rus
Issue #8/2016
A.Melnikov, A.Rodygin, K.Grafskaya, D.Anokhin, D.Ivanov
High temporal resolution nanocalorimetry and its combination with micro- and nanofocus x-ray diffraction for study of functional nanostructured materials
High temporal resolution nanocalorimetry and its combination with micro- and nanofocus x-ray diffraction for study of functional nanostructured materials
Сombination of high temporal resolution nanocalorimetry with micro- and nanofocus x-ray diffraction allows to study complex structure formation processes in nanostructured functional materials of different nature.
Теги: microstructure nanocalorimetry structure formation микроструктура нанокалориметрия структурообразование
Nanocalorimetry, or ultra-fast chip calorimetry, in recent years, gaining popularity as one of the promising methods of thermal analysis. The rapid development of this method is caused by the fact that an increasing number of materials is created or used in states far from thermodynamic equilibrium. High speeds of heating/cooling and high sensitivity make it extremely useful in the study of organic and inorganic materials including polymers, composites, nanostructured crystalline and liquid crystalline system. In addition, the possibility of using samples of very small mass (from 1 ng) opens completely new perspectives for the application of nanocalorimetry, for example, in the pharmaceutical industry and for the study of modern energy-intensive explosives, where the increase in mass of the material involved in the experiment is undesirable from the point of view of economy or security.
The first works devoted to the nanocalorimetry, was published in 1994–1998 [1–3]. Using the created instruments the quantitative thermal measurements on the samples of ultrathin organic and inorganic films, as well as on a polymer single crystals have been carried out [4–6]. The development of nanocalorimetry was promoted considerably by the emergence of new MEMS sensors, the main part of which is nitride-silicon membrane with low thermal conductivity and a thickness of less than 1 µm. The active area of the sensor located on the membrane is bounded by two pairs of heating elements of aluminum and the six series-connected thermocouples. Heating of the sample placed in the center of the active area, occurs by passing an electric current through the heating elements, and temperature of the sample is measured using thermocouples. Sensors of this type have low thermal inertia and, as a consequence, the rate of heating and cooling of the sample can reach 106 °C/s [7–10].
The unique Nanocalorimeter device developed at the Laboratory of Material Science Engineering at Lomonosov Moscow State University uses MEMS sensors of the latest generation and offers a number of advantages in comparison with analogues:
• wide range of operating temperature from –100 to 500 °C;
• high sensitivity of nanocalorimetric sensor to an electric signal;
• wide range of temperature modulation from 1.0 Hz to 40 kHz (so-called AC mode);
• measurement accuracy of the phase shift of the temperature response of the sample is higher than 0.05°;
• maximum sampling frequency (temporal resolution) of 5 µs;
• temperature resolution of 1 °C.
Possible rate of heating of the active area of nanocalorimetric sensor in the DC modes is up to 1 million °C/s, controlled rate of cooling is up to 5,000 °C/s.
The developed device has the design of the open type, which allows combining thermal analysis with other methods of physicochemical analysis to identify the mechanisms of complex transitions that occur during the heat treatment of materials, and for a more detailed study of functional nanostructured materials. In particular, for the experiment on the combination of nanocalorimetry with micro- and nanofocus x-ray diffraction the holders were developed, which provide accurate positioning and spatial stability of nanocalorimetric sensor in the focus of the x-ray beam and also protect the analog signal from interference while it is being transferred from nanocalorimetric sensor to electronic unit of Nanocalorimeter. The device was installed in the ID13 beam-line of the European synchrotron radiation facility (ESRF) in Grenoble (France). In the experiments we used the x-ray beam focused to sizes of about 100 nm with the use of Fresnel lenses, which provide the focus with the lowest loss of intensity. Schematic diagram and photo of the system for the combination of nanocalorimetry with micro- and nanofocus synchrotron x-ray diffraction is shown in Fig.1. This system allows to scan the samples using nanosized x-ray beam with pitch of less than 1 µm and to obtain structural maps based on two-dimensional high-resolution diffraction patterns [13–14].
As an example, Fig.2 and Fig.3 present the results of studying of the samples of nanostructured poly(trimethylene terephthalate) (PTT). Particles of a polymer were melted at 230 °C followed by rapid cooling (5 000 °C/s) and isothermal crystallization at 150 °C. The upper part of Fig.2 presents the characteristic nanocalorimetry curve obtained when heating the PTT sample at rate of 1 000 °C/s, which shows multiple melting of the crystallized material. The middle curve in Fig.2 corresponds to partial melting of the sample at 192 °C, and the lower curve – to re-heating after partial melting and rapid hardening. As can be seen from the graphs, the first melting peak in the thermogram is missing for heating of the partially-melted sample.
Partially melted at 192 °C, the sample was scanned with nanoscale x-ray beam (scan area is marked with dashed lines in the left part of Fig.3). Two-dimensional SAXS diffraction patterns obtained at different points of the sample with a pitch of 1.33 µm and an exposure time of 10 s are shown as a composite image (Fig.3, right side). Also the different types of SAXS diffraction patterns, such as oriented and streaky diffraction patterns that are typical for the scattering from individual crystals are highlighted in the figure. The experiment shows the melting of PTT crystals of the smallest stability and their recrystallization in a more stable form [11], which is different from the classical model of melting-recrystallization [12–15].
With a new generation of Dectris Eiger 4M high speed x-ray detectors it has become possible to conduct experiments on the microfocus x-ray scattering with simultaneous obtaining of nanocalorimetry thermograms [14–15]. The detector operates at a frequency of 200 Hz with a continuous reading of the signal intensity of x-rays, which allows to obtain x-ray patterns of high quality with the temperature resolution, e.g., of 1 °C at a heating rate of 5,000 °C/s.
Aqueous microgels on the polymer basis are one of the most interesting functional nanostructured materials for study by this method. The microgels can find wide practical application after modification by the reaction groups [16, 17], polymer chains [18, 19], proteins [20–22], noble metals and oxides [23–27], and also by biominerals. By modification of aqueous microgels using amphiphilic ligands, having a V-like shape (Fig.4), the new adaptive composite nanomaterials (ACNM) are developed. They can be used, for example, for drug delivery. The amphiphilic mesogens in the structure of the sample allows to monitor the thermal behavior of these materials.
For the study of structural changes in ACNM during heat exposure we carried out a comprehensive analysis of the source amphiphilic ligands using combination of nanocalorimetry and microfocus x-ray scattering. During heating of the V-like amphiphiles to 270 °C with speeds of 5 °C/min and 1 000 °C/min and subsequent ultra-fast hardening at room temperature the significant differences in the phase composition of the sample are observed. In particular, the formation of columnar phase was observed during slow heating (Fig.4c), and at increased rate of heating the lamellar phase (Fig.4d) was formed in the sample. As can be seen, the heating speed has a great influence on the phase behavior of nanostructured material. Therefore, adjusting the rate of temperature change, we can stabilize particular phase.
It can be concluded that developed by authors high temporal resolution nanocalorimetry and its combination with micro- and nanofocus x-ray diffraction allow to study complex structure formation processes in nanostructured functional materials of different nature. In the presented method, the measurement of thermodynamic parameters using nanocalorimetry is complemented by simultaneous x-ray diffraction studies using high-speed detection of x-rays. We can predict that this method would be popular in academic and industrial laboratories working in various areas of materials science. ■
The project is executed at financial support of the Ministry of education and science of the Russian Federation (contract No. 14.575.21.0093 (RFMEFI57514X0093) from 21 Oct 2014), the Federal targeted programme for research and development in priority areas of development of the russian scientific and technological complex for 2014–2020. The authors are grateful to M. Rosenthal, M. Burghammer and other members of the ID13 beam-line of the European synchrotron radiation facility (ESRF) in Grenoble (France) for their help in conducting experiments.
The first works devoted to the nanocalorimetry, was published in 1994–1998 [1–3]. Using the created instruments the quantitative thermal measurements on the samples of ultrathin organic and inorganic films, as well as on a polymer single crystals have been carried out [4–6]. The development of nanocalorimetry was promoted considerably by the emergence of new MEMS sensors, the main part of which is nitride-silicon membrane with low thermal conductivity and a thickness of less than 1 µm. The active area of the sensor located on the membrane is bounded by two pairs of heating elements of aluminum and the six series-connected thermocouples. Heating of the sample placed in the center of the active area, occurs by passing an electric current through the heating elements, and temperature of the sample is measured using thermocouples. Sensors of this type have low thermal inertia and, as a consequence, the rate of heating and cooling of the sample can reach 106 °C/s [7–10].
The unique Nanocalorimeter device developed at the Laboratory of Material Science Engineering at Lomonosov Moscow State University uses MEMS sensors of the latest generation and offers a number of advantages in comparison with analogues:
• wide range of operating temperature from –100 to 500 °C;
• high sensitivity of nanocalorimetric sensor to an electric signal;
• wide range of temperature modulation from 1.0 Hz to 40 kHz (so-called AC mode);
• measurement accuracy of the phase shift of the temperature response of the sample is higher than 0.05°;
• maximum sampling frequency (temporal resolution) of 5 µs;
• temperature resolution of 1 °C.
Possible rate of heating of the active area of nanocalorimetric sensor in the DC modes is up to 1 million °C/s, controlled rate of cooling is up to 5,000 °C/s.
The developed device has the design of the open type, which allows combining thermal analysis with other methods of physicochemical analysis to identify the mechanisms of complex transitions that occur during the heat treatment of materials, and for a more detailed study of functional nanostructured materials. In particular, for the experiment on the combination of nanocalorimetry with micro- and nanofocus x-ray diffraction the holders were developed, which provide accurate positioning and spatial stability of nanocalorimetric sensor in the focus of the x-ray beam and also protect the analog signal from interference while it is being transferred from nanocalorimetric sensor to electronic unit of Nanocalorimeter. The device was installed in the ID13 beam-line of the European synchrotron radiation facility (ESRF) in Grenoble (France). In the experiments we used the x-ray beam focused to sizes of about 100 nm with the use of Fresnel lenses, which provide the focus with the lowest loss of intensity. Schematic diagram and photo of the system for the combination of nanocalorimetry with micro- and nanofocus synchrotron x-ray diffraction is shown in Fig.1. This system allows to scan the samples using nanosized x-ray beam with pitch of less than 1 µm and to obtain structural maps based on two-dimensional high-resolution diffraction patterns [13–14].
As an example, Fig.2 and Fig.3 present the results of studying of the samples of nanostructured poly(trimethylene terephthalate) (PTT). Particles of a polymer were melted at 230 °C followed by rapid cooling (5 000 °C/s) and isothermal crystallization at 150 °C. The upper part of Fig.2 presents the characteristic nanocalorimetry curve obtained when heating the PTT sample at rate of 1 000 °C/s, which shows multiple melting of the crystallized material. The middle curve in Fig.2 corresponds to partial melting of the sample at 192 °C, and the lower curve – to re-heating after partial melting and rapid hardening. As can be seen from the graphs, the first melting peak in the thermogram is missing for heating of the partially-melted sample.
Partially melted at 192 °C, the sample was scanned with nanoscale x-ray beam (scan area is marked with dashed lines in the left part of Fig.3). Two-dimensional SAXS diffraction patterns obtained at different points of the sample with a pitch of 1.33 µm and an exposure time of 10 s are shown as a composite image (Fig.3, right side). Also the different types of SAXS diffraction patterns, such as oriented and streaky diffraction patterns that are typical for the scattering from individual crystals are highlighted in the figure. The experiment shows the melting of PTT crystals of the smallest stability and their recrystallization in a more stable form [11], which is different from the classical model of melting-recrystallization [12–15].
With a new generation of Dectris Eiger 4M high speed x-ray detectors it has become possible to conduct experiments on the microfocus x-ray scattering with simultaneous obtaining of nanocalorimetry thermograms [14–15]. The detector operates at a frequency of 200 Hz with a continuous reading of the signal intensity of x-rays, which allows to obtain x-ray patterns of high quality with the temperature resolution, e.g., of 1 °C at a heating rate of 5,000 °C/s.
Aqueous microgels on the polymer basis are one of the most interesting functional nanostructured materials for study by this method. The microgels can find wide practical application after modification by the reaction groups [16, 17], polymer chains [18, 19], proteins [20–22], noble metals and oxides [23–27], and also by biominerals. By modification of aqueous microgels using amphiphilic ligands, having a V-like shape (Fig.4), the new adaptive composite nanomaterials (ACNM) are developed. They can be used, for example, for drug delivery. The amphiphilic mesogens in the structure of the sample allows to monitor the thermal behavior of these materials.
For the study of structural changes in ACNM during heat exposure we carried out a comprehensive analysis of the source amphiphilic ligands using combination of nanocalorimetry and microfocus x-ray scattering. During heating of the V-like amphiphiles to 270 °C with speeds of 5 °C/min and 1 000 °C/min and subsequent ultra-fast hardening at room temperature the significant differences in the phase composition of the sample are observed. In particular, the formation of columnar phase was observed during slow heating (Fig.4c), and at increased rate of heating the lamellar phase (Fig.4d) was formed in the sample. As can be seen, the heating speed has a great influence on the phase behavior of nanostructured material. Therefore, adjusting the rate of temperature change, we can stabilize particular phase.
It can be concluded that developed by authors high temporal resolution nanocalorimetry and its combination with micro- and nanofocus x-ray diffraction allow to study complex structure formation processes in nanostructured functional materials of different nature. In the presented method, the measurement of thermodynamic parameters using nanocalorimetry is complemented by simultaneous x-ray diffraction studies using high-speed detection of x-rays. We can predict that this method would be popular in academic and industrial laboratories working in various areas of materials science. ■
The project is executed at financial support of the Ministry of education and science of the Russian Federation (contract No. 14.575.21.0093 (RFMEFI57514X0093) from 21 Oct 2014), the Federal targeted programme for research and development in priority areas of development of the russian scientific and technological complex for 2014–2020. The authors are grateful to M. Rosenthal, M. Burghammer and other members of the ID13 beam-line of the European synchrotron radiation facility (ESRF) in Grenoble (France) for their help in conducting experiments.
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