The nature of anisotropic particles with short-range interactions
| Author(s) | Murphy, Ryan P. | |
| Date Accessioned | 2018-05-17T13:46:25Z | |
| Date Available | 2018-05-17T13:46:25Z | |
| Publication Date | 2017 | |
| SWORD Update | 2018-02-22T20:26:15Z | |
| Abstract | Anisotropic particles are used widely to control the thermodynamic and rheological properties of pharmaceuticals, cosmetics, food products, composite materials, and cements. In particular, rod-like particle suspensions exhibit unique equilibrium and non-equilibrium states at low particle loadings due to large excluded volumes and orientation-dependent attractions. However, the coupled effects of particle shape and interactions are not quantitatively understood with regard to dynamically arrested states, such as colloidal gels and glasses. To better quantify these effects, a tunable model system of adhesive hard rods (AHR) was developed to independently control the particle aspect ratio and the temperature-dependent, short-range attractions. AHR suspensions were composed of octadecyl-coated silica rods suspended in tetradecane, which exhibit thermoreversible dynamic arrest transitions. The dynamic moduli and particle dynamics were systematically quantified using macroscopic rheological methods and microscopic quasi-elastic light scattering methods, providing a quantitative map of the gel and glass boundaries as a function of aspect ratio (L/D=3-7), particle volume fraction (0.1-0.5), and absolute critical temperatures (Tgel=25-30 C). Small-angle neutron and X-ray scattering methods were applied to probe the arrested AHR microstructure to extract an effective interaction strength between rods on a reduced temperature scale, as defined by a dimensionless sticky parameter. ☐ AHR suspensions exhibited qualitatively similar gel and glass transition behavior, but the boundaries were quantitatively shifted in L/D, volume fraction, and T. On an absolute temperature scale, the critical gel-like boundary increased with L/D, while the critical glass volume fraction decreased significantly with L/D. However, on a reduced temperature scale, the measured gel boundary was nearly independent of L/D for conditions below the hard rod glass line. This finding suggested an extended theory of corresponding states might also apply to anisotropic particle systems with short-range attractions, as observed for similar isotropic systems. These results prompted the mapping of a fundamental AHR state diagram in terms of L/D, volume fraction, and effective stickiness to compare with various rod-like systems in literature. The results of the AHR experiments showed good agreement with mode-coupling theories for adhesive rods, which closely followed the predicted hard rod glass boundaries. The proposed state diagram links the behavior of hard spheres, adhesive hard spheres, hard rods, and adhesive hard rods, providing a way to map the intersecting boundaries between states that compete for fluidity, connectivity, rigidity, phase separation, and liquid crystal formation. The tunable AHR system and dimensionless state diagram developed in this work can be used to define, guide, and predict the non-equilibrium state boundaries for other rigid molecules, polymers, anisotropic colloids, and proteins. | en_US |
| Advisor | Wagner, Norman J. | |
| Degree | Ph.D. | |
| Department | University of Delaware, Department of Chemical and Biomolecular Engineering | |
| Unique Identifier | 1035844692 | |
| URL | http://udspace.udel.edu/handle/19716/23213 | |
| Language | en | |
| Publisher | University of Delaware | en_US |
| URI | https://search.proquest.com/docview/2024177806?accountid=10457 | |
| Keywords | Applied sciences | en_US |
| Keywords | Anisotropy | en_US |
| Keywords | Colloids | en_US |
| Keywords | Dynamic arrest | en_US |
| Keywords | Gelation | en_US |
| Keywords | Glass transition | en_US |
| Keywords | Nanoparticles | en_US |
| Title | The nature of anisotropic particles with short-range interactions | en_US |
| Type | Thesis | en_US |