Interactions between anionically modified hydroxyethyl cellulose and cationic surfactants

Abstract

Macroscopic properties of aqueous solutions of several modified hydroxyethyl cellulose (HEC) samples and their interactions with cationic surfactants are studied by solubility, light scattering, electric birefringence, rheology, and surface tension measurements. Modified HEC samples carry anionic groups (an-HEC D0) and anionic and hydrophobic groups in random distribution (HM-an-HEC D1-D4). The molar substitution of anionic (an) groups is about 0.07 in all samples while that of the hydrophobic (HM) groups ranges from 0 in an-HEC D0 to 0.012 in HM-an-HEC D4. In a 1 wt% solution this corresponds to 2.7 mM anionic and 0 to 0.46 mM hydrophobic groups. In the dilute concentration range the polymers behave like typical polyelectrolytes whereas in the semi-dilute range they resemble uncharged polymers. On addition of oppositely charged surfactants the phase behavior of all polyelectrolytes is similar. With increasing surfactant concentrations the transparent solutions become turbid and the phases separate. Finally, resolubilization takes place with excess surfactant concentrations. With the HM-an-HEC compounds viscoelastic solutions are formed with cationic surfactants. The intermolecular interaction between hydrophobic parts of the polymers and the surfactants and interactions of oppositely charged ionic groups of the two components lead to formation of a temporary network with gel-like properties. With an-HEC the interaction can only take place via charges. Viscosity enhancement with increasing surfactant concentration is therefore lower with an-HEC than with HM-an-HEC compounds.Paper no. S1120 in JSD 2, 181-191 (April 1999).KEY WORDS: Cationic surfactants, electric birefringence measurements, modified hydroxyethyl cellulose;.Water-soluble cellulose derivatives like hydroxyethyl cellulose (HEC) are used as thickeners in food and cosmetic products and in water-based paints (1). Semidilute aqueous solutions of HEC are highly viscous. To optimize the properties for different industrial applications HEC samples are modified by ionic or hydrophobic groups. This modification causes an increase in viscosity. Properties of such systems can be improved by adding small amounts of surfactants. Macroscopic properties of these polymers and their ability to interact with surfactants have been studied in recent years (for a review, see Ref.2). Investigations on the macroscopic properties of polymers carrying both hydrophobic and ionic groups show that polymer solutions exhibit higher viscosities, and that addition of oppositely charged surfactants results in stronger viscoelastic gels, than for those systems that were only hydrophobically or cationically modified.For a sample of HEC in which the substituent is both hydrophobic and charged, Goddard and Leung (3,4) showed that the phase behavior of this polymer following addition of an oppositely charged surfactant corresponds to the behavior of an unmodified cationic (cat)-HEC. Association of the two oppositely charged compounds results in strong viscoelastic gels with high yield str...

Homogeneous Quaternization of Cellulose in NaOH/Urea Aqueous Solutions as Gene Carriers

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