INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Non-Isothermal Model for a Nematic/Isotropic Transition
Autor/es:
N. M. ABUKHDEIR; E. R. SOULÉ; A. D. REY
Lugar:
Toronto, canadá
Reunión:
Congreso; 58th Canadian Chemical Engineering Conference (CsChe 2008); 2008
Resumen:
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; mso-hyphenate:none; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:AR-SA;} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 90.0pt 72.0pt 90.0pt; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1; mso-footnote-position:beneath-text;} -->             A two-dimensional computational study of the isotropic/nematic transition of 5CB (pentyl-cyanobiphenyl) was performed, using a tensorial Landau-de Gennes tensorial model. An energy balance, taking anisotropy and latent heat into account, was derived and incorporated into the time-dependent model. It is shown that latent heat, which is typically neglected for this phase transition, has a non-negligible effect.             First, spherulite growth was studied and the two main findings were that I) in order to reproduce the experimentally observed growth laws (R~t for deep quenches and R~t0.5 for shallow quenches) and latent heat must be taken into account (without latent heat, we always get R~t) and ii) as the texturing process is temperature dependent, latent heat has an effect on the texture of the spherulite.             The shape stability of a planar interface in the presence of perturbations was also studied. Dispersion diagrams (grow velocity vs. wavelength of the perturbation) were constructed, in the small-amplitude regime and a texturing process was observed when the perturbation grows to large amplitudes (as observed experimentally). The main contributions of this work are: 1) An energy balance that takes into account anisotropy was derived that incorporates a coupling of the latent heat and nematic order parameter.  This, in combination with a tensorial-order parameter model, accounts for the most relevant characteristics of a liquid crystal: anisotropy and elastic effects. 2) Latent heat, which is typically neglected for these types of phase transitions, is found to have non-negligible effects on the isotropic/nematic transition.