Wetting induced instabilities in miscible polymer blends

Thomas, Kerrie L.; Clarke, Nigel; Poetes, Rosa; Morariu, M.; Steiner, Ullrich

doi:10.1039/c0sm00046a

Cited by 37 publications

(40 citation statements)

References 35 publications

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“…38,39 For PVME/PS this was demonstrated for instance by X-ray photoelectron spectroscopy (XPS) 40 or spectroscopic ellipsometry. 41 The preferential surface segregation of the one component will lead to thickness-dependent phase transition and dewetting temperatures. 42−44 From a general point of view the surface segregation can be considered as a self-assembling process, which leads to a structure with a nanometer thin layer on the polymer/air interface, having a higher molecular mobility.…”

Section: Introductionmentioning

confidence: 99%

Unambiguous Evidence for a Highly Mobile Surface Layer in Ultrathin Polymer Films by Specific Heat Spectroscopy on Blends

2015

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Despite the decade long controversial discussion on the effect of nanometer confinement on the glass transition temperature (T g ) of ultrathin polymer films, there is still no consistent picture. Here, the dynamic calorimetric glass transition of ultrathin films of a blend, which is miscible in the bulk, is directly investigated by specific heat spectroscopy. By a self-assembling process, a nanometer thick surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic calorimetric T g in dependence on the film thickness, it was shown that the T g of the whole film was strongly influenced by that nanometer thick surface layer, with a lower T g . Since the observed thickness dependence of the dynamic T g is similar to the thickness dependence of the T g for thin films of homopolymers, it is concluded that also for homopolymer a highly mobile surface layer is relevant for the widely observed T g depression.

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Section: Introductionmentioning

confidence: 99%

Unambiguous Evidence for a Highly Mobile Surface Layer in Ultrathin Polymer Films by Specific Heat Spectroscopy on Blends

2015

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“…Several general theoretical results have emerged, in particular that instabilities leading to dewetting can be triggered through the coupling of phase separation and height variation [68,76] and that a binary component film will be less stable due to coupling of fluctuations of height and composition than if these fluctuations were not coupled [77]. These studies clearly indicate the importance of the coupling between phase separation and dewetting/surface roughening.…”

Section: Surface Roughening In Polymer-blend Filmsmentioning

confidence: 89%

Fundamentals of Phase Separation in Polymer Blend Thin Films

Coveney¹

2015

Springer Theses

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confidence: 99%

“…Pattern formation in polymer blend thin films, in which surface roughening shadows the phase separated morphology, is incredibly common [9,10]. Theoretical results suggest that, generally, the coupling of phase separation and height variation makes films less stable [11] and can trigger instabilities [12,13].A variety of models for multicomponent deformable fluid films have been investigated. The "Clarke model" (name introduced here) utilized nonequilibrium thermodynamics based upon a free energy functional, demonstrating that phase separation generally couples to dewetting [12].…”

mentioning

confidence: 99%

Pattern Formation in Polymer Blend Thin Films: Surface Roughening Couples to Phase Separation

Coveney

Clarke

2014

Phys. Rev. Lett.

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We introduce a model for thin films of multicomponent fluids that includes lateral and vertical phase separation, preferential component attraction at both surfaces, and surface roughening. We apply our model to thin films of binary polymer blends, and use simulations of different surface-blend interaction regimes to investigate pattern formation. We demonstrate that surface roughening couples to phase separation. For films undergoing lateral phase separation via a transient wetting layer, this results in distinct stages of roughening as the film evolves between different phase equilibria. DOI: 10.1103/PhysRevLett.113.218301 PACS numbers: 82.35.Lr, 64.75.St, 64.75.Va, 68.55.am Semiconducting polymer devices, such as photovoltaic films, can gain performance enhancements from phase separated morphologies. Since polymer films are prone to surface roughening, understanding how phase separation couples to dewetting is particularly important. This interplay was highlighted by Walheim et al. for spin-cast polymer films [1] and has been repeatedly observed, e.g., phase separation in symmetrically surface-segregating films [2-5], lateral phase separation via a transient wetting layer [6,7], and phase separation proceeding from the surface as the solvent evaporates [8]. Pattern formation in polymer blend thin films, in which surface roughening shadows the phase separated morphology, is incredibly common [9,10]. Theoretical results suggest that, generally, the coupling of phase separation and height variation makes films less stable [11] and can trigger instabilities [12,13].A variety of models for multicomponent deformable fluid films have been investigated. The "Clarke model" (name introduced here) utilized nonequilibrium thermodynamics based upon a free energy functional, demonstrating that phase separation generally couples to dewetting [12]. A model based on the Navier-Stokes Cahn-Hilliard equations in the lubrication approximation showed that concentration gradients can create a roughened pattern that mirrors the underlying phase separation [14]. However, the film composition has no vertical dependence in these models, so a meaningful preferential surface attraction of blend components cannot be included. Two-layer models exist, including models with immiscible fluid layers [15,16] and layers with a diffuse boundary for films with no preferential surface attraction [17]. However, a general vertical composition dependence, which could allow vertical phase separation to occur during a simulation, is typically not included [9], though such a case has been studied with regards to stability but not simulated [18]. An exception is a model of surface roughening of polymer blend films, although this model is not based upon a dewetting film [19].This Letter presents a model formulation of a binary blend thin film which, by way of including a general vertical dependence of composition, can be utilized for a full time simulation of coupled dewetting and phase separation, including (i) both lateral and vertical phase separat...

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Wetting induced instabilities in miscible polymer blends

Cited by 37 publications

References 35 publications

Unambiguous Evidence for a Highly Mobile Surface Layer in Ultrathin Polymer Films by Specific Heat Spectroscopy on Blends

Unambiguous Evidence for a Highly Mobile Surface Layer in Ultrathin Polymer Films by Specific Heat Spectroscopy on Blends

Fundamentals of Phase Separation in Polymer Blend Thin Films

Pattern Formation in Polymer Blend Thin Films: Surface Roughening Couples to Phase Separation

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