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Clay-vesicle interactions: fluorescence measurements and structural implications for slow release formulations of herbicides

By Tomás Undabeytia López, Shlomo Nir and María J. Gómara

Abstract

6 pages, 5 tables, 2 figures, 26 references. The authors acknowledge Dr. Justo for help in the XRD section.Clay-vesicle systems exhibit a potential for environmental applications, such as herbicide formulations for reduced leaching. Clay-vesicle interactions were addressed by combining adsorption and XRD measurements with fluorescence studies for didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DDOB), and montmorillonite. XRD and adsorption data indicated that the adsorbing vesicles were transformed after 3 days into paraffinic and bilayer structures. Fluorescence studies revealed that adsorption was almost complete within 5 min for a loading below the cation exchange capacity (CEC). Aggregation and sedimentation of clay-surfactant particles occurred within several minutes. Fluorescent measurements of supernatants indicated decomposition of vesicles at a high clay/surfactant ratio due to rapidly adsorbing cationic monomers. The kinetics of energy transfer between vesicles labeled by NBD-PE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)) and montmorillonite labeled by rhodamine-B follows that of aggregation of surfactant-clay particles and structural changes of the vesicles at times of minutes to hours. Experiments following the reduction of NBD fluorescence by addition of dithionite indicate faster permeabilization of DDOB than DDAB vesicles, which was confirmed by leakage experiments. The faster permeabilization of DDOB vesicles in the presence of clay was correlated with their inferior suitability for the preparation of clay-based formulations of anionic herbicides for slow release.Financial support of the Spanish Ministry of Science and Technology under projects AGL2002-00993 and REN2000-1540 and Junta de Andalucia (PAI RNM166) is acknowledged herewith. Dr. Undabeytia is also grateful to the Spanish Government for a Ramon y Cajal research contract.Peer reviewe

Publisher: 'Japanese Society of Applied Entomology & Zoology'
Year: 2004
DOI identifier: 10.13039/501100006280
OAI identifier: oai:digital.csic.es:10261/40081
Provided by: Digital.CSIC
Journal:

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