Numerical study of surface agglomeration of ultraviolet-polymeric ink and its control during 3D nano-inkjet printing process

There is a pressing need in very small scale three-dimensional (3D) inkjet printing to control and reduce agglomeration, as agglomeration often leads to nozzle clogging. While agglomeration within ultraviolet ink has been studied, there has been, to our knowledge, no extensive studies conducted for surface agglomeration of the ink on nozzle's wall. This numerical study therefore focuses on investigating if surfactants can effectively control surface agglomeration during nanodroplet formation. Many-body dissipative particle dynamics is the numerical method of choice here. We found that small amount of surfactant of about 1 wt % is sufficient to effectively reduce ink deposition on the nozzle's wall. However, by using the properties of a commercially available surfactant, sodium dodecyl sulfate, it was found that the maximum reduction achieved by its addition is only 60%. Thus, further physical or chemical deagglomeration techniques are required, and we show that by considering these other techniques, reduction of surface agglomeration to nearly 92% can be achieved. Finally, we found that adding surfactants has the additional benefit of improving total kinetic energy of the ink compositions, lowering possibility of agglomerations within the ink. It also raises the nanodroplet velocity while reducing nanodroplet breakup time, which can help speed up the process of 3D printing process. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1615–1624     

紫外光固化水性油墨及墨膜耐磨性能

传统紫外光固化(UV)油墨具有粘度低、固化速度快、应用范围广等优点。 但存在使用少量有机溶剂、交联程度低等缺陷。 本文通过自由基聚合制备的苯乙烯丙烯酸共聚物与甲基丙烯酸羟乙酯(HEMA)反应制备水性预聚物。 通过甲基丙烯酸缩水甘油酯(GMA)和乙二胺反应制备了含有四丙烯酸官能团的活性稀释剂。 最后,通过水性预聚物、活性稀释剂、光引发剂以及少量溶剂制备了UV光固化水性油墨。 探讨了光引发剂的种类和质量分数、预聚物的相对分子质量和质量分数、活性稀释剂的结构和质量分数对UV油墨的光固化速度以及耐磨度的影响。 当预聚物的数均相对分子质量为1.98×10⁵且质量分数为30%、光引发剂质量分数为4%、活性稀释剂的官能团数目为4且质量分数为40%的UV水性油墨的光固化速率为1 s,经50次磨损质量损失为9%。 该方法所制得的UV水性油墨可用于柔版印刷、凹印、数字印刷等。     

Vinyl Sulfonate Esters: Efficient Chain Transfer Agents for the 3D Printing of Tough Photopolymers without Retardation

The formation of networks through light‐initiated radical polymerization allows little freedom for tailored network design. The resulting inhomogeneous network architectures and brittle material behavior of such glassy‐type networks limit the commercial application of photopolymers in 3D printing, biomedicine, and microelectronics. An ester‐activated vinyl sulfonate ester (EVS) is presented for the rapid formation of tailored methacrylate‐based networks. The chain transfer step induced by EVS reduces the kinetic chain length of the photopolymer, thus shifting the gel point to higher conversion, which results in reduced shrinkage stress and higher overall conversion. The resulting, more homogeneous network is responsible for the high toughness of the material. The unique property of EVS to promote nearly retardation‐free polymerization can be attributed to the fact that after the transfer step no polymerizable double bond is formed, as is usually seen in classical chain transfer agents. Laser flash photolysis, theoretical calculations, and photoreactor studies were used to elucidate the fast chain transfer reaction and exceptional regulating ability of EVS. Final photopolymer networks exhibit improved mechanical performance making EVS an outstanding candidate for the 3D printing of tough photopolymers.     

Paper‐Based Inkjet‐Printed Microfluidic Analytical Devices

Rapid, precise, and reproducible deposition of a broad variety of functional materials, including analytical assay reagents and biomolecules, has made inkjet printing an effective tool for the fabrication of microanalytical devices. A ubiquitous office device as simple as a standard desktop printer with its multiple ink cartridges can be used for this purpose. This Review discusses the combination of inkjet printing technology with paper as a printing substrate for the fabrication of microfluidic paper‐based analytical devices (μPADs), which have developed into a fast‐growing new field in analytical chemistry. After introducing the fundamentals of μPADs and inkjet printing, it touches on topics such as the microfluidic patterning of paper, tailored arrangement of materials, and functionalities achievable exclusively by the inkjet deposition of analytical assay components, before concluding with an outlook on future perspectives.     

Nanoinks in inkjet metallization — Evolution of simple additive-type metal patterning

Recent advances in the development of stable dispersions of nanophase metal particles have allowed the direct fabrication of metal patterns (e.g., printed circuits, RFID tags, touch screens, etc.) by simple additive type inkjet processes. Such processes replace the more costly and less environmentally friendly subtractive lithographic type photoprocesses involving selective etching of photoresists and metal layers and more complex additive type process using photocatalysts for patterned metal deposition by electroless plating processes and inkjet patterning of metal catalyst or catalyst precursor for subsequent metallization by electroless plating. The recent development of electrohydrodynamic jet printing (e-jet printing), in which the ink drop is ejected under the influence of an electric field, has allowed a significant resolution increase vs. conventional inkjet printing with a piezoelectric head (printing resolution of ca. 100 nm for e-jet printing vs. ca. 20 μm for inkjet printing).     

印制电子用阻焊油墨及其发展趋势

本文介绍了PCB制造过程中所用阻焊油墨的研究现状及其发展趋势,重点介绍了可喷墨打印阻焊油墨、柔性电路板用阻焊油墨、水溶性碱显影感光阻焊油墨和LED封装用白色阻焊油墨的研究现状及趋势。     

Recent Advances in 3D Printing of Photocurable Polymers: Types,Mechanism, and Tissue Engineering Application

The conversion of liquid resin into solid structures upon exposure to light of a specific wavelength is known as photopolymerization. In recent years, photopolymerization-based 3D printing has gained enormous attention for constructing complex tissue-specific constructs. Due to the economic and environmental benefits of the biopolymers employed, photo-curable 3D printing is considered an alternative method for replacing damaged tissues. However, the lack of suitable bio-based photopolymers, their characterization, effective crosslinking strategies, and optimal printing conditions are hindering the extensive application of 3D printed materials in the global market. This review highlights the present status of various photopolymers, their synthesis, and their optimization parameters for biomedical applications. Moreover, a glimpse of various photopolymerization techniques currently employed for 3D printing is also discussed. Furthermore, various naturally derived nanomaterials reinforced polymerization and their influence on printability and shape fidelity are also reviewed. Finally, the ultimate use of those photopolymerized hydrogel scaffolds in tissue engineering is also discussed. Taken together, it is believed that photopolymerized 3D printing has a great future, whereas conventional 3D printing requires considerable sophistication, and this review can provide readers with a comprehensive approach to developing light-mediated 3D printing for tissue-engineering applications.     

Use of functional microgels with vinyl groups to accelerate photopolymerization reaction

Three types of functional microgels with vinyl groups on their surface were prepared. For the first type, the counter anion from clorin was exchanged with β-methacryloylethyl sulfonic acid, styrene sulfonic acid or allyl sulfonic acid in a microgel with ammonium anions. For the second and third types, a quaternization with N,N-dimethylaminoethyl methacrylate of 3-chloro-2-hydroxypropyl methacrylate in the presence of microgel particles was prepared by emulsion copolymerization of styrene, chloromethylstyrene or N,N-dimethylamino-methylbenzene, and divinylbenzene. The resulting samples show good dispersibility in organic solvents without an emulsifier. A functional microgel-based photopolymer combined with an acrylate monomer and ultraviolet (UV) or visible (VIS) light-absorbing photoinitiators provides oleophilic images when exposed to UV or VIS light and developed in tap water. This photopolymer has a higher sensitivity than those of photopolymers based on microgels with an analogous composition but without vinyl groups. Photopolymers pepared by using functional microgels with a methacryloyl group exhibited a higher rate of polymerization (R_p) than that of photopolymers based on microgels without a vinyl group. The R_p of photopolymers prepared by using a functional microgel with either an allyl group or vinylphenyl group was nearly equal to that of photopolymers based on microgels with ammonium ions. Their high sensitivities are attributed to the rapid photopolymerization in the methacryloyl group. To determine how the photoreaction mechanism enhances sensitivity, the photoreaction products were investigated using a model photopolymerization system. It was found that the gelation reactions enhancing sensitivity are predominantly the polymerization and crosslinking ones when a microgel with the methacryloyl group is used, and the graft copolymerization with acrylate monomers when a microgel with either the allyl group or vinylphenyl group is used.     

Patterned Paper Sensors Printed with Long‐Chain DNA Aptamers

There is growing interest in developing printable paper sensors to enable rapid testing of analytes for environmental, food safety, and clinical applications. A major challenge is to find suitable bioinks that are amenable to high‐speed printing and remain functional after printing. We report on a simple and effective approach wherein an aqueous ink composed of megadalton‐sized tandem repeating structure‐switching DNA aptamers (concatemeric aptamers) is used to rapidly create patterned paper sensors on filter paper by inkjet printing. These concatemeric aptamer reporters remain immobilized at the point of printing through strong adsorption but retain sufficient segmental mobility to undergo structure switching and fluorescence signaling to provide both qualitative and quantitative detection of small molecules and protein targets. The convenience of inkjet printing allows for the patterning of internally referenced sensors with multiplexed detection, and provides a generic platform for on‐demand printing of sensors even in remote locations.     

Electrical circuits from capillary flow driven evaporation deposition of carbon nanotube ink in non-porous V-grooves

Low cost pliable electronics portend the advancement of novel inexpensive microfluidic electrochemical devices. In the direct printing approach, the manner of deposition of conductive material from a liquid suspension to ensure electrical continuity is crucial. We describe here an approach in which V-groove networks that make up the path of circuitry are first scribed on non-porous inexpensive surfaces. Liquid drops of carbon nanotube ink are then placed on the surface adjacent to the V-grooves to enable wicking to produce the electrical circuit. This method essentially bypasses the need for inkjet printing. We investigate the basic efficacy of the conductive networks developed using this approach and demonstrate its use in generating electrically driven liquid flow of particles in a simple open capillary channel.     

Three-component photopolymer based on a novel mechanism: acid-catalyzed polymerization and decoupling of crosslinks

Three-component photopolymers comprising a photoacid generator, a bifunctional vinyl ether monomer and an aqueous base-soluble polymer as matrix were developed. These photopolymers exhibit either positive- or negative-working character, depending on the prebake temperature and the concentration of the photoacid generator. When the prebake temperature is high, the photo-polymer film is made insoluble in aqueous base and organic solvents by the formation of crosslinks. However, on exposure to light, the crosslinks are decoupled by the photogenerated acid and the photopolymer layer becomes again soluble in aqueous base, resulting in a positive-working character. When the concentration of the photoacid generator is low enough, the photopolymer has a negative-working character due to the cationic polymerization of vinyl ethers. The mechanism of the photochemical reaction of the photopolymers was investigated to elucidate the complicated behavior.     

Polycaprolactone solution–based ink for designing microfluidic channels on paper via 3D printing platform for biosensing application

This work reports a novel fabrication technique for development of channels on paper‐based microfluidic devices using the syringe module of a 3D printing syringe–based system. In this study, printing using polycaprolactone (PCL)‐based ink (Mw 70 000‐90 000) was employed for the generation of functional hydrophobic barriers on Whatman qualitative filter paper grade 1 (approximate thickness of 180 μm and pore diameter of 11 μm), which would effectively channelize fluid flow to multiple assay zones dedicated for different analyte detection on a microfluidic paper‐based analytical device (μPAD). The standardization studies reveal that a functional hydrophilic channel for sample conduction fabricated using the reported technique can be as narrow as 460.7 ± 20 μm and a functional hydrophobic barrier can be of any width with a lower limit of about 982.2 ± 142.75 μm when a minimum number of two layers of the ink is extruded onto paper. A comparison with the hydrodynamic model established for writing with ink is used to explain the width of the line printed by this system. A fluid flow analysis through a single channel system was also carried out to establish its conformity with the Washburn model, which governs the fluid flow in two‐dimensional μPAD. The presented fabrication technique proves to be a robust strategy that effectively taps the advantages of this 3D printing technique in the production of μPADs with enhanced speed and reproducibility.     

MODs vs. NPs: Vying for the Future of Printed Electronics

This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution-based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.     

PEDOT∶PSVMA/AuNPs导电墨水的合成及应用

本文以苯乙烯磺酸钠(SS)、7-(4-乙烯基苄氧基)-4-甲基香豆素(VM)和丙烯酸(AA)作为反应单体,合成了一种光敏性双亲共聚物PSVMA,利用1 HNMR与UV-Vis光谱对其结构和组成进行了表征。以PSVMA作为软模板和掺杂剂,氯金酸作为氧化剂,通过化学氧化法聚合得到水分散的PEDOT∶PSVMA/AuNPs导电复合物,平均粒径是66.7±0.5nm。将其作为基础墨水,调节配方制得了PEDOT∶PSVMA/AuNPs喷墨打印墨水,分别以相纸和PET膜为基材制得了图案化的柔性导电膜,该柔性导电膜具有较好的导电性,经紫外光引发导电膜中的香豆素基团二聚后,其耐水性大大提高。     

Synthesis and evaluation as a visible‐light polymerization photoinitiator of a new dye‐linked bis(trichloromethyl)‐1,3,5‐triazine

A dye‐linked initiator consisting of a merocyanine dye, which has an absorption maximum at 460 nm, and a substituted bis(trichloromethyl)‐1,3,5‐triazine initiator was prepared in order to achieve an efficient photopolymerization in a visible‐light region. The spectroscopic studies clearly showed that the dye‐linked initiator exhibit a marked increase in the efficiency of fluorescence quenching than a simple mixture of the dye/initiator. These results are reasonably explained in terms of the efficiency of electron transfer between the dye and the initiator. The relative photoinitiating efficiency of dye‐linked initiators in photopolymerization of acrylate monomers was evaluated and the results clearly indicated that the dye‐linked photoinitiator exhibited a marked increase in the photoinitiating efficiency of photopolymerization of acrylates compared to a simple mixture of the dye/initiator in photopolymer coatings particularly at a lower concentration of the initiator. This was explained in terms of the active quenching sphere of the dye/initiator system. Superior photosensitivity in the linked compound at a lower concentration indicates that this would be particularly useful as a visible‐light photoinitiator in holographic‐recording photopolymers. Copyright © 2004 John Wiley & Sons, Ltd.     

Control of viscoelasticity using redox reaction

The viscoelasticity of a fluid was tuned with the Faradaic reaction of (11-ferrocenylundecyl)trimethylammonium bromide (FTMA), a "redox-switchable" surfactant. An aqueous solution of the reduced form of FTMA exhibited a remarkable viscoelasticity in the presence of sodium salicylate (NaSal) because of the formation of three-dimensional entanglement of wormlike micelles. Electrolytic oxidation of FTMA caused the viscosity of the system to dramatically decrease and the elasticity to disappear. This drastic decrease in viscoelasticity arose from the disruption of wormlike micelles. This novel electrorheological phenomenon is expected to be applicable to ink for inkjet printers, the electrochemically controlled release of substances entrapped in wormlike micelles of FTMA, and fluid flow rate control using electric signals.     

Highly efficient alginate-based macromolecular photoinitiator for crosslinking and toughening gelatin hydrogels

Constructing gelatin hydrogels through photopolymerization is getting increasingly attractive due to their excellent biocompatibility and unparalleled flexibility in fabricating complex structures. In this study, an alginate-based macromolecular photoinitiator (Alg-2959) is synthesized by grafting Irgacure2959, a widely used hydrophilic small molecular photoinitiator, onto the framework of alginate. The characterization of Alg-2959 is carried out by ¹H nuclear magnetic resonance (¹HNMR), Fourier infrared spectroscopic (FTIR), Thermogravimetric analysis (TGA), and UV–Vis absorption spectrum. It is shown that Alg-2959 can induce the polymerization of acrylate monomer poly(ethylene glycol) diacrylate (PEGDA400) and glycidyl methacrylate modified gelatin (Gel-GM) with similar initiation efficiency as Irgacure2959. Compared with the pure hydrogels prepared using Irgacure2959, the hybrid hydrogels containing Alg-2959 can be further crosslinked by Ca²⁺ to form the double-network hydrogels, which exhibit enhanced toughness and elasticity. In addition, due to the introduction of alginate, the migration stability of Alg-2959 in the hydrogel networks is significantly improved compared with Irgacure2959. These results indicate the great potential of Alg-2959 in preparing biocompatible and resilient photopolymers.     

Inkjet deposition of alkanethiolate monolayers and DNA oligonucleotides on gold: evaluation of spot uniformity by wet etching

Inkjet printing allows localized, contact-free deposition of liquids onto arbitrary substrates. In this article we demonstrate the fast formation of high-quality self-assembled monolayers (SAMs) on gold surfaces. Using a selective etch process, we verify the uniformity of the deposited spots. A direct comparison with microcontact-printed SAMs on Au revealed similar resist quality as inkjet-deposited alkanethiolate SAMs. Likewise, inkjet printing of thiol-functionalized and non-thiolated single-stranded DNA oligomers formed molecular layers protecting Au from etchants. For all compounds used, we achieved etched patterns that were homogeneous and free of defects. These results indicate that an inkjet is a convenient tool for surface functionalization and the direct writing of molecular films and resists.     

Sonochemical Degradation of Gelatin Methacryloyl to Control Viscoelasticity for Inkjet Bioprinting

Inkjet printing enables the mimicry of the microenvironment of natural complex tissues by patterning cells and hydrogels at a high resolution. However, the polymer content of an inkjet-printable bioink is limited as it leads to strong viscoelasticity in the inkjet nozzle. Here it is demonstrated that sonochemical treatment controls the viscoelasticity of a gelatin methacryloyl (GelMA) based bioink by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups. The rheological properties of treated GelMA inks are evaluated by a piezo-axial vibrator over a wide range of frequencies between 10 and 10 000 Hz. This approach enables to effectively increase the maximum printable polymer concentration from 3% to 10%. Then it is studied how the sonochemical treatment effectively controls the microstructure and mechanical properties of GelMA hydrogel constructs after crosslinking while maintaining its fluid properties within the printable range. The control of mechanical properties of GelMA hydrogels can lead fibroblasts more spreading on the hydrogels. A 3D cell-laden multilayered hydrogel constructs containing layers with different physical properties is fabrictated by using high-resolution inkjet printing. The sonochemical treatment delivers a new path to inkjet bioprinting to build microarchitectures with various physical properties by expanding the range of applicable bioinks.     

Two‐photon microfabrication of poly(ethylene glycol) diacrylate and a novel biodegradable photopolymer—comparison of processability for biomedical applications

Two‐photon polymerization (2PP) is a versatile microfabrication tool for biomedical applications as it provides unparalleled resolution for accurate three‐dimensional (3D) replication of biological microstructures. To widen the selection of biomaterials suitable for 2PP, this paper presents the processing of a methacrylated poly(ε‐caprolactone)‐based oligomer (PCL‐o) and a poly(ethylene glycol) diacrylate (PEGda) hydrogel into microstructures. PCL‐o is a novel biodegradable photopolymer that has not been previously processed with 2PP, and the fabrication of both polymers with an Nd:YAG laser is reported here for the first time. The overall 2PP processability and achievable resolution were studied by polymerizing arbitrary microstructures on glass substrates. The samples were characterized with scanning electron microscopy. Additionally, the effect of photoinitiator concentration on the resolution was investigated. Also, a preliminary cell attachment test was performed with UV cured films in order to investigate the impact of the used material–initiator combination on cell viability and migration. As a result, laser‐induced polymerization of both PCL‐o and PEGda was successfully demonstrated, and the Nd:YAG laser was proven adequate for the 2PP processing of the novel biodegradable photoresist. Resolution in the order of 1 µm was achieved with PCL‐o. With the easy processing of both PEGda and PCL‐o, these materials have great potential for different biomedical applications. Copyright © 2011 John Wiley & Sons, Ltd.