Effect of Thermal Stimulus on Kinetic Rehydration of Thermoresponsive Poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate) Thin Films Probed by In Situ Neutron Reflectivity

Abstract

The kinetic rehydration of thin di-block copolymer poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate) (PO 2 -b-PO 300 ) films containing two thermoresponsive components is probed by in situ neutron reflectivity (NR) with different thermal stimuli in the D 2 O vapor atmosphere. The transition temperatures (TTs) of PO 2 and PO 300 blocks are 25 and 60 °C, respectively. After the one-step stimulus (rapid decrease in temperature from 60 to 20 °C), the film directly switches from a collapsed to a fully swollen state. The rehydration process is divided into four steps: (a) D 2 O condensation, (b) D 2 O absorption, (c) D 2 O evaporation, and (d) film reswelling. However, the film presents a different rehydration behavior when the thermal stimulus is separated into two smaller steps (first decrease from 60 to 40 °C and then to 20 °C). The film first switches from a collapsed to a semiswollen state caused by the rehydrated PO 300 blocks after the first step of thermal stimulus (60 to 40 °C) and then to a swollen state induced by the rehydrated PO 2 blocks after the second step (40 to 20 °C). Thus, the kinetic responses are distinct from that after the one-step thermal stimulus. Both the time and extent of condensation as well as evaporation processes are significantly reduced in these two smaller steps. However, the final states of the rehydrated PO 2 -b-PO 300 films are basically identical irrespective of the applied thermal stimulus. Thus, the final state of thermoresponsive di-block copolymer films is not affected by the external thermal stimuli, which is beneficial for the design and preparation of sensors or switches based on thermoresponsive polymer films.

Kinetics of Water Transfer Between the LCST and UCST Thermoresponsive Blocks in Diblock Copolymer Thin Films Monitored by In Situ Neutron Reflectivity

“…In the second step, the temperature is rapidly increased further from 40 °C to 80 °C (second thermal stimulus). According to our previous investigation, [ 37,44,50 ] due to the interaction with the solid substrate, the thermoresponsive polymer thin films tend to show a much broader transition region compared to aqueous solutions. Also in the present study, both blocks (PNIPAM and PSBP) show a broader transition region in the thin film format than in aqueous solution.…”

Thermo-responsive block copolymers: assembly and application

“…One is composed of two blocks with different LCSTs, such as poly( N -isopropylacrylamide)- b -poly(dimethylaminoethyl methacrylate) (PNIPAM- b -PDMAEMA), 12 poly( N -acryloylsarcosine methyl ester)- b -poly( N -isopropylacrylamide) (PNASME- b -PNIPAM) 20 and poly(diethylene glycol monomethyl ether methacrylate)- b -poly[poly(ethylene glycol) methyl ether methacrylate] (PO 2 - b -PO 300 ). 45 The other is made up of a non-ionic hydrophilic block with a LCST and a zwitterionic block with an UCST, such as poly(sulfobetaine methacrylate)- b -poly( N -isopropylmethacrylamide) (PSBMA- b -PNIPMAM), 21 polysulfobetaine- b -poly( N -isopropylmethacrylamide) (PSPP- b -PNIPMAM), 22 polysulfobetaine- b -poly( N -isopropylacrylamide) (PSPP- b -PNIPAM) 25 and poly(dimethylaminoethyl methacrylate)- b -poly(sulfobetaine methacrylate) (PDMAEMA- b -PSBMA). 101 All the above diblock copolymers are listed in Table 3.…”

“…In 2022, Zhong et al , prepared thin films of the thermo-responsive PO 2 - b -PO 300 diblock copolymer showing two different LCSTs. 45 The phase transition temperatures of the PO 2 block and the PO 300 block are 25 °C and 60 °C, respectively. The effect of different cooling processes (one-step: 60 to 20 °C and two-step: 60 to 40 °C and then to 20 °C) on film swelling behavior was investigated by in situ neutron reflectivity (NR) and two different response processes are shown in Fig.…”

“…Thermo-responsive block copolymers, 1–35 which can respond to external temperature stimuli, are block copolymers containing one or more than one thermo-responsive blocks. They have received wide attention in the fields of catalysis, 36–41 adsorption and separation, 42 wastewater treatment, 43 sensors, 44,45 imaging, 46,47 drug delivery 48 and so on. Thermo-responsive block copolymers are widely studied for three reasons.…”

Easy care of silk fabrics realized by crosslinking thermo‐responsive copolymer film on its surface

“…[21][22][23] It should be noted that this transition behavior is reversible, indicating that the polymer returned to its more hydrophilic state when the external temperature is below the TT again. 24 Among all these thermo-responsive polymers, acrylamide-and acrylate-based ones are well investigated and extensively applied in smart textiles, 25 catalyst carriers, 26 drug delivery, 27 and biosensors. 28 In our previous investigation, 29 the smart cleaning of cotton fabrics was realized by immobilization of a crosslinked thermo-responsive P(MEO 2 MA-co-EGMA) film on the surface.…”