Quantitative orientation studies of crystalline polymer films by small angle light scattering

Two new analyses for small angle light scattering (SALS) were tested in the quantitative study of orientation in polymer films. Uniaxially oriented samples of linear low density polyethylene (LLDPE) and polypropylene (PP) were prepared and then characterized by SALS. These results were contrasted with measurements made by infrared dichroism. It was found that the SALS results correlated with those measured by the infrared dichroism. These results revealed that molecular orientation is concurrent with morphological anisotropy which was measured by SALS. Further support of this observation is given by optical microscopy which showed morphological changes with increasing orientation. The first analysis used was the application of the pseudo-invariant with an angular weighting function, sin²μ The average value of sin²μ was calculated over the range of 0 to π/2 and then used in an orientation factor which allowed comparisons with infrared studies. The second analysis employed an inverse two dimensional Fourier transform of the scattering pattern. The computation produced a two dimensional correlation function in which the correlation length was calculated in the machine direction (MD) and the transverse direction (TD). This analysis allowed an evaluation of the orientation in the sample as well as giving characteristic structural lengths in the sample.