Gradient Polymer Nanofoams for Encrypted Recording of Chemical Events

Ultrafast Flame-Induced Pyrolysis of Poly(dimethylsiloxane) Foam Materials toward Exceptional Superhydrophobic Surfaces and Reliable Mechanical Robustness

Superhydrophobic surfaces are imperative in flexible polymer foams for diverse applications; however, traditional surface coatings on soft skeletons are often fragile and can hardly endure severe deformation, making them unstable and highly susceptible to cyclic loadings. Therefore, it remains a great challenge to balance their mutual exclusiveness of mechanical robustness and surface water repellency on flexible substrates. Herein, we describe how robust superhydrophobic surfaces on soft poly(dimethylsiloxane) (PDMS) foams can be achieved using an extremely simple, ultrafast, and environmentally friendly flame scanning strategy. The ultrafast flame treatment (1-3 s) of PDMS foams produces microwavy and nanosilica rough structures bonded on the soft skeletons, forming robust superhydrophobic surfaces (i.e., water contact angles (WCAs) > 155° and water sliding angles (WSAs) < 5°). The rough surface can be effectively tailored by simply altering the flame scanning speed (2.5-15.0 cm/s) to adjust the thermal pyrolysis of the PDMS molecules. The optimized surfaces display reliable mechanical robustness and excellent water repellency even after 100 cycles of compression of 60% strain, stretching of 100% strain, and bending of 90° and hostile environmental conditions (including acid/salt/alkali conditions, high/low temperatures, UV aging, and harsh cyclic abrasion). Moreover, such flame-induced superhydrophobic surfaces are easily peeled off from ice and can be healable even after severe abrasion cycles. Clearly, the flame scanning strategy provides a facile and versatile approach for fabricating mechanically robust and surface superhydrophobic PDMS foam materials for applications in complex conditions.

"Shape-Coding": Morphology-Based Information System for Polymers and Composites

Fiber-reinforced composites have become the material of choice for aerospace structures because of their favorable strength-to-weight ratio. Given the increasing amounts of counterfeit composite parts showing up in the complex aerospace supply chain, it is absolutely vital to track a composite part throughout its lifecycle-from production to usage and to disposal. Existing barcoding methods are invasive, affect the structural properties of composites, and/or are vulnerable to tampering. We describe a universal method to store information in fiber-reinforced composites based on solid-state in situ reduction leading to embedded nanoparticles with controlled morphologies. This simple, cost-effective, mild, surfactant-free, and one-step protocol for the fabrication of embedded platinum nanostructures leads to morphology-based barcodes for polymeric composites. We also describe a coding methodology wherein a 1 × 1 cm code can represent 3.4 billion parts to 95 trillion parts, depending on the resolution required along with access to morphology-based chemical encryption systems.

Towards sensor applications of a polymer/Ag nanoparticle nanocomposite film

We have demonstrated the capability of a nanocomposite film made of a 2D array of Ag nanoparticles embedded into a poly(glycidyl methacrylate), PGMA, matrix to monitor the presence of organic vapors in the atmosphere. Specifically, changes in the extinction spectra of the submicron nanocomposite film are used to sense the vapors. The transformations of the spectra are fully reversible and reproducible upon multiple exposures. We associate this reversibility and reproducibility with the construction of the nanocomposite film where the cross-linked PGMA network is able to spatially restore its structure upon deswelling. The structure of the extinction spectrum of the film is governed by a collective surface plasmon mode excited in the Ag NPs array. It was found that spectral bands associated with normal and tangential components of the plasmon mode change their width and position when the nanocomposite is exposed to organic vapors. This is due to increasing the spacing between neighboring NPs and a decrease of the refractive index of the polymer caused by swelling of the PGMA matrix. Therefore, the level of spectral transformation is directly related to the level of polymer–solvent thermodynamic affinity where the higher affinity corresponds to the higher level of the swelling. Therefore, we expect that the nanocomposite films (when designed for a particular solvent) can be effectively used as a sensing element in a low-cost volatile organic compounds (VOC) sensor device operating in visual light.

We demonstrated the capability of a nanocomposite film made of Ag nanoparticles embedded into a polymer matrix to detect presence of organic vapors.

Molecular reorganization in bulk bottlebrush polymers: direct observation via nanoscale imaging

Bottlebrush polymers are important for a variety of applications ranging from drug delivery to electronics. The functional flexibility of the branched sidechains has unique assembly properties when compared to linear block polymer systems. However, reports of direct observation of molecular reorganization have been sparse. This information is necessary to enhance the understanding of the structure-property relationships in these systems and yield a rational design approach for novel polymeric materials. In this work, we report direct visualization of bottlebrush molecular organization and the formation of nematic-type ordering in an amorphous polymer bottlebrush system, captured with plasma etching and helium ion microscopy. By observing the unperturbed structure of this material at high resolution and quantifying image features, we were able to qualitatively link experimental results with structures predicted by coarse-grained molecular dynamics simulations. The direct visualization and computation workflow developed in this work can be applied to a broad variety of polymers with different architectures, linking imaging results with other, independent channels of information for better understanding and control of these classes of materials.

En Route to Practicality of the Polymer Grafting Technology: One-Step Interfacial Modification with Amphiphilic Molecular Brushes

Surface modification with polymer grafting is a versatile tool for tuning the surface properties of a wide variety of materials. From a practical point of view, such a process should be readily scalable and transferable between different substrates and consist of as least number of steps as possible. To this end, a cross-linkable amphiphilic copolymer system that is able to bind covalently to surfaces and form permanently attached networks via a one-step procedure is reported here. This system consists of brushlike copolymers (molecular brushes) made of glycidyl methacrylate, poly(oligo(ethylene glycol) methyl ether methacrylate), and lauryl methacrylate, which provide the final product with tunable reactivity and balance between hydrophilicity and hydrophobicity. The detailed study of the copolymer synthesis and properties has been carried out to establish the most efficient pathway to design and tailor this amphiphilic molecular brush system for specific applications. As an example of the applications, we showed the ability to control the deposition of graphene oxide (GO) sheets on both hydrophilic and hydrophobic surfaces using GO modified with the molecular brushes. Also, the capability to tune the osteoblast cell adhesion with the copolymer-based coatings was demonstrated.

Terpyridine-Based Monolayer Electrochromic Materials

Novel electrochromic (EC) materials were developed and formed by a two-step chemical deposition process. First, a self-assembled monolayer (SAM) of 2,2':6',2″-terpyridin-4'-ylphosphonic acid, L, was deposited on the surface of a nanostructured conductive indium-tin oxide (ITO) screen-printed support by simple submerging of the support into an aqueous solution of L. Further reaction of the SAM with Fe or Ru ions results in the formation of a monolayer of the redox-active metal complex covalently bound to the ITO support (Fe-L/ITO and Ru-L/ITO, respectively). These novel light-reflective EC materials demonstrate a high color difference, significant durability, and fast switching speed. The Fe-based material shows an excellent change of optical density and coloration efficiency. The results of thermogravimetric analysis suggest high thermal stability of the materials. Indeed, the EC characteristics do not change significantly after heating of Fe-L/ITO at 100 °C for 1 week, confirming the excellent stability and high EC reversibility. The proposed fabrication approach that utilizes interparticle porosity of the support and requires as low as a monolayer of EC active molecule benefits from the significant molecular economy when compared with traditional polymer-based EC devices and is significantly less time-consuming than layer-by-layer growth of coordination-based molecular assemblies.

Novel Antibacterial Coating on Orthopedic Wires To Eliminate Pin Tract Infections

Novel approaches to the prevention of microbial infections after the insertion of orthopedic external fixators are in great demand because of the extremely high incidence rates of such infections, which can reach up to 100% with longer implant residence times. Monolaurin is an antimicrobial agent with a known safety record that is broadly used in the food and cosmetic industries; however, its use in antimicrobial coatings of medical devices has not been studied in much detail. Here, we report the use of monolaurin as an antibacterial coating on external fixators for the first time. Monolaurin-coated Kirschner wires (K-wires) showed excellent antibacterial properties against three different bacterial strains, i.e., methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and Staphylococcus epidermidis Approximately 6.0-log reductions of both planktonic and adherent bacteria were achieved using monolaurin-coated K-wires, but monolaurin-coated K-wires did not show any observable cytotoxicity with mouse osteoblast cell cultures. Overall, monolaurin-coated K-wires could be promising as potent antimicrobial materials for orthopedic surgery.

Multi-Frequency Measurement of Volatile Organic Compounds With a Radio-Frequency Interferometer

We present a radio-frequency (RF) sensor and its measurement results of three volatile organic compounds (VOCs) at multiple frequency points from ∼ 2 to ∼ 11 GHz, which is a convenient range in our examination. The sensor is based on a simple RF interferometer and uses two coplanar waveguides (CPWs), A and B of 5 and 25 mm length, respectively, as VOC sensing electrodes. Approximately 70-nm-thick poly copolymer films are coated on CPW surfaces for VOC adsorption and concentration. It is shown that ethanol, acetone, and isopropyl (IPA) induce frequency-dependent RF responses, which are also VOC-dependent. Thus, the frequency-dependent properties provide a possible new approach for better VOC sensing selectivity. With CPW A, the limit-of-detections (LODs) are ∼ 600 ppm for ethanol, ∼ 270 ppm for acetone, and ∼ 330 ppm for IPA at 9.29 GHz. With CPW B, the LODs are roughly four times better. These LODs are also better than most of other RF VOC sensor results. In the future work, it is promising to further improve RF sensitivity and selectivity significantly.