Robert H. Lambeth

Cationic comb polymer superdispersants for colloidal silica suspensions.

We investigate the ability of a cationic comb polymer composed of a poly(trimethylammonium iodide ethyl methacrylate) (PTMAM) backbone and uncharged poly(ethylene glycol) (PEG) teeth to stabilize aqueous silica suspensions of varying ionic strength and pH. Both PTMAM-g-PEG and its homopolymer backbone, PTMAM, are synthesized via reversible addition-fragmentation chain transfer followed by quaternization of the pendant amine groups with methyl iodide. Through a combination of polymer adsorption, zeta potential, and sedimentation measurements as well as confocal imaging of sediment structures, we find that PTMAM-g-PEG imparts stability over a broad range of solution conditions, where pure PTMAM fails.

Proximity field nanopatterning of azopolymer thin films

A method for inscribing surface relief gratings in azopolymer thin films via proximity field nanopatterning is reported. Azopolymers prepared by ring opening metathesis polymerization were cast as thin films and brought into conformal contact with transparent polydimethylsiloxane phase masks. Irradiation of the film surface through the phase masks induces mass transport of azopolymer that generates surface relief structures on the basis of the intensity modulation of the light by structures on the phase mask. The experimental images obtained matched well with those produced by optical simulation. A wide variety of structures could be inscribed in the film surface which depended on the molecular weight of the azopolymer and irradiation time. Control experiments conducted suggest that the process is entirely photonic and that the presence of the phase mask on the film surface did not affect the inscription process.