Direct Measurement of Temperature Diffusivity of Nanocellulose-Doped Biodegradable Composite Films

Detection of dynamic temperature modulation using a thermal scanning probe lithography (t-SPL) system

Nanoscale measurements of thermophysical properties, based on detecting temperature responses to periodic heat stimulation, can be achieved using a localized heating point instead of a localized sensing point. However, the concept of determining localized thermophysical properties via nano-heating as an alternative to nano-sensing has not yet been validated. In this study, we demonstrate the measurement of thermal diffusivity within a nanoscale-confined volume using a thermal scanning probe lithography (t-SPL) system. The sharp tip of the t-SPL probe is employed to locally and periodically heat the sample, which is placed on a pre-fabricated micro-thermocouple. Using the temperature wave analysis method, the thermal diffusivity of the sample is inferred from the frequency-dependent phase shift in the temperature response of a thermocouple. This technique was applied to the microscale structure of a chemically amplified negative-tone photoresist (mr-DWL). We show that confining the heat source to a nanoscale point contact can achieve spatial resolution at the nanoscale (10-100 nm), offering an alternative approach to miniaturizing the detector sensor.

Analyses of chemiluminescence reactions of fluorophore-linked 1,2-dioxetane isomers in crystals heating at elevated temperature including a development of a simultaneous measurement method of thermal diffusivity and light emission for a single crystal

It has been found that a fluorophore-linked adamantylideneadamantane 1,2-dioxetane derivative showed an isomeric difference in the reactivities of crystalline-state chemiluminescence (CL) under isothermal heating conditions, while there are still unsolved problems on the conditions for intracrystalline reactions. To confirm the suitable heating conditions for initiating crystalline-state CL reactions of the isomers, the CL reactions in their crystal samples heated at elevated temperature were investigated with monitoring of CL light emission and thermogravimetry-differential thermal analysis (TG-DTA) measurements together with a simultaneous measurement method of thermal diffusivity and light emission, to provide the information on suitable temperature range for the crystalline-state CL reactions and on the reactivities depending on open and closed conditions of the crystal samples. The newly developed simultaneous measurement method provides a methodology for a single crystal to analyze the relationship between a change of the thermophysical property of inside of the crystal and the progress of a crystalline-state CL reaction.

Microfluidics Temperature Compensating and Monitoring Based on Liquid Metal Heat Transfer

Microfluidic devices offer excellent heat transfer, enabling the biochemical reactions to be more efficient. However, the precision of temperature sensing and control of microfluids is limited by the size effect. Here in this work, the relationship between the microfluids and the glass substrate of a typical microfluidic device is investigated. With an intelligent structure design and liquid metal, we demonstrated that a millimeter-scale industrial temperature sensor could be utilized for temperature sensing of micro-scale fluids. We proposed a heat transfer model based on this design, where the local correlations between the macro-scale temperature sensor and the micro-scale fluids were investigated. As a demonstration, a set of temperature-sensitive nucleic acid amplification tests were taken to show the precision of temperature control for micro-scale reagents. Comparations of theoretical and experimental data further verify the effectiveness of our heat transfer model. With the presented compensation approach, the slight fluorescent intensity changes caused by isothermal amplification polymerase chain reaction (PCR) temperature could be distinguished. For instance, the probability distribution plots of fluorescent intensity are significant from each other, even if the amplification temperature has a difference of 1 °C. Thus, this method may serve as a universal approach for micro–macro interface sensing and is helpful beyond microfluidic applications.

Probe-based microscale measurement setup for the thermal diffusivity of soft materials

Based on the principle of the periodic heating method by using cantilever thermocouple nanoprobes, we developed a method and an apparatus to measure the thermal diffusivity of soft materials on a microscale. The contact position of the probe tip with the sample surface was defined by using the phenomenon that the DC component of the thermal electromotive force (EMF) of the probe changes significantly upon contact (i.e., the vertical temperature gradient near the sample surface changes significantly). This contact position was set as the surface reference position where the variation of the thermal contact conductance between the sample surface and the sensor probe is minimized. The phase shift from the micro-heater was measured by the AC component of the probe's thermal EMF and used to accurately determine the thermal diffusivity of micro-sized soft materials. The thermal diffusivity of the microstructured photoresist was determined with a deviation of ±3%.

Measurement Method of Thermal Diffusivity of the Building Wall for Summer and Winter Seasons in Poland

The thermal diffusivity of building materials is an extremely important parameter influencing the subsequent thermal comfort of building users. By definition, thermal diffusivity describes how quickly heat from a hot source can flow through a material. Therefore, this parameter includes both the thermal conductivity and the heat capacity of the material. This parameter is often neglected in heat-related calculations which, in the case of dynamic problems, leads to unreliable results. It should be taken into account that heat flows through all materials at a finite speed. On the other hand, knowing the correct thermal diffusivity value of building materials, it is possible to accurately determine the internal parameters in rooms over time. There are several methods for determining thermal diffusivity, most of which are destined to determine this property in laboratories. The aim of the present research is to show how the thermal diffusivity of materials can be determined in existing buildings. The presented method can be used to determine more real thermal parameters used for thermal calculations in buildings, for example, during energy audits or when calculating the demand for cooling for air conditioning or heat for space heating. This research presents the results for a 60 cm brick wall. Thermal diffusivity was determined for specific summer and winter days—most representative of the whole year. This research has shown that the applied method should be used in the summer period, due to the fact that the wall has greater temperature fluctuations. The obtained results are comparable with the previously mentioned laboratory methods. However, due to the fact that the materials analyzed on the spot, the results are more reliable, and also take into account changes in the value of thermal diffusivity resulting from the use of binders, inaccuracies in joining and external layers made of other materials.

Photothermally Driven High-Speed Crystal Actuation and Its Simulation

Mechanically responsive crystals have been increasingly explored, mainly based on photoisomerization. However, photoisomerization has some disadvantages for crystal actuation, such as a slow actuation speed, no actuation of thick crystals, and a narrow wavelength range. Here we report photothermally driven fast-bending actuation and simulation of a salicylideneaniline derivative crystal with an o-amino substituent in enol form. Under ultraviolet (UV) light irradiation, these thin (<20 μm) crystals bent but the thick (>40 μm) crystals did not due to photoisomerization; in contrast, thick crystals bent very quickly (in several milliseconds) due to the photothermal effect, even by visible light. Finally, 500 Hz high-frequency bending was achieved by pulsed UV laser irradiation. The generated photothermal energy was estimated based on the photodynamics using femtosecond transient absorption. Photothermal bending is caused by a nonsteady temperature gradient in the thickness direction due to the heat conduction of photothermal energy generated near the crystal surface. The temperature gradient was calculated based on the one-dimensional nonsteady heat conduction equation to simulate photothermally driven crystal bending successfully. Most crystals that absorb light have their own photothermal effects. It is expected that the creation and design of actuation of almost all crystals will be possible via the photothermal effect, which cannot be realized by photoisomerization, and the potential and versatility of crystals as actuation materials will expand in the near future.

Second Harmonic Generation from Phase-Engineered Metasurfaces of Nanoprisms

Metasurfaces of gold (Au) nanoparticles on a SiO2-Si substrate were fabricated for the enhancement of second harmonic generation (SHG) using electron beam lithography and lift-off. Triangular Au nanoprisms which are non-centro-symmetric and support second-order nonlinearity were examined for SHG. The thickness of the SiO2 spacer is shown to be an effective parameter to tune for maximising SHG. Electrical field enhancement at the fundamental wavelength was shown to define the SHG intensity. Numerical modeling of light enhancement was verified by experimental measurements of SHG and reflectivity spectra at the normal incidence. At the plasmonic resonance, SHG is enhanced up to ∼3.5 × 103 times for the optimised conditions.