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Publications - 1996

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The adsorption of tri-block copolymers at the solid-liquid and liquid-liquid interfaces

Terence Cosgrove, Shar Jabir, Tim Obey, Robert Richardson, Brian Clifton, Peter C. Griffiths, Colin Booth and Ga Er Yu
School of Chemistry, University of Bristol, Bristol, UK

Book of Abstracts, 212th ACS National Meeting, Orlando, FL, August 25-29 (1996), COLL-153. Publisher: American Chemical Society, Washington, D. C


Tri-block copolymers comprising of either propylene oxide or butylene oxide with ethylene oxide have been studied by a variety of methods to establish the conformation the polymers adopt at interfaces. In particular adsorption isotherms, vol. fraction profiles and hydrodynamic thickness measurements have been made as function of the relative block sizes and compn. at the solid-liq. and liq.-liq. interfaces. In ethylene oxide "rich" samples the "pluronic-type" polymers behave in a similar manner to the ethylene oxide homopolymer, but as the ratio of propylene oxide to ethylene oxide increases the block copolymer nature becomes evident. The interfacial structure of butylene oxide polymers depends on the connectivity and relative size of the two block types. The results are compared with predictions from Monte Carlo simulations.

The structure of sodium dodecyl sulfate bound to a poly(nipam) microgel

S.J. Mears, Y. Deng, T. Cosgrove and R. Pelton
School of Chemistry, University of Bristol, Cantocks Close, Bristol, UK

Book of Abstracts, 212th ACS National Meeting, Orlando, FL, August 25-29 (1996), COLL-103. Publisher: American Chemical Society, Washington, D. C


Dynamic light scattering (DLS), small-angle neutron scattering (SANS) and binding isotherm measurements have been performed on an aq. microgel in the presence of the surfactant sodium dodecyl sulfate (SDS). In the presence of the microgel, at concns. just above the CMC, the surfactant existed as small, polymer bound aggregates of less than 5 monomer units, rather than larger micelles. This is in stark contrast to other homopolymer/surfactant systems such as SDS/poly(ethylene oxide) where the polymer bound micelles have structures similar to free micelles obtained without polymer. Both DLS and SANS measurements indicated that microgel swelling with water increased in the presence of surfactant.

Neutron reflection studies of compressed polymer layers

J.K. Cox and T. Cosgrove
School of Chemistry, University of Bristol, Bristol, UK

Book of Abstracts, 212th ACS National Meeting, Orlando, FL, August 25-29 (1996), COLL-098. Publisher: American Chemical Society, Washington, D. C


The interactions of two polymer layers when compressed together is of fundamental importance in the understanding of the steric stabilization of colloidal systems. A no. of studies have looked at the interlayer forces. However until now little has been known of the effect on the shape of the polymer layers. We have developed an app. which allows the detn. of the conformation of polymer layers when compressed. Results form two complementary systems will be presented. These are the homopolymer polyethylene oxide in aq. salt solns. and polystyrene in toluene and cyclohexane. Neutron reflection data on the compressed layers will be compared with surface force measurements and related to the existing theories on the interactions of polymer layers.

A Self-Diffusion Study of the Complex Formed by Sodium Dodecyl Sulfate and Gelatin in Aqueous Solutions

P.C. Griffiths, P. Stilbs, A.M. Howe and T. Cosgrove
Department of Chemistry, University of Wales Cardiff, Cardiff, UK

Langmuir (1996), 12(12), 2884-2893


The diffusion behavior of both the anionic surfactant SDS and gelatin were studied by pulsed-gradient spin-echo NMR spectroscopy (PGSE-NMR) in aq. solns. at 44° (well above the setting temp.). Both surfactant and gelatin concn. were varied for 2 different lime-processed gelatin samples, one the std. photog. material, the other a fractionated sample. Above c*, the fractionated and std. gelatins exhibit different behavior in both the presence and absence of SDS. Adding SDS slows the diffusion of the gelatin, which passes through a min. with increasing surfactant concn. The diffusion data are compared to light scattering, small-angle neutron scattering and viscosity data from similar systems. An isotherm characterizing the SDS binding to the gelatin was derived from the self-diffusion data.

Self-diffusion and spin-spin relaxation in blends of linear and cyclic polydimethylsiloxane melts

T. Cosgrove, M.J. Turner, P.C. Griffiths, J. Hollingshurst, M.J. Shenton and J.A. Semlyen
School of Chemistry, University of Bristol, Bristol, UK

Polymer (1996), 37(9), 1535-1540


Self-diffusion and spin-spin relaxation measurements have been performed on a series of blends of narrow-fraction linear and cyclic polydimethylsiloxane polymers in the melt by pulsed NMR techniques. The results obtained are compared to the viscosity behavior on the same samples and discussed in terms of the reptation and Rouse theories commonly invoked for the dynamics of single-component systems. The dynamics of the blends deviated from the expected behavior above a crit. ring size which can be understood through a mechanism based on ring threading.

The adsorption of polystyrene saturated-polydiene block copolymers on silica substrates

S. M. King, T. Cosgrove and A. Eaglesham
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot Oxfordshire, UK

Colloids Surf., A (1996), 108(2/3), 159-71


The adsorption of AB- and ABA-type block copolymers of polystyrene (the A or anchor blocks) and either poly(ethylene-random-propylene) or poly(ethylene-random-butylene) (the B or buoy blocks) onto normal (hydroxy) and surface-modified (alkylated) colloidal silica particles has been investigated and compared with that of the constituent polymers. Markedly different behavior has been obsd. depending on the solvency of the anchor blocks and on the type of silica surface. In all cases the buoy blocks were well solvated but non-adsorbing. The results are discussed in the context of the Marques-Joanny (MJ) and Marques-Joanny-Leibler (MJL) scaling descriptions of block copolymer adsorption from non-selective and selective solvents resp. For the case of adsorption onto normal silica from a non-selective solvent, high-affinity polymer adsorption isotherms were obtained. As the polystyrene content of the polymer increased, the affinity of that polymer for the surface was generally enhanced and a higher adsorbed amt. was recorded. The corresponding surface d. of polymer shows reasonable agreement with the MJ scaling prediction for the anchor regime. Similar trends were obsd. in selective solvents, although the adsorption regime was somewhat ambiguous and so there was less satisfactory agreement with MJL scaling predictions. In addn., the highest adsorbed amt. did not occur in the most selective solvent. This is thought to be due to extensive, and largely irreversible, micellization. The thicknesses of the adsorbed polymer layers in selective solvents again showed semi-quant. agreement with the MJL predictions but it was not possible to differentiate conclusively between normal adsorption from soln. and micellar adsorption. By comparison, very low affinity polymer adsorption isotherms were obtained with the modified silicas, the shape of the isotherm being dependent on the polystyrene content of the polymer and on the nature of the surface modifying group.

Small-angle neutron scattering studies of sodium dodecyl sulfate interactions with gelatin. Part 2. Effect of temperature and pH

Terence Cosgrove, Sarah J. White, Ali Zarbakhsh, Richard K. Heenan and Andrew M. Howe
School of Chemistry, University of Bristol, Bristol, UK

J. Chem. Soc., Faraday Trans. (1996), 92(4), 595-9


Structural perturbations and interactions between the anionic surface sodium dodecyl sulfate (SDS) and the biopolymer and polyampholyte gelatin have been studied using small-angle neutron scattering. The effects of temp. and changes in pH have been investigated. Although the phys. properties of the systems change dramatically with temp., from a gel at 25° to a fluid at 65°, the effects on the structure over the dimensions probed by small-angle neutron scattering are rather weak. Changes in pH, which alter the net charge of the gelatin, lead to dramatic changes in the scattering for pure gelatin solns. and for surfactant-gelatin mixts.

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