New NMR methods for studying dynamics in solids

There is currently much interest in the investigation of dynamics in solids and the primary goal of this thesis is to present well-known and new NMR methods used for studying motion on Larmor and spectral timescale. The quadrupolar interaction usually dominates solid-state NMR spectra of quadrupolar nuclei. When the magnitude of quadrupolar interaction is large then the second-order correction to the dominant Zeeman Hamiltonian must be considered. Owing to this second-order quadrupolar effect, NMR peaks can be displaced from their chemical shift positions by a second-order shift. When considering motional averaging of the second-order shift, the critical frequency is the Larmor frequency, 0. In the case of motion that is faster than the Larmor precession, the isotropic quadrupolar shift is affected. This analogous phenomenon in solution-state NMR is known as the "dynamic shift". In Chapter 4, it will be shown that multiple-quantum NMR measurements of isotropic second-order quadrupolar shifts are a simple way to probe nanosecond timescale motions in solids. An analysis of one- and two-dimensional 11B MAS NMR spectra of three isomers of the closo-carboranes gives the results that provide the first evidence for the presence of solid-state dynamic shifts. There are several experiments that provide a sensitive test for the presence of dynamics on spectral timescale. One piece of evidence for dynamics on the spectral timescale is a motional broadening of quadrupolar satellite-transition spinning sidebands. Therefore, it is possible to investigate the influence of dynamic reorientation on satellite-transitions MAS spectra by recording variable-temperature one-dimensional spectra with wide spectral width or by comparing two-dimensional STMAS spectra with MQMAS spectra. These methods can be extended to 2H NMR spectroscopy as the sidebands observed in the magic angle spinning (MAS) NMR spectrum of a spin I = 1 2H nucleus may be very strongly broadened due to interference between the line-narrowing effects of MAS and the dynamics-driven reorientation of the 2H quadrupole tensor, if motion is present in the solid. In the last chapter, the 27Al, 31P and 2H NMR study of AlPO-34 type materials with the topology of chabazite are undertaken and the use of the full range of NMR methods to develop a structure and dynamic behaviour of these materials is presented. In addition, the NMR calculations are performed in order to combine DFT calculations with experimental data. Finally, GaPO-34 samples were investigated to extract information about the effects of Ga substitution in AlPO-34 on dynamical behaviour

Second-order quadrupolar shifts as an NMR probe of fast molecular-scale dynamics in solids

Molecular-scale dynamics on the nanosecond timescale or faster can have a measurable influence on isotropic NMR frequencies of quadrupolar nuclei. Although previously studied in solution, where it is usually referred to as the ‘dynamic shift’, this effect is less well known in solids. Here we demonstrate that multiple-quantum NMR measurements of isotropic quadrupolar shifts are a simple way to probe nanosecond timescale motions in solids. We measure the <sup>11</sup>B (spin I = 3/2) shifts of the resolved boron sites in ortho-carborane as a function of temperature and interpret the results in terms of the known rapid tumbling dynamics

A multinuclear NMR study of six forms of AlPO-34:structure and motional broadening

We report a study of the CHA-type aluminophosphate AlPO-34, prepared with six different structure-directing agents (SDAs): piperidine (pip), morpholine (mor), pyridine (pyr), 1,4,8,11-tetraazacyclotetradecane (cyclam), 1,3 dimethylimidazolium (dmim) chloride and 1-ethyl-3-methylimidazolium (emim) bromide. Using a combination of solid-state NMR spectroscopy, periodic density functional theory (DFT) calculations and synchrotron X-ray diffraction, we show that, even in crystallographically well-ordered materials such as AlPO-34 with dmim as the SDA, local disorder may be present. For such disordered structures, where it is challenging to use DFT to assign NMR spectra, we show that the 31P isotropic chemical shift can be predicted accurately using the mean P-O bond length and P-O-Al bond angle, in an extension of previous work. Variable-temperature 27Al NMR reveals the presence of microsecond-timescale dynamics in all forms of AlPO- 34, with two different motional regimes observed, depending on whether structural H2O is also present. H2O is detected in AlPO-34 prepared with mor as the SDA, although this material was previously reported as anhydrous, suggesting that this form of AlPO-34 may be hygroscopic despite the presence of the SDAs within the pores

Inspiracje twórcze a dzieło stworzone

Praca recenzowana / peer-reviewed pape

Solid-State Dynamics in the closo-Carboranes:A (11)B MAS NMR and Molecular Dynamics Study

This work explores the dynamic behaviour of the three closo-carborane isomers (formula C2B10H12) using modern solid-state magic angle spinning (MAS) NMR techniques and relates the experimental measurements to theoretical results obtained using molecular dynamics simulations. At high temperatures and at B0 = 9.4 T, the 11B MAS linewidths are narrow (40-90 Hz) for the three isomers. The rotational correlation times (tauc) calculated by molecular dynamics are on the picosecond timescale, showing a quasi-isotropic rotation at these temperatures, typical for liquid systems. For all three isomers, the values of the 11B spin-lattice relaxation times (T1) show discontinuities as the temperature is decreased, confirming the phase changes reported in the literature. At low temperatures, the 11B MAS spectra of all three isomers exhibit much broader lines. The simulations showed that the molecular reorientation was anisotropic around different symmetry axes for each isomer, and this was supported by the values of the reduced quadrupolar parameter PQeff derived from “dynamic shift” measurements using 11B MQMAS NMR spectroscopy. The behaviour of PQeff as a function of temperature for para-carborane suggests that molecular reorientation is about the C5 symmetry axis of the molecule at low temperatures and this was supported by the molecular dynamics simulations

Exploring Liu Kang’s Paris Practice (1929–1932): Insight into Painting Materials and Technique

This paper presents the results of an extensive study of 14 paintings by the pioneering Singapore artist Liu Kang (1911–2004). The paintings are from the National Gallery Singapore and Liu family collections. The aim of the study is to elucidate the painting technique and materials from the artist’s early oeuvre, Paris, spanning the period from 1929 to 1932. The artworks were studied with a wide array of non- and micro-invasive analytical techniques, supplemented with the historical information derived from the Liu family archives and contemporary colourmen catalogues. The results showed that the artist was able to create compositions with a limited colour palette and had a preferential use of commercially available ultramarine, viridian, chrome yellow, iron oxides, organic reds, lead white, and bone black bound in oil that was highlighted. This study identified other minor pigments that appeared as hue modifications or were used sporadically, such as cobalt blue, Prussian blue, emerald green, cadmium yellow, cobalt yellow, and zinc white. With regard to the painting technique, the artist explored different styles and demonstrated a continuous development of his brushwork and was undoubtedly influenced by Modernists’ artworks. This comprehensive technical study of Liu Kang’s paintings from the Paris phase may assist art historians and conservators in the evaluation of the artist’s early career and aid conservation diagnostics and treatment of his artworks. Furthermore, the identified painting materials can be compared with those used by other artists active in Paris during the same period

A Multi-Analytical Investigation of Liu Kang’s Colour Palette and Painting Technique from the Shanghai Period (1933–1937)

This study presents the analytical characterisation of Liu Kang’s paint mixtures and the painting technique used during the important Shanghai artistic phase (1933−1937). Liu Kang (1911–2004) was a Chinese artist who received an academic art education in Shanghai (1926–1928) and Paris (1929–1932). He settled permanently in Singapore in 1945 and became a leading contributor to the national art scene. This study showcases 12 paintings on canvas from the collections of the National Gallery Singapore and the Liu family. An integrated approach combined non- and micro-invasive analytical methods supplemented with archival sources and enabled characterising the investigated paint mixtures and revealing details of the artist’s painting technique. The study has proved the artist’s ability to produce a variety of hues by utilising a conventional palette of colours. The predilection for ultramarine, viridian, yellow and red iron-rich earth pigments, umber, yellow chromate pigments, as well as lead white, zinc white or Zn-base compounds like lithopone and barium white was recorded. The study emphasises a minor use of Prussian blue, emerald green, cadmium yellow or its variant and bone black. Although it remains unknown what brands of paints Liu Kang used, the available archival sources give insights into the painting materials available in Shanghai that the artist could have had at his disposal during the period under review. The archival information is based on the Chinese and overseas colourmen advertisements printed in Chinese journals and the respective contemporary colourmen catalogues. The artist’s painting technique departs from the experimental approach of his Paris phase. In Shanghai, he focused on synthesising the painting principles of the School of Paris with traditional Chinese calligraphy. The outcomes of this research may support future technical studies of works by other artists contemporary to Liu Kang and who were active in pre-war Shanghai

Painting Materials and Technique for the Expression of Chinese Inheritance in Liu Kang’s Huangshan and Guilin Landscapes (1977–1996)

Liu Kang (1911–2004) was a Chinese artist who settled in Singapore in 1945 and eventually became a leading modern artist in Singapore. He received academic training in Shanghai (1926–1928) and Paris (1929–1932). Liu Kang’s frequent visits to China from the 1970s to the 1990s contributed to a special artistic subject—the Huangshan and Guilin mountains. This subject matter triggered an uncommon painting approach for his oeuvre. In this context, this study elucidates the artist’s choice of materials and methods for the execution of 11 paintings, dating between 1977 and 1996, depicting Huangshan and Guilin landscapes. The paintings belong to the collection of the National Gallery Singapore. They were investigated with a combination of non- and micro-invasive techniques, supplemented by a wealth of documentary sources and art history research. The obtained results highlight the predominant use of hardboards resembling Masonite® Presdwood® without the application of an intermediate ground layer. Commercially prepared cotton and linen painting supports were used less frequently, and their structure and ground composition were variable. This study revealed the use of a conventional colour base for the execution of the paintings—a consistent colour scheme favouring ultramarine, yellow and red iron-containing earths, viridian and titanium white. Less commonly used pigments include Prussian blue, cobalt blue, phthalocyanine blue, phthalocyanine green, naphthol red AS-D, umber, Cr-containing yellow(s), cadmium yellow or its variant(s), Hansa yellow G, lithopone and/or barium white and zinc white and bone black. The documentary sources indirectly pointed to the use of Royal Talens, Rowney and Winsor & Newton, brands of oil paints. Moreover, technical and archival findings indicated the artist’s tendency to recycle rejected compositions, thereby strongly suggesting that the paintings were executed in the studio. Although this study focuses on the Singapore artist and his series of paintings relating to China, it contributes to existing international studies of modern artists’ materials

Evolution of Liu Kang’s Palette and Painting Practice for the Execution of Female Nude Paintings: The Analytical Investigation of a Genre

The comprehensive technical investigation of female nude paintings by the Singapore pioneer artist Liu Kang (1911–2004) provided the evidence for a discussion of the evolution of his palette of colours and his working process for expression in this genre, particularly the execution of female bodies. As the artist’s free expression in classical nude paintings was limited by the censorship imposed by the Singapore government, the investigated artworks span two periods, 1927–1954 (early career) and 1992–1999 (the “golden years”, during which censorship policies were relaxed). Hence, eight paintings from the Liu family and National Gallery Singapore were selected for non- and micro-invasive analyses of the paint layers. The obtained results were supplemented with archival sources to elucidate certain aspects of Liu Kang’s working practice. The investigation revealed the importance of drawing and sketching studies in the development of artistic ideas. The analytical techniques, such as polarised light microscopy (PLM), field emission scanning electron microscope with energy dispersive spectroscopy (FE-SEM-EDS) and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), enabled us to observe a transition from the yellow iron-based tonal ranges of skin colours to complex pigment mixtures composed of additions of cobalt blue, ultramarine, Prussian blue, Cr-containing yellow(s) and green(s), cadmium yellow, orange and/or red and organic reds, revealing the artist’s more liberal use of colours and his experimentation with their contrasting and complementary juxtaposes. In terms of painting technique, the artist’s comparatively laborious paint application using small brushes quickly gave way to a more effortless manipulation of the paint using bigger brushes and the incorporation of palette knives. Moreover, visible light (VIS), near-infrared (NIR) and X-ray radiography (XRR) imaging techniques led to the discovery of a hidden composition in one investigated artwork, which bears resemblance to the nude painting known only from an archival photograph. Additionally, for the first time, the archival search provided photographic evidence that Liu Kang used oil paint tubes from Royal Talens and Rowney in the 1990s. Overall, this in-depth investigation contributes to the understanding of Liu Kang’s approach to the female nude painting and may assist conservators and art historians in studies of twentieth-century commercial paints