The Morphology of Block Copolymer Micelles in Supercritical Carbon Dioxide by Small-Angle Neutron and X-ray Scattering

Abstract

Above its critical point, carbon dioxide forms a super‐critical fluid, which promises to be an environmentally responsible replacement for the organic solvents traditionally used in polymerizations. Many lipophilic polymers such as polystyrene (PS) are insoluble in CO2, though polymerizations may be accomplished via the use of PS‐fluoropolymer stabilizers, which act as emulsifying agents. Small‐angle neutron and X‐ray scattering have been used to show that these molecules form micelles with a CO2‐phobic PS core and a CO2‐philic fluoropolymer corona. When the PS block was fixed in length and the fluorinated corona block was varied, the number of block copolymer molecules per micelle (six to seven) remained constant. Thus, the coronal block molecular weight exerts negligible influence on the aggregation number, in accordance with the theoretical predictions of Halperin, Tirrell & Lodge [Adv. Polym. Sci. (1992), 100, 31–46]. These observations are relevant to understanding the mechanisms of micellization and solubilization in supercritical fluids.

Phase Behavior of Poly(methyl methacrylate)/Poly(vinylidene fluoride) Blends in the Presence of High‐Pressure Carbon Dioxide

“…The data, once converted to absolute intensities (I) with a calibrated secondary standard, [57] were azimuthally averaged to yield I(q) patterns, where q is the scattering vector given by (4p/l)sin (y/2) and y denotes the scattering angle. Each blend was placed in the same diamond-window, stainless-steel vessel used in previous highpressure scattering studies, [58] and additional scattering data were collected from the 12 and 31 wt.-% PVDF blends (in the absence of CO 2 ) for 2 and 4 h, respectively. After each jump to a new CO 2 pressure, scattering data were acquired in 1-to 2-h intervals until the intensity profile remained constant.…”

Frontiers in green chemistry utilizing carbon dioxide for polymer synthesis and applications

“…The graft copolymer with a PFOA backbone and poly(ethylene oxide) (PEO) grafts formed micelles which stabilized water in CO 2 , while the PTFE-b-PEO copolymer formed reverse micelles, and F(CF 2 ) 10 (CH 2 ) 10 H formed small aggregates of at most four chains. The block copolymer PS-b-PFOA forms micelles in CO 2 with a PS core and a PFOA shell and the data fits a polydisperse spherical core-shell model [45,46]. With an increase in CO 2 density, the change in polydispersity suggests the existence of a critical micelle density, or a density of CO 2 above which the micelles are broken up into soluble unimers.…”

Raspberry-like Pt clusters with controlled spacing produced by deposition of loaded block copolymer micelles from supercritical CO2

“…Londono et al studied BCP micelle morphologies in sc CO 2 , along with other published results essentially proving that micelles and microemulsions in fact may exist in sc CO 2 [37][38][39]. Though rather limited classes of polymers are soluble in sc CO 2 , there are still choices, which include the selection of non-polar, fluorinated or silicon-containing polymers with selectively sc CO 2 -soluble block [40][41][42][43][44] thus forming the outer corona of the micelle.…”