Full Citation: Fluorescence Analysis of Thermoresponsive Polymers. A.G. Ryder and C. Morris, Reviews in Fluorescence 2015 ,
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 19 of 31
telechelic PNIPAm (C18-PNIPAM-C18) involved the use of ANS and the measurement of steady-state
emission spectra. When the emission was measured over the 10 to 50 C temperature range one
observed at approximately 29 C a sharp increase in fluorescence intensity coupled with a blue shift
in the emission band maximum (Figure 9). This was clear evidence for a very significant change in
the micropolarity sensed by ANS, as with increasing temperature ANS passes from a hydrophilic
environment of “highly hydrated rosettes”, formed at lower temperatures to the “hydrophobic medium
of collapsed and associated polymeric micelles” [124].
Figure 9: Temperature dependence of the ANS fluorescence intensity and wavelength of emission band
maximum in polymer solution (polymer concentration is 0.1gL
-1
). Reproduced with permission from ref [124].
Copyright © 2005, Springer Berlin / Heidelberg.
Another method for analyzing thermoresponsive polymer transitions near the LCST is to utilize
polarization anisotropy in conjunction with fluorescence quenching studies.
The use of
acenaphthylene (ACE) covalently labeled PNIPAm for studying the effect of urea on polymer
structure/dynamics in solution has been demonstrated several times [129,130]. ACE was used
because there is no rotation independent of the segment to which the ACE probe is attached. Steadystate anisotropy studies showed that below the LCST, anisotropy was small irrespective of the presence
of urea (a quencher), which was consistent to the open structure of the loose coil polymer conformation
[130]. Above the LCST, large anisotropy values were recorded in the absence of the quencher
indicating that the polymer had adopted a compact conformation. However, when urea was added,
the anisotropy decreased very significantly indicating that the polymer conformation had opened up.
A combination of anisotropy and FRET has been used to probe the behavior of mesoglobular
phases formed when PNIPAm was heated in solution [66]. Anisotropy measurements conducted on
napthyl labeled PNIPAm gave an indication of the rotational freedom of the pendant fluorophore and
this was related to the micro-viscosity of the phase in which it was dissolved. The results indicated
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 19 of 31
telechelic PNIPAm (C18-PNIPAM-C18) involved the use of ANS and the measurement of steady-state
emission spectra. When the emission was measured over the 10 to 50 C temperature range one
observed at approximately 29 C a sharp increase in fluorescence intensity coupled with a blue shift
in the emission band maximum (Figure 9). This was clear evidence for a very significant change in
the micropolarity sensed by ANS, as with increasing temperature ANS passes from a hydrophilic
environment of “highly hydrated rosettes”, formed at lower temperatures to the “hydrophobic medium
of collapsed and associated polymeric micelles” [124].
Figure 9: Temperature dependence of the ANS fluorescence intensity and wavelength of emission band
maximum in polymer solution (polymer concentration is 0.1gL
-1
). Reproduced with permission from ref [124].
Copyright © 2005, Springer Berlin / Heidelberg.
Another method for analyzing thermoresponsive polymer transitions near the LCST is to utilize
polarization anisotropy in conjunction with fluorescence quenching studies.
The use of
acenaphthylene (ACE) covalently labeled PNIPAm for studying the effect of urea on polymer
structure/dynamics in solution has been demonstrated several times [129,130]. ACE was used
because there is no rotation independent of the segment to which the ACE probe is attached. Steadystate anisotropy studies showed that below the LCST, anisotropy was small irrespective of the presence
of urea (a quencher), which was consistent to the open structure of the loose coil polymer conformation
[130]. Above the LCST, large anisotropy values were recorded in the absence of the quencher
indicating that the polymer had adopted a compact conformation. However, when urea was added,
the anisotropy decreased very significantly indicating that the polymer conformation had opened up.
A combination of anisotropy and FRET has been used to probe the behavior of mesoglobular
phases formed when PNIPAm was heated in solution [66]. Anisotropy measurements conducted on
napthyl labeled PNIPAm gave an indication of the rotational freedom of the pendant fluorophore and
this was related to the micro-viscosity of the phase in which it was dissolved. The results indicated