Enhanced resistance to decay of imprinted nanopatterns in thin films by bare nanoparticles compared to polymer-grafted nanoparticles.

We extend a previous study on the influence of nanoparticles on the decay of nanoimprinted polymer film patterns to compare the effects of "bare" silica (SiO) nanoparticles and SiO nanoparticles with grafted polymer layers having the same chemical composition as the polymer matrix. This method involves nanoimprinting substrate-supported polymer films using a pattern replicated from a digital versatile disc (DVD), and then annealing the patterned polymer nanocomposite films at elevated temperatures to follow the decay of the topographic surface pattern with time by atomic force microscopy imaging after quenching. We quantified the relaxation of the pattern height ("slumping") and determined the relaxation time for this pattern decay process as a function of nanoparticle filler type and concentration to determine how nanoparticle additives influence relative film stability.

Observation of General Entropy-Enthalpy Compensation Effect in the Relaxation of Wrinkled Polymer Nanocomposite Films.

Surface-textured polymer nanocomposite (PNC) films are utilized in many device applications, and therefore understanding the relaxation behavior of such films is important. By extending an in situ wrinkle relaxation method, we observed that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (), is proportional to a film's nanoparticle (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature () that is determined to be in the vicinity of the film's . This provides unambiguous confirmation of entropy-enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications.

Nanoscale Pattern Decay Monitored Line by Line via In Situ Heated Atomic Force Microscopy.

We combine in situ heated atomic force microscopy (AFM) with automated line-by-line spectral analysis to quantify the relaxation or decay phenomenon of nanopatterned composite polymer films above the glass-transition temperature of the composite material. This approach enables assessment of pattern fidelity with a temporal resolution of ≈1 s, providing the necessary data density to confidently capture the short-time relaxation processes inaccessible to conventional ex situ measurements. Specifically, we studied the thermal decay of nanopatterned poly(methyl methacrylate) (PMMA) and PMMA nanocomposite films containing unmodified and PMMA-grafted silica nanoparticles (SiO NP) of varying concentrations and film thicknesses using this new approach.

Tuning the Relaxation of Nanopatterned Polymer Films with Polymer-Grafted Nanoparticles: Observation of Entropy-Enthalpy Compensation.

Polymer films provide a versatile platform in which complex functional relief patterns can be thermally imprinted with a resolution down to few nanometers. However, a practical limitation of this method is the tendency for the imprinted patterns to relax ("slump"), leading to loss of pattern fidelity over time. While increasing temperature above glass transition temperature ( T) accelerates the slumping kinetics of neat films, we find that the addition of polymer-grafted nanoparticles (PGNP) can greatly enhance the thermal stability of these patterns.