Phase interpenetration

If the hydrolyses in organosilicate-polymer systems are carried out with increased amounts of the silicate, bicontinuous phases can be obtained (with the silica and polymer phases interpenetrating one another) [213]. At still-higher concentrations of the silicate, the silica generated becomes the continuous phase, with the polymer dispersed in it. The result is a polymer-modified ceramic, variously called an "ORMOCER" [214,215], "CERAMER" [216,217], or "POLY-CERAM" [218,219]. It is obviously of considerable importance to determine how the elastomeric phase modifies the ceramic in which it is dispersed. 

Elastomer blends consisting of two immiscible components are heterogeneous rubberlike materials both components of which are in the rubbery state. Such blends consist usually of either a matrix and a discrete phase or two interpenetrating continuous phases (interpenetrating networks). At homogeneous deformations of such blends, the contribution of either component to the thermomechanical behaviour of the material is determined by the content of the component and the individual characteristics of its chains. 

Although polymers and monomers in any form such as latexes, water-soluble polymers, liquid resins, and monomers are used in cement composites such as mortar and concrete, it is very important that both cement hydration and polymer phase formation (coalescence of polymer particles and the polymerization of monomers) proceed well to yidd a monolithic matrix phase widi a network structure in which the hydrated cement phase and polymer phase interpenetrate. In the polymer-modified mortar and concrete structures, aggregates are bound by such a co-matrbc phase, resulting in the superior properties of polymer-modified mortar and conoete compared to conventional. 

Third Step. Ultimately, with water withdrawal by cement hydration, the close-packed polymer particles on the cement hydrates coalesce into continuous films or membranes, and the films or membranes bind the cement hydrates together to form a monolithic network in which the polymer phase interpenetrates throughout the cement hydrate phase. Such a structure acts as a matrix phase for latex-modified mortar and concrete, and the aggregates are bound by the matrix phase to the hardened mortar and concrete. 

At some compositions and under some hydrolysis conditions, bicontinuous phases can be obtained (with the silica and polymer phases interpenetrating one another). The mechanism may be spinodal decomposition, occuning either before or after the polymerization. Since the two networks interpenetrate one another, the mechanical properties first exhibited by the material can be very peculiar. In a first deformation, the silica network would give a very high initial modulus, but once this structure is broken, additional deformation cycles would indicate much lower values of the modulus. 

French, J.D., M.P. Harmer, H.M. Chan, and G.A. Miller. 1990. Coarsening resistant dual-phase interpenetrating miorostruotures. Journal of the American Ceramic Society 73(8) 2508-10. ... 

Frischinger, 1., Muturi,P. and Dirlikov, S. (1994) Two-phase interpenetrating epoxy thermosets that contain epoxidized triglyceride oUs. Part 11. Applications. Advances in Chemistry Series, 239, 539-556. 

At a composition of 50% polyurethane, the polyurethane particles touch, as illustrated in Figure 6.7b. Beyond this composition range, both phases display cocontinuity (Figure 6.7c). Molecular interpenetration is restricted to the interfaces, however. Thus, only the phases interpenetrate in any real sense. 

In general, the use of the IPN concept yields better control over phase domain size and extent of molecular mixing. By various mechanisms, processibility is attained, yet the final products are all crosslinked. Because in many cases the phases interpenetrate to develop dual-phase continuity, a new type of bonding is achieved, to hold the two components in juxtaposition. 

J. L. Thiele and R. E. Cohen, Synthesis and Characterization of Single-Phase Interpenetrating Polymer Networks, Polym. Prepr. 19(1), 137 (1978). Swelling and modulus behavior Polystyrene/polystyrene IPNs. Swelling equation. 

In a certain sense, the term interpenetrating polymer networks is a misnomer, since most of these materials phase separate, rather than being mutually soluble on the molecular level. One could argue that the phases interpenetrate, and/or that true molecular interpenetration takes place at the interphase. However, the term describes the general S5mthesis and structure of the materials. 

This limited phase interpenetration was best manifested in a NR/PUR blend wherein the NR latex was initially pre-vulcanized. Varghese et al prepared NR/PUR blends of 50/50 and 20/80 weight ratios. This sulfur pre-vulcanized NR latex was concentrated with 1 % ammonia and presented 60% DRC. The NR latex was mixed with a polyester-based PUR latex of 50% DRC followed by stirring. Due to the different preparation routes of both latices, their particle size in the water dispersion differed significantly. The related mixture was cast in a mould built of glass plates and allowed to dry in air until transparent. It was then tempered for 30 min at 100 °C in an oven. 

Ricardo et <2/. used chloroform to mix NR with PUR. These rubbers had initially been prepared individually by the latex route. It was found that the rubber phase interpenetration in the solid film (after the total evaporation of the solvent) was very limited. 

Fig. 19.7 Schematic models of possible continuous seam structures in a (continuous) polymer matrix. (A, B) Seams and matrix, both continous phases, interpenetrating network, simplified representation (C, D) seams.

Such consideration supposes that the interpenetration proceeds only in one part of the system, in accordance with the two-phase structure of IPNs. It was assumed that two phases interpenetrate only in the intermediate regions between two phases. However, the concept of interphase was introduced for-... 

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