Investigating Nanoparticle Organization in Polymer Matrices during Reaction-Induced Phase Transitions and Material Processing

Abstract

Controlling nanoparticle organization in polymer matrices has been and is still a long-standing issue and directly impacts the performance of the materials. In the majority of instances, simply mixing nanoparticles and polymers leads to macroscale aggregation, resulting in deleterious effects. An alternative method to physically blending independent components such as nanoparticle and polymers is to conduct polymerizations in one-phase monomer/nanoparticle mixtures. Here, we report on the mechanism of nanoparticle aggregation in hybrid materials in which gold nanoparticles are initially homogeneously dispersed in a monomer mixture and then undergo a two-step aggregation process during polymerization and material processing. Specifically, oleylamine-functionalized gold nanoparticles (AuNP) are first synthesized in a methyl methacrylate (MMA) solution and then subsequently polymerized by using a free radical polymerization initiated with azobis(isobutyronitrile) (AIBN) to create hybrid AuNP and poly(methyl methacrylate) (PMMA) materials. The resulting products are easily pressed to obtain bulk films with nanoparticle organization defined as either welldispersed or aggregated. Polymerizations are performed at various temperatures (T) and MMA volume fractions (Φ MMA ) to systematically influence the final nanoparticle dispersion state. During the polymerization of MMA and subsequent material processing, the initially homogeneous AuNP/MMA mixture undergoes macrophase separation between PMMA and oleylamine during the polymerization, yet the AuNP are dispersed in the oleylamine phase. The nanoparticles then aggregate within the oleylamine phase when the materials are processed via vacuum drying and pressing. Nanoparticle organization is tracked throughout the polymerization and processing steps by using a combination of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The resulting dispersion state of AuNPs in PMMA bulk films is ultimately dictated by the thermodynamics of mixing between the PMMA and oleylamine phases, but the mechanism of nanoparticle aggregation occurs in two steps that correspond to the polymerization and processing of the materials. Flory−Huggins mixing theory is used to support the PMMA and oleylamine phase separation. The reported results highlight how the integration of nonequilibrium processing and mean-field approximations reveal nanoparticle aggregation in hybrid materials synthesized by using reaction-induced phase transitions.

Controlling Polymer Material Structure during Reaction-Induced Phase Transitions

“…Alternatively, it is possible to synthesize polymer nanocomposites with multiscale structures by inducing macrophase separation and nanoparticle aggregation in a two-step process during polymerization (Figure ). Gold nanoparticles (AuNPs) functionalized with oleylamine were first synthesized in a methyl methacrylate (MMA) solution (Figure a, b), which was adapted from a previous method using toluene as the solvent . The AuNP/MMA solution is dark red, similar in appearance to AuNPs produced using toluene as the solvent (Figure b) .…”

“…e) Room temperature SAXS plots and f–h) TEM images of the AuNP/PMMA material directly after polymerization (red SAXS curve), f) vacuum drying (blue SAXS curve), g) thermally pressing (green SAXS curve), and h) annealing at 105 °C (purple SAXS curve). Reproduced with permission from ref . Copyright 2021 American Chemical Society.…”

“…Therefore, with the right nanoparticle surface functionalization and/or reaction mixture composition (i.e., minimizing the enthalpic penalty), many nanoparticles will disperse within the monomer reaction mixture . Numerous different nanoparticles such as carbon, , SiO 2 , , TiO 2 , ZnO, ZrO 2 , and Au have been incorporated within polymer matrices through the described polymerization method, but most of the reports have focused on synthesizing the materials without exploring how the polymerization impacted nanoparticle distribution.…”

Temperature Sensors based on Polymer Fiber Optic Interferometer

“…by using carbon and producing carbon fiber-reinforced plastic [47] or by applying the multilayer of various types of polymer [48,49]. However, nanoparticle control remains an unsolved challenge because the simplest method, mixing nanoparticles with polymer, causes nanoparticle aggregation [50]. It can be solved by the layered structure of polymer with a different solution of nanoparticles [51].…”

Synthesis and stability of switchable CO2-responsive foaming coupled with nanoparticles

“…In recent years, nanotechnology has been rapidly developed, and SiO 2 nanoparticles have been synthesized with specific surfaces, which can be well dispersed, adsorbed, etc. Nanoparticles are widely used in materials ( Lanasa et al., 2021 ), medicine ( Yadid et al., 2019 ), oil development fields ( Xu et al., 2020a , 2020b ), and other fields and have become an important material in some applications with good development prospects. Experimental studies have illustrated that nanoparticles can be adsorbed on the gas–liquid interface to improve the strength of the liquid film, reduce the drainage rate, and inhibit the aggregation of multiphase bubbles ( Lv et al., 2020 ).…”