Interdomain spacing

Sample Interdomain spacing, nm Scattering intensity, a.u. Graft MW... 

PUs usually possess the microphase separated structure with interdomain spacing of 10-20 nm. But what happens if the film thickness is smaller than the spacing As a rule, PUs block copolymers loose the microphase separated structure with the thickness which is smaller than the periodic structure, or forms an island structure, in which the periodic structure exists [197]. Decreasing the PUs film thickness, the size of the microphase separated domains decrease as evidenced by AFM. Decreasing the film thickness the aggregation of the HS chains becomes weaker [131]. 

SAXS is a more precise tool to quantitatively evaluate the two-phase structure of PU by providing the data of interdomain spacing, domain size, and interfacial thickness [40]. Figure 7.28 illustrated typical SAXS intensity profiles (/(S)S vs. 20) for PU/C20A nanocomposites. The one-dimensional correlation function F(Z) that is related to the electron density distribution within specimens is expressed as follows ... 

Figure 3. The changes of the interdomain spacing (D) with temperatures obtained during heating at a rate of 1 "C/min for the as-cast samples of (a) Vector 4111 and (b) SI-Cl.

As indicated in Fig. 2.6, the 1-D interdomain spaces correspond to the primary maxima on the curves of the correlation function / (r). In addition, the domain sizes of the hard and soft phases can be extracted from the curves of the correlation function / (r). The 3- and 1-D inderdomain spaces of the segmented polyurethanes are presented in Table 2.3. 

In general, the interdomain space of the segmented polyurethanes decreases with an increase of HSC. But at HSC = 45%, the interdomain space increases slightly. This may be attributed to the discontinuity-continuity transition of the hard phase. The decrease of the interdomain space with the increase of HSC suggests the increasing concentration of the hard domains, i.e., the physical cross-linking density of the polyurethane cross-linked networks. 

From the positions of the maxima of the scattering profiles, the interdomain spaces, d, of the segmented polyurethanes can be evaluated with Bragg s law ... 

Table 4.6 Thermal properties and interdomain spacings of T -SIVIPUs with urethane chains as soft segments...

Ryan and coworkers investigated the effect of chain extenders on the morphology of flexible PU foams by using SAXS, Fourier transform infrared spectroscopy and rheometry [44]. By the addition of chain extenders, the onset of microphase separation was delayed and the interdomain spacing was increased. The effect was found to strongly depend on the chemical structure of the chain extenders and the compatibility between chain extenders and urea segments... 

Table 10. SAXS-based parameters of the microphase-separated structure of the acid polyurethanes of Table 9. Dj and are values of the interdomain spacing, the calculated thickness of the HS lamellar-like microdomains, and the HS length [65]...

For the acid ionomers, SAXS curves show the intensity maximum, characteristic of the microphase-separated PUs [7], only for E1.5B2H. For the salt ionomers, a second intensity maximum is observed at higher q values, characteristic of ionic aggregation [58-60]. The results suggest that for the acid ionomers the DMS increases upon HS extension [7]. For the salt ionomers the microphase separation is preserved, but is less pronounced [49]. The values of the Lorentz-corrected interdomain spacing are about 16 nm for the microphase-separated morphology and about 6 nm for the ionic aggregation, i.e., similar to those in the M series. 

Figure 4 (a) Interfacial area A and (b) interdomain spacing D as functions of composition for different levels of segregation. The inserts show the corresponding values for the double diamond (D) and hexagonally perforated lamellar (PL) structures (dashed lines) in comparison to the double gyroid (solid line). Reprinted with permission from Matsen, M. W. Bates, F. S. J. Chem. Phys. 1997, 106 6), 2436-2448. ... 

Background scattering corrected SAXS spectra are represented in figure 3. The peak position is related to the mean interdomain spacing, d, by d=27t/qniax where q ax is the peak scattering vector. 

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