Colloid Polymer Interactions and Aggregation in Aqueous Mixtures of Polystyrene Latex, Sodium Dodecyl Sulfate, and a Hydrophobically Modified Polymer:  A Dynamic Light Scattering Study

Abstract

The kinetics of clusters formed in the flocculation process of polystyrene latex particles (PSL) in the presence of hydrophobically modified ethyl(hydroxyethyl)cellulose (HM-EHEC) and sodium dodecyl sulfate (SDS) in the concentration interval of 2-4 mmolal have been investigated with the aid of dynamic light scattering measurements at different temperatures. For this system (HM-EHEC/SDS/PSL) we observe an intriguing time-dependent cluster growth over a restricted (2-4 mmolal) surfactant concentration range. The rate of flocculation and the aggregation mechanism are affected by both the level of surfactant addition and temperature. The value of the homogeneity exponent λ, used to characterize the aggregation mechanism, depends on temperature and concentration of surfactant. Flocculation behaviors between the reactionlimited and diffusion-limited regimes are observed. The picture that emerges is that polymer-surfactant complexes are adsorbed onto the PSL particles in form of fuzzy layers with hydrophobic stickers. The sticking probability seems to be influenced by temperature and the level of surfactant addition. Upon collision, these particles form aggregates through hydrophobic interactions, and macroscopic flocs are evolved at long times. When the sample is exposed to ultrasonic perturbation, the flocs break up, but a rapid reformation of flocs is found upon removal of the ultrasonic perturbation.

Temperature-induced adsorption and optical properties of an amphiphilic diblock copolymer adsorbed onto flat and curved silver surfaces

“…In this study, a nonexponential behavior of the autocorrelation function was observed, and in accordance with previous DLS studies on colloidal particles [33][34][35][36] a stretched exponential function was employed in the analysis of correlation function data to allow deviations from a single exponential behavior…”

Adsorption of cellulose derivatives on flat gold surfaces and on spherical gold particles

“…A conspicuous feature is the high amount of adsorbed HM-HEC, on both surfaces, in comparison with that of HEC. Previous adsorption studies [20][21][22] of aqueous solutions of EHEC and HM-EHEC have revealed that the more hydrophobic counterpart has usually a higher affinity to adsorb onto different substrates. An interesting feature is the fact that a higher surface coverage is observed for gold surfaces with citrate-layer, and this effect is more pronounced for HEC than HM-HEC (see Fig.…”

“…Hydroxyethylcellulose (HEC), on the other hand, is essentially a hydrophilic polymer and this cellulose derivative displays rather weak thermoresponsive properties. It has been established in previous papers that a large amount of EHEC is adsorbed onto polystyrene latex particles [20][21][22]. If we take into account that the EHEC polymer contains hydrophobic microdomains in addition to regions of hydrophilic nature, one would expect the adsorption behavior to be altered when surfaces of different hydrophobicity are employed and the polymer is exposed to further hydrophobic modification.…”

Assessment of formulation robustness for nano-crystalline suspensions using failure mode analysis or derisking approach

“…In fact, all suspensions having particle size less than 1 mm are inherently thermodynamically unstable due to the natural tendency decrease the large specific surface area and excess surface energy (Patel, 2010). For this purpose, wetting/dispersing agents are used to stabilize the suspension against flocculation (Holthoff et al, 1996;Lauten et al, 2001) and crystal growth (Ostwald ripening (Ostwald, 1901)). …”