{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,4]],"date-time":"2026-03-04T07:08:40Z","timestamp":1772608120437,"version":"3.50.1"},"reference-count":37,"publisher":"MDPI AG","issue":"20","license":[{"start":{"date-parts":[[2024,10,15]],"date-time":"2024-10-15T00:00:00Z","timestamp":1728950400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"FCT\u2014Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","award":["UIDB\/05256\/2020"],"award-info":[{"award-number":["UIDB\/05256\/2020"]}]},{"name":"FCT\u2014Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","award":["UIDP\/05256\/2020"],"award-info":[{"award-number":["UIDP\/05256\/2020"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Nanomaterials"],"abstract":"<jats:p>The exponential demand for real-time monitoring applications has altered the course of sensor development, from sensor electronics miniaturization, e.g., resorting to printing techniques, to low-cost, flexible and functional wearable materials. Humidity sensing has been used in the prevention and diagnosis of medical conditions, as well as in the assessment of physical comfort. This paper presents a resistive flexible humidity sensor composed of silver interdigitated electrodes (IDTs) screen printed onto polyimide film and an active layer of multiwall carbon nanotubes (MWCNT) dispersed in a water-soluble polymer, polyvinyl alcohol (PVA). Different MWCNT\/PVA sensor sizes and MWCNT percentages are tested to study their effect on the initial electrical resistance (Ri) values and sensor response at different humidity percentages. The results show that the Ri values decrease with the increase in % MWCNT. The sensor size did not influence the sensor response, while the % MWCNT affected the sensor behavior upon relative humidity (RH) increments. The 1% MWCNT\/PVA sensor showed the best response, reaching a relative electrical resistance, \u0394R\/R0, of 509% at 99% RH. Comparable with other reported sensors, the produced MWCNT\/PVA flexible sensor is simpler, greener and shows a good sensitivity to humidity, being easily incorporated in wearable monitoring applications, from sports to medical fields.<\/jats:p>","DOI":"10.3390\/nano14201653","type":"journal-article","created":{"date-parts":[[2024,10,15]],"date-time":"2024-10-15T08:09:08Z","timestamp":1728979748000},"page":"1653","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":10,"title":["The Development of a Flexible Humidity Sensor Using MWCNT\/PVA Thin Films"],"prefix":"10.3390","volume":"14","author":[{"given":"Ana R.","family":"Santos","sequence":"first","affiliation":[{"name":"IPC\u2014Institute for Polymers and Composites, University of Minho, 4804-533 Guimar\u00e3es, Portugal"}]},{"given":"J\u00falio C.","family":"Viana","sequence":"additional","affiliation":[{"name":"IPC\u2014Institute for Polymers and Composites, University of Minho, 4804-533 Guimar\u00e3es, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2024,10,15]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"3256","DOI":"10.1021\/acs.langmuir.8b03433","article-title":"Highly Responsive PEG\/Gold Nanoparticle Thin-Film Humidity Sensor via Inkjet Printing Technology","volume":"35","author":"Su","year":"2019","journal-title":"Langmuir"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1007\/BF03218844","article-title":"Inkjet Printing of Polymeric Resistance Humidity Sensor Using UV-Curable Electrolyte Inks","volume":"16","author":"Cho","year":"2008","journal-title":"Macromol. Res."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"140","DOI":"10.1016\/j.snb.2012.12.046","article-title":"Ink-Jet Printed Conducting Polyaniline Based Flexible Humidity Sensor","volume":"178","author":"Kulkarni","year":"2013","journal-title":"Sens. Actuators B Chem."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"77","DOI":"10.4028\/www.scientific.net\/AST.80.77","article-title":"Feasibility of Printing Woven Humidity and Temperature Sensors for the Integration into Electronic Textiles","volume":"80","author":"Kinkeldei","year":"2012","journal-title":"Adv. Sci. Technol."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Soukup, R., Ham\u00e1\u010dek, A., and \u0158eboun, J. (2012, January 17\u201320). Advanced Screen Printing for the Fabrication of Organic Humidity Sensors. Proceedings of the 2012 4th Electronic System-Integration Technology Conference, ESTC 2012, Amsterdam, The Netherlands.","DOI":"10.1109\/ESTC.2012.6542183"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"47498","DOI":"10.1039\/C6RA03050E","article-title":"Humidity Sensor Fabricated by Inkjet-Printing Photosensitive Conductive Inks PEDOT:PVMA on a Paper Substrate","volume":"6","author":"Yuan","year":"2016","journal-title":"RSC Adv."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"012008","DOI":"10.1088\/1742-6596\/939\/1\/012008","article-title":"Flexible and Highly Sensitive Humidity Sensors Using Screen-Printed TiO2 Nanoparticles as Sensitive Layer","volume":"939","author":"Dubourg","year":"2017","journal-title":"J. Phys. Conf. Ser."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Gaspar, C., Olkkonen, J., Passoja, S., and Smolander, M. (2017). Paper as Active Layer in Inkjet-Printed Capacitive Humidity Sensors. Sensors, 17.","DOI":"10.3390\/s17071464"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Hassan, G., Sajid, M., and Choi, C. (2019). Highly Sensitive and Full Range Detectable Humidity Sensor Using PEDOT:PSS, Methyl Red and Graphene Oxide Materials. Sci. Rep., 9.","DOI":"10.1038\/s41598-019-51712-w"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Descent, P., Izquierdo, R., and Fayomi, C. (2018, January 27\u201330). Printing of Temperature and Humidity Sensors on Flexible Substrates for Biomedical Applications. Proceedings of the IEEE International Symposium on Circuits and Systems 2018, Florence, Italy.","DOI":"10.1109\/ISCAS.2018.8351869"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"5599","DOI":"10.1039\/C7NR08115D","article-title":"Fully Printed High Performance Humidity Sensors Based on Two-Dimensional Materials","volume":"10","author":"He","year":"2018","journal-title":"Nanoscale"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"134486","DOI":"10.1016\/j.snb.2023.134486","article-title":"Laser-Direct-Writing Assisted Preparation of Flexible Humidity Sensors Based on Semi-Interpenetrating Polymer Network for Applications in Non-Contact Human-Machine Interaction","volume":"394","author":"Chen","year":"2023","journal-title":"Sens. Actuators B Chem."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"27746","DOI":"10.1039\/D3RA05232J","article-title":"A Highly Sensitive Flexible Humidity Sensor Based on Conductive Tape and a Carboxymethyl Cellulose@graphene Composite","volume":"13","author":"Wang","year":"2023","journal-title":"RSC Adv."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"869","DOI":"10.1166\/sl.2011.1633","article-title":"Printed Capacitive Based Humidity Sensors on Flexible Substrates","volume":"9","author":"Reddy","year":"2011","journal-title":"Sens. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"134","DOI":"10.1179\/17535557A15Y.000000017","article-title":"Highly Sensitive Humidity Sensors Made from Composites of HEC Filled by Carbon Nanofillers","volume":"30","author":"Ma","year":"2015","journal-title":"Mater. Technol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"120","DOI":"10.1016\/j.proeng.2011.12.030","article-title":"Fully Printed Flexible Humidity Sensor","volume":"25","author":"Reddy","year":"2011","journal-title":"Procedia Eng."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Martadi, S., Sulthoni, M.A., Wiranto, G., Surawijaya, A., and Herminda, I.D.P. (2019, January 8\u20139). Design and Fabrication of PVA-Based Relative Humidity Sensors Using Thick Film Technology. Proceedings of the 2019 International Symposium on Electronics and Smart Devices, ISESD 2019, Badung, Indonesia.","DOI":"10.1109\/ISESD.2019.8909519"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1038\/s41528-023-00290-z","article-title":"A Skin-Conformal and Breathable Humidity Sensor for Emotional Mode Recognition and Non-Contact Human-Machine Interface","volume":"8","author":"Li","year":"2024","journal-title":"npj Flex. Electron."},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Turkani, V.S., Narakathu, B.B., Maddipatla, D., Bazuin, B.J., and Atashbar, M.Z. (2018, January 15\u201319). A Fully Printed CNT Based Humidity Sensor on Flexible PET Substrate. Proceedings of the 17th International Meeting on Chemical Sensors\u2014IMCS 2018, Vienna, Austria.","DOI":"10.5162\/IMCS2018\/P1FW.5"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4788","DOI":"10.1021\/acsami.6b12448","article-title":"Highly Sensitive Wearable Textile-Based Humidity Sensor Made of High-Strength, Single-Walled Carbon Nanotube\/Poly(Vinyl Alcohol) Filaments","volume":"9","author":"Zhou","year":"2017","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Arunachalam, S., Gupta, A.A., Izquierdo, R., and Nabki, F. (2018). Suspended Carbon Nanotubes for Humidity Sensing. Sensors, 18.","DOI":"10.3390\/s18051655"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"707303","DOI":"10.1155\/2011\/707303","article-title":"Humidity Sensor Based on Multi-Walled Carbon Nanotube Thin Films","volume":"2011","author":"Cao","year":"2011","journal-title":"J. Nanomater."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"1714","DOI":"10.3390\/s90301714","article-title":"Humidity Sensitivity of Multi-Walled Carbon Nanotube Networks Deposited by Dielectrophoresis","volume":"9","author":"Liu","year":"2009","journal-title":"Sensors"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"28248","DOI":"10.1021\/acsami.3c04283","article-title":"Flexible Humidity Sensor with High Sensitivity and Durability for Respiratory Monitoring Using Near-Field Electrohydrodynamic Direct-Writing Method","volume":"15","author":"Pan","year":"2023","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2311","DOI":"10.1039\/C9NA00179D","article-title":"A Highly Sensitive Printed Humidity Sensor Based on a Functionalized MWCNT\/HEC Composite for Flexible Electronics Application","volume":"1","author":"Turkani","year":"2019","journal-title":"Nanoscale Adv."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"512","DOI":"10.1016\/j.snb.2005.12.048","article-title":"Layer-by-Layer Assembly and Humidity Sensitive Behavior of Poly(Ethyleneimine)\/Multiwall Carbon Nanotube Composite Films","volume":"119","author":"Yu","year":"2006","journal-title":"Sens. Actuators B Chem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"80","DOI":"10.1016\/j.sse.2013.05.001","article-title":"A Resistive-Type Sensor Based on Flexible Multi-Walled Carbon Nanotubes and Polyacrylic Acid Composite Films","volume":"87","author":"Lee","year":"2013","journal-title":"Solid State Electron."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"1600153","DOI":"10.1002\/admi.201600153","article-title":"Effective Enhancement of Humidity Sensing Characteristics of Novel Thermally Treated MWCNTs\/Polyvinylpyrrolidone Film Caused by Interfacial Effect","volume":"3","author":"Pan","year":"2016","journal-title":"Adv. Mater. Interfaces"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"120","DOI":"10.1016\/j.snb.2009.11.041","article-title":"Novel Resistive-Type Humidity Sensor Based on Multiwall Carbon Nanotube\/Polyimide Composite Films","volume":"145","author":"Yoo","year":"2010","journal-title":"Sens. Actuators B Chem."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"99","DOI":"10.1016\/j.snb.2010.09.016","article-title":"Fast Response Resistive Humidity Sensitivity of Polyimide\/Multiwall Carbon Nanotube Composite Films","volume":"152","author":"Tang","year":"2011","journal-title":"Sens. Actuators B Chem."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1186\/s40580-022-00326-6","article-title":"Wearable CNTs\u2014Based Humidity Sensors with High Sensitivity and Flexibility for Real\u2014Time Multiple Respiratory Monitoring","volume":"9","author":"Kim","year":"2022","journal-title":"Nano Converg."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"128","DOI":"10.2174\/2210681206666160328201458","article-title":"Humidity Sensing Properties of Multiwalled Carbon Nanotube\/Polyvinyl Alcohol Nanocomposite Films","volume":"6","author":"Manohara","year":"2017","journal-title":"Nanosci. Nanotechnol.-Asia"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1002\/app.39726","article-title":"Humidity Switching Properties of Sensors Based on Multiwalled Carbon Nanotubes\/Polyvinyl Alcohol Composite Films","volume":"131","author":"Fei","year":"2014","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_34","unstructured":"Myung, J.L., Cheol-Jin, L., Singh, V.R., Kum-Pyo, Y., and Nam-Ki, M. (2008, January 26\u201329). Humidity Sensing Characteristics of Plasma Functionalized Multiwall Carbon Nanotube-Polyimide Composite Films. Proceedings of the IEEE Sensors, Lecce, Italy."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"1474","DOI":"10.1021\/acs.langmuir.2c02827","article-title":"Fast-Speed, Highly Sensitive, Flexible Humidity Sensors Based on a Printable Composite of Carbon Nanotubes and Hydrophilic Polymers","volume":"39","author":"Ding","year":"2023","journal-title":"Langmuir"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"115372","DOI":"10.1016\/j.sna.2024.115372","article-title":"Preparation of PVA\/CNTs Film with High Stability and Humidity Sensitivity Based on Multiple Process","volume":"372","author":"Ni","year":"2024","journal-title":"Sens. Actuators A Phys."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"89","DOI":"10.6028\/jres.081A.011","article-title":"Humidity Fixed Points of Binary Saturated Aqueous Solutions","volume":"81A","author":"Greenspan","year":"1977","journal-title":"J. Res. Natl. Bur. Stand. Sect. A Phys. Chem."}],"container-title":["Nanomaterials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2079-4991\/14\/20\/1653\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T16:13:29Z","timestamp":1760112809000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2079-4991\/14\/20\/1653"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2024,10,15]]},"references-count":37,"journal-issue":{"issue":"20","published-online":{"date-parts":[[2024,10]]}},"alternative-id":["nano14201653"],"URL":"https:\/\/doi.org\/10.3390\/nano14201653","relation":{},"ISSN":["2079-4991"],"issn-type":[{"value":"2079-4991","type":"electronic"}],"subject":[],"published":{"date-parts":[[2024,10,15]]}}}