The solid–polymer melt interface is of great scientific interest due to its vital importance in governing a wide array of physical and mechanical properties of polymer thin films. Recent studies have elucidated the coexistence of two different chain conformations of polymer chains adsorbed on a solid (i.e., loosely adsorbed chains and flattened chains). In this work, film stabilities of the polystyrene (PS) “interfacial sublayer” (composed of outer loosely adsorbed chains and inner flattened chains) and flattened layer (composed of the lone flattened chains) prepared on silicon (Si) substrates are investigated. The atomic force microscopy studies reveal that the as‐rinsed PS flattened layer is subjected to spinodal‐like dewetting during a post‐thermal annealing process even at temperatures below the bulk glass transition temperature. Furthermore, it is found that the surface morphology of the flattened layer can be reversibly changed from a homogeneous pattern under good solvent conditions to spinodal‐like droplets under poor solvent conditions. By contrast, it is found that the PS interfacial sublayer remains stable under both good and poor solvent conditions. These findings illuminate the role which density variations within the adsorbed layers play in the mechanism behind the wetting‐dewetting transition.
- Award ID(s):
- 1944887
- NSF-PAR ID:
- 10298893
- Date Published:
- Journal Name:
- Journal of Polymer Science
- ISSN:
- 2642-4150
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract -
Sequence control in synthetic copolymers remains a tantalizing objective in polymer science due to the influence of sequence on material properties and self-organization. A greater understanding of sequence development throughout the polymerization process will aid the design of simple, generalizable methods to control sequence and tune supramolecular assembly. In previous simulations of solution-based step-growth copolymerizations, we have shown that weak, non-bonding attractions between monomers of the same type can produce a microphase separation among the lengthening nascent oligomers and thereby alter sequence. This work explores the phenomenon further, examining how effective attractive interactions, mediated by a solvent selective for one of the reacting species, impact the development of sequence and the supramolecular assembly in a simple A–B copolymerization. We find that as the effective attractions between monomers increase, an emergent self-organization of the reactants causes a shift in reaction kinetics and sequence development. When the solvent-mediated interactions are selective enough, the simple mixture of A and B monomers oligomerize and self-assemble into structures characteristic of amphiphilic copolymers. The composition and morphology of these structures and the sequences of their chains are sensitive to the relative balance of affinities between the comonomer species. Our results demonstrate the impact of differing A–B monomer–solvent affinities on sequence development in solution-based copolymerizations and are of consequence to the informed design of synthetic methods for sequence controlled amphiphilic copolymers and their aggregates.more » « less
-
null (Ed.)Water + elastin-like polypeptides (ELPs) exhibit a transition temperature below which the chains transform from collapsed to expanded states, reminiscent of the cold denaturation of proteins. This conformational change coincides with liquid–liquid phase separation. A statistical-thermodynamics theory is used to model the fluid-phase behavior of ELPs in aqueous solution and to extrapolate the behavior at ambient conditions over a range of pressures. At low pressures, closed-loop liquid–liquid equilibrium phase behavior is found, which is consistent with that of other hydrogen-bonding solvent + polymer mixtures. At pressures evocative of deep-sea conditions, liquid–liquid immiscibility bounded by two lower critical solution temperatures (LCSTs) is predicted. As pressure is increased further, the system exhibits two separate regions of closed-loop of liquid–liquid equilibrium (LLE). The observation of bimodal LCSTs and two re-entrant LLE regions herald a new type of binary global phase diagram: Type XII. At high-ELP concentrations the predicted phase diagram resembles a protein pressure denaturation diagram; possible “molten-globule”-like states are observed at low concentration.more » « less
-
Colloidal gelation phase diagram has been traditionally characterized using three key factors: particle volume fraction, strength of attraction, and range of attraction. While there's a rich body of literature on the role of attraction strength and particle volume fraction, majority of studies have been limited to short range interactions. Using Brownian dynamics simulations, we explored the effect that the range of attractions has on the microstructure and dynamics of both weakly and strongly attractive colloidal systems. Although gelation occurs significantly faster at high attraction strength, by an order of magnitude compared to low strength, we did not observe any clear trend in gelation-rate with respect to a change in the range of interaction. However, as the attraction range increases in both systems, the final structure undergoes a transition from a single connected network to a fluid of dense clusters. This results in a new gelation phase boundary for long range attractive colloids.
-
Abstract The introduction of oligomeric polystyrene (PS) side chains into the conjugated backbone is proven to enhance the processability and electronic properties of semiconducting polymers. Here, two series of donor and acceptor polymers are prepared with different molar percentages of PS side chains to elucidate the effect of their substitution arrangement on the all‐polymer solar cell performance. The observed device performance is lower when the PS side chains are substituted on the donor polymer and higher when on the acceptor polymer, indicating a clear arrangement effect of the PS side chain. The incorporation of PS side chains to the acceptor polymer contributes to the decrease in phase separation domain size in the blend films. However, the reduced domain size was still an order of magnitude larger than the typical exciton diffusion length. A detailed morphological study together with the estimation of solubility parameter of the pristine PS, donor, and acceptor polymers reveals that the relative value of solubility parameter of each component dominantly contributes to the purity of the phase separated domain, which strongly impacts the amount of generated photocurrent and overall solar cell performance. This study provides an understanding of the design strategies to improve the all‐polymer solar cells.