Measuring the Degree of Crystallinity in Semicrystalline Regioregular Poly(3-hexylthiophene)

By using a combination of wide-angle X-ray diffraction (WAXD), mass density, and ¹³C solid-state nuclear magnetic resonance (NMR) measurements, a quantification of the absolute degree of crystallinity in regioregular poly­(3-hexylthiophene) (rr-P3HT) is presented. A regiorandom P3HT (rra-P3HT), lacking long-range order, was used to separate the crystalline contribution from the total scattering in WAXD, thus yielding degrees of crystallinity in the range of 47–56% at room temperature for three different rr-P3HTs. For the same rr-P3HT with identical processing history, NMR yields degrees of crystallinity that are consistently ∼10% greater than that obtained by WAXD, which can only be explained by ordered chain segments in the amorphous phase. NMR results also suggest that rra-P3HT contains weakly ordered chain segments, which likely contribute to an underestimation of degree of crystallinity when determined from mass density measurements, if rra-P3HT is used to approximate a fully amorphous P3HT. The results shown in this study provide direct proof of three different types of P3HT chain segments: crystallites (i.e., long-range ordered chain packing), amorphous phase (i.e., disordered chain packing), and short-range ordered chain packing embedded in the amorphous phase. The presence of the short-range ordered chain packing is particularly important when correlating the morphology to macroscopic charge transport properties in P3HT-based devices. In general, those locally ordered chain segments, though not constituting a distinct phase, are believed to be of critical importance in determining the transport characteristics of conjugated semiconducting polymers with or without a distinct crystalline phase present

MWF maps generated by simulation of MESE data using brain phantom.

<p>Brain phantom (A) was used to simulate MESE data, and rMSE was calculated at different SNRs (B). The corresponding MWF maps are shown in C at SNR = 100, 500, 1000 (top to bottom).</p

MWF maps of healthy MESE scans acquired at 1.5T.

<p>MWF computed from healthy <i>in vivo</i> anisotropic MESE scans acquired at 1.5T. Conventional reconstruction (top), spatial constrained reconstruction (middle) and anatomical T2 FLAIR images (bottom). Two consecutive axial slices at the level of thalamus and putamen are shown.</p

Examination of elevated MWF, relaxation curves and T2 distribution.

<p>Detailed investigation of elevated MWF in deep gray matter. Relaxation curves for three brain areas are shown on the middle panel: WM, GM and deep brain GM – these areas are denoted by circles on the MWF map generated from spatial constrained method (left panel). Dark red circle indicates the WM area, blue indicates the GM area, and green indicates the GM with fast relaxation rate area. The fitted T2 distribution from each region is shown in the right panel - curves correspond to the ROI average</p

MESE experiment using test tubes.

<p>MESE experiment at 1.5T on 10 test tubes filled with water doped with varying concentrations of Gd and MnCl2, hence varying T2 times measured by single exopnential fit. Raw MR signal intensities of a middle slice of the 5^th echo (40 ms) are shown using idicated color scale (arbitrary scanner units). The text arrows show the average MWF estimated by the propsoed algorithm within each test tube and its nominal T2 in parentheses. The “true” MWF would be 100% for the two right-most tubes, and 0% for the rest. These results indicated good accuracy of our agorithm on MESE data.</p

List of parameters to be fitted, per voxel.

<p>Their initial guess and allowable range, used during constrained optimization, are also shown.</p

Illustration of demyelinating lesion in MWF map of a MS patient.

<p>Two axial slices of proposed MWF map of a MS patient. Note the excellent depiction of demyelinating lesions (arrows) and improved definition of callosal and peripheral white matter.</p

Comparisons of Mean Coefficient of Variance (COV) of MWF obtained for the T2prep spiral sequence in various ROIs between proposed and conventional methods.

<p>Comparisons of Mean Coefficient of Variance (COV) of MWF obtained for the T2prep spiral sequence in various ROIs between proposed and conventional methods.</p

MWF maps of another healthy 3D T2prep adiabatic spiral brain scan.

<p>Another healthy brain 3D T2prep adiabatic spiral example, with MWF (top) and T2-weighted image (bottom) of two adjacent axial slices.</p

Histogram and COV of regional MWF, histogram averaged over all regions.

<p>(A) Histogram of regional MWF of each ROI averaged over 10 MS subjects. MWF in WM has a higher distribution than GM, and the two are statistically well separated, with p<0.001 from a student’s t-test between the WM and GM regions (B) Histogram from different subjects of MWF averaged over all regions. A t-test between the WM and GM groups yielded p<0.001. (C) COV of regional MWF for each subject, indicating low variability in regional variations in both WM and GM.</p