The influence of energetic surface heterogeneity on proton desorption during capillary filling of silica nanochannels
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The influence of energetic surface heterogeneity on proton desorption during capillary filling of silica nanochannels W. Piasecki • R. Charmas
Received: 31 October 2012 / Accepted: 25 January 2013 / Published online: 9 February 2013 Ó The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract We applied the surface complexation model to describe the deprotonation of silica nanochannel walls as a function of pH and ionic strength of filling solution. We took into account energetic heterogeneity of silanol groups. We found that more heterogeneous walls of silica nanochannel will be more charged and can interact more strongly with ionic solutes. The modeling of nanochannels coated with 3-cyanopropydimethylchlorosilane is uncertain because charging mechanism of coated silica should take into account increased autolysis of interfacial water. Keywords Silica Nanochannels Nanofluidics Deprotonation Energetic heterogeneity Surface complexation
1 Introduction A phenomenon where surface chemistry has a dominant influence on the properties of bulk fluid is the process of capillary filling of silicon dioxide nanochannels. In this case the key parameter is pH which has a dominant influence on electric charge of channel walls and the properties of molecules in the solution (Eijkel and Berg 2010; Napoli et al. 2010).
(Janssen et al. 2008) investigated the filling of silicon nanochannels with fluorescein solutions. They observed two zones in the fluid introducing into nanochannels. The front part of liquid was dark, and the back part exhibited fluorescence. The ratio of lengths of two zones was constant in time (Fig. 1a). The fluorescein molecule exhibits intense light emission when it is doubly deprotonated (for pH [ 7), and it is inactive in protonated form (for pH \ 4). It means that the pH in the dark zone is significantly lower than the pH in the bright zone. This increase in the concentration of hydrogen ions results from titration of solution by protons released from nanochannel walls (Fig. 2b). The research on filling of silica nanochannels was continued by (Andersen et al. 2011) who analyzed the dependence of electrokinetic potential and the ratio of dark and fluorescent lengths on ionic strength for bare and 3-cyanopropydimethylchlorosilane coated silica nanochannels. In this paper, we have developed the model describing surface deprotonation of silica nanochannels taking into account energetic heterogeneity of silanol groups. Next, we apply our model to describe experimental results published in literature so far. Finally, we give concise critical discussion of the modeling of coated silica nanochannels.
2 Theory W. Piasecki (&) The Laboratory of Cosmetic Chemistry, The Faculty of Physical Education and Sport in Biała Podlaska, Jo´zef Piłsudski University of Physical Education in Warsaw, Warsaw, Poland e-mail: [email protected] R. Charmas The State Higher School of Computer Science and Business Administration in Łom_za, Łom_za, Poland
According to (Janssen et al. 2008) the
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