Publications - 2000
Previous year | Overview | Next year
Pseudo rotaxanes: the effects of molecular architecture
T. Cosgrove and J. Joseph
School of Chemistry, University of Bristol, Cantocks Close, Bristol, UK
Cyclodextrin: From Basic Research to Market, International Cyclodextrin Symposium, 10th, Ann Arbor, MI, United States, May 21-24, 2000 (2000), 554-559. Publisher: Wacker Biochem Corp., Adrian, Mich
Abstract
We have formed rotaxanes between cyclodextrins (CDs) and guest ethylene oxide polymers. If CD is mixed with Pluronic F127 (a triblock polymer of the structure PEO100-PPO65-PPO100) the resulting rotaxanes formed are sol. in water. We have investigated the structure of these rotaxanes using small angle neutron scattering: a technique allowing us to investigate structures in the range 0.5-1000nm. We have explored the effect on the polymer's crit. micelle concn. (CMC) as CD is added. We have found that the CMC is significantly altered. At 3% w/v F127 is above the CMC, as can be seen the scattered intensity is high indicating that the polymer has micellized and a large species is present in soln. However, on addn. of mβ-CD-sufficient to give full coverage of the polymer; the intensity drops dramatically. This indicates that as CD has been added it has caused the micelles to break up forming rotaxanes. We have also studied the action of PEO adsorbed at a surface - and the effect of adding α-CD. Oscillations can be seen in the data indicating the monodispersity of the polystyrene particles. PEO was adsorbed on to the latex and then challenged with α-CD. The scattering can be seen to change dramatically and this may indicate an enhanced adsorbed amt. The PEO layer re-conforms on addn. of α-CD, indicating the formation of an inclusion adsorbed complex.
Using SANS to study adsorbed layers in colloidal dispersions
Editor(s): Gabrys, Barbara J.
Stephen M. King, Peter C. Griffiths and Terry Cosgrove
Large-Scale Structures Group, ISIS Facility, Rutherford Appleton Laboratory, Oxon, UK
Applications of Neutron Scattering to Soft Condensed Matter (2000), 77-105. Publisher: Gordon & Breach Science Publishers, Amsterdam, Netherlands
Abstract
A review with 66 refs. on the technique of SANS and a comprehensive discussion of its application in the study of adsorbed polymer and surfactant layers in colloidal dispersions.
A Neutron Reflectivity Study of Poly(N-isopropylacrylamide) at the Air-Water Interface with and without Sodium Dodecyl Sulfate
Robert M. Richardson, Robert Pelton, Terence Cosgrove and Ju Zhang
School of Chemistry, Bristol University, Bristol, UK
Macromolecules (2000), 33(17), 6269-6274
Abstract
The properties of poly(N-isopropylacrylamide) (polyNIPAM) at the air/water interface, with and without sodium dodecyl sulfate (SDS), were measured by neutron reflectivity and surface tension. Below the lower crit. soln. temp. (LCST), polyNIPAM adsorbs at the air/water interface to give a thin (δ .apprx. 1.5 nm) layer with a low water content approx. equal to phase-sepd. polyNIPAM above the LCST. Above the LCST the adsorbed polymer layer increases by a factor of 10 approx. equal to the effective diam. of a single phase-sepd. polymer chain (a globule). Polymer-bound SDS lowers the d. of adsorbed polyNIPAM because of electrostatic effects.
Computer simulation of water molecules at kaolinite and silica surfaces
M.R. Warne, N.L. Allan and T. Cosgrove
School of Chemistry, University of Bristol, Bristol, UK
hys. Chem. Chem. Phys. (2000), 2(16), 3663-3668
Abstract
Mol. dynamics simulations of water mols. at the surface of kaolinite, and of amorphous SiO2, were carried out. In contrast to previous work, clay and SiO2 atoms are not kept fixed at their crystallog. positions; all atoms are allowed to move. In both cases water mols. at the surface show a marked decrease in the self-diffusion coeff. and an increase in the rotational correlation time. We consider the effects of increasing the ionic strength of the water. Comparison with exptl. data is made by linking calcd. diffusion and rotational correlation times to available pulse field gradient NMR spectroscopy and relaxation measurements.
Novel microgel-particle colloids: the detailed characterization of the layer structure and chain topology of silica:poly(NIPAM) core-shell particles
N. Hatto, T. Cosgrove and M.J. Snowden
chool of Chemistry, University of Bristol, Bristol, UK
Polymer (2000), 41(19), 7133-7137
Abstract
A monodisperse core-shell microgel was synthesized in which silica provides the core (av. diam. 1367 .ANG.), and poly(N-isopropylacrylamide) [poly(NIPAM)] the cross linked shell. TEM and photon correlation spectroscopy (PCS) measurements have confirmed the existence of a thick polymer layer. PCS measurements have shown that the hydrodynamic thickness of the layer is .apprx.2450 .ANG. at 25°, collapsing to 600 .ANG. when heated to 70°. Small-angle neutron scattering (SANS) expts. on the core-shell microgels show a high vol. fraction near the surface and suggest an exponential vol. fraction profile. PCS and SANS measurements have also been used to measure the de-swelling of the layer with change in temp. and the results are compared with classical microgel particles.
Polymer bristles: a SANS study
Stephen King, Clive Washington, David Attwood, Colin Booth, Shaomin Mai, Yung-Wei Yang and Terence Cosgrove
ISIS Facility, Rutherford Appleton Laboratory, Didcot, UK
J. Appl. Crystallogr. (2000), 33(3, Pt. 1), 664-668
Abstract
We report the results of a SANS study into the structure of the adsorbed layers formed at the interface in a dil. perfluorodecalin-in-water emulsion by five short chain diblock copolymers of oxyethylene (OE) and oxybutylene (OB). The results are discussed in the context of the Marques-Joanny-Leibler scaling description of block copolymer adsorption from selective solvents. The vol. fraction profiles are best described by parabolic and, to a lesser extent, Gaussian functional forms. On increasing the temp. the buoy segments of one copolymer were found to contract toward the surface, giving rise to profiles that were more block-like in accordance with the mean-field predictions of Wijmans and Zhulina.
NMR spin-spin relaxation studies of reinforced poly(dimethyl siloxane) melts
Terence Cosgrove, Michael J. Turner, Ian Weatherhead, Claire Roberts, Tania Garasanin, Randall G. Schmidt, Glenn V. Gordon and Jonathan P. Hannington
School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK
ACS Symp. Ser. (2000), 729(Silicones and Silicone-Modified Materials), 204-213
Abstract
NMR relaxation anal. was used to investigate the dispersion of silicate type materials in poly(di-Me siloxane) melts. The results show that several different regions of mobility are found, within the bulk melt, which depend on the particle size and chem. properties of the interface.
Hydrodynamic Layer Thickness of a Polybase Brush in the Presence of Salt
Robin D. Wesley, Terence Cosgrove, Laurie Thompson, Steven P. Armes, Norman C. Billingham and Fiona L.Baines
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2000), 16(10), 4467-4469
Abstract
A grafted weak polyelectrolyte brush has been prepd. by the incorporation of one block of a diblock copolymer inside a latex particle. The preformed brush shows a max. in its hydrodynamic layer thickness radius as a function of added salt. Beyond 0.025 M NaCl, the data can be fitted to the scaling relationship for the salted-brush regime wherein the layer thickness varies as the inverse cubed root of the ionic strength.
Polymer Bristles: Adsorption of Low Molecular Weight Poly(oxyethylene)-Poly(oxybutylene) Diblock Copolymers on a Perfluorocarbon Emulsion
Clive Washington, Stephen M. King, David Attwood, Colin Booth, Shao-Min Mai, Yung-Wei Yang and Terence Cosgrove
School of Pharmaceutical Sciences, University of Nottingham, University Park Nottingham, UK
Macromolecules (2000), 33(4), 1289-1297
Abstract
Small-angle neutron scattering was used to study the structure of adsorbed layers formed at the interface of dil. perfluorodecalin-in-water emulsion and short chain diblock copolymers of oxyethylene (OE) and oxybutylene (OB) (OE26OB13, OE29OB11, OE30OB7, OE27OB6, and OE58OB13). The Marques-Joanny-Leibler (C. Marques, J. Joanny, L. Leibler (1988)) scaling description of block copolymer adsorption from selective solvents was used to describe the adsorption mechanism; data validate the theory in the unusual limit of short chain lengths and small anchor blocks, close to the boundary between the buoy-dominated and the van der Waals-buoy regimes. The vol. fraction profiles are best described by parabolic and, to a lesser extent, Gaussian functional forms. When the temp. was increased, the buoy blocks contracted toward the surface, giving rise to profiles that were more block-like, in accordance with theor. predictions by C. M. Wijmans and E. B. Zhulina (Macromols., 1993, 26, 7214).
A Rheological and Small-Angle Neutron Scattering Study of the Structure of Gelatin/Polyelectrolyte Complexes under Shear
J.H.E. Hone, A.M. Howe and T. Cosgrove
School of Chemistry, University of Bristol, Cantock's Close Bristol, UK
Macromolecules (2000), 33(4), 1199-1205
Abstract
The small-angle neutron scattering and rheol. of gelatin/polyanion complexes have been studied as a function of shear rate and ionic strength. It was found that the addn. of very small amts. of sodium poly(styrenesulfonate) caused a massive increase in the viscosity of gelatin solns. through the formation of a complex between the two net neg. charged polymers. The scattering data showed a max. in intensity at a specific value of the momentum transfer, reminiscent of the pattern produced by more concd. pure polyelectrolyte solns. At high shear rates the complex systems displayed anisotropic behavior: the scattering intensity at the peak was suppressed parallel to the direction of flow, indicating a change in the structure of the complex, but remained approx. const. perpendicular to the flow.
A Small-Angle Neutron Scattering Study of the Structure of Gelatin/Polyelectrolyte Complexes
J.H.E. Hone, A.M. Howe and T. Cosgrove
School of Chemistry, University of Bristol, Bristol, UK
Macromolecules (2000), 33(4), 1206-1212
Abstract
Mixts. of a fractionated gelatin polyampholyte with low concns. of anionic polyelectrolytes, sodium poly(styrenesulfonate) (NaPSS) and sodium poly(2-acrylamido-2-methylpropanesulfonate) (NaPAMPS) and were studied by small-angle neutron scattering. The gelatin chain is not a globular protein, but has a random coil configuration under the conditions studied. The scattering pattern obsd. from the system is reminiscent of that from pure polyelectrolyte solns., however the max. has a much greater intensity. The position of the scattering peak is independent of the mol. wt. of the polyelectrolyte, but moves to larger momentum transfer, Q, with increasing concn. The scattering intensity at higher Q reflects the extent of complexation of the gelatin and polyanion. The addn. of monovalent salt, NaCl, Na acetate, removes the peak from the scattering pattern and high salt concns. weaken the complexes. Raising the pH also weakens the complexes. At high pH (≥10), scattering data indicate that there is no interaction between gelatin and the polyanions. The extent of complex formation for similar polyelectrolytes depends on the charge d. and distribution in the chain.
Methods for calculating solvent enthalpy of vaporisation values by a molecular modelling technique - effect of charge and method
B.J. Clifton, T. Cosgrove and M.R. Warne
School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK
Colloids Surf., A (2000), 164(2-3), 163-173
Abstract
The enthalpy of vaporization (ΔHvap) of the solvents methane, ethane, butane, chloromethane, chloroform, carbon tetrachloride, carbon disulfide, cyclohexane, and Et acetate have been calcd. by a free space mol. modeling method. This technique is based on evaluating contact energies and co-ordination nos. using two com. software packages (Polygraf and Cerius). The total potential energy of the solvent is calcd. by the use of the Dreiding II semi-empirical force field where non-bonded van der Waals interactions are modeled using a Lennard-Jones 12-6 potential. A bulk solvent (an isolated solvent shell with a co-ordination no. of approx. 12) surrounding a central solvent mol. is created and the total energy is calcd. Re-calcg. without the central mol. 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 calcd. 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 vaporization is very sensitive to the co-ordination no., accompanying contact energy and spatial sepn. The conclusion is, that because of the uncertainty in the co-ordination nos., ΔHvap can only be estd. up to an accuracy of .apprx.20%.
Previous year | Overview | Next year
