PMAA/MAA/Water

For the PMAA/water system that has become a prelude to studies of the PMAA/MAA/water reactive system, Fig. 1.1.5 shows phase curves and points that were obtained by our research group. 

For the PMAA/MAA/water system, water is also a solvent for PMAA to a certain degree thus, the phase behavior is different from non-solvent/solvent/polymer systems. On the other hand, inter- and intra-association effects accompanying the... 

Fig. 1.1.6 CPC (binodal points) of PMAA/MAA/ water system at 80 and 90° C (Reproduced with permission from Shi, 1997)...

Figures 1.1.9-1.1.12 show more phase diagrams of the PMAA/MAA/water system. Figure 1.1.12 shows the CPC with several tie lines.

Note that D and M are applied only to the overall or starting weight fi ac-tions hence the superscript o applied on them. Also, note that Du is a negative number, because the polymer phase separates from the solvent/precipitant. For simulation work, initial weight fraction of 7%/3%/90% were used for PMAA (component 1)/MAA (component 2)/water (component 3), respectively. The phase diagram, shown in Fig. 1.1.9 (Shi, 1997) for the PMAA/MAA/water system, indicates approximate values for the equilibrium compositions in the polymer-rich phase (c i = 12%, c s = 82%, c 2= 6%) and polymer-lean phase (c i =. 5%, c 3 = 97%, c 2 = 0.5%). 

Aldrich Chemical Company. Binary mixtures of PMAA in water, as well as the ternary solutions of PMAA/MAA/water, were prepared in quartz cells with an interior thickness of 1 mm. The cells containing binary and ternary solutions were sealed and rotated at room temperature to provide mixing. The initial solutions were mixed for at least 2 days in this fashion to ensure a homogeneous system. 

In order to shift to PMAA/water and PMAA/MAA/water systems, phase separation is effected by starting the system at a lower temperature, and then placing it at a higher temperature. This is because such a system has an LCST, instead of a UCST. We note the plots in Figs. 1.1.5-1.1.7, which show points that were subject to light scattering studies. 

Figures 1.4.29 shows plots of relative intensities I t) vs q for the ternary PMAA/MAA/water system (7 wt%/3 wt%/90 wt%) at 80°C. In Fig. 1.4.30, the plot of / [2sal(0] vs the time for the ternary PMAA/MAA/water system at 80°C is shown, whereby the straight-line section was used to determine diffusion coefficients and spinodal temperatures.

Fig. 1.4.29 Plot of / [6sal(0] vs the wavenumber q and time for the ternary PMAA/MAA/-water system at 75°C (Reproduced with permission from Saxena, 2001)...

Table 1.4.3 lists the specifications about each membrane prepared from the ternary PMAA/MAA/water system. 

PMAA/MAA/ water composition Phase separation temperature, Tps ( C) Phase separation time, tps Drying time, td (h) Smallest pore size ( xm) Comment (type of stiucture, etc.)... 

Figure 1.4.36-1.4.38 shows SEM micrographs of the PMAA membranes formed via thermal inversion process starting with a 7%/3%/90% solution of PMAA/MAA/water at room temperature and quenched at 80°C. The micrographs show fibrous, interconnected network, with open pores, indicative of spinodal decomposition. As phase separation time increases to about 2 min, a cellular... 

The above data reveal a structure similar to those obtained from PS/cyclohexanol binary systems in Section PMAA/MAA/Water System. Network structures are generally larger in the ternary PMAA/MAA/water system, and the smallest structure or pore size obtained here is in the order of 1-2 gm. In further calculations, the interdomain distance of 1 gm was used as a result of this experimental study. 

Based on Saxena s efforts (Saxena, 2001) and the adjustment on the timescales of phase separation to make numerical simulation data coincide with hght scattCT-ing results, the following phenomenological diffusion coefficients for the ternary PMAA/MAA/water (7 wt%/3 wt%/90 wt%) system at 80°C were obtained ... 

In order to attempt to quantitatively analyze the kinetics of phase separation of the reactive ternary PMAA/MAA/water system, the derivation in the Appendix was initially used, starting with Eq. (A.l) up to Eq. (A.39). For the continuity equation, a more general form was used ... 

For the experimental system extensively analyzed in Section 1.4, concentrations of 7 wt%/3 wt%/90 wt% were used for PMAA/MAA/water, respectively. However, for the FRRPP process, simulation was started with only MAA and water, at 10 wt% MAA (Cj = 0.10) in water (Cj = 0.90). The MAA polymerized to form of PMAA due to the decomposition of the initiator molecules. The final composition, assuming that all monomers reacted, was 10 wt% PMAA in water. Here, it was assumed that the specific gravity of MAA is almost equal to that of PMAA. 

It was assumed that the diffusivity values obtained for the 7%/3%/90% PMAA/ MAA/water system were applicable over the entire concentration range, i.e., from monomer concentration of 10 wt% to zero. The diagram below shows one iteration for the technique used to solve for the FRRPP process ... 

Table 2.1.1 shows radii of gyration of poly(methacrylic acid) in reactive FRRPP PMAA/MAA/water systems that are in the nanometer scale. Based on the phase diagram for PMAA/water system (Fig. 1.1.5), the experimental reactive system at 60°C barely makes it above the LOST, and yet the domain sizes are still relatively small. It seems that the polymer domains at 80°C have been into coarsening... 

Relevant phase envelopes for the PMAA/MAA/water system are shown in Section 1.1. Also, kinetics of phase separation results are presented for this system in Sections 1.4 and 1.5. 

PS/S/ether, PS/S/acetone, and PMAA/MAA/water systems. The following key features were observed and summarized for the FRRPP process (Aggarwal et al., 1996) ... 

It was fortuitous that the coil-globule transition had been advanced and validated in recent years. It was believed that for FRRPP of styrene in ether, what was occurring was a modified version of this phenomenon (Fig. 2.4.1). If one looks into the results in Section 2.1, the same can be said with the PMAA/MAA/water system. However, it was harder for this to be accepted, due to the relatively high conversions obtained in this type of FRRPP system. Still, a modification of the coil-globule transition picture was presented to involve a collection of chains in isolated domains for FRRPP systems, before they agglomerated into larger domains. The underlying reason is the fact that initiation of new chain polymerization events can occur within these domains. 

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