Photopyroelectric technique to follow gelation and drying processes in alginate: a proof-of-concept

• Published in: Journal of sol-gel science and technology Vol. 107; no. 3; pp. 513 - 522
• Main Authors: Pessoa, Pedro A. C., Moll, Pedro A. A. M. M., Pereira, Nádia R., Waldman, Walter R., da Silva, Edson C., Soffner, Max E., Guimarães, André O.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-09-2023; Springer Nature B.V
• Subjects: Biological properties; Calcium ions; Ceramics; Change detection; Chemistry and Materials Science; Composites; Crosslinking; Diffusivity; Drying; Evaporation; Gelation; Glass; Heat exchange; Heat transfer; Heat transmission; Inorganic Chemistry; Materials Science; Moisture effects; Nanotechnology; Natural Materials; Optical and Electronic Materials; Original Paper: Characterization methods of sol-gel and hybrid materials; Phase transitions; Polymers; Sodium alginate; Thermal diffusivity; Thermal effusivity; Thermodynamic properties; Water loss; Internal/external gelation; Thermal diffusivity; Thermal conductivity; Alginate; Photothermal techniques; Thermal effusivity
• DOI: 10.1007/s10971-023-06146-2
• EISSN: 1573-4846
• ISSN: 0928-0707

The photopyroelectric (PPE) is a versatile technique to assess thermal properties, and it was used in a proof-of-concept experiment to track the gelation and drying processes of sodium alginate (SA). The technique is based on the detection of thermal waves generated by the absorption of modulated light, using a pyroelectric transducer in contact with the sample. It is widely used for the thermal characterization of liquid, gaseous, and pasty materials and, as it works with temperature oscillations of the order of mK, it is suitable for investigating biological samples and phase transition phenomena. The back (BPPE) and front (FPPE) photopyroelectric configurations were used to determine, respectively, thermal diffusivity and thermal effusivity of solutions with 1, 2, and 3% (w/w), with errors around 0.7%. The thermal diffusivity reveals how fast the heat flows in a medium, while the effusivity measures the thermal impedance of the sample in transient heat flow, reflecting thus the ability of materials to exchange heat with the surroundings. The gelation processes, simultaneously with drying, were followed with both properties and determined as a function of the time, after Ca
2+
addition. The thermal diffusivity fluctuates around 1.45 × 10
−7
 m
2
/s in the first 30 min, increasing afterward, while the thermal effusivity decreases during 30 min and then tends to stabilize around 1.44 × 10
3
 Ws
1/2
m
−2
K
−1
. In our experiments, gelation and drying occur simultaneously and the thermal diffusivity showed to be sensitive to the polymer chains crosslinking, while the effusivity is sensitive to the evaporation of surface and unbound moisture. Thus, the PPE technique could be explored as a valuable tool to track the gelation and drying/evaporation of such systems.
Graphical Abstract
Highlights
PPE technique could be explored as a valuable tool to track the gelation and drying/evaporation of gel systems.
Photopyroelectric technique detects changes in thermal properties due to changes in both polymer-polymer interactions and polymer-water interactions of gel-like systems.
Thermal effusivity is more sensitive to the alginate gelation process than water loss.
Thermal diffusivity is more sensitive to the drying process.