New Field Model of Polymer/Nanoparticle Mixture-Realizing Discreteness in the Continuous Description

Field-theoretical method is efficient in predicting the assembling structures of polymeric systems. However, for the polymer/nanoparticle mixture, the continuous density description is not suitable to capture the realistic assembly of particles, especially when the size of particle is much larger than the polymer segment. Here, we developed a field-based model, in which the particles are eventually discrete and hence it can overcome the drawbacks of the conventional field descriptions, e.g., inadequate and crude treatment on the polymer-particle interface and the excluded-volume interaction. We applied the model to study the simplest system of nanoparticles immersed in dense homopolymer solution. Our model can address the depletion effect and interfacial interaction in a more delicate way. Insights into the enthalpic and/or entropic origin of the structural variation due to the competition between depletion and interfacial interaction are obtained. New phenomena such as depletion-enhanced bridging aggregation are observed in the case of strong interfacial attraction and large depletion length. This approach is readily extendable to studying more complex polymer-based nanocomposites or biology-related systems, such as dendrimer/drug encapsulation and membrane/particle assembly.