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 8 of 31
Another very significant environmental factor to consider when dealing with bulk or thin films of
thermoresponsive polymers is the issue of water uptake. Many thermoresponsive polymers like
PNIPAm are appreciably hydrophilic because of the presence of polar amide groups and will absorb
water from the atmosphere [61]. Thus in many cases where one wishes to study the behavior of
thermoresponsive polymer thin films one will need to control, or account for the presence of water in
the thin films [62].
The potential range of fluorophores available for the analysis of thermoresponsive polymers is
vast and a detailed analysis is outside the scope of this article. However, once a fluorophore has been
selected there are only two general modes of employment: covalent attachment of the probe to the
polymer [63], or deployment as a freely diffusing probe which is then introduced to polymer solutions
or doped into thin films of the polymer. There are several drawbacks to the use of freely diffusing
fluorophores ranging from the fact that they are free to diffuse out of the polymer structures, that they
may aggregate, and that there is no control over where the probe interacts with the polymer. This
obviously limits the potential applications; however, the approach is intrinsically very simple and
lessens the risk of modifying polymer structure. One can minimize/eliminate many of these issues
by covalently attaching the probe to the polymer; however, this may not always be feasible or
straightforward. One critical aspect of the covalent labeling approach is to decide if it is possible to
introduce the fluorophore during or after the polymerization process. For characterization of
thermoresponsive polymers there are a wide range of covalently labeled fluorophores described in the
literature.
Some examples include pyrene and napthalene [63-66],
N,N(dimethy1amino)naphthalenesulfonamide (dansyl) [67], and the cyanine Cy5/Cy5.5 pair for FRET
studies [68].
5 THERMORESPONSIVE POLYMER CHARACTERIZATION.
The fluorescence analysis of thermoresponsive polymer systems can be categorized, for the sake
of textual organization, as either physiochemical or physical characterization. We note that there is
a considerable degree of overlap and that in practice these factors should never be considered in
isolation. The chemistry influences the physical factors and vice-versa. Here, we begin with
physiochemical characterization and the crucial factor of water absorption, which then leads to the
measurement of the chemical and polarity properties of thermoresponsive polymers. For the physical
characterization, we start with Critical Micelle Concentration (CMC) and aggregation measurements
and then progress to the study of phase transitions around the LCST, before finally showing how
fluorescence can be utilized to study the assembly/behavior of thermoresponsive particles and surfaces.
When undertaking a physicochemical characterization of thermoresponsive polymers we have to
consider first the chemical structure of the polymer and second the environment created by the polymer
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 8 of 31
Another very significant environmental factor to consider when dealing with bulk or thin films of
thermoresponsive polymers is the issue of water uptake. Many thermoresponsive polymers like
PNIPAm are appreciably hydrophilic because of the presence of polar amide groups and will absorb
water from the atmosphere [61]. Thus in many cases where one wishes to study the behavior of
thermoresponsive polymer thin films one will need to control, or account for the presence of water in
the thin films [62].
The potential range of fluorophores available for the analysis of thermoresponsive polymers is
vast and a detailed analysis is outside the scope of this article. However, once a fluorophore has been
selected there are only two general modes of employment: covalent attachment of the probe to the
polymer [63], or deployment as a freely diffusing probe which is then introduced to polymer solutions
or doped into thin films of the polymer. There are several drawbacks to the use of freely diffusing
fluorophores ranging from the fact that they are free to diffuse out of the polymer structures, that they
may aggregate, and that there is no control over where the probe interacts with the polymer. This
obviously limits the potential applications; however, the approach is intrinsically very simple and
lessens the risk of modifying polymer structure. One can minimize/eliminate many of these issues
by covalently attaching the probe to the polymer; however, this may not always be feasible or
straightforward. One critical aspect of the covalent labeling approach is to decide if it is possible to
introduce the fluorophore during or after the polymerization process. For characterization of
thermoresponsive polymers there are a wide range of covalently labeled fluorophores described in the
literature.
Some examples include pyrene and napthalene [63-66],
N,N(dimethy1amino)naphthalenesulfonamide (dansyl) [67], and the cyanine Cy5/Cy5.5 pair for FRET
studies [68].
5 THERMORESPONSIVE POLYMER CHARACTERIZATION.
The fluorescence analysis of thermoresponsive polymer systems can be categorized, for the sake
of textual organization, as either physiochemical or physical characterization. We note that there is
a considerable degree of overlap and that in practice these factors should never be considered in
isolation. The chemistry influences the physical factors and vice-versa. Here, we begin with
physiochemical characterization and the crucial factor of water absorption, which then leads to the
measurement of the chemical and polarity properties of thermoresponsive polymers. For the physical
characterization, we start with Critical Micelle Concentration (CMC) and aggregation measurements
and then progress to the study of phase transitions around the LCST, before finally showing how
fluorescence can be utilized to study the assembly/behavior of thermoresponsive particles and surfaces.
When undertaking a physicochemical characterization of thermoresponsive polymers we have to
consider first the chemical structure of the polymer and second the environment created by the polymer