Abstract
This work presents the first investigation on the crystallization behavior of partially wet droplets in immiscible ternary blends. Poly(lactide), poly(ε-caprolactone), and poly(butylene succinate) (PLA, PCL, and PBS, respectively) were melt blended in a 10/45/45 weight ratio to produce a “partial wetting” morphology with droplets of the PLA minor phase located at the interface between the other two major components. The crystallization process of the higher melting PLA droplets was studied by polarized light optical microscopy, while the other components remain in the molten state. We found that neighboring partially wet droplets nucleate in close sequence. This is unexpected since partially wet droplets display points of three-phase contact and, hence, should not touch each other. Moreover, the onset of poly(lactide) crystallization is frequently observed at the interface with molten PCL or PBS, with a significant preference for the former polymer. The observed sequential droplet-to-droplet crystallization is attributed to the weak partial wetting behavior of the PCL/PLA/PBS ternary system. In fact, the contact between the interfacially confined droplets during crystallization due to their mobility can lead to a transition from a partial to a completely wet state, with the formation of thin continuous layers bridging larger partially wet droplets. This allows crystallization to spread sequentially between neighboring domains. Using a simple heterogeneous nucleation model, it is shown that the nucleation of PLA on either PCL or PBS melts is energetically feasible. This study establishes a clear relationship between the unique partial wetting morphology of ternary blends and the nucleation of the minor component, paving the way to the understanding and control of crystallization in multiphasic polymer blends for advanced applications.
Highlights
Polymer blending is an extensively used method for tailoring and/or modifying the properties of polymers
A partial wetting morphology was successfully produced in all three types of ternary blends, i.e., Poly(lactic acid) (PLA), PCL, and Poly(butylene succinate) (PBS) droplets were located at the PCL/PBS, PLA/PBS, and PLA/PCL interfaces, respectively, when present as a minor component
Asymmetric PLA droplets are observed at the interface due to the substantially different PLA/PCL and PLA/PBS interfacial tensions
Summary
Polymer blending is an extensively used method for tailoring and/or modifying the properties of polymers. A variety of phase morphologies can be obtained, in multiphase polymer blends, which offers the possibility to tune the properties of the resulting material.[11−26] For example, in ternary blends composed of two principal phases (A and B) and one minor phase (C), four types of morphologies are possible.[14] Phase C may be completely engulfed by either phase A or phase B, or it can form a thin layer completely wetting the A/B interface. We focus on this issue, considering, in particular, the nucleation behavior of PLA partially wet droplets, located at the interface with PBS and PCL phases in their immiscible ternary blend
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