Hard shell particles

Heil et al. [38] employed a three-reactor CSTR. A latex seed was fed to the first reactor and monomer feeds of different compositions were fed to the first two reactors to produce a soft core, hard shell particle morphology. The three-reactor series would also have a narrower PSD than a single CSTR. Scott and Feast [31] used a single CSTR to carry out a high temperature (80-100 °C) adiabatic polymerization with cold feed streams. 

Here, the active agents were placed in the internal oil phase of the O/W/O emulsion to provide an appropriate rate of release. Similar approaches have been used in other treatments using W/O/W emulsions [37] and multiple emulsions, whose continuous phase has been polymerized or otherwise soUdified to form a hard-shell particle [23]. 

Soot deposited on the chamber wall contained mostly carbonaceous particles, where no MWNTs were contained. The deposits on the cathode consist of two portions the inside is black fragile core and the outside hard shell. The inside include MWNTs scad poljd ral graphitic nanoparticles. The outer-shell part ojnsisted of the crystd of graphite. 

A cylindrical hard deposit, which is grown on the tip of a cathode (A in Fig. 10.2.2), consists of two regions an inner fibrous black core and an outer gray hard shell (15). The inner core had a columnar structure that was made up of bundles of nanotubes and flocks of polyhedral graphitic particles (32). On the other hand, the hard shell was made of stacked graphitic flakes. 

The deformation behaviors have been interpreted in terms of the two basic models(11), (i) the deformed two-phase model in which the interparticle distances and the particles, initially giving rise to Debye s hard-sphere type scattering(1U), are affinely deformed under constant volumes (designated as "deformed hard-particles") and (ii) the deformed core-shell particle model in which a spherical core-shell particle is affinely deformed under constant volume into an ellipsoidal core-shell particle. 

This investigation of silicone-modified hybrid composites demonstrates that compatibilized, segmented liquid rubbers can be tailored to promote the formation of colloidal rubber dispersions, which enhance the toughness of the epoxy matrix. Furthermore, such segmented liquid rubbers can in situ-modify filler surfaces to form core-shell particles with a hard filler core and a thin... 

The small particle size of the silica is important not only in enabling the silica to flow to the peripheral region of the porous microsphere but also in forming the hard peripheral oxide-rich shell. Particles of silica 2-3 nm in diameter sinter together to some extent even under the temperature conditions encountered in a conventional spray drying process, whereas particles 10-100 nm do not sinter below 700-1000°C. As a result, attrition resistance of the catalyst, catalyst precursor or catalyst support particle is a function of the particle size and degree of aggreggation of the silica formed by dehydration. 

Discrete particles of silica 2-3 nm in diameter, such as those present in the polysilicic acid described above, form hard shells on the resulting porous microspheres under conventional drying conditions. The green attrition resistance, that is, the attrition resistance before calcinations, of the porous microspheres of, for example, a... 

Ottewill RH, Schofield AB, Waters JA, Williams NSJ (1997) Preparation of core-shell polymer colloid particles by encapsirlation. Colloid Polym Sd 275 274-283 Okubo M, Lu Y, Wang Z (1999) Analysis of stepwise heterocoagulation for the preparation of soft core/hard shell composite polymer particles. Colloid Polym Sd 277 77-82 Xu Y, Brittain WJ, Xue C, Eby RK (2004) Effect of clay type on morphology and thermal stability of PMMA-clay nanocomposites prepared by heterocoagulation method. Polymer 45(ll) 3735-3746... 

Latexes made out of composite polymer particles (i.e., particles containing different phases) present definitive advantages in many applications. Thus, particles formed by an elastic core and a hard shell are used as impact modifiers for polymer matrices [14]. Hard-core, soft-shell particles are particularly useful for paints because they have a low MEET and are not sticky at higher temperatures [16]. Hollow particles are efficient opacifiers [15], and... 

Hence this equation is a natural generalization of the Einstein-Smallwood reinforcement law. For rigid and spherical filler particles at low volume firaction, the Einstein-Smallwood formula is recovered, since in this case the intrinsic modulus [/a] = 5/2 (the intrinsic modulus [/a] follows from the solution of a single-particle problem). Exact analytical results can be obtained for the most relevant cases, such as uniform soft spheres, which describe the softening of the material in a proper way, as well as in the case of soft cores and hard shells [5]. 

Particles with a copolymer soft core of poly-n-butyl acrylate/PMM A and a homopolymer hard shell of PMMA were characterised by TEM and solid-state NMR spectroscopy. Two synthesis parameters were investigated, the phase ratio of the core and the shell, and the compatibility of the two phases. A series of core-to-shell ratios from 100/0 to 25/75 was synthesised and characterised. The compatibility between the phases was changed, either by using acrylic acid in either the core and the shell or in both, or by synthesising a homopolymer or a copolymer core, or by introducing crosslinking points in the core. The combination of TEM and solid-state NMR spectroscopy allowed quantitative determination of the extent of coverage of the core by the shell polymer and the... 

The morphology of rubber latex formation was followed as a function of time during the maturation of prevulcanization, and morphological features were shown to correlate with cross-link densities. Inhomogeneous latex particles cross-linked on the surface with imcross-linked cores were obtained during this process. It is proposed that these hard-shell/soft core structures coalesce to form the characteristic dimpled surface films (130). 

Bivalves, snails, and cephalopods, biologically united as molluscs, often protect themselves with hard shells. These shells are a composite, comprising an organic matrix with included ceramic particles, with a particle volume fraction of 95% or even more [144]. 

Often, very small rubber particles or modifier particles are used to enhance the toughness, for instance, of PMMA or PP at lower temperatures. Figure 5.12 shows schematically one example with PBA core shell particles they consist of a hard core of PMMA (diameter about 180 nm) and a rubbery shell of poly(bu-tyl acrylate-co-styrene) (PBA) (approximately 40 nm thick). An outer PMMA shell increases compatibility between particles and matrix. The particles were preformed and possess spherical shapes with a narrow size distribution. Under load, the plastic deformation starts in the particles with cavitation and fibrillation of the rubbery shell. The second step is deformation in highly stressed zones between the particles in the form of crazes or homogeneous yielding. 

Core/ shell particles can be less efficient than bulk rubbers as toughening agents, because they contain less rubbery material. On the other hand, the hard shell has been well documented to have a less deleterious effect on matrix stiffness than that observed with bulk rubbers. 

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