In Situ Characterization of Thermo‐Responsive Poly(N‐Isopropylacrylamide) Films with Sum‐Frequency Generation Spectroscopy

Abstract

The thermo-responsive behaviour of thiol modified poly(N-isopropylacrylamide) (pNIPAM) films immobilized on gold are probed by in situ broadband sum-frequency generation (SFG) spectroscopy. The pNIPAM films were prepared by atom transfer radical polymerization (ATRP) using a nitro-biphenyl-thiol (NBT)-SAM on a polycrystalline gold surface as a substrate. Additionally, Raman and infrared reflection absorption spectroscopy (IRRAS) are applied to spin-coated pNIPAM films. Molecular groups involved in the reorientation and disordering of the polymer chains during the LCST (lower critical solution temperature) transition of pNIPAM are identified. The characteristic vibrations of the CH(3) groups show a gradual reorientation of the isopropyl groups within the pNIPAM film and instantaneous reorientation of the outermost CH(3) groups around 32 degrees C.

Wet-spinning assembly of continuous, neat and macroscopic graphene fibers

“…Furthermore, the FT-IR spectra of the single GO and GO/PNIPAM fiber confirm the existence of the polymer in the fiber, as reflected from the characteristic bands belonging to PNIPAM (see Supplementary Fig. S11 online)33. After treated with HI, the GO/PNIPAM fiber is reduced to graphene/PNIPAM fiber as shown from the improved value of I D /I G and the existence of 2D band of the Raman spectra (see Supplementary Fig.…”

Hofmeister Effect of Sodium Halides on the Switching Energetics of Thermoresponsive Polymer Brushes

“…For a discussion of the results, it is illustrative to consider general structural changes, which are observed during the collapse of PNiPAAm brushes 16–18. The chemical structure of PNiPAAm consists of a hydrocarbon backbone with amide and isopropyl side groups and hence exhibits both hydrophilic and hydrophobic functionalities.…”

“…At room temperature, the polymer chains are strongly hydrated and extend into the solution 16, 17. Hydrogen bonds stabilize additional water within the brush rendering the swollen polymer film surface hydrophilic 17, 18. With increasing temperature, dehydration and collapse of the polymer chains take place 16, 17.…”

“…With increasing temperature, dehydration and collapse of the polymer chains take place 16, 17. Because of a rearrangement of the isopropyl groups, the polymer film surface becomes more hydrophobic 18. The release of water during this hydrophobic collapse is endothermic but entropically favorable.…”

Novel SiO2-Deposited CaF2 Substrate for Vibrational Sum-Frequency Generation (SFG) Measurements of Chemisorbed Monolayers in an Aqueous Environment

“…The technique can be applied to all surfaces accessible by light even if they are buried in bulk media. 1–11 Biomolecular interfaces play a vital role in biological processes. Insights into the chemical composition and molecular structure of such functional interfaces are therefore challenging and of great importance.…”