The interfacial behaviour of single poly(N,N-dimethylacrylamide) chains as a function of pH

Zhenyu Zhang, Mike Tomlinson, Ramin Golestanian, Mark Geoghegan

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

We have studied the pH-dependent conformational behaviour of poly(N,N-dimethylacrylamide) (PDMAc) at silicon and gold surfaces using single-molecule force spectroscopy and a quartz crystal microbalance (QCM). Despite the pH dependence, nuclear magnetic resonance and titration experiments demonstrate that PDMAc is not a weak polybase. The interaction between single chains and a silicon surface (with native oxide layer intact) in aqueous solution was investigated using force spectroscopy. Single-molecule force measurements were performed using thiol-functionalized PDMAc and gold-coated AFM cantilevers. The forces of interaction between PDMAc and the native oxide-coated silicon surface vary with the pH. The shape of the retraction curve for low pH solution includes a greater number of 'train' conformations, which suggests a stronger interaction with the surface relative to the surrounding media at low pH. The adsorption behaviour of PDMAc, from liquid onto silicon surfaces, was monitored using a QCM, which shows greater PDMAc adsorption onto silicon at low pH. The force spectroscopy and QCM investigations confirm that the PDMAc chain is more extended and stiffer in low pH solution. We attribute the pH-dependent behaviour to an increased number of hydrogen bonding sites on the silicon surface at low pH.
Original languageEnglish
Article number035505
Number of pages10
JournalNanotechnology
Volume19
Issue number3
DOIs
Publication statusPublished - 13 Dec 2007

Keywords

  • single molecule force spectroscopy
  • polymer
  • adsorption
  • quartz crystal microbalance

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