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http://dr.iiserpune.ac.in:8080/xmlui/handle/123456789/7943| Title: | Defect Dynamics in Amorphous Colloidal Monolayers under Shear |
| Authors: | CHIKKADI, VIJAYAKUMAR S, RHUTHWIK Dept. of Physics 20181053 |
| Keywords: | Defects Dynamics Soft condensed matter Holographic optical tweezers Soft condensed matter colloids microscopy Holographic optical tweezers Optical traps amorphous solids Defects |
| Issue Date: | May-2023 |
| Citation: | 83 |
| Abstract: | Studying amorphous/disordered solids is challenging compared to their ordered counter parts, crystals. Lattice imperfections or defects in crystals are known to play a significant role in deformation, as the defects within crystals begin to move when an external load is applied, resulting in permanent deformation or plasticity. These defects are referred to as plasticity carriers. However, amorphous materials lack a reference lattice to identify defects. In this study, we use optical tweezers and dense colloidal suspensions to investigate the relationship between plastic activity and microscopic structure in amorphous substances. Shear fields in a colloidal monolayer are generated using a holographic optical trap with Laguerre Gaussian beam and a spatial light modulator. With this setup, we examine the relationships between defect dynamics and microstructure in a quasi-2D system of colloidal glasses, including the orientation of defects with respect to the shear direction. We have built the instrumentation of time-shared optical traps to investigate the effect of random pinning on phonon modes in colloidal crystals and glasses. |
| Description: | In conclusion, our results demonstrate that the application of shear to a colloidal glass system using LG beam manipulation leads to interesting dynamics and rearrangements of particles. We successfully tracked the trajectories of particles using the Cocker and Grier algorithm, and found that the system exhibits glassy behavior based on the plateau observed in the Mean Squared Displacement (MSD) analysis. The MSD is higher during shear, indicating faster relaxation of the system, and the slope of the MSD in the log-log plot is higher during shear, suggesting that the system is under drive. We also observed that even though the shear was applied only at the edge of the system, inner particles also rotated, as confirmed by the displacement profile and angular velocity analysis. The angular velocity of particles varied with distance from the center of the trap, and after an initial peak, it converged to a constant value for particles inside the trapping ring, indicating rigid body rotation. However, a shear band was observed at a certain distance from the center, suggesting localized rearrangements of particles. Furthermore, we utilized the D2min parameter to identify locations of defects in the amorphous solid and found that regions with higher D2min values corresponded to areas of more particle rearrangements, analogous to defects in crystalline solids. Overall, our findings provide insights into the dynamics of colloidal glass systems under shear and shed light on the role of defects in the shear deformation and relaxation of amorphous systems. We also found out that there is a preferred orientation (45 degrees) of these defects with respect to the shear direction. Further studies can be conducted to investigate the effects of shear on different types of colloidal glasses and explore potential applications in materials science and engineering. We also demonstrated the instrumentation of time-shared optical traps using AOD to have a large trapping field of around 150 µm and 200 particles so that we can investigate the effect of random pinning of colloidal crystals on phonon mode. |
| URI: | http://dr.iiserpune.ac.in:8080/xmlui/handle/123456789/7943 |
| Appears in Collections: | MS THESES |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 20181053_Rhuthwik_S_MS_Thesis | MS Thesis | 8.95 MB | Adobe PDF | View/Open Request a copy |
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