Water Is a Poor Solvent for Densely Grafted Poly(ethylene oxide) Chains: A Conclusion Drawn from a Self-Consistent Field Theory-Based Analysis of Neutron Reflectivity and Surface Pressure-Area Isotherm Data

Title
Water Is a Poor Solvent for Densely Grafted Poly(ethylene oxide) Chains: A Conclusion Drawn from a Self-Consistent Field Theory-Based Analysis of Neutron Reflectivity and Surface Pressure-Area Isotherm Data
Authors
Hoyoung LeeDae Hwan KimKevin N. WitteKimberly OhnJe ChoiBulent AkgunSushil Satija원유연
Issue Date
2012-05
Publisher
The journal of physical chemistry. B, Condensed matter, materials, surfaces, interfaces & biophysical
Citation
VOL 116, 7367-7378
Abstract
By use of a combined experimental and theoretical approach, a model poly(ethylene oxide) (PEO) brush system, prepared by spreading a poly(ethylene oxide)− poly(n-butyl acrylate) (PEO−PnBA) amphiphilic diblock copolymer onto an air−water interface, was investigated. The polymer segment density profiles of the PEO brush in the direction normal to the air−water interface under various grafting density conditions were determined by using the neutron reflectivity (NR) measurement technique. To achieve a theoretically sound analysis of the reflectivity data, we used a data analysis method that utilizes the self-consistent field (SCF) theoretical modeling as a tool for predicting expected reflectivity results for comparison with the experimental data. Using this data analysis technique, we discovered that the effective Flory−Huggins interaction parameter of the PEO brush chains is significantly greater than that corresponding to the θ condition in Flory−Huggins solutions (i.e., χPEO−water(brush chains)/ χPEO−water(θ condition) ≈ 1.2), suggesting that contrary to what is more commonly observed for PEO in normal situations (χPEO−water(free chains)/χPEO−water(θ condition) ≈ 0.92), the PEO chains are actually not “hydrophilic” when they exist as polymer brush chains, because of the many body interactions that are forced to be effective in the brush situation. This result is further supported by the fact that the surface pressures of the PEO brush calculated on the basis of the measured χPEO−water value are in close agreement with the experimental surface pressure−area isotherm data. The SCF theoretical analysis of the surface pressure behavior of the PEO brush also suggests that even though the grafted PEO chains experience a poor solvent environment, the PEO brush layer exhibits positive surface pressures, because t
URI
http://pubs.kist.re.kr/handle/201004/43797
ISSN
15206106
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KIST Publication > Article
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