Ronan Daly

Polymer mechanochemistry harnesses mechanical strain to control chemical reactivity. Here, we study an ultrahigh molecular weight polymechanophore system, poly(BCH‐Naph). We first activate the polymechanophore through the standard and accepted method of ultrasonication, which relies on many localized flows driven by cavitation. Second, we compare these results with activation during flow through nozzles, where the flow conditions can be fully characterised and are a step toward real production processes. We find that each method of activation has its own unique distribution of strain and strain rate, demonstrating that we cannot rely on standard ultrasonication testing when considering flow‐based applications as the results are not correlated quantitatively. It is a common observation that below a limiting chain length, there is insufficient force generated to activate mechanophores. Here, using the ultrahigh molecular weight system, we found fragments of much smaller molecular weights than previously achieved under single‐pass flow conditions. We can see that the already‐elongated polymer can undergo multiple scission events when it is trapped within a high shear flow region. This research on the mechanoactivation of polymechanophore solutions in nozzle flow is an important step toward the informed design of mechanophore‐containing systems programmed to activate during specific, industrially‐relevant fluid flows.

There is a need for direct-write patterning alternatives to support trends in low-volume and late-stage manufacturing of devices and integrating sensors directly to existing products or formed materials. This is particularly challenging when trying to take advantage of the sensing properties linked to vertically aligned carbon nanotube forests. The catalyst layer thickness is a critical parameter when growing these forests by chemical vapor deposition, as it determines the size of catalyst nano-islands that form and act as seeds for nanotube growth. Physical vapor deposition is a standard technique for catalyst deposition, with photolithography used across the literature to pattern layers of catalyst and enable device design. However, wide-area direct-write techniques face a major barrier in reliably controlling layer thickness to the nanoscale precision required. In this paper, we combine deposition of iron oxide nanoparticles by the direct-write technique of inkjet printing with material removal by laser ablation to deliver both patterning and fine control of the layer thickness. First, we show that there is an optimum printed layer thickness to ensure a good quality forest growth and second that laser ablation can be used to enhance, reduce, or stop this growth. Detailed analysis of the catalyst with AFM, sXRD, and electron microscopy shows that these controls stem from their influence over nano-island formation of the catalyst at the start of the CVD process. Finally, we demonstrate the potential for applications by fabricating a simple gas sensor with this hybrid approach.

In recent years, microfluidic systems have evolved to incorporate increasingly complex multi-layer and multi-material structures. While conventional 2-dimensional microfluidic systems are typically fabricated with lithographic techniques, the increase in system complexity necessitates a more versatile set of fabrication techniques. Similarly, although 3D printing can easily produce intricate microfluidic geometries, integrating multiple membranes and electrode components remains challenging. This study proposes a toolkit for fabricating free-standing 3-dimensional microfluidic systems for biomedical devices, incorporating flow channels, electrodes, and membranes. The fabrication techniques include molding separation using 3D printed molds, laser-based processing, and component assembly, each achieving micron resolution. Here, we introduce a novel approach to integrate membranes into microfluidics by directly curing elastomer-based microfluidics with the membrane through replica molding, while preserving membrane functionality by effectively removing elastomer residues through reactive ion etching. The resulting membrane-elastomer microfluidic component significantly simplifies the assembly of intricate microfluidic systems, reducing the device size to millimeter dimensions, suitable for implantable applications. The toolkit’s versatility is demonstrated by a redox flow iontophoretic drug delivery prototype at the millimeter scale, featuring two electrodes, four membranes, and four microfluidic channels.

The ability to convert light to higher energies through triplet–triplet annihilation upconversion (TTA-UC) is attractive for a range of applications including solar energy harvesting, bioimaging and anti-counterfeiting. Practical applications require integration of the TTA-UC chromophores within a suitable host, which leads to a compromise between the high upconversion efficiencies achievable in liquids and the durability of solids. Herein, we present a series of methacrylate copolymers as TTA-UC hosts, in which the glass transition temperature (T_g), and hence upconversion efficiency can be tuned by varying the co-monomer ratios (n-hexyl methacrylate (HMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA)). Using the model sensitiser/emitter pair of palladium(II) octaethylporphyrin (PdOEP) and diphenylanthracene (DPA), the upconversion quantum yield was found to increase with decreasing glass transition temperature, reaching a maximum of 1.6 ± 0.2% in air at room temperature. Kinetic analysis of the upconversion and phosphorescence decays reveal that increased PdOEP aggregation in the glassy polymers leads to a competitive non-radiative relaxation pathway that quenches the triplet state. Notably, the threshold intensity is highly sensitive to the glass transition temperature, ranging from 1250 mW cm⁻² for PHMA₉₀TFEMA₁₀ (T_g = −9.4 °C) to ∼200 mW cm⁻² for more ‘glassy’ hosts, e.g. PHMA₃₃TFEMA₆₇ (T_g = 20.1 °C), suggesting the TTA-UC mechanism switches from diffusion-based collisions to triplet exciton migration at localised sensitiser–emitter pairs.

It is crucial to consider both solvent strain and strain rate when predicting mechanochemistry of polymer solutions in arbitrary flows.

Drug delivery into the brain and spinal cord is fundamentally limited by the blood‐brain barrier which impedes the use of the vast majority of drugs. Implants based on iontophoresis use an applied voltage to deliver charged drug molecules, allowing solvent‐free delivery directly into the site of interest and overcoming issues associated with systemic exposure to the drug. However, during continuous delivery over long periods, electrochemical reactions occur at the electrodes leading to corrosive gas formation. Here, the concept of redox flow iontophoresis is presented, where a redox mediator solution is used to control electrode reactions and sustain continuous delivery for theoretically unlimited duration. As a proof‐of‐concept, a redox flow iontophoresis‐based brain implant that can continuously deliver the cancer drug doxorubicin at stable rates exceeding 2 nmol min⁻¹ is demonstrated. This new concept enables the continuous delivery of various potent drugs into the brain and spinal cord and therefore has the potential to improve treatment options for various diseases.

The attachment point of the polymer chain to a force‐responsive molecular unit (mechanophore) is a decisive parameter determining bond scission rate and ultimately the mechanochemical reaction outcome. However, such regiochemical polymer substituent effects have not yet been investigated for 9‐π‐extended anthracene‐maleimide Diels‐Alder adducts. Here we combine three methods, namely ultrasonication, CoGEF computation, and flow activation, to understand the influence of the pulling point location on the mechanochemical reactivity of this mechanophore class. We find minor mechanochemical reactivity differences between the investigated constitutional mechanophore isomers. Concomitantly, our results highlight the capabilities and limitations of the employed experimental techniques for such delicate variances and raise the question whether these are relevant for mechanochemical applications in a material context.