Charge-Dependent Microphase Separation in Thin Films from a Multiresponsive Pentablock Quaterpolymer: A GISAXS Investigation

Abstract

Tunable electrostatic interactions in thin films from (C-co-D)-b-B-b-A-b-B-b-(C-co-D)-type pentablock quaterpolymers featuring hydrophobic end blocks as well as pH-responsive and hydrophilic midblocks allow controlling their morphology both by the choice of the pH value during film preparation and the solvent polarity during solvent vapor swelling. The morphological changes were characterized using grazing-incidence small-angle X-ray scattering, and the data analysis was carried out on the basis of simulations of two-dimensional scattering patterns. Dry films prepared at low and at high pH values feature either weakly ordered spheres or totally lack order, respectively. Swelling the former films in water vapor triggers an order-to-disorder transition, which is reversed upon drying, whereas films prepared at a high pH value remain disordered. Upon swelling in toluene vapor, the morphology of films prepared at a low pH value is stable, whereas the ones prepared at a high pH value microphase-separate into a spherical morphology.

Recent advances on the structure–properties relationship of multiblock copolymers

“…When the phase contrast allows it, neutrons scattering is often used as an alternative (“SANS” and “WANS”) but usually suffers from a lower incident flux limiting the resolution in time, being yet of great interest to study phase transitions. Graze incidence small angle X‐ray scattering (GISAXS), where photons are backscattered, is also growingly used to characterize block copolymers thin films 117–119 ; we will, however, not focus on it in this review. Lastly, the backscattered counterpart of WAXS is usually referred as X‐ray diffraction (XRD) by materials scientists studying hard matter in which photons can hardly be transmitted.…”

Highly Tunable Nanostructures in a Doubly pH‐Responsive Pentablock Terpolymer in Solution and in Thin Films

“…Weak diffuse scattering is overall present as a background signal and can be attributed to air scattering and/or scattering from the sample holder (see ref. [ 54 ] for a detailed analysis of the background contributions in the GISAXS patterns). At q z ≈ 0.3 nm −1 , the Yoneda band is located (marked Y in Figure 8), i.e., the region of enhanced intensity between the critical angles of the polymer film (α c,film ≈ 0.17°) and the Si substrate (α c,Si ≈ 0.22°).…”

“…[ 82,83 ] For a spherical nanostructure, the rod would be absent, as was shown by us previously. [ 54 ] Up to pH 7.1, these features remain, and the q y position of the Bragg peak increases to ≈0.30 nm −1 corresponding to D ≈ 21 nm. At pH 7.1 and 8.2, two additional features appear: strong scattering at small q y values especially near the specular peak, which also leads to an apparent broadening of the off‐specular diffuse scattering, and an additional scattering peak below the specular peak at q z ≈ 0.2 nm −1 (marked P in Figure 8).…”

“…Here, the self‐assembly behavior is mainly driven by the segment‐segment interaction parameters between the blocks with additional contributions from the electrostatic interactions and the presence of counterions in regimes I‐a, I‐b, and II. [ 54 ] Based on theoretical work [ 25 ] , the nanostructures in the uncharged state (regime III) are expected to be mainly due to the segregation between the central P2VP blocks and the intermediate PDMAEMA blocks, which form the matrix. The electrostatic interactions in regimes I‐a, I‐b, and II are expected to alter the segregation strength and the phase behavior, facilitated by the difference in dielectric constants of PMMA (dielectric constant ε ≈ 3, ref.…”

GISAXS: A versatile tool to assess structure and self‐assembly kinetics in block copolymer thin films

“…With powerful computer simulations of BCP dynamics such as DPD 81,100,101 and highly flexible software for scattering simulations such as HipGISAXS 42 and Bor-nAgain 43 to calculate GISAXS patterns directly based on DPD output 82 or to fit GISAXS data in delicate detail, a much more detailed understanding of BCP rearrangement processes is evolving. In addition machinelearning approaches are in development to optimize probing the parameter space in autonomous experiments 89 and for automatic identification of scattering features [102][103][104] which will be of significant importance as more complex BCPs with new functionalities are investigated, such as in the study of a pentablock quaterpolymer thin film by Jung et al 105 Not much exploited for polymer science so far is the combination of GISAXS and anomalous scattering. This is due to the fact that there are no relevant absorption edges in the hard X-ray regime (5-20 keV), with the exception of the bromine edge.…”