The iridescence of structural color and its polarization characteristics originate from the nanoscale organization of materials. A major challenge in materials science is generating the bright, ...lustrous hues seen in nature through nanoscale engineering, while simultaneously controlling interaction of the material with different light polarizations. In this work, a suitable chiral nematic liquid crystal elastomer ink is synthesized for direct ink writing, which self‐assembles into a chiral photonic structure. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis, which exhibits atypical iridescence and polarization selectivity. After crosslinking, a freely programmable, chiroptical photonic polymer material is obtained. The strongly perspective‐dependent appearance of the material can function as specialized anticounterfeit markers, as optical elements in decorative iridescent coatings, or, as demonstrated here, in optically based signaling features.
Inspired by natural examples of patterned iridescence, an ink based on a chiral nematic liquid crystal that can be processed with a direct ink writer 3D printer is shown. Tuning the writing direction and speed leads to the programmed formation of a slanted photonic axis that exhibits atypical iridescence and polarization selectivity.
For many applications of polycarbonate (PC) from packaging to micro-electronics improved barrier properties are necessary. In this contribution, silica thin films were deposited from ...hexamethyldisiloxane/oxygen (HMDSO/O
2
) on polycarbonate substrate in three step plasma processes by combining a microwave (MW) surface wave discharge of 2.45 GHz with an optional radio-frequency (RF) bias of 13.56 MHz. The influence of interlayer thickness, HMDSO flow and oxygen to HMDSO ratio on barrier performance for three step-coating processes was investigated. The morphology and surface properties of the coated surface of PC were studied by atomic force microscopy (AFM). The surface topography showed a silica particles distribution on the PC substrate with relatively smooth surface roughness. AFM-QNM provides more insight into the surface morphology and stiffness. The results identify the coating structure for PC film coated with and without bias. High barrier improvement of the deposited films on PC substrates was obtained after plasma silicon coating process with a barrier improvement factor up to 337. It was found that the deposition process is optimal for food packaging applications by using combined MW-RF PECVD technology.
Abstract The mechanical properties of single electrospun collagen fibers were investigated using scanning mode bending tests performed with an AFM. Electrospun collagen fibers with diameters ranging ...from 100 to 600 nm were successfully produced by electrospinning of an 8% w/v solution of acid soluble collagen in 1,1,1,3,3,3-hexafluoro-2-propanol (HFP). Circular dichroism (CD) spectroscopy showed that 45% of the triple helical structure of collagen molecules was denatured in the electrospun fibers. The electrospun fibers were water soluble and became insoluble after cross-linking with glutaraldehyde vapor for 24 h. The bending moduli and shear moduli of both non- and cross-linked single electrospun collagen fibers were determined by scanning mode bending tests after depositing the fibers on glass substrates containing micro-channels. The bending moduli of the electrospun fibers ranged from 1.3 to 7.8 GPa at ambient conditions and ranged from 0.07 to 0.26 MPa when immersed in PBS buffer. As the diameter of the fibrils increased, a decrease in bending modulus was measured clearly indicating mechanical anisotropy of the fiber. Cross-linking of the electrospun fibers with glutaraldehyde vapor increased the shear modulus of the fiber from ∼30 to ∼50 MPa at ambient conditions.
Micromechanical bending experiments using atomic force microscopy were performed to study the mechanical properties of native and carbodiimide-cross-linked single collagen fibrils. Fibrils obtained ...from a suspension of insoluble collagen type I isolated from bovine Achilles tendon were deposited on a glass substrate containing microchannels. Force-displacement curves recorded at multiple positions along the collagen fibril were used to assess the bending modulus. By fitting the slope of the force-displacement curves recorded at ambient conditions to a model describing the bending of a rod, bending moduli ranging from 1.0
GPa to 3.9
GPa were determined. From a model for anisotropic materials, the shear modulus of the fibril is calculated to be 33
±
2
MPa at ambient conditions. When fibrils are immersed in phosphate-buffered saline, their bending and shear modulus decrease to 0.07–0.17
GPa and 2.9
±
0.3
MPa, respectively. The two orders of magnitude lower shear modulus compared with the Young's modulus confirms the mechanical anisotropy of the collagen single fibrils. Cross-linking the collagen fibrils with a water-soluble carbodiimide did not significantly affect the bending modulus. The shear modulus of these fibrils, however, changed to 74
±
7
MPa at ambient conditions and to 3.4
±
0.2
MPa in phosphate-buffered saline.
A supramolecular strategy is used for oriented positioning of proteins on surfaces. A viologen-based guest molecule is attached to the surface, while a naphthol guest moiety is chemoselectively ...ligated to a yellow fluorescent protein. Cucurbit8uril (CB8) is used to link the proteins onto surfaces through specific charge-transfer interactions between naphthol and viologen inside the CB cavity. The assembly process is characterized using fluorescence and atomic force microscopy, surface plasmon resonance, IR-reflective absorption, and X-ray photoelectron spectroscopy measurements. Two different immobilization routes are followed to form patterns of the protein ternary complexes on the surfaces. Each immobilization route consists of three steps: (i) attaching the viologen to the glass using microcontact chemistry, (ii) blocking, and (iii) either incubation or microcontact printing of CB8 and naphthol guests. In both cases uniform and stable fluorescent patterns are fabricated with a high signal-to-noise ratio. Control experiments confirm that CB8 serves as a selective linking unit to form stable and homogeneous ternary surface-bound complexes as envisioned. The attachment of the yellow fluorescent protein complexes is shown to be reversible and reusable for assembly as studied using fluorescence microscopy.
Vitrimers are a new class of heterogeneous polymers that combine the best features of thermosets with those of thermoplastics. The introduction of cross-links strongly changes the viscoelastic ...behavior of vitrimer materials. However, the characterization and understanding of the nanostructures and interfaces in vitrimers resulting from dynamic cross-linking formation remain a major challenge. Here, using dynamic modes of atomic force microscopy (AFM), namely intermodulation AFM (ImAFM) and AFM-based dynamic mechanical analysis (AFM-nDMA), local viscoelastic properties and interfaces at the nanoscale length of high-density polyethylene (HDPE) vitrimer materials are reported. ImAFM imaging in combination with the k-means clustering algorithm clearly reveals two distinct phases in the vitrimer system with highly different viscoelastic properties. AFM-nDMA further provides quantitative nanoviscoelastic properties at the nanoscale to confirm that there is a cross-linking-rich aggregation area forming a nanosize network structure in the cross-linking-poor matrix phase. The cross-linking-rich region shows a similar elastic modulus but much higher adhesion force measured by AFM compared to the cross-linking-poor HDPE matrix. Furthermore, the frequency influence on the local viscoelastic properties of HDPE vitrimer at the nanoscale was initially screened. The observed HDPE vitrimer nanostructures and viscoelastic properties at the nanoscale also provide explanations on the observed bulk HDPE vitrimer crystallinity decrease and dimensional stability increase compared to HDPE. Therefore, probing the viscoelastic properties and interfaces of HDPE vitrimer provides important insights into understanding of the correlations between the vitrimer nanostructure and the bulk mechanical and rheological behaviors.
Selective laser sintering, also called laser sintering (LS), is an additive manufacturing process that requires micronized plastic powder. Recently, we showed poly (ethylene terephthalate (PET) ...powder is a suitable material for LS, with a comparable printing performance as the current front-runner, polyamide 12 (PA12). However, the LS process, by its nature, leaves unused powder that has been exposed to heat for prolonged time, and this powder may not be fully re-usable due to degradation.
In this work, the re-use potential of heat-exposed PET powder is established. This is a matter of crucial importance as powders suitable for LS are very expensive, and the powder left after a building episode has to be re-used. Heat-exposed PA12 has to be blended or refreshed with virgin powder, to avoid printing defects. In contrast, heat-exposed PET powder, after 96 h at 210 °C, could be used, without refreshing with a portion of virgin powder. The printed articles from heat-exposed powders were as good as those from the fresh powder. There was no cross-linking and there was only a minor increase in the molecular weight of the powder after 96 h, at 210 °C.
The functional and responsive properties of elastomeric materials highly depend on crosslink density and molecular weight between crosslinks. However, tedious analytical steps are needed to obtain ...polymer network structure–property relationships. In this article, an in situ structure–property characterization method is reported by monitoring the structural color change in a photonic elastomeric material. The photonic materials are prepared in a two‐step polymerization process. First, linear chain extension occurs via Michael addition. Second, photopolymerization ensures crosslinking, resulting in the formation of an elastomeric photonic network. During the first step, the step‐growth polymer process can be monitored by following the photonic reflection band redshift, allowing to program the molecular weight between the crosslinks. During network formation, the crosslink density, chain length between crosslinks, and the colors are “frozen in.” These processes can be locally controlled creating both single‐layered multicolor patterned and broadband reflective coatings at room temperature. The scalability of the coating process is further demonstrated by using a gravure printing technique. Additionally, the final coatings are made responsive toward specific solvents and temperature. Here the modulus, response, and color of the coating are controlled by tuning the crosslink density and molecular weight between crosslinks of the elastomeric material.
An in situ structure–property characterization method is reported by monitoring the color change in a photonic elastomeric material. By a two‐step polymerization process, the coatings are first linearly chain‐extended and subsequently crosslinked, for which the color redshifts during chain extension, and is “frozen in” during network formation. Additionally, patterned coatings are made responsive toward specific solvents and temperature.
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