Chemical and Biomolecular Engineering - Research Publications
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ItemMechanochromophore-Linked Polymeric Materials with Visible Color Changes.(Wiley, 2022-05)Mechanical force as a type of stimuli for smart materials has obtained much attention in the past decade. Color-changing materials in response to mechanical stimuli have shown great potential in the applications such as sensors and displays. Mechanochromophore-linked polymeric materials, which are a growing sub-class of these materials, are discussed in detail in this review. Two main types of mechanochromophores which exhibit visible color change, summarized herein, involve either isomerization or radical generation mechanisms. This review focuses on their synthesis and incorporation into polymer matrices, the type of mechanical force used, factors affecting the mechanochromic properties, and their applications.
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ItemCrosslinked Polypeptide Films via RAFT-Mediated Continuous Assembly of Polymers(WILEY-V C H VERLAG GMBH, 2022-01-12)Polypeptide coatings are a cornerstone in the field of surface modification due to their widespread biological potential. As their properties are dictated by their structural features, subsequent control thereof using unique fabrication strategies is important. Herein, we report a facile method of precisely creating densely crosslinked polypeptide films with unusually high random coil content through continuous assembly polymerization via reversible addition-fragmentation chain transfer (CAP-RAFT). CAP-RAFT was fundamentally investigated using methacrylated poly-l-lysine (PLLMA) and methacrylated poly-l-glutamic acid (PLGMA). Careful technique refinement resulted in films up to 36.1±1.1 nm thick which could be increased to 94.9±8.2 nm after using this strategy multiple times. PLLMA and PLGMA films were found to have 30-50 % random coil conformations. Degradation by enzymes present during wound healing reveals potential for applications in drug delivery and tissue engineering.
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ItemRegulating Color Activation Energy of Mechanophore-Linked Multinetwork Elastomers(American Chemical Society, 2020-05-26)To lower color activation stress/strain while maintaining excellent mechanical properties for mechanochromic materials has been a challenge. Here, a structure of multinetwork polyacrylates was adopted to incorporate a widely studied mechanophore, spiropyran (SP), to investigate the regulation of mechanochromic sensitivity by varying network compositions. In situ color channel intensity analysis was used to characterize deformation-induced ring-opening of SP to merocyanine (MC) for color changes. The multinetwork strategy could substantially reduce the onset of mechanochromic activation strain and stress, and the resulted double networks and triple networks exhibited remarkable mechanochromic performance with excellent mechanical properties. The network formation conditions, including solvent ratio and type of monomers, were shown to have great impact on regulating the mechanochromic activities. A triple-network sample achieved the lowest macroscopic color activation energy compared to previously reported SP-linked elastomers. In addition, the ratio of SP to MC conversion activated by stretching was first shown higher than that by UV light.
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ItemReversible Nontoxic Thermochromic Microcapsules.(American Chemical Society, 2020-02-26)Thermochromic materials exhibit a color change in response to a change in temperature. Creating nontoxic microcapsules containing thermochromic materials for applications in ink and film materials is historically challenging. In this study, we develop a nontoxic chlorophenol red (CPR)-water thermochromic system and its microcapsules with silicone shells via a reaction between water and octadecyltrichlorosilane (OTS) at the interface of a w/o emulsion. The obtained microcapsules exhibit a clear color change with full reversibility and are successfully used as inks by screen printing and as additives in films. Nontoxicity of both microcapsules and films is demonstrated through cell cytotoxicity assays. These features make these novel materials applicable to the next generation of intelligent sensors, coating, and food packaging materials.
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ItemA nontoxic reversible thermochromic binary system via pi-pi stacking of sulfonephthaleins(Royal Society of Chemistry, 2019-08-14)The mechanisms of thermochromic materials are mostly based on Bragg reflection, surface plasmon absorption, molecular structure changes, conformational stretching or aggregation. Here, a simple class of dye–solvent binary systems with clear and reversible thermochromism around ambient temperatures is reported with an alternative mechanism. This system comprises commercially available sulfonephthaleins dissolved in liquid linear chain esters, acids or alcohols, which demonstrate colour changes at different temperatures when the solvents transition from solid to liquid states. The colour changing mechanism is based on π–π stacked aggregation or disaggregation of the sulfonephthalein dyes. Cell toxicity tests confirmed that the sulfonephthalein dyes are less toxic to NIH-3T3 cells than cyanidin chloride, which is the only reported nontoxic food dye affording thermochromism, while this is based on an alternative mechanism. With the choice of a nontoxic solvent, this binary system can form a nontoxic thermochromic material.
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ItemColor-Switchable Polar Polymeric Materials(American Chemical Society, 2019-08-14)Spiropyran is an important mechanophore, which has rarely been incorporated as a cross-linker in polar polymer matrices, limiting its applications in innovative mechanochromic devices. Here, three spiropyrans with two- or three-attachment positions were synthesized and covalently bonded in polar poly(hydroxyethyl acrylate) (PHEA), to achieve color-switchable materials, triggered by light and when swollen in water. The negative photochromism in the dark and mechanical activation by swelling in water were investigated. Measurements of negative photochromism were conducted in solution and cross-linked PHEA bulk polymers, with both showing color reversibility when stored in the dark or on exposure to visible light. The force of swelling in water was sufficient to induce the ring-opening reaction of spiropyran. It was found that tri-substituted spiropyran (SP3) was less influenced by the polar matrix but showed the fastest color activation during swelling. SP3 also showed accelerated ring opening to the colored state during the swelling process. Bleaching rates and color switchability were investigated under swollen and dehydrated conditions. The effect of cross-link density on the swelling activation was explored to better understand the interaction between the mechanophore and the polar environment. The results demonstrated that influences from both the polar environment and the mechanochromic nature of spiropyran had an impact on the absorption intensity, rate of change, and the decoloration rate of the materials. This study provides the opportunity to manipulate the properties of spiropyrans to afford materials with a range of color-switching properties under different stimuli.
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