Chip Calorimeter Research Articles

Calorimetric Glass Transition of Poly(2,6-dimethyl-1,5-phenylene oxide) Thin Films

The glass transition of poly(2,6-dimethyl-1,5-phenylene oxide) (PPO) films with thickness ranging from about 6 nm (approximately half of radius of gyration, Rg) to 330 nm (∼29 Rg) was studied by the recently developed differential alternating current chip calorimeter with sensitivity on the order of tenths of a pJ K−1. No thickness dependence of the glass temperature Tg was found for this polymer. Tgs of all the films measured in the available frequency range (∼0.5 to ∼1000 Hz) can be fit by a single Vogel−Fulcher−Tammann function in the activation plot within an uncertainty of ±3 K, thus showing no deviation from the common VFT behavior even for the thinnest film. There is also no detectable change in the shape or width of the step in heat capacity at Tg. Finally, we found that calorimetric relaxation strength at the glass transition was proportional to the thickness of the film within an uncertainty of about 25%. Consequently, we estimate the thickness of the layer deviated from the bulky behavior to be...

Chip calorimetry and its use for biochemical and cell biological investigations

The presented paper analyzes the potential of chip calorimetry for biochemical and cell biological investigations. From the thermo-physical properties of the heat power detectors of a chip calorimeter can be deduced that relevant applications mainly refer to fast reactions in extremely small samples. In contrast, the use of chip calorimeters for studying slow processes such as biochemical or microbial reactions is restricted. However, careful optimization of chip calorimeters concerning signal resolution and sample volume enables the investigation of enzymatically catalyzed reactions and the measurement of microbial growth heat as subsequently demonstrated with some typical examples from the literature.

Chip calorimeters for the investigation of liquid phase reactions: Design rules

Rules for the design of silicon chip based devices for liquid phase calorimetry are discussed. In contrast to the study of fast reactions the investigation of slow processes like the metabolic heat production requires sample volumes of at least a few micro-liters if a signal resolution in the mW l −1 range is necessary. On the other hand, increasing sensitivity gradients inside the reaction chamber and external temperature perturbations restrict its enlargement. Therefore, a careful optimization of the device with respect to the sample volume is necessary if one likes to use the advantages of chip calorimeters. The presented study was performed by use of a new designed flow-through chip calorimeter.

Metastability of polymer crystallites formed at low temperature studied by ultra fast calorimetry: Polyamide 6 confined in sub-micrometer droplets vs. bulk PA6

It is shown that the application of a chip calorimeter, allowing very fast cooling and heating rates up to 10,000 K/s, can be successfully applied to study reorganization phenomena in crystallizable polymers. In this research both bulk Polyamide 6 (PA6) as well as an immiscible (polystyrene/styrene-maleic anhydride copolymer)/Polyamide 6 blend with dispersed Polyamide 6 droplets of sub-micrometer size have been studied. The blends with sub-micrometer PA6 droplets have been shown to crystallize at low temperature via a homogeneous nucleation mechanism, due to a lack of heterogeneities in the small droplets. Upon fast cooling with more than 500 K/s crystallization of PA6 could be totally prevented. No cold crystallization takes place upon subsequent heating with 500 K/s. Upon fast heating of 2000 K/s after isothermal crystallization, the ‘real’, initial melting of the crystallites formed at very low temperature could be obtained, which was not possible with standard DSC apparatus or HPer DSC. However, even heating with 5000 K/s was not fast enough to completely avoid reorganization. Annealing experiments in the melt-range clearly show the fast reorganization of PA6 crystallites, resulting in improved stability within a timescale in the order of 0.01–0.1 s. Most probably reorganization takes place mainly in the crystalline state, and only to a lesser extent via a melting–recrystallization–remelting process. The reorganization process is not hindered by the confined dimensions of the Polyamide 6 droplets, because both bulk PA6 as well as the confined (PS/SMA2)/PA6 blend give rise to identical reorganization phenomena.

Melting and reorganization of the crystalline fraction and relaxation of the rigid amorphous fraction of isotactic polystyrene on fast heating (30,000 K/min)

For polymers the origin of the multiple melting peaks observed in DSC curves is still controversially discussed. This is due to the difficulty to investigate the melting of the originally formed crystals exclusively. Recrystallization is a fast process and most experimental techniques applied so far do not allow fast heating in order to prevent recrystallization totally. Developments in thin-film (chip) calorimetry allow scanning rates as high as several thousand Kelvin per second. We utilized a chip calorimeter based on a commercially available vacuum gauge, which is operated under non-adiabatic conditions. The calorimeter was used to study the melting of isothermally crystallized isotactic polystyrene (iPS). Our results on melting at rates up to 30,000K/min (500K/s) give evidence for the validity of a melting–recrystallization–remelting process for iPS at low scanning rates (DSC). At isothermal conditions iPS forms crystals, which all melt within a few dozens of K slightly above the isothermal crystallization temperature. There is no evidence for the formation of multimodal populations of crystals with significantly different stability (melting temperatures). Furthermore, relaxation (devitrification) of the rigid amorphous fraction occurs in parallel to melting. Superheating of the crystals is of the order of 25K at 30,000K/min.

Chip calorimetry for the monitoring of whole cell biotransformation

Efficient control of whole cell biotransformation requires quantitative real-time information about the thermodynamics and kinetics of growth and product formation. Heat production contains such information, but its technical application is restricted due to the high price of calorimetric devices, the difficulty of integrating them into existing bio-processes and the slow response times of established microcalorimeters. A new generation of chip or nanocalorimeters may overcome these weaknesses. We thus tested a highly sensitive chip calorimeter for its applicability in biotechnological monitoring. It was used to monitor aerobic growth of suspended and immobilized Escherichia coli DH5alpha DSM 6897 and anaerobic growth of suspended Halomonas halodenitrificans CCM 286(T). The chip data corresponded well with enthalpy balance calculations and measurements with a conventional calorimeter, indicating the applicability of the chip calorimeter for bio-process control.

Highly sensitive thermopile heat power sensor for micro-fluid calorimetry of biochemical processes

A micro-fluid chip calorimeter measuring system with highly stable thermostat (0.1 mK) was developed based on an improved nano calorimetry thin-film thermopile chip with excellent chemical and mechanical reliability fabricated in SU-8 technology for insulation and passivation layers. Biochemical processes (e.g. enzyme catalyzed reaction) can be investigated with heat power detection limit <100 nW.

High Sensitive Differential AC-Chip Calorimeter for Nanogram Samples

A differential AC chip calorimeter based on commercially available sensors is described. Due to the differential setup pJK －1 sensitivity is achieved. Heat capacity can be measured for sample masses below one nanogram. This corresponds to heat capacities below one nJK －1 even above room temperature as needed for the study of the glass transition in nanometer thin polymeric films. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the broad frequency range from 1 Hz to 1 kHz for sample masses of some nanograms. 解 説

Melting and reorganization of poly(ethylene terephthalate) on fast heating (1000 K/s)

For poly(ethylene terephthalate) (PET) and other polymers the origin of the multiple melting peaks observed in differential scanning calorimetry (DSC) curves is still controversially discussed. This is due to the difficulty to investigate the melting of the originally formed crystals exclusively. Recrystallization is a fast process and most experimental techniques applied so far do not allow fast heating in order to prevent recrystallization totally. Developments in thin-film (chip) calorimetry allow scanning rates as high as several thousand Kelvin per second. We utilized a chip calorimeter based on a commercially available vacuum gauge, which is operated under non-adiabatic conditions. The calorimeter was used to study the melting of isothermally crystallized PET. Our results on melting at rates as high as 2700 K/s give clear evidence for the validity of a melting–recrystallization–remelting process for PET at low scanning rates (DSC). At isothermal conditions PET forms crystals, which all melt within a few dozens of K slightly above the isothermal crystallization temperature. There is no evidence for the formation of different populations of crystals with significantly different stability (melting temperatures) under isothermal conditions. Superheating of the crystals is of the order of 10 K at 2700 K/s.

Direct monitoring of biochemical processes using micro-structured heat power detectors

An improved flow-through chip calorimeter useful for liquid samples is presented. The heat power detection limit could be decreased to a level of 180 nW. Main features of the new micro-sized calorimeter are a differential chip arrangement, a small sized thermostat with a precision in the micro-kelvin range and the application of micro-pumps for liquid flow control. The improved heat power resolution enables the monitoring of biochemical processes under relevant conditions. As applications have shown a pulsed fluid injection can increase the degree of mixing. For the determination of the degree of mixing a new method was developed.

Chip reactor for microfluid calorimetry

A microchip module with integrated flow channel and highly sensitive thin-film thermoelements of Bi0.87Sb0.13 and Sb was developed in order to realize a microcalorimeter for small volumes and flows in the μl and μl/min range, respectively. It was designed according to the principle of flow-injection analysis (FIA) and prepared using means of micromachining technology. The flow channel comprises two inlets, a mixing region, a measurement region and one outlet. In this way, the initiation of chemical reactions by interdiffusion takes place in the closest possible contact with the sensing elements. Three thermopiles (i.e. thermoelements connected in series) are arranged on a thin-film membrane covering the fluid channel. A thin-film heater of an NiCr alloy is integrated for internal electrical calibration. The microreactor was first tested in the neutralization reaction between sodium hydroxide and sulphuric acid for different NaOH concentrations, flows, and sample volumes, investigating for the present the integral signal of the three thermopiles connected in series. From the collected data, the minimum detectable power, minimum detectable NaOH concentration, and the reaction enthalpy were calculated. The results characterize the module as a sensitive chip calorimeter, showing the suitability of the micromachining technology for calorimetry.