Experimental and theoretical studies of the system n-decyl-beta-D-maltopyranoside plus water

A class of non-ionic surfactants that is useful for formulating microemulsi ons, and that is becoming increasingly important for industrial purposes, i s the series of alkyl polyglucosides (C(X)G(Y)). These surfactants have x c arbons in the hydrophobic alkyl chain and y glucose units in the hydrophili c headgroup, with commercial products typically containing noninteger value s of both x and y. Commercial C(X)G(Y) blends contain many other compounds besides alkyl-beta -D-glucopyranosides, including n-alkyl-alpha -glucopyran osides, n-alkyl-beta -D-maltopyranosides, and other isomers and materials t hat contain a larger number of glucose units. In this paper, we investigate the physical properties of the system n-decyl-beta -D-maltopyranoside (C(1 0)G(2)) + water over a wide concentration range, using various experimental techniques (surface tension measurement, rotation rheometer, DSC, polarisi ng microscopy) and a molecular aggregation formation model. The theory is b ased on calculating the size distribution of the aggregates, which in turn depends on the free energy of forming an aggregate. This free energy is mod elled as the sum of several free-energy contributions and an ideal entropy of mixing. For each free-energy contribution, we have highlighted schematic ally only the relevant characteristics of the surfactant tails or the surfa ctant heads. The theoretical results are compared to those found in the lit erature for alkyl-beta -D-glucopyranosides (C(X)G(1)) aqueous solutions. In surfactant solutions, theological behaviour is intimately linked to intern al microstructure and micellar architecture. The diluted surfactant system demonstrates Newtonian behaviour and complex non-Newtonian behaviour within the high shear stress regime. In the middle concentration range, the surfa ctant solutions exhibit an unexpected rheological behaviour, where the visc osities are not dependent on temperature. At high surfactant concentration phase transition, especially liquid-crystalline to isotropic solution, coul d be followed using theological experiments. In performing DSC experiments, emphasis is put on the melting behaviour for the dry surfactant and C(10)G (2) + water systems at high surfactant concentrations. The melting behaviou r can be characterised by transitions from a crystalline phase to a liquid crystalline phase and finally to an isotropic solution. The identification of the liquid-crystalline phase was carried out from textural observation, using polarising microscopy. The lyotropic behaviour follows the classical pattern established for the surfactants. Applying polarising microscopy, te xtures of the hexagonal and lamellar phases could be observed for the syste m C(10)G(2) + water. (C) 2001 Elsevier Science B.V. All rights reserved.