Expert in colloid and polymer science especially polymer adsorption. Designing low adhesion additives. Pioneered NMR methods and scattering in studying colloidal dispersions. Discovering and implementing methods to promote and suppress colloid stability. Address: Bristol, Bristol, City of, United Kingdom
A range of different stabilizers have been used to render natural kaolin clay particles hydrophob... more A range of different stabilizers have been used to render natural kaolin clay particles hydrophobic and dispersible in nonpolar solvents such as heptane. Both silanol and aluminol groups are known to be present at the kaolin surface. Use of a Hammett indicator showed that silanes would not neutralize the acidic aluminol sites, whereas amines would neutralize these sites. Both types of stabilizer adsorbed chemically onto the clay. In addition, a combined silane + amine treatment and a polyisobutylene-based stabilizer with a succinimide/amine head group (SAP230) were also considered. Both would neutralize the acid sites. The final sediment density after settling under gravity was used to gauge suspension stability, which varied with the kaolin surface treatment as silanes < amines < silane + amine < SAP230. This behavior was very similar for suspensions in heptane and in a higher molecular weight branched alkane, polydecene. This trend of increasing stability correlated very well with an increase in surface coverage of the stabilizing moieties, a decrease in particle size found using small-angle light scattering, and a decrease in Bingham yield stress obtained by fitting rheological data.
Abstract The rates of adsorption and desorption of polystyrene at the solid/solution interface ha... more Abstract The rates of adsorption and desorption of polystyrene at the solid/solution interface have been measured using nuclear magnetic resonance. The fraction of segments of adsorbed polymer chains detected by high resolution NMR has been estimated using the ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2000
The enthalpy of vaporisation (ΔHvap) of the solvents methane, ethane, butane, chloromethane, chlo... more The enthalpy of vaporisation (ΔHvap) of the solvents methane, ethane, butane, chloromethane, chloroform, carbon tetrachloride, carbon disulphide, cyclohexane, and ethyl acetate have been calculated by a free space molecular modelling method. This technique is based on evaluating contact energies and co-ordination numbers using two commercial software packages (Polygraf™ and Cerius2™). The total potential energy of the solvent is calculated by the use of the Dreiding II semi-empirical force field where non-bonded van der Waals interactions are modelled using a Lennard-Jone 12-6 potential. A bulk solvent (an isolated solvent shell with a co-ordination number of approximately 12) surrounding a central solvent molecule is created and the total energy is calculated. Re-calculating without the central molecule yields the solvent–solvent interaction energy and hence ΔHvap. The contact energy is pair-wise and additive and can be compared with literature values for ΔHvap. Three methods for generating solvent shells and a non-shell method are compared. For one method, the effect of charge generation is studied. The ΔHvap values calculated, show large discrepancies between the different shell methods used. However, values obtained by different charge generation methods are relatively similar. The coulombic term is therefore considered unimportant in the energy terms for the solvents studied here. Rather, the results show that the enthalpy of vaporisation is very sensitive to the co-ordination number, accompanying contact energy and spatial separation. The conclusion is, that because of the uncertainty in the co-ordination numbers, ΔHvap can only be estimated up to an accuracy of ∼20%.
Journal of Physics E: Scientific Instruments, Dec 1, 1974
A current pulse generator is described which has been developed for use in connection with a puls... more A current pulse generator is described which has been developed for use in connection with a pulsed nuclear magnetic resonance (NMR) spectrometer. It is capable of producing current regulated pulses in the range 30-120 A at pulse widths of 0.1-10 ms. Twin pulse separations of 0.1 ms at repetition frequencies of 3 Hz have been achieved. Typical rise times into resistive loads are of the order of mu s( approximately 80%) for a 120 A pulse.
The dispersion of particles in polymer melts is used in many formulations to improve their mechan... more The dispersion of particles in polymer melts is used in many formulations to improve their mechanical strength, rheological behaviour and to reduce weight and cost. The segmental mobility in polymer melts has been widely discussed in the literature, both from a ...
A range of different stabilizers have been used to render natural kaolin clay particles hydrophob... more A range of different stabilizers have been used to render natural kaolin clay particles hydrophobic and dispersible in nonpolar solvents such as heptane. Both silanol and aluminol groups are known to be present at the kaolin surface. Use of a Hammett indicator showed that silanes would not neutralize the acidic aluminol sites, whereas amines would neutralize these sites. Both types of stabilizer adsorbed chemically onto the clay. In addition, a combined silane + amine treatment and a polyisobutylene-based stabilizer with a succinimide/amine head group (SAP230) were also considered. Both would neutralize the acid sites. The final sediment density after settling under gravity was used to gauge suspension stability, which varied with the kaolin surface treatment as silanes < amines < silane + amine < SAP230. This behavior was very similar for suspensions in heptane and in a higher molecular weight branched alkane, polydecene. This trend of increasing stability correlated very well with an increase in surface coverage of the stabilizing moieties, a decrease in particle size found using small-angle light scattering, and a decrease in Bingham yield stress obtained by fitting rheological data.
Abstract The rates of adsorption and desorption of polystyrene at the solid/solution interface ha... more Abstract The rates of adsorption and desorption of polystyrene at the solid/solution interface have been measured using nuclear magnetic resonance. The fraction of segments of adsorbed polymer chains detected by high resolution NMR has been estimated using the ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, May 1, 2000
The enthalpy of vaporisation (ΔHvap) of the solvents methane, ethane, butane, chloromethane, chlo... more The enthalpy of vaporisation (ΔHvap) of the solvents methane, ethane, butane, chloromethane, chloroform, carbon tetrachloride, carbon disulphide, cyclohexane, and ethyl acetate have been calculated by a free space molecular modelling method. This technique is based on evaluating contact energies and co-ordination numbers using two commercial software packages (Polygraf™ and Cerius2™). The total potential energy of the solvent is calculated by the use of the Dreiding II semi-empirical force field where non-bonded van der Waals interactions are modelled using a Lennard-Jone 12-6 potential. A bulk solvent (an isolated solvent shell with a co-ordination number of approximately 12) surrounding a central solvent molecule is created and the total energy is calculated. Re-calculating without the central molecule yields the solvent–solvent interaction energy and hence ΔHvap. The contact energy is pair-wise and additive and can be compared with literature values for ΔHvap. Three methods for generating solvent shells and a non-shell method are compared. For one method, the effect of charge generation is studied. The ΔHvap values calculated, show large discrepancies between the different shell methods used. However, values obtained by different charge generation methods are relatively similar. The coulombic term is therefore considered unimportant in the energy terms for the solvents studied here. Rather, the results show that the enthalpy of vaporisation is very sensitive to the co-ordination number, accompanying contact energy and spatial separation. The conclusion is, that because of the uncertainty in the co-ordination numbers, ΔHvap can only be estimated up to an accuracy of ∼20%.
Journal of Physics E: Scientific Instruments, Dec 1, 1974
A current pulse generator is described which has been developed for use in connection with a puls... more A current pulse generator is described which has been developed for use in connection with a pulsed nuclear magnetic resonance (NMR) spectrometer. It is capable of producing current regulated pulses in the range 30-120 A at pulse widths of 0.1-10 ms. Twin pulse separations of 0.1 ms at repetition frequencies of 3 Hz have been achieved. Typical rise times into resistive loads are of the order of mu s( approximately 80%) for a 120 A pulse.
The dispersion of particles in polymer melts is used in many formulations to improve their mechan... more The dispersion of particles in polymer melts is used in many formulations to improve their mechanical strength, rheological behaviour and to reduce weight and cost. The segmental mobility in polymer melts has been widely discussed in the literature, both from a ...
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