Publications - 2005
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Narrowly distributed surfactant-free polystyrene latex with a water-soluble comonomer
Dong Qiu, Terence Cosgrove and Andrew M. Howe
School of Chemistry, University of Bristol, Bristol, UK
Macromolecular Chemistry and Physics (2005), 206(22), 2233-2238
Abstract
The surfactant-free synthesis of latex polymers of styrene and sodium styrenesulfonate (NaSS) was investigated. The development of size and size distribution of the particles was studied by photo-correlation spectroscopy (PCS) and transmission electronic microscopy (TEM). The effects of NaSS concn. and the order of addn. of reactants were examd. in detail. The results showed that the particle size decreases with an increase in the styrene sulfonate concn. The polydispersity index can be reduced by mixing NaSS with styrene homogeneously before adding initiator, but this leads to a slightly larger mean particle size.
Small-Angle Neutron Scattering Studies of an Adsorbed Non-Ionic Surfactant (C12E24) on Hydrophobised Silica Particles in Water
Phillip J. Dale, Brian Vincent, Terence Cosgrove and Johan Kijlstra
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(26), 12244-12249
Abstract
Small-angle neutron scattering (SANS) studies of aq. dispersions of Stoeber silica particles (which have been hydrophobised by having 1-octadecanol grafted to their surface), carrying an adsorbed layer of the nonionic surfactant C12E24, in water, have been performed as a function of temp. Using mixts. of D2O and H2O, the compn. of the continuous phase was adjusted to have the same scattering length d. as the silica particles. Hence, only the scattering from the 1-octadecanol and C12E24 layers was detected. The data have been analyzed using both a surface Guinier anal. and a two-layer structure model. It has been found that a step profile best describes the inner combined adsorbed layer (1-octadecanol grafted chains, plus the penetrating alkyl chains from the surfactant) and a semi-Gaussian profile the extended poly(ethylene oxide) outer layer. Both analyses demonstrated that the combined surface layer contracted with increasing temp.
Microscopic Signature of a Microgel Volume Phase Transition
B. Sierra-Martin, Y. Choi, M.S. Romero-Cano, T. Cosgrove, B. Vincent and A. Fernandez-Barbero
Department of Applied Physics, University of Almeria, Almeria, Spain
Macromolecules (2005), 38(26), 10782-10787
Abstract
This paper discusses the dynamics of water mols. in poly(NIPAM) microgel dispersions. 1H NMR spectroscopy is used to det. the self-diffusion coeff. of the water mols. The capability of the microgel particles to restrict the motion of water mols. depends on the degree of swelling, as detd. by dynamic light scattering. The dependence of mol. diffusion on the network d. is established. This is tested against Yasuda's free vol. model and Ogston's obstruction model, which have been modified to account for the dependence of the network pore size on the extent of swelling.
Solvent relaxation of swelling PNIPAM microgels by NMR
B. Sierra-Martin, M. S. Romero-Cano, Terence Cosgrove, B. Vincent and A. Fernandez-Barbero
Group of Complex Fluids Physics, Department of Applied Physics, University of Almeria, Almeria, Spain
Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2005), 270-271(Complete), 296-300
Abstract
The dynamics of solvent inside swelling microgel particles is studied using 1H NMR. Solvent relaxation is sensitive to the microgel vol. transition after temp. changes, showing the effect of the local environmental conditions on solvent confinement. A microscopic view of the vol. phase transition of microgel particles is then shown. NMR measurements indicate that solvent dynamics is controlled only by the swelling degree of the microgel particles. Along the vol. phase transition, the collapse of the polymer network restricts the mobility of bound water defining the confinement state. The effect of the amt. of microgel polymer on the solvent mols. mobility is also investigated. In the collapsed state, water mols. still exist inside the microgel particles, being strongly confined within the polymer network. Despite that there are not many bound mols. under this circumstance, they contribute so strongly to the total averaged relaxation time that the behavior is controlled by the presence of those. On the other hand, the solvent mols. were found to be weakly constrained for swollen microgels.
Novel Self-Assembly of Amphiphilic Copolymers into Nanotubes: Characterization by Small-Angle Neutron Scattering
C. Malardier-Jugroot, T.G.M. Van de Ven, T. Cosgrove, R.M. Richardson and M.A. Whitehead
Department of Chemistry, McGill University, Montreal, Canada
Langmuir (2005), 21(22), 10179-10187
Abstract
The self-assembly into nanotubes in soln. of an amphiphilic copolymer is characterized by small-angle neutron scattering (SANS). This study confirmed the shape and the size of the tubular assocn. and the 3-D assocn. of the tubes predicted by MO theory. Moreover, the characterization of the stability of the assocn. has revealed that the addn. of a very small amt. of salt to the soln. increases the size of the assocn. When more salt is added, the size of the assocn. decreases, and the structure is altered. The assocn. was found to be independent of temp. and therefore is very stable.
Small-Angle Neutron Scattering Study of Adsorbed Pluronic Tri-Block Copolymers on Laponite
Andrew Nelson and Terence Cosgrove
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(20), 9176-9182
Abstract
The adsorption of selected poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymers on synthetic clay particles (laponite) has been investigated. The adsorbed amt. and distribution of polymer was detd. as a function of relative block compn. and size, using the technique of contrast variation small-angle neutron scattering. The pluronic mols. appear to adsorb via a preferential segregation of hydrophobic PPO segments at the surface, with hydrophilic PEO segments dangling into soln. The effect of the PPO segments is substantial with large increases in adsorbed amt. and layer thickness as the anchor fraction decreases/PEO chain length increases. This is in direct contrast to the behavior obsd. for PEO homopolymer adsorption (of much higher mol. wts.) where the adsorbed amt. and layer thickness are smaller and change little with mol. wt.
Wormlike Micelles Mediated by Polyelectrolyte
Charlie Flood, Cecile A. Dreiss, Vania Croce, Terence Cosgrove and Göran Karlsson
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(17), 7646-7652
Abstract
Aq. solns. of the anionic surfactant potassium oleate (K-oleate) were studied using small-angle neutron scattering (SANS), steady-state rheol., and cryogenic TEM (cryo-TEM). The micelle structural changes induced by addn. of KCl and sodium polystyrenesulfonate (PSS) of different mol. wts. were studied. Upon addn. of KCl, a transition from spherical to wormlike micelles was detected from the SANS data and confirmed by the cryo-TEM pictures. The rheol. measurements revealed a strong dependence of the low-shear viscosity on the concn. of salt: a broad max. in the viscosity curve was obsd. upon addn. of KCl, characteristic of the growth of micelles into long worms, followed by branching. The addn. of PSS to salt-free solns. of K-oleate had a significant effect on the scattering patterns, revealing partial growth of the spherical micelles into rodlike micelles. In contrast, in the presence of high salt concns., addn. of PSS to solns. of wormlike micelles did not bring any noticeable modifications in the scattering. However, in the same salt conditions, a clear effect was obsd. on the low shear viscosity upon addn. of PSS, which was found to depend significantly on mol. wt.
Small-Angle Neutron Scattering Study of Concentrated Colloidal Dispersions: The Interparticle Interactions between Sterically Stabilized Particles
Dong Qiu, Cecile A. Dreiss, Terence Cosgrove and Andrew M. Howe
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(22), 9964-9969
Abstract
Small-angle neutron scattering (SANS) was used to investigate the interparticle interactions in concd. dispersions of colloidal silica stabilized either by steric or by electrostatic repulsive interactions. In 10 mM NaCl, an adsorbed PEO layer is required to prevent flocculation, and particles are stabilized by steric repulsions. The adsorbed layer was made invisible to neutrons by contrast matching with the aq. continuous phase. Dispersions of the same particles at the same concns. but in the absence of added salt and adsorbed PEO were also studied. In both cases, the SANS spectra of concd. dispersions show a peak at low Q, which is due to interparticle interactions: a structure factor. The SANS data can be described rather well by a homogeneous spherical form factor and a structure factor based on the Hayter-Penfold/Yukawa potential model. The steric potential was compared to the electrostatic potential obtained by fitting the SANS data of the bare silica dispersions. The steric potential shows a greater dependence on the particle vol. fraction, which we ascribe to the penetration and compression of the adsorbed PEO layer as the particles approach.
Giant Micellar Worms under Shear: A Rheological Study Using SANS
Vania Croce, Terence Cosgrove, Cecile A. Dreiss, Stephen King, Geoff Maitland and Trevor Hughes
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(15), 6762-6768
Abstract
Flow-SANS expts. were performed on viscoelastic aq. solns. of erucyl bis(hydroxyethyl) methylammonium chloride in the presence of potassium chloride. This cationic surfactant has the ability to form very long and flexible wormlike micelles upon addn. of salt. The effects of the key-parameters-shear rate, temp., surfactant and salt concn.-on the ability of the micelles to align in the flow-field were investigated. The scattering data were analyzed in terms of an anisotropy factor (Af). It was found that the wormlike micelles aligned in the direction of the applied shear rate and that the anisotropy factor increased with shear rate. In addn., an increase in temp. caused a decrease of the anisotropy factor (Af) due to the formation of shorter worms. Furthermore, the branching of the micelles at high ionic strength caused the anisotropy factor to decrease in comparison with the values obtained from linear wormlike micelles, hence revealing that the formation of 3-way junctions restricts the alignment of the micelles in the shear-flow. Furthermore, the total surfactant concn. was found to affect the shear-induced patterns significantly, and different behaviors were obsd. depending on the ionic strength.
Structure of a Hydrophilic-Hydrophobic Block Copolymer and Its Interactions with Salt and an Anionic Surfactant
Robin D. Wesley, Cecile A. Dreiss, Terence Cosgrove, Steven P. Armes, Laurie Thompson, Fiona L. Baines and Norman C. Billingham
School of Chemistry, University of Bristol, Bristol, UK
Langmuir (2005), 21(11), 4856-4861
Abstract
The aggregation of a hydrophilic-hydrophobic diblock copolymer consisting of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(Me methacrylate) (PMMA) in aq. soln. has been investigated by small-angle neutron scattering. This polybase is extensively protonated at low pH and forms micelles with a dense core of PMMA and a diffuse coronal layer of cationic PDMAEMA. Addn. of salt induced micellar growth, brought about by charge screening and more efficient packing of the chains. As a result, the aggregation no. increased from 8 up to 31. A similar effect was obsd. at low concns. of an anionic surfactant, sodium dodecyl sulfate (SDS) since the net cationic charge in the hydrophilic coronal layer was reduced due to surfactant binding. However, at higher surfactant concns., a drastic structural reorganization occurred, as the PMMA became solubilized into the SDS micellar cores and the PDMAEMA chains interacted with the surfactant micelles, resulting in a "pearl-necklace" structure. The presence of the cationic polyelectrolyte significantly increased the population of SDS micelles by effectively lowering the crit. micelle concn. of this anionic surfactant.
SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles
Marite Cardenas, Cecile A. Dreiss, Tommy Nylander, Chau P. Chan, Terence Cosgrove and Björn Lindman
Center for Chemistry and Chemical Engineering, Physical Chemistry 1, University of Lund, Lund, Sweden
Langmuir (2005), 21(8), 3578-3583
Abstract
The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was obsd. at a neg.-to-pos. charge ratio far below the phase sepn. region, at a neg.-to-pos. charge ratio of 18. Addnl., large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addn. of a cationic surfactant to the DNA-coated latex particles at a neg.-to-pos. charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the neg.-to-pos. charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.
NMR and SANS studies of nanoparticle polymer interactions
Terence Cosgrove, Roy Hughes, Paul Reynolds, Eloise Stattersfield, Andrew Howe and Andrew Nelson
School of Chemistry, University of Bristol, Bristol, UK
Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2005), 46(1), 438-439
Abstract
Two systems of nanoparticles with at least one dimension in the nanometer range and polymer solns. were studied using NMR relaxation, small-angle neutron scattering, and mol. dynamics methods. Nanostructures of high mol. wt. poly(ethylene oxide) with nanosized hydrophilic silica have unique rheol., showing shear thinning and shear thickening. The ratio of polymer mol. wt. to particle size is a crucial factor in detg. rheol. Adsorption of PEO onto nanosized synthetic Laponite disk shaped clay results in asym. and very flat layers.
Nanocomposites with PDMS
Terence Cosgrove, Natalie Benton, Claire Roberts, Robert Richardson, Randall G. Schmidt, Glenn Gordon and Makoto Yoshitake
School of Chemistry, University of Bristol, Bristol, UK
Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (2005), 46(1), 57-58
Abstract
The incorporation of nanoparticles into polymer melts leads to an array of fascinating behaviors. Both reinforcement and solvation effects are seen. The extent of these effects can be seen clearly in bulk viscosity measurements and in the local scale dynamics as perceived by NMR. The effect of particle size and surface morphol. have been investigated showing that for solid particles an increase in size can lead to an increase in the enhanced mobility at least for the largest nanoparticle that has been studied. Siloxane-based dendrimers also show these effects though at lower concns. Quasielastic neutron scattering (QENS) data only show a redn. in dynamics but with the realization that this method works on different spatial and time scales relative to NMR and viscosity measurements.
NMR and SANS Studies of nanoparticle polymer interactions
Terence Cosgrove, Roy Hughes, Paul Reynolds, Eloise Stattersfield, Andrew Howe, and Andrew Nelson
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
Abstracts of Papers, 229th ACS National Meeting, San Diego, CA, United States, March 13-17, 2005 (2005), POLY-467. Publisher: American Chemical Society, Washington, D.C.
Abstract
In this talk I will be discuss two new systems in which we have used particles with at least one dimension in the nanometer range to modify the properties of polymer solns. The first area relates to nanostructures formed by high mol. wt. poly(ethylene oxide) polymers with nanosized hydrophilic silicas. These systems have unique rheol. properties and their behavior is quite unexpected showing both shear thinning and shear thickening behavior. In particular it appears that the ratio of polymer mol. wt. to particle size is a crucial factor. The second system is the adsorption of the same polymers onto nanosized synthetic Laponite, a disk shaped synthetic clay. Here again very unexpected adsorption occurs and the layers formed are asym. and very flat. NMR relaxation, small-angle neutron scattering and mol. dynamics have been used to probe the properties of these systems.
Nanocomposties with PDMS
Terence Cosgrove, Natalie Benton, Claire Roberts, Robert Richardson, Randall G. Schmidt, Glenn V. Gordon and Makoto Yoshitake
School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK
Abstracts of Papers, 229th ACS National Meeting, San Diego, CA, United States, March 13-17, 2005 (2005), POLY-141. Publisher: American Chemical Society, Washington, D.C.
Abstract
In this talk I will discuss systems in which we use particles with nanometer dimensions to modify the properties of polymer melts. In the first poly(di-Me siloxanes) are mixed with nanosized hydrophobic resin like materials. These systems have unique rheol. properties and their behavior is quite unexpected. The effects of polymer mol. wt. and particle size have been studied systematically using rheol., DSC, NMR relaxation/diffusion and neutron scattering. Model systems have also been prepd. using dendrimers which are monodisperse. In all these systems the ratio of the size of the particle to the radius of gyration of the polymer proves to be the dominant factor in detg. their behavior.
Polymer adsorption: The ups and downs
Terence Cosgrove
School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
Abstracts of Papers, 229th ACS National Meeting, San Diego, CA, United States, March 13-17, 2005 (2005), POLY-072. Publisher: American Chemical Society, Washington, D.C.
Abstract
In this tutorial I shall outline some of the basic aspects of the conformation polymer chains exhibit at interfaces. The focus will be on homopolymers but some aspects of block and random copolymers will also be presented. Where possible the marriage of expt. and theory will be consummated.
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