Electric Properties of Multiwalled Carbon Nanotubes Dispersed in Liquid Crystals and Their Influence on Freedericksz Transitions.

Liquid crystal composites with multiwalled carbon nanotubes present dielectric properties considerably different from those of pure liquid crystal (LC). Using a proper dispersion of nanotubes in the LC-sample and a theoretical model in agreement with the experimental configuration, the dielectric permittivities of multiwalled carbon nanotubes are calculated. The influence of dielectric properties on the Freedericksz transition threshold is discussed. Theoretical values for dielectric permittivities of multiwalled carbon nanotubes are calculated for different temperatures.

The Influence of Single-Walled Carbon Nanotubes on the Dynamic Properties of Nematic Liquid Crystals in Magnetic Field.

This article aims to study the impact of carbon nanotube dispersions in liquid crystals. A theoretical model for the system's dynamics is presented, considering the elastic continuum theory and a planar alignment of liquid crystal molecules on the nanotube's surface. Experimental calculation of the relaxation times in the magnetic field was made for two cases: when the field was switched on (τon), and when it was switched off (τoff). The results indicate an increase of the relaxation time by about 25% when the magnetic field was switched off, and a smaller increase (about 10%) when the field was switched on, where both were in good agreement with the theoretical values.

Dynamic behavior of nematic liquid crystal mixtures with quantum dots in electric fields.

The dynamic behavior of a mixture consisting of liquid crystalline 4-cyano-4'-pentylbiphenyl (5CB) and CdSe/ZnS quantum dots in electric fields was theoretically studied. The model was based on elastic continuum theory considering the interaction of the nematic molecules with the surrounding molecules, with the quantum dots and with the electric field. Experimental data obtained by dynamic measurements on a sample containing 0.89% (mass fraction) of CdSe/ZnS quantum dots revealed a decrease of the relaxation time compared to pure 5CB.

Dynamic behavior of a nematic liquid crystal with added carbon nanotubes in an electric field.

The dynamic behavior of a nematic liquid crystal with added carbon nanotubes (CNTs) in an electric field was analyzed. A theoretical model based on elastic continuum theory was developed and the relaxation times of nematic liquid crystals with CNTs were evaluated. Experiments made with single-walled carbon nanotubes dispersed in nematic 4-cyano-4'-pentylbiphenyl (5CB) indicated a significant difference of the relaxation time when compared to pure liquid crystal. We also noticed that the relaxation time when the field is switched off depends on how long the field was applied. It is shorter when the field is switched off immediately after application and longer when the field was applied for at least one hour.

Dynamic behavior of a nematic liquid crystal mixed with CoFe2O4 ferromagnetic nanoparticles in a magnetic field.

The dynamic behavior of a mixture of 4-cyano-4'-pentylbiphenyl (5CB) with 1% CoFe2O4 nanoparticles was analyzed. Experimental data indicate a high stability of the nematic director in the mixture compared to a reference 5CB sample in the magnetic field. The ferrite nanoparticles agglomerate forming long chains as observed in polarized microscopy images. These chains have a very high influence on the magneto-optic effect of the cell. When the magnetic field is applied on the mixture, the chains tend to align with the field direction but, due to their large size, they remain oriented obliquely between the support plates. Thus, the nematic molecules anchored on their surface can not reorient with the field and only a small distortion angle of the liquid crystal molecular director is observed. A comparison with a previously developed theoretical model confirms this small deviation.

An Analysis of Human Dorsal Hand Skin Texture Using Hyperspectral Imaging Technique for Assessing the Skin Aging Process.

Skin texture has become an important issue in recent research with applications in the cosmetic industry and medicine. In this paper, we analyzed the dependence of skin texture features on wavelength as well as on different parameters (age and gender) of human participants using grey-level co-occurrence matrix and hyperspectral imaging technique for a more accurate quantitative assessment of the aging process. A total of 42 healthy participants (men and women; age range, 20-70 years) was enrolled in this study. A region of interest was selected from the hyperspectral images. The results were analyzed in terms of texture using the gray-level co-occurrence matrix which generated four features (homogeneity, contrast, entropy, and correlation). The results showed that most of these features displayed variations with wavelength (the exception was entropy), with higher variations in women. Only correlation in both sexes and contrast in men proved to vary statistically significant with age, making them the targeted variables in future attempts to characterize aging skin using the complex method of hyperspectral imaging. In conclusion, by using hyperspectral imaging some measure of the degree of damage or the aging process of the hand skin can be obtained, mainly in terms of correlation values. At the present time, reasonable explanations that can link the process of skin aging and the above mentioned features could not be found, but deeper investigations are on the way.

Increased number of fractionated irradiation sessions does not improve the cellular response to methyl aminolevulinate-mediated photodynamic therapy.

BACKGROUND: In the search to improve the efficacy of photodynamic therapy different approaches have been investigated until now. One of these approaches is the use of double fractionated irradiation schemes. This study aims to investigate the effect of increasing the numbers of fractionated irradiation sessions in methyl aminolevulinate-mediated photodynamic therapy on dysplastic oral keratinocytes by monitoring the changes in optical properties of cell culture. METHODS: Forty cell cultures were divided into four experimental groups (single, double and triple fractionated irradiation scheme and control). Cells were incubated with 1mM methyl aminolevulinate and after 2h they were exposed to laser radiation (λ=635 nm, P=15 mW). The exposure time was 900 s for the single irradiation scheme, 300 s + 600 s for the double fractionated irradiation scheme with dark interval between sessions of 30 min and 300 s + 300 s + 300 s for the triple fractionated irradiation scheme with two dark intervals between sessions of 30 min. Two optical parameters (refractive index and extinction coefficient) were calculated from diffuse reflectance spectra of cell cultures using the Kramers-Kronig relations. RESULTS: The results demonstrate that the use of double fractionated irradiation scheme led to changes in optical parameters of cell cultures more important than the use of the single and triple fractionated irradiation schemes in photodynamic therapy. CONCLUSIONS: In conclusion, increasing too much the number of irradiation sessions cannot lead to an improved photodynamic effect.