This article is an overview of extensive research efforts in the area of temperature‐controlled electrochemical systems. Electrochemical reactions, including electrocatalytic and bioelectrocatalytic processes, have been reversibly activated and inhibited by temperature changes. This was achieved by modification of electrode surfaces with thermo‐sensitive polymers (e.g., poly(N‐isopropylacrylamide), PNIPAM) which are reversibly switched by temperature changes between two different structures: swollen expanded coil conformation and shrunken collapsed globule state. While the swollen hydrophilic state allows penetration of redox species to the electrode conducting support and activates electrochemical reactions, the collapsed hydrophobic state isolates the electrode surface and inhibits electrochemical processes. Electrodes modified with the thermo‐switchable polymers have been additionally functionalized with photo‐switchable molecules (e.g., spiropyran derivatives) to achieve double‐controlled electrochemical reactions switchable by temperature changes and light signals. Incorporation of metallic nanoparticles or graphene species in the temperature‐sensitive polymer films resulted in sophisticated features and multi‐signal controlled behavior of the nano‐composite systems. 相似文献
Photochromic spiropyran molecules were embedded in electrospun polymer microfibers. Electrospinning of a clear viscous chloroform solution containing a spiropyran and a matrix polymer, such as polystyrene and polyethylene oxide, affords polymer microfibers that are photoswitchable. Photomasked, 365 nm UV irradiation of the microfibers results in the generation of patterned color images owing to the selective transformation of the spiropyran molecules from their ring‐closed SP to ring‐opened MC form. The UV‐irradiated areas display brilliant red fluorescence, which changes to green fluorescence upon prolonged irradiation.
We report a neutron-scattering study to characterize the ordering and local dynamics of spherical micelles formed by the triblock copolymer polyethylene oxide (PEO)--polypropylene oxide (PPO)--polyethylene oxide (Pluronic) in aqueous solution. The study focuses on two Pluronic species, F68 and F108, that have the same weight fraction of PEO but that differ in chain length by approximately a factor of 2. At sufficiently high concentration, both species undergo a sequence of phase changes with increasing temperature from dissolved chains to micelles with liquid-like order to a cubic crystal phase and finally back to a micelle liquid phase. A comparison of the phase diagrams constructed from small-angle neutron scattering indicates that crystallization is suppressed for shorter chain micelles due to fluctuation effects. The intermediate scattering function I(Q,t)I(Q,0) determined by neutron spin echo displays a line shape with two distinct relaxations. Comparisons between I(Q,t)I(Q,0) for fully hydrogenated F68 chains in D2O and for F68 with deuterated PEO blocks reveal that the slower relaxation corresponds to Rouse modes of the PPO segments in the concentrated micelle cores. The faster relaxation is identified with longitudinal diffusive modes in the PEO corona characteristic of a polymer brush. 相似文献
The effect of potassium chloride on the micellization of a poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymer (Pluronic F88: EO103PO39EO103.) in water was studied by fluorescence, FTIR, 1H NMR, dynamic light scattering, and dye solubilization. The critical micellization temperature (CMT) values of the copolymer decreased with an increase of KCl concentration while micellar core gets progressively dehydrated. The results reveal the leading role of salt‐water interaction in promoting the micellization of PEO‐PPO‐PEO copolymer by the addition of salt. No significant micellar growth was seen even at temperatures close to cloud point. 相似文献
Well-defined, reversibly light-responsive amphiphilic diblock copolymer grafted with spiropyran, was prepared by reversible addition–fragmentation chain transfer(RAFT) polymerization. The copolymer self-assembles into polymeric micelles in water and exhibits reversible dissolution and re-aggregation characteristics upon ultraviolet(UV) and visible(Vis)-light irradiation. The fluorescence response of spiropyran immobilized onto the copolymer was light switchable. When nitrobenzoxadiazolyl derivative(NBD) dyes are encapsulated into the core of the micelles, a reversible, light-responsive, dual-color fluorescence resonance energy transfer(FRET) system is constructed and processed, which is well regulated by alternatively UV/vis irradiation. We anticipate these photoswitchable and FRET lighting up nanoparticles will be useful in drug delivery and cell imaging or tracking synchronously. 相似文献
The first main‐chain conjugated copolymers based on alternating spiropyran (SP) and 9,9‐dioctylfluorene (F8) units synthesized via Suzuki polycondensation (SPC) are presented. The reaction conditions of SPC are optimized to obtain materials of type P(para‐SP‐F8) with appreciably high molecular weights up to Mw ≈ 100 kg mol−1. 13C NMR is used to identify the random orientation of the non‐symmetric SP unit in P(p‐SP‐F8). Ultrasound‐induced isomerization of P(p‐SP‐F8) to the corresponding merocyanine form P(p‐MC‐F8) yields a deep‐red solution. This isomerization reaction is followed by 1H NMR in solution using sonication, whereby the color increasingly changes to deep red. The possibility to incorporate multiple SP units into main‐chain polymers significantly broadens existing SP‐based polymeric architectures. 相似文献
Here the synthesis and characterization of a new class of spiropyran‐based protease inhibitor is reported that can be reversibly photoswitched between an active spiropyran (SP) isomer and a less active merocyanine (MC) isomer upon irradiation with UV and visible light, respectively, both in solution and on a surface of a microstructured optical fiber (MOF). The most potent inhibitor in the series ( SP ‐ 3 b ) has a C‐terminal phenylalanyl‐based α‐ketoester group and inhibits α‐chymotrypsin with a Ki of 115 nM . An analogue containing a C‐terminal Weinreb amide ( SP‐2 d ) demonstrated excellent stability and photoswitching in solution and was attached to the surface of a MOF. The SP isomer of Weinreb amide 2 d is a competitive reversible inhibitor in solution and also on fiber, while the corresponding MC isomer was significantly less active in both media. The ability of this new class of spiropyran‐based protease inhibitor to modulate enzyme activity on a MOF paves the way for sensing applications. 相似文献
Summary: Spherical micelles have been formed by mixing, in DMF, a poly(styrene)‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐block‐P2VP‐block‐PEO) triblock copolymer with either poly(acrylic acid) (PAA) or a tapered triblock copolymer consisting of a PAA central block and PEO macromonomer‐based outer blocks. Noncovalent interactions between PAA and P2VP result in the micellar core while the outer corona contains both PS and PEO chains. Segregation of the coronal chains is observed when the tapered copolymer is used.
Inclusion of comb‐like chains with short PEO teeth in the corona triggers the nanophase segregation of PS and PEO as illustrated here (PS = polystyrene; PEO = poly(ethylene oxide)). 相似文献
We report a stimuli‐responsive fluorescent nanomaterial, based on graphene oxide coupled with a polymer conjugated with photochromic spiropyran (SP) dye and hydrophobic boron dipyrromethane (BODIPY) dye, for application in triggered target multicolor bioimaging. Graphene oxide (GO) was reduced by catechol‐conjugated polymers under mildly alkaline conditions, which enabled to formation of functionalized multicolor graphene nanoparticles that can be induced by irradiation with UV light and by changing the pH from acidic to neutral. Investigation of these nanoparticles by using AFM, fluorescence emission, and in vitro cell and in vivo imaging revealed that they show different tunable colors in bioimaging applications and, more specifically, in cancer‐cell detection. The stability, biocompatibility, and quenching efficacy of this nanocomposite open a different perspective for cell imaging in different independent colors, sequentially and simultaneously. 相似文献
Based on the 1H relaxation of transverse nuclear magnetization of triblock-copolymer Pluronic F-127 in D2O, we proposed a model of the associated pluronic structure in which the polyethylene oxide of molecules in neighboring micelles are intertwined in regions of overlapping micellar coronas, while the polypropylene oxide cores of the micelles play a role of nodes in the 3D network. 相似文献
Pluronic F108 block copolymers have shown a great promise to achieve the desirable high resolution in the conformation‐sensitive separation of ssDNA using CE‐SSCP. However, fundamental understanding of the structures and properties of Pluronic matrix affecting the resolution is still limited. Unlike conventional gel‐forming homopolymers, Pluronic F108 block copolymers are amphiphilic macromolecules consisting of poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide) triblock copolymers, which are capable of forming a highly ordered micellar structure in aqueous solution. In this study, we have performed a series of experiments by blending different types of Pluronic polymers to control the formation of micelles and to study the correlation between separation and rheological characteristics of Pluronic gels affecting the resolution of CE‐SSCP. Our experiments have been specifically designed to elucidate how the micellar structure affects the resolution of CE‐SSCP upon altering the size uniformity and constituent homogeneity of the micelles. Our results suggest that uniformly sized micelle packing is the primary structural feature of Pluronic gel matrix for the high‐resolution separation, while the size and constituent of the micelle themselves need to be considered as secondary factors. 相似文献
We present a morphological study of the micellization of an asymmetric semicrystalline block copolymer, poly(butadiene)‐block‐poly(ethylene oxide), in the selective solvent n‐heptane. The molecular weights of the poly(butadiene) (PB) and poly(ethylene oxide) (PEO) blocks are 26 and 3.5 kg · mol−1, respectively. In this solvent, micellization into a liquid PEO‐core and a corona of PB‐chains takes place at room temperature. Through a thermally controlled crystallization of the PEO core at −30 °C, spherical micelles with a crystalline PEO core and a PB corona are obtained. However, crystallization at much lower temperatures (−196 °C; liquid nitrogen) leads to the transition from spherical to rod‐like micelles. With time these rod‐like micelles aggregate and form long needles. Concomitantly, the degree of crystallinity of the PEO‐cores of the rod‐like micelles increases. The transition from a spherical to a rod‐like morphology can be explained by a decrease of solvent power of the solvent n‐heptane for the PB‐corona chains: n‐Heptane becomes a poor solvent at very low temperatures leading to a shrinking of the coronar chains. This favors the transition from spheres to a morphology with a smaller mean curvature, that is, to a cylindrical morphology.