Complete Set of Enthalpy Recovery Data Using Flash DSC: Experiment and Modeling

Abstract

Enthalpy recovery of a single polystyrene thin film is quantified by both experiments using Flash DSC and modeling using a new modified TNM model. Experimental data include Kovacs' three signatures of structural recovery: intrinsic isotherms after temperature down jumps, the asymmetry of approach after temperature down and up jumps of the same size, and the memory effect after a two-step history. A new modified TNM model is proposed to quantitatively fit all three signatures of structural recovery with a single set of model parameters. Here, we elucidate the detailed derivation of the new modified model and demonstrate its applicability to the experimental Flash DSC results.

Glass Transition Phenomenon for Conjugated Polymers

“…However, the sample preparation is time consuming since it requires the stacking of several hundred layers of ultrathin film in order to meet the mass requirement . With the new developments of the nanocalorimetry, including flash DSC and AC‐chip calorimetry (We note here that the modulated DSC and the AC‐chip calorimetry are considered as dynamic measurements of T g ), which has the mass requirement of nanogram, measuring the T g of sub‐100 nm a single layer of polymer ultrathin film with DSC becomes possible and has drawn increasing attention …”

“…For example, the aged polymer exhibits a overshoot in enthalpy or volume; in addition, Kovacs [325] catalogued three aging signatures for glassy polymers, intrinsic isotherms, asymmetry of approach, and memory effect, which demonstrate the kinetics of structure recovery of polymers being nonexponential, nonlinear, and path dependent. [171] The aging rate depends on the aging temperature T a and the distance from T g , or in other words, the driving force and the molecular mobility. [32,170] At high T a , the mobility is high, but the driving force is low; while at low T a , it is opposite.…”

“…[333][334][335][336][337][338] Recently, the effect of nanoconfinement, for example, ultrathin film on the physical aging has drawn significant interest. [32,160,162,165,170,171,330,332,[339][340][341][342][343][344][345][346][347] In comparison to the bulk, despite the lower aging rate, an acceleration in physical aging in terms of the timescale to reach equilibrium is observed at the same aging temperature, [32,340] which is related to the depression in T g . By shifting the aging temperature to the same distance from relevant T g , Koh and Simon [32] showed that the aging rates for bulk and ultrathin film PS are comparable.…”

“…The investigations of physical aging in polymer thin films were initially focused on polymer membranes, in which an accelerated aging is observed, and the gas permeability reduces with aging time due to the decrease of free volume . Recently, the effect of nanoconfinement, for example, ultrathin film on the physical aging has drawn significant interest . In comparison to the bulk, despite the lower aging rate, an acceleration in physical aging in terms of the timescale to reach equilibrium is observed at the same aging temperature, which is related to the depression in T g .…”

Nonisothermal Crystallization Kinetics of an Ethylene‐Vinyl‐Acetate: I Calorimetry Versus Rheology

“…Here, we only treat about the basic bulk crystallization kinetics of a commercial ethylene‐vinyl‐acetate (EVA) copolymer normally used in the industrial sectors of packaging with objective to widen the knowledge of its crystallization kinetics as a basic requirement for process modeling and control. The crystallization kinetics is typically investigated with Differential Scanning Calorimetry (DSC) measurements , which are sensitive to phase transitions and material structure reorganization . Shear and elongational rheometry was also proved to be very powerful to investigate complex fluids or microstructured materials and deeply correlate the structural changes in the time and frequency domain .…”