Photothermal effect

IR photothermal beam deflection spectroscopy (PBDS) and measurements of IR spectra of solids over the range 3950-450 cm l made with an interferometer coupled with a detector which senses the photothermal effect by the deflection of a laser beam are described. PBDS is a general technique and requires no sample preparation all that is needed is to hold the sample at the IR focus. The sample must have a flat spot about 2 mm in diameter accessible to the IR and laser beams. As no sample cells per se are... 

The technique employed is IR-FT photothermal beam deflection spectroscopy (PBDS). It is an off-shoot of photoacoustic spectroscopy (PAS) [1] and is based on the "mirage detection of the photothermal effect invented by Boccara et al. [2] and shown to result in a spectroscopic technique of remarkable versatility and utility. Some applications of "mirage spectroscopy," mainly in the visible, and theoretical treatments, have been described [3 6]. The method has now been developed for use in the IR. The spectrometer and techniques are described in detail elsewhere [7], but it will be useful to give a brief outline of the principles. 

The very large absorption cross-sections of Au nanoparticles give rise to photothermal effects, that is, an increase in local temperature upon plasmon resonance excitation. The concept of Au nanoparticles as photothermal transducers has inspired numerous efforts to develop biomedical applications such as localized hyperthermal therapy,63-65 photothermal contrast agents,66 and optothermally controlled drug release,67-69 and also novel platforms for information storage.70... 

Surface plasmon effects result in useful photothermal effects [73] and have been used to enhance the surface sensitivity of various spectroscopic measurements [74], including fluorescence, Raman scattering, and second-harmonic generation. 

Photothermal effect An effect produced by photoexcitation resulting partially or totally in the production of heat. 

An alternative technique is the so-called Photothermal Beam Deflection Spectroscopy [PBDS], based on the so-called mirage effect first reported by Boccarra and coworkers [39, 40]. In this case, the periodic temperature rise caused by the absorption of the modulated IR radiation (i.e. the photothermal effect) is detected optically because it causes periodic deflections of a laser beam passing close to the surface of the solid sample. The PBDS technique has some advantages over the PAS technique, because of its lower Hmits of sample dimensions, but it has disadvantages because of the critical geometric setup. Like PAS, PBDS can have advantages with respect to traditional IR technique for the detection of surface... 

Photons, therefore, provide the activation energy needed for the initiation of a reaction. Whether or not the drug itself will absorb energy can be deduced from an examination of its UV-VIS spectrum. Since the incident photonic energy may be converted to heat, a photolytic reaction may be accompanied by a thermal reaction, resulting in a photothermal effect. Once a thermal reaction is initiated, it may proceed even in the dark (25). 

Another original feature of the photothermal effect is the derivative dn/dT, typically on the order of 10 but which can be enhanced dramatically close to phase transitions or to critical points of the matrix or solvent around the particle to be detected (provided the response is faster than the modulation time t). 

Fig. 10.5 Schematic illustrations of the photothermal effect of nanomateiials and the mechanism of the photomechanical behavior induced by the photothermal effect of nanomaterials...

In this optical technique based on photothermal effects, pump light is shone on a transmission grating in front of a fluid channel and the inside liquid is heated with a pattern of the grating due to the Talbot effect [11]. Another probe light is... 

Metal-Polyaniline Nanocomposites Based on Polyaniline Nanofibers Electrical Properties of Metal-Polyaniline Nanocomposite Materials Other Methods to Make Metal-Polyaniline Nanocomposites Growth of Inorganic Nanoparticles by In Situ Metathesis Reactions Unusual Photothermal Effect of the Polyaniline Nanofibers Flash Welding.7-30... 

Photothermal Effect in Nanostructured Materials Flash Welding of Polyaniline Nanofibers Flash Welding of Other Materials Outlook Polyaniline Derivatives and Other... 

Unusual Photothermal Effect of the Polyaniline Nanofibers Flash Welding... 

The nanoscale structure of polyaniline nanofibers produces enhanced polymer functionalities their polymeric nature also yields new nanoscale physicochemical phenomena that have not been observed in inorganic nanostructured materials. In this section, a flash welding technique is presented based on an enhanced photothermal effect discovered with the polyaniline nanofibers. 

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