Role of Molecular Architecture on the Vitrification of Polymer Thin Films

Glynos, Emmanouil; Frieberg, Bradley; Oh, Hyunjoon; Liu, Ming; Gidley, David W.; Green, Peter

doi:10.1103/physrevlett.106.128301

Cited by 93 publications

(141 citation statements)

References 34 publications

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“…The kink in the plot at a temperature T=103˚C is evidence of a glass transition temperature, T g , which is 25 degrees higher than the bulk T g . It is consistent with prior measurements of the thickness dependence of T g of thin films of this polymer, in a larger thickness range [18]. The important point is that the film is strongly adsorbed to the substrate.…”

supporting

confidence: 81%

Wetting of a Multiarm Star-Shaped Molecule

2011

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supporting

confidence: 81%

Wetting of a Multiarm Star-Shaped Molecule

2011

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“…The T g onset was further increased up to >220 °C in the case of thermal imidization at 250 °C for 90 min. Here it is noted that the T g of thin films (interlayers) can be further reduced from the values measured for bulk (powder) samples as reported in previous studies 41, 43, 44, 45…”

Section: Resultsmentioning

confidence: 69%

High‐Efficiency Polymer:Nonfullerene Solar Cells with Quaterthiophene‐Containing Polyimide Interlayers

et al. 2018

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Interfacial layers (interlayers) are one of the emerging approaches in organic solar cells with bulk heterojunction (BHJ) layers because the solar cell efficiency can be additionally improved by their presence. However, less attention is paid to the use of interlayers for polymer:nonfullerene solar cells, which have strong advantages over polymer:fullerene solar cells. In addition, most polymers used for the interlayers possess a low glass transition temperature (T g). Here, it is demonstrated that two types of quarterthiophene‐containing polyimides (PIs) with high T g (>198 °C), which are synthesized using pyromellitic dianhydride (PMDA) and cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CTCDA), can act as an interfacial layer in the polymer:nonfullerene solar cells with the BHJ layers of poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) and 3,9‐bis(2‐methylene(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene) (ITIC), or (3‐(1,1‐dicyanomethylene)‐1‐methyl‐indanone)‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene) (IT‐M). Interestingly, the efficiency and stability of devices are improved by the PMDA‐based PI interlayers with a stretched chain structure but degraded by the CTCDA‐based PI interlayers with a bended chain structure.

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“…58 Here, compared to the linear polymer (which showed the most T g suppression), as the number of arms increased or as arms got shorter, systems generally showed less T g suppression and ultimately, in some cases, T g enhancement. With respect to qualitative interpretation in the context of our model, this would correspond to a stronger interaction (λ) between the branched polymer and substrate, and this might not be surprising given the expectation (discussed in ref 58) that star polymers should tend to be attracted toward an interface (relative to linear).…”

Section: Resultsmentioning

confidence: 96%

Effect of Interfaces on the Glass Transition of Supported and Freestanding Polymer Thin Films

2015

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We investigate the glass transition behavior in polymer thin films using a model equation-of-state approach, which involves molecular parameters whose values are determined from fits to bulk information only (pressure− volume−temperature and surface tension data). Following an earlier proof-ofconcept application to freestanding polystyrene (PS) films, here we both extend the study to poly(methyl methacrylate) (PMMA) films and generalize the model so that it is applicable for either freestanding or supported films. In the case of the freestanding PMMA film, model predictions for the T g suppression (relative to bulk) as a function of film thickness are in very good agreement with the corresponding experimental data, reflecting the fact that freestanding PMMA films are evidently less perturbed by the presence of free surfaces than those made of PS. We then turn to the case of PMMA films supported on a silica substrate by accounting for possible polymer−substrate interactions, such that when these are switched off the same model maps smoothly back to the case of a PMMA freestanding film. We then probe the origin of the interaction required such that the model can capture the experimentally observed T g enhancement for supported PMMA films while also accounting for the relative lack of impact on the T g behavior of supported PS films relative to their freestanding counterparts. Finally, we make connections between related experimental and simulation studies and our own results for the differences between supported PMMA and PS films. INTRODUCTIONThe study of the effect of confinement on glassy polymeric systems has continued to draw strong research interest over the past two decades. 1−5 Polymer thin films have been a particularly popular system to study. Beyond important material and engineering applications, they show a diverse range of behavior, depending both on the polymer's characteristic properties and on the nature of the confinement. Films of interest include both freestanding films (two free surfaces) and films supported on a substrate. These supported films have one free surface and one surface in contact with a substrate (e.g. silica, gold, a substrate coating, a polymeric underlayer, or other). The effect that confinement has on a film's glass transition temperature (T g ) has been of particularly strong interest and much remains to be understood. Although many experimental investigations have shown that there can be a strong and varied change in the film T g relative to the corresponding bulk value, other investigations have shown little or no change in T g , and adding to this is evidence that such effects can depend on cooling rate. 6−9 In general, experimental results show that for freestanding films (e.g., refs 10−12), as the film gets thinner (e.g., less than 100 nm) the film T g is suppressed (lowered) compared to the corresponding bulk T g value. For supported films, the behavior can be quite diverse. In these cases, the film T g can either be enhanced or suppressed relative to the bulk, dependi...

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Role of Molecular Architecture on the Vitrification of Polymer Thin Films

Cited by 93 publications

References 34 publications

Wetting of a Multiarm Star-Shaped Molecule

Wetting of a Multiarm Star-Shaped Molecule

High‐Efficiency Polymer:Nonfullerene Solar Cells with Quaterthiophene‐Containing Polyimide Interlayers

Effect of Interfaces on the Glass Transition of Supported and Freestanding Polymer Thin Films

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