Thermotropic properties of organic nanocrystals embedded in ultrasmall crystallization chambers

Journal of Physical Chemistry B

Volumn 109, Issue 4, 2005, Pages 1392-1399

  Ha, Jeong Myeong ^a   Hillmyer, Marc A ^a   Ward, Michael D ^a  

^a UNIVERSITY OF MINNESOTA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CRYSTALLIZATION CHAMBERS; ORGANIC NANOCRYSTALS; POLYLACTIDE (PLA); THERMOTROPIC PROPERTIES;

ALCOHOLS; BLOCK COPOLYMERS; CRYSTALLIZATION; GLASS; MELTING; ORGANIC ACIDS; POLYSTYRENES; POROUS MATERIALS;

NANOSTRUCTURED MATERIALS;

EID: 13444274463     PISSN: 15206106     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp045488v     Document Type: Article

References (27)

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16. HFPD is a precursor to a fluorinated polymer. See Johncock, P.; Hewins, M. A. H. J. Polym. Sci., Part A: Polym. Chem. 1975, 13, 807-814.
17. Haller, W. Nature 1965, 206, 693-696.
18. The CPG used here was obtained from CPG, Inc., Lincoln Park, NJ. CPG is prepared from borate-silicate composite glass from which the borate phase is leached to produce a silica glass with uniform pores.
19. The amount of HFPD loading when imbibed from the melt ranged from 70 to 120 wt% in p-PS and 70-170 wt% in CPG, the larger values achieved for the largest pore sizes. These values are consistent with nearly complete loading of the available pore volume.
20. 3, Z = 2, 173 K).
21. inst, is the instrumental peak broadening], and 6 is the Bragg angle. See Cullity, B. D. Elements of X-ray Diffraction; Addison-Wesley: Reading, MA, 1978. Klug, H. P.; Alexander, L. E. X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials; Wiley: New York, 1974.
22. inst, is the instrumental peak broadening], and 6 is the Bragg angle. See Cullity, B. D. Elements of X-ray Diffraction; Addison-Wesley: Reading, MA, 1978. Klug, H. P.; Alexander, L. E. X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials; Wiley: New York, 1974.
23. The sizes of HFPD nanocrystals were estimated from the Scherrer equation, using the fwhm for the (010) reflection (after baseline correction and fitting to a Gaussian form). This analysis revealed that the fwhm of the nanocrystals was always greater than that of the bulk crystals, as anticipated. The crystal sizes never exceeded the channel diameter, with the crystals grown in the larger channels appearing to be much smaller than the channel dimensions (crystal size = 16, 17, and 23 nm for 23-, 32-, and 40-nm p-PS and 17, 21, and 37 nm for 7.5-, 23-, and 55-nm CPG, respectively). This apparent discrepancy is likely due to the increased difficulty in measuring the fwhm accurately because the breadth of the peak approaches the instrument limit as the crystal size is increased. The sizes of the R-MAA nanocrystals were estimated from the fwhm of the diffraction peak at 2θ = 20.2°. The reliability of these measurements, however, is questionable because the single-crystal structure is unknown and the existence of multiple (bkl) reflections under this diffraction peak, which would affect the fwhm, cannot be excluded.
24. According to the manufacturer's specifications at least 80% of the pore volume lies within 10% of the nominal pore size. The remaining 20% of the pore volume is unspecified.
25. Scherer, G. W. Cem. Concr. Res. 1999, 29, 1347-1358.
26. melt-sub, is smaller on glass surfaces than on PS surfaces, which in turn suggests that the slopes in Figure 6 for CPG should be larger than those for PS, contrary to the observation. This apparent discrepancy most likely reflects the unique environment of the ultrasmall channels, in which the walls are predominantly in contact with either the solid phase or the melt, with little free surface in contact with air. Consequently, deductions based on simple contact angle measurements, in which the substrate surface is in contact with air and may dominate the wetting characteristics, may be not valid. This argues that the model in Scheme 2 may indeed be a reasonable one.
27. Sands, B. W.; Kim, Y. S.; Bass, J. L. J. Chromatogr. 1986, 360, 353-369.