et al.
(författare)
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Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper
- 2014
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 456, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- Papers coated with salts containing divalent cations exhibit superior inkjet print quality, which has been suggested to be due to fast aggregation of the colorant pigments close to, or even on, the surface of the paper. In this work we show the pivotal role of the carboxylic acid containing dispersing polymer. We report a series of aggregation and sedimentation experiments with commercial inks, generic ink formulations and specific ingredients comprising these formulations, and find differences in their response to the presence of MgCl2 or CaCl2. In particular, flocs and sediments formed in the presence of MgCl2 are denser than those formed in the presence of CaCl2. These differences are not predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We suggest that ion specific interactions occurring between Mg2+ or Ca2+, and charged carboxylate groups residing on the dispersing polymers, provoke the observed behavior.
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| 2. |
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| 3. |
- Oko, Asaf, et al.
(författare)
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Imbibition and Evaporation of Water Droplets on Paper and Solid Substrates
- 2011
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Ingår i: Journal of Imaging Science and Technology. - 1062-3701 .- 1943-3522. ; 55:1, s. 010201-
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Tidskriftsartikel (refereegranskat)abstract
- Imbibition and evaporation of picoliter (pL) sized water droplets on paper media commonly used for inkjet printing is measured using high speed imaging system. Three types of uncoated and coated paper samples were chosen: multipurpose uncoated paper (80 g/m(2)), matte coated paper (230 g/m2), and gloss coated paper (240 g/m(2)). As a reference, the rate of the evaporation process was quantified by using three impermeable solid substrates with different wetting characteristics, i.e., silicon, glass, and hydrophobized glass. It is shown that for water droplets of about 60 pL, imbibition is the dominant phenomenon on the matte and gloss coated paper leading to a total drying time (imbibition plus evaporation) of 10-15 ms for gloss coated paper and 30-150 ms on the matte coated paper. In the latter sample, different regimes in the imbibition process were correlated with the layered structure of the sample. The drying process on the multipurpose paper is dominated by evaporation, with initial drying rate of 0.4-0.6 pL/ms.
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| 4. |
- Oko, Asaf, et al.
(författare)
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Infiltration and dimensional scaling of inkjet droplets on papers with different surface chemistry
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigate experimentally and theoretically the spontaneous imbibition of complex inkjet formulations utilizing paper capillary rise and imbibition of inkjet drops. We compare two commercially available papers of the same structure but with different chemistry, one of them surface treated with CaCl. This additive is known to improve print quality when water based pigmented inkjet inks are used by rapidly aggregating the colorant pigments close to, or even on, the surface of the paper. In a previous publication we showed that the key components in the destabilization mechanism of the ink are the dispersing polymers that contain carboxylate groups which interact specifically with the Ca2+ cation. Here we demonstrate the impact of this destabilization effect on the spontaneous imbibition of ink formulations comprised of these polymers, and find that on large scale and long time the imbibition rate is slower in the CaCl2 containing paper compare to the CaCl2 free paper, as shown in paper capillary rise experiments, but on a much smaller scale and shorter times relevant for single inkjet drops no significant differences are observed. We approximate the paper structure to a two dimensional anisotropic porous material, and using Darcy’s law as a base derive dimensionless groups that scale drop imbibition.. This derivation is an expansion of the previously published dimensional scaling of drop imbibition on thick isotropic porous material. We obtain the average global system properties required, by performing sets of drop imbibition experiments where drops are impinged on random paper locations, and use the results to calculate the average volume loss of a single imbibing drop. This averageing procedure is then used in the dimensional scaling.
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| 5. |
- Oko, Asaf, et al.
(författare)
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Infiltration and dimensional scaling of inkjet droplets on thick isotropic porous materials
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 17:2, s. 413-422
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Tidskriftsartikel (refereegranskat)abstract
- We study the imbibition of picoliter (pL)-sized inkjet droplets on controlled pore glass membranes (CPG), as a suitable model for isotropic three-dimensional porous materials. We do so using a variety of liquids, i.e., water, formamide and diiodomethane, and measure the evolution of the imbibition process using high-speed digital imaging. Here, experiments were conducted on 2-280 nm CPG membranes with drops with initial volumes ranging from 100 to 600 pL. We derive scaling laws for imbibition through dimensional analysis and advance the argument that the rate of absorption is related to two-dimensionless groups where v(t) is the imbibed volume, as determined from experiments, t is the time, v (tot) the total liquid volume, the porosity, mu the liquid viscosity, k the permeability, and p (c) the Laplace capillary pressure. We show this scaling to well describe the system at intermediate T values and report that V alpha T-0.8.
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| 6. |
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| 7. |
- Oko, Asaf, et al.
(författare)
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Measurements and dimensional scaling of spontaneous imbibition of inkjet droplets on paper
- 2016
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Ingår i: Nordic Pulp & Paper Research Journal. - : SPCI. - 0283-2631 .- 2000-0669. ; 31:1, s. 156-169
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Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically and experimentally the spontaneous imbibition of water based inkjet formulations utilizing paper capillary rise and imbibition of inkjet drops. We approximate the paper structure to a two dimensional anisotropic porous material, and using Darcy's law as a base, we derive dimensionless groups that scale drop imbibition. This derivation is based on a previous dimensional scaling of drop imbibition on thick isotropic porous material. We apply this scaling to a paper substrate by measuring the average drop imbibition rate, and perform paper capillary rise experiments to obtain the average system parameters required for the scaling. The results suggest that this approach is a valuable tool to predict drop imbibition rates on paper. We then continue and perform the same sets of experiments on a different paper with similar structure that is surface treated (surface sized) with CaCl2 salt, an additive that is known to improve print quality. We find that due to rapid aggregation of the colorant ink by the CaCl2, the imbibition rate is slowed down in the capillary rise experiments, i.e., on much larger scales compared to a single inkjet drop. However, the presence of CaCl2 has only minor effect over the average imbibition rates of single drops. Imbibition rates on the CaCl2 surface sized paper did not give adequate scaling as a result of the fact that the aggregation was not included the theoretical assumptions behind the scaling.
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| 8. |
- Oko, Asaf, 1977-
(författare)
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Spontaneous imbibition and colloidal aspects of inkjet printing
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water-based inkjet is one of the most abundant and versatile digital printing technologies. The subject of this thesis work is processes that take place once an inkjet drop lands on the surface of a porous printing media, with focus on liquid penetration due to capillary action (spontaneous imbibition) and aggregation of ink components. Knowing the details of these two sub-processes would allow optimization of printing processes as well as prediction of the final print result, based on material properties.The dynamics of drops as they land on different surfaces is captured at adequate time and length-scales by an optical imaging system coupled to an inkjet dispensing unit. The evaporation rate of drops is quantified and distinguished from imbibition, and their spreading behavior on porous substrates is characterized. A set of paper grades is used as examples to conclude that the events are captured accurately. Scaling laws for imbibition are derived from Darcy’s law for liquid flow through dimensional analysis and it is shown that the imbibition rate of drops is related to dimensionless volume and time groups, defined by the volume of the drop, porosity and permeability of the substrate, viscosity of the liquid and the Laplace capillary pressure that drives the imbibition. The approach is applied for two types of systems, one that includes simple liquids imbibing homogeneous and isotropic porous glass and the other that includes complex liquids imbibing heterogeneous and anisotropic paper.The addition of simple divalent salts to the paper surface is widely used to increase the print quality of water-based pigmented inkjet inks. Salt ions quickly diffuse into the inkjet droplets as they land on the paper and cause the ink to aggregate. This effect leads to the accumulation of colorant-pigments close to, or even on, the surface of the paper. Two salts, CaCl2 and MgCl2, are used to aggregate inkjet inks and their components. The interactions between the aggregated compounds are investigated by a set of experimental measurements that include sedimentation, confocal Raman microscopy, turbidity, rheology and electrophoretic mobility. It is concluded that the salt induced aggregation is led by a non-color polymeric ink component used as a pigment dispersant, and that CaCl2 induces stronger interactions between polymeric carboxylate groups compared to MgCl2. This ion specific effect cannot be explained by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for electrostatic interaction in colloidal systems.
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| 9. |
- Sanandaji, Nima, et al.
(författare)
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Inkjet printing as a possible route to study confined crystal structures
- 2012
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Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057 .- 1873-1945. ; 49:1, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- Inkjet printing is a technique for the precise deposition of liquid droplets in the pL-volume range in well-defined patterns. Previous studies have shown that inkjet printing is attractive in polymer technology since it permits the controlled deposition of functional polymer surfaces. We suggest that the technique might also be useful for studying crystallization, in particular confined crystallization. Inkjet printing is a non-contact deposition method with minimal risk of contamination, which allows the exact deposition of both polymer solutions and polymer melts. This paper demonstrates the possibility of utilizing the technique to create surfaces where polymer chains form isolated small structures. These structures were confined by both the low polymer content in each droplet and the time constraint on crystal formation that arose as the result of the rapid solvent evaporation from the pL-sized droplets. In theory, inkjet printing enables the exact deposition of systems with as few as a single polymer chain in the average droplet. With appropriate instrumentation, the versatile inkjet technology can be utilized to create whole surfaces covered with polymer structures formed by the crystallization of small, dilute and rapidly evaporating droplets. 110 pL droplets of a 10 -6 g L -1 poly(ε-caprolactone) solution in 1-butanol have been deposited and studied by atomic force microscopy. Small structures of ca. 10 nm thickness and ca. 50 nm diameter also seemed to exhibit crystalline features. Some of the small structures had unusual rectangular forms whilst others were interpreted to be early precursors to six-sided single crystals previously observed for poly(ε-caprolactone). The unusual forms observed may have resulted from the entrapment of crystal structures into metastable phases, due to the limited amount of polymer material present and the rapid evaporation of the droplets.
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| 10. |
- Svanström, Andreas, et al.
(författare)
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Optimized alginate-based 3D printed scaffolds as a model of patient derived breast cancer microenvironments in drug discovery
- 2021
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Ingår i: Biomedical Materials (Bristol). - : IOP Publishing Ltd. - 1748-6041 .- 1748-605X. ; 16:4
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Tidskriftsartikel (refereegranskat)abstract
- The cancer microenvironment influences tumor progression and metastasis and is pivotal to consider when designing in vivo-like cancer models. Current preclinical testing platforms for cancer drug development are mainly limited to 2D cell culture systems that poorly mimic physiological environments and traditional, low throughput animal models. The aim of this work was to produce a tunable testing platform based on 3D printed scaffolds (3DPS) with a simple geometry that, by extracellular components and response of breast cancer reporter cells, mimics patient-derived scaffolds (PDS) of breast cancer. Here, the biocompatible polysaccharide alginate was used as base material to generate scaffolds consisting of a 3D grid containing periostin and hydroxyapatite. Breast cancer cell lines (MCF7 and MDA-MB-231) produced similar phenotypes and gene expression levels of cancer stem cell, epithelial-mesenchymal transition, differentiation and proliferation markers when cultured on 3DPS and PDS, contrasting conventional 2D cultures. Importantly, cells cultured on 3DPS and PDS showed scaffold-specific responses to cytotoxic drugs (doxorubicin and 5-fluorouracil) that were different from 2D cultured cells. In conclusion, the data presented support the use of a tunable alginate-based 3DPS as a tumor model in breast cancer drug discovery. © 2021 The Author(s). Published by IOP Publishing Ltd.
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