Lateral structure latex

In solution, block copolymers display interesting colloidal and interfacial properties. They can be used as emulsifying agents in water-oil and oil-oil systems (6 ). In the later case, the oil phases are solid and they give rise to polymeric alloys (7.) or they are liquid and they allow the preparation of latexes in organic medium (8 ). However, the molecular structure of block copolymers based on polybutadiene PB (70 ) and polystyrene PS behave as thermoplastic elastomers when engaged in multiblock (PB-PS)n or triblock (PS-PB-PS) structures but never when implied in inverse triblock or diblock arrangements. Similarly the... 

Glutaminyl cyclase (QC), EC 2.3.2.5, an acyltransferase responsible for N-terminal pyroglutamate formation from glutaminyl precursors in peptides and proteins. The first QC was isolated from the latex of Car-ica papaya in 1963. Later, it was established that glutaminyl cyclases occur in both animal and plant sources. They are abundant in mammalian neuroendocrine tissues, such as hypothalamus and pituitary, and are highly conserved from yeast to human. From the crystal structure of human glutaminyl cyclase it follows that a single zinc ion in the active site is coordinated... 

The creation of 2D crystals of both micron sized and nanometre sized particles remains a somewhat empirical process due to the ill-defined role of the substrate or surface on which nucleation takes place. Perrin first observed diffusion and ordering of micron sized gamboge 2D crystals in 1909 under an optical microscope [32]. Several techniques have been proposed for the formation of 2D arrays at either solid-liquid surfaces or at the air-water interface. Pieranski [33], Murray and van Winkle [34] and later Micheletto et al. [14] have simply evaporated latex dispersions. Dimitrov and coworkers used a dip-coating procedure, which can produce continuous 2D arrays [35,36]. The method involves the adsorption of particles from the bulk solution at the tricontact phase line. Evaporation of the thin water film leads to an attractive surface capillary force which aids condensation into an ordered structure. By withdrawing the film at the same rate as deposition is occurring, a continuous film of monolayered particles is created. Since the rate of deposition is measured with a CCD camera, it is not possible to use nanometer sized particles with this method, unless a nonoptical monitor for the deposition process can be found. 

The pore structure of latex-modified systems is influenced by the type of polymer in the latexes used and polymer-cement ratio as discussed in detail later. The total porosity or pore volume generally tends to decrease with an increase in the polymer-cement ratio. This contributes to improvements in the impermeability, resistance to carbonation, and freeze-thaw durability. 

Nevertheless, much is known about the structure of adsorbed 6-casein, certainly more flian is known for any other food protein, and various techniques have been used to study the adsorbed protein. The first evidence from DLS showed that 6-casein adsorbed to a polystyrene latex caused an increase in the radius of the particle by 10 to 15 nm (84). Later studies using small-angle X-ray scattering confirmed this and showed, in addition, that the bulk of the mass of the protein was close to the interface, so the interfacial layer was not of uniform density throughout (85). Neutron-reflectance studies also showed that most of the mass of protein was close to the interface (86). Only a relatively small portion of the mass of the adsorbed protein extends from the tightly packed interface into the solution, but it is this part which determines the hydrodynamics of the particle and which is almost certainly the soiuce of the steric stabilization which the 6-casein affords to emulsion droplets (84). It is to be noted that all of the studies just described were performed on latex particles or on planar interfaces however, it has also been demonstrated that the inter-facial structiues of 6-casein adsorbed to emulsion dro plets resemble those of the model particles (39, 85). Although detailed control of emulsion droplets dining their... 

Core/shell latexes refer to systems with a submicroscopic particle morphology of one polymer forming the center part (the core) and the other polymer covering the core (the shell layer). Core/shell latexes are made via two consecutive emulsion polymerization stages, usually forming a particle structure with the initially polymerized material at the center and the later-formed polymer as the outer layer. If more than two stages are employed in the emulsion polymerization process, latex particles with multilayered morphology can be obtained. 

In 1993, Goh, et al. (77) used atomic force microscopy to study the film formation behavior of poly(butyl methacrylate) latexes. In the early stages of film formation, the surface latex particles have a protruding structure not unlike a basket of eggs. With time, the surface smoothes via lateral diffusion. 

Modification of the cementitious binder with poiymers The use of polymer dispersions (latex) as an additive to cementitious binders is well established. The polymer particles are smaller by orders of magnitude than the cement grains, and they coalesce to form a continuous film. The use of water dispersed acrylics and PVA polymers (which can more readily be placed at the fibre interface and later on coalesce into a film which could be interlaced within the gel particles) resulted in a fine interfacial structure with much higher bond strength. 

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