1. INFLUENCE OF THE POLYMERS NATURE ON POLYMER-OXIDE COMPOSITE INTERACTION WITH WATER O.Goncharuk1, K. Terpilowski2, I.Sulym1 1 – Institute of Surface Chemistry, Kyiv, Ukraine, 2 – Department of of Physical Chemistry-Interfacial Phenomena, Faculty of Chemistry, Maria Curie-Sklodowska University, Lublin, Poland
Polymer–oxide composites are widely used in various fields of industry, medicine, etc. Adsorption modification with polymers significantly changes properties of oxides surface. Due to disguising the active sites on the surface of oxides and the emergence of belonging to polymers new functional groups the surface of such composites acquires other adsorptive properties which depend on the polymer nature and the peculiarities of its interaction with the structure of the surface layer.
The aim of this study was to investigate the influence of the polymer nature and its relative content in the surface layer of the polymer-oxide composites on their interaction with water. The heats of immersion in water (Q) were determined for all these composites. Hydrophobic properties of prepared samples were studied by means of measuring the contact angles of a water drop (). Water–soluble nonionic polymers such as polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG) and hydrophobic polymer poly(dimethylsiloxane) (PDMS) were used for modification of fumed SiO2 (S = 245 m2/g).
All used polymers interact with the silica surface through the formation of hydrogen bonds between their functional groups and the silanol groups of the silica surface as shown in Fig.1 [1–3]. If silica is modified with PVP the hydrogen bonds between polymer and the silanol groups of the silica are formed featuring oxygen of lactam groups, with PVA – by oxygen of OH group of PVA, in the case of modification with PEG and PDMS the oxygen of polymer backbones interact with hydrogen of silanol groups. According to the IR spectroscopy the polymer monolayer on silica surface is formed when the band at 3750 cm-1 disappears. That band corresponds to the free silanol groups. The amount of polymer for modification was varied in order to obtain polymer coating less and more than monolayer at surface of silica particles. In the first case the interaction of composites surface with water was additively determined by both functional groups of the polymer and the silanol groups of the silica surface unbonded with polymer. In the second case, when the polymer concentration was more than it was needed for monolayer formation, the interaction of composites surface with water predominantly was determined by functional groups of the polymer
Fig.1. Scheme of interaction of polymers with the surface of silica: a-PVA, b – PVP, c - PEG, d - PDMS. The hydrophilic groups of polymers and silica are marked by molecule of water
Fig.2. Dependence of the heat of immersion in water normalized to 1 g of the sample (a) and 1 m2 of the surface (b) on the relative content of polymer adsorbed on fumed silica
Fig.3. Dependence of the contact angle of water drops  on PDMS content
As it can be seen from Fig. 2 all investigated composites are characterized by decreasing the heat of immersion with rising of polymer content. This can be caused by a change in the surface character and a decrease in the specific surface area. Since such decrease is various for different composites, the values of their heat of immersion were normalized to 1 m2 of surface.
Fig. 2b shows that the modification of fumed silica with PVA and PVP leads to some increase in the Q values that indicates an increase in surface hydrophilicity. However, the modification of SiO2 with PEG and PDMS leads to decrease of the heat of immersion with increasing polymer content that indicates a decrease in surface hydrophilicity. According to the contact angles of a water drop only composites modified with PDMS can be classified as hydrophobic (Fig. 3).
It was established that the contact angles of a water drop linearly increases with increasing of CPDMS. It was found that such composites are most hydrophobic at CPDMS = 15 – 40 wt. %.
Acknowledgment. The research leading to these results was funded by from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/ / under REA grant agreement no PIRSES-GA
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