Abstract
A method for direct visualization of the position of nanoscale colloidal particles at air-water interfaces is presented. After assembling hard (polystyrene, poly(methyl methacrylate), silica) or soft core-shell gold-hydrogel composite (Au@PNiPAAm) colloids at the air-water interface, butylcyanoacrylate is introduced to the interface via the gas phase. Upon contact with water, an anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air-water interface depending of the amount of charge present on the particle surface. We find that the degree of deprotonation of the carboxyl group shifts the air-water contact angle, which is further confirmed by colloidal probe atomic force microscopy. Remarkably, the contact angles determined for individual colloidal particles feature a significant distribution that greatly exceeds errors attributable to the size distribution of the colloids. This finding underlines the importance of accessing soft matter on an individual particle level.
Highlights
The investigation and understanding of the behaviour of colloidal particles at air–water interfaces are of paramount importance in the description of a variety of everyday problems, ranging from oil otation to self-cleaning surfaces, food industries and cosmetics.[1]
We find that the degree of deprotonation of the carboxyl group shifts the air–water contact angle, which is further confirmed by colloidal probe atomic force microscopy
We have presented a technique to trap colloids of a wide size range and arbitrary composition at an air–water interface by embedding them in a PBCA lm
Summary
A method for direct visualization of the position of nanoscale colloidal particles at air–water interfaces is presented. An anionic polymerization reaction of the monomer is initiated and a film of poly(butylcyanoacrylate) (PBCA) is generated, entrapping the colloids at their equilibrium position at the interface. We apply this method to investigate the formation of complex, binary assembly structures directly at the interface, to visualize soft, nanoscale hydrogel colloids in the swollen state, and to visualize and quantify the equilibrium position of individual micro- and nanoscale colloids at the air– water interface depending of the amount of charge present on the particle surface. This finding underlines the importance of accessing soft matter on an individual particle level
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