Optical characterization of salt-induced swelling behavior of poly(N -isopropylacrylamide) terpolymer hydrogel layers

This study reports for the first time the effect of different sodium halide salts (NaClO4 , NaI, and Na 2 CO3)in the low concentration range (in the range of 10 −7–1 M) on the swelling behavior of photo-crosslinked, surfaceimmobilized poly(N -isopropyl acrylamide) (PNIPAAm) terpolymer layers. PNIPAAm terpolymer (consisting of N -isopropylacrylamide, methacrylic acid, and 4-methacryloxybenzophenone) was synthesized via free radical polymerization. The PNIPAAm terpolymer layers were prepared on gold substrates via spin coating and crosslinked and surface attached via UV radiation. The swelling behavior of the layers in monovalent (NaClO4 and NaI) and divalent (Na 2 CO3) solutions was monitored by surface plasmon/optical waveguide spectroscopy. The terpolymer layers did not swell significantly at very low salt concentrations (10 −7 –10 −5 M), whereas an increase in swelling upon the addition of salt upto 10 −2 –0.1 M depending on the salt was observed. Further increase in the salt concentration up to 1 M led to collapse of the terpolymer PNIPAAm layers due to the reduction in solvent quality of the salt solution. The full collapse of the terpolymer PNIPAAm layers with 1 M salt solution was observed only when divalent kosmotropic Na 2 CO3 salt was used.

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1. Hirokawa Y, Tanaka T. Volume phase transition in a nonionic gel. The Journal of Chemical Physics 1984; 81: 6379-6380. doi: 10.1063/1.447548
2. Junk MJN, Jonas U, Hinderberger D. EPR spectroscopy reveals nanoinhomogeneities in the structure and reactivity of thermoresponsive hydrogels. Small 2008; 4 (9): 1485-1493. doi: 10.1002/smll.200800127
3. Tanaka T, Fillmore D, Sun ST, Nishio I, Swislow G et al. Phase transitions in ionic gels .Physical Review Letters 1980; 45: 1636-1639. doi: 10.1103/PhysRevLett.45.1636
4. Eichenbaum GM, Kiser PF, Simon SA, Needham D. pH and ion-triggered volume response of anionic hydrogel microspheres. Macromolecules 1998; 31 (15): 5084-5093. doi: 10.1021/ma970897t
5. Krasovitski E, Cohen Y, Bianco-Peled HJ. The effect of salts on the conformation and microstructure of poly(Nisopropylacrylamide) (PNIPA) in aqueous solution. Journal of Polymer Science: Part B Polymer Physics 2004; 42 (20): 3713-3720. doi:10.1002/polb.20221
6. Harmon ME, Jakob TAM, Knoll W, Frank CW. A surface plasmon resonance study of volume phase transitions in n-isopropylacrylamide gel films. Macromolecules 2002; 35 (15): 5999-6004. doi: 10.1021/ma010985k
7. Kato N, Yamanobe S, Takahashi F. Property of magneto-driven poly (N-isopropylacrylamide) gel containing γ - Fe 2 O3 in NaCl solution as a chemomechanical device. Materials Science and Engineering: C Materials for Biological Applications 1997; 5 (2): 141-147. doi: 10.1016/S0928-4931(97)00030-1
8. Tanaka T, Nishio I, Sun ST, Ueno-Nishio S. Collapse of gels in an electric field. Science 1982; 218 (4571): 467-469. doi: 10.1126/science.218.4571.4674
9. Schmaljohann D. Thermo- and pH-responsive polymers in drug delivery. Advanced Drug Delivery Reviews 2006; 58 (15), 1655-1670. doi: 10.1016/j.addr.2006.09.020
10. Lewis G, Coughlan DC, Lane ME, Corrigan OI. Preparation and release of model drugs from thermally sensitive poly(N -isopropylacrylamide) based macrospheres. Journal of Microencapsulation 2006; 23 (6): 677-685. doi:10.1080/02652040600789237
11. Reber N, Spohr R, Wolf A, Omichi H, Tamada M et al. Closure characteristics of a thermally responsive single ion-track pore determined by size exclusion method. Journal of Membrane Science 1998; 140 (2): 275-281. doi:10.1016/S0376-7388(97)00279-2
12. Liang L, Feng XD, Martin PFC, Peurrung LM. Temperature-sensitive switch from composite poly(N-isopropylacrylamide) sponge gels. Journal of Applied Polymer Science 2000; 75 (14): 1735-1739. doi:10.1002/(SICI)1097- 4628(20000401)75:14<1735::AID-APP7>3.0.CO;2-R
13. Wang Y, Brunsen A, Jonas U, Dostalek J, Knoll W. Prostate specific antigen biosensor based on long range surface plasmon-enhanced fluorescence spectroscopy and dextran hydrogel binding matrix. Analytical Chemistry 2009; 81 (23): 9625-9632. doi: 10.1021/ac901662e.
14. Kanazawa H, Matsushima Y, Okano T. Temperature-responsive chromatography. In: Brown PR, Grushka E (editors). Advances in Chromatography. New York, NY, USA: CRC Press, 2001, volume 41, pp. 311-316.
15. Tokarev I, Minko S. Stimuli-responsive hydrogel thin films. Soft Matter 2009; 5: 511-524. doi: 10.1039/B813827C
16. Anac I, Aulasevich A, Junk MJN, Jakubowicz P, Roskamp RF et al. Optical characterization of co-nonsolvency effects in thin responsive PNIPAAm-based gel layers exposed to ethanol/water mixtures. Macromolecular Chemistry and Physics 2010; 211: 1018-1025. doi: 10.1002/macp.200900533
17. Junk MJ N, Anac I, Menges B, Jonas U. Analysis of optical gradient profiles during temperature- and saltdependent swelling of thin responsive hydrogel films. Langmuir 2010; 26 (14): 12253-12259. doi: 10.1021/la101185q
18. Harmon ME, Kuckling D, Frank CW. Photo-cross-linkable PNIPAAm copolymers. 2. Effects of constraint on temperature and pH-responsive hydrogel layers. Macromolecules 2003; 36 (1): 162-172. doi: 10.1021/ma021025g
19. Harmon ME, Kuckling D, Pareek P, Frank CW. Photo-cross-linkable PNIPAAm copolymers. 4. Effects of copolymerization and cross-linking on the volume-phase transition in constrained hydrogel layers. Langmuir 2003; 19 (26): 10947-10956. doi: 10.1021/la030217h
20. Toomey RG, Freidank D, Ruhe J. Swelling behavior of thin, surface-attached polymer networks. Macromolecules 2004; 37 (3): 882-887. doi: 10.1021/ma034737v
21. Schmidt S, Motschmann H, Hellweg T, von Klitzing R. Thermoresponsive surfaces by spin-coating of PNIPAM-coPAA microgels: a combined AFM and ellipsometry study. Polymer 2008; 49 (4): 749-756. doi: 10.1016/j.polymer. 2007.12.025
22. Beines PW, Klosterkamp I, Menges B, Jonas U, Knoll W. Responsive thin hydrogel layers from photo-cross-linkable poly(N -isopropylacrylamide) terpolymers. Langmuir 2007; 23 (4): 2231-2238. doi: 10.1021/la063264t
23. Vidyasagar A, Smith HL, Majewski J, Toomey RG. Continuous and discontinuous volume-phase transitions in surface-tethered, photo-crosslinked poly(N -isopropylacrylamide) networks. Soft Matter 2009; 5 (23), 4733-4738. doi: 10.1039/B904963K
24. van den Brom C, Anac I, Roskamp RF, Retsch M, Jonas U et al. The swelling behaviour of thermoresponsive hydrogel/silica nanoparticle composites. Journal of Materials Chemistry 2010; 20 (23): 4827-4839. doi: 10.1039/b927314j
25. Gianneli M, Beines PW, Roskamp RF, Koynov K, Fytas G et al. Local and global dynamics of transient polymer networks and swollen gels anchored on solid surfaces. Journal of Physical Chemistry C 2007; 111 (35): 13205-13211. doi: 10.1021/jp0728959
26. Raccis R, Roskamp R, Hopp I, Menges B, Koynov K et al. Probing mobility and structural inhomogeneities in grafted hydrogel films by fluorescence correlation spectroscopy. Soft Matter 2011; 7 (15): 7042-7053. doi: 10.1039/C0SM01438A
27. Gianneli M, Roskamp RF, Jonas U, Loppinet B, Fytas G et al. Dynamics of swollen gel layers anchored to solid surfaces. Soft Matter 2008; 4 (7): 1443-1447. doi: 10.1039/B801468J
28. Gianneli M, Anac I, Roskamp R, Menges B, Loppinet B et al. Dynamic response of anchored poly(N -isopropylacrylamide-co-methacrylic acid-co-benzophenone methacrylate) terpolymer hydrogel layers to physicochemical stimuli. Macromolecular Chemistry and Physics 2015; 216: 277-286. doi: 10.1002/macp.201400361
29. Ishida N, Biggs S. Salt-induced structural behavior for poly(N -isopropylacryamide) grafted onto solid surface observed directly by AFM and QCM-D. Macromolecules 2007; 40 (25): 9045-9052. doi:10.1021/ma071878e
30. Naini CA, Thomas M, Franzka S, Frost S, Ulbricht M et al. Hofmeister effect of sodium halides on the switching energetics of thermoresponsive polymer brushes. Macromolecular Rapid Communications 2013; 34 (5): 417-422. doi:10.1002/marc.201200681
31. Murdoch TJ, Humphreys BA, Willott JD, Gregory KP, Prescott SW et al. Specific anion effects on the internal structure of a poly(N -isopropylacrylamide) brush. Macromolecules 2016; 49 (16): 6050-6060. doi: 10.1021/acs.macromol.6b01001
32. Humphreys BA, Willott JD, Murdoch TJ, Webber GB, Wanless EJ. Specific ion modulated thermoresponse of poly(N -isopropylacrylamide) brushes. Physical Chemistry Chemical Physics 2016; 18 (8): 6037-6046. doi: 10.1039/C5CP07468A
33. Koenig M, Rodenhausen KB, Rauch S, Bittrich E, Eichhorn KJ et al. Salt sensitivity of the thermoresponsive behavior of PNIPAAm brushes. Langmuir 2018; 34 (7): 2448-2454. doi: 10.1021/acs.langmuir.7b039
34. Schild HG. Poly(N-isopropylacrylamide): experiment, theory and application. Progress in Polymer Science 1992; 17 (2): 163-249. doi:10.1016/0079-6700(92)90023
35. Prucker O, Naumann CA, Rühe J, Knoll W, Frank CW. Photochemical attachment of polymer films to solid surfaces via monolayers of benzophenone derivatives. Journal of American Chemical Society 1999; 121 (38): 8766- 8770. doi: 10.1021/ja990962+
36. Biesalski M, Johannsmann D, Rühe J. Synthesis and swelling behavior of a weak polyacid brush. The Journal of Chemical Physics 2002; 117: 4988-4994. doi: 10.1063/1.1490924
37. Knoll W. Interfaces and thin films as seen by bound electromagnetic waves. Annual Review of Physical Chemistry 1998; 4: 569-638. doi: 10.1146/annurev.physchem.49.1.569
38. Born M, Wolf E. Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light. Cambridge UK: Cambridge University Press, 1999.
39. Acikbas Y, Taktak F, Capan F, Tuncer C, Butun V et al. An optical vapor sensor based on amphiphilic block copolymer Langmuir–Blodgett films. IEEE Sensors Journal 2018; 18 (13): 5313-5320. doi:10.1109/JSEN.2018.2833491
40. Acikbas Y, Capan F, Erdogan M, Bulut L, Soykan C. Optical characterization and swelling behaviour of Langmuir– Blodgett thin films of a novelpoly[(Styrene (ST)-co-Glycidyl Methacrylate (GMA)]. Sensor and Actuators B: Chemical 2017; 241: 1111-1120. doi: 10.1016/j.snb.2016.10.025