Browsing by Subject "Thermotropic"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    A Numerical Evaluation of Thermotropic Materials for Polymer Solar Thermal Collectors
    (2014-07) Gladen, Adam
    A series of numerical studies of thermotropic materials are conducted to develop a theoretical basis for the selection and design of phase change thermotropic materials for polymer collectors. The optical requirements for a thermotropic material to provide overheat protection are identified. In the clear state, high solar-weighted transmittance (≥80%, preferably ≥85%). To protect an absorber of polypropylene, material temperature limit of 115 �C, the solar-weighted reflectance of the thermotropic material must be ≥50%. To determine how to achieve these optical requirements, the radiative transfer within thermotropic materials is modeled with a Monte Carlo ray tracing algorithm. A parametric study of the radiative transfer in thermotropic materials is conducted. The results are presented as dimensionless plots of transmittance and reflectance as a function of the overall optical thickness τL, the scattering albedo ω, and the particle size parameter x. The study demonstrates that to achieve ≥85% transmittance in the clear state, the optical thickness must be low. To achieve ≥50% reflectance in the translucent state necessitates a significant increase in optical thickness with temperature. Additionally, the material must have small particles (x ≤ 2.5) and be weakly absorbing (ω ≥ 0.990). For example, for a size parameter of 2, the optical thickness in the clear state must be ≤0.35. The optical thickness in the translucent state must be ≥10 for a scattering albedo of 0.995. The data contained in these dimensionless plots can be used to identify and optimize thermotropic materials. A method for indentifying potential thermotropic material combinations is presented. Using encapsulated particles in a thermotropic material is also investigated. The transmittance and reflectance of hydroxystearic acid in poly(methyl methacrylate) are predicted as a function of shell refractive index, shell thickness, and particle volume fraction. The study demonstrates that a thermotropic material with encapsulated particles can achieve the optical requirements for use in a solar collector. Additionally, the study reveals that a wide range of shell relative refractive indices, from 0.95 to 1.0, and thicknesses, up to 35 nm, provide acceptable optical performance.
  • Thumbnail Image
    Item
    Supporting Data for Self-Assembly of Unusually Stable Thermotropic Network Phases by Cellobiose-Based Guerbet Glycolipids
    (2024-04-08) Das, Soumi; Zheng, Caini; Calabrese, Michelle A; Reineke, Theresa M; Siepmann, Ilja J; Mahanthappa, Mahesh K; Lodge, Timothy P; treineke@umn.edu; Reineke, Theresa M; University of Minnesota
    These files contain data along with associated output from instrumentation supporting all results reported in the referenced paper. Bicontinuous thermotropic liquid crystal (LC) materials, such as double gyroid (DG) phases, are highly promising for various applications due to their intricate 3D network structures. However, the lack of robust molecular design rules for shape-filling amphiphiles hinders their utility. To address this, we synthesized cellobiose-based glycolipids with Guerbet-type branched alkyl tails and examined their thermotropic LC self-assembly. Through techniques including differential scanning calorimetry (DSC), polarized optical microscopy (POM), and small-angle X-ray scattering (SAXS), we found that Guerbet cellobiosides have a strong propensity to form DG morphology across broad thermotropic phase ranges. The stability of these assemblies depends on the alkyl tail structure and anomeric configuration of the glycolipid in a previously unrecognized manner. Molecular simulations provide further insights, revealing molecular motifs crucial for network phase self-assembly, paving the way for future designs and applications of network LC materials.