Giant Cushioning Effect in Facile Polymer/Nanoclay-Coated Flexible Polyurethane Foams.

In this work, a flexible polyurethane (PU) foam/polymer/clay (PUF/PAASep) composite is prepared via a simple dip-coating method. The composite exhibits excellent damping properties under quasi-static compression, vibration transmissibility, and impact resistance. For the composite preparation, sepiolite (Sep) dispersion in a polyacrylic acid (PAA) solution is first homogenized and evaluated using microscopy, and the obtained PAASep suspension is used to coat the PU foam uniformly for optimization of the quasi-static mechanical performance of the foam composites.

Modified Sepiolite Nanoclays in Advanced Composites for Engineering Applications.

Clay-polymer nanocomposites (CPNs) containing a small weight fraction of nanoclay are known to display enhanced mechanical and thermal properties compared to neat polymers. However, the preparation and application of such nanocomposites remain challenging owing to the difficulties in dispersing nanoclays in polymer matrices. This study focuses on two surfactant-modified organophilic sepiolite clays to demonstrate the simplicity of the modification process, as well as on the use of a benzoxazine monomer (i.

Properties and Curing Kinetics of a Processable Binary Benzoxazine Blend.

A benzoxazine system is presented combining liquid cardanol-based benzoxazine (CA-a) and an effective initiator (3,3'-thiodipropionic acid, TDA) to bisphenol A-based benzoxazine (BA-a). The resultant mixture of monomeric precursors shows excellent fluidity and a relatively low peak polymerization temperature of around 200 °C. Moreover, the cured polybenzoxazine displays a high thermal decomposition temperature ( > 330 °C), a moderately high glass transition temperature (∼148 °C), and robust mechanical strength (storage modulus ∼ 2.

Identification of β-carotene oxidation products produced by bleaching clay using UPLC-ESI-MS/MS.

The removal of plant pigments such as β-carotene is an aspect of vegetable oil processing often desired by the food and pharmaceutical industries. Adsorption of β-carotene to acid-activated clay (AAC) is a well-established method for purification. Despite this, the removal mechanism of β-carotene is not well understood.

Competing active and passive interactions drive amoebalike crystallites and ordered bands in active colloids.

Swimmers and self-propelled particles are physical models for the collective behavior and motility of a wide variety of living systems, such as bacteria colonies, bird flocks, and fish schools. Such artificial active materials are amenable to physical models which reveal the microscopic mechanisms underlying the collective behavior. Here we study colloids in a dc electric field.

Anisotropic viscoelastic phase separation in polydisperse hard rods leads to nonsticky gelation.

Spinodal demixing into two phases having very different viscosities leads to viscoelastic networks-i.e., gels-usually as a result of attractive particle interactions.

Polyphosphates can stabilize but also aggregate colloids.

Phosphates are well known as dispersants for a variety of colloidal particles. Here however we use rheological measurements to show that high molecular weight polyphosphates (PP) can instead act as a flocculant for LAPONITE® clay platelets. The proposed mechanism is bridging of PP between clay particle edges, leading to highly charged clusters forming a Wigner glass.

Stabilisation of water-in-water emulsions by montmorillonite platelets.

The formation of water-in-water emulsions from the aqueous two phase system containing polyethylene oxide and pullulan, stabilised by montmorillonite platelets, was investigated. A novel approach of preparing the emulsions at non-equilibrium polymer concentrations was successfully utilised to control viscosity during mixing and allow the use of low energy emulsification methods. Polyethylene oxide adsorbed to the platelets much more strongly than pullulan favouring the formation of pullulan-in-polyethylene oxide emulsions which remained stable for a period of weeks.

The role of initiator on the dispersibility of polystyrene microgels in non-aqueous solvents.

Non-aqueous microgel particles are commonly synthesised in water, dried, and then redispersed in non-aqueous solvents. An important factor to consider when synthesising such particles is the initiator, which can determine how well the particles disperse in solvents. Polystyrene microgel particles were made with three different initiators.

Controlling the Rheology of Montmorillonite Stabilized Oil-in-Water Emulsions.

The rheology of hexadecane-in-water emulsions stabilized by montmorillonite platelets was investigated. In these systems excess particles form a network in the continuous phase which strongly dictates their rheological behavior. The emulsions were modified by the addition of NaCl and NaPO to the continuous phase at varying concentrations.

Steady-state droplet size in montmorillonite stabilised emulsions.

The formation of hexadecane-in-water emulsions stabilised by montmorillonite platelets was studied. In this system the platelets form a monolayer around the droplets and the droplet size decreases with increasing platelet volume fraction. However, the number of platelets present exceeds that required for monolayer coverage.

Three-Phase Coexistence in Colloidal Rod-Plate Mixtures.

Aqueous suspensions of clay particles, such as montmorillonite (MMT) platelets and sepiolite (Sep) rods, tend to form gels at concentrations around 1 vol %. For Sep rods, adsorbing sodium polyacrylate to the surface allows for an isotropic-nematic phase separation to be seen instead. Here, MMT is added to such Sep suspensions, resulting in a complex phase behavior.

Isotropic-nematic phase transition of polydisperse clay rods.

Rod-like colloidal particles are known to display an isotropic-nematic phase transition on increase of concentration, as predicted already by Onsager. Both natural clay particles and synthetic rods tend to be polydisperse, however, and the question arises how to allow for this in comparing experimental observations with theory. Experimental data for a wide range of samples (both from the literature and the new results) have been collated, with aspect ratios ranging from 14 to 35.

Controlling Clusters of Colloidal Platelets: Effects of Edge and Face Surface Chemistries on the Behavior of Montmorillonite Suspensions.

The structural and rheological consequences of adsorbing pyrophosphate anions to the edges and polyetheramines to the faces of montmorillonite platelets in aqueous suspension were investigated. Oscillatory rheology and scattering experiments showed that the two surface treatments act in different regions of the phase diagram and that this can be attributed to modifications of local particle interactions resulting in changes to the behavior and morphology of platelet clusters. The polyetheramine was found to neutralize surface charge, reducing electrostatic repulsion between platelets and therefore allowing them to come into closer proximity.

Isotropic-nematic phase transition in aqueous sepiolite suspensions.

Aqueous suspensions of sepiolite clay rods in water tend to form gels on increase of concentration. Here it is shown how addition of a small amount (0.1% of the clay mass) of a common stabiliser for clay suspensions, sodium polyacrylate, can allow the observation of an isotropic-nematic liquid crystal phase transition.

Competition between polymers for adsorption on silica: a solvent relaxation NMR and small-angle neutron scattering study.

The competition between poly(vinylpyrrolidone) and poly(ethylene oxide) for adsorption at the silica surface was studied by solvent relaxation nuclear magnetic resonance and small-angle neutron scattering. The additive nature of the NMR relaxation rate enhancement was used to observe changes in the train layer when the two polymers were in direct competition for an increasing weight percentage of silica. PVP is shown to displace preadsorbed PEO from the particle surface, and this was observed for a range of PVP molecular weights.

Modifying the structure and flow behaviour of aqueous montmorillonite suspensions with surfactant.

Colloidal suspensions of plate-like particles undergo a variety of phase transitions. The predicted isotropic/nematic transition is often pre-empted by a sol/gel transition, especially in suspensions of the most commonly used natural swelling clay montmorillonite (MMT). A number of factors, including charge interactions, flexibility and salt concentration, may contribute to this competition.

Floating nematic phase in colloidal platelet-sphere mixtures.

The phase behaviour of colloidal dispersions is interesting for fundamental reasons and for technological applications such as photonic crystals and electronic paper. Sedimentation, which in everyday life is relevant from blood analysis to the shelf life of paint, is a means to determine phase boundaries by observing distinct layers in samples that are in sedimentation-diffusion equilibrium. However, disentangling the effects due to interparticle interactions, which generate the bulk phase diagram, from those due to gravity is a complex task.

Colloidal particles in competition for stabilizer: a solvent relaxation NMR study of polymer adsorption and desorption.

The competitive adsorption of poly(vinylpyrrolidone) onto silica and alumina-modified silica particles was studied using solvent relaxation nuclear magnetic resonance. The additive nature of the measured relaxation rate enabled predictions to be made of the relaxation rate in different polymer adsorption scenarios. Preferential adsorption of the poly(vinylpyrrolidone) onto the unmodified silica particles occurred when there was insufficient polymer in the system to coat the entire available surface area.

Microcapsules composed of cross-linked organoclay.

Polyelectrolyte-modified montmorillonite particles were used to stabilize oil-in-water Pickering emulsions, which were then bound together by an oil-soluble cross-linker to obtain microcapsules. It was determined how the morphology and rigidity of the microcapsules changed as polyelectrolyte and cross-linker concentrations were varied. Well-defined microcapsules could be formed by using a moderate concentration of polyelectrolyte, and the higher the cross-linker concentration, the more rigid the microcapsules.

Optimizing organoclay stabilized Pickering emulsions.

Oil-in-water emulsions were prepared using montmorillonite clay platelets, pre-treated with quaternary amine surfactants. In previous work, cetyl trimethylammonium bromide (CTAB) has been used. In this study, two more hydrophilic quaternary amine surfactants, Berol R648 and Ethoquad C/12, were used and formed Pickering emulsions, which were more stable than the emulsions prepared using CTAB coated clay.

Two-stage phase separation in ternary colloid-polymer mixtures.

Whilst binary colloid-polymer mixtures have been studied in detail over the past few decades, here the first results are presented on a ternary mixture involving two particle sizes. Novel and unusual phase separation kinetics are found, with a liquid phase separating from an aggregate phase.

Adsorption of polyetheramines on montmorillonite at high pH.

Adsorption of a series of polyetheramines on montmorillonite in aqueous suspension was investigated by a range of methods: elemental analysis, atomic absorption spectroscopy, measurement of pH, conductivity and electrophoretic mobility, and small-angle X-ray scattering. Adsorption proceeds through an ion exchange mechanism. The maximum surface coverage attained is equivalent to about 40% of the cationic exchange capacity of the clay.

The phase behavior of dispersions of silica particles in mixtures of polystyrene and dimethylformamide.

Depletion-induced phase separation in mixtures of charged silica particles and nonadsorbing polymer near theta conditions (polystyrene in dimethylformamide) was studied. The colloid-polymer size ratio q was varied through the particle size and the electrical double layer thickness (kappa(-1)) through addition of lithium chloride (LiCl). The dependence of the phase boundaries, and the nature of the separated phases, on q and kappa is reported and is found to be in good agreement with recent theoretical predictions (Gogelein, C.

Scaling the structure factors of protein limit colloid-polymer mixtures.

The scaling of the phase boundaries and structure factors of protein limit colloid-polymer mixtures has been investigated through the addition of large nonadsorbing polymer chains to a solution of small microemulsion droplets. The colloid-polymer size ratio has been varied between 10 and 16 by changing the microemulsion droplet size; the phase boundaries were shown previously to observe theoretical scaling relations very well [Langmuir 2009, 25 (7), 3944-3952]. These thermodynamic scaling relations are now shown to also hold extremely well for the individual and cross-term partial structure factors.