Water‐assisted mechanical testing of polymeric thin‐films

Abstract

Thin films with a nanometer-scale thickness are of great interest to both scientific and industrial communities due to their numerous applications and unique behaviors different from the bulk. However, the understanding of thinfilm mechanics is still greatly hampered due to their intrinsic fragility and the lack of commercially available experimental instruments. In this review, we first discuss the progression of thin-film mechanical testing methods based on the supporting substrate: film-on-solid substrate method, film-on-water tensile tests, and water-assisted free-standing tensile tests. By comparing past studies on a model polymer, polystyrene, the effect of different substrates and confinement effect on the thin-film mechanics is evaluated. These techniques have generated fruitful scientific knowledge in the field of organic semiconductors for the understanding of structure-mechanical property relationships. We end this review by providing our perspective for their bright prospects in much broader applications and materials of interest.

Unraveling the Stretch‐Induced Microstructural Evolution and Morphology–Stretchability Relationships of High‐Performance Ternary Organic Photovoltaic Blends

“…This is largely limited by the lack of advanced structural characterization methods for organic thin films. [ 42 ] Hence, the fundamental relationships between microstructural robustness, stretchability, and morphology of the merging high‐efficiency ternary OSCs were to be answered.…”

Designing for Softness in Semiconducting Conjugated Polymers

“…The FOW test addresses the limitations of the buckling methodology of characterizing sub-100 nm thin films, in which confinement effects arise, obscuring the true properties of the polymer, and allows facile manipulation of the thin film for testing (Figure B) . In this pseudo-free-standing tensile test, stress–strain curves of semiconducting polymer thin films are obtained to determine tensile modulus, as shown by Kim, Gu, and co-workers. , A thin film is spin-cast on a substrate with a water-soluble sacrificial layer and placed in water; the sacrificial layer dissolves, leaving the polymer thin film floating at the surface to be stretched with tensile grips. Gu and co-workers employed FOW to better understand the viscoelastic properties of semiconducting polymers, specifically thickness dependence, strain-rate dependence, hysteresis tests, and stress-relaxation tests. , They observed a strong relationship between tensile moduli with chain confinement, in which reduced thin film thickness resulted in increased self-chain entanglement and lower tensile modulus.…”

“…Gu and co-workers employed FOW to better understand the viscoelastic properties of semiconducting polymers, specifically thickness dependence, strain-rate dependence, hysteresis tests, and stress-relaxation tests. 6,9 They observed a strong relationship between tensile moduli with chain confinement, in which reduced thin film thickness resulted in increased self-chain entanglement and lower tensile modulus.…”

Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability

“…Time dependent thin film tensile tests of PNDI-C5 were performed on a water surface through the pseudo-freestanding tensile tester at room temperature, as described in our previous publication and recent review. 38,39 Dogbone shaped films of 85 nm in thickness were tested after 15, 30, 60, 120, 240, 360, and 720 min post spin casting to capture the effect of slow crystallization on the mechanical property. During this waiting period samples were kept under an inert nitrogen atmosphere at room temperature.…”