Structures of Partially Fluorinated Bottlebrush Polymers in Thin Films

Abstract

We performed multiscale molecular dynamics (MD) simulations of bottlebrush polymers with fluorinated side chains to investigate the influence of the bottlebrush architecture on the spatial distribution of fluorinated moieties. In thin films, coarse-grained MD simulations reveal that interfaces are characterized by backbone depletion with side chains at the interface oriented parallel to the surface. At the molecular level, atomistic MD simulations show that fluorine atoms in the bottlebrush are preferentially located at air–film interfaces. Both simulation results indicate enrichment of fluorinated moieties at the air–film interface. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) confirms the enhancement of fluorinated moieties in both bottlebrush and linear copolymer films. ToF-SIMS also shows that for long linear chains the difference between the concentration of fluorinated moieties at the air–film interface and the concentration at the bulk or at the middle of the film is relatively higher than those observed in shorter linear chains (macromonomers) or bottlebrushes. Although there are differences in the distributions of fluorine moieties between linear chains and bottlebrushes, simulations suggest that the effect of polymer architecture on contact angle and surface energy is only significant at low molecular weights. Measurements of the contact angle of films composed of different modestly high molecular weights of linear chains and bottlebrushes do not show a significant difference in the value of the contact angle, in a way restricting the tunability of surface energy and contact angle via polymer architecture. With these results, our study provides insights into the effective use of partially fluorinated bottlebrush polymer for directed self-assemblies at surfaces in thin films. Specifically, achieving a high degree of difference in surface energies for fluorinated thin films is limited to films with low molecular weight constituents, and the effect of molecular architecture is subtle, suggesting it is insufficient to only rely on this strategy to further lower the surface energy of these films for applications directed toward tuned wettability, adhesive interactions, and fouling resistance.

Mapping the Interfacial Chemistry and Structure of Partially Fluorinated Bottlebrush Polymers and Their Linear Analogues

“…This physical picture is in line with current and previous MD simulations. 25 Based on these observations, one would expect to see a much larger range of orientational angles for the −OCH 2 groups, which is indeed observed and tabulated in Table 2. Notably, the orientational angles for the −OCH 2 group span a range from 32.5°± 11.5°to 78.75°± 10.75°for the linear and bottlebrush polymers, qualitatively indicating that the topmost layer, i.e., the air exposed functional groups, for the polymers is different from a structural perspective but is chemically terminated with the same species.…”

“…This is consistent with contact angle measurements recently reported that show similar wetting for polymer samples; only for very small oligomers are changes in the energies predicted. 25 This makes sense since the fluorinated side chains are preferentially arranged at the surface, which then forces the −CH 3 groups attached to the methacrylate chain to align more parallel to the interface, which is observed in the orientational angles measured by SFG.…”

“…24 Those simulations and experiments suggested that the effects of entropic constraints of bottlebrush architecture on the spatial distribution of fluorinated moieties are not as strong as the effects of the low surface energy of fluorinated groups when the molecular weight of the bottlebrush is sufficiently large. While previous experiments including TOF-SIMS and contact angle measurements 25 have provided some information about the surface properties and distributions, here we seek to better understand how bottlebrush architecture can affect the surface conformation and distribution of chemical moieties at the level of functional groups.…”

Adaptive Coatings with Anticorrosion and Antibiofouling Properties

“…σ S of the PTFEM coating was close to the σ S values of PTFEM coatings reported in the literature (20-22 mJ m −2 ). [130,131] The σ S of PTFEM, PL, and PH coatings were in the range of 20-25 mJ m −2 , which is considered as a surface energy yielding a minimal adhesion between biofouling and material surfaces. [132,133] After 15 days, PL and PH coatings were less fouled compared with PTFEM and PMMA coatings.…”

Helium Ion Microscopy with Secondary Ion Mass Spectrometry (HIM-SIMS) for the analysis and quantitation of polyolefins

“…[2][3][4][5] As such, research has primarily been focused on characterization of copolymers and polymer blends using ToF-SIMS. [6][7][8][9][10][11] ToF-SIMS has been used to investigate surface chemistry, interfaces, microscopic phases, and to quantitatively map surface specific polymers in blends including styrene-methyl methacrylate random copolymers, ethylene-propylene-diene terpolymers, and polypropylene/ethylene-propylene copolymer blends [12][13][14][15] as well as to determine the molecular weight for a variety of polymers including PE, PP, and polystyrene (PS). 16 The possibility to analyze and distinguish polymers in a blend with nanosized structures becomes increasingly important as properties and performance of such materials can depend on the interfacial segregation, phase separation, and phase coarsening, which can vary in size down to tens of nanometers.…”