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Special Issue "Materials for Photolithography and 3D Printing"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (15 June 2016)

Special Issue Editors

Guest Editor
Prof. Dr. Roberta Bongiovanni

Department of Applied Science and Technology-DISAT Politecnico di Torino Corso Duca degli Abruzzi 24, 10129 Torino, Italy
Website | E-Mail
Interests: photopolymerisation and related processes, and their application
Guest Editor
Dr. Alessandra Vitale

Department of Chemical Engineering, Imperial College London, South Kensington Campus, London, UK
Website | E-Mail
Interests: photopolymerization; Patterning; 3D printing; Wrinkling and surface instabilities

Special Issue Information

Dear Colleagues,

Photolithography (PL) is a well-established optical means for transferring patterns onto a substrate. First conceived for producing printed circuits, it is a key process in the semiconductor industry where it is used for creating small structures on a silicon wafer using a photomask, which contains the pattern to be transferred, and a photosensitive material (the photoresist). The photoresist is an organic monomer or polymer, which changes its chemical structure when exposed to light, either becoming soluble or insoluble. Features appear upon selective exposure to light and removal of the soluble material, then the pattern obtained can subsequently be processed (e.g., used as a mask for substrate etching).

As PL can produce extremely small patterns down to tens of nanometers in size, and it provides exact control over the shape and size of the pattern, its applications over the years have extended from electronics to a variety of domains of micro- and nano-fabrication, such as microfluidics, photovoltaics, optics, sensors, and tissue engineering.

In 1986, photolithography went 3D and the term “stereolithography” (SLA) was coined in C. W. Hull’s patent: the technique became a method for making solid objects slice by slice, by successively “printing” thin layers of a light sensitive material one on top of the other. SLA, together with other methodologies associated to photopolymerization processes, is one of the most reliable and versatile techniques of additive manufacturing, often referred as 3D printing. 3D printing, encompassing a wide range of technologies, is regarded as a new ‘turning point’ in industrial production, which will “disrupt business as we know it” (from Forbes, 29 June 2015).

We believe that the growth of 3D printing will also depend on the performance of the materials employed and the development of new materials. Aiming to highlight this concept, this Special Issue will focus on the monomeric and polymeric materials currently used in photolithography, stereolithography, 3D printing, and other additive manufacturing techniques, as well as featuring emerging material-based developments.

We kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. Roberta Bongiovanni
Dr. Alessandra Vitale
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • photopolymers
  • photoresists
  • photolithography
  • stereolithography
  • 3D printing
  • additive manufacturing

Published Papers (7 papers)

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Research

Open AccessArticle Anisotropy of Photopolymer Parts Made by Digital Light Processing
Materials 2017, 10(1), 64; doi:10.3390/ma10010064
Received: 18 September 2016 / Revised: 27 December 2016 / Accepted: 6 January 2017 / Published: 13 January 2017
Cited by 4 | PDF Full-text (5970 KB) | HTML Full-text | XML Full-text
Abstract
Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this
[...] Read more.
Digital light processing (DLP) is an accurate additive manufacturing (AM) technology suitable for producing micro-parts by photopolymerization. As most AM technologies, anisotropy of parts made by DLP is a key issue to deal with, taking into account that several operational factors modify this characteristic. Design for this technology and photopolymers becomes a challenge because the manufacturing process and post-processing strongly influence the mechanical properties of the part. This paper shows experimental work to demonstrate the particular behavior of parts made using DLP. Being different to any other AM technology, rules for design need to be adapted. Influence of build direction and post-curing process on final mechanical properties and anisotropy are reported and justified based on experimental data and theoretical simulation of bi-material parts formed by fully-cured resin and partially-cured resin. Three photopolymers were tested under different working conditions, concluding that post-curing can, in some cases, correct the anisotropy, mainly depending on the nature of photopolymer. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Open AccessArticle Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation
Materials 2016, 9(9), 760; doi:10.3390/ma9090760
Received: 29 July 2016 / Revised: 31 August 2016 / Accepted: 2 September 2016 / Published: 7 September 2016
Cited by 3 | PDF Full-text (2642 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We investigate the impact of the non-uniform spatio-temporal conversion, intrinsic to photopolymerisation, in the context of light-driven 3D printing of polymers. The polymerisation kinetics of a series of model acrylate and thiol-ene systems, both neat and doped with a light-absorbing dye, is investigated
[...] Read more.
We investigate the impact of the non-uniform spatio-temporal conversion, intrinsic to photopolymerisation, in the context of light-driven 3D printing of polymers. The polymerisation kinetics of a series of model acrylate and thiol-ene systems, both neat and doped with a light-absorbing dye, is investigated experimentally and analysed according to a descriptive coarse-grained model for photopolymerisation. In particular, we focus on the relative kinetics of polymerisation with those of 3D printing, by comparing the evolution of the position of the conversion profile (zf) to the sequential displacement of the object stage (∆z). After quantifying the characteristic sigmoidal monomer-to-polymer conversion of the various systems, with a combination of patterning experiments, FT-IR mapping, and modelling, we compute representative regimes for which zf is smaller, commensurate with, or larger than ∆z. While non-monotonic conversion can be detrimental to 3D printing, for instance in causing differential shrinkage of inhomogeneity in material properties, we identify opportunities for facile fabrication of modulated materials in the z-direction (i.e., along the illuminated axis). Our simple framework and model, based on directly measured parameters, can thus be employed in photopolymerisation-based 3D printing, both in process optimisation and in the precise design of complex, internally stratified materials by coupling the z-stage displacement and frontal polymerisation kinetics. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Open AccessArticle A Facile in Situ and UV Printing Process for Bioinspired Self-Cleaning Surfaces
Materials 2016, 9(9), 738; doi:10.3390/ma9090738
Received: 8 July 2016 / Revised: 24 August 2016 / Accepted: 25 August 2016 / Published: 30 August 2016
Cited by 2 | PDF Full-text (2713 KB) | HTML Full-text | XML Full-text
Abstract
A facile in situ and UV printing process was demonstrated to create self-cleaning synthetic replica of natural petals and leaves. The process relied on the spontaneous migration of a fluorinated acrylate surfactant (PFUA) within a low-shrinkage acrylated hyperbranched polymer (HBP) and its chemical
[...] Read more.
A facile in situ and UV printing process was demonstrated to create self-cleaning synthetic replica of natural petals and leaves. The process relied on the spontaneous migration of a fluorinated acrylate surfactant (PFUA) within a low-shrinkage acrylated hyperbranched polymer (HBP) and its chemical immobilization at the polymer-air interface. Dilute concentrations of 1 wt. % PFUA saturated the polymer-air interface within 30 min, leading to a ten-fold increase of fluorine concentration at the surface compared with the initial bulk concentration and a water contact angle (WCA) of 108°. A 200 ms flash of UV light was used to chemically crosslink the PFUA at the HBP surface prior to UV printing with a polydimethylsiloxane (PDMS) negative template of red and yellow rose petals and lotus leaves. This flash immobilization hindered the reverse migration of PFUA within the bulk HBP upon contacting the PDMS template, and enabled to produce texturized surfaces with WCA well above 108°. The synthetic red rose petal was hydrophobic (WCA of 125°) and exhibited the adhesive petal effect. It was not superhydrophobic due to insufficient concentration of fluorine at its surface, a result of the very large increase of the surface of the printed texture. The synthetic yellow rose petal was quasi-superhydrophobic (WCA of 143°, roll-off angle of 10°) and its self-cleaning ability was not good also due to lack of fluorine. The synthetic lotus leaf did not accurately replicate the intricate nanotubular crystal structures of the plant. In spite of this, the fluorine concentration at the surface was high enough and the leaf was superhydrophobic (WCA of 151°, roll-off angle below 5°) and also featured self-cleaning properties. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Open AccessArticle A Novel Fabrication Technique for Liquid-Tight Microchannels by Combination of a Paraffin Polymer and a Photo-Curable Silicone Elastomer
Materials 2016, 9(8), 621; doi:10.3390/ma9080621
Received: 16 June 2016 / Revised: 11 July 2016 / Accepted: 25 July 2016 / Published: 27 July 2016
Cited by 2 | PDF Full-text (3686 KB) | HTML Full-text | XML Full-text
Abstract
The development and growth of microfluidics has been mainly based on various novel fabrication techniques for downsizing and integration of the micro/nano components. Especially, an effective fabrication technique of three-dimensional structures still continues to be strongly required in order to improve device performance,
[...] Read more.
The development and growth of microfluidics has been mainly based on various novel fabrication techniques for downsizing and integration of the micro/nano components. Especially, an effective fabrication technique of three-dimensional structures still continues to be strongly required in order to improve device performance, functionality, and device packing density because the conventional lamination-based technique for integrating several two-dimensional components is not enough to satisfy the requirement. Although three-dimensional printers have a high potential for becoming an effective tool to fabricate a three-dimensional microstructure, a leak caused by the roughness of a low-precision structure made by a 3D printer is a critical problem when the microfluidic device is composed of several parts. To build a liquid-tight microchannel on such a low-precision structure, we developed a novel assembly technique in which a paraffin polymer was used as a mold for a microchannel of photo-curable silicone elastomer on a rough surface. The shape and roughness of the molded microchannel was in good agreement with the master pattern. Additionally, the seal performance of the microchannel was demonstrated by an experiment of electrophoresis in the microchannel built on a substrate which has a huge roughness and a joint. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Figure 1

Open AccessFeature PaperArticle In Situ Thermal Generation of Silver Nanoparticles in 3D Printed Polymeric Structures
Materials 2016, 9(7), 589; doi:10.3390/ma9070589
Received: 10 June 2016 / Revised: 8 July 2016 / Accepted: 12 July 2016 / Published: 19 July 2016
Cited by 8 | PDF Full-text (3153 KB) | HTML Full-text | XML Full-text
Abstract
Polymer nanocomposites have always attracted the interest of researchers and industry because of their potential combination of properties from both the nanofillers and the hosting matrix. Gathering nanomaterials and 3D printing could offer clear advantages and numerous new opportunities in several application fields.
[...] Read more.
Polymer nanocomposites have always attracted the interest of researchers and industry because of their potential combination of properties from both the nanofillers and the hosting matrix. Gathering nanomaterials and 3D printing could offer clear advantages and numerous new opportunities in several application fields. Embedding nanofillers in a polymeric matrix could improve the final material properties but usually the printing process gets more difficult. Considering this drawback, in this paper we propose a method to obtain polymer nanocomposites by in situ generation of nanoparticles after the printing process. 3D structures were fabricated through a Digital Light Processing (DLP) system by disolving metal salts in the starting liquid formulation. The 3D fabrication is followed by a thermal treatment in order to induce in situ generation of metal nanoparticles (NPs) in the polymer matrix. Comprehensive studies were systematically performed on the thermo-mechanical characteristics, morphology and electrical properties of the 3D printed nanocomposites. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Open AccessArticle UV-Assisted 3D Printing of Glass and Carbon Fiber-Reinforced Dual-Cure Polymer Composites
Materials 2016, 9(7), 583; doi:10.3390/ma9070583
Received: 15 June 2016 / Revised: 10 July 2016 / Accepted: 11 July 2016 / Published: 16 July 2016
Cited by 5 | PDF Full-text (2107 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Glass (GFR) and carbon fiber-reinforced (CFR) dual-cure polymer composites fabricated by UV-assisted three-dimensional (UV-3D) printing are presented. The resin material combines an acrylic-based photocurable resin with a low temperature (140 °C) thermally-curable resin system based on bisphenol A diglycidyl ether as base component,
[...] Read more.
Glass (GFR) and carbon fiber-reinforced (CFR) dual-cure polymer composites fabricated by UV-assisted three-dimensional (UV-3D) printing are presented. The resin material combines an acrylic-based photocurable resin with a low temperature (140 °C) thermally-curable resin system based on bisphenol A diglycidyl ether as base component, an aliphatic anhydride (hexahydro-4-methylphthalic anhydride) as hardener and (2,4,6,-tris(dimethylaminomethyl)phenol) as catalyst. A thorough rheological characterization of these formulations allowed us to define their 3D printability window. UV-3D printed macrostructures were successfully demonstrated, giving a clear indication of their potential use in real-life structural applications. Differential scanning calorimetry and dynamic mechanical analysis highlighted the good thermal stability and mechanical properties of the printed parts. In addition, uniaxial tensile tests were used to assess the fiber reinforcing effect on the UV-3D printed objects. Finally, an initial study was conducted on the use of a sizing treatment on carbon fibers to improve the fiber/matrix interfacial adhesion, giving preliminary indications on the potential of this approach to improve the mechanical properties of the 3D printed CFR components. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)
Figures

Open AccessArticle Forming Spacers in Situ by Photolithography to Mechanically Stabilize Electrofluidic-Based Switchable Optical Elements
Materials 2016, 9(4), 250; doi:10.3390/ma9040250
Received: 23 February 2016 / Revised: 12 March 2016 / Accepted: 24 March 2016 / Published: 30 March 2016
Cited by 2 | PDF Full-text (4907 KB) | HTML Full-text | XML Full-text
Abstract
Electro-Fluidic Displays (EFD) have been demonstrated to be an attractive technology for incorporation into portable display devices. EFDs have excellent optical efficiency and fast switching enabling video content. Ensuring mechanical stability of EFD display cells is a key challenge and essential for developing
[...] Read more.
Electro-Fluidic Displays (EFD) have been demonstrated to be an attractive technology for incorporation into portable display devices. EFDs have excellent optical efficiency and fast switching enabling video content. Ensuring mechanical stability of EFD display cells is a key challenge and essential for developing large area as well as flexible displays. Although the electro-optic performance of an EFD, unlike a liquid crystal display (LCD), is insensitive to cell-gap, extreme changes in cell-gap can result in irreversible collapse of the cell. Here we use photolithography to develop spacers to prevent cell-gap collapse and provide the required mechanical stability for EFD devices. The spacer is formed directly on the cover plates (ITO/glass) after cell assembly with UV light induced phase separation polymerization in the illuminated area. Phase separation behavior between polar aqueous solution and polymer is closely related to the solubility of acrylate monomers. In this work, polyethylene glycol diacrylate (PEGDA) as cross-linker, 2-hydroxyethyl acrylate (HEA) and acrylic acid or acrylamide as co-monomers are investigated for fabricating the spacers. PEGDA was added to the mixtures in order to increase the mechanical strength of the spacer. The spacers showed excellent performance for cell-gap control in EFD devices. Full article
(This article belongs to the Special Issue Materials for Photolithography and 3D Printing)

Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Dear Colleagues,

Photolithography (PL) is a well-established optical means for transferring patterns onto a substrate. First conceived for producing printed circuits, it is a key process in the semiconductor industry where it is used for creating small structures on a silicon wafer using a photomask, which contains the pattern to be transferred, and a photosensitive material (the photoresist). The photoresist is an organic monomer or polymer, which changes its chemical structure when exposed to light, either becoming soluble or insoluble. Features appear upon selective exposure to light and removal of the soluble material, then the pattern obtained can subsequently be processed (e.g., used as a mask for substrate etching).

As PL can produce extremely small patterns down to tens of nanometers in size, and it provides exact control over the shape and size of the pattern, its applications over the years have extended from electronics to a variety of domains of micro- and nano-fabrication, such as microfluidics, photovoltaics, optics, sensors, and tissue engineering.

In 1986, photolithography went 3D and the term “stereolithography” (SLA) was coined in C. W. Hull’s patent: the technique became a method for making solid objects slice by slice, by successively “printing” thin layers of a light sensitive material one on top of the other. SLA, together with other methodologies associated to photopolymerization processes, is one of the most reliable and versatile techniques of additive manufacturing, often referred as 3D printing. 3D printing, encompassing a wide range of technologies, is regarded as a new ‘turning point’ in industrial production, which will “disrupt business as we know it” (from Forbes, 29 June 2015).

We believe that the growth of 3D printing will also depend on the performance of the materials employed and the development of new materials. Aiming to highlight this concept, this Special Issue will focus on the monomeric and polymeric materials currently used in photolithography, stereolithography, 3D printing, and other additive manufacturing techniques, as well as featuring emerging material-based developments.

We kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. Roberta Bongiovanni and Dr. Alessandra Vitale

Guest Editor

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