Spatially Controlled Uv Light Generation at Depth Using Upconversion Micelles.
Advanced materials (Deerfield Beach, Fla.)
Ultraviolet (UV) light can trigger a plethora of useful photochemical reactions for diverse applications, including photocatalysis, photopolymerization, and drug delivery. These applications typically require penetration of high energy photons deep into materials, yet delivering these photons beyond the surface is extremely challenging due to absorption and scattering effects. Triplet-triplet annihilation upconversion (TTA-UC) shows great promise to circumvent this issue by generating high energy photons from incident lower energy photons. However, molecules that facilitate TTA-UC usually have poor water solubility, limiting their deployment in aqueous environments. To address this challenge, a nanoencapsulation method is leveraged to fabricate water-compatible UC micelles, enabling on-demand UV photon generation deep into materials. Two iridium-based complexes are presented for use as TTA-UC sensitizers with increased solubilities that facilitate the formation of highly emissive UV-upconverting micelles. Furthermore, this encapsulation method is shown to be generalizable to nineteen UV-emitting UC systems, accessing a range of upconverted UV emission profiles with wavelengths as low as 350 nm. As a proof-of-principle demonstration of precision photochemistry at depth, UV-emitting UC micelles are used to photolyze a fluorophore at a focal point nearly a centimeter beyond the surface, revealing opportunities for spatially controlled manipulation deep into UV-responsive materials. This article is protected by copyright. All rights reserved.
View details for DOI 10.1002/adma.202301563
View details for PubMedID 37548335
- Flow-concentration coupling determines features of nonhomogeneous flow and shear banding in entangled polymer solutions JOURNAL OF RHEOLOGY 2023; 67 (1): 219-239
Flow-Induced Concentration Nonuniformity and Shear Banding in Entangled Polymer Solutions
PHYSICAL REVIEW LETTERS
2021; 126 (20): 207801
Recent models have predicted entangled polymer solutions could shear band due to unstable flow-induced demixing. This work provides the first experimental probe of the in situ concentration profile of entangled polymer solutions under shear. At shear rates above a critical value, we show that the concentration and velocity profiles can develop bands, in quantitative agreement with steady-state model predictions. These findings highlight the critical importance of flow-concentration coupling in entangled polymer solutions.
View details for DOI 10.1103/PhysRevLett.126.207801
View details for Web of Science ID 000652840600012
View details for PubMedID 34110187
Cellulose nanocrystals for gelation and percolation-induced reinforcement of a photocurable poly(vinyl alcohol) derivative
2020; 16 (37): 8602-8611
Nanomaterials are regularly added to crosslinkable polymers to enhance mechanical properties; however, important effects related to gelation behavior and crosslinking kinetics are often overlooked. In this study, we combine cellulose nanocrystals (CNCs) with a photoactive poly(vinyl alcohol) derivative, PVA-SbQ, to form photocrosslinked nanocomposite hydrogels. We investigate the rheology of PVA-SbQ with and without CNCs to decipher the role of each component in final property development and identify a critical CNC concentration (1.5 wt%) above which several changes in rheological behavior are observed. Neat PVA-SbQ solutions exhibit Newtonian flow behavior across all concentrations, while CNC dispersions are shear-thinning <6 wt% and gel at high concentrations. Combining semi-dilute entangled PVA-SbQ (6 wt%) with >1.5 wt% CNCs forms a percolated microstructure. In situ photocrosslinking experiments reveal how CNCs affect both the gelation kinetics and storage modulus (G') of the resulting hydrogels. The modulus crossover time increases after addition of up to 1.5 wt% CNCs, while no modulus crossover is observed >1.5 wt% CNCs. A sharp increase in G' is observed >1.5 wt% CNCs for fully-crosslinked networks due to favorable PVA-SbQ/CNC interactions. A percolation model is fitted to the G' data to confirm that mechanical percolation is maintained after photocrosslinking. A ∼120% increase in G' for 2.5 wt% CNCs (relative to neat PVA-SbQ) confirms that CNCs provide a reinforcing effect through the percolated microstructure formed from PVA-SbQ/CNC interactions. The results are testament to the ability of CNCs to significantly alter the storage moduli of crosslinked polymer gels at low loading fractions through percolation-induced reinforcement.
View details for DOI 10.1039/d0sm01376e
View details for Web of Science ID 000573714400003
View details for PubMedID 32845269
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