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The order-disorder transition of a sphere-forming block copolymer thin film was numerically studied through a Cahn-Hilliard model. Simulations show that the fundamental mechanisms of pattern formation are spinodal decomposition and nucleation and growth. The range of validity of each relaxation process is controlled by the spinodal and order-disorder temperatures. The initial stages of spinodal decomposition are well approximated by a linear analysis of the evolution equation of the system. In the metastable region, the critical size for nucleation diverges upon approaching the order-disorder transition, and reduces to the size of a single domain as the spinodal is approached. Grain boundaries and topological defects inhibit the formation of superheated phases above the order- disorder temperature. The numerical results are in good qualitative agreement with experimental data on sphere-forming diblock copolymer thin films. [ABSTRACT FROM AUTHOR]

ABSTRACT This work explores coatings with thermally switchable wetting behavior, based on block copolymers that possess both hydrophilic and hydrophobic segments. The amphiphilic block copolymers were synthesized by coupling allyl-ended poly(ethylene oxide) (PEO) and hydride-ended poly(dimethylsiloxane) (PDMS) oligomers via a Pt catalyst. One near-symmetric diblock possessed an order-disorder transition temperature ( TODT) of 64 °C. When cooled through TODT in ambient air, the PDMS domains wet the film's surface, producing a hydrophobic coating with a water contact angle (CA) = 90°. However, when cooled in humidified air, hydrophilic PEO domains form at the surface, yielding CA = 30-40°. The coatings can be reversibly switched between the two states by reheating above TODT, in the appropriate environment, and then cooling, rapidly generating the desired room-temperature surface wettability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 135-140 [ABSTRACT FROM AUTHOR]

In this contribution, we use dissipativeparticle dynamics simulations to investigate the orientations of lamella-formingcopolymers with two blocks of equal molecular weight confined in thinfilms. We employ neutral and symmetric interactions between the copolymerblocks and the walls, a situation for which contradicting observationshave been made in experiments and previous theoretical studies. Ourmodel takes into account a realistic degree of conformational asymmetrybetween the blocks, which stems from unequal Kuhn lengths of the constituentmonomers. We perform a thorough scaling analysis to exclude finitesize effects, and find, in agreement with experiments, a remarkablecascade of morphological transitions from parallel to perpendicularorientations when the film height is varied. We demonstrate that theemergence of a stable parallel configuration stems from entropic effectsdue to the conformational asymmetry and the confinement of the system. [ABSTRACT FROM AUTHOR]

Thin films of cylinder-forming polystyrene–poly(n-hexyl methacrylate) diblock copolymers, PS–PHMA,are attractive as nanolithographic templates, an application whichdemands good control over the thin-film structureyet the qualityof order achieved to date in PS–PHMA films has fallen shortof this ideal. In the present work, a series of PS–PHMA diblocksof varying composition, all forming PS cylinders, are synthesizedand their morphology studied as a function of film thickness in bothnonsheared and shear-aligned films. In nonsheared films, the cylinderaxis orientation relative to the surface switches from parallel toperpendicular as a function of film thickness; this oscillation isdamped out as the fraction of the cylinder-forming block (PS) increases,away from the sphere–cylinder phase boundary. In aligned films,thicknesses which possess the highest coverage of parallel cylindersprior to shear show the highest quality of alignment postshear, asmeasured by the in-plane orientational order parameter of the cylinderaxis. In well-aligned samples of optimal thickness, the quality ofalignment is limited by isolated dislocations, whose density is highestat high PS contents, and by undulations in the cylinders’ trajectories,whose impact is most severe at low PS contents; consequently, polymerswhose compositions lie in the middle of the cylinder-forming regionexhibit the highest quality of alignment. [ABSTRACT FROM AUTHOR]

The control of structure and thermal stability in semicrystalline polymer films remains an important challenge in applications ranging from solar energy devices to packaging films. Here, we demonstrate the ability to dramatically alter the morphology and melting temperature (Tm) of low-molecular-weight linear polyethylene (PE) by employing an innovative vapor-assisted deposition process termed matrix assisted pulsed laser evaporation (MAPLE). We report the ability to tune Tm of PE films by 20 °C by simply adjusting the deposition temperature during MAPLE processing. This unique capability stems from the ability of MAPLE to exploit confined crystallization during thin film growth. In addition, we demonstrate the ability to exploit MAPLE to design PE films that exhibit the same Tm as their melt-crystallized analogues but have an ~25% higher degree of crystallinity. Our investigation offers new insights into how confinement effects in polymer crystallization can be utilized in the emerging field of polymer film fabrication by MAPLE to control structure and key material properties of semicrystalline polymer films. [ABSTRACT FROM AUTHOR]

We study the dynamics of coarsening of a cylinder-forming block copolymer thin film deposited on a prepatterned substrate made of a well-ordered block copolymer monolayer. During thermal annealing the shear-aligned bottom layer drives extinction of the disclinations and promotes a strong orientational correlation, disturbed only by dislocations and undulations along the cylinders of the minority phase. The thin film bilayer system remains stable during annealing, in agreement with self-consistent field theory results that indicate that although the thickness of a stack of two monolayers is not at the optimum thickness condition, it is very close to equilibrium. Phase field simulations indicate that the bottom layer remains undisturbed during annealing and acts as a periodic external field that stabilizes the orientation of those domains that share its orientation. Misoriented cylinders are rapidly reorganized through an instability mechanism that drives the fragmentation of the cylinders. As annealing proceeds, the fragmented cylinders are reconstructed along the direction imposed by the ordered bottom layer. This mechanism removes the disclinations completely while leaving dislocations that can be slowly annihilated during annealing. These results indicate that with appropriate control over a single self-assembling polymeric layer, it should be possible to propagate order in thick block copolymer films and to obtain structures with controlled orientational order. [ABSTRACT FROM AUTHOR]

Flowcoating is a popular techniquefor generating thin (5–200nm), substrate-supported polymer films. In this process, a reservoirof coating fluid is held between the horizontal substrate and a nearlyhorizontal blade above the substrate; a film of fluid is drawn outof the reservoir by moving the substrate. Accelerating the substrateproduces a film with a thickness gradient, particularly useful forhigh-throughput measurements where film thickness is an importantparameter. The present work compares experimental film thickness profileswith a model based on a Landau–Levich treatment to identifythe experimental parameters which govern film thickness. The key parametersare the capillary number and the radius of curvature of the reservoir’sstatic meniscus, which is set by the blade angle, gap height, solutionreservoir volume, and contact angles of the fluid with the blade andsubstrate. The results show excellent quantitative agreement withthe first-principles model; the model thus provides a design approachwhich allows a user to produce polymer thin films of virtually anydesired thickness profile. [ABSTRACT FROM AUTHOR]

Experimental data on thin films of cylinder-forming block copolymers (BC)--free-standing BC membranes as well as supported BC films--strongly suggest that the local orientation of the BC patterns is coupled to the geometry in which the patterns are embedded. We analyze this phenomenon using general symmetry considerations and numerical self-consistent field studies of curved BC films in cylindrical geometry. The stability of the films against curvature-induced dewetting is also analyzed. In good agreement with experiments, we find that the BC cylinders tend to align along the direction of curvature at high curvatures. At low curvatures, we identify a transition from perpendicular to parallel alignment in supported films, which is absent in free-standing membranes. Hence both experiments and theory show that curvature can be used to manipulate and align BC patterns. [ABSTRACT FROM AUTHOR]