Three‐Dimensional Printing with Biomass‐Derived PEF for Carbon‐Neutral Manufacturing

Biomass‐derived poly(ethylene‐2,5‐furandicarboxylate) (PEF) has been used for fused deposition modeling (FDM) 3D printing. A complete cycle from cellulose to the printed object has been performed. The printed PEF objects created in the present study show higher chemical resistance than objects printed with commonly available materials (acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), glycol‐modified poly(ethylene terephthalate) (PETG)). The studied PEF polymer has shown key advantages for 3D printing: optimal adhesion, thermoplasticity, lack of delamination and low heat shrinkage. The high thermal stability of PEF and relatively low temperature that is necessary for extrusion are optimal for recycling printed objects and minimizing waste. Several successive cycles of 3D printing and recycling were successfully shown. The suggested approach for extending additive manufacturing to carbon‐neutral materials opens a new direction in the field of sustainable development.     

Super-hydrophobic, highly adhesive, polydimethylsiloxane (PDMS) surfaces

Super-hydrophobic surfaces have been fabricated by casting polydimethylsiloxane (PDMS) on a textured substrate of known surface topography, and were characterized using contact angle, atomic force microscopy, surface free energy calculations, and adhesion measurements. The resulting PDMS has a micro-textured surface with a static contact angle of 153.5° and a hysteresis of 27° when using de-ionized water. Unlike many super-hydrophobic materials, the textured PDMS is highly adhesive, allowing water drops as large as 25.0 μL to be inverted. This high adhesion, super-hydrophobic behavior is an illustration of the "petal effect". This rapid, reproducible technique has promising applications in transport and analysis of microvolume samples.     

Self-assembly of catecholic macroinitiator on various substrates and surface-initiated polymerization

A catechol-containing macroinitiator has been designed for the surface-initiated atom transfer radical polymerization (SI-ATRP) from various substrates at ambient temperature. Temperature-sensitive poly(N-isopropyl acrylamide) (PNIPAM) brushes were successfully grafted from a range of substrates surfaces, including metals and polyimides, via SI-ATRP using the resulting macroinitiator, which were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle measurements, and atomic force microscopy (AFM). Effects of the temperature response behavior of PNIPAM brushes on the water contact angles and the impedance of the modified surfaces were also exhibited. The self-assembled film of macroinitiator and the resulting polymer brushes were both stable to soaking of basic solvents, and the brushes did not show any exfoliation or delamination even after 2 h of ultrasonic test. The advantages of the macroinitiator in strong interactions with surfaces and high stability and convenience make it possible to modify the native materials with polymer brushes in a convenient and nondestructive way. Importantly, the macroinitiator is compatible with microcontact printing, and patterned polymer brushes on Ti plate were demonstrated by microcontact printing of BrDOPAMA and the following SI-ATRP.     

Strain-induced reversal of charge transfer in contact electrification

We have contact! Material strain can have a dominating effect on contact electrification. When a deflated (relaxed) balloon is rubbed against teflon, the teflon surface charges positively, but when the same balloon is inflated (strained), the teflon surface charges negatively. This result illustrates that material strain can control contact electrification and alter the driving force of some (yet unknown) charge-transfer species.     

Duplication of photoinduced azo polymer surface-relief gratings through a soft lithographic approach

In this work, a soft lithographic approach has been developed to duplicate photoinduced surface-relief-gratings (SRGs) of azo polymer films to generate the surface pattern replicas composed of different materials on various substrates. For this purpose, thin films of an epoxy-based azo polymer (BP-AZ-CA) were prepared by spin-coating, and SRGs with different structures were inscribed by exposing the films to interference patterns of Ar(+) laser beams at modest intensity (150 mW/cm(2)). Using the azo polymer films as masters, stamps of poly(dimethylsiloxane) (PDMS) were prepared by replica molding. The PDMS stamps were then used to transfer the solutions of poly(3-hexylthiophene) (P3HT), multiwalled carbon nanotube (MWNT), and BP-AZ-CA to different substrates by contact printing. Through this process, surface pattern replicas made of the functional materials were obtained. The pattern formation and quality depended on the factors such as the solution concentration, contacting time in the printing process, and printing pressure. Under the proper conditions, the printed patterns showed the same grating periods as the masters and the same relief depths as the stamps (replicas of the masters). This approach, showing some attractive characteristics such as the easiness of master preparation and the versatility of soft fabrication processes, can be applied to the fabrications of optical functional surfaces, sensors, and photonic devices.     

Topography printing to locally control wettability

This paper reports a new patterning method, which utilizes NaOH to facilitate the irreversible binding between the PDMS stamp and substrates and subsequent cohesive mechanical failure to transfer the PDMS patterns. Our method shows high substrate tolerance and can be used to "print" various PDMS geometries on a wide range of surfaces, including Si100, glass, gold, polymers, and patterned SU8 photoresist. Using this technique, we are able to locally change the wettability of substrate surfaces by printing well-defined PDMS architectures on the patterned SU8 photoresist. It is possible to generate differential wetting and dewetting properties in microchannels and in the PDMS printed area, respectively.     

The mechanism of group (I) chloride initiated filiform corrosion on iron

The initiation and propagation of filiform corrosion (FFC) on polymer-coated iron following contact with aqueous group (I) chloride salts is investigated using in situ scanning Kelvinprobe (SKP) and ex situ SIMS measurements. Prior to the onset of FFC a circular area of cathodic delamination is observed to grow radially from a penetrative coating defect. The delaminated zone is abundant in group (I) cations, whereas Cl⁻ anions are substantially excluded. As cathodic delamination slows to a halt corrosion filaments initiate at the coating defect and propagate across the delaminated zone at ca. 0.33 μm min⁻¹. Filaments travelling beyond the delaminated zone show only a small (<20%) decrease in propagation rate. It is shown that Cl⁻ is substantially conserved in the filament-head electrolyte, whereas group (I) cations are effectively excluded. When FeCl₂ is used as the initiating salt, a cathodic delamination phase is not observed but FFC occurs as before. The implications of these findings are discussed with respect to the role of cathodic delamination processes in FFC on iron.     

Binary self-assembled monolayers of alkanethiols on gold: deposition from solution versus microcontact printing and the study of surface nanobubbles

The coadsorption of alkanethiols on noble metals has been recognized for a long time as a suitable means of affording surfaces with systematically varied wettability and other properties. In this article, we report on a comparative study of the composition of the mixed self-assembled monolayers (SAMs) obtained (i) by the coadsorption of octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) from ethanol and chloroform onto gold substrates and (ii) by microcontact printing using poly(dimethyl siloxane) (PDMS) stamps. SAMs prepared by coadsorption from solution showed a preferential adsorption of ODT for both solvents, but this trend was reversed in microcontact-printed SAMs when using chloroform as a solvent, as evidenced by contact angle and Fourier transform infrared (FTIR) spectroscopy measurements. An approximately linear relationship between the static contact angle and the degree of swelling with different solvents was observed, which suggests that the surface composition can be controlled by the interaction of the solvent and the PDMS elastomer. The altered preference is attributed to the different partitioning of the two thiols into solvent-swelled PDMS, as shown by (1)H NMR spectroscopy. Finally, molecularly mixed binary SAMs on ODT and MHDA on template-stripped gold were applied to study the effect of surface nanobubbles on wettability by atomic force microscopy (AFM). With a decreasing macroscopic contact angle measured through water, the nanoscopic contact angle was found to decrease as well.     

A method of printing uniform protein lines by using flat PDMS stamps

In this paper, we report a method of printing uniform protein lines on glass slides by using UV-treated flat PDMS stamps. Unlike traditional microcontact printing (μCP) which requires microstructured PDMS stamps, this μCP method only requires a flat PDMS stamp, an UV lamp and a number of straight needles. Our results show that lines of bovine serum albumin (BSA), immunoglobin (IgG), anti-biotin, anti-human IgG and anti-mouse IgG can be printed evenly on glass slides by using this μCP method. We also demonstrate that the printed protein lines are suitable for applications such as microfluidic immunoassays.     

Application of the JKR Method to the Measurement of Adhesion to Langmuir-Blodgett Cellulose Surfaces

The JKR method has been applied for studying adhesion between poly(dimethylsiloxane) (PDMS) caps and Langmuir–Blodgett cellulose surfaces including the substrate, hydrophobized mica, and two flat mineral surfaces, bare mica and glass. The self-adhesion of PDMS caps and oxidized PDMS caps are included as a reference to compare with literature data. The results of the measurements have been compared with previous studies using the surface force apparatus and similar systems. A satisfactory agreement is obtained for simple systems showing no, or very limited, hysteresis between loading and unloading curves. In several cases, however, a large hysteresis is found between loading and unloading curves, with a larger adhesion measured from the pull-off force than from the JKR-curve determined on loading. This is, for instance, the case for PDMS against cellulose. The situation is analogous to that found in wetting studies showing a large hysteresis between advancing and receding contact angles.     

Synthesis,adsorption and adhesive properties of a cationic amphiphilic block copolymer for use as compatibilizer in composites

In this work, the objective was to synthesize a compatibilizer that can electrostatically adsorb onto cellulose fibers, in fiber-based composites, to enhance the interaction between the fibers and non-polar polymer matrices. This physical route to attach the compatibilizer onto and thereby modify a fiber surface is convenient since it can be performed in water under mild conditions. Polystyrene (PS) was used for the high molecular weight, non-polar, block and poly(dimethylamino)ethyl methacrylate (PDMAEMA) was used as the polar block, which was subsequently quaternized to obtain cationic charges. The block copolymer self-assembles in water into cationic micelles and the adsorption to both silicon oxide surfaces and cellulose model surfaces was studied. The micelles spread out on the surface after heat treatment and contact angle measurements showed that the contact angles against water increased significantly after this treatment. AFM force measurements were performed with a PS probe to study the adhesive properties. The adhesion increased with increasing contact time for the treated surfaces, probably due to entanglements between the polystyrene blocks at the treated surface and the probe. This demonstrates that the use of this type of amphiphilic block copolymer is a promising route to improve the compatibility between charged reinforcing materials, such as cellulose-based fibers/fibrils, and hydrophobic matrices in composite materials.     

Conformation of microcontact-printed proteins by atomic force microscopy molecular sizing

We investigated the structural changes occurring in proteins patterned via microcontact printing. This was done by molecular sizing using atomic force microscopy to observe the structure of printed individual metalloprotein molecules in the unlabeled and untreated states. We observed that the size of the printed proteins were more than 2-fold smaller than the native shape, which indicates that some deformations take place upon the contact-assisted adsorption on silanized silicon dioxide. This can be attributed to simultaneously occurring effects, and particularly to the sandwiching between surfaces of very different hydrophilic/hydrophobic properties during contact lithography.     

Inkjet-printed monolayers as platforms for tethered polymers

Combining inkjet printing and atom-transfer radical polymerization (ATRP) provides a straightforward and versatile method for producing patterned polymer surfaces that may serve as platforms for a variety of applications. We report the use of drop-on-demand technology to print binary chemical gradients and simple patterns onto solid substrates and, by using surface-confined ATRP, amplify these patterns and gradients. Chemically graded monolayers prepared by inkjet printing dodecanethiol and backfilling with 11-mercaptoundecanol showed continuous changes in the water contact angle along the gradient. These samples also exhibited a distinct change in the intensity of methyl group and C-O stretching modes along the gradient. Graded or patterned polymer layers were produced by growing, with ATRP, tethered poly(methyl methacrylate) (PMMA) layers from gradient or patterned printed monolayers that contained a bromo-capped initiator. Atomic force microscopy and optical microscopy confirmed that the PMMA layers amplified the underlying printed initiator layer with remarkable fidelity.     

High-density fabrication of normally closed microfluidic valves by patterned deactivation of oxidized polydimethylsiloxane

The use of polydimethylsiloxane (PDMS) in microfluidic devices is extensive in academic research. One of the most fundamental treatments is to expose PDMS to plasma oxidation in order to render its surface temporarily hydrophilic and capable of permanent bonding. Here, we show that changes in the surface chemistry induced by plasma oxidation can spatially be counteracted very cleanly and reliably in a scalable manner by subsequent microcontact printing of residual oligomers from a PDMS stamp. We characterize the surface modifications through contact angle, atomic force microscopy, X-ray photoelectron spectroscopy, and bond-strength measurements. We utilize this approach for negating the bonding of a flexible membrane layer within an elastomeric valve and demonstrate its effectiveness by integration of over one thousand normally closed elastomeric valves within a single substrate. In addition, we demonstrate that surface energy patterning can be used for "open microfluidic" applications that utilize spatial control of surface wetting.     

Design and fabrication of a multilayered polymer microfluidic chip with nanofluidic interconnects via adhesive contact printing

The design and fabrication of a multilayered polymer micro-nanofluidic chip is described that consists of poly(methylmethacrylate) (PMMA) layers that contain microfluidic channels separated in the vertical direction by polycarbonate (PC) membranes that incorporate an array of nanometre diameter cylindrical pores. The materials are optically transparent to allow inspection of the fluids within the channels in the near UV and visible spectrum. The design architecture enables nanofluidic interconnections to be placed in the vertical direction between microfluidic channels. Such an architecture allows microchannel separations within the chip, as well as allowing unique operations that utilize nanocapillary interconnects: the separation of analytes based on molecular size, channel isolation, enhanced mixing, and sample concentration. Device fabrication is made possible by a transfer process of labile membranes and the development of a contact printing method for a thermally curable epoxy based adhesive. This adhesive is shown to have bond strengths that prevent leakage and delamination and channel rupture tests exceed 6 atm (0.6 MPa) under applied pressure. Channels 100 microm in width and 20 microm in depth are contact printed without the adhesive entering the microchannel. The chip is characterized in terms of resistivity measurements along the microfluidic channels, electroosmotic flow (EOF) measurements at different pH values and laser-induced-fluorescence (LIF) detection of green-fluorescent protein (GFP) plugs injected across the nanocapillary membrane and into a microfluidic channel. The results indicate that the mixed polymer micro-nanofluidic multilayer chip has electrical characteristics needed for use in microanalytical systems.     

Contribution toward comprehension of contact angle values on single polydimethylsiloxane and poly(ethylene oxide) polymer networks

The large application ranges of polydimethylsiloxane (PDMS) and poly(ethylene oxide) (PEO) based materials justify the importance of controlling polymer surface properties including morphology and wettability behavior. However, it appears that the reported contact angle values of PDMS surfaces show significant scattering which cannot always be interpreted in terms of sole chemical data. In addition, few values are reported concerning pure PEO surfaces, since the polymer generally swells in the presence of water. Thus, in order to correlate surface properties with sample preparation, several single PDMS and PEO polymer networks were synthesized with varying cross-linkers and different cross-linking densities. First, the sample surface topography was systematically analyzed by atomic force microscopy (AFM). It was proven that the removal process of the polymer film from the mold plays a significant role in surface topography according to the vitreous or rubbery state of the given polymer network at room temperature irrespective of mold surface treatment. AFM-scale smooth surfaces can be obtained for all the samples by removing them systematically from the mold at a temperature below the α-relaxation temperature. Dynamic water contact angles were then measured and the values analyzed as a function of cross-linker nature and cross-linking density.     

Flexible Triboelectric Nanogenerator from Micro-nano Structured Polydimethylsiloxane

Triboelectric nanogenerator (TENG) can convert mechanical energy to electrical energy through contact electrification and electrostatic induction. Single-friction-surface triboelectric nanogenerator (STENG) extends potential application because a finger can be used as one friction surface in the contact electrification. In this work, a fully flexible STENG has been made, consisting of polydimethylsiloxane(PDMS) with micro-nano structures on its observe side and a flexible electrode on its reverse side. The femtosecond laser ablation was introduced to make micro-nano structures on PDMS and Ag nanowires (Ag NWs) were embedded in PDMS to serve as flexible induction electrode. It has been demonstrated that the energy conversion efficiency increases greatly because of the existing micro-nano structures on PDMS. Further, the mechanism of STENG was proved. Owing to the fully flexible characteristics in both the electrode and PDMS, STENG works well when it is adhered on any subject, for example, on clothes by tape.     

Diffusion of alkanethiols in PDMS and its implications on microcontact printing (muCP)

n-Alkanethiols HS-(CH2)n-CH3 such as hexadecanethiol (HDT, n = 15), octadecanethiol (ODT, n = 17), and eicosanethiol (ECT, n = 19) have been shown to provide highly protective etch resists on microcontact-printed noble metals. As the quality of the printed pattern strongly depends on the mobility of the ink compound, we focused on understanding the diffusion behavior of HDT, ODT, and ECT in poly(dimethylsiloxane) (PDMS) stamps. We used a commercial PDMS material (Sylgard184), which is commonly used for microcontact printing (muCP), and a custom-synthesized one with a higher modulus. On the basis of linear-diffusion experiments, which maintained realistic printing conditions, we showed that the ink transport in the stamp follows Fick's law of diffusion. We then determined the diffusion coefficient by analytical and numerical modeling of the diffusion experiments. Numerical calculations were carried out with the finite-difference method applying more realistic boundary conditions (ink adsorption). Values for the diffusion coefficients of the three ink compounds in the two different PDMS materials all are on the order of (4-7) x 10(-7) cm2 s(-1). The scope and limits of the mathematical models are discussed. To demonstrate the potential of such models for microcontact printing, we simulate multiple printing cycles of an inked stamp and compare the results with experimental data.     

Top-down fabrication of crystalline metal-organic framework nanosheets

Crystalline metal-organic framework (MOF) nanosheets have been fabricated via top-down delamination from bulk crystals of a layered MOF, {Zn(TPA)(H(2)O)·DMF}(n) (MOF-2), and characterized by Tyndall scattering, scanning electron microscopy and atomic force microscopy measurements. The delaminated MOF-2 nanosheets exhibit remarkable amine intercalation property and reversible amine exchangeability.     

Structural characterization of microcontact printed arrays of hexa(ethylene glycol)-terminated alkanethiols on gold

This paper reports on the structural characteristics of microcontact printed oligo(ethylene glycol)-terminated alkanethiol layers, HS(CH2)15CONH-(CH2CH2O)6-H (hereafter EG6), on gold. Microwetting, contact angle goniometry, imaging null ellipsometry, and infrared reflection-absorption spectroscopy (IRAS) are used to characterize the printed EG6 layers, and the quality of these layers in terms of layer thickness and the crystallinity of the alkyl and ethylene glycol portions is compared with data obtained from analogous layers prepared by solution self-assembly. The outcome of the printing process is critically dependent on the experimental parameters used to prepare the patterns. It is found that high quality layers, consisting of densely packed all-trans alkyl chains terminated with relatively helical hexa(ethylene glycol) tails, are formed by inking the poly(dimethylsiloxane) (PDMS) stamp with a 1 mM EG6 solution and contacting it with gold for 15 min. The homogeneity of printed layers is not as good as the homogeneity of those prepared from solution under similar conditions, most likely because of simultaneous transfer of low molecular weight residues from the PDMS stamp. These residues, however, can be easily removed upon ultrasonication in ethanol without affecting the quality of the printed layer. Further on, the microscopic square-shaped bare gold patterns formed after microcontact printing (muCP) are subsequently filled with 16-hexadecanoic acid (hereafter THA) or HS(CH2)15CONH-(CH2CH2O)6-COOH (hereafter EG6COOH) to provide a microarray platform for further covalent attachment of biomolecules. Well-defined structures in terms of wettability contrast, sharpness, and height differences between the printed and back-filled areas are confirmed by imaging null ellipsometry and microscopic wetting.