Role of Polymer–Nanoparticle Interactions on the Fracture Toughness of Polymer-Infiltrated Nanoparticle Films

Abstract

Polymer–nanoparticle (NP) composite films (PNCFs) with extremely high loadings of NPs (>50 vol %) have superb transport, thermal, and electrical properties. A new class of highly loaded PNCFs known as polymer-infiltrated NP films (PINFs) have been recently developed and applied as multifunctional coatings and membranes. PINFs also represent a powerful platform to study the interfacial and confinement effects on thermal, transport, and mechanical properties of polymers. In this work, we investigate the role of the polymer–NP interface on the fracture behavior of PINFs prepared by capillary rise infiltration of polymer into silica (SiO2) NP packings. We tune the polymer–NP interaction strength by using SiO2 NPs with two different surface functional groups (hydroxyl and trimethylsilyl) and two polymers [polystyrene and poly(2-vinyl-pyridine)] with different interaction strengths with SiO2 NPs. For PINFs composed of small NPs, passivation of NPs with trimethylsilyl groups significantly impacts the fracture toughness by changing the sliding shear stress at polymer–NP interface. Polystyrene and poly(2-vinyl-pyridine) show a similar level of sliding shear stress likely due to strong adsorption on hydroxylated SiO2 NPs. In contrast, for PINFs consisting of large NPs, the fracture toughness is more strongly affected by the fracture properties of the polymers than the polymer–NP interactions. Our results illustrate the importance of understanding the interplay between confinement and polymer–NP interactions in controlling and tuning the fracture properties of PINFs for a wide range of applications.

Water‐Induced Separation of Polymers from High Nanoparticle‐Content Nanocomposite Films

“…PDMS has a low glass transition temperature (<−100 °C), [ 36 ] thus its fate can be observed at room temperature. When a PDMS solution is spin‐coated onto a SiO 2 NP film, a bilayer film consisting of a PDMS overlayer and a SiO 2 NP packing partially filled with PDMS is initially formed; this bilayer film then spontaneously evolves into a PDMS‐infiltrated SiO 2 NP film as the PDMS layer atop the SiO 2 NP packing infiltrates into the interstitial voids of the NP packing via capillary rise infiltration (CaRI); [ 9,16–20,24–26 ] when the void volume of the NP packing and the volume of dry PDMS are the same, a PINF with no residual PDMS overlayer is prepared. We fabricate such PINFs with thicknesses of ≈250 nm (Figure S1, Supporting Information) to study the fate of PDMS under high humidity or liquid water.…”

“…PINFs have emerged as a versatile class of nanocomposites with exceptional mechanical and transport properties owing to the high concentrations of NPs (>64 vol%), large polymer-NP interfacial area, and extreme nanoconfinement of polymers. [9,[16][17][18][19][20][24][25][26][27] PINFs for this study are prepared by infiltrating a hydrophobic polymer, PDMS into the interstices of dense disordered packings of hydrophilic SiO 2 NPs. PDMS has a low glass transition temperature (<−100 °C), [36] thus its fate can be observed at room temperature.…”

“…PDMS has a low glass transition temperature (<−100 °C), [36] thus its fate can be observed at room temperature. When a PDMS solution is spin-coated onto a SiO 2 NP film, a bilayer film consisting of a PDMS overlayer and a SiO 2 NP packing partially filled with PDMS is initially formed; this bilayer film then spontaneously evolves into a PDMS-infiltrated SiO 2 NP film as the PDMS layer atop the SiO 2 NP packing infiltrates into the interstitial voids of the NP packing via capillary rise infiltration (CaRI); [9,[16][17][18][19][20][24][25][26] 1a. This refractive index value is slightly smaller than the theoretically estimated value based on the sum of the refractive indices per volume of the constituents (1.440), likely because a small volume of water exists within the film due to capillary condensation (<10 vol.%).…”

“…202302676 research has shown that it is possible to emulate the structure of these natural composites, resulting in nanocomposite films with high strength and toughness ideal for protective and structural applications. [1][2][3][4][5][15][16][17][18] Highly loaded nanocomposite films also exhibit excellent thermal and electrical conductivities due to the percolation of NPs, when thermally and electrically conductive NPs are used. [19][20][21][22] Various strategies have been developed to produce highly loaded nanocomposite films, coatings, and membranes, such as layer-by-layer processes, [3,4] polymerizing monomers in the interstitial pores of pre-assembled NP packings, [13,20,22,23] inducing infiltration of polymers into the voids of NP packings by capillary rise infiltration (CaRI) [9,[16][17][18][19][20][24][25][26] or solvent-driven infiltration of polymer (SIP).…”

“…[1][2][3][4][5][15][16][17][18] Highly loaded nanocomposite films also exhibit excellent thermal and electrical conductivities due to the percolation of NPs, when thermally and electrically conductive NPs are used. [19][20][21][22] Various strategies have been developed to produce highly loaded nanocomposite films, coatings, and membranes, such as layer-by-layer processes, [3,4] polymerizing monomers in the interstitial pores of pre-assembled NP packings, [13,20,22,23] inducing infiltration of polymers into the voids of NP packings by capillary rise infiltration (CaRI) [9,[16][17][18][19][20][24][25][26] or solvent-driven infiltration of polymer (SIP). [19,27] To enable widespread utilization of these nanocomposites with extremely high loadings of NPs, it will become increasingly important to develop strategies for recycling these composites, which inevitably will require the separation and reclamation of NPs and polymers.…”