Studies of phase separation dynamics and interfaces in ternary systems.

摘要

The phase separation dynamics and interfaces in ternary A-B-C mixtures are studied. Particular attention is given to the interfacial properties of A-B blends when a third minority homopolymer C is added as a way to improve the interfacial properties of immiscible blends.; The dynamics of phase separation of ternary mixtures into two and three phases are analyzed numerically solving the non-linear spinodal decomposition equations (NLSD). Between any two phases rich in components I and J respectively, the third component K segregates in the I-rich/J-rich interfaces. This segregation phenomenon influences strongly the growth of a third phase with lowest equilibrium volume fraction. Coarsening of the minority phase occurs at the junction of multiple majority phase domain boundaries. The dynamical scaling and the growth laws for the late stages of phase separation are examined. In the absence of hydrodynamics, the growth law {dollar}R(tau) sim tausp{lcub}1/3{rcub}{dollar} is always obeyed even when the structures are not self-similar. The self-similar regime is achieved very slowly in ternary systems.; The adsorption per interfacial thickness of the minority C in the A/B interfaces is analyzed as a function of the Flory interaction parameters, {dollar}chisb{lcub}IJ{rcub},{dollar} and initial compositions {dollar}barvarphisb{lcub}C{rcub} < barvarphisb{lcub}A{rcub} = barvarphisb{lcub}B{rcub}.{dollar} It is obtained from the NLSD in the steady-state. When C is non-selective, {dollar}chisb{lcub}AC{rcub}= chisb{lcub}BC{rcub} = etachisb{lcub}AB{rcub},{dollar} different numerical methods are proposed for finding the equilibrium interface profiles minimizing the interfacial energy. The interfacial properties are analyzed as a function of {dollar}chisb{lcub}AB{rcub}, eta,{dollar} and {dollar}barvarphisb{lcub}C{rcub}.{dollar} As more C adsorbs at the interfaces, the interfacial thickness increases and the interfacial energy decreases. A typical application of this study is proposed in case-hardened polymer gears.; The effect of the gradient energy coefficients {dollar}barkappasb{lcub}II{rcub}{dollar} on the interface profiles of ternary alloys is examined solving the NLSD in the steady-state. As {dollar}barkappasb{lcub}CC{rcub}{dollar} increases, the adsorption of the minority C in the A/B interfaces decreases. It has a strong influence on the formation of the third phase rich in C. The two-phase equilibrium interface profiles are also obtained numerically solving the Euler-Lagrange equations minimizing the interfacial energy. They are identical to the steady-state solutions of the NLSD.