Luke S. Egan

Luminescence studies on sterically stabilized polymer colloid particles: pyrene excimer formation

Abstract Detailed information about the conformation and dynamics of fluorescently labelled polymer chains free in solution and bound to colloidal sized particles can be obtained using luminescence techniques. Copolymers of pyrenealkyl methacrylate and 2-ethylhexyl methacrylate (EHMA) were used as stabilizers (St-Py) in the dispersion polymerization of vinyl acetate. In this way, poly(vinyl acetate) particles (0.3 μm) labelled in the stabilizer phase with pyrene (SLP) were prepared. Results from steady-state and time-resolved fluorescence studies on solutions of St-Py and dispersions of SLP are compared. In these systems, pyrene excimers are formed with a distribution of rate constants. We find that the mobility and dimensions of particle-bound stabilizer chains are less than the corresponding free stabilizer chains in solution, a consequence of the mechanism of particle synthesis. When the spacer separating pyrene from the stabilizer backbone is increased, excimer formation is facilitated, inferring an increase in stabilizer chain mobility relative to the systems with short spacer units. Studies on particles prepared with a mixture of labelled and unlabelled PEHMA showed that inter-chain interactions in the stabilizer phase are negligible.

Energy transfer studies from polymer bound naphthalene to anthracene in solution: translational and segmental diffusion rates

Abstract A graft copolymer of polyisobutylene with poly(methyl methacrylate) [PMMA] was prepared containing naphthalene [N] groups statistically distributed along the PMMA backbone. Fluorescence studies of dilute solutions of the polymer in ethyl acetate showed small amounts of N-excimer emission when the NMA/MMA ratio was 1:9, and undetectable excimer when the ratio was 2 98 . Energy transfer experiments were carried out between polymer-bound naphthalene and anthracene [A] added to the solution. The rate constant for energy transfer, kET, for the process N∗ + A → N + A ∗ was found to be 1.1 × 1010 M−1 s−1 at 22°, slightly smaller than that (1.2 × 1010 M−1 s−1) for energy transfer from naphthylmethyl pivalate to A. From the value of the rate constants, a value for the segmental diffusion coefficient of polymer bound naphthalene was calculated.

Fluorescence quenching studies on poly(methyl methacrylate) particles : Matching of the refraction index of the stabilizer phase to that of the solvent with added carbon disulphide

Abstract Detailed information about the interior morphology of sterically stabilized colloid particles ought to be accessible from light-scattering measurements when the index of refraction of the stabilizer layer is matched to that of the diluent. When carbon disulphide is added to dispersions of poly(methyl methacrylate) (PMMA) latex particlesstabilized with poly(12-hydroxystearic acid) (PHSA) is dodecane, the scattered light intensity varies continuously with time; a permanent match of indices of refraction in this system is not achieved. Fluorescence quenching experiments with CS2 as quencher were performed on similar particles containing 0.02 mol% anthracene groups covalently bound to the PMMA chains in order to obtain information about CS2 swelling of these particles. Time-dependent quenching experiments indicate rapid panetration of CS2 (

Molecular details of the solvent induced flocculation of dilute sterically stabilised polymer colloids

Abstract The incipient flocculation behaviour of sterically stabilised nonaqueous dispersions has been extensively investigated. These studies have identified the flocculation conditions either visually or using turbidity measurements. Such techniques identify the gross flocculation behaviour of the colloid but do not furnish any information about the flocculation process at the molecular level. In this paper we outline fluorescence energy transfer experiments which allow us to follow the change in conformation of the steric barrier as the solvency of the dispersion medium is varied. It is concluded from such experiments that in dilute sterically stabilised dispersions the steric barrier collapses in the vicinity of the flocculation point. The data also suggests that interpenetration of the stabiliser chains on different particles does not take place during the flocculation process.