RESUMEN
The fast and global spread of bacterial resistance to currently available antibiotics results in a great and urgent need for alternative antibacterial agents and therapeutic strategies. Recent studies on the application of nanomaterials as antimicrobial agents have demonstrated their potential for the management of infectious diseases. Among the diverse palette of nanomaterials currently used in biomedical applications, carbon nanotubes (CNTs) have gained massive interest given their many valuable properties, such as high thermal and electrical conductivity, tensile strength, flexibility convenient aspect ratio, and low fabrication costs. All these features are augmented by facile conjugation with functional groups. CNTs are currently available in many configurations, with two main categories being single-walled and multi-walled CNTs, depending on the number of rolled-up single-layer carbon atoms sheets making up the nanostructure. Both classes have been identified over the past years as promising antibacterial agents but the current level of understanding of their efficiency still harbors many pending questions. This mini-review surveys recent progress on the topic of antibacterial effects of CNTs and examines the proposed mechanisms of action(s) of different CNT typologies, placing the main focus on past studies addressing the antibacterial activity on Staphylococcus aureus and Escherichia coli, two prototypical Gram-positive and Gram-negative pathogens, respectively.
RESUMEN
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.
RESUMEN
A theoretical evaluation of the electric Freedericksz transition threshold and saturation field is proposed for a liquid crystals composite with ferroelectric particles. Existing models consider a strong anchoring of nematic molecules on the glass support of the cell, but in this paper a soft molecular anchoring of molecules on the glass support and also on the ferroelectric nanoparticle's surface is assumed. Thus, a finite saturation field was obtained in agreement with real systems. Calculations are made for planar configuration of positive dielectric anisotropy liquid crystals. The results are compared with data obtained on similar systems from different publications and the differences are discussed.
Asunto(s)
Cristales Líquidos/química , Simulación de Dinámica Molecular , Campos Electromagnéticos , Nanopartículas/química , Tamaño de la Partícula , Propiedades de SuperficieRESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
