Optical Properties of Polyisocyanurate–Polyurethane Aerogels: Study of the Scattering Mechanisms

Abstract

Highly transparent polyisocyanurate–polyurethane (PUR–PIR) aerogels were synthesized, and their optical properties were studied in detail. After determining the density and structural parameters of the manufactured materials, we analyzed their optical transmittance. It was demonstrated that the catalyst content used to produce the aerogels can be employed to tune the internal structure and optical properties. The results show that the employment of lower catalyst amounts leads to smaller particles forming the aerogel and concomitantly to higher transmittances, which reach values of 85% (650 nm) due to aerogel particles acting as scattering centers. Thus, it was found that the lower this size, the higher the transmittance. The effect of the sample thickness on the transmittance was studied through the Beer–Lambert law. Finally, the scattering mechanisms involved in the light attenuation were systematically evaluated by measuring a wide range of light wavelengths and determining the transition between Rayleigh and Mie scattering when the particles were larger. Therefore, the optical properties of polyurethane aerogels were studied for the first time, opening a wide range of applications in building and energy sectors such as glazing windows.

Thermal Conductivity of Nanoporous Materials: Where Is the Limit?

“…The structure of these materials is similar to that of the silica aerogels, being formed by small spherical particles in the nanometric scale and branched mesopores. The small size of these features has recently led to the obtention of the first polyisocyanurate-polyurethane (PUR-PIR) aerogels presenting transparency [91,92]. The main research showing low values of thermal conductivity for these aerogels is gathered in Table 5.…”

“…It is noticeable that the pores forming these aerogels are mainly mesopores, thus contributing to reducing the gaseous contribution to the effective thermal conductivity. In some cases, these pores are larger than 100 nm ( [92,95,96,98]) owing to the difficulty to measure the pore size in a system with interconnected pores and being of few nanometres.…”

Super-Insulating Transparent Polyisocyanurate-Polyurethane Aerogels: Analysis of Thermal Conductivity and Mechanical Properties

“…Moreover, the combination of excellent thermal insulation with adequate mechanical [ 29 , 30 ] and optical properties has recently been attracting attention [ 31 , 32 ]. In our previously published works, we synthesized for the very first time PUR-PIR aerogels with tunable optical properties, ranging from opaque to transparent aerogels [ 33 , 34 ]. In the present study, we analyze in depth their mechanical and insulating properties reaching, as far as the authors know, the lowest thermal conductivity values up to now for aerogels based on a PU-PIR matrix.…”

Improving the Insulating Capacity of Polyurethane Foams through Polyurethane Aerogel Inclusion: From Insulation to Superinsulation

“…when light passes through them owing to the gel transparency [23,34], as observed in Fig ure 3b. This supports the notion that the foam pores are completely filled with the aeroge which forms a continuous network with the polymeric skeleton of PU foam.…”

“…Examples of the PU F -PU A gel composites obtained are depicted in Figure 3a. Their reticulated structure can be differentiated when light passes through them owing to the gel transparency [23,34], as observed in Figure 3b. This supports the notion that the foam pores are completely filled with the aerogel, which forms a continuous network with the polymeric skeleton of PU foam.…”