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Publications - 1993

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Adsorption of end-functionalized and cyclic polymers

T. Cosgrove, R.D.C. Richards, J.A. Semlyen and J.R.P. Webster
School of Chemistry, University of Bristol, Bristol, UK

ACS Symp. Ser. (1993), 532(Colloid-Polymer Interactions), 111-20


The effect of the end groups of polymer chains on adsorption at the solid-soln. interface has been studied by comparing adsorption of hyroxy- vs. methyl-terminated PEO and linear vs. cyclic polystyrene. The results show the changes in the end group moiety can be sufficient to enable one polymer to displace an otherwise identical polymer from the interface. The preferential adsorption of end groups is also shown by comparing the adsorption isotherms of linear and cyclic polymers.

Self-diffusion, viscosity and spin-spin relaxation in liquid poly(propylene oxide) melts

T. Cosgrove, P.C. Griffiths and J.R.P. Webster
School of Chemistry, University of Bristol, Bristol, UK

Polymer (1994), 35(1), 140-4


Self-diffusion, viscosity and spin-spin relaxation have been measured for a series of low-mol.-wt. liq. poly(propylene oxide) melts. The data are discussed within the framework of theories commonly invoked for polymer dynamics including the Rouse chain and free-vol. effects. The av. diffusion coeffs. of a range of bimodal blends have also been measured and the results interpreted using the Rouse model.

Neutron reflection studies of copolymers at the hexane/water interface

J.S. Phipps, R.M. Richardson, T. Cosgrove and A. Eaglesham
School of Chemistry, University of Bristol, Bristol, UK

Langmuir (1993), 9(12), 3530-7


The conformations of three copolymers at the hexane/water interface have been studied using neutron reflection. A specially-designed app. is used in which a thin (.apprx.10 μm) layer of hexane is spread on a water surface, thus allowing acceptable transmission of a neutron beam incident at a grazing angle to the surface. Since none of the polymers used was deuterated, sensitivity to the polymer structure was achieved using contrast variation of the two solvents. A triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) adopts a conformation that extends beyond the micellar radius in water and, thus, appears quite stretched. A random copolymer of poly(vinyl alc.-co-acetate) adopts a very flat conformation at the interface, forming a dense layer ≤20 Å. thick. While both of these polymers have hydrophobic moieties, hexane is not a good solvent for either. In contrast, the hydrophobic block of a diblock copolymer of poly(dimethylsiloxane)-poly(2-vinylpyridine-N-oxide) is very sol. in hexane, and in this case the hexane appears to have a much greater influence over the polymer structure. A substantial proportion of the polymer is found on the hexane side of the interface.

A dynamical Monte Carlo model of polymer adsorption

Stephen M. King and Terence Cosgrove
Sci. Div., ISIS, Chilton/Didcot/Oxfordshire, UK

Macromolecules (1993), 26(20), 5414-22


A novel dynamic Monte Carlo computer model designed to investigate the configurational relaxation of homopolymers at the solid/soln. interface is described. Ensembles of polymer chains, each ≤99 segments in length, are generated by n-step random self-avoiding walks throughout a simple cubic lattice, the basal face of which represented an impenetrable solid surface. To model adsorption, each chain is generated "in soln." at the center of the lattice and then displaced to the surface and allowed to approach its equil. adsorbed conformation through a succession of elementary moves operating on randomly selected segments. Each chain was considered to be in an athermal solvent environment, and the effect of surface coverage was simulated by the inclusion of a periodic boundary constraint. When the enthalpy of adsorption is low, it is possible to observe chains that have initially adsorbed, relaxed, completely desorbed, and then readsorbed. For isolated nonadsorbed chains, root-mean-square end-to-end distance data from the model provided an est. of the universal scaling exponent of 0.591, which is in good agreement with the Flory value of 0.6 for polymers in athermal solvents. By introduction of a probability of desorption, the model was also used to study the evolution of the structure of the adsorbed layer for polymers undergoing both chem. (irreversible) and phys. adsorption at the interface.

A study of chemisorption of poly(hydrogen methylsiloxane) using neutron reflectometry and small-angle neutron scattering

T. Cosgrove, A. Patel, J.A. Semlyen, J.R.P. Webster and A. Zarbakhsh
Department of Physical Chemistry, School of Chemistry, University of Bristol, Bristol, UK

Langmuir (1993), 9(9), 2326-9


Neutron reflectivity and small-angle neutron scattering have been used to study the chemisorption of poly(hydrogen methylsiloxane), on quartz and porous silica. The results indicate an increase in layer thickness and d. near the solid interface upon increasing the grafting reaction temp. The results are compared qual. with adsorption data obtained from FTIR expts. on alumina and with theor. predictions.

Adsorbed block copolymer of poly(2-vinylpyridine) and polystyrene studied by neutron reflectivity and surface force techniques

Terence Cosgrove, John S. Phipps, Robert M. Richardson, Michael L. Hair and David A. Guzonas
School of Chemistry, University of Bristol, Bristol, UK

Macromolecules (1993), 26(16), 4363-7


The adsorption of a small block copolymer of poly-(2-vinylypyridine) and polystyrene has been studied as a function of solvency. Both neutron reflectometry and surface force measurements were used to study the structure of the adsorbed layer. The adsorbed polymer is highly extended in good solvency conditions for the polystyrene but collapses when the solvent worsens. The results are compared with the self-consistent mean-field theory of Evers-Scheutjens-Fleer (1990) for the adsorption of block copolymers. Both the extended length of the polymer and the amt. of polymer adsorbed on mica were measured independently. For this small polymer, both the extended length and the amt. adsorbed are about twice as large as would be expected from theor. predictions based on the size of the blocks but are consistent both with each other and with the neutron data.

NMR self-diffusion study of poly(ethylene oxide)-block-poly(dimethylsiloxane) diblock copolymers in organic solvents and in poly(ethylene oxide) melts

Zoltan Kiraly, Terence Cosgrove and Brian Vincent
School of Chemistry, University of Bristol, Bristol, UK

Langmuir (1993), 9(5), 1258-62


The self-diffusion coeffs. of two poly(ethylene oxide) (I)-di-Me siloxane diblock copolymers were measured by the pulsed field-gradient spin-echo NMR technique. The solvents used were CDCl3, PhMe-d8, and THF-d8 at 30°, cyclohexane-d12 at 50°, DMF-d7 at 25-60° and protonated I melts of mol. wt. of 222, 480, and 980 at 25-150°. The copolymers formed micelles in DMF and I melts and micellar breakup took place as the temp. was raised. The temp. dependence of the crit. micelle concn. in I melts was detd. by a turbidimetric method. The hydrodynamic radii of the micelles, calcd. using the Stokes-Einstein equation, were virtually independent of solvency and had a value of .apprx.5 and 8 nm for the shorter and longer chain copolymer, resp. The corresponding aggregation nos. were 25 and 31.

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