Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions
The weak absorption of a laser beam generates in a fluid an inhomogeneous refractive index profile acting as a negative lens. This self-effect on beam propagation, known as Thermal Lensing (TL), is extensively exploited in sensitive spectroscopic techniques, and in several all-optical methods for th...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2023-03-01
|
| Series: | Polymers |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2073-4360/15/5/1283 |
| _version_ | 1797614523757101056 |
|---|---|
| author | Vincenzo Ruzzi Stefano Buzzaccaro Roberto Piazza |
| author_facet | Vincenzo Ruzzi Stefano Buzzaccaro Roberto Piazza |
| author_sort | Vincenzo Ruzzi |
| collection | DOAJ |
| description | The weak absorption of a laser beam generates in a fluid an inhomogeneous refractive index profile acting as a negative lens. This self-effect on beam propagation, known as Thermal Lensing (TL), is extensively exploited in sensitive spectroscopic techniques, and in several all-optical methods for the assessment of thermo-optical properties of simple and complex fluids. Using the Lorentz–Lorenz equation, we show that the TL signal is directly proportional to the sample thermal expansivity <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>, a feature allowing minute density changes to be detected with high sensitivity in a tiny sample volume, using a simple optical scheme. We took advantage of this key result to investigate the compaction of PniPAM microgels occurring around their volume phase transition temperature, and the temperature-driven formation of poloxamer micelles. For both these different kinds of structural transitions, we observed a significant peak in the solute contribution to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>, indicating a decrease in the overall solution density—rather counterintuitive evidence that can nevertheless be attributed to the dehydration of the polymer chains. Finally, we compare the novel method we propose with other techniques currently used to obtain specific volume changes. |
| first_indexed | 2024-03-11T07:12:53Z |
| format | Article |
| id | doaj.art-8964723c75e548bfa3f49cf31f8bcfa3 |
| institution | Directory Open Access Journal |
| issn | 2073-4360 |
| language | English |
| last_indexed | 2024-03-11T07:12:53Z |
| publishDate | 2023-03-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Polymers |
| spelling | doaj.art-8964723c75e548bfa3f49cf31f8bcfa32023-11-17T08:28:41ZengMDPI AGPolymers2073-43602023-03-01155128310.3390/polym15051283Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer SolutionsVincenzo Ruzzi0Stefano Buzzaccaro1Roberto Piazza2Department of Chemistry, Materials Science and Chemical Engineering (CMIC) “Giulio Natta”, Politecnico di Milano, Edificio 6, Piazza Leonardo da Vinci 32, 20133 Milano, ItalyDepartment of Chemistry, Materials Science and Chemical Engineering (CMIC) “Giulio Natta”, Politecnico di Milano, Edificio 6, Piazza Leonardo da Vinci 32, 20133 Milano, ItalyDepartment of Chemistry, Materials Science and Chemical Engineering (CMIC) “Giulio Natta”, Politecnico di Milano, Edificio 6, Piazza Leonardo da Vinci 32, 20133 Milano, ItalyThe weak absorption of a laser beam generates in a fluid an inhomogeneous refractive index profile acting as a negative lens. This self-effect on beam propagation, known as Thermal Lensing (TL), is extensively exploited in sensitive spectroscopic techniques, and in several all-optical methods for the assessment of thermo-optical properties of simple and complex fluids. Using the Lorentz–Lorenz equation, we show that the TL signal is directly proportional to the sample thermal expansivity <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>, a feature allowing minute density changes to be detected with high sensitivity in a tiny sample volume, using a simple optical scheme. We took advantage of this key result to investigate the compaction of PniPAM microgels occurring around their volume phase transition temperature, and the temperature-driven formation of poloxamer micelles. For both these different kinds of structural transitions, we observed a significant peak in the solute contribution to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>α</mi></semantics></math></inline-formula>, indicating a decrease in the overall solution density—rather counterintuitive evidence that can nevertheless be attributed to the dehydration of the polymer chains. Finally, we compare the novel method we propose with other techniques currently used to obtain specific volume changes.https://www.mdpi.com/2073-4360/15/5/1283thermal expansivitythermosensitive polymersPniPAMpoloxamersoptothermal methods |
| spellingShingle | Vincenzo Ruzzi Stefano Buzzaccaro Roberto Piazza Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions Polymers thermal expansivity thermosensitive polymers PniPAM poloxamers optothermal methods |
| title | Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions |
| title_full | Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions |
| title_fullStr | Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions |
| title_full_unstemmed | Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions |
| title_short | Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions |
| title_sort | thermal lens measurements of thermal expansivity in thermosensitive polymer solutions |
| topic | thermal expansivity thermosensitive polymers PniPAM poloxamers optothermal methods |
| url | https://www.mdpi.com/2073-4360/15/5/1283 |
| work_keys_str_mv | AT vincenzoruzzi thermallensmeasurementsofthermalexpansivityinthermosensitivepolymersolutions AT stefanobuzzaccaro thermallensmeasurementsofthermalexpansivityinthermosensitivepolymersolutions AT robertopiazza thermallensmeasurementsofthermalexpansivityinthermosensitivepolymersolutions |