PMID- 34640813 OWN - NLM STAT- MEDLINE DCOM- 20211014 LR - 20211016 IS - 1424-8220 (Electronic) IS - 1424-8220 (Linking) VI - 21 IP - 19 DP - 2021 Sep 29 TI - Synthesis and Characterization of N-Isopropylacrylamide Microspheres as pH Sensors. LID - 10.3390/s21196493 [doi] LID - 6493 AB - Swellable polymer microspheres that respond to pH were prepared by free radical dispersion polymerization using N-isopropylacrylamide (NIPA), N,N(')-methylenebisacrylamide (MBA), 2,2-dimethoxy-2-phenylacetylphenone, N-tert-butylacrylamide (NTBA), and a pH-sensitive functional comonomer (acrylic acid, methacrylic acid, ethacrylic acid, or propacrylic acid). The diameter of the microspheres was between 0.5 and 1.0 mum. These microspheres were cast into hydrogel membranes prepared by mixing the pH-sensitive swellable polymer particles with aqueous polyvinyl alcohol (PVA) solutions followed by crosslinking with glutaric dialdehyde for use as pH sensors. Large changes in the turbidity of the PVA membrane were observed as the pH of the buffer solution in contact with the membrane was varied. These changes were monitored by UV-visible absorbance spectroscopy. Polymer swelling of many NIPA copolymers was reversible and independent of the ionic strength of the buffer solution in contact with the membrane. Both the degree of swelling and the apparent pK(a) of the polymer microspheres increased with temperature. Furthermore, the apparent pK(a) of the polymer particles could be tuned to respond sharply to pH in a broad range (pH 4.0-7.0) by varying the amount of crosslinker (MBA) and transition temperature modifier (NTBA), and the amount, pK(a), and hydrophobicity of the pH-sensitive functional comonomer (alkyl acrylic acid) used in the formulation. Potential applications of these polymer particles include fiber optic pH sensing where the pH-sensitive material can be immobilized on the distol end of an optical fiber. FAU - Lavine, Barry K AU - Lavine BK AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Kaval, Necati AU - Kaval N AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Oxenford, Leah AU - Oxenford L AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Kim, Mariya AU - Kim M AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Dahal, Kaushalya Sharma AU - Dahal KS AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Perera, Nuwan AU - Perera N AUID- ORCID: 0000-0002-0012-4199 AD - Department of Chemistry and Physics, Western Carolina University, Cullowhee, NC 28723, USA. FAU - Seitz, Rudolf AU - Seitz R AD - Department of Chemistry, University of New Hampshire, Durham, NH 03824, USA. FAU - Moulton, James T AU - Moulton JT AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. FAU - Bunce, Richard A AU - Bunce RA AD - Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA. LA - eng GR - RD-830911101-0/U.S. Environmental Protection Agency/ PT - Journal Article DEP - 20210929 PL - Switzerland TA - Sensors (Basel) JT - Sensors (Basel, Switzerland) JID - 101204366 RN - 0 (Acrylamides) RN - 0 (Hydrogels) RN - 0 (Polymers) RN - B7GFF17L9U (N-isopropylacrylamide) SB - IM MH - Acrylamides MH - *Hydrogels MH - Hydrogen-Ion Concentration MH - Microspheres MH - *Polymers PMC - PMC8512897 OTO - NOTNLM OT - N-isopropylacrylamide OT - nonionic polymer swelling OT - optical pH sensing OT - thermodynamics of pH-induced polymer swelling OT - turbidimetry COIS- The authors declare no conflict of interest. EDAT- 2021/10/14 06:00 MHDA- 2021/10/15 06:00 PMCR- 2021/09/29 CRDT- 2021/10/13 01:12 PHST- 2021/08/03 00:00 [received] PHST- 2021/09/24 00:00 [revised] PHST- 2021/09/24 00:00 [accepted] PHST- 2021/10/13 01:12 [entrez] PHST- 2021/10/14 06:00 [pubmed] PHST- 2021/10/15 06:00 [medline] PHST- 2021/09/29 00:00 [pmc-release] AID - s21196493 [pii] AID - sensors-21-06493 [pii] AID - 10.3390/s21196493 [doi] PST - epublish SO - Sensors (Basel). 2021 Sep 29;21(19):6493. doi: 10.3390/s21196493.