Observing different dynamic behaviors of weakly and strongly adsorbed polystyrene chains at interfaces

Abstract

Understanding the dynamic behavior of polymer chains adsorbed onto a solid surface is of great importance for elucidating polymer-surface interactions. Here by using sum frequency generation (SFG) vibrational spectroscopy, we probed the conformational changes of weakly adsorbed and strongly adsorbed polystyrene (PS) chains on sapphire surfaces perturbed by a nonsolvent (deuterated water, D2O) and a good solvent (carbon tetrachloride, CCl4). The SFG results indicated that the PS chains in the weakly adsorbed state were flexible and the chain conformation could easily be altered. Differently, the PS chains in the strongly adsorbed state were rigid and the chain conformation could not be changed. The local structural variations of the weakly and strongly adsorbed PS chains at the interfaces were also discussed in detail with respect to the SFG spectral characteristics. These intriguing experimental results shed light on our understanding of molecular behaviors of polymer chains adsorbed onto a solid surface.

Evolution of Irreversibly Adsorbed Layer Promotes Dewetting of Polystyrene Film on Sapphire

“…First, it is worth mentioning that the vibrational signal contribution from the loops need to be neglected since such nanoarchitectures basically hold the ensemble-averaged inversion symmetry at the interface. Second, according to the reported literature, 29,47,50 the strong interaction with the substrate should keep the adsorbed chains in the irreversibly adsorbed layer rigid. It is thus feasible to attribute the signal change (after ∼45 h, Figure 3) to the local structural alteration within the train segments.…”

“…The polymer thin films were annealed at ∼150 °C up to ∼160 h. At different time intervals, the SFG spectra of the sapphire/PS interface were collected. As shown in Figure 2, at the beginning, i.e., ∼5 h, the following vibrational bands can be observed, which include symmetric stretching (ss) mode of the backbone methylene group (∼2850 cm −1 , CH 2 ), ss mode of the end methyl group from the initiator (∼2875 cm −1 , CH 3 , weak here), stretching of the backbone methyne group (∼2910 cm −1 , CH), 47 asymmetric stretching (as) mode of the backbone methylene group (CH 2 , ∼2935 cm −1 , strong here, which may overlap with the Fermi resonance of the end methyl group, weak here), as mode of the end methyl group (∼2960 cm −1 , CH 3 ), combination mode (∼2990 cm −1 ), ν 20b (∼3023 cm −1 ), ν 7a (∼3035 cm −1 ), ν 7b (∼3050 cm −1 ), ν 2 (∼3060 cm −1 ), and ν 20a (∼3085 cm −1 ) modes of the pendent phenyl ring group. 47−51 Table 1 lists the detailed band assignments.…”

Interfacial Irreversibly and Loosely Adsorbed Layers Abide by Different Evolution Dynamics

“…A polymer chain can be adsorbed even onto a weakly attractive substrate since the enthalpy gain for individual segments in contact with the substrate can add up to a big one, leading to the difficulty of the reverse process, namely, chain desorption. − The collective strong physisorption between polymer chains and a substrate affects a number of practical applications, such as adhesion, coating, wetting, and colloidal stabilization. − When the adsorption occurs from the polymer melt or concentrated solution, an irreversibly adsorbed layer (or Guiselin layer) can be formed over time . To date, study on the irreversibly adsorbed layer has been a focusing point in the field of polymer physics, with plenty of experimental, theoretical, and simulation investigations covering chain conformation, density, coverage, thickness, loop size distribution, and structural relaxation. ,− Here, our interest will focus on the chain structural evolution within the melt/substrate interface.…”

“…In Panel A of Figure , taking the PS sample with M w of 168 kDa as an example, the trace of the SFG spectra in the frequency range from 2800 to 3000 cm –1 for the irreversibly adsorbed layer was shown. The observed vibrational bands, summarized in Table , included the symmetric stretching (ss) mode of the backbone methylene group (∼2850 cm –1 , CH 2 ), the ss mode of the end methyl group from the initiator (∼2875 cm –1 , CH 3 ), the stretching mode of the backbone methylene group (∼2905 cm –1 , CH), and the asymmetric stretching (as) mode of the backbone methylene group (CH 2 , ∼2935 cm –1 ). − These spectra were fitted by using the Lorentz equation. It is worth mentioning that the vibrational signals from the side phenyl groups were not considered because of their local freedom. ,, To reveal the interfacial evolution dynamics, the vibrational band area in this frequency range was integrated and plotted in terms of the annealing time, as shown in Panel B of Figure .…”

“…It is worth mentioning that the vibrational signals from the side phenyl groups were not considered because of their local freedom. 12,13,35 To reveal the interfacial evolution dynamics, the vibrational band area in this frequency range was integrated and plotted in terms of the annealing time, as shown in Panel B of Figure 3. In this way, the statistical error due to the spectral shape distortion can be minimized.…”