NMR study of the nanomorphology in thin films of polymer blends used in organic PV devices: MDMO‐PPV/PCBM

The disclosure of the nanomorphology of thin films in organic solar cells, prepared from blends of conjugated polymers and PCBM, is of key importance for a better understanding of the occurring photovoltaic (PV) mechanisms. Hereto solid‐state NMR relaxometry has been evaluated as a complementary technique to traditional microscopic techniques like atomic force microscopy and transmission electron microscopy. It is demonstrated that proton wide‐line solid‐state NMR relaxometry is a useful and innovative tool to study the phase morphology of blends used in semi‐conducting polymer based PV devices. Attention is focused on the influence of the blend composition and casting conditions on the resulting phase morphology. Two different casting techniques, i.e. spincoating and Doctor Blading, were compared. To demonstrate the applicability of NMR relaxometry in this field, MDMO‐PPV/PCBM blends where used, since these are known for their significant phase separation behavior in combination with toluene as solvent. In films prepared from blends in toluene with a PCBM content ≥70 wt %, a fraction of the PCBM is phase separated into crystalline domains, whereas the remaining part remains homogeneously mixed with the MDMO‐PPV. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 138–145, 2008     

Characterization of blends of poly(vinyl chloride) and poly(N‐vinyl pyrrolidone) by FTIR and 13C CP/MAS NMR spectroscopy

Blends of poly(vinyl chloride) (PVC) with Poly(N‐vinyl pyrrolidone) (PVP) were investigated by Fourier infrared spectroscopy (FTIR) and high‐resolution solid‐state ¹³C cross‐polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The intermolecular interactions between PVP and PVC are weaker than the self‐association of PVP and the inclusion of the miscible PVC results in the decreased self‐association of PVP chains, which was evidenced by the observation of high‐frequency shift of amide stretching vibration bands of PVP with inclusion of PVC. This result was further substantiated by the study of ¹³C CP/MAS spectra, in which the chemical shift of carbonyl resonance of PVP was observed to shift to a high field with inclusion of PVC, indicating that the magnetic shielding of the carbonyl carbon nucleus is increased. The proton spin‐lattice relaxation time in the laboratory frame (T₁ (H)) and the proton spin‐lattice relaxation time in the rotating frame (T_1ρ(H)) were measured as a function of the blend composition to give the information about phase structure. It is concluded that the PVC and PVP chains are intimately mixed on the scale of 20–30Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2412–2419, 1999     

Thermal stability of P3HT and P3HT:PCBM blends in the molten state

The thermal stability of poly(3-hexylthiophene) (P3HT) in its molten state was investigated in air and nitrogen atmospheres under no illumination conditions, with the aim of testing the feasibility of processing it using polymer melt techniques. A large set of different experimental characterization techniques was used including thermogravimetric analysis (TGA), rotational rheometry, infrared spectroscopy (FTIR-ATR), proton nuclear magnetic resonance spectroscopy (¹H-NMR), gel permeation chromatography (GPC), UV-Vis and fluorescence spectroscopy. The results obtained strongly suggest that the processing of P3HT in its molten state is possible, without noticeable degradation, if carried out under nitrogen atmosphere and if the processing (residence) times are relatively short. Conversely, as expected, in a normal air atmosphere P3HT degrades rapidly at temperatures above its melting point. The effect of PCBM on the thermal stability of P3HT:PCBM blends in the molten state was also studied using TGA, and in air atmosphere PCBM is shown to delay oxidation.     

Solid‐State NMR investigations of anhydrous proton‐conducting acid–base poly(acrylic acid)– poly(4‐vinyl pyridine) polymer blend system: A study of hydrogen bonding and proton conduction

NMR studies of the structure and dynamics of a system composed of the acidic polymer poly(acrylic acid) (PAA) and the basic polymer poly(4‐vinyl pyridine) (P4VP) are presented. This system aims at the application of anhydrous proton‐conducting membranes that can be used at elevated temperatures at which the proton conduction of hydrated membranes breaks down. The ¹H NMR measurements have been preformed under fast magic angle spinning (MAS) conditions to achieve sufficient resolution and the applied ¹H NMR methods vary from simple ¹H MAS to double‐quantum filtered methods and two‐dimensional ¹H double‐quantum spectroscopy. The dynamic behavior of the systems has been investigated via variable temperature ¹H MAS NMR. ¹³C cross‐polarization MAS NMR provides additional aspects of dynamic and structural features to complete the picture. Different types of acidic protons have been identified in the studied PAA‐P4VP systems that are nonhydrogen‐bonded free acidic protons, hydrogen‐bonded dicarboxylic dimers, and protons forming hydrogen bonds between carboxylic protons and ring nitrogens. The conversion of dimer structures in dried PAA to free carboxylic acid groups is accomplished at temperatures above 380 K. However, the stability of hydrogen‐bonding strongly depends on the hydration level of the polymer systems. The effect of hydration becomes less apparent in the complexes. An inverse proportionality between hydrogen‐bonding strength and proton conduction in the PAA‐P4VP acid–base polymer blend systems was established. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 138–155, 2009     

Effect of polydispersity on the bulk‐heterojunction morphology of P3HT:PCBM solar cells

Bulk heterojunctions (BHJs) based on semiconducting electron–donor polymer and electron–acceptor fullerene have been extensively investigated as potential photoactive layers for organic solar cells (OSCs). In the experimental studies, poly‐(3‐hexyl‐thiophene) (P3HT) polymers are hardly monodisperse as the synthesis of highly monodisperse polymer mixture is a near impossible task to achieve. However, the majority of the computational efforts on P3HT: phenyl‐C61‐butyric acid methyl ester (P3HT:PCBM)‐based OSCs, a monodisperse P3HT is usually considered. Here, results from coarse‐grained molecular dynamics simulations of solvent evaporation and thermal annealing process of the BHJ are shared describing the effect of variability in molecular weight (also known as polydispersity) on the morphology of the active layer. Results affirm that polydispersity is beneficial for charge separation as the interfacial area is observed to increase with higher dispersity. Calculations of percolation and orientation tensors, on the other hand, reveal that a certain polydispersity index ranging between 1.05 and 1.10 should be maintained for optimal charge transport. Most importantly, these results point out that the consideration of polydispersity should be considered in computational studies of polymer‐based OSCs. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 895–903     

Solid‐state NMR as a tool to describe and quantify the morphology of photoactive layers used in plastic solar cells

The optimization and control of the nanomorphology of thin films used as active layer in bulk heterojunction (BHJ) plastic solar cells is of key importance for a better understanding of the photovoltaic mechanisms and for increasing the device performances. Hereto, solid‐state NMR relaxation experiments have been evaluated to describe the film morphology of one of the “work‐horse” systems poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene‐vinylene)/[6, 6]‐phenyl‐C₆₁butyric acid methyl ester (MDMO‐PPV/PCBM) in a quantitative way. Attention is focused on the influence of the processing solvent (toluene vs. chlorobenzene), the blend composition, and the casting technique, that is, spin coating versus doctor blading. It is demonstrated that independently of the solvent and casting technique, part of the PCBM becomes phase separated from the mixed phase. Whereas casting from toluene results in the development of well‐defined PCBM crystallites, casting from chlorobenzene leads to the formation of PCBM‐rich domains that contain substructures of weakly organized PCBM nanoclusters. The amount and physico‐chemical state of the phase separated PCBM is quantified by solid‐state NMR relaxation times experiments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Fast Li Ion Dynamics in the Solid Electrolyte Li7P3S11 as Probed by 6,7Li NMR Spin‐Lattice Relaxation

The development of safe and long‐lasting all‐solid‐state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic‐scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long‐range as well as short‐range Li ion dynamics in the glass‐ceramic Li₇P₃S₁₁. Li⁺ diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li⁺ diffusivity, which is reflected in a so‐called diffusion‐induced ⁶Li NMR spin‐lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×10⁸ s^?1, which corresponds to a Li⁺ ion conductivity in the order of 10^?4 to 10^?3 S cm^?1. Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li₇P₃S₁₁. In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through‐going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li₇P₃S₁₁ crystallites. As a result of this, long‐range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long‐range ionic conduction. If we are to succeed in solid‐state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation of samples that are free of any amorphous regions that block fast ion transport.     

Solid‐state NMR characterizations on phase structures and molecular dynamics of poly(ethylene‐co‐vinyl acetate)

Solid‐state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene‐co‐vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room‐temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well‐defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin‐lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt‐like amorphous phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2864–2879, 2006     

SBA‐15‐Oxynitrides as a Solid‐Base Catalyst: Effect of Nitridation Temperature on Catalytic Activity

Solid bases, such as SBA‐15‐oxynitrides, have attracted considerable interest for potential applications as catalysts in important industrial processes. Reported herein is that by simply tuning the temperature of nitridation (ammonolysis), the catalytic activity of these solid bases can be enhanced. Solid‐state NMR spectroscopy and XPS studies provided the reasoning behind this change in activity.     

Synthesis and phase behaviors of side‐chain liquid‐crystalline polymers containing azobenzene mesogen with the different length alkyl tail

A series of side‐chain liquid‐crystal polymers, poly[6‐[4‐(4′‐n‐alkyl benzoateazo)phenoxy]‐hexylmethacrylate]s (PMAzoCOOR_m, m = 1, 2, 3, 4, 5, 6, 8, 10, 14, and 18) have been prepared by two synthetic methods. The chemical structure of the monomers was confirmed by ¹H NMR and mass spectrometry. The molecular characterizations of the polymers were performed with ¹H NMR and gel permeation chromatograph. The phase behaviors of polymers were investigated by the combination of techniques including differential scanning calorimetry, polarized optical microscopy, and small‐angle X‐ray scattering. For m = 1, 2, 3, 4, 5, and 6, the polymers exhibited a monosmectic A phase in which the smectic layer period was almost identical to the side‐chain length. In addition, for m = 2, 3, 4, and 5, they presented the monosmectic C phase in low temperature; moreover, the tilt angle increased from 23.3 to 40.5°. For m = 8, 10, 14, and 18, the polymers showed a bilayer smectic A phase in which the layer spacing was larger than a fully extended side chain but less than two extended chains. On the other hand, for the clearing point, with the increasing of m, it first decreased, and then increased. All of these indicated that the length of alkyl tails played an important role in the phase behaviors of these polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2759–2768     

Studies on the phase structure of ethylene‐vinyl acetate copolymers by solid‐state 1H and 13C NMR

The phase structure of a series of ethylene‐vinyl acetate copolymers has been investigated by solid‐state wide‐line ¹H NMR and solid‐state high‐resolution ¹³C NMR spectroscopy. Not only the degree of crystallinity but the relative contents of the monoclinic and orthorhombic crystals within the crystalline region varied with the vinyl acetate (VA) content. Biexponential ¹³C NMR spin–lattice relaxation behavior was observed for the crystalline region of all samples. The component with longer ¹³C NMR spin–lattice relaxation time (T₁) was attributed to the internal part of the crystalline region, whereas the component with shorter ¹³C NMR T₁ to the mobile crystalline component was located between the noncrystalline region and the internal part of the crystalline region. The content of the mobile crystalline component relative to the internal part of the crystalline region increased with the VA content, showing that the ¹³C NMR spin–lattice relaxation behavior is closely related to the crystalline structure of the copolymers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2199–2207, 2002     

An Investigation of Poly(dimethylsiloxane) Chain Dynamics and Order in Its Inclusion Compound with γ‐Cyclodextrin by Fast‐MAS Solid‐State NMR Spectroscopy

The dynamics of poly(dimethylsiloxane) in its inclusion compound with γ‐cyclodextrin are elucidated using modern fast‐MAS solid‐state NMR techniques. Measurements of methyl ¹H–¹H and ¹H–¹³C dipolar coupling constants indicate that the polymer undergoes a uniform motion, rendering all methyl groups equivalent. The dynamics of the Si—C bond is characterized by either a dynamic order parameter of S = 0.72, or, assuming a stably rotating helical structure, an inclination angle of 73° relative to the rotation axis.     

Study of triacylglycerol polymorphs by nuclear magnetic resonance: effects of temperature and chain length on relaxation parameters

It is very important to monitor the characteristics of triacylglycerol crystal network in fats, as these crystals have an impact on many food properties such as texture, sensory taste, and extended shelf life. Although time-domain NMR (TD-NMR) is now the reference technique to determine the solid fat index in food, the entire possibilities of this technique are not used. Some NMR studies have been performed to determine its power for the discrimination of polymorphism. In this study, extended investigations proved that TD-NMR could evaluate triacylglycerol (TA) polymorphism, independently from temperature and chain length. Study of the dipolar interactions through second moment M(2), which is characteristic of proton mobility in solid-state samples, provided a new understanding of the structural organization of crystal molecules. Proton spin-lattice relaxation, which has been proved to be a true probe of polymorphism, has provided information on crystal networks. Combination of the two techniques revealed two very interesting kinds of results, i.e. the presence of a minimum spin-lattice relaxation time T(1) for tristearin alpha, which is a characteristic of a dynamic molecular process, and differences in behavior between long and short chain lengths, both at a molecular and a crystal level.     

Crystalline structure of polyamide 12 as revealed by solid‐state 13C NMR and synchrotron WAXS and SAXS

The crystalline structure of polyamide‐12 (PA12) was studied by solid‐state ¹³C nuclear magnetic resonance (NMR) as well as by synchrotron wide‐ and small‐angle X‐ray scattering (WAXS and SAXS). Isotropic and oriented PA12 showed different NMR spectra ascribed to γ‐ and γ′‐crystalline modifications, respectively. On the basis of the position of the first diffraction peak, the isotropic γ‐form and the oriented γ′‐form were shown to be with hexagonal crystalline lattice at room temperature. When heated, the two PA12 polymorphs demonstrated different behaviors. Above 140 °C, the isotropic γ‐PA12 partially transformed into α‐modification. No such transition was observed with the oriented γ′‐PA12 phase even after annealing at temperatures close to melting. A γ′–γ transition was observed here only after isotropization by melting point. Various structural parameters were extracted from the WAXS and SAXS patterns and analyzed as a function of temperature and orientation: the degree of crystallinity, the d‐spacings, the Bragg's long spacings, the average thicknesses of the crystalline (l_c) and amorphous (l_a) phases, and the linear crystallinity x_cl within the lamellar stacks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3720–3733, 2005     

Effect of the tail‐group length and degree of polymerization on the order parameter of side‐chain liquid‐crystalline polymethacrylates containing phenylbenzoate mesogenic groups

The orientation of the side‐chain liquid‐crystalline polymers (LCP) containing phenylbenzoate mesogenic groups in the magnetic field was examined with ²H NMR spectroscopy. The influence of the degree of polymerization as well as the length of the methylene tail group (n = 1–4) have been established. The decrease of the order parameter S of the LCPs with an increased length of the tail group was found. The order parameter S of LCPs does not depend on the degree of polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2044–2048, 2002     

Synthesis of optically active conjugated polymers containing platinum in the main chain: Control of the higher‐order structures by substituents and solvents

The Sonogashira–Hagihara coupling polymerization of d ‐hydroxyphenylglycine‐derived diiodo monomers 1–4 and platinum‐containing diethynyl monomer 5 gave the corresponding polymers [poly( 1–5 )–( 2–5 )] with number‐average molecular weights of 19,000–25,000 quantitatively. The polymers were soluble in CHCl₃, CH₂Cl₂, THF, and DMF. CD and UV–vis spectroscopic analysis revealed that amide‐substituted polymers [poly( 1–5 ) and poly( 2–5 )] formed chiral higher‐order structures in solution, while ester‐substituted polymers [poly( 3–5 ) and poly( 4–5 )] did not. Poly( 1–5 ) formed one‐handed helices in THF/toluene mixtures, while it formed chiral aggregates in THF/MeOH mixtures. Poly( 1–5 ) emitted fluorescence with quantum yields ranging from 0.8 to 1.3%. The polymers usually aggregated in the solid state. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2452–2461     

Nanoparticles of [Fe(NH2‐trz)3]Br2⋅3 H2O (NH2‐trz=2‐Amino‐1,2,4‐triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin‐Crossover Properties

By changing the surfactant/water ratio , nanoparticles of the iron(II) spin crossover material, [Fe(NH₂‐trz)₃]Br₂ ? 3 H₂O (with NH₂‐trz=4‐amino‐1,2,4‐triazole), have been synthesised from 1 μm down to 30 nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50 nm, and powder X‐ray diffraction shows that particles of about 30 nm are constituted by about one coherent domain.

     

Heteronuclear NMR Spectroscopy as a Surface‐Selective Technique: A Unique Look at the Hydroxyl Groups of γ‐Alumina.

The surface hydroxyl groups of γ‐alumina dehydroxylated at 500 °C were studied by a combination of one‐ and two‐dimensional homo‐ and heteronuclear ¹H and ²⁷Al NMR spectroscopy at high magnetic field. In particular, by harnessing ¹H–²⁷Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the ¹H magic‐angle spinning (MAS) NMR spectrum was demonstrated thanks to ¹H–²⁷Al RESPDOR (resonance‐echo saturation‐pulse double‐resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {¹H}‐²⁷Al dipolar heteronuclear multiple quantum correlation (D‐HMQC), which was used to establish a first coordination map. Then, in combination with ¹H–¹H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO₂ reactivity with alumina.     

NOESY,HOESY, T1 and solid‐state NMR studies on [RuH(η6‐toluene)(Binap)](CF3SO3): a molecule with a strongly distorted piano‐stool structure

Detailed solution‐NMR studies on the distorted ruthenium hydride complex [RuH(η⁶‐toluene)(Binap)](CF₃SO₃) (2) are reported. NOE‐spectroscopy, together with low‐temperature ¹H and ³¹P NMR data, reveals restricted rotation around a P—C bond for a specific axial P—phenyl ring with the activation energy determined via simulation. From ¹⁹F, ¹H HOESY data, the approach of the triflate anion relative to the hydride ligand is established. Comparison of the quadrupole coupling constant C_QF from both solution‐ and solid‐state MAS‐NMR on the deuteride [RuD(η⁶‐benzene)(Binap)](CF₃SO₃) (1‐D) provide information on the nature of the Ru—H bond. Copyright © 2003 John Wiley & Sons, Ltd.