Advances in single-sided NMR of polymer and cultural heritage science

The advent of mobile and single-sided NMR enabled performance of non-destructive and non-invasive analysis, boosting NMR experiments in polymer and cultural heritage sciences. Relying on arrangements of permanent magnets, this technology is not as expensive as conventional NMR and supports possibilities of measuring different parts of a heterogeneous sample. The available techniques for assessment of recrystallization as evidence of thermal fusion in joints of PE pipes or the evaluation of polymer cross-link density heretofore required sample destruction or expensive methodology in order to generate accurate conclusions; unilateral NMR can easily provide good results. The depth-dependent monomer mobility in a photo-curing reaction could also be explored with single-sided sensors to probe the reaction kinetics with spatial resolution. Many studies in the field of cultural heritage, such as the evaluation of damaged stone arti- facts, must be carried out in situ, which is possible using single-sided NMR devices. Analysis of the degradation state of ancient paper and parchment, as well evaluations of canvas conditions from easel paintings and studies of ancient pottery, require fully non-invasive methodology. This work proposes innovative utilization of a single-sided sensor, the NMR-MOUSE, to ascertain crystallization, cross-linking and real-time curing observations of polymers and to evaluate a new self-developed inorganic dispersion solution for restoring degraded stones, to detect elementary composition in old pottery, to characterize the damage level of parchments and handmade Chinese paper and, finally, to characterize techniques for canvas reinforcement. It was possible to detect the increase of crystallization generated by a cold-fusion process and the increase in cross-link density of polyethylene created by absorption of β radiation, and also understanding spatiotemporally the photo-curing process of dental resins. Another result indicates changes in porosity of stones due to consolidation and helps to identify the optimum treatment. Furthermore, the transverse magnetization decay in ancient pot- tery showed excellent correlation with the iron quantity and good correlation with the carbon content. Experiments with damaged parchment revealed details of aging, partic- ularly through the use of an innovative two-dimensional NMR experiment. Through a relaxation experiment, it was noted that ancient hemp paper is the kind of paper least sensitive to aging, followed by rice paper and bamboo paper, the most aging-sensitive. Several analyses were made with the help of multivariate data analysis, mainly partial least square (PLS), a robust method that reduces the number of variables. In sum, this thesis explores the NMR-MOUSE sensor as a tool for studying spin relaxation of polymer and cultural heritage samples and supports the feasibility of data processing by exponential curve-fitting, inverse Laplace transformation and multivariate data analysis

Analysis of spectral influence of the NMR CWFP parameters in flow quantitative measurements

A seqüência de pulsos RMN-CWFP (Ressonância Magnética Nuclear - Precessão Livre de Onda Contínua) tem encontrado diversas aplicações na ciência. O presente trabalho analisa a grande sensibilidade dessa seqüência em relação a variações de seus parâmetros espectrais, exclusivamente em uma caracterização teórico-experimental da RMN-CWFP em fluxos do tipo plug-flow, exemplificados por medidas online através do transporte de sementes por uma esteira sob um campo magnético constante no tempo. Foram feitas simulações e medições em várias condições, variando os fatores que influenciam as medidas, como ângulo de nutação (?), ângulo de offset (?), tempo entre pulsos (Tp), gradiente (G), velocidade (v) e tempos de relaxação longitudinal (T1) e transversal (T2). Em determinadas condições fixas de ângulo de nutação, precessão, tempo entre pulsos, gradiente e velocidade, foi observado que poderia existir um ponto nulo com dependência entre T1 e T2. Esse fenômeno foi estudado e algumas aplicações foram sugeridas. O trabalho também validou a seqüência de pulsos CWFP em fluxo como ferramenta para análises quantitativas da massa de óleo em sementes.The NMR-CWFP pulse sequence (Nuclear Magnetic Resonance - Continuous Wave Free Precession) has met several applications in the science. The present work analyses the high sensibility of this sequence to its spectral parameters variation, exclusively in a theoretical and experimental characterization of the flow NMR-CWFP of the kind plug-flow, exemplified by online measures by seeds transport through a mat under a magnetic field constant in time. Simulations and measurements were made on several conditions, varying the factors that have measurement influence, like flip angle (??, offset angle (??, time between pulses (Tp), gradient (G), velocity (v) and longitudinal and transversal relaxation times (T1 and T2). Under certain conditions of flip angle, precession, time between pulses, gradient and velocity, it was noticed that there might be a null point with T1 and T2 dependence. This phenomenon was studied and some applications have been suggested. The work has also validated the CWFP pulse sequence as a quantitative tool to quantitative analysis of seeds oil mass

Advances in single-sided NMR of polymer and cultural heritage science

The advent of mobile and single-sided NMR enabled performance of non-destructive and non-invasive analysis, boosting NMR experiments in polymer and cultural heritage sciences. Relying on arrangements of permanent magnets, this technology is not as expensive as conventional NMR and supports possibilities of measuring different parts of a heterogeneous sample. The available techniques for assessment of recrystallization as evidence of thermal fusion in joints of PE pipes or the evaluation of polymer cross-link density heretofore required sample destruction or expensive methodology in order to generate accurate conclusions; unilateral NMR can easily provide good results. The depth-dependent monomer mobility in a photo-curing reaction could also be explored with single-sided sensors to probe the reaction kinetics with spatial resolution. Many studies in the field of cultural heritage, such as the evaluation of damaged stone arti- facts, must be carried out in situ, which is possible using single-sided NMR devices. Analysis of the degradation state of ancient paper and parchment, as well evaluations of canvas conditions from easel paintings and studies of ancient pottery, require fully non-invasive methodology. This work proposes innovative utilization of a single-sided sensor, the NMR-MOUSE, to ascertain crystallization, cross-linking and real-time curing observations of polymers and to evaluate a new self-developed inorganic dispersion solution for restoring degraded stones, to detect elementary composition in old pottery, to characterize the damage level of parchments and handmade Chinese paper and, finally, to characterize techniques for canvas reinforcement. It was possible to detect the increase of crystallization generated by a cold-fusion process and the increase in cross-link density of polyethylene created by absorption of β radiation, and also understanding spatiotemporally the photo-curing process of dental resins. Another result indicates changes in porosity of stones due to consolidation and helps to identify the optimum treatment. Furthermore, the transverse magnetization decay in ancient pot- tery showed excellent correlation with the iron quantity and good correlation with the carbon content. Experiments with damaged parchment revealed details of aging, partic- ularly through the use of an innovative two-dimensional NMR experiment. Through a relaxation experiment, it was noted that ancient hemp paper is the kind of paper least sensitive to aging, followed by rice paper and bamboo paper, the most aging-sensitive. Several analyses were made with the help of multivariate data analysis, mainly partial least square (PLS), a robust method that reduces the number of variables. In sum, this thesis explores the NMR-MOUSE sensor as a tool for studying spin relaxation of polymer and cultural heritage samples and supports the feasibility of data processing by exponential curve-fitting, inverse Laplace transformation and multivariate data analysis

Use of Carr-Purcell pulse sequence with low refocusing flip angle to measure T-1 and T-2 in a single experiment

The Carr-Purcell pulse sequence, with low refocusing flip angle, produces echoes midway between refocusing pulses that decay to a minimum value dependent on T*(2). When the refocusing flip angle was pi/2 (CP90) and tau > T*(2), the signal after the minimum value, increased to reach a steady-state free precession regime (SSFP), composed of a free induction decay signal after each pulse and an echo, before the next pulse. When tau < T*(2), the signal increased from the minimum value to the steady-state regime with a time constant (T*) = 2T(1)T(2)/(T-1 + T-2). identical to the time constant observed in the SSFP sequence, known as the continuous wave free precession (CWFP). The steady-state amplitude obtained with M-cp90 = M0T2/(T-1+T-2) was identical to CWFP. Therefore, this sequence was named CP-CWFP because it is a Carr-Purcell sequence that produces results similar to the CWFP. However, CP-CWFP is a better sequence for measuring the longitudinal and transverse relaxation times in single scan, when the sample exhibits T-1 similar to T-2. Therefore, this sequence can be a useful method in time domain NMR and can be widely used in the agriculture, food and petrochemical industries because those samples tend to have similar relaxation times in low magnetic fields. (C) 2011 Elsevier Inc. All rights reserved.FAPESP (Brazilian Agency)CNPq (Brazilian Agency)FINEP (Brazilian Agency

Qualitative analysis by online nuclear magnetic resonance using Carr-Purcell-Meiboom-Gill sequence with low refocusing flip angles

The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence has been used in many applications of magnetic resonance imaging (MRI) and low-resolution NMR (LRNMR) spectroscopy. Recently. CPMG was used in online LRNMR measurements that use long RF pulse trains, causing an increase in probe temperature and, therefore, tuning and matching maladjustments. To minimize this problem, the use of a low-power CPMG sequence based on low refocusing pulse flip angles (LRFA) was studied experimentally and theoretically. This approach has been used in several MRI protocols to reduce incident RF power and meet the specific absorption rate. The results for CPMG with LRFA of 3 pi/4 (CPMG(135)), pi/2 (CPMG(90)) and pi/4 (CPMG(45)) were compared with conventional CPMG with refocusing pi pulses. For a homogeneous field, with linewidth equal to Delta nu = 15 Hz, the refocusing flip angles can be as low as pi/4 to obtain the transverse relaxation time (T(2)) value with errors below 5%. For a less homogeneous magnetic field. Delta nu = 100 Hz, the choice of the LRFA has to take into account the reduction in the intensity of the CPMG signal and the increase in the time constant of the CPMG decay that also becomes dependent on longitudinal relaxation time (T(1)). We have compared the T(2) values measured by conventional CPMG and CPMG(90) for 30 oilseed species, and a good correlation coefficient, r = 0.98, was obtained. Therefore, for oilseeds, the T(2) measurements performed with pi/2 refocusing pulses (CPMG(90)), with the same pulse width of conventional CPMG, use only 25% of the RF power. This reduces the heating problem in the probe and reduces the power deposition in the samples. (C) 2011 Elsevier B.V. All rights reserved.FAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPqFINEPFinanciadora de Estudos e Projetos (FINEP