Structural Evolution of Nanograins during Cold Crystallization of Poly(9,9-di-n-octyl-2,7-fluorene) As Revealed via in Situ Small-Angle X-ray Scattering/Wide-Angle X-ray Scattering/Differential Scanning Calorimetry

Abstract

By means of in situ small-angle X-ray scattering/wide-angle X-ray scattering/differential scanning calorimetry (SAXS/WAXS/DSC), structural evolution of poly(9,9-di-n-octyl-2,7-fluorene) (PFO) in a cold crystallization process was quantitatively examined. After removal of background scattering from the fractal-like structure, SAXS profiles obtained during programmed heating of an amorphous PFO specimen unveil a sequence of stages of structural evolution. These include (1) a frozen-in stage below the glass transition temperature (T g ≈ 62 °C), (2) the nucleation of prolate nanograins with radius of gyration R g ≈ 3.3 nm from 65 to 85 °C, (3) growth of the prolate ellipsoids up to R g ≈ 5.0 nm between 95 and 105 °C, and (4) coalescence (and thickening) of the nanocrsytals into oblates (of R g ≈ 10 nm) upon further heating to 145 °C. There were no further changes in morphological features in the subsequent isothermal annealing at 145 °C for up to 1 h, as the size of the coalesced nanograins quickly reached a threshold value where the orientation and attachment of neighboring nanograins via thermally activated Brownian rotation became seriously hindered. Developments in the DSC-determined crystallinity (X c,DSC) and the degree of heterogeneity (Q inv from SAXS) coincided with the nucleation and growth stages, respectively; in contrast, buildup of the WAXS-determined crystallinity (X c,WAXS) proceeded mainly in the subsequent coalescence stage where large nanocrystallites were developed.

Nanoporous Silver Thin Films: Multifunctional Platforms for Influencing Chain Morphology and Optical Properties of Conjugated Polymers

“…For PFO (Figure e,h), the broad backgrounds at q ≈ 0.4 Å −1 and at q ≈ 1.4 Å −1 in both in‐plane and out‐of‐plane profiles were interpreted as scattering from PFO's disordered amorphous or glassy phase and β‐phase chain conformations . The strong and narrow peak with d ‐spacing ≈12.5 Å that can be observed in both in‐plane and out‐of‐plane profiles was believed to correspond to the side chain distance between adjacent interchain‐ordered PFO chains ((200) reflection peak).…”

Formation of mesomorphic domains associated with dimer aggregates of phenyl rings in cold crystallization of poly(trimethylene terephthalate)

“…The mean spacing ξ of the particles is deduced from n p determined by the volume fraction and the size of hard sphere [13].…”

“…50 nm) featuring unusual small-angle scattering emerged; an accompanying formation of nanocrystalline grains (of several nanometer-scale) then evolved within the mesomorphic domains. The formation of the mesomorphic domains indicated the transient coexistence of liquids in two forms in the induction stage of cold crystallization of PTT, as a liquid-liquid phase separation, whereas the physical origin and structural characters of the large-scale mesomorphic domains remained elusive, even though we investigated the crystallization behavior of PTT [22][23][24][25][26][27][28], and Jeng and co-workers clarified the mechanism of nanograin growth during the cold crystallization of poly (9,9-di-n-octyl-2,7-fluorene) [13], syndiotactic poly(styrene) [14] and poly (9,9-di-n-hexyl-2,7-fluorene) [15] on the basis of simultaneous SAXS/WAXS/DSC. Somewhat similar to our observation of the unusual small-angle scattering in the cold crystallization of PTT (devitrification), but in vitrification of noncystalline polymers, Debye and Bueche [29] found an unusual small-angle scattering associated with the existence of long-range fluctuations of correlation length ca.…”

“…[1][2][3][4][5][6] These chain activities before three-dimensional (3D) chain packing (crystallization), a so-called 'pre-ordering', are an important aspect of understanding the relation between structural formation and physical properties. Several authors have considered mesomorphic (or intermediate) phases [7][8][9][10][11][12][13][14][15] or liquid-liquid phase separation [16][17][18][19][20][21] (via mechanism of nucleation and growth or spinodal decomposition) during the preordering. Such a formation of mesomorphic structures during the preordering is associated with a more-or-less ordered packing of parallel chains with significantly favored conformations and enhanced density in zones of semi-ordered arrangements.…”

“…These mesomorphic structures have commonly been observed when crystallization occurs in deep supercooling or near glass transitions. Various interpretative models or mechanisms for the mesomorphic structures (e.g., paracrystalline [7,8], nodular [9], bundle [10,11], nanograin [13][14][15] and spinodal-like [16][17][18][19][20] ) have hence been proposed for various polymers.…”