Phase separation of polymer mixtures driven by photochemical reactions: current status and perspectives

Abstract

Phase separation of polymer mixtures induced by photo-crosslinking and photopolymerization is summarized from the viewpoint of competing interactions in polymeric systems. First, the kinetics of photo-crosslinking and photopolymerization are reviewed with particular emphasis on the Trommsdorff − Norrish effect in polymerization, which leads to the formation of a bimodal distribution of molecular weight at long irradiation time. The emergence of a very large molecular weight and the characteristic time for this effect to set in are utilized as a tool to control the temporal development of the resulting morphology. The shrinkage associated with the reaction and particularly its effect on the phase separation and the morphology are discussed together with the influence of the Trommsdorff − Norrish effect. Experiments on polymerization-induced phase separation extended from binary to ternary mixtures are described where the interfacial interactions give rise to a wide variety of morphologies. Taking advantages of light, experiments using spatial and temporal modulation have been performed to control and manipulate the phase separation. These experimental results are summarized and briefly discussed in relation to the elastic deformation induced by polymerization. Finally, an overview of theoretical studies and numerical simulation of reaction-induced phase separation is given with some comments on the complexity of the phenomena.

Direct printing of functional 3D objects using polymerization-induced phase separation

“…Here, we demonstrate that by using purposely formulated resins, material phases within objects can be controlled using vat polymerization. The method utilizes polymerization-induced phase separation (PIPS), a process previously used to generate 2D patterns in holographic polymerization 24 – 29 . Exploiting concomitant changes in the thermodynamics of mixing that occur during polymerization, as well as spatio-temporal variations in monomer to polymer conversion, materials can be spatially directed towards the surface of the 3D printed object.…”

Nanocrystals Assembled by the Chemical Reaction of the Dispersion Solvent

“…We found that Φ is largely non‐linear, which is similar to the evolution of W (after a slow increase, Φ increases quickly at a certain time and then levels off) (Figure a). This autoacceleration of the reaction is plausibly due to the Trommsdorff–Norrish effect that is caused by a dramatic decrease in the rate constant for termination, which is associated with an increase in the viscosity of the polymerizing mixture . Therefore, similar to the analysis of W (Figure f), Φ was fitted to the sigmoid function (solid curves in Figure a).…”

Triphase Separation of a Ternary Symmetric Highly Viscous Mixture

“…Presented herein is a numerical study of isothermal spinodal decomposition of a very viscous ternary liquid mixture in the limit of zero fluidity coefficient (further addressed below), following a thermal quench from a stable state in the one-phase region to an unstable location within the tie triangle of its phase diagram. Although our attention in this work will be restricted to nonreactive (symmetric) ternary liquid mixtures, it should be acknowledged that the behavior of reactive (not necessarily symmetric) ternary mixtures has received considerable attention over the past two decades [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. In fact, even though spinodal decomposition in a number of reaction-diffusion systems is usually triggered by a thermal or compositional quench, actually the necessary displacement from a stable state in the one-phase region into the spinodal range can also occur by reaction, e.g., polymerization of a monomer when the polymer being formed is incompatible with one or more of the other components in the mixture.…”