2012
DOI: 10.1140/epje/i2012-12129-3
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Competition between substrate-mediated π-π stacking and surface-mediated Tg depression in ultrathin conjugated polymer films

Abstract: Abstract. We report surface and interface effects in dynamics and chain conformation in the thin film of conjugated polymer PCDTBT. To probe dynamic anomalies, we measure the glass transition temperature (T g ) of PCDTBT films as a function of thickness, and find that there is a significant depression in Tg for films less than 100 nm thick; a result qualitatively similar to that observed in many other polymer film systems. However, for films less than 40 nm, the T g converges to a constant value of 20 K below … Show more

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Cited by 36 publications
(51 citation statements)
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“…The application of ellipsometry in characterizing the T g of conjugated polymers has been successfully demonstrated by different groups for various conjugated polymers. Figure plots the temperature dependence of ellipsometric angle Ψ for the supported poly[ N ‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT) ultrathin film with different thicknesses, measured by Wang et al as an example. The T g is determined from the intersection of two linear fits.…”
Section: Experimental Techniques To Measure Tgmentioning
confidence: 99%
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“…The application of ellipsometry in characterizing the T g of conjugated polymers has been successfully demonstrated by different groups for various conjugated polymers. Figure plots the temperature dependence of ellipsometric angle Ψ for the supported poly[ N ‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT) ultrathin film with different thicknesses, measured by Wang et al as an example. The T g is determined from the intersection of two linear fits.…”
Section: Experimental Techniques To Measure Tgmentioning
confidence: 99%
“…A T g depression with film thickness is readily observed. Adapted with permission . Copyright 2012, The Authors.…”
Section: Experimental Techniques To Measure Tgmentioning
confidence: 99%
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“…Moreover, this value depends on several aspects such as the thermal history of the sample, the technique/method followed and the thermal rate used for the measurement [41]. For example, recent experiments [42,43] and simulation [44] studies have demonstrated a pronounced thickness-dependent confinement effect on Tg, together with a strong dependence on the solvent and on the substrate used [45]. These effects are totally disregarded if a technique like DSC is employed.…”
Section: Introductionmentioning
confidence: 99%
“…In contrast, a full treatment of waveguiding effect in a thin film system has the potential to quantitatively characterize the precise location, thickness, and orientation of the stratified crystalline layers including a precise measure of transition widths between layers.In cases where angular dependence has been employed to study a surface/bulk difference spin coated conjugated polymer thin films, distinct crystalline surface layers have not been detected, rather only changes in the level of crystallinity have been noted. [16][17][18][19] A quantitative measurement of crystalline stratification within thin organic electronic films has yet to be clearly demonstrated.In self-assembled thin film systems, whether because of surface disorder, film roughness, or lack of highly collimated X-ray beams (with an experimental angular resolution of ~0.0025 degrees), diffractive waveguiding has not been demonstrated. This level of experiment is often judged unnecessary if the primary measurement goal is to examine overall thin film molecular packing, in which case only the angle with the highest overall scattering intensity is analyzed.However in applications such as organic-field effect transistors, where the thin (as little as 2 nm) 20 near-surface layers are responsible for charge transport, 21 simply measuring the average film properties can miss important surface structure that is distinct from the thickness-averaged microstructure.…”
mentioning
confidence: 99%