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Publications - 1998

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Self-Consistent Brownian Dynamics Simulation of Polymer Brushes under Shear

Marina G. Saphiannikova, Victor A. Pryamitsyn and Terence Cosgrove
School of Chemistry, University of Bristol, Bristol, UK

Macromolecules (1998), 31(19), 6662-6668


A novel Brownian dynamics method has been developed to simulate the properties of polymer brushes under shear. Simulations of 100 chains with a chain length of 100 segments have been carried out for a range of shear rates. Compared to previous methods there is a substantial saving in computational time as the self-consistent mol. field method has been chosen to calc. the vol. interactions between polymer segments. An important criterion for observing significant deformations of the brush is that the chains must be stretched to beyond the Gaussian threshold. D. profiles and end segment distribution functions for the grafted chains have been detd. and show a collapse of the brush under shear in a way similar to that in which a brush contracts in a poor solvent. In particular, the free ends of the chains become concd. in a narrow region at the periphery of the brush. The no. of chains that are affected by shear has also been calcd. and shows that there is a progressive transmission of shear into the brush.

A small-angle neutron scattering study of the structure of gelatin at the surface of polystyrene latex particles

T. Cosgrove, J.H.E. Hone, A.M. Howe and R.K. Heenan
School of Chemistry, University of Bristol, Bristol, UK

Langmuir (1998), 14(19), 5376-5382


Small-angle neutron scattering has been employed to investigate the effects of salt and pH on the structure of gelatin at the surface of neg. charged polystyrene latex particles. Measurements were made with the scattering length d. of the particles matched with the solvent. The data have been fitted to a combination of the scattering due to the av. vol. fraction profile of the layer and scattering from spatial concn. fluctuations. It has been shown that the scattering from the bare latex particles, the gelatin in soln., and the adsorbed layer have very different forms. The difference in the gelatin scattering indicates a significant change in the structure of the polymer on adsorption. The vol. fraction profiles derived from the fits show that, on increasing the pH, the concn. of chains at the interface decreased but the extension of the chains from the surface increased. Varying the ionic strength of the continuous phase gave unexpected results.

Dynamic Light Scattering and Small-Angle Neutron Scattering Studies on the Poly(ethylene oxide)/Sodium Dodecyl Sulfate/Polystyrene Latex System

S.J. Mears, T. Cosgrove, T. Obey, L. Thompson and I. Howell
Department of Physical Chemistry School of Chemistry, University of Bristol, Bristol, UK

Langmuir (1998), 14(18), 4997-5003


Dynamic light scattering and small-angle neutron scattering measurements have been performed on aq. polystyrene latex dispersions with physisorbed polymer, poly(ethylene oxide), in the presence of the surfactant sodium dodecyl sulfate (SDS). Dynamic light scattering measurements suggested that the polymer layer is partially desorbed at surfactant concns. close to the crit. micelle concn. At surfactant concns. above the normal crit. micelle concn., the hydrodynamic thickness increased close to the value in the absence of surfactant. Small-angle neutron scattering measurements suggested that as the normal crit. micelle concn. of the surfactant was approached, very thin layers were formed. It was possible to obtain the vol. fraction profiles of the adsorbed polymer layer, along with information on the structure of the surfactant micelles. Two types of SDS structures were obsd., one corresponding to SDS existing bound to bulk polymer and the other to SDS bound to adsorbed polymer.

Imaging and other techniq seeing is believing: the role of microscopy in determining morphology and kinetics of colloids

Terence Cosgrove and Joseph A. Zasadzinski
Department of Chemistry, University of Bristol, Bristol, UK

Curr. Opin. Colloid Interface Sci. (1998), 3(2), 123-124


No abstract available

The structure of block copolymers at the fluid/fluid interface

B.J. Clifton, T. Cosgrove, R.M. Richardson, A. Zarbakhsh and J.R.P. Webster
School of Chemistry, University of Bristol, Bristol, UK

Physica B (Amsterdam) (1998), 248 289-296


We have developed a method of measuring the distribution of polymer segments at a liq./liq. interface using neutron reflection. The method consists of forming a stable (1-4 μm) hexane layer on top of an aq. sub-phase so that two interfaces contribute to the measured reflectivity. This has been done by condensing vapor onto the surface in an accurately temp.-controlled environment. The neutron reflectivity was measured at four angles of incidence on the SURF reflectometer. The attenuation of the reflectivity from the lowest angle is used to det. the thickness of the hexane layer. A series of poly(ethylene oxide) poly(propylene oxide) ABA block copolymers adsorbed at the hexane/water interface have been investigated. Since the polymers were hydrogenous, measurements were made with D2O as the aq. phase and with either null reflecting hexane or 60% D-hexane as the oil phase in order to obtain adequate contrast. The polymer vol. fraction profile has been detd. by simultaneous fits to the data from these combinations of solvent contrasts. It was found that there was a good correlation between the molar mass of the poly(ethylene oxide) block and the thickness of the polymer layer in the aq. phase and that the chains were stretched beyond their radii of gyration expected for bulk soln.

The structure of block copolymers of ethylene oxide and butylene oxide at fluid/fluid interfaces

Editor(s): Ottewill, Ronald H.; Rennie, Adrian R.

S. Calpin-Davies, B.J. Clifton, T. Cosgrove, R.M. Richardson, A. Zarbakhsh, C. Booth and G. Yu

School of Chemistry, University of Bristol, Bristol, UK

Mod. Aspects Colloidal Dispersions, Results DTI Colloidal Technol. Programme (1998), Meeting Date 1997, 159-171. Publisher: Kluwer, Dordrecht, Netherlands


Neutron reflection and small-angle scattering have been used to investigate the structure of block copolyethers at fluid-fluid interfaces. Contrast variation methods have been used in both techniques to give vol. fraction profiles and adsorbed amts. The block copolymers are found to straddle the oil-water interface with the more hydrophobic butylene oxide group being attracted into the oil phase. The extent of this effect depends on the ratio of the block sizes. The ethylene oxide layer is stretched significantly into the aq. phase. The results are compared with self-consistent mean-field predictions of the detailed interfacial structure.

Simulation of liquid benzene between two graphite surfaces: a molecular dynamics study

Brian Clifton and Terence Cosgrove
School of Chemistry, University of Bristol, Bristol, UK

Mol. Phys. (1998), 93(5), 767-776


Mol. dynamics simulations have been used to study the structure of nonpolar solvent confined between two surface planes with 'mol.' sepn. The system is periodic in two dimensions, with a static external two-dimensional surface potential along the third dimension. The atom-surface potential is obtained by integrating over the vol. of a cone projected from each atom center (apex) onto the surface (if an atom falls below a set cutoff). Hence, no surface atom detail is required except the surface atom d. and Lennard-Jones parameters. This method is applied to benzene adsorbing on the basal plane of graphite. Our results test the method and provide a mol. picture of the surface induced structure of the liq., which extends further than the direct range of the liq.-surface potential.

NMR spin-spin relaxation studies of reinforced polydimethylsiloxane melts

T. Cosgrove, I. Weatherhead, M.J. Turner, R. Schmidr, G. Gordon and J. Hannington
School of Chemistry, University of Bristol, Bristol, UK

Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) (1998), 39(1), 545


The title technique is used to characterize PDMS polymers.

Adsorption studies of polyethers. Part 1. Adsorption onto hydrophobic surfaces

J.A. Shar, T.M. Obey and T. Cosgrove
School of Chemistry, University of Bristol, Bristol, UK

Colloids Surf., A (1998), 136(1-2), 21-33


The influences of copolymer molar mass and PEO/PPO block molar masses, anchor fraction and soln. concn. on the adsorption characteristics of Pluronic triblock copolymers adsorbed onto model polystyrene latexes have been investigated. The adsorbed amt. was detd. by the std. depletion method and the hydrodynamic thickness of the adsorbed layer by photon correlation spectroscopy. The adsorbed amt. and the hydrodynamic layer thickness were found to be strongly dependent on the copolymer molar mass, PEO/PPO block masses and the copolymer soln. concn. The conformation of the adsorbed copolymer is detd. by the surface-copolymer interaction and, principally, by interaction of the hydrophobic PPO block with the latex surface.

Role of Copolymer Architecture on Adsorption at the Solid/Liquid Interface

P.C. Griffiths, T. Cosgrove, J. Shar, S.M. King, Ga-Er Yu, C. Booth and M. Malmsten
Department of Chemistry, University of Wales Cardiff, Cardiff, UK

Langmuir (1998), 14(7), 1779-1785


The adsorption of monodisperse block copolymers comprising poly(ethylene oxide)-poly(butylene oxide) onto polystyrene latex from aq. soln. was investigated by small-angle neutron scattering and photon correlation spectroscopy with particular ref. to the role of mol. architecture. Chain architecture is (i) a weak factor in the adsorption behavior when the hydrophobic block is located in the center of the polymer, since the triblock E100B15E100 behaved very similarly to the cyclic c-E200B15, but (ii) a significant factor when the hydrophobic block is located at the end of the copolymer chain, as shown by the more dense and thicker layer formed by E200B15 compared to the triblock E100B15E100. The hydrodynamic thickness of the layer formed by the small diblock E100B15 was approx. half that exhibited by the larger diblock E200B15. Good agreement was obsd. between depletion and SANS-derived adsorbed amts. Theor. predictions and self-consistent mean-field calcns. of the adsorption also show excellent qual. agreement with expt.

NMR spin-spin relaxation studies of reinforced polydimethylsiloxane melts

Terence Cosgrove, Ian Weatherhead, Randy Schmidt, Glenn Gordon and Jon Hannington
School of Chemistry, University of Bristol, Bristol, UK

Book of Abstracts, 215th ACS National Meeting, Dallas, March 29-April 2 (1998), POLY-366. Publisher: American Chemical Society, Washington, D. C


NMR spin-spin relaxation measurements have been used to investigate the mobility of polydimethylsiloxane polymers when reinforced by silica particles consisting of a wide range of sizes. The results show that the incorporation of filler particles significantly reduces chain mobility. The relaxation decays have been deconvoluted into multiple exponential decays which can be assocd. with "free" and "bound" chains. The effects of chem. grafting and surface modification of the participles have also been examd. The results are compared with rheol. measurements and theor. calcns. added steric hinderance.

NMR relaxation studies of concentrated clay dispersions with adsorbed polymers

Terence Cosgrove and Nick Green
School Chemistry, University Bristol, Bristol, UK

Book of Abstracts, 215th ACS National Meeting, Dallas, March 29-April 2 (1998), COLL-280. Publisher: American Chemical Society, Washington, D. C


The technique of 1H NMR solvent relaxation has been used to probe the effect of the adsorption of poly(ethylene glycol) at the clay-water interface. Montmorillonite and laponite surfaces have been studied, and the nature of the surface has been shown to have a significant effect on polymer adsorption, with the laponite showing a lower affinity for water than the montmorillonite. The effect of mol. wt. and end group functionality of poly(ethylene glycol) on the structure of the adsorbed polymer at the clay surface have been investigated. Dramatically different trends occur with respect to mol. wt. for the two different surfaces.

Solvent relaxation NMR measurements on polymer, particle, surfactant systems

S.J. Mears, T. Cosgrove, L. Thompson and I. Howell
chool of Chemistry, University of Bristol, Bristol, UK

Langmuir (1998), 14(5), 997-1001


1H NMR solvent relaxation has been used to probe the effect of SDS on the adsorption of poly(ethylene oxide) at the silica-water interface. In the absence of SDS an enhancement in the relaxation rate resulting from the adsorption of PEO was obsd. while for PEO alone in the absence of particles only a negligible enhancement was obsd. However, upon addn. of SDS to the PEO/silica system a sequential redn. in the relaxation rate with increasing SDS was found. The results are discussed in terms of the levels of adsorbed polymer and its conformation.

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