pH-responsive microcapsules synthesized via a water-in-oil-in-water emulsion template

Biological agents, such as peptides and nucleic acids (siRNA or dsRNA), are becoming increasingly employed in both the therapeutic and agrochemical industries as alternatives to synthetic chemicals. These agents have a number of advantages, including their specificity for a target, ease of registration and low human toxicity.1 Chemical pesticides are currently the most common method of crop protection, but have a number of drawbacks including their toxicity and effects on non-target species.2 Therefore, there is an ever-shifting move to the use of more eco-friendly biological control measures; however, these also have negative attributes. Bio-control agents are often unstable3 and, upon ingestion, are subjected to degradation by hydrolytic enzymes and conditions favouring acid hydrolysis. As a result, these water soluble agents must be protected by encapsulation in a water continuous phase. This provides a protective shell, ensuring their stability during delivery and giving the ability to control and trigger release, which facilitates a more efficient use. Please click Additional Files below to see the full abstract

From dilute polyelectrolyte solutions to entangled polyelectrolyte networks: a study of sodium carboxymethyl cellulose in water by light scattering and rheology

Sodium carboxymethyl cellulose (Na CMC) is widely used in industry for its thickening and swelling properties. Applications are very broad and include pharmaceutical, food, home and personal care products as well as the paper industry, water treatment and mineral processing. Na CMC is a linear negatively charged water-soluble polymer derived from cellulose. Its behaviour in water is known to be very complex and a function of several parameters including the characteristics of the polymer itself [1] such as molecular weight and degree of substitution as well as the solution concentration and dissolution conditions [2] (e.g. addition order of the system components) [3]. While Dynamic Light Scattering (DLS) has been widely used to study the behaviour of polyelectrolytes, relatively few DLS studies have been conducted on Na CMC and, to our knowledge, none in pure water; this is most likely due to the difficulty of preparing salt-free Na CMC solutions of DLS grade. Indeed, the presence of even a few poorly substituted Na CMC fibres suffices to prevent proper DLS data from being collected. The aim of the present study was to investigate the behaviour of Na CMC (Mw = 700,000 g/mol; DS = 0.9) in pure water using both DLS and rheology measurements. A method was developed to prepare samples of appropriate quality for DLS measurements, which could then be successfully run over a wide range of concentrations. Rheology measurements were run in parallel to identify the different concentration regimes, facilitating comparisons to the behaviour typically found for polyelectrolytes (see Figure 1). Both DLS and rheology measurements were combined to look at the relationships between the structure of the Na CMC solutions and their rheological properties. Please click Additional Files below to see the full abstract

Measurements of Submicron Particle Adsorption and Particle Film Elasticity at Oil-Water Interfaces

The influence of particle adsorption on liquid/liquid interfacial tension is not well understood, and much previous research has suggested conflicting behaviors. In this paper we investigate the surface activity and adsorption kinetics of charge stabilized and pH-responsive polymer stabilized colloids at oil/water interfaces using two tensiometry techniques: (i) pendant drop and (ii) microtensiometer. We found, using both techniques, that charge stabilized particles had little or no influence on the (dynamic) interfacial tension, although dense silica particles affected the "apparent" measured tension in the pendent drop, due to gravity driven elongation of the droplet profile. Nevertheless, this apparent change additionally allowed the study of adsorption kinetics, which was related qualitatively between particle systems by estimated diffusion coefficients. Significant and real interfacial tension responses were measured using ∼53 nm core-shell latex particles with a pH-responsive polymer stabilizer of poly(methyl methacrylate)-b-poly(2-(dimethylamino)ethyl methacrylate) (pMMA-b-pDMAEMA) diblock copolymer. At pH 2, where the polymer is strongly charged, behavior was similar to that of the bare charge-stabilized particles, showing little change in the interfacial tension. At pH 10, where the polymer is discharged and poorly soluble in water, a significant decrease in the measured interfacial tension commensurate with strong adsorption at the oil-water interface was seen, which was similar in magnitude to the surface activity of the free polymer. These results were both confirmed through droplet profile and microtensiometry experiments. Dilational elasticity measurements were also performed by oscillation of the droplet; again, changes in interfacial tension with droplet oscillation were only seen with the responsive particles at pH 10. Frequency sweeps were performed to ascertain the dilational elasticity modulus, with measured values being significantly higher than previously reported for nanoparticle and surfactant systems, and similar in magnitude to protein stabilized droplets.</p

Numerical and experimental analysis of the sedimentation of spherical colloidal suspensions under centrifugal force

Understanding the sedimentation behaviour of colloidal suspensions is crucial in determining their stability. Since sedimentation rates are often very slow, centrifugation is used to expedite sedimentation experiments. The effect of centrifugal acceleration on sedimentation behaviour is not fully understood. Furthermore, in sedimentation models, interparticle interactions are usually omitted by using the hard-sphere assumption. This work proposes a one-dimensional model for sedimentation using an effective maximum volume fraction, with an extension for sedimentation under centrifugal force. A numerical implementation of the model using an adaptive finite difference solver is described. Experiments with silica suspensions are carried out using an analytical centrifuge. The model is shown to be a good fit with experimental data for 480 nm spherical silica, with the effects of centrifugation at 705 rpm studied. A conversion of data to Earth gravity conditions is proposed, which is shown to recover Earth gravity sedimentation rates well. This work suggests that the effective maximum volume fraction accurately captures interparticle interactions and provides insights into the effect of centrifugation on sedimentation

Poly(dimethylsiloxane)-Stabilized Polymer Particles from Radical Dispersion Polymerization in Nonpolar Solvent: Influence of Stabilizer Properties and Monomer Type

Particles used in electrophoretic display applications (EPD) must possess a number of specific properties ranging from stability in a nonaqueous solvent, high reflectivity, low polydispersity, and high charge density to name but a few. The manufacture of such particles is best carried out in the solvent of choice for the EPD. This opens up new interests in the study of nonaqueous dispersion polymerization methods, which deliver polymer particles suspended in low dielectric constant solvents. We explore in this article the use of a poly(dimethylsiloxane) macromonomer for the stabilization of poly(methyl methacrylate) polymer particles in dodecane, a typical solvent of choice for EPDs. The use of this stabilizer is significant for this method as it is directly soluble in the reaction medium as opposed to traditionally used poly(12-hydroxystearic acid)-based stabilizers. Additionally, the present study serves as a baseline for subsequent work, where nonaqueous dispersion polymerization will be used to create polymer particles encapsulating liquid droplets and solid pigment particles. In this article, the influence of the macromonomer molecular weight and concentration on the properties of the synthesized particles is studied. In addition, we investigate the possibility of synthesizing polymer particles from other monomers both as a comonomer for methyl methacrylate and as the only monomer in the process. The influence of macromonomer concentration is also studied throughout all experiments

Synthesis and tribological testing of poly(methyl methacrylate) particles containing encapsulated organic friction modifier

The tribological behaviour of polymer particles containing an encapsulated, organic friction modifier (FM) is presented. Particles comprising of a poly (methyl methacrylate) (PMMA) shall and a methanol core, into which FM was dissolved, were produced via a dispersion polymerization producing a core-shell morphology. The inclusion of these particles dramatically increased the overall concentration of FM which could be blended into dodecane. The tribological behaviour of the particles produced, both with and without encapsulated FM, was tribologically tested in pure dodecane. The addition of as little as 1.5 wt% particles was found to decrease the friction coefficient and measured wear volumes below those for dodecane saturated with FM. Data suggests that the FM delivery method may be dominated by a bursting mechanism

Accelerated spreading of inviscid droplets prompted by the yielding of strongly elastic interfacial films

The complexity associated with droplets spreading on surfaces has attracted significant interest for several decades. Sustained activity results from the many natural and manufactured systems that are reliant on droplet-substrate interactions and spreading. Interfacial shear rheology and its influence on the dynamics of droplet spreading has to date received little attention. In the current study, saponin β-aescin was used as an interfacial shear rheology modifier, partitioning at the air-water interface to form a strongly elastic interface (G’/G” ∼ 6) within 1 min aging. The droplet spreading dynamics of Newtonian (water, 5 wt% ethanol, 0.0015 wt% N-dodecyl β-D-glucopyranoside) and non-Newtonian (xanthan gum) fluids were shown to proceed with a time-dependent power-law dependence of ∼0.50 and ∼0.10 (Tanner’s law) in the inertial and viscous regimes of spreading, respectively. However, water droplets stabilized by saponin β-aescin were shown to accelerate droplet spreading in the inertial regime with a depreciating time-dependent power-law of 1.05 and 0.61, eventually exhibiting a power-law dependence of ∼ 0.10 in the viscous regime of spreading. The accelerated rate of spreading is attributed to the potential energy as the interfacial film yields as well as relaxation of the crumpled interfacial film during spreading. Even though the strongly elastic film ruptures to promote droplet spreading, interfacial elasticity is retained enhancing the dampening of droplet oscillations following detachment from the dispensing capillary

Hollow microspheres with binary colloidal and polymeric membrane: Effect of polymer and particle concentrations

We report here the preparation of hollow microspheres with a binary shell structure consisting of a precipitated polymer film with a layer of colloidal particles embedded on its outer surface. We recently demonstrated a method for the preparation of microspheres from solid-stabilised emulsion templates using various colloidal particle systems as emulsifiers. In the present work we use colloidal silica as an emulsifier for the preparation of the emulsion template for the microspheres and study the effect of polymer and particle concentrations on the obtained structures. Observations using optical microscopy showed that decreasing the polymer concentration led to a reduction in the capsule wall thickness and apparent strength of the microspheres when dried. Importantly, all microspheres preserved their integrity when in suspension. SEM studies confirmed the differences observed in the thickness of the precipitated film at the oil/water interface. In addition, we also demonstrate that a larger particle concentration leads to microspheres with a lower degree of porosity

Hollow microspheres with binary porous membranes from solid-stabilised emulsion templates

We report a simple one pot procedure for the preparation of hollow microspheres with a shell comprised of an inner polymeric porous membrane and an outer layer of colloidal particles. Solid-stabilised emulsions are used as templates for the precipitation of a high molecular weight polymer at the oil-water interface via internal phase separation of a volatile solvent. As the solvent is extracted from the droplets, the polymer forms a porous membrane on their surface and entraps the colloidal monolayer adsorbed at the interface. We demonstrate the versatility of this method by using several types of particle emulsifiers and by preparing hollow microspheres of different size, porosity and surface properties. We also investigate the use of gold nanoparticles in this process and successfully entrap a large number of nanoparticles on the surface of the polymeric membrane by modifying the surface of the nanoparticles in-situ