Ellipsometric determination of Flory-Huggins interaction parameters in solution

Elbs, Hubert; Krausch, Georg

doi:10.1016/j.polymer.2004.09.021

Cited by 74 publications

(90 citation statements)

References 28 publications

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“…[69][70][71][72][73][74] In these measurements the changes in a conjugated polymer fi lm's refractive index and thickness are monitored in a non-absorbing spectral region while the sample is exposed to controlled amounts of the co-solvent vapor (for experimental details, see the Supporting Information (SI)). Since most of the previous work on SqP is focused on P3HT, [ 20,22,37,38,48,56,57 ] we begin by examining the volume changes of swollen thin fi lms of P3HT that have varying degrees of crystallinity.…”

Section: Using Porosimetry-ellipsometry To Quantify Conjugated Polymementioning

confidence: 99%

“…[ 83 ] Instead, we can quantify the solvent-polymer fi lm interaction by calculating Flory-Huggins interaction parameters ( χ ) from the results of our swelling experiments (see SI for Flory-Huggins calculation details). [ 51,70,71,74,84 ] Figure 3 a shows the calculated values of χ for the solventpolymer fi lm pairs explored in Figure 2 ; stronger solvent-polymer fi lm interactions give lower values for χ . As expected, toluene-the better solvent for both PTB7 and PSDTTT-gives uniformly lower χ values than IPA.…”

Section: (4 Of 11)mentioning

confidence: 99%

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Sequential Processing for Organic Photovoltaics: Design Rules for Morphology Control by Tailored Semi‐Orthogonal Solvent Blends

Aguirre

Hawks

Ferreira

et al. 2015

Advanced Energy Materials

166

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Design rules are presented for significantly expanding sequential processing (SqP) into previously inaccessible polymer:fullerene systems by tailoring binary solvent blends for fullerene deposition. Starting with a base solvent that has high fullerene solubility, 2‐chlorophenol (2‐CP), ellipsometry‐based swelling experiments are used to investigate different co‐solvents for the fullerene‐casting solution. By tuning the Flory‐Huggins χ parameter of the 2‐CP/co‐solvent blend, it is possible to optimally swell the polymer of interest for fullerene interdiffusion without dissolution of the polymer underlayer. In this way solar cell power conversion efficiencies are obtained for the PTB7 (poly[(4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)(3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl)]) and PC61BM (phenyl‐C61‐butyric acid methyl ester) materials combination that match those of blend‐cast films. Both semicrystalline (e.g., P3HT (poly(3‐hexylthiophene‐2,5‐diyl)) and entirely amorphous (e.g., PSDTTT (poly[(4,8‐di(2‐butyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)‐alt‐(2,5‐bis(4,4′‐bis(2‐octyl)dithieno[3,2‐b:2′3′‐d]silole‐2,6‐diyl)thiazolo[5,4‐d]thiazole)]) conjugated polymers can be processed into highly efficient photovoltaic devices using the solvent‐blend SqP design rules. Grazing‐incidence wide‐angle x‐ray diffraction experiments confirm that proper choice of the fullerene casting co‐solvent yields well‐ordered interdispersed bulk heterojunction (BHJ) morphologies without the need for subsequent thermal annealing or the use of trace solvent additives (e.g., diiodooctane). The results open SqP to polymer/fullerene systems that are currently incompatible with traditional methods of device fabrication, and make BHJ morphology control a more tractable problem.

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Section: Using Porosimetry-ellipsometry To Quantify Conjugated Polymementioning

confidence: 99%

Section: (4 Of 11)mentioning

confidence: 99%

Sequential Processing for Organic Photovoltaics: Design Rules for Morphology Control by Tailored Semi‐Orthogonal Solvent Blends

Aguirre

Hawks

Ferreira

et al. 2015

Advanced Energy Materials

166

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“…These differences are surprising considering that PMMA and P(tert-BMA) have similar glass transition temperatures and bulk moduli. The χ parameter for the P(tert-BMA) /toluene system, for a polymer volume fraction of 0.8 is around 0.25-0.3 19 ,20,21 , similar to the PS/toluene system, while for PMMA/toluene the value is higher, at around 0.45 10,19,20 . One can argue that if the chemical potential is higher (as is the case for the toluene/PMMA) and when there is some solvent in the vapour phase -such as during the spin-casting process -it will be thermodynamically favourable to have more solvent in the polymer solution.…”

Section: Tablementioning

confidence: 79%

Some insights into the structural relaxation of spin-cast, glassy polymer thin films

García

Keddie

Sferrazza

2010

Polym J

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The widespread use of thin films in a range of applications and industries, from coatings, inks and lithography to nano-imprinting, optoelectronics, and memory devices 1 , has made the understanding of thin films, particularly the changes induced by structural relaxation and solvent evaporation, very important. There is a need to know if a film will change in dimensions after its deposition and how fast these changes will occur. Physical ageing of thin polymer systems is, more generally, an important phenomenon in polymer physics: when a polymer is cooled quickly below its glass transition temperature (T g ) at which point freezing of the matrix takes place 2 , it is in a non-equilibrium state. When it is aged at temperatures below T g , a structural relaxation towards the equilibrium volume can take place 2 3 . (The equilibrium volume represents the volume obtained through infinitely slow cooling.) Recent works have shown that the structure, wetting, and mobility of polymers in thin films can differ greatly from those of the bulk 3 4 5 . For example, a well-documented property of thin polymer films that exhibits thickness dependence is its T g 6 7 .In many applications, thin films are prepared by depositing a dilute solution of polymer onto a substrate; then the substrate is spun at high velocity during which the solution spreads, thereby ejecting any excess off the substrate 8 . Subsequently during this process, as * Corresponding author: msferraz@ulb.ac.be

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“…For PS films we used chloroform and toluene, both of which are known as good solvents for the polymer. The solvent vapor pressure in the chamber was adjusted using a home-made apparatus [21,22]. Mass-flow controllers (MKS Instruments Model 1179A with a PR4000F readout) regulated the flux of the carrier gas, N 2 , through two lines.…”

Section: Methodsmentioning

confidence: 99%

“…The protocol was as follows: a 215 nm thick PS film was exposed to chloroform vapor with p/p sat = 0.7 until an equilibrium film thickness of ca. 1.5 times the initial film thickness [21,22] was reached after 20 min. The mold was lowered onto the sample for 5 min, followed by quenching the film in dry N 2 for 35 min.…”

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confidence: 96%