Browsing by Author "Griffiths P.C."

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    Studying the interaction of hydrophobically modified ethoxylated urethane (HEUR) polymers with sodium dodecylsulfate (SDS) in concentrated polymer solutions
    (Academic Press Inc., 2018) Ibrahim M.S.; Valencony J.; King S.; Murray M.; Szczygiel A.; Alexander B.D.; Griffiths P.C.; Faculty of Engineering and Science; University of Greenwich; Medway Campus; Chatham MaritimeKent ME4 4TB; United Kingdom; Pharmaceutics Department; Faculty of Pharmacy; Modern Science and Arts University; 26 July Mehwar Road Intersection with Wahat Road; Cairo; Egypt; Science and Technology Facilities Council; ISIS Facility; Rutherford Appleton Laboratory; Didcot; Oxfordshire OX11 OQX; United Kingdom; AkzoNobel; Wexham Road; Slough; Berkshire SL2 5DS; United Kingdom
    Hypothesis: Hydrophobically modified ethoxylated urethane polymers (HEURs) are widely used to control the rheological profile of formulated particulate dispersions through associative network formation, the properties of which are perturbed by the presence of surfactants. At high polymer concentrations and in the presence of surfactants, it is hypothesised that the dominant factors in determining the rheological profile are the number and composition of the mixed hydrophobic aggregates, these being defined by the number and distribution of the hydrophobic linkers along the polymer backbone, rather than the end-group hydrophobe characteristics per se that dominate the low polymer concentration behaviour. Experiments: Three different HEUR polymers with formulae (C6-L-(EO100-L)9-C6, C10-L-(EO200-L)4-C10 and C18-L-(EO200-L)7-C18 (where L = urethane linker, Cn = hydrophobic end-group chain length, and EO = ethylene oxide block) have been studied in the absence and presence of SDS employing techniques that quantify (a) the bulk characteristics of the polymer surfactant blend, (b) the structure and composition of the hydrophobic domains, (c) the dynamics of the polymer and surfactant, and (d) the polymer conformation. Collectively, these experiments demonstrate how molecular-level interactions between the HEURs and sodium dodecylsulfate (SDS) define the macroscopic behaviour of the polymer/surfactant mixture. Findings: Binding of the SDS to the polymer via two mechanisms � monomeric anti-cooperative and micellar cooperative � leads to surfactant-concentration-specific macroscopic changes in the viscosity. Binding of the surfactant to the polymer drives a conformational rearrangement, and an associated redistribution of the polymer end-groups and linker associations throughout the hydrophobic domains. The composition and size of these domains are sensitive to the polymer architecture. Therefore, there is a complex balance between polymer molecular weight, ethylene oxide block size, and number of urethane linkers, coupled with the size of the hydrophobic end-groups. In particular, the urethane linkers are shown to play a hitherto largely neglected but important role in driving the polymer association. � 2018 Elsevier Inc.
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    Surfactant modulated interaction of hydrophobically modified ethoxylated urethane (HEUR) polymers with impenetrable surfaces
    (Academic Press Inc., 2019) Ibrahim M.S.; Rogers S.; Mahmoudy N.; Murray M.; Szczygiel A.; Green B.; Alexander B.D.; Griffiths P.C.; Faculty of Engineering and Science; University of Greenwich; Medway Campus; Chatham Maritime; Kent ME4 4TB; United Kingdom; Pharmaceutics Department; Faculty of Pharmacy; Modern Science and Arts University; 26 July Mehwar Road Intersection with Wahat Road; Cairo; Egypt; Science and Technology Facilities Council; ISIS Facility; Rutherford Appleton Laboratory; Didcot; Oxfordshire OX11 OQX; United Kingdom; AkzoNobel; Wexham Road; Slough; Berkshire SL2 5DS; United Kingdom
    Hypothesis: The presence of surfactant modulates the surface-chemistry-specific interaction of hard colloidal particles (latex) with HEUR polymers, principally through introducing a preferential solution interaction rather than a competitive surface interaction; addition of surfactant leads to a preponderance of polymer/surfactant solution complexes rather than surface-bound complexes. Experiments: A range of model formulations comprising a hexyl end-capped urethane polymer (C6-L-(EO100-L)9-C6), sodium dodecylsulfate (SDS) and a series of polystyrene-butylacrylate latices (PS-BA-L) have been characterised in terms of rheology, particle surface area (solvent relaxation NMR), polymer conformation (small-angle neutron scattering) and solution composition to build up a detailed picture of the distribution of the HEUR in the presence of both surfactant and latex. Findings: There is very weak adsorption of C6-L-(EO100-L)9-C6 to only the most hydrophobic latex surface studied, an adsorption that is further weakened by the addition of low levels of surfactant. Macroscopic changes in the hydrophobic latex system may be interpreted in terms of bridging flocculation at low polymer concentrations. No adsorption of C6-L-(EO100-L)9-C6 is observed in the case of hydrophilic surfaces. In most cases, the observed behaviour of the ternary system (polymer/surfactant/particle) is highly reminiscent of the binary (polymer/surfactant) system at the appropriate composition, suggesting that the polymer/surfactant solution interaction is the dominant one. 2018