Investigating Static Charges in Liquid for Controlling Molecular Assembly

Singh, Balwinder (2025) Investigating Static Charges in Liquid for Controlling Molecular Assembly. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Balwinder Singh (19MS031)) 19MS031_Thesis_file.pdf Restricted to Repository staff only Download (42MB)

Abstract

This thesis investigates the use of free-standing static charges in organic liquids as a novel stimulus to control supramolecular self-assembly. We first developed and validated two custom instruments—a nanocoulombmeter and a high-impedance voltmeter—and established a method to assess whether sample containers can retain charge by measuring their wall capacitance and leakage resistance. We then established protocols for triboelectric charging of liquids via contact electrification of nylon and PTFE surfaces. Three rubbing methods (slab-slab, PTFE-tape foam, nylon-brush) and two transfer techniques (spread and pipette, direct-flow) were optimized for five π-conjugated dye systems: two naphthalene diimide (NDI) derivatives (FNDICN2 variants) and three perylene diimide (PDI) analogues (including an o-picolyl PBI). Charge densities up to 6 nC/mL were reproducibly achieved, and capacitance-resistance measurements of sample vials quantified charge retention times on the order of tens of minutes. Using UV-Vis spectroscopy, we show that static charge has minimal effect on final aggregate morphology but profoundly modulates assembly kinetics. FNDICN2 in methylcyclohexane aggregates instantaneously when uncharged yet exhibits an 18-19 min induction delay in both positively and negatively charged solvents. Conversely, o-picolyl PBI in 40 % dioxane/water precipitates within minutes under static charge but remains clear for hours when uncharged. We propose that localized electric fields around static charges induce solvent polarization and reorganization of the first solvation shell, adding an electrostatic term to the assembly free energy (ΔG = ΔGO + ΔGelec) that selectively stabilizes monomers or early nuclei. This work establishes static-charge control as a field-free, contamination-free stimulus for liquid-phase self-assembly, opening new avenues for responsive soft materials and electro-programmable nanostructures.

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