Effect of a static non-uniform magnetic field on the surface properties of acrylic resin

INTRODUCTION: The acrylic resin is a polymeric material with several applications in different scientific and technological fields, especially in medicine and biotechnology. Its physical characteristics or their possible modifications can imply new ways of utilization and applicability. OBJECTIVE: To study the effect of a magnetic field on the surface physico-chemical properties usually implied in bacterial adhesion, especially surface hydrophobicity. METHODS: the hydrophobicity of the resin surface was determined by sessile drop contact angle measurements, using van Oss (1994) methodology. Accordingly, a substance (i) is considered hydrophobic when the variation of the free energy of interaction between two entities of substance (i) immersed in water is negative (DGiwi<0). That is to say, the two entities of substance (i) interact preferentially between them then with water. On the contrary, if DGiwi>0, substance (i) is hydrophilic. Two types of resin samples were used: hydrated and non-hydrated ones. The hydrated samples were obtained by autoclaving at 121ºC. Before contact angle measurements, the samples submitted to the magnetic field were exposed during 24 hours to a field of 500gauss generated between to parallel magnetite plates. RESULTS AND DISCUSSION: The principal results are summarized in Table 1. As could be expected the hydrated resin is hydrophilic, while the dehydrated is hydrophobic. However, when the hydrated resin is submitted to the magnetic field it becomes even more hydrophobic than when dehydrated. This can be explained by the effect of the magnetic field on the orientation of the water molecules of hydration. Consequently, there is an evident alteration of surface properties promoted by the magnetic field

Thermal lens spectrometry to study complex fluids

We describe applications of Thermal Lens Spectrometry to study optical and thermal properties of lyotropic liquid crystal. In particular, we refer to methods for measurements of thermal diffusivity anisotropy at different temperatures and as a function of the ferrofluids doping. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations as compared with conventional methods. Finally, future developments of photothermal techniques for these applications are assessed.0000Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Discotic Nematic - Calamitic Nematic Phase Transition in Sodium Dodecyl (lauryl) Sulphate-Decanol-D2O

The optical characterization of uniaxial nematic liquid crystals gives basic information on its birefringence and on the shape anisotropy of micelles in nematic lyotropic phases. In this work, these optical parameters were determined as a function of temperature along the sequence discotic nematic (ND) - coexistence (ND+NC) - calamitic nematic (NC) - isotropic (I) in a lyotropic mixture of the sodium dodecyl (lauryl) sulphate (SDS) - decanol (DeOH) and D2O for a specific concentration. Results for the uniaxial phases agree with previous assignments. Results in the coexistence region indicate an inhomogeneous mixture of the two uniaxial phases.CAPESCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação AraucáriaFundacao Araucaria (PR)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)INCT of Complex Fluids (CNPq/MCT/FAPESP

Temperature Dependence Of The Refractive Index Near The Reentrant-isotropic--calamitic-nematic Phase Transition.

The laser-induced nonlinear optical response of a lyotropic liquid crystal system in the reentrant-isotropic and calamitic-nematic phases is investigated by the use of the thermal lens technique. The occurrence of an inversion in the temperature coefficient of the ordinary refractive index, dn(radially)/dT, near the reentrant-isotropic-calamitic-nematic phase transition, is discussed. This effect is attributed to the behavior of the electronic polarizability due to the change in micelle shape near the isotropic-nematic transition, and correlated with the results obtained near the nematic-isotropic transition, previously reported.6401270