title: Using the sessile drop geometry to measure fluid and elastic block copolymer interfaces.
abstract: There is considerable interest in the fabrication and mechanics of soft spheres and capsules because of their use in a large number of applications ranging from targeted drug delivery to cosmetically active agents. Many systems, such as lipid and block copolymer vesicles, are already finding considerable industrial use where the performance of soft spheres depends intimately on their mechanics. New advanced features such as fast cargo delivery can be realized only if they fit into the existing mechanical niche of the system in question. Here we present a model system to demonstrate how a capsule structure can be fundamentally changed while maintaining its overall mechanical response as well as a simple, universal method to measure the resulting capsule material properties. Specifically, we use confocal microscopy to adapt the sessile drop geometry to a measurement of the static properties of an ensemble of polystyrene-b-poly(ethylene oxide) (PS-PEO)-stabilized oil droplets. We then synthesize a polystyrene-b-poly(acrylic acid)-b-polystyrene (PS-PAA-PS) elastic-shell-coated emulsion drop that shows an identical deformation to the fluidlike PS-PEO droplets. Both systems, in sessile geometry, can be related to their basic material properties through appropriate modeling. We find that the elastic shell is dominated by its surface tension, easily enabling it to match the static response of a purely fluid drop.
authors.affiliation: Materials and Nanotechnology and ‡Department of Physics, North Dakota State University , Fargo, North Dakota 58108, United States.
authors.forename: Damith P
authors.initials: DP
authors.lastname: Rozairo
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Croll
mesh_terms: D000179:Acrylates / Q000737:chemistry*; D004548:Elasticity; D004655:Emulsions; D018613:Microscopy, Confocal; D011092:Polyethylene Glycols / Q000737:chemistry*; D011137:Polystyrenes / Q000737:chemistry*
chemical_list: D000179:Acrylates; D004655:Emulsions; D011137:Polystyrenes; C509855:poly(styrene-b-acrylic acid); C541965:polystyrene-b-poly(ethylene oxide); D011092:Polyethylene Glycols