18.4 The small-angle X-ray seattering data for a polystyrene-block-polyisoprene copolymer with a lamellar morphology in Figure 18.12 show maxima at q values of approximately 0.264,0.542 and 0.819 nm-' Determine the lamellar plane spacing of the domains and the thickness of the polyisoprene layers, given that the volume fraction of polystyrene frs is 0.64. Justify any assumptions you might make. Figure 18.12 3 2 logNq)] 15 gm To solve this problem use : ni = 2d sin e Bragg's law for X-ray scattering is d is the spacing of the planes, n is the order of the reflection 40 sin e 2 d = q= 2 9 =