Effect of polymer network inhomogeneity on the volume phase transitions of thermo- and pH-sensitive weakly charged microgels


Environmentally sensitive polymer gels exhibit pronounced swelling and deswelling upon changes in temperature and pH, which has been discussed in mean-field pictures to assess at which conditions it occurs continuously or discontinuously. However, such treatment disregards nanometer-scale inhomogeneities of the distribution of cross-links and pH-sensitive groups in the polymer gel networks. To check for the impact of such inhomogeneity, we use droplet-based microfluidics to fabricate submillimeter-sized gel particles with either homogeneous-random or inhomogeneous-arranged polymer cross-linking and/or acrylic acid (AAc) group densities. These particles are then used to study their volume phase behavior from macroscopic and microscopic perspectives. Our results show that a systematic variation of the spatial distribution of ionizable groups inside the gels notably impacts the continuity and critical temperature of their volume phase transitions. This is remarkable, because even though our samples are just weakly charged, we observe effects similar to earlier findings made for strong polyelectrolytes.

This is a preview of subscription content, access via your institution.

We’re sorry, something doesn't seem to be working properly.

Please try refreshing the page. If that doesn't work, please contact support so we can address the problem.

Fig. 1
Fig. 2
Fig. 3
Fig. 4


  1. 1.

    Schild HG (1992) Poly (N-isopropylacrylamide)—experiment, theory and application. Prog Polym Sci 17(2):163–249. doi:10.1016/0079-6700(92)90023-R

    CAS  Article  Google Scholar 

  2. 2.

    Polotsky AA, Plamper FA, Borisov OV (2013) Collapse-to-swelling transitions in pH- and thermoresponsive microgels in aqueous dispersions: the thermodynamic theory. Macromolecules 46(21):8702–8709. doi:10.1021/ma401402e

    CAS  Article  Google Scholar 

  3. 3.

    Lapeyre V, Gosse I, Chevreux S, Ravaine V (2006) Monodispersed glucose-responsive microgels operating at physiological salinity. Biomacromolecules 7(12):3356–3363. doi:10.1021/bm060588n

    CAS  Article  Google Scholar 

  4. 4.

    Hoare T, Pelton R (2007) Engineering glucose swelling responses in poly(N-isopropylacrylamide)-based microgels. Macromolecules 40(3):670–678. doi:10.1021/ma062254w

    CAS  Article  Google Scholar 

  5. 5.

    Han DM, Zhang QM, Serpe MJ (2015) Poly (N-isopropylacrylamide)-co-(acrylic acid) microgel/Ag nanoparticle hybrids for the colorimetric sensing of H2O2. Nanoscale 7(6):2784–2789. doi:10.1039/c4nr06093h

    CAS  Article  Google Scholar 

  6. 6.

    Chen Y, Chen YB, Nan JY, Wang CP, Chu FX (2012) Hollow poly(N-isopropylacrylamide)-co-poly(acrylic acid) microgels with high loading capacity for drugs. J Appl Polym Sci 124(6):4678–4685. doi:10.1002/app.35515

    CAS  Google Scholar 

  7. 7.

    Buchholz FL, Graham AT (eds) (1997) Modern superabsorbent polymer technology. Wiley-VCH, New York

  8. 8.

    Li Y, Tanaka T (1992) Phase-transitions of gels. Annu Rev Mater Sci 22(1):243–277. doi:10.1146/annurev.ms.22.080192.001331

    Article  Google Scholar 

  9. 9.

    Hirotsu S (1994) Static and time-dependent properties of polymer gels around the volume phase-transition. Phase Transit 47(3–4):183–240. doi:10.1080/01411599408200347

    CAS  Article  Google Scholar 

  10. 10.

    Shibayama M (1998) Spatial inhomogeneity and dynamic fluctuations of polymer gels. Macromol Chem Phys 199(1):1–30. doi:10.1002/(SICI)1521-3935(19980101)199:1<1::AID-MACP1>3.0.CO;2-M

    CAS  Article  Google Scholar 

  11. 11.

    Hirotsu S (1993) Coexistence of phases and the nature of first-order phase transition in poly-N-isopropylacrylamide gels. In: Dušek K (ed) Responsive Gels: Volume Transitions II. Springer, Berlin Heidelberg, Berlin, Heidelberg, pp. 1–26. doi:10.1007/BFb0021126

    Google Scholar 

  12. 12.

    Hirotsu S, Hirokawa Y, Tanaka T (1987) Volume-phase transitions of ionized N-isopropylacrylamide gels. J Chem Phys 87(2):1392–1395. doi:10.1063/1.453267

    CAS  Article  Google Scholar 

  13. 13.

    Shibayama M (2011) Small-angle neutron scattering on polymer gels: phase behavior, inhomogeneities and deformation mechanisms. Polym J 43(1):18–34. doi:10.1038/pj.2010.110

    CAS  Article  Google Scholar 

  14. 14.

    Shibayama M, Tanaka T, Han CC (1992) Small-angle neutron-scattering study on weakly charged temperature sensitive polymer gels. J Chem Phys 97(9):6842–6854. doi:10.1063/1.463637

    CAS  Article  Google Scholar 

  15. 15.

    Jha PK, Solis FJ, de Pablo JJ, de la Cruz MO (2009) Nonlinear effects in the nanophase segregation of polyelectrolyte gels. Macromolecules 42(16):6284–6289. doi:10.1021/ma901035e

    CAS  Article  Google Scholar 

  16. 16.

    Wu KA, Jha PK, de la Cruz MO (2010) Control of nanophases in polyelectrolyte gels by salt addition. Macromolecules 43(21):9160–9167. doi:10.1021/ma101726v

    CAS  Article  Google Scholar 

  17. 17.

    Nasimova I, Karino T, Okabe S, Nagao M, Shibayama M (2004) Effect of ionization on the temperature- and pressure-induced phase transitions of poly(N-isopropylacrylamide) gels. J Chem Phys 121(19):9708–9715. doi:10.1063/1.1804491

    CAS  Article  Google Scholar 

  18. 18.

    Shibayama M, Ikkai F, Inamoto S, Nomura S, Han CC (1996) pH and salt concentration dependence of the microstructure of poly(N-isopropylacrylamide-co-acrylic acid) gels. J Chem Phys 105(10):4358–4366. doi:10.1063/1.472252

    CAS  Article  Google Scholar 

  19. 19.

    Ikkai F, Shibayama M (2005) Inhomogeneity control in polymer gels. Journal of Polymer Science Part B-Polymer Physics 43(6):617–628. doi:10.1002/polb.20358

    CAS  Article  Google Scholar 

  20. 20.

    Ikkai F, Suzuki T, Karino T, Shibayama M (2007) Microstructure of N-isopropylacrylamide−acrylic acid copolymer gels having different spatial configurations of weakly charged groups. Macromolecules 40(4):1140–1146. doi:10.1021/ma062216c

    CAS  Article  Google Scholar 

  21. 21.

    Moussaid A, Candau SJ, Joosten JGH (1994) Structural and dynamic properties of partially charged poly(acrylic acid) gels—nonergodicity and inhomogeneities. Macromolecules 27(8):2102–2110. doi:10.1021/ma00086a019

    CAS  Article  Google Scholar 

  22. 22.

    Norisuye T, Masui N, Kida Y, Ikuta D, Kokufuta E, Ito S, Panyukov S, Shibayama M (2002) Small angle neutron scattering studies on structural inhomogeneities in polymer gels: irradiation cross-linked gels vs chemically cross-linked gels. Polymer 43(19):5289–5297. doi:10.1016/S0032-3861(02)00343-9

    CAS  Article  Google Scholar 

  23. 23.

    Shibayama M, Ikkai F, Shiwa Y, Rabin Y (1997) Effect of degree of cross-linking on spatial inhomogeneity in charged gels. I. Theoretical predictions and light scattering study. J Chem Phys 107(13):5227. doi:10.1063/1.474886

    CAS  Article  Google Scholar 

  24. 24.

    Ikkai F, Shibayama M, Han CC (1998) Effect of degree of cross-linking on spatial inhomogeneity in charged gels. 2. Small-angle neutron scattering study. Macromolecules 31(10):3275–3281. doi:10.1021/ma971468y

    CAS  Article  Google Scholar 

  25. 25.

    Shibayama M, Kawakubo K, Norisuye T (1998) Comparison of the experimental and theoretical structure factors of temperature sensitive polymer gels. Macromolecules 31(5):1608–1614. doi:10.1021/ma971641q

    CAS  Article  Google Scholar 

  26. 26.

    Ikkai F, Shibayama M (1997) Anomalous cross-link density dependence of scattering from charged gels. Phys Rev E 56(1):R51–R54. doi:10.1103/PhysRevE.56.R51

    CAS  Article  Google Scholar 

  27. 27.

    Shibayama M, Fujikawa Y, Nomura S (1996) Dynamic light scattering study of poly(N-isopropylacrylamide-co-acrylic acid) gels. Macromolecules 29(20):6535–6540. doi:10.1021/ma960320w

    CAS  Article  Google Scholar 

  28. 28.

    Ilmain F, Tanaka T, Kokufuta E (1991) Volume transition in a gel driven by hydrogen-bonding. Nature 349(6308):400–401. doi:10.1038/349400a0

    CAS  Article  Google Scholar 

  29. 29.

    Quesada-Perez M, Maroto-Centeno JA, Martin-Molina A (2012) Effect of the counterion valence on the behavior of thermo-sensitive gels and microgels: a Monte Carlo simulation study. Macromolecules 45(21):8872–8879. doi:10.1021/ma3014959

    CAS  Article  Google Scholar 

  30. 30.

    McCoy JL, Muthukumar M (2010) Dynamic light scattering studies of ionic and nonionic polymer gels with continuous and discontinuous volume transitions. Journal of Polymer Science Part B-Polymer Physics 48(21):2193–2206. doi:10.1002/polb.22101

    CAS  Article  Google Scholar 

  31. 31.

    Li Y, Tanaka T (1989) Study of the universality class of the gel network system. J Chem Phys 90(9):5161–5166. doi:10.1063/1.456559

    CAS  Article  Google Scholar 

  32. 32.

    Norisuye T, Kida Y, Masui N, Tran-Cong-Miyata Q (2003) Studies on two types of built-in inhomogeneities for polymer gels: frozen segmental concentration fluctuations and spatial distribution of cross-links. Macromolecules 36(16):6202–6212. doi:10.1021/ma030067h

    CAS  Article  Google Scholar 

  33. 33.

    Kratz K, Hellweg T, Eimer W (2001) Structural changes in PNIPAM microgel particles as seen by SANS, DLS, and EM techniques. Polymer 42(15):6631–6639. doi:10.1016/S0032-3861(01)00099-4

    CAS  Article  Google Scholar 

  34. 34.

    Senff H, Richtering W (2000) Influence of cross-link density on rheological properties of temperature-sensitive microgel suspensions. Colloid Polym Sci 278(9):830–840. doi:10.1007/s003960000329

    CAS  Article  Google Scholar 

  35. 35.

    Quesada-Perez M, Maroto-Centeno JA, Forcada J, Hidalgo-Alvarez R (2011) Gel swelling theories: the classical formalism and recent approaches. Soft Matter 7(22):10536–10547. doi:10.1039/c1sm06031g

    CAS  Article  Google Scholar 

  36. 36.

    Matsuo ES, Orkisz M, Sun ST, Li Y, Tanaka T (1994) Origin of structural inhomogeneities in polymer gels. Macromolecules 27(23):6791–6796. doi:10.1021/ma00101a018

    CAS  Article  Google Scholar 

  37. 37.

    Hoare T, Pelton R (2007) Functionalized microgel swelling: comparing theory and experiment. J Phys Chem B 111(41):11895–11906. doi:10.1021/jp072360f

    CAS  Article  Google Scholar 

  38. 38.

    Fernandez-Barbero A, Fernandez-Nieves A, Grillo I, Lopez-Cabarcos E (2002) Structural modifications in the swelling of inhomogeneous microgels by light and neutron scattering. Phys Rev E Stat Nonlinear Soft Matter Phys 66(5 Pt 1):051803. doi:10.1103/PhysRevE.66.051803

    CAS  Article  Google Scholar 

  39. 39.

    Sierra-Martin B, Lietor-Santos JJ, Fernandez-Barbero A, Nguyen TT, Fernandez-Nieves A (2011) Swelling thermodynamics of microgel particles. In: Microgel Suspensions. Wiley-VCH Verlag GmbH & Co, KGaA, pp. 71–116. doi:10.1002/9783527632992.ch4

    Google Scholar 

  40. 40.

    Wu C, Zhou SQ (1997) Volume phase transition of swollen gels: discontinuous or continuous? Macromolecules 30(3):574–576. doi:10.1021/ma960499a

    CAS  Article  Google Scholar 

  41. 41.

    Kokufuta E, Wang BL, Yoshida R, Khokhlov AR, Hirata M (1998) Volume phase transition of polyelectrolyte gels with different charge distributions. Macromolecules 31(20):6878–6884. doi:10.1021/ma971565r

    CAS  Article  Google Scholar 

  42. 42.

    Ogawa K, Ogawa Y, Kokufuta E (2002) Effect of charge inhomogeneity of polyelectrolyte gels on their swelling behavior. Colloids and Surfaces a-Physicochemical and Engineering Aspects 209(2–3):267–279. doi:10.1016/S0927-7757(02)00189-9

    CAS  Google Scholar 

  43. 43.

    Liu RG, Oppermann W (2006) Spatial inhomogeneities of polystrene gels prepared from semidilute solutions. Macromolecules 39(12):4159–4167. doi:10.1021/ma060359t

    CAS  Article  Google Scholar 

  44. 44.

    Rabin Y, Panyukov S (1997) Scattering profiles of charged gels: frozen inhomogeneities, thermal fluctuations, and microphase separation. Macromolecules 30(2):301–312. doi:10.1021/ma960826e

    CAS  Article  Google Scholar 

  45. 45.

    Travas-Sejdic J, Easteal A, Knott R, Pedersen JS (2000) Small-angle neutron scattering from poly(NIPA-co-AMPS) gels. J Appl Crystallogr 33(1):735–739. doi:10.1107/S002188980009988x

    CAS  Article  Google Scholar 

  46. 46.

    Hoare T, Pelton R (2006) Titrametric characterization of pH-induced phase transitions in functionalized microgels. Langmuir 22(17):7342–7350. doi:10.1021/la0608718

    CAS  Article  Google Scholar 

  47. 47.

    Hoare T, Pelton R (2004) Highly pH and temperature responsive microgels functionalized with vinylacetic acid. Macromolecules 37(7):2544–2550. doi:10.1021/ma035658m

    CAS  Article  Google Scholar 

  48. 48.

    Vo CD, Kuckling D, Adler HJP, Schohoff M (2002) Preparation of thermosensitive nanogels by photo-cross-linking. Colloid Polym Sci 280(5):400–409. doi:10.1007/s003960100559

    CAS  Article  Google Scholar 

  49. 49.

    Seiffert S, Oppermann W, Saalwaechter K (2007) Hydrogel formation by photocrosslinking of dimethylmaleimide functionalized polyacrylamide. Polymer 48(19):5599–5611. doi:10.1016/j.polymer.2007.07.013

    CAS  Article  Google Scholar 

  50. 50.

    Habicht A, Schmolke W, Lange F, Saalwachter K, Seiffert S (2014) The non-effect of polymer-network inhomogeneities in microgel volume phase transitions: support for the mean-field perspective. Macromol Chem Phys 215(11):1116–1133. doi:10.1002/macp.201400114

    CAS  Article  Google Scholar 

  51. 51.

    Chu LY, Utada AS, Shah RK, Kim JW, Weitz DA (2007) Controllable monodisperse multiple emulsions. Angew Chem Int Ed Engl 46(47):8970–8974. doi:10.1002/anie.200701358

    CAS  Article  Google Scholar 

  52. 52.

    Utada AS, Fernandez-Nieves A, Stone HA, Weitz DA (2007) Dripping to jetting transitions in coflowing liquid streams. Phys Rev Lett 99(9):094502. doi:10.1103/PhysRevLett.99.094502

    Article  Google Scholar 

  53. 53.

    Debye PP (1946) A photoelectric instrument for light scattering measurements and a differential refractometer. J Appl Phys 17(5):392–398. doi:10.1063/1.1707729

    CAS  Article  Google Scholar 

  54. 54.

    Debye P, Bueche AM (1949) Scattering by an inhomogeneous solid. J Appl Phys 20(6):518–525. doi:10.1063/1.1698419

    CAS  Article  Google Scholar 

  55. 55.

    Pekeris CL (1947) Note on the scattering of radiation in an inhomogeneous medium. Phys Rev 71(4):268–269. doi:10.1103/PhysRev.71.268

    Article  Google Scholar 

  56. 56.

    Nie J, Du B, Oppermann W (2004) Influence of formation conditions on spatial inhomogeneities in poly(N-isopropylacrylamide) hydrogels. Macromolecules 37(17):6558–6564. doi:10.1021/ma049169d

    CAS  Article  Google Scholar 

  57. 57.

    Di Lorenzo F, Seiffert S (2016) Effect of droplet size in acrylamide-based microgel formation by microfluidics. Macromol React Eng 10(3):201–205. doi:10.1002/mren.201500061

    CAS  Article  Google Scholar 

  58. 58.

    Debye P (1959) Angular dissymmetry of the critical opalescence in liquid mixtures. J Chem Phys 31(3):680–687. doi:10.1063/1.1730446

    CAS  Article  Google Scholar 

  59. 59.

    Bueche F (1970) Light scattering from swollen gels. J Colloid Interface Sci 33(1):61. doi:10.1016/0021-9797(70)90072-X

    CAS  Article  Google Scholar 

  60. 60.

    Soni VK, Stein RS (1990) Light-scattering-studies of poly(dimethylsiloxane) solutions and swollen networks. Macromolecules 23(25):5257–5265. doi:10.1021/ma00227a013

    CAS  Article  Google Scholar 

  61. 61.

    Sato Matsuo E, Tanaka T (1988) Kinetics of discontinuous volume–phase transition of gels. J Chem Phys 89(3):1695. doi:10.1063/1.455115

    Article  Google Scholar 

  62. 62.

    Tanaka T, Sato E, Hirokawa Y, Hirotsu S, Peetermans J (1985) Critical kinetics of volume phase transition of gels. Phys Rev Lett 55(22):2455–2458. doi:10.1103/PhysRevLett.55.2455

    CAS  Article  Google Scholar 

  63. 63.

    Tanaka T, Fillmore DJ (1979) Kinetics of swelling of gels. J Chem Phys 70(3):1214–1218. doi:10.1063/1.437602

    CAS  Article  Google Scholar 

  64. 64.

    Chang CW, Nguyen TH, Maynard HD (2010) Thermoprecipitation of glutathione S-transferase by glutathione-poly(N-isopropylacrylamide) prepared by RAFT polymerization. Macromol Rapid Commun 31(19):1691–1695. doi:10.1002/marc.201000333

    CAS  Article  Google Scholar 

  65. 65.

    Dong LC, Hoffman AS (1991) A novel-approach for preparation of pH-sensitive hydrogels for enteric drug delivery. J Control Release 15(2):141–152. doi:10.1016/0168-3659(91)90072-L

    CAS  Article  Google Scholar 

  66. 66.

    Feil H, Bae YH, Feijen J, Kim SW (1993) Effect of comonomer hydrophilicity and ionization on the lower critical solution temperature of N-isopropylacrylamide copolymers. Macromolecules 26(10):2496–2500. doi:10.1021/ma00062a016

    CAS  Article  Google Scholar 

  67. 67.

    Li X, Zuo J, Guo YL, Cai LB, Tang S, Yang WB (2007) Volume phase transition temperature tuning and investigation of the swelling-deswelling oscillation of responsive microgels. Polym Int 56(8):968–975. doi:10.1002/pi.2221

    CAS  Article  Google Scholar 

  68. 68.

    Ohmine I, Tanaka T (1982) Salt effects on the phase-transition of ionic gels. J Chem Phys 77(11):5725–5729. doi:10.1063/1.443780

    CAS  Article  Google Scholar 

  69. 69.

    Pelton RH, Pelton HM, Morphesis A, Rowell RL (1989) Particle sizes and electrophoretic mobilities of poly(N-isopropylacrylamide) latex. Langmuir 5(3):816–818. doi:10.1021/la00087a040

    CAS  Article  Google Scholar 

  70. 70.

    Annaka M, Motokawa K, Sasaki S, Nakahira T, Kawasaki H, Maeda H, Amo Y, Tominaga Y (2000) Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel. J Chem Phys 113(14):5980–5985. doi:10.1063/1.1290135

    CAS  Article  Google Scholar 

  71. 71.

    Woodward NC, Snowden MJ, Chowdhry BZ, Jenkins P, Larson I (2002) Measurement of the interaction forces between poly(N-isopropylacrylamide−acrylic acid) microgel and silica surfaces by colloid probe microscopy. Langmuir 18(6):2089–2095. doi:10.1021/la0105580

    CAS  Article  Google Scholar 

  72. 72.

    Horkay F, Hecht A-M, Geissler E (1994) Small angle neutron scattering in poly(vinyl alcohol) hydrogels. Macromolecules 27(7):1795–1798. doi:10.1021/ma00085a019

    CAS  Article  Google Scholar 

  73. 73.

    Koizumi S, Monkenbusch M, Richter D, Schwahn D, Farago B (2004) Concentration fluctuations in polymer gel investigated by neutron scattering: static inhomogeneity in swollen gel. J Chem Phys 121(24):12721–12731. doi:10.1063/1.1823411

    CAS  Article  Google Scholar 

  74. 74.

    Shibayama M, Tanaka T (1993) Volume phase transition and related phenomena of polymer gels. In: Dušek K (ed) Responsive gels: volume transitions I. Springer, Berlin Heidelberg, Berlin, Heidelberg, pp. 1–62. doi:10.1007/3-540-56791-7_1

    Google Scholar 

Download references


Part of this work was carried out at Freie Universität Berlin and Helmholtz-Zentrum Berlin within the collaborative framework of the Berlin Joint Lab for Supramolecular Polymer Systems, supported by the Focus Area NanoScale at FU Berlin. SANS experiments at the V16 beamline at BER II, Helmholtz-Zentrum Berlin, were assisted by Daniel Clemens, whom we gratefully acknowledge.

Author information



Corresponding author

Correspondence to Sebastian Seiffert.

Ethics declarations

Conflict of interest

The authors declare that they have no conflict of interest.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Rochette, D., Kent, B., Habicht, A. et al. Effect of polymer network inhomogeneity on the volume phase transitions of thermo- and pH-sensitive weakly charged microgels. Colloid Polym Sci 295, 507–520 (2017). https://doi.org/10.1007/s00396-017-4029-5

Download citation


  • Environmentally sensitive polymer gels
  • Microgels
  • Polyelectrolytes
  • Polymer network inhomogeneity
  • Volume phase transition