AsianScientist (Sep. 6, 2017) – Scientists in Japan have shown that changing the length of alkyl chain spacers in betaine materials can affect how they absorb water. Their findings, published in Langmuir, could lead to new lubricants and anti-fouling materials.
Betaines are materials with both a positively charged functional group and a negatively charged functional group linked by an alkyl chain spacer. This combination of functional groups causes betaines to strongly attract water, which makes them useful for water retention. Betaines are important in numerous organisms, where they help to prevent cell dehydration and also play roles in some reactions. Commercially, betaines are used in DNA amplification and chemical synthesis.
Betaine groups can be included in polymer brushes, which are polymers that have been tethered to a surface. The resulting polymer brushes are attractive for use in lubrication and anti-fouling applications because the hydrated betaine groups help to prevent adhesion of other materials. However, the hydration states of polymer brushes are still poorly understood.
In this study, scientists from Kyushu University in Japan investigated how the charged group spacer length of betaines in polymer brushes affects their hydration state. The researchers first synthesized a series of polymer brushes containing alkyl chain spacers of different lengths on silicon wafers. The polymer brushes were then characterized using a range of techniques.
In particular, neutron reflectivity was used to probe the hydration states of the polymer brushes. The scientists revealed that the ionic strength sensitivity of the polymer brushes during hydration became more significant with increasing chain spacer length because the partial charges of betaine were augmented by charged group separation. However, they noted that water uptake by the polymer brushes did not depend on chain spacer length.
“We found that the polymer brushes swelled in humid air and water because the hydration of the charged betaine groups led to a decrease in the interfacial free energy between water and the brushes,” said study co-author Assistant Professor Yuji Higaki of Kyushu University.
“Our findings reveal how the charged group spacer length of betaines modulates the interaction of polymer brushes with water,” said Professor Atsushi Takahara of Kyushu University who led the research.
The team’s results should aid the development of lubricating and anti-fouling surfaces for use in marine environments or under physiological conditions.
The article can be found at: Higaki et al. (2017) Effect of Charged Group Spacer Length on Hydration State in Zwitterionic Poly(sulfobetaine) Brushes.
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Source: Kyushu University; Photo: Pexels.
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