ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Wetting parameters, surface free energy, and wettability enhancement of Ocimum sanctum leaves through adjuvants

Pawan Shah, Manoj Bhandari, Roshna Pokhrel, and Ajaya Bhattarai

Department of Chemistry, Mahendra Morang Adarsh Multiple Campus, Tribhuvan University, Biratnagar, Nepal

E-mail: bkajaya@yahoo.com

Received: 22 October 2024  Accepted: 15 March 2025

Abstract:

Ocimum sanctum is cultivated worldwide due to its wide medicinal applications. Its leaves often get infected by various fungi, bacteria, pests, and nutrition deficiencies, and to overcome those infections and deficiencies, proper foliar application of antifungal, antimicrobial, or pesticides is essential. Wettability knowledge is very necessary for effective foliar spray to the plants. Wettability is described by the contact angle (CA) estimation where a lower CA value suggests higher wettability. The wettability of leaves is enhanced by using the liquid of low surface tension which is achieved by using various surfactants and wetting agents. The CA of water on both abaxial (aba) and adaxial (ada) surfaces of O. sanctum leaves was measured through a Kruss drop shape analyzer. Surface tension (γ) measurements were carried out through the pendant drop method using the same DSA. Molar free energy (ΔG) and wetting free energy (Δg), surface free energy (γ_sv), interphase free energy (γ_sl), and solubility parameter (δ) of both ada and aba leaf surfaces were detected using ADVANCE software version 1.9.0.8. Two different surfactants: cationic, N-cetyl-N, N, N-trimethyl ammonium bromide (CTAB) and anionic, bis(2-ethylhexyl)sodium sulfosuccinate (AOT), and two commercial agro-wetting agents: Gorkha stick more, a Nepali wetting agent and Keeper, an Indian wetting agent were utilized to enhance the wettability of leaves. The adhesion tension (T_a) and adhesion work (W_a) of water and all solutions were measured to describe wettability. T_a, W_a, γ, ΔG, and Δg were compared in the presence and absence of surfactants/wetting agents, among the surfactants and wetting agents and between adaxial and abaxial leaf surfaces to characterize and improve the wettability. The aba surface was characterized by low γ_sv, low Δg, high solubility parameter difference with water, high CA, and thus lower wettability compared to the adaxial surface. AOT shows better wettability efficiency among all the surfactant and wetting agents. A behavior similar to the rose petal effect was observed between CA and W_a on both ada and aba surfaces.

Keywords: Oils; Plant Materials; Soft Materials; Surface Chemistry; Wetting; Surfaces, Interfaces and Thin Film; Ocimum sanctum; Contact angle; Adhesion tension; Surface free energy; Solubility parameter

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04018-3

Chemical Papers 79 (7) 4165–4179 (2025)