Abstract
In this study, the cononsolvency transition of poly(N-isopropylacrylamide) (PNiPAAm) brushes in aqueous ethanol mixtures was studied by using Vis-spectroscopic ellipsometry (SE) discussed in conjunction with the adsorption-attraction model. We proved that the cononsolvency transition of PNiPAAm brushes showed features of a volume phase transition, such as a sharp collapse, reaching a maximum decrease in thickness for a very narrow ethanol volume composition range of 15% to 17%. These observations are in agreement with the recently published preferential adsorption model of the cononsolvency effect.
Highlights
Cononsolvency occurs if a mixture of two good solvents causes the collapse and segregation of polymer solutions into a polymer-rich phase in a certain range of compositions of these two solvents [1,2].A prominent example [3] is poly(N-isopropylacrylamide) (PNiPAAm) in a water and methanol mixture. both solvents are good solvents for PNiPAAm, in a certain range of compositions of methanol and water PNiPAAm segregates from the mixed solution
In order to check whether the cononsolvency transition of that polymer brushes is an transition equilibrium
In order to checkof whether the cononsolvency transition of swollen polymer brush brushesthickness is an equilibrium transition, shown in Except for the condition where the ethanol volume fraction is around
Summary
Cononsolvency occurs if a mixture of two good solvents causes the collapse and segregation of polymer solutions into a polymer-rich phase in a certain range of compositions of these two solvents [1,2].A prominent example [3] is poly(N-isopropylacrylamide) (PNiPAAm) in a water and methanol mixture. both solvents are good solvents for PNiPAAm, in a certain range of compositions of methanol and water PNiPAAm segregates from the mixed solution. It is notable that a discontinuous, or jump-like, volume phase transition as it is observed for gels in such solvent mixtures would not be expected for a transition from a good to poor solvent within the common Flory-Huggins scheme because of the absence of translational degrees of freedom of the chains here [5,6]. This indicates a new kind of transition due to the solvent–cosolvent–polymer interaction. It is interesting to explore the possibility of a jump-like collapse transition for polymers on surfaces, in particular for polymer brushes
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