Thermodynamics and kinetics of crystallization of flexible molecules

Time and Temperature Evolution of the Rigid Amorphous Fraction and Differently Constrained Amorphous Fractions in PLLA

“…The classical description of semi-crystalline polymers as constituted by two distinct phases, amorphous and crystalline, was proven to be incomplete and insuffi cient for a full rationalization of the micro and macroscopic properties. [ 1 ] As the decoupling between the crystalline and amorphous phases is in general partial, due to the length of the polymer molecules, which is much higher of its higher free volume. [6][7][8][9] The quantifi cation of this nano phase is therefore a crucial step in the characterization of a polymeric material, since different processing conditions affect in different ways the evolution of the crystalline and amorphous fractions.…”

“…It is generally named rigid amorphous (RA) fraction, its mobility being lower than that of the unconstrained amorphous phase, which is usually addressed as mobile amorphous (MA) fraction. [ 1 ] It was recently proved that many macroscopic properties, such as, for example, thermal, mechanical, and gas permeability properties, can be properly rationalized by taking into account not only the relative percentage of the crystalline and amorphous phases but also the content of the RA interphase. [2][3][4][5][6][7][8][9] For example, the RA fraction infl uences the elastic modulus, with a behavior close to that of the crystal phase, [2][3][4][5] and affects also the gas barrier properties, but, in this case, with a behavior completely different from that of the crystal phase, because…”

An Emerging Unified View of Dynamic Interphases in Polymers

“…[ 9 ] While this fi eld has most heavily focused on polymers [ 4,6 ] and small molecules liquids [ 7,10,11 ] confi ned in thin fi lm or pore geometries, polymers with internal nanostructure, such as those shown [ 12 ] in Figure 1 , have been reported to exhibit similar alterations in dynamics for half a century or more. These observations include the following: deviations of T g from pure-state values in block copolymer nanodomains, noted as early as the 1960s; [13][14][15][16][17][18][19][20][21] shifts in segmental dynamics around particles in nanocomposites [22][23][24][25][26][27][28][29] and fi lled rubbers, [30][31][32][33][34] which are believed to contribute to mechanical reinforcement effects in these systems; observation of a rigid amorphous fraction with suppressed segmental dynamics and enhanced T g around crystalline domains in semicrystalline polymers; [ 35 ] and evidence of suppressedmobility domains surrounding ionic aggregates in ionomers. [36][37][38] Despite strong parallels in the phenomenology of near-interface dynamics in these materials, they have commonly been treated as fundamentally distinct systems, each with unique underlying physics.…”

“…The proposed mechanisms underlying these observations can generally be divided into three categories. First, the literatures of ionomers and semicrystalline polymers have viewed chain connectivity effects related to cross-linking and dangling or bridging chains [ 35,39 ] as being mechanistically central to these observations. On the other hand, the block copolymer literature has often attributed T g shifts to thermodynamic mixing effects near interfaces.…”

Two timescales in polymer solidification: processing vs polymer crystallization

“…By far the most important is certainly Differential Scanning Calorimetry able to collect, in different modes, data on crystallization and melting with characteristic times down to 10-100s, certainly the "fastest" method if one compares with the majority of those available. A high accuracy is obtained and one can collect all sort of information related to temperature dependence of overall crystallization kinetics or identify peculiar mechanisms recently summarized [1 ] Although this work is not aiming to examine all these efforts in detail it is clear that the time range explored is by far different with respect to processing conditions where characteristic times are of the order of 1-10ms at least 4 orders of magnitude smaller. A situation encountered only on studying another dynamic process: that of glass transition.…”