Individual and mixed adsorption of alkylcarboxylbetaines and fatty amide ethoxylates at Daqing sandstone/water interface

摘要

The individual adsorption of a series of alkylcarboxylbetaines, including single long-alkyl dimethylcarboxylbetaine (C _(12)B, C _(14)B, C _(16)B, and C _(18)B) and didodecylmethyl-carboxylbetaine (diC _(12)B), as well as fatty amide ethoxylates (C _(12)MEA-EO _1 and CMEA-EO _2), at negatively charged Daqing sandstone/water interface at 45°C were studied and compared with that of typical anionic and cationic surfactants. The results show that the saturated adsorption of surfactants at solid/water interface can be well characterized by a layer number, n, defined as the ratio of the saturated adsorption at solid/water interface to that at air/water interface, and in general the saturated adsorption of different species follows an order of anionic (n<0.5)1)2). The adsorption of the alkylcarboxylbetaines is initially driven by the electrostatic interaction between the positive charges in surfactant molecules and negative charges on surface followed by the chain-chain interaction which inducing admicelle formation on the solid surface. The single long-alkyl carboxylbetaines have similar saturated adsorption, i.e. with n between 1.49 and 1.71, but the double long-alkyl carboxylbetaine, diC _(12)B, gives a relatively lower n value (1.07) although it has a comparative saturated adsorption at solid/water interface due to its high adsorption at air/water interface. Lacking of the electrostatic interaction, the saturated adsorption of the fatty amide ethoxylates is in general low, as indicated by their low n values (0.595 and 0.526).For mixed adsorption systems nearly ideal mixing and middle synergism are observed for diC _(12)B/C _(12)B (homologous mixture), and diC _(12)B/C _(12)MEA-EO _1/(zwitterioniconionic) mixtures, but strong synergisms are observed for SDS/C _(12)B and SDS/C _(16)B (anionic/zwitterionic) mixtures. Thus for surfactant-polymer flooding the achievement of low adsorption retention depends strongly on the species selected if mixed surfactants are necessary.