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Achieving a high encapsulation efficiency and loading capacity of proteins in lecithin-based liposomes has always been a challenge. Here, we use Flash Nano-Precipitation (FNP) to produce liposomes and investigated the encapsulation of model protein (Bovine Serum Albumin, BSA). Through rapid turbulent mixing, we obtained liposomes with small size, low polydispersity, and good batch repeatability at a high production rate. We demonstrated that the bilayer of liposomes prepared solely using lecithin was defective, which led to the fusion, and increased size and polydispersity. When cholesterol was added to reach a lecithin-to-cholesterol molar ratio of 5:3, a compact bilayer formed to effectively inhibit liposome fusion. The encapsulation efficiency and loading capacity of BSA was as high as ∼ 68% and ∼ 6% in lecithin-cholesterol liposome, respectively, far exceeding the values reported in the literature. Further study by Quartz Crystal Microbalance with Dissipation (QCM-D) revealed that the highly effective encapsulation was due to the rapid mutual adsorption between BSA and defective/curved lecithin double layers during the liposome formation. Such rapid mutual adsorption leads to the layer-by-layer assembly and formation of onion-like compact liposome structure as revealed by Cryo-TEM. This simple FNP method provides a scalable manufacturing approach for liposomes with efficient protein encapsulation. The revealed adsorption mechanism between protein and lecithin bilayers could also serve as a guide for similar studies.

Due to the rapid reaction kinetics, the morphology of chitosan/tripolyphosphate nanoparticles was difficult to control. We mixed chitosan and tripolyphosphate through a multi-inlet vortex mixer at different mixing efficiency and characteristic mixing time (τ

Nonionic surfactant-activated microgels (SAMs), composed of hydrophobic alkyl acrylates and hydrophilic hydroxyalkyl esters that utilize the effects of surfactant mediated swelling and interaction to provide pH-independent rheological properties, were previously reported as a new pathway to the rheology modification of surfactant solutions. Crosslinking was shown to play an important role in the properties of these soft microgel systems. To understand the impact of crosslinking chemistry on SAM polymers, we have compared two types of SAM polymers: a conventionally crosslinked SAM polymer via allyl pentaerythritol and a novel SAM polymer, where the surface is self-crosslinked via a reactive surfactant. We have systematically characterized the polymer's swelling, rheology and microstructure in a model system containing the polymer, sodium dodecyl sulfate (SDS) and water. Surface self-crosslinking is demonstrated to be a more effective crosslinking approach to create surfactant-mediated interactions between the microgel particles, resulting in more effective rheology modification. Internal crosslinking hinders both the full swelling of the SAM polymer as well as inter-particle bridging interactions, and is therefore less effective. To our best knowledge, this is the first report on creating a novel surface self-crosslinked microgel via a dual-functional reactive surfactant that interacts with a non-reactive surfactant to create a yield stress fluid.

The microstructure and rheological properties of micellar solutions of Pluronic block copolymers (PEOx–PPOy–PEOx) in deuterated ethylammonium nitrate (dEAN, a protic ionic liquid) are studied by small- and ultrasmall-angle neutron scattering (SANS and USANS), fluorescence microscopy, and shear rheology. A homologous series of three Pluronics with similar PPO block length (F127 (PEO106–PPO70–PEO106), P123 (PEO20–PPO70–PEO20), and L121 (PEO5–PPO70–PEO5)) are examined to explore the effect of the relative balance of solvophilic to solvophobic block size on the self-assembled microstructure. Both F127 and P123 form spherical micelles in dEAN that assemble into face-centered and body-centered cubic supramolecular crystals, respectively, upon increasing concentration or temperature. The transition from disordered to crystalline (ordered) structures manifests as a sol–gel rheological transition. A richer phase diagram is observed in the L121/dEAN system: due to its low solvophilicity in dEAN, L121 self-assembles...

In this work an improved description of isothermal calorimetric titration data for surfactants binding to polyelectrolytes is derived and presented. Mixtures of polyelectrolytes and surfactants show a highly complex association behavior, and often a cooperative adsorption of surfactants, following the Satake–Yang binding isotherm is observed. The binding of surfactants is a multistep process, where a non-cooperative adsorption is followed, at higher coverages, by a cooperative process. Accordingly, three processes are considered in the derivation of the ITC formalism: the non-cooperative and cooperative binding and, as the newly introduced contribution, the transition of non-cooperatively bound surfactants to cooperatively bound state. This approach has been tested on sodium dodecyl sulfate binding to the cationic cellulose derivate JR-400 and the results compared with existing models. While similar binding constants are obtained, different values of the binding enthalpies are found, which should be closer to the real values, thereby yielding a more realistic thermodynamic description.

The search for stable vesicular structures is a long-standing topic of research because of the usefulness of these structures and the scarcity of surfactant systems that spontaneously form vesicles in true thermodynamic equilibrium. We report the first experimental evidence of spontaneous formation of vesicles for a pure cationic double tail surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle neutron scattering, rheology and bright field microscopy, we identify the coexistence of two vesicle containing phases in compositions ranging from 2 to 68 wt %. A low density highly viscous solution containing giant vesicles (D ? 30 ?m) and a sponge (L3) phase coexists with a dilute high density phase containing large vesicles (D ? 2.5 ?m). Vesicles form spontaneously via different thermodynamic routes, with the same size distribution, which strongly supports that they exist in a true thermodynamic equilibrium. The formation of equilibrium vesicles and the L3 phase is facilitated by ion exchange between the cationic surfactant and the ionic liquid, as well as the strength of the solvophobic effect in the protic ionic liquid. � 2012 American Chemical Society.

Oppositely charged polyelectrolyte-surfactant mixtures are ubiquitous in biology and the basis of numerous consumer healthcare products. Despite their broad use, however, a rational approach to their formulation remains challenging because of the complicated association mechanisms. Through compilation and analysis of literature reports and our own research, we have developed a semiempirical correlation of the binding strength of surfactants to polyelectrolytes in salt-free mixtures as a function of the polyion linear charge density and the surfactant hydrophobicity. We have found that the cooperative binding strength increases as the square of the polyelectrolyte's linear charge density and in proportion to the surfactant's hydrophobicity, such that a quantitative relationship holds across a broad range of polyelectrolytes. Deviations from the correlation reveal the role of system-specific interactions not considered in the analysis. This engineering relationship aids in the rational design of oppositely charged polyelectrolyte-surfactant formulations for consumer products and biomedicines by enabling the prediction of binding strengths in polyelectrolyte-surfactant mixtures based on mesoscale parameters determined from the chemical composition.

Coacervation in mixtures of polyelectrolytes and surfactants with opposite charge is common in nature and is also technologically important to consumer health care products. To understand the complexation behavior of these systems better, we combine multiple experimental techniques to systematically study the polymer/surfactant binding interactions and the phase behavior of anionic sodium dodecyl sulfate (SDS) surfactant in cationic JR 400 polymer aqueous solutions. The phase-behavior study resolves a discrepancy in the literature by identifying a metastable phase between the differing redissolution phase boundaries reported in the literature for the surfactant-rich regime. Isothermal titration calorimetry analyzed within the framework of the simple Satake-Yang model identifies binding parameters for the surfactant-lean phase, whereas a calculation for polymer-bound micelles coexisting with free micelles is analyzed in the surfactant-rich redissolution regime. This analysis provides a preliminary understanding of the interactions governing the observed phase behavior. The resulting thermodynamic properties, including binding constants and the molar Gibbs free energies, enthalpies, and entropies, identify the relative importance of both hydrophobic and electrostatic interactions and provide a first approximation for the corresponding microstructures in the different phases. Our study also addresses the stability and metastability of oppositely charged polyelectrolytes and surfactant mixtures.

The adsorption of cationic polyelectrolytes (PEs) onto anionic silicone emulsion droplets, suspended in a sodium chloride solution is studied via electrophoretic mobility measurements and isothermal titration calorimetry. These model systems are studied to better understand the interactions governing PE adsorption-induced emulsion flocculation, which is relevant to many industrial applications. Electrophoretic mobility measurements provide critical information for rationalizing the effect of the PE charge density on the loss of stability of silicone emulsions. The interaction strength is calculated from a Langmuir adsorption isotherm determined by a ζ-potential titration measurement. Microcalorimetry measurements independently validate the adsorption free energy. Emulsion flocculation and coacervation are observed in the visual phase behavior as well as the ζ-potential titration measurements. The effect of PE charge density shows that PE-surfactant coacervation is the driving force in these PE-emulsion systems.