Self-cleaning superhydrophobic epoxy coating based on fibrous silica-coated iron oxide magnetic nanoparticles.

Inspired by the self-cleaning lotus leaf, a facile method of fabricating superhydrophobic silica coated magnetite nanoparticles using a cost-effective process is presented in this work. The structural characterizations and magnetic properties of the obtained core-shell magnetic nanoparticles were characterized by means of X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). TEM analysis revealed that the particles present flower-like dendrimeric fibers morphology. The particles were uniformly dispersed on the surface of an epoxy resin coating with the purpose to increase the roughness and reduce the surface energy of the surface. The resulting superhydrophobic surface provides robust water-repellent surface under harsh conditions, thanks to its self-cleaning characteristic. The superhydrophobicity of this surface was confirmed based on the measurements of a water contact angle around 175°, which surpasses the theoretical limit of the superhydrophobicity. The simplicity and the cost-effectiveness of the process developed in this study appears to be a promising route for the preparation of other magnetic superhydrophobic organic-inorganic hybrid materials that would be beneficial in a wide variety of applications.

Magnetic field switchable dry adhesives.

A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field.

Neodymium-doped LaF(3) nanoparticles for fluorescence bioimaging in the second biological window.

The future perspective of fluorescence imaging for real in vivo application are based on novel efficient nanoparticles which is able to emit in the second biological window (1000-1400 nm). In this work, the potential application of Nd(3+) -doped LaF(3) (Nd(3+) :LaF(3) ) nanoparticles is reported for fluorescence bioimaging in both the first and second biological windows based on their three main emission channels of Nd(3+) ions: (4) F(3/2) →(4) I(9/2) , (4) F(3/2) →(4) I(11/2) and (4) F(3/2) →(4) I(13/2) that lead to emissions at around 910, 1050, and 1330 nm, respectively. By systematically comparing the relative emission intensities, penetration depths and subtissue optical dispersion of each transition we propose that optimum subtissue images based on Nd(3+) :LaF(3) nanoparticles are obtained by using the (4) F3/2 →(4) I11/2 (1050 nm) emission band (lying in the second biological window) instead of the traditionally used (4) F(3/2) →(4) I(9/2) (910 nm, in the first biological window). After determining the optimum emission channel, it is used to obtain both in vitro and in vivo images by the controlled incorporation of Nd(3+) :LaF(3) nanoparticles in cancer cells and mice. Nd(3+) :LaF(3)nanoparticles thus emerge as very promising fluorescent nanoprobes for bioimaging in the second biological window.

Subtissue thermal sensing based on neodymium-doped LaF3 nanoparticles.

In this work, we report the multifunctional character of neodymium-doped LaF3 core/shell nanoparticles. Because of the spectral overlap of the neodymium emission bands with the transparency windows of human tissues, these nanoparticles emerge as relevant subtissue optical probes. For neodymium contents optimizing the luminescence brightness of Nd³âº:LaF3 nanoparticles, subtissue penetration depths of several millimeters have been demonstrated. At the same time, it has been found that the infrared emission bands of Nd³âº:LaF3 nanoparticles show a remarkable thermal sensitivity, so that they can be advantageously used as luminescent nanothermometers for subtissue thermal sensing. This possibility has been demonstrated in this work: Nd³âº:LaF3 nanoparticles have been used to provide optical control over subtissue temperature in a single-beam plasmonic-mediated heating experiment. In this experiment, gold nanorods are used as nanoheaters while thermal reading is performed by the Nd³âº:LaF3 nanoparticles. The possibility of a real single-beam-controlled subtissue hyperthermia process is, therefore, pointed out.

Effect of sodium chloride on the binding of polyaromatic hydrocarbon guests with sodium cholate aggregates.

Sodium cholate aggregates are adaptable host systems. The effect of changing the ionic strength with the addition of NaCl on the properties for guest binding to sodium cholate aggregates was investigated by using pyrene, perylene and 1-ethylnaphthalene as guests. Fluorescence, anisotropy and laser flash photolysis studies provided information on the protection efficiency of the aggregate bound guest, and provided information on the dynamics and correlation times for the host-guest system. Different trends for the protection efficiency of the bound guests were observed when the NaCl concentration was raised depending on the charge of the aqueous solubilized quencher. The increase in ionic strength was also shown to lengthen the correlation time of the aggregate bound guest and led to faster dynamics for the host-guest complex. These results show that the properties of sodium cholate aggregates as a supramolecular host system are significantly altered with changes in the ionic strength of the medium.

Directional study of the optical properties of Tb3+- and Eu3+-doped nanoparticles embedded in silica photonic crystals.

The effects of the stop band (SB) in colloidal photonic crystals composed of silica spheres containing Eu(3+)- and Tb(3+)-doped yttria nanoparticles are analysed. Reflection and transmission spectra indicate movement of the stop band, due to the 111 series of planes, towards shorter wavelengths with increasing angle of observation. The profile of the emission spectra is modified by the presence of the SB depending on the angle of measurement. Such a modification is more effective for a narrow emission band and it is thus more evident in the case of Tb(3+) than Eu(3+). An angular effect is also observed in the lifetime, which presents two maxima and one minimum. In the case of Tb(3+) the maxima are at observation angles of 35 and 50 degrees, and the minimum at 45 degrees. We attribute this behaviour to penetration of the excitation beam at 475 nm modulated by the stop band. The ions excited in this way emit from different depths in the crystal, and therefore their lifetime will be affected differently by the same stop band, depending on the thickness of the crystal that must be crossed. Eu(3+) shows a similar but less pronounced effect for two reasons: first, the main stop band (due to the 111 planes) is not effective at the excitation wavelength of 392 nm; second, the broadness of the Eu(3+) emission is comparable to the width of the SB, and a decrease in the transition rate at the wavelength of the SB maximum is compensated by an increase at the sides of the SB.

Determination of the Förster distance in polymer films by fluorescence decay for donor dyes with a nonexponential decay profile.

Fluorescence resonance energy transfer (FRET) experiments were carried out on three pairs of donor-acceptor dyes in polymer films in which the donor dyes had absorption maxima in the range of 350-450 nm. Two of the donors, a coumarin dye and a naphthalimide dye covalently bound to polystyrene, gave nonexponential decays in the absence of acceptors. The decay profiles could be fitted to a stretched exponential form with a beta value on the order of 0.9. We developed equations for analyzing donor fluorescence intensity decay profiles for donor-acceptor mixtures in rigid matrices for the case of donors showing relatively small deviations from exponentiality. To test these equations, we calculate values of the Förster radius (R0(FR)) from the decay profile data and compare these values to the Förster radius R0(SO) determined by the traditional spectral overlap method. Agreement between these values validates the methodology developed here for the use of such donor dyes in FRET studies of more complex polymer systems.

Wavelength redistribution and color purification action of a photonic crystal.

Currently, photonic crystals are attracting a lot of interest because of their ability to harvest light from a device into specific directions and wavelengths. In this work we have proven the theoretical prediction that in the case of an emission overlapping with the photonic stop band, the intensity is redistributed at different wavelengths. This prediction has two major consequences: (i) the total QY remains the same and (ii) the intensity increases just outside the band gap. In our case, Eu(2+) is the responsible emitter in a hybrid material based on GaN on silica, which has a fairly broad emission with its maximum at 500 nm. The GaN and Eu(2+) were placed inside an inverse opal of silica (air voids in silica matrix). The size of the holes in the different samples was varied between 300 and 600 nm, in order to tune the stop band in different positions with respect to the Eu(2+) emission. The measured quantum yield was constant for the different samples at about 5%, the lifetime of the Eu(2+) increased in the forbidden range, and its emission intensity was squeezed toward the side of the stop band, with a concomitant decrease of the lifetime. The enhancement of the emission intensity at a certain energy range opens new possibilities for the design of more efficient devices, providing color purification and intensification at whichever wavelength is needed.