High-precision method for measuring the photothermal properties of transparent media with digital holography

Quantitative phase microscopy by digital holography provides direct access to the phase profile of a transparent subject with high precision. This is useful for observing phenomena that modulate phase, but are otherwise difficult or impossible to detect. In this letter, a carefully constructed digital holographic apparatus is used to measure optically induced thermal lensing with an optical path difference precision of less than 1 nm. Furthermore, by taking advantage of the radial symmetry of a thermal lens, such data are processed to determine the absorption coefficient of transparent media with precisions as low as 1 × 10-5cm-1 using low power （30 mW） continuous wave （CW） excitation.

Characterizations and Photothermal Properties of Narrow Bandgap Conjugated Polymer Nanoparticles

Photothermal therapy(PTT)is a minimally invasive treatment that kills cancer cells by converting photon energy into heat.The past few decades have witnessed the booming development of photothermal materials,mainly focusing on precious metal nanomaterials and carbon nanomaterials,such as nanogold and silver and nanocarbon materials for near-infrared(NIR)light-triggered PTF.As precious metals are expensive and potentially harmful to humans,exploration and development of a new type of photothermal materials has become a research hotspot in this field.Herein,we report narrow bandgap conjugated polymer nanoparticles(PDPP NPs)based on pyrrolo[3,4-c]pyrrole-1,4-dione(DPP)with intense NIR absorption at 900 nm,as well as a photothermal energy conversion efficiency of 75%.This polymer nanoparticle is essentially non-toxic,as the cell viability of mouse remained more than 90%,even when the concentration of PDPP NPs was at 0.5 mg·mL^-1.

Recent Advancements on Photothermal Conversion and Antibacterial Applications over MXenes-Based Materials

The pernicious bacterial proliferation and emergence of super-resistant bacteria have already posed a great threat to public health,which drives researchers to develop antibiotic-free strategies to eradicate these fierce microbes.Although enormous achievements have already been achieved,it remains an arduous challenge to realize efficient sterilization to cut off the drug resistance generation.Recently,photothermal therapy(PTT)has emerged as a promising solution to efficiently damage the integrity of pathogenic bacteria based on hyperthermia beyond their tolerance.Until now,numerous photothermal agents have been studied for antimicrobial PTT.Among them,MXenes(a type of two-dimensional transition metal carbides or nitrides)are extensively investigated as one of the most promising candidates due to their high aspect ratio,atomic-thin thickness,excellent photothermal performance,low cytotoxicity,and ultrahigh dispersibility in aqueous systems.Besides,the enormous application scenarios using their antibacterial properties can be tailored via elaborated designs of MXenes-based materials.In this review,the synthetic approaches and textural properties of MXenes have been systematically presented first,and then the photothermal properties and sterilization mechanisms using MXenes-based materials are documented.Subsequently,recent progress in diverse fields making use of the photothermal and antibacterial performances of MXenes-based materials are well summarized to reveal the potential applications of these materials for various purposes,including in vitro and in vivo sterilization,solar water evaporation and purification,and flexible antibacterial fabrics.Last but not least,the current challenges and future perspectives are discussed to provide theoretical guidance for the fabrication of efficient antimicrobial systems using MXenes.

Silver Nanowires Contained Nanofluids with Enhanced Optical Absorption and Thermal Transportation Properties

Two kinds of silver nanowires(100 nm in diameter, 20 μm and 100 μm in length) are prepared. The thermo-physical characteristics, viscosity, and photothermal conversion performance of the silver nanowires(AgNWs)contained ethylene glycol nanofluids are investigated in detail. It is found that thermal conductivity of 100 μm AgNWs contained nanofluids is higher than that of 20 μm AgNWs with the same diameters of 100 nm. Viscosity test shows that the nanofluid is a Newtonian fluid, and the longer silver nanowires, the greater viscosity. In addition, photothermal conversion efficiency of silver nanowires contained nanofluid is studied. We can observe that the 100 μm AgNWs contained nanofluid has a higher photothermal conversion efficiency than that containing 20 μm AgNWs. Moreover, we find that there is a certain correlation between heat transfer and photothermal conversion of nanofluid. It demonstrates that the high heat transfer property of nanofluid will benefit for its photothermal conversion efficiency and the mechanism is proposed. This work provides a new idea to improve photothermal conversion efficiency. We can choose materials with high thermal conductivity and strong light absorption ability to enhance the photothermal conversion performance of nanofluids.

Numerical and Experimental Investigation on Photothermal Performance of Polyimide/High-Electrical-Performance-Coating Composite Films Considering Surface Roughness

Polyimide(PI)films are the common and important components on spacecraft for thermal control.Their parameter design accuracy has an important impact on the spacecraft thermal balance but there are few studies focusing on the effect of film surface defects.In the present study,photothermal properties of composite films made of PI films and germanium/indium tin oxide/aluminum coatings are obtained by UV-VIS-NIR spectrophotometer.The film surface morphology of composite films is obtained by the atomic force microscope.The present study creatively introduces surface roughness into modeling from the perspective of finite-difference time-domain(FDTD)model.The FDTD method considering surface roughness is used to present a comprehensive investigation on the coating effect on the photothermal properties including transmittance and reflectance of composite films.Based on the random rough surface generated by root-mean-square(RMS)roughness and correlation length,the FDTD method is applied to characterize the electromagnetic field of composite films.It has been found that the numerical accuracy is greatly improved and the numerical results agree well with the experimental data when surface roughness is considered.The results also show that coating material and thickness have remarkable impacts on photothermal properties of the composite films.