Publications - 1999
Previous year | Overview | Next year
Interactions of Star Polymers with Surfactants
Robin David Wesley, Terence Cosgrove and Laurie Thompson
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (1999), 15(24), 8376-8382
Abstract
Binding isotherms between star poly(ethylene glycol) (s-PEG) and the anionic surfactant sodium dodecyl sulfate (SDS) have been measured. The onset of SDS/s-PEG binding happens at the same concn. for both star and linear PEG, but satn. of the star occurs at a lower surfactant concn. The size of the star has been measured as a function of SDS concn. by NMR self-diffusion and small-angle neutron scattering (SANS) techniques. The star decreases in size at the normal crit. micelle concn. (CMC) of the SDS but increases at higher SDS concns. These results echo the findings of photocorrelation spectroscopy and SANS studies on phys. adsorbed PEG on polystyrene latex. At high surfactant concns. the star adopts an elongated conformation. The surfactant binds to the star mols. in the form of spherical micelles, which are of similar size to free soln. micelles.
Calculation of Silberberg's Polymer Segmental Adsorption Energy by a Free Space Molecular Modeling Technique
B.J. Clifton, T. Cosgrove and M.R. Warne
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (1999), 15(25), 8659-8667
Abstract
Free space mol. modeling has been employed to calc. the segmental heat of adsorption (χs) for poly(ethylene) and poly(vinyl acetate) adsorbing from a carbon tetrachloride solvent onto a graphite surface. The technique manipulates contact energies and coordination nos. which are calcd. using the com. software packages Cerius2 and Polygraf. The estn. of the segmental heat of adsorption is extended to a range of poly(ethylene-vinyl acetate) (P(E-VAc)) copolymers by use of a two-state model. Both the ethylene and vinyl acetate segments are predicted to adsorb onto graphite from carbon tetrachloride; however, the value of χs for ethylene was found to be significantly higher than that of vinyl acetate. Investigation of the energetic terms revealed that the van der Waals contribution was significantly greater than the Coulombic contribution in the adsorption process of either of the polymer segment types. The effective χs for P(E-VAc) random copolymers of varying compn. allowed adsorbed amts. to be calcd. by use of the Scheutjens-Fleer lattice model.
NMR solvent relaxation studies on concentrated particulate dispersions
Terence Cosgrove, Kevin S. Jack, Nicholas Green, Timothy M. Obey and Matthew Wood
Department of Physical Chemistry, School of Chemistry, University of Bristol, Bristol, UK
ACS Symp. Ser. (1999), 736(Supramolecular Structure in Confined Geometries), 153-168
Abstract
The technique of 1H NMR solvent relaxation was used to probe the effect of the adsorption of polymers at particle/H2O interfaces. On inorg. oxide surfaces the pure H2O relaxation was strongly enhanced but on a latex surface, the effect was much weaker due to its more hydrophobic character. The effect of polymer adsorption on all the oxide materials studied increased the specific relaxation wt. of H2O: the effect for poly(vinyl pyrrolidone) (PVP) adsorption on SiO2 was much stronger than for poly(ethylene oxide) (PEO) and in a competitive adsorption study the PVP was found to displace the PEO. On a clay surface, a strong mol. wt. effect was found on the bound solvent probability (p). Similar data for PEO samples with a similar mol. wt. but different end groups and for a cyclic polymer also showed very different effects. The results are discussed in terms of different surface conformations. The NMR method is a very simple tool to measure competitive adsorption.
Adsorption Studies of Diblock Copolymers at the Cyclohexane/Carbon Black Interface
J.A. Shar, T. Cosgrove, T.M. Obey, M.R. Warne and D.J. Wedlock
School of Chemistry, Cantock's Close, University of Bristol, Bristol, UK
Langmuir (1999), 15(22), 7688-7694
Abstract
The adsorption of copolymers of polystyrene and hydrogenated polyisoprene block copolymers adsorbed from cyclohexane onto carbon black has been investigated. The adsorption of the copolymers was found strongly dependent on copolymer compn. The conformation of the adsorbed polymer is largely detd. by the surface-copolymer interaction, esp. by the interaction of the polystyrene block with the carbon black surface. Computer simulations of a polystyrene/hydrogenated polyisoprene diblock copolymer tethered to a cyclohexane-carbon interface were performed. Interfacial vol. fraction profiles are presented. An estn. of the relative adsorption affinities of the two polymers has been obtained by theor. calcns. using the self-consistent mean field model of Scheutjens and Fleer. The data show good qual. agreement between the exptl. results and the theor. predictions.
Small-angle neutron methods in polymer adsorption studies
Editor(s): Farinato, Raymond S.; Dubin, Paul L.
Terence Cosgrove, Stephen M. King and Peter C. Griffiths
School of Chemistry, University of Bristol, Bristol, UK
Colloid-Polym. Interact. (1999), 193-204. Publisher: Wiley, New York, N. Y
Abstract
The application of small-angle neutron scattering in detg. the vol. fraction profiles of adsorbed polymers is described and results from 3 different exptl. systems are cited. The technique is suitable for particles, porous solids, and for emulsions and gives a unique insight into the structure of adsorbed layers.
Poly(NIPAM) microgel particle de-swelling: a light scattering and small-angle neutron scattering study
Helen M. Crowther, Brian R. Saunders, Sarah J. Mears, Terence Cosgrove, Brian Vincent, Stephen M. King and Ga-Er Yu
School of Chemistry, University of Bristol, Bristol, UK
Colloids Surf., A (1999), 152(3), 327-333
Abstract
Small-angle neutron scattering (SANS) has been used to investigate structural changes during the de-swelling of poly(N-isopropylacrylamide) [poly(NIPAM)] microgel particles induced by temp. variation and the addn. of free polymer [poly(ethylene oxide)]. The extent of particle de-swelling was characterized by photon correlation spectroscopy (PCS). Thermally induced de-swelling of poly(NIPAM)/deuterated water dispersions occurred on increasing the temp. in the region of the lower crit. soln. temp. (LCST). The latter was found to be 34°C, which is 2°C higher than the value reported for poly(NIPAM) particles dispersed in water. The SANS data exhibit a Porod form (Q-4) of scattering in regard to the size of the colloidal particles. However, in the swollen state, the scattering measured at temps. less than the LCST, also has a contribution from poly(NIPAM) chains in a soln.-like environment (Ornstein-Zernike scattering). The trends obsd. in the SANS data as a function of temp. were simulated using a model comprised of Porod and Ornstein-Zernike scattering terms. The SANS data confirm earlier PCS measurements showing that addn. of free polymer induces particle de-swelling. The SANS data obtained using added free polymer are the first examples of their type to be reported.
Polymer, particle, surfactant interactions
T. Cosgrove, S.J. Mears, T. Obey, L. Thompson and R.D. Wesley
School of Chemistry, University of Bristol, Bristol, UK
Colloids Surf., A (1999), 149(1-3), 329-338
Abstract
The effect of the surfactant sodium dodecyl sulfate (SDS) on the adsorption properties of the homopolymer poly(ethylene oxide) (PEO) at the solid-liq. interface has been studied using a variety of techniques: photon correlation spectroscopy (PCS), NMR spectroscopy and small-angle neutron scattering (SANS). Physisorbed, grafted, and dendritic polymers have been studied. Across the range of systems studied, a remarkably consistent general picture has emerged. For the physisorbed system, the surfactant affected both the adsorption of the polymer and the extension of its adsorbed layer. For systems where the adsorbed amt. was held at a const. value, the polymer structure was significantly perturbed by the addn. of surfactant. It is proposed that the polymer layer structure is not governed by competitive adsorption for the interface, but by a competitive polymer-surfactant interaction.
Factors affecting the swelling of poly(N-isopropylacrylamide) microgel particles: fundamental and commercial implications
Brian R. Saunders, Helen M. Crowther, Gayle E. Morris, Sarah J. Mears, Terence Cosgrove and Brian Vincent
School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK
Colloids Surf., A (1999), 149(1-3), 57-64
Abstract
A microgel particle is a crosslinked latex particle which is swollen by a good solvent. Particle swelling is intrinsically related to the nature of the interaction between the polymer and continuous phase. Microgel particles based on PNP [PNP=poly(N-isopropylacrylamide)] are particularly interesting since the parent homopolymer undergoes a coil-to-globule transition in water when the temp. increases above 32°C. In this work, PCS (photon correlation spectroscopy) and SANS (small-angle neutron scattering) are employed in a complementary manner to study the environmentally induced de-swelling of PNP particles. Further, we show that particle de-swelling may be induced at room temp. by addn. of alcs. or excluded free polymer (i.e. non-adsorbing free polymer) to the continuous phase. The extents of particle de-swelling obsd. using these additives are similar to those achieved by heating the pure microgel particles in water above 32°C. Particle de-swelling in the presence of added alc. or free polymer arises from co-non-solvency and osmotic de-swelling effects, resp. Copolymn. of N-isopropylacrylamide (NP) with acrylic acid yields microgel particles whose diams. are sensitive to both pH and temp. These particles adsorb PbII ions from soln. in a reversible manner. The latter property has potential application in water purifn.
Adsorption studies of polyethers. Part II: Adsorption onto hydrophilic surfaces
J.A. Shar, T.M. Obey, T. Cosgrove
School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK
Colloids Surf., A (1999), 150(1-3), 15-23
Abstract
The adsorption of BAB-type triblock copolymers (B = poly(ethylene oxide); A = poly(propylene oxide)) from aq. soln. onto hydrophilic silica particles is described with particular ref. to the role of the copolymer compn. The adsorbed amt. and the layer thickness were detd. by the std. depletion method and photon correlation spectroscopy, resp. Snowtex-YL silica was used as the adsorbent. The results show an increase in the adsorbed amt. with increasing molar masses of both PEO and PPO blocks. The adsorbed layer thickness is found to depend strongly on PEO block mass. Both these parameters (adsorbed amt. and hydrodynamic layer thickness) show a max. as a function of the mole fraction of the PPO block present in the copolymer. The conformation of the adsorbed layer is detd. by the surface-copolymer interaction; principally by the interaction of the hydrophilic PEO block with the silica surface. A good qual. agreement of the exptl. results with theor. predictions and self-consistent mean field calcns. has been found.
Previous year | Overview | Next year
