Effect of Added Surfactant on Temperature-Induced Gelation of Emulsions

Abstract

This paper involves an investigation of the effect of added ionic surfactant on the temperature-induced gelation of oil-in-water (O/W) emulsions stabilized by a responsive copolymer. The oil phase used in this study is 1-bromohexadecane. The copolymer is poly(NIPAM-co-PEGMa) (NIPAM and PEGMa are N-isopropylacrylamide and poly(ethylene glycol) methacrylate, respectively). The lower critical solution temperature for the copolymer was 39.5 °C. The ionic surfactant used in this work was sodium dodecylbenzenesulfonate (NaDBS). The critical association concentration for NaDBS and poly(NIPAM-co-PEGMa) was measured at 0.30 mM using fluorescence measurements (pyrene was the probe molecule). Gelation temperatures were measured for the O/W emulsions to establish the effect of added NaDBS and copolymer concentration (C p) on the gelation temperature (T gel). The strength of the gels was measured using dynamic oscillatory measurements. These measurements allowed the shear modulus of the gel at T gel to be estimated as 100 Pa. A theoretical model based on transient network theory was developed that predicts the dependence of T gel on C p. The study revealed that NaDBS has two effects on the overall cross-link density of the emulsion gels: it contributes a source of cross-linking via micellar cross-links and also decreases the proportion of transient cross-links due to electrostatic repulsion.

Thermally-triggered gelation of PLGA dispersions: Towards an injectable colloidal cell delivery system

“…12 3.0 280,000 29.5 a The cloud point temperature was taken at the onset of the turbidity increase. 1 For interpretation of color in Fig. 9, the reader is referred to the web version of this article.…”

“…Thermoresponsive dispersions can form gels when heated and are attracting increased attention [1][2][3][4][5]. They are academically interesting because of fundamental questions concerning the role of interparticle forces and aggregation in network elasticity [4].…”

Study of pH-triggered heteroaggregation and gel formation within mixed dispersions

“…It is well known that dispersion aggregation leads to aggregates with a fractal structure in the absence of shear [14,15]. Emulsion or latex gels stabilised by synthetic temperature-responsive NIPAM copolymers form particle gels when heated and have been studied extensively [16,17]. In those studies a temperature-responsive copolymer stabiliser was used to trigger a change from repulsive inter-particle interactions at room temperature to attractive interactions at elevated temperature.…”

Biodegradable Thermoresponsive Microparticle Dispersions for Injectable Cell Delivery Prepared Using a Single‐Step Process

“…The PEGMA-PPGMA copolymers are similar to other thermoresponsive materials in that they undergo conformational or phase changes with temperature, but for this application have important advantages. Poly(N-isopropylacrylamide) (PNIPAm) has been the most widely studied polymer of this class, and has previously been used for tissue-engineering applications, [5][6][7][8][9][10][11] but is perceived as insufficiently biocompatible for in vivo use. Certain poly(ethylene oxide)-co-poly(propylene oxide) (PEO-PPO) copolymers exhibit reverse thermal-gelation behavior in water, forming semisolid gels when heated above their lower critical solution temperature (LCST), and are used in the pharmaceutical industry, as the base polymers PEO and PPO are biocompatible.…”