Added Surfactant Can Change the Phase Behavior of Aqueous Polymer−Particle Mixtures

Abstract

The phase behavior of aqueous mixtures of the "clouding" polymer ethyl(hydroxyethyl)cellulose (EHEC) mixed with colloidal particles and surfactants has been studied. These types of mixtures are important in many technical formulations. Two types of particles, polystyrene latex and silica, and two types of EHEC, nonmodified EHEC (N-EHEC) and hydrophobically modified EHEC (HM-EHEC), were studied. The EHECs adsorb to both kinds of particles. Both the amount and the type of added surfactant were seen to dramatically influence the partitioning of the particles between the EHEC-rich and EHEC-poor phases of phase-separated mixtures (above the cloud point temperature). Surfactants that are known not to associate with the EHEC backbone, that is, nonionic surfactants and short-chain cationic surfactants, changed the interaction between EHEC and the colloidal particles from attraction to repulsion above a specific surfactant concentration, resulting in a change in the partitioning of the particles from the EHEC-rich to the EHEC-poor phase. No such particle inversion was observed for ionic surfactants that bind to the EHEC backbone. An analysis considering both the binding of surfactant to EHEC and the competitive adsorption of surfactant to the particle surfaces could rationalize all observations, including the large variations observed, among the studied mixtures, in the surfactant concentration required for particle inversion.

Temperature-dependent interactions between hydrophobically modified ethyl(hydroxyethyl)cellulose and methyl nanocellulose

“…It was noticed that the addition of methyl nanocellulose increased the cloud point. According to the literature, association between EHEC and anionic surfactants changes the phase behavior and cloud point increases when the degree of surfactant binding is high, while a lower degree of surfactant binding reduces the cloud point (Thuresson et al 1995;Olsson et al 2005). In addition, it is known that a high concentration of NaCl decreases the cloud point.…”

“…The cloud point was detected visually and the change in turbidity measured using a turbidimeter (Hach 2100AN IS Turbidimeter) for 1 wt% solutions. The suspensions were heated from 20 to 70°C in sealed glass tubes using a water bath at a heating rate of 0.5°C/min and equilibrated at each temperature (Kjøniksen et al 1998;Olsson et al 2005). In addition, solutions were heated above the cloud point until separation into two separate phases occurred, the phase separation being detected visually.…”

Interaction of anionic surfactant with polymeric nanoparticles of similar charge

“…Indeed, in the case of HMPs it has been reported that the value of CIC is very low or zero [40,41]. On the other hand, Piculell and coworkers have studied interactions of hydrophobically modified hydroxyethylcellulose (HM-HEC) with a range of anionic and cationic surfactants and have shown that the CIC value is a function of the CMC value, surfactant chain length, and nature of the headgroup [42,43].…”

Salt Effect on the Cloud Point Phenomenon of Amphiphilic Drug-Hydroxypropylmethyl Cellulose System

“…Due to its prominent viscoelastic and structure forming properties, it is employed as a flow developer, as a tablet binder, as a tablet disintegrant, as a wet granulation binder, and also as an suspending and thickening agent [3,4]. When heated up to a certain temperature (known as cloud point, CP, or lower critical solution temperature, LCST), aqueous solutions of some polymers have a tendency for reversible phase separation [5][6][7][8][9][10][11]. The LCST implies that the effective solute-solute interactions have a noteworthy temperature dependences and alterations from repulsive to attractive with increasing temperature.…”

“…The LCST implies that the effective solute-solute interactions have a noteworthy temperature dependences and alterations from repulsive to attractive with increasing temperature. The CP phenomenon of cellulose ethers is believed to be due to the decrease in the dipolar character of the C-O bond as a result of either increase in temperature or making the solvating environment less polar [5][6][7][8][9][10][11]. The cloud point of HPMC is affected by the presence of amphiphiles as well as electrolytes, but both of them influence it differently [10,11].…”