Mechanical and viscoelastic properties of confined amorphous polymers

Abstract

Confinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (T g ) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. 1,2 These concerns persist for polymeric nanostructures, where mechanical properties are critical to feature stability. 3 The mechanical properties of many polymers are dependent on their processing history,

Glass Transition Phenomenon for Conjugated Polymers

“…The nanoconfinement effect has a strong influence on the T g . Inspired by the pioneering work of Jackson and McKenna on the T g depression for the organic liquids confined in nanopores, the T g of polymers in the nanometer scales has received significant interest . The T g of thin films, defined by a simple nanoconfined physical model, has been characterized by different types of measurements, including dynamic, thermodynamic, and pseudothermodynamic (see subsequently for the definitions).…”

Impact of bottlebrush chain architecture on Tg‐confinement and fragility‐confinement effects enabled by thermo‐cleavable bottlebrush polymers synthesized by radical coupling and atom transfer radical polymerization

“…In comparison with bulk films of the same polymer, thin films of linear, freely deposited polymers that are a few tens of nanometers thick may exhibit significantly different properties, for example, glass transition temperature ( T g ), fragility, and stiffness among others. [ 1–48 ] For instance, in comparison with a bulk polystyrene (PS) film and as measured by ellipsometry, a 21‐nm‐thick, substrate‐supported high molecular weight (MW) PS film exhibits a T g reduction of 10°C. [ 18 ] Understanding such nanoscale T g ‐confinement effects in polymers is important for many advanced technological applications, for example, thin films used in nanolithography processes for microchip manufacturing.…”

Role of Glassy Bridges on the Mechanics of Filled Rubbers under Pressure

“…Our approach is based on the understanding of the dynamics of confined polymers built over the last 20 years from experimental measurements, theories and simulations. Vogt, 28 and references therein, has provided a good review on the significant impact of the confinement of amorphous polymers in nanoscale dimensions on their mechanical properties. Many authors [29][30][31][32] have revealed that the glass transition temperature T g of thin polymer films strongly interacting with a solid substrate increases with decreasing film thickness.…”