Afsaneh Abareshi

Рhotothermal heat decrease in nanocomposite due to the high heat capacity of gold metal compared to covalent compounds MoS2@CuS. Silver has an even higher specific heat capacity compared to gold. The effect is similar to water with a high heat capacity when you feel the coolness near a river on a hot day.

The decrease in photothermal heat in nanocomposites can be attributed to a combination of interdependent factors. Here are the main reasons, categorized for clarity:

1. Optical Scattering and Absorption:

• Increased Light Scattering: Introducing nanoparticles into a matrix can significantly increase light scattering. Instead of being absorbed efficiently, the incident light is scattered in various directions. This reduces the intensity of light reaching the nanoparticles, and consequently less energy is absorbed and converted into heat. The extent of scattering depends on the size, concentration, and refractive index contrast between the nanoparticles and the matrix.

• Shielding Effect: An excessively high concentration of nanoparticles can lead to a "shielding" effect, where surface particles absorb most of the incident light, leaving particles deeper inside the material with less light to absorb. This reduces the overall photothermal efficiency.

• Altered Optical Absorption Properties: Agglomeration of the nanoparticles, or chemical interactions with the matrix, can alter their optical absorption properties. They may no longer absorb efficiently at the excitation wavelength. This can be due to changes in plasmon resonance (for metallic nanoparticles) or changes in energy levels.

• Light Reflection: The addition of nanoparticles can increase the overall reflectivity of the material, reducing the amount of light that enters the material and can be absorbed.

2. Thermal Properties:

• Low Thermal Conductivity of the Matrix: If the matrix of the nanocomposite has low thermal conductivity, the heat generated by the nanoparticles will be less efficiently dissipated and may accumulate locally. This can lead to reduced overall photothermal efficiency. A matrix with good thermal conductivity helps to spread the heat more evenly.

• Thermal Interface Resistance: The thermal resistance at the interface between the nanoparticles and the matrix can be significant. If heat transfer across this interface is limited, the heat generated in the nanoparticles will not be efficiently transferred to the matrix, reducing the overall photothermal effect. This is also known as the Kapitza resistance.

• Specific Heat Capacity: If the nanocomposite has a higher specific heat capacity than the nanoparticles alone, it will require more energy to raise the temperature of the material. This can give the appearance of a decreased photothermal effect, even if the amount of heat generated is the same.

3. Nanoparticle Stability:

• Nanoparticle Degradation: The generated heat, or chemical interactions with the matrix, can cause the degradation of the nanoparticles, reducing their ability to absorb light and generate heat. This is especially a concern at higher laser powers.

• Nanoparticle Agglomeration: Over time, or under the influence of heat, the nanoparticles may agglomerate or aggregate. Agglomeration changes the optical properties of the nanoparticles, reducing their photothermal efficiency.