Particles soft phase

Such materials essentially contain PS as the matrix polymer and uniformly dispersed in this matrix are elastomeric types of particles, which form the soft phase (3). The soft phase is essentially composed of poly(butadiene) or of block copolymers of butadiene and styrene. This soft phase can be also addressed as the impact modifier for PS. 

The impact strength increases almost linearly with gel content and thus with the degree of crosslinking (17). Figure 9.3 shows the increase of the molecular mobility with the impact strength for ABS. For HIPS it is claimed that the situation is quite similar. The molecular mobility of the soft phase particles is determined by nuclear magnetic-resonance spectroscopy relaxation measurements (16). 

A conversion of the "hard" phase adjacent to the filler particles to the soft phase... 

In order to explain such a microhardness depression, AH = Heal — Hexp (Table 5.4), it is convenient to consider the behaviour of the harder component dispersed in the liquid component (with zero hardness). It seems reasonable here to assume that the total microhardness of such a system will also depend on the viscosity of the soft component in which the particles of the harder component are floating . The deviation of Hexp from Hcai may actually reflect the viscosity of the soft-segment phase which also contributes to the resistance of the total system against the applied load. The viscosity of the soft phase introduces two important effects. 

All materials subject to size reduction through grinding will exhibit a distribution of particle sizes, often skewed in shape, with the result that a single estimate of size will not represent the sample as a whole. In addition, the grinding of multiphase samples most often results in differential size reduction of hard and soft phases. In practice, the difficulty in obtaining an accurate estimate of individual particle sizes usually means that analysts make an informed guess at the value of D. Thus, the value used may be empirically based to achieve a desired phase abundance rather than a value based on sound measurement. Widespread misuse of microabsorption correction was clearly demonstrated in the lUCr quantitative phase analysis round robin. ... 

Foams (cellular structures) made by expanding a material by growing bubbles in it [11]. A foam has at least two components. At a macroscopic scale, there are the solid and liquid phases. The solid phase can be a polymer, ceramic or metal. The fluid phase is a gas in most synthetic foams, and a liquid in most natural foams. At a microscopic scale, the solid phase may itself consist of several components. For example, the solid phase of an amorphous polystyrene foam has only one component. On the other hand, the solid phase of a polyethylene foam or a flexible polyurethane foam typically has two components. These components are the crystalline and amorphous phases in polyethylene foams, and the hard and soft phases formed by the phase separation of the hard and soft segment blocks in flexible polyurethane foams. The solid phase of a polyurethane foam may, in fact, have even more than two components, since additional reinforcing components such as styrene-acrylonitrile copolymer or polyurea particles are often incorporated [12,13]. The solid is always a continuous phase in a foam. Foams can generally be classified as follows, based on whether the fluid phase is co-continuous with the solid phase ... 

Figure 10.15. Schematic illustrations of theories of stress softening, (a) Mullins and Tobin (1956) considered the filled rubber as a heterogeneous system comprised of hard and soft phases. Deformation breaks down the hard phase, but the degree of breakdown depends on the maximum extension of the sample, (b) F. Bueche (1965) attributed stress-softening to the breakage of network chains attached to adjacent filler particles (A molecule breaks first), (c) Dannenberg (1966) and Boonstra (1965) suggested that reinforcement can be understood through chain slippage mechanisms. The slippage is shown by the chain marks. (Smith and Rinde, 1969.)...

The dissipative particle dynamics (DPD) method is a recent variation of the molecular dynamics technique. Here, in addition to Newtonian forces between hard particles, soft forces between particles are also introduced. These pairwise damping and noise forces model slower molecular motions. The dissipative forces also reduce the drift in kinetic energy that occurs in molecular dynamics simulations. These two reasons mean that DPD can be used to model longer time-scale processes, such as hydrodynamic flows or phase separation processes. 

Very often, the basic elements of a soft phase will be charged, and the distribution of these charges can lead to assembly in solution. There is an attractive force between oppositely charged particles represented by the Coulomb force,... 

They consist of at least two different polymers one with low MFFT and one with high MFFT. Figure 9.8(a) shows an electron micrograph of a two-phase latex particle. The soft phase was stained and is partly engulfed by the hard phase. This picture only represents one possibility of how domains of the different phases can be arranged. The particle structure can be varied largely by the choice of monomers and process conditions (Rudin, 1995). 

In the previous section, non-equilibrium behaviour was discussed, which is observed for particles with a deep minimum in the particle interactions at contact. In this final section, some examples of equilibrium phase behaviour in concentrated colloidal suspensions will be presented. Here we are concerned with purely repulsive particles (hard or soft spheres), or with particles with attractions of moderate strength and range (colloid-polymer and colloid-colloid mixtures). Although we shall focus mainly on equilibrium aspects, a few comments will be made about the associated kinetics as well [69, 70]. 

Charged particles in polar solvents have soft-repulsive interactions (see section C2.6.4). Just as hard spheres, such particles also undergo an ordering transition. Important differences, however, are that tire transition takes place at (much) lower particle volume fractions, and at low ionic strengtli (low k) tire solid phase may be body centred cubic (bee), ratlier tlian tire more compact fee stmcture (see [69, 73, 84]). For tire interactions, a Yukawa potential (equation (C2.6.11)1 is often used. The phase diagram for the Yukawa potential was calculated using computer simulations by Robbins et al [851. 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

One prominent example of rods with a soft interaction is Gay-Berne particles. Recently, elastic properties were calculated [89,90]. Using the classical Car-Parrinello scheme, the interactions between charged rods have been considered [91]. Concerning phase transitions, the sohd-fluid equihbria for hard dumbbells that interact additionally with a quadrupolar force was considered [92], as was the nematic-isotropic transition in a fluid of dipolar hard spherocylinders [93]. The influence of an additional attraction on the phase behavior of hard spherocylinders was considered by Bolhuis et al. [94]. The gelation transition typical for clays was found in a system of infinitely thin disks carrying point quadrupoles [95,96]. In confined hquid-crystalline films tilted molecular layers form near each wall [97]. Chakrabarti has found simulation evidence of critical behavior of the isotropic-nematic phase transition in a porous medium [98]. 

The structure formation in an ER fluid was simulated [99]. The characteristic parameter is the ratio of the Brownian force to the dipolar force. Over a wide range of this ratio there is rapid chain formation followed by aggregation of chains into thick columns with a body-centered tetragonal structure observed. Above a threshold of the intensity of an external ahgn-ing field, condensation of the particles happens [100]. This effect has also been studied for MR fluids [101]. The rheological behavior of ER fluids [102] depends on the structure formed chainlike, shear-string, or liquid. Coexistence in dipolar fluids in a field [103], for a Stockmayer fluid in an applied field [104], and the structure of soft-sphere dipolar fluids were investigated [105], and ferroelectric phases were found [106]. An island of vapor-liquid coexistence was found for dipolar hard spherocylinders [107]. It exists between a phase where the particles form chains of dipoles in a nose-to-tail... 

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

PETP flakes produced from used soft drinks bottles were subjected to alkaline hydrolysis in aqueous sodium hydroxide. A phase transfer catalyst (trioctylmethylammonium bromide) was used to enable the depolymerisation reaction to take place at room temperature and under mild conditions. The effects of temperature, alkali concentration, PETP particle size, PETP concentration and catalyst to PETP ratio on the reaction kinetics were studied. The disodium terephthalate produced was treated with sulphuric to give terephthalic acid of high purity. A simple theoretical model was developed to describe the hydrolysis rate. 17 refs. 

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