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High resolution characterisation of microcapsule structure, adhesion and release properties
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Lee, Isabel R. (2005) High resolution characterisation of microcapsule structure, adhesion and release properties. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1788814~S1
Abstract
This thesis aims to characterise the structural, adhesion and release properties of
polymeric microcapsules which are used ina griculture for t he controlled delivery of
pesticides to crops.
An adaptation of atomic force microscopy (AFM) known as chemical force
microscopy (CFM) has been used to investigate the adhesion characteristics of
functionalised polyurea microcapsules to surfaces. The adhesion properties of
microcapsules (attached to AFM cantilevers) to self-assembled monolayers (SAMs) of
alkyl thiols on gold have been investigated at the single capsule level, and as a function
of polymer wall surface functionality. Measurements have been made to OHterminated,
CH3-terminated and mixed CH3: COOH-terminated SAMs. The importance
of microcapsule topography and elasticity on adhesion measurements has been
discussed. The surface pK1I2 of a capsule with a surface modified with a sulfonateterminated
molecule has been estimated using force titration methodology. The
adhesion properties of functionalised microcapsules to the leaf cuticle of Prunus
laurocerasus have been examined, highlighting areas of hydrophilicity on the surface of
the leaf.
The release properties of a ctive ingredients from p olyurea microcapsules into
solution using confocal laser scanning microscopy (CLSM) have been investigated.
Preliminary studies obtained the optimum species to use inside the microcapsule and the
solution into which the species should be released. The release characteristics 0 f six
varieties of microcapsule, differing in the wall thickness and cross linking density were
examined and from the release profiles obtained, the product of the mass transfer
coefficient and solubility coefficient could be calculated.
The high resolution imaging capabilities of the confocal microscope have been
demonstrated, providing detail on the structure of the leaf of the Prunus Laurocerasus
plant and t he caterpillars Heliothis virescens and P lutella xylostella, two of t he most
common pests, which the microcapsules of interest are aimed at controlling. The
release properties to leaf surfaces of two types of polyurea microcapsules, which have
different release mechanisms, were investigated using CLSM. Detailed release studies
to model surfaces showed that one type of capsule (lambda cyhalothrin) released in the
dry state and the other (emamectin benzoate) did not. A release rate was determined in
the former case.
A technique has been developed which is capable of visualising the release and
diffusion of a species (Cd2+) from a hemisphere. Voltammetry has been used in
conjunction with CLSM to monitor quantitatively and visually the preconcentration and
release of Cd2+ into and away from a mercury hemisphere UME. The fluorescent
indicator used was Calcium Green-5N, which is a cadmium-sensitive fluorophore that
fluoresces upon binding Cd2+and can thus be detected by CLSM. A delay was observed
between the release of C d2+ from t he hemisphere (determined voltammetrically) and
binding to the fluorophore (visualised using CLSM).
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry S Agriculture > SB Plant culture |
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Library of Congress Subject Headings (LCSH): | Artificial cells, Pesticides -- Application | ||||
Official Date: | March 2005 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Unwin, Patrick R. ; Macpherson, Julie V. | ||||
Extent: | xviii, 169 leaves | ||||
Language: | eng |
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