More fluorous surface modifier makes it less oleophobic: fluorinated siloxane copolymer/PDMS coatings.
A copolyacrylate with semifluorinated and polydimethylsiloxane side chains (D5-3) was used as a surface modifier for a condensation-cured PDMS coating. The decyl fluorous group is represented by "D"; "5" is a 5 kDa silicone, and "3" is the mole ratio of fluorous to silicone side chains. Wetting behavior was assessed by dynamic contact angle (DCA) analysis using isopropanol, which differentiates silicone and fluorous wetting behavior. Interestingly, a maximum in surface oleophobicity was found at low D5-3 concentration (0.4 wt %). Higher concentrations result in decreased oleophobicity, as reflected in decreased contact angles. To understand this unexpected observation, dynamic light scattering (DLS) studies were initiated on a model system consisting of hydroxyl-terminated PDMS (18 kDa) containing varying amounts of D5-3. DLS revealed D5-3 aggregation to be a function of temperature and concentration. A model is proposed by which D5-3 surface concentration is depleted via phase separation favoring D5-3 aggregation at concentrations >0.4 wt %, that is, the cmc. This model suggests increasing aggregate/micelle concentrations at increased D5-3 concentration. Bulk morphologies studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) support this model by showing increased aggregate concentrations with increased D5-3 > 0.4 wt %.
Zhang
Wei
W
Department of Chemical and Life Science Engineering, Virginia Commonwealth University, 601 West Main Street, Richmond, Virginia 23284-3028, USA.
Zheng
Ying
Y
Orsini
Lorenzo
L
Morelli
Andrea
A
Galli
Giancarlo
G
Chiellini
Emo
E
Carpenter
Everett E
EE
Wynne
Kenneth J
KJ
D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D005465:Fluorocarbon Polymers / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D004129:Dimethylpolysiloxanes; D005465:Fluorocarbon Polymers; D011108:Polymers; C013830:baysilon