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Principles Of Fluorescence Spectroscopy

Functional π-Gelators and Their Applications

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self-healing and self-recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self-healing hydrogels generally either possess mechanically robust or rapid self-healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self-healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self-healing hydrogels are reviewed. Specifically, methods to test self-healing efficiencies and recoveries, mechanisms of autonomous self-healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self-heal better also achieve self-healing faster, as compared to gels that only partially self-heal. Recommendations to guide future development of self-healing hydrogels are offered and the potential relevance of self-healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.

Self-Healing Hydrogels

Detection Ying Zhou,†,‡ Jun Feng Zhang, and Juyoung Yoon*,† †Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea ‡Key Laboratory of Medicinal Chemistry for Natural Resource, School of Chemical Science and Technology, Yunnan University, Kunming, 650091, P. R. China College of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650500, P. R. China

Fluorescence and colorimetric chemosensors for fluoride-ion detection.

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

Low molecular weight fluorescent organogel for fluoride ion detection.

Modified binders exhibit complex rheological behaviour due to the interaction of the modifiers with the base binder and the manner in which they age during field applications. Quantification of the interaction and the ageing of such modified binders is currently a necessity. In this investigation, three modified binders (elastomer, plastomer, and crumb rubber) and the base bitumen were subjected to different ageing conditions and the evolution of the chemical functionalities during ageing were tracked using FTIR spectroscopy. Analysis of the spectra of modified binders immediately after the production process showed that while the elastomer modified binders exhibited physical interaction, the plastomer and crumb rubber modified binders exhibited physical and chemical interactions. During ageing, there was no subsequent evolution of the interactions and one could only see chemical functionalities related to oxidation. Analysis of the spectra showed that the carbonyl and sulphoxide exhibit identical trends ...

Ageing in modified bitumen using FTIR spectroscopy

The effects of proton donors (alcohols and water) on the rate of reduction of acetophenone by SmI2 have been examined utilizing stopped-flow spectrophotometric studies. The rate orders with respect to proton source and the kinetic isotope effects were determined as well. The reaction was first-order in phenol, 2,2,2-trifluoroethanol, methanol, and ethanol and zero-order in 2-propanol and 2-methyl-2-propanol when 25 equiv of proton source were used in the reduction. Methanol, ethanol, 2,2,2-trifluoroethanol, and phenol also showed a direct correlation between the pKa of the alcohol and the rate of reduction. Under the same conditions, water had a fractional rate order of 1.4. Further studies showed that water has a rate order of 1 at lower concentrations ( 80 equiv). These results clearly indicate that the nature of the proton donor and its concentration affects the rates of reduction. Water has a high affinity for SmI2 (compared to that of the alco...

The role of proton donors in SmI2-mediated ketone reduction: new mechanistic insights.

The effect of HMPA on the electron transfer (ET) rate of samarium diiodide reduction reactions in THF was analyzed for a series of ketones (2-butanone, methyl acetoacetate, and N,N-dimethylacetoacetamide) and alkyl iodides (1-iodobutane and 2-iodobutane) with stopped flow spectrophotometric studies. Activation parameters for the ET processes were determined by temperature-dependence studies over a range of 30-50 degrees C. The ET rate constants and the activation parameters obtained for the above systems in the presence of different equivalents of HMPA were compared to understand the mechanism of action of HMPA on various substrates. The results obtained from these studies indicate that coordination or chelation is possible in the transition state geometry for SmI(2)/ketone systems even in the presence of the sterically demanding ligand HMPA. After the addition of 4 equiv of HMPA the ET rate and activation parameters for ketone reduction by Sm is unaffected by further HMPA addition while a linear dependence of ET rate on the equivalents of HMPA was found in the SmI(2)/alkyl iodide system. The results of these studies are consistent with an inner-sphere-type ET for the reduction of ketones by SmI(2) (and SmI(2)[bond]HMPA complexes) and an outer-sphere-type ET for the reduction of alkyl iodides by SmI(2) or SmI(2)[bond]HMPA complexes.

Reduction of ketones and alkyl iodides by SmI(2) and Sm(II)-HMPA complexes. Rate and mechanistic studies.

The mechanistic impact of water addition to SmI2 on the ground state and rate-limiting transition state structures in the reduction of benzyl bromide was determined using UV−vis spectroscopy, cyclic voltammetry, vapor pressure osmommetry, and stopped-flow spectrophotometric studies. The results obtained from these studies show that, upon addition of water, SmI2 in THF (or DME) becomes partially water-solvated by displacing metal-coordinated solvent. Further addition of water displaces remaining bound solvent and induces a monomer−dimer equilibrium of the SmI2−water complex. Concomitant with this process, a thermodynamically more powerful reductant is created. Rate studies on the reduction of benzyl bromide by SmI2−water are consistent with reaction occurring through a dimeric transition state with the assembly of the activated complex requiring an equivalent of water at low concentrations but not at higher concentrations. The mechanistic complexity of the SmI2−water system shows that simple empirical mode...

Edamana Prasad

Papers

Low molecular weight fluorescent organogel for fluoride ion detection.

Ageing in modified bitumen using FTIR spectroscopy

The role of proton donors in SmI2-mediated ketone reduction: new mechanistic insights.

Reduction of ketones and alkyl iodides by SmI(2) and Sm(II)-HMPA complexes. Rate and mechanistic studies.

Mechanistic Impact of Water Addition to SmI2: Consequences in the Ground and Transition State