Polarity Assessment of Thermoresponsive Poly(NIPAM-co-NtBA) Copolymer Films Using Fluorescence Methods

Abstract

The in-situ, non-contact, and non-destructive measurement of the physicochemical properties such as the polarity of thin (nm to µm), hydrophilic polymer films is desirable in many areas of polymer science. Polarity is a complex factor and encompasses a range of noncovalent interactions including dipolarity/polarizability and hydrogen bonding. A polarity measurement method based on fluorescence would be ideal, but the key challenge is to identify suitable probes which can accurately measure specific polarity related parameters. In this manuscript we assess a variety of fluorophores for measuring the polarity of a series of relatively hydrophilic, thermoresponsive N-isopropylacrylamide/N-tert-butylacrylamide (NIPAM/NtBA) copolymers. The emission properties of both pyrene and 3-Hydroxyflavone (3-HF) based fluorophores were measured in dry polymer films. In the case of pyrene, a relatively weak, linear relationship between polymer composition and the ratio of the first to the third vibronic band of the emission spectrum (I 1 /I 3 ) is observed, but pyrene emission is very sensitive to temperature and thus not suitable for robust polarity measurements. The 3-

Fluorescence Analysis of Thermoresponsive Polymers

“…They reported a decrease in the I 1 /I 3 ratio of pyrene with increasing NtBA fraction indicating a reduction in polarity with increasing NtBA content (Fig. 4.7), which is in agreement with previous results obtained in a solvatochromic study involving the same polymers [19,100].…”

“…Specifically, for many applications, the concentrations required of the solvatochromic probes for absorption spectroscopy in these condensed media is relatively high (typical weight ratios of 36-20 to 1) [99], and it would be preferable to utilize much lower concentrations such as the levels employed in fluorescence spectroscopy (typical weight ratios of 1900-2230 to 1) [100]. Another need is the requirement for standoff measurements in sealed environments and in such cases, fluorescence may be the only feasible option.…”

“…For aqueous solutions of PNIPAm one observes approximately a 60 ns increase in average lifetime from 115 ns to~175 ns as the temperature increases from 30 to 40 C [103]. Szczupak et al assessed the polarity of poly(NIPAm-coNtBA) copolymer films by means of fluorescence based methods, using pyrene and 3-HF derivatives as polarity sensitive fluorescent probes [100]. They reported a decrease in the I 1 /I 3 ratio of pyrene with increasing NtBA fraction indicating a reduction in polarity with increasing NtBA content (Fig.…”

Assessing protein–surface interactions with a series of multi-labeled BSA using fluorescence lifetime microscopy and Förster Energy Resonance Transfer

“…The hydrophobic (or hydrophilic) character of a surface is usually expressed by its wettability, which is typically measured by the contact angle that a drop of water makes on the surface [9,31] or recently by fluorescence probes [ 54 ]. In aqueous solutions, the polar residues of BSA are, in general, more exposed to the bulk solution than non polar groups.…”

Study of Water Adsorption in Poly(N-isopropylacrylamide) Thin Films Using Fluorescence Emission of 3-Hydroxyflavone Probes

“…This is because of heterogeneity in the ground state hydrogen-bonding, which are evidenced by excitation wavelength dependence and the time-resolved fluorescence data obtained for the N* and T* band emission. 40,49,50 In medical device manufacturing where thin polymer films are widely used, the ability to observe water adsorption and understand its subtle characteristics will be important for the development of robust manufacturing practices. Here we study water uptake in pNIPAM thin films supported on quartz surfaces by studying the fluorescence emission properties of a series of 3-HF fluorophores to determine which probe offers the best sensitivity to water uptake and to study in detail the dynamic hydration processes in thin film hydrophilic polymers.…”